Preface

The book in your hands, *Paraffin – an Overview*, can teach you the basics of paraffin. It covers all the paraffin pathways from exploration to the applications. Taken as a whole, these five chapters aim to help academic researchers and those connected with the petroleum industry (such as petroleum engineers) to easily understand the value of paraffins as a petroleum byproduct. The chapters cover the separation, transportation, and application technology of paraffins and these chapters are presented in a careful and clear manner to provide an easy and enjoyable read. Data and discussions are presented by highly qualified experts and the text is edited to simplify the information. This book is valuable for those who are interested in making a connection between natural resources, science, and industry.

> **Fathi Samir Soliman** Egyptian Petroleum Research Institute, Egypt

**1**

**Chapter 1**

Paraffins

**1. Introductory**

temperature.

properties [1].

frequently called petrolatum [8].

of heavy petroleum distillates or residues.

**1.1 Composition of petroleum waxes**

compared to the other two waxes.

*Fathi Samir Soliman*

Introductory Chapter: Petroleum

Waxes separated from petroleum are defined as the waxes present naturally in various fractions of crude petroleum [1]. Petroleum waxes are complex mixtures of hydrocarbons, amongst which are n-paraffin, branched chain paraffins and cycloparaffins in the range of C18–C70 [2–4]. The quality and quantity of waxes manufactured from crude oils depend on the crude source and the degree of refining to

Paraffin waxes constitute the major bulk of such waxes, the other two types; produced in comparative quantities; also command a good market because of their certain specific end uses [2]. The paraffin waxes are solid hydrocarbons at room

Slack wax is a refinery term for the crude paraffin wax separated from the solvent dewaxing of base stocks. Slack wax contains varying amounts of oil (ranging from 20 to 50 wt.%) and must be removed to produce hard or finished waxes [1, 7]. If the slack wax separated from residual oil fractions, the oil-bearing slack is

Petrolatum is a general name applied to a slightly oiled crude microcrystalline wax. It is semi-solid, jelly-like materials. Petrolatum is obtained from a certain type

Ozokerite wax is naturally occurring mineral wax. It is also a microcrystalline wax. Ceresin is a microcrystalline wax; it is the name formerly given to the hard white wax obtained from fully refined ozokerite. Petroleum ceresin is a similar microcrystalline wax but separated from petroleum. Ceresin and petroleum ceresins appear to have the same composition, structure, physical and chemical

Petroleum waxes are substance, which is solid at normal temperatures. Paraffin and microcrystalline waxes in their pure form consist only solid saturated hydrocarbons. Petrolatum, in contrast to the other two waxes, contains both solid and liquid hydrocarbons. Petrolatum is semi-solid at normal temperatures and is quite soft as

Paraffin wax is a solid and crystalline mixture of hydrocarbons; it is usually obtained in the form of large crystals. It consists generally of normal paraffin ranging from C16 to C30 and may be higher. Proportions of slightly branched chain paraffin ranging from C18 to C36 and naphthenes; especially alkyl-substituted derivatives

The average molecular weight of these paraffin waxes is about 360–420 [9, 11]. A paraffin wax melting at 53.5°C showed a space lattice having C—C bond length

of cyclopentane and cyclohexane; are also present [1, 5, 8–10].

which it has been subjected prior to wax separation [5, 6].

## **Chapter 1**

## Introductory Chapter: Petroleum Paraffins

*Fathi Samir Soliman*

## **1. Introductory**

Waxes separated from petroleum are defined as the waxes present naturally in various fractions of crude petroleum [1]. Petroleum waxes are complex mixtures of hydrocarbons, amongst which are n-paraffin, branched chain paraffins and cycloparaffins in the range of C18–C70 [2–4]. The quality and quantity of waxes manufactured from crude oils depend on the crude source and the degree of refining to which it has been subjected prior to wax separation [5, 6].

Paraffin waxes constitute the major bulk of such waxes, the other two types; produced in comparative quantities; also command a good market because of their certain specific end uses [2]. The paraffin waxes are solid hydrocarbons at room temperature.

Slack wax is a refinery term for the crude paraffin wax separated from the solvent dewaxing of base stocks. Slack wax contains varying amounts of oil (ranging from 20 to 50 wt.%) and must be removed to produce hard or finished waxes [1, 7]. If the slack wax separated from residual oil fractions, the oil-bearing slack is frequently called petrolatum [8].

Petrolatum is a general name applied to a slightly oiled crude microcrystalline wax. It is semi-solid, jelly-like materials. Petrolatum is obtained from a certain type of heavy petroleum distillates or residues.

Ozokerite wax is naturally occurring mineral wax. It is also a microcrystalline wax. Ceresin is a microcrystalline wax; it is the name formerly given to the hard white wax obtained from fully refined ozokerite. Petroleum ceresin is a similar microcrystalline wax but separated from petroleum. Ceresin and petroleum ceresins appear to have the same composition, structure, physical and chemical properties [1].

#### **1.1 Composition of petroleum waxes**

Petroleum waxes are substance, which is solid at normal temperatures. Paraffin and microcrystalline waxes in their pure form consist only solid saturated hydrocarbons. Petrolatum, in contrast to the other two waxes, contains both solid and liquid hydrocarbons. Petrolatum is semi-solid at normal temperatures and is quite soft as compared to the other two waxes.

Paraffin wax is a solid and crystalline mixture of hydrocarbons; it is usually obtained in the form of large crystals. It consists generally of normal paraffin ranging from C16 to C30 and may be higher. Proportions of slightly branched chain paraffin ranging from C18 to C36 and naphthenes; especially alkyl-substituted derivatives of cyclopentane and cyclohexane; are also present [1, 5, 8–10].

The average molecular weight of these paraffin waxes is about 360–420 [9, 11]. A paraffin wax melting at 53.5°C showed a space lattice having C—C bond length

of 1.52°A, a C—C—C bond angle of 110°A, a C—H bond length of 1.17°A and an H—C—H bond angle of 105°A [12].

Microcrystalline waxes are obtained from the vacuum residue. The source for the production of microcrystalline wax is petrolatum or bright stock [13].

Microcrystalline waxes consist of highly branched chain paraffin; in contrast to the macrocrystalline; cycloparaffins and small amounts of n-paraffins and alkylated aromatics [1, 5, 9]. The actual chain length of the n-alkanes is approximately C34–C50. Long-chain, branched iso-alkanes predominantly contain chain lengths up to C70 [13].

The branched-chain structures of the composition CnH2n + 2 are found. Branched mono-methyl alkane, 2-methyl alkanes being found. As the position of the methyl group moves farther from the end of the chain, the amount of the corresponding alkane becomes smaller. The branched chains in the microcrystalline waxes are presented at random along the carbon chain, meanwhile in paraffin wax, they are located at the end of the chain [14].

The cyclo-alkanes, however, consist mainly of monocyclic systems. Monocyclopentyl, monocyclohexyl, dicyclohexyl paraffin and polycyclo paraffin are also found. Some microcrystalline waxes are mainly composed of multiplebranched isoparaffins and monocycloparaffins [1]. Moreover, non-hydrogenated micro waxes also mainly contain mono-cyclic and heterocyclic aromatic compounds [13].

Microcrystalline waxes have higher molecular weights (600–800), densities and refractive indices than paraffin waxes [1, 5, 6, 9].

#### **1.2 Properties of petroleum waxes**

#### *1.2.1 Physical properties*

Almost all, the physical properties of petroleum waxes are affected by the length of hydrocarbon chain, distribution of their individual components and degree of branching [10, 15].

Paraffin waxes are composed of 40–90 wt.% normal paraffins of about 22–30 carbon atoms and possibly higher, accordingly, they differ very little in physical and chemical properties. The remainder is C18–C36 isoalkanes and cycloalkanes [5, 16]. Straight chain alkanes in the range from 20 up to 36 carbon atoms show transition points in the solid phase. Thus two modifications, stable at different temperatures and different crystal habits, are known [1].

Microcrystalline waxes contain substantial proportions of highly branched or cyclic hydrocarbons in the range from 30 to 75 carbon atoms [5, 6, 17].

Paraffin waxes, relatively simple mixtures, usually have a narrow melting range and are generally lower in melting point than microcrystalline waxes. They usually melt between 46 and 68°C. The melting point of paraffin waxes increases in parallel with molecular weight. The branching of the carbon chain, at identical molecular weights, results in a decrease in the melting point. Paraffin waxes can be classified according to the melting point to soft (lower m.p.) and hard (higher m.p.) paraffin waxes.

Microcrystalline waxes are more complicated so it melts over a much wider temperature range. They usually melt between 60–93°C and 38–60°C, respectively [6, 9, 10].

Oil content is a fingerprint of the quality of the wax. The method of determination depends upon the differential solubility of oil and wax in a given solvent.

Paraffin wax, microcrystalline wax and petrolatum have a different degree of affinity for oil content. Paraffin wax has little affinity for oil content. It may be

**3**

mixing).

solution.

*Introductory Chapter: Petroleum Paraffins DOI: http://dx.doi.org/10.5772/intechopen.87090*

*1.2.2 Mechanical properties*

and microcrystalline waxes [1].

with food and non-food grade [19, 20].

**1.3 Crystal structure of petroleum waxes**

*1.3.1 Macrocrystalline waxes (paraffin waxes)*

researchers. They have come to the following conclusions:

*1.2.3 Food grade properties*

1–4 wt.%, depending on the grade of wax [9].

the test specimens are subjected to short-time stresses [10].

<0.5%.

content [18].

taken as a degree of refinement. Fully refined wax usually has an oil content of

Microcrystalline waxes have a higher affinity for oil than paraffin waxes because of their smaller crystal structure. The oil content of microcrystalline wax is

The hardness and crystallization behavior of macrocrystalline paraffin waxes are interfered distinctly by their distribution width, average chain length and n-alkane

Hardness is the resistance against the penetration of a body (needle, cone or plunger rod) under a defined load, this body is made of a harder material than the substance being tested. To measure the hardness of paraffin waxes, penetration tests are widely accepted. It is a common feature of strength and hardness tests that

The penetration test is the most widespread technique for determining the hardness and the thermal sensitivity of petroleum waxes. Macrocrystalline waxes change to a greater extent with temperature than that of microcrystalline waxes. An increase in oil content results in an increase in penetration values of both macro-

These properties concern waxes and petrolatums for food grade. Their potential toxicity could be attributed to aromatic residues. The latter are characterized directly by using UV spectra in the spectral zone corresponding to aromatics.

Each country has adopted its own code governing waxes, which come in contact

The class of organic crystals represents a broad range of geometries, including needles, plates, cubes, rods, prisms, pentagons, octagons, hexagons, rhomboids and pyramids. Each of these forms results from crystallization from a solution. The geometry of the crystals formed is determined by the solute/solvent interaction and the physical conditions of the system (e.g., temperature, pressure and mechanical

One interesting characteristic of crystals is that they can form a variety of shapes, which are due to the environmental conditions under which they form. They can be large or small, extend long distances or short, be well-defined or diffuse; in short, they can display an impressive array of forms. It is this variety of

All petroleum waxes are crystalline in some degree and it is possible to classify waxes in terms of the type of crystals formed, when the wax crystallizes out of

The paraffin crystals appear in three different forms: plates, needles and mal shapes; the latter are small size, undeveloped crystals, which often agglomerates. The conditions for the formation of these shapes have been studied by many

form upon which crystal modifiers are intended to take advantage [21].

#### *Introductory Chapter: Petroleum Paraffins DOI: http://dx.doi.org/10.5772/intechopen.87090*

taken as a degree of refinement. Fully refined wax usually has an oil content of <0.5%.

Microcrystalline waxes have a higher affinity for oil than paraffin waxes because of their smaller crystal structure. The oil content of microcrystalline wax is 1–4 wt.%, depending on the grade of wax [9].

### *1.2.2 Mechanical properties*

*Paraffin - an Overview*

to C70 [13].

pounds [13].

H—C—H bond angle of 105°A [12].

located at the end of the chain [14].

**1.2 Properties of petroleum waxes**

and different crystal habits, are known [1].

*1.2.1 Physical properties*

branching [10, 15].

refractive indices than paraffin waxes [1, 5, 6, 9].

of 1.52°A, a C—C—C bond angle of 110°A, a C—H bond length of 1.17°A and an

the production of microcrystalline wax is petrolatum or bright stock [13].

The cyclo-alkanes, however, consist mainly of monocyclic systems.

Monocyclopentyl, monocyclohexyl, dicyclohexyl paraffin and polycyclo paraffin are also found. Some microcrystalline waxes are mainly composed of multiplebranched isoparaffins and monocycloparaffins [1]. Moreover, non-hydrogenated micro waxes also mainly contain mono-cyclic and heterocyclic aromatic com-

Microcrystalline waxes have higher molecular weights (600–800), densities and

Almost all, the physical properties of petroleum waxes are affected by the length of hydrocarbon chain, distribution of their individual components and degree of

Paraffin waxes are composed of 40–90 wt.% normal paraffins of about 22–30 carbon atoms and possibly higher, accordingly, they differ very little in physical and chemical properties. The remainder is C18–C36 isoalkanes and cycloalkanes [5, 16]. Straight chain alkanes in the range from 20 up to 36 carbon atoms show transition points in the solid phase. Thus two modifications, stable at different temperatures

Microcrystalline waxes contain substantial proportions of highly branched or

Paraffin waxes, relatively simple mixtures, usually have a narrow melting range and are generally lower in melting point than microcrystalline waxes. They usually melt between 46 and 68°C. The melting point of paraffin waxes increases in parallel with molecular weight. The branching of the carbon chain, at identical molecular weights, results in a decrease in the melting point. Paraffin waxes can be classified according to the melting point to soft (lower m.p.) and hard (higher m.p.) paraffin

Microcrystalline waxes are more complicated so it melts over a much wider temperature range. They usually melt between 60–93°C and 38–60°C, respectively

tion depends upon the differential solubility of oil and wax in a given solvent. Paraffin wax, microcrystalline wax and petrolatum have a different degree of affinity for oil content. Paraffin wax has little affinity for oil content. It may be

Oil content is a fingerprint of the quality of the wax. The method of determina-

cyclic hydrocarbons in the range from 30 to 75 carbon atoms [5, 6, 17].

Microcrystalline waxes are obtained from the vacuum residue. The source for

Microcrystalline waxes consist of highly branched chain paraffin; in contrast to the macrocrystalline; cycloparaffins and small amounts of n-paraffins and alkylated aromatics [1, 5, 9]. The actual chain length of the n-alkanes is approximately C34–C50. Long-chain, branched iso-alkanes predominantly contain chain lengths up

The branched-chain structures of the composition CnH2n + 2 are found. Branched mono-methyl alkane, 2-methyl alkanes being found. As the position of the methyl group moves farther from the end of the chain, the amount of the corresponding alkane becomes smaller. The branched chains in the microcrystalline waxes are presented at random along the carbon chain, meanwhile in paraffin wax, they are

**2**

waxes.

[6, 9, 10].

The hardness and crystallization behavior of macrocrystalline paraffin waxes are interfered distinctly by their distribution width, average chain length and n-alkane content [18].

Hardness is the resistance against the penetration of a body (needle, cone or plunger rod) under a defined load, this body is made of a harder material than the substance being tested. To measure the hardness of paraffin waxes, penetration tests are widely accepted. It is a common feature of strength and hardness tests that the test specimens are subjected to short-time stresses [10].

The penetration test is the most widespread technique for determining the hardness and the thermal sensitivity of petroleum waxes. Macrocrystalline waxes change to a greater extent with temperature than that of microcrystalline waxes. An increase in oil content results in an increase in penetration values of both macroand microcrystalline waxes [1].

#### *1.2.3 Food grade properties*

These properties concern waxes and petrolatums for food grade. Their potential toxicity could be attributed to aromatic residues. The latter are characterized directly by using UV spectra in the spectral zone corresponding to aromatics.

Each country has adopted its own code governing waxes, which come in contact with food and non-food grade [19, 20].

#### **1.3 Crystal structure of petroleum waxes**

The class of organic crystals represents a broad range of geometries, including needles, plates, cubes, rods, prisms, pentagons, octagons, hexagons, rhomboids and pyramids. Each of these forms results from crystallization from a solution. The geometry of the crystals formed is determined by the solute/solvent interaction and the physical conditions of the system (e.g., temperature, pressure and mechanical mixing).

One interesting characteristic of crystals is that they can form a variety of shapes, which are due to the environmental conditions under which they form. They can be large or small, extend long distances or short, be well-defined or diffuse; in short, they can display an impressive array of forms. It is this variety of form upon which crystal modifiers are intended to take advantage [21].

All petroleum waxes are crystalline in some degree and it is possible to classify waxes in terms of the type of crystals formed, when the wax crystallizes out of solution.

#### *1.3.1 Macrocrystalline waxes (paraffin waxes)*

The paraffin crystals appear in three different forms: plates, needles and mal shapes; the latter are small size, undeveloped crystals, which often agglomerates. The conditions for the formation of these shapes have been studied by many researchers. They have come to the following conclusions:


Normal paraffin, C17–C34, may exist in three and possibly four crystal forms. Near the melting point, hexagonal crystals are the stable form. At somewhat lower temperatures, the odd-numbered from C19 to C29 are orthorhombic, even numbered ones from C18 to C26 is triclinic and those C28–C36 is monoclinic [22, 23].

#### *1.3.2 Microcrystalline waxes*

Both n-paraffin and isoparaffins crystallize in needle forms; they differ in that the latter does so at all temperatures, while higher temperatures are required for the former. The needle form of the isoparaffins differs from that of ceresins or paraffin waxes containing ceresins, in that the crystals of former are large and loose, while those of the latter are extremely small and dense [14].

Microcrystalline waxes may contain substantial percentages up to 30% of paraffin which, when separated, crystallize well as high-melting macro crystalline or paraffin wax. The microcrystalline wax material interferes and imposes its crystallizing habit on the other material [16, 24].

Although the classification of petroleum waxes into macro crystalline and microcrystalline waxes on the basis of crystal size is valid to a great extent, there is no sharp line separating the two groups. Indeed, there is a large group of waxes that could fall in either classes and these waxes are called intermediate waxes, blended waxes, mal-crystalline waxes and semi-microcrystalline waxes. But semi-microcrystalline wax adopted [17].

**5**

*Introductory Chapter: Petroleum Paraffins DOI: http://dx.doi.org/10.5772/intechopen.87090*

**1.4 Manufacture of petroleum waxes**

• Refining of the wax products.

• Percolation process.

• Acid treatment.

tions [4, 10, 26–30].

**2. Conclusion**

• Adsorption process.

**1.5 Applications of petroleum waxes**

• Hydrofinishing process.

• Deoiling and fractional crystallization.

processes:

The manufacture of petroleum waxes is closely related to the manufacture of lubricating oils. The raw paraffin distillates and residual oils contain wax and they are normally solid at ambient temperature. Removal of wax from these fractions is necessary to permit the manufacture of lubricating oil with a satisfactory low pour point. Manufacture of petroleum waxes includes the following technological

• Production of slack waxes and petrolatums by dewaxing petroleum products.

As the consumption of wax products in the world wax market increases; especially for food, pharmaceutical and cosmetic grades and specialty wax; the increase of profitability of wax production will lie on the improvement of blending and modification techniques for macro- and microcrystalline waxes as base materials as

Petroleum waxes are based in a wide variety of applications. Some of its most important applications were used in industry such as, paper industry, household chemicals, cosmetics industry, dental industry, match industry, rubber industry, building constructions, electrical industry, inks industry and powder injection molding industry beside that of hydrogen production and energy storage applica-

Fractions of petroleum wax can be achieved to separate more than one type of paraffin wax such as macrocrystalline and microcrystalline waxes, the waxes characterization such as carbon number, hardness, crystal shape, composition and molecular weight depend on the condition of separating the wax, paraffin wax act like a joker in different industries such as inks, papers, cosmetics and ceramic

well as the development and applications of new wax products [25].

fabricating using powder injection molding industry.

## **1.4 Manufacture of petroleum waxes**

*Paraffin - an Overview*

shapes.

very slight.

1.The three crystal forms of paraffin waxes depend on both the conditions of the

3.For a given molecular weight limit, the higher melting point constituents crystallize in plate type in which the crystals are hexagonal plate. The low-melting ones crystallize in needles while the medium-melting ones crystallize in mal

4.Normal paraffin crystallize in plates. Needle crystals contain both aliphatic and cyclic hydrocarbons, while mal-shaped crystals are characterized by their

5.Low-cooling rates during crystallization will result in large crystals for both plate and needle forms, while the crystal growth for mal-shaped crystals is

6.The solubility of paraffin in a solvent is inversely proportional to their melting points. In the presence of solvent, wax mixtures begin to crystallize at relatively low temperatures in the form of plates followed by mal-shaped crystals. However, the constituents crystallizing in needles are more soluble than those crystallizing in plates. Therefore, needles crystals will appear only at lower

7.Plate crystals can readily be transformed into needle and mal-shaped crystals. Under appropriate conditions, the needle crystals can be transformed into

Normal paraffin, C17–C34, may exist in three and possibly four crystal forms. Near the melting point, hexagonal crystals are the stable form. At somewhat lower temperatures, the odd-numbered from C19 to C29 are orthorhombic, even numbered

Both n-paraffin and isoparaffins crystallize in needle forms; they differ in that the latter does so at all temperatures, while higher temperatures are required for the former. The needle form of the isoparaffins differs from that of ceresins or paraffin waxes containing ceresins, in that the crystals of former are large and loose, while

Microcrystalline waxes may contain substantial percentages up to 30% of paraffin which, when separated, crystallize well as high-melting macro crystalline or paraffin wax. The microcrystalline wax material interferes and imposes its crystal-

Although the classification of petroleum waxes into macro crystalline and microcrystalline waxes on the basis of crystal size is valid to a great extent, there is no sharp line separating the two groups. Indeed, there is a large group of waxes that could fall in either classes and these waxes are called intermediate waxes, blended waxes, mal-crystalline waxes and semi-microcrystalline waxes. But semi-micro-

ones from C18 to C26 is triclinic and those C28–C36 is monoclinic [22, 23].

2.Plate crystals are obtained from lower boiling points paraffinic distillates, while the needle and mal-shaped crystals are obtained from the higher boiling

crystallization process and the chemical composition of the wax.

points ones and from vacuum residues.

content of branched hydrocarbons.

temperature and higher concentrations

those of the latter are extremely small and dense [14].

lizing habit on the other material [16, 24].

crystalline wax adopted [17].

mal-shaped crystals [10].

*1.3.2 Microcrystalline waxes*

**4**

The manufacture of petroleum waxes is closely related to the manufacture of lubricating oils. The raw paraffin distillates and residual oils contain wax and they are normally solid at ambient temperature. Removal of wax from these fractions is necessary to permit the manufacture of lubricating oil with a satisfactory low pour point. Manufacture of petroleum waxes includes the following technological processes:


## **1.5 Applications of petroleum waxes**

As the consumption of wax products in the world wax market increases; especially for food, pharmaceutical and cosmetic grades and specialty wax; the increase of profitability of wax production will lie on the improvement of blending and modification techniques for macro- and microcrystalline waxes as base materials as well as the development and applications of new wax products [25].

Petroleum waxes are based in a wide variety of applications. Some of its most important applications were used in industry such as, paper industry, household chemicals, cosmetics industry, dental industry, match industry, rubber industry, building constructions, electrical industry, inks industry and powder injection molding industry beside that of hydrogen production and energy storage applications [4, 10, 26–30].

## **2. Conclusion**

Fractions of petroleum wax can be achieved to separate more than one type of paraffin wax such as macrocrystalline and microcrystalline waxes, the waxes characterization such as carbon number, hardness, crystal shape, composition and molecular weight depend on the condition of separating the wax, paraffin wax act like a joker in different industries such as inks, papers, cosmetics and ceramic fabricating using powder injection molding industry.

*Paraffin - an Overview*

## **Author details**

Fathi Samir Soliman Egyptian Petroleum Research Institute, Cairo, Egypt

\*Address all correspondence to: fathisamir@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**7**

*Introductory Chapter: Petroleum Paraffins DOI: http://dx.doi.org/10.5772/intechopen.87090*

[1] Mazee W. Modern Petroleum Technology. Great Britain: Applied Science Publishers Ltd., on behalf of The Institute of Petroleum; 1973. p. 782 Doklady Akademii Nauk SSSR.

[13] Meyer G. Thermal properties of micro-crystalline waxes in dependence on the degree of deoiling. SOFW journal. 2009;**135**(8):43-50

spectrophotometric determination of microgram amounts of lauroyl and benzoyl peroxide. Analytical Chemistry.

[16] Corson B. In: Brooks BT, Kurtz SS Jr, Boord CE, Schmerling L, editors. The Chemistry of Petroleum Hydrocarbons.

[18] Meyer G. Interactions between chain length distributions, crystallization behaviour and needle penetration of paraffin waxes. Erdöl, Erdgas, Kohle.

[19] Hopkins TD, N.C.F.P. Analysis, the costs of federal regulation. National

[20] USP, U.P. 34, NF 29. The United States pharmacopeia and the National formulary. Rockwille, MD: The United States Pharmacopeial Convention; 2011

[21] Becker J. Crude Oil Waxes, Emulsions and Asphaltenes. Tulsa, OK, USA: Penn

[22] Smith A. The crystal structure of the normal paraffin hydrocarbons.

Well Publishing Company; 1997

[15] Kuszlik A et al. Solvent-free slack wax de-oiling—Physical limits. Chemical Engineering Research and Design. 2010;**88**(9):1279-1283

1950;**72**(1):53-56

[14] Levy E et al. Rapid

1961;**33**(6):696-698

Vol. Ill. 1955. pp. 310-312

Industry; 1963. pp. 1-19

2006;**122**(1):16-18

Chamber Foundation. 1992

[17] Ferris S. Petroleum Waxes: Characterization, Performance, and Additives. New York, USA: Technical Association of the Pulp and Paper

[2] Prasad R. Petroleum Refining Technology. Delhi, India: Khanna; 2000

D. Characterization of petroleum waxes by high temperature gas chromatography-correlation with physical properties. Petroleum Science and Technology. 1997;**15**(9-10):943-957

[4] Bennett H. Industrial Waxes. New York: Chemical Pub Co; 1975

New York. 1984. pp. 466-481

[5] Letcher C. Waxes. John Wiley & Sons

[6] Avilino S Jr. Lubricant Base Oil and Wax Processing. New York: Morcel Dekker, Inc.; 1994. pp. 17-36

[7] Guthrie VB. Petroleum Products Handbook. McGraw-Hill; 1960

[8] Concawe. Petroleum Waxes and Related Products. Boulevard du Souverain, Brussels, Belgium; 1999

[9] Gottshall R, McCue C, Allinson J. Criteria for Quality of Petroleum Products. London, Great Britian: Applied Science Publishers Ltd. On

[10] Freund M. et al. Paraffin Products Properties, Technologies, Applications.

[11] Nakagawa H et al. Characterization of hydrocarbon waxes by gas-liquid chromatography with a high-resolution glass capillary column. Journal of Chromatography A. 1983;**260**:391-409

[12] Vainshtein B, Pinsker Z. Opredelenie polozheniya vodoroda v kristallicheskoi reshetke parafina.

behalf; 1973

1982. p. 14

[3] Gupta A, Severin

**References**

*Introductory Chapter: Petroleum Paraffins DOI: http://dx.doi.org/10.5772/intechopen.87090*

## **References**

*Paraffin - an Overview*

**6**

**Author details**

Fathi Samir Soliman

Egyptian Petroleum Research Institute, Cairo, Egypt

\*Address all correspondence to: fathisamir@gmail.com

provided the original work is properly cited.

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

[1] Mazee W. Modern Petroleum Technology. Great Britain: Applied Science Publishers Ltd., on behalf of The Institute of Petroleum; 1973. p. 782

[2] Prasad R. Petroleum Refining Technology. Delhi, India: Khanna; 2000

[3] Gupta A, Severin D. Characterization of petroleum waxes by high temperature gas chromatography-correlation with physical properties. Petroleum Science and Technology. 1997;**15**(9-10):943-957

[4] Bennett H. Industrial Waxes. New York: Chemical Pub Co; 1975

[5] Letcher C. Waxes. John Wiley & Sons New York. 1984. pp. 466-481

[6] Avilino S Jr. Lubricant Base Oil and Wax Processing. New York: Morcel Dekker, Inc.; 1994. pp. 17-36

[7] Guthrie VB. Petroleum Products Handbook. McGraw-Hill; 1960

[8] Concawe. Petroleum Waxes and Related Products. Boulevard du Souverain, Brussels, Belgium; 1999

[9] Gottshall R, McCue C, Allinson J. Criteria for Quality of Petroleum Products. London, Great Britian: Applied Science Publishers Ltd. On behalf; 1973

[10] Freund M. et al. Paraffin Products Properties, Technologies, Applications. 1982. p. 14

[11] Nakagawa H et al. Characterization of hydrocarbon waxes by gas-liquid chromatography with a high-resolution glass capillary column. Journal of Chromatography A. 1983;**260**:391-409

[12] Vainshtein B, Pinsker Z. Opredelenie polozheniya vodoroda v kristallicheskoi reshetke parafina. Doklady Akademii Nauk SSSR. 1950;**72**(1):53-56

[13] Meyer G. Thermal properties of micro-crystalline waxes in dependence on the degree of deoiling. SOFW journal. 2009;**135**(8):43-50

[14] Levy E et al. Rapid spectrophotometric determination of microgram amounts of lauroyl and benzoyl peroxide. Analytical Chemistry. 1961;**33**(6):696-698

[15] Kuszlik A et al. Solvent-free slack wax de-oiling—Physical limits. Chemical Engineering Research and Design. 2010;**88**(9):1279-1283

[16] Corson B. In: Brooks BT, Kurtz SS Jr, Boord CE, Schmerling L, editors. The Chemistry of Petroleum Hydrocarbons. Vol. Ill. 1955. pp. 310-312

[17] Ferris S. Petroleum Waxes: Characterization, Performance, and Additives. New York, USA: Technical Association of the Pulp and Paper Industry; 1963. pp. 1-19

[18] Meyer G. Interactions between chain length distributions, crystallization behaviour and needle penetration of paraffin waxes. Erdöl, Erdgas, Kohle. 2006;**122**(1):16-18

[19] Hopkins TD, N.C.F.P. Analysis, the costs of federal regulation. National Chamber Foundation. 1992

[20] USP, U.P. 34, NF 29. The United States pharmacopeia and the National formulary. Rockwille, MD: The United States Pharmacopeial Convention; 2011

[21] Becker J. Crude Oil Waxes, Emulsions and Asphaltenes. Tulsa, OK, USA: Penn Well Publishing Company; 1997

[22] Smith A. The crystal structure of the normal paraffin hydrocarbons.

The Journal of Chemical Physics. 1953;**21**(12):2229-2231

[23] Ohlberg SM. The stable crystal structures of pure n-Paraffins Contalmng an even number of carbon atoms in the range C30 to C36. The Journal of Physical Chemistry. 1959;**63**(2):248-250

[24] Higgs P. The utilization of paraffin wax and petroleum ceresin. Journal of the Institution of Petroleum Technology. 1935;**21**:1-14

[25] Zaky MT et al. Raising the efficiency of petrolatum deoiling process by using non-polar modifier concentrates separated from paraffin wastes to produce different petroleum products. RSC Advances. 2015;**5**(88):71932-71941

[26] Maillefer S, Rehmann A, Zenhaeusern B. Hair wax products with a liquid or creamy consistency. Google Patents. 2011

[27] Saleh A, Ahmed M, Zaky M. Manufacture of high softening waxy asphalt for use in road paving. Petroleum Science and Technology. 2008;**26**(2):125-135

[28] Zaky M, Soliman F, Farag A. Influence of paraffin wax characteristics on the formulation of wax-based binders and their debinding from green molded parts using two comparative techniques. Journal of Materials Processing Technology. 2009;**209**(18-19):5981-5989

[29] El Naggar AM et al. New advances in hydrogen production via the catalytic decomposition of wax by-products using nanoparticles of SBA frameworked MoO3. Energy Conversion and Management. 2015;**106**:615-624

[30] Mohamed NH et al. Thermal conductivity enhancement of treated petroleum waxes, as phase change material, by α nano alumina: Energy

storage. Renewable and Sustainable Energy Reviews. 2017;**70**:1052-1058

**Chapter 2**

Oils

**Abstract**

**1. Introduction**

monly found [2].

**9**

Wax Chemical and Morphological

The waxes in petroleum can precipitate and form unwanted gels and deposition

methods of quantification and physicochemical and morphological characterization of waxes and how this information can help in understanding this deposition. Information such as the quantity of waxes and the chemical structures in the oil is fundamental to predict the possible deposition and its ability to aggregate with other crystals. For example, the knowledge about the wax morphology may

contribute to explain the nucleation and growth of the deposits. The polarized light microscopy, the most common technique to visualize wax crystals, and the brightfield microscopy, the most simple technique, able to show crystal details that have

**Keywords:** waxes, crude oil, quantification, characterization, microscopy, DSC

Petroleum is a complex mixture of hydrocarbons of varying nature and small fractions of nitrogen, oxygen, sulfur, and metal compounds. At room temperature, petroleum can be gas, liquid, and/or solid, being considered as gases and solids dispersing in a liquid phase [1]. Under high temperature and pressure, as encountered at reservoirs (e.g., 8000–15,000 psi and 70–150°C), Newtonian rheological behavior prevails, whereas at low temperatures the pseudoplastic behavior is com-

A large portion of the Brazilian oil production comes from offshore fields, from the pre-salt layer. These oils have high levels of waxes, which are alkanes (linear or branched) encompassing carbonic chains of 15–75 carbons [3, 4]. This class of compounds has a high precipitation potential, due to the low sea temperatures (about 4–5°C) [5–7]. In temperatures below the wax appearance temperature (WAT), the wax crystallization takes place with subsequent deposition [2]. The wax deposition is dominated by the molecular diffusion mechanism [8] in which the waxes initially precipitate at the cold pipeline walls and subsequently generate a radial gradient of precipitation causing deposit [9, 10]. This can lead to a strong waxy crystal interlocking network, which causes pipeline clogs and dramatically

when exposed to low temperatures. The idea of this chapter is to approach

Investigation of Brazilian Crude

*Erika C.A. Nunes Chrisman, Angela C.P. Duncke,*

*Márcia C.K. Oliveira and Márcio N. Souza*

not been seen on the polarized light, was used.

affects the rheological fluid behavior [9, 11–13].

## **Chapter 2**

*Paraffin - an Overview*

1953;**21**(12):2229-2231

1959;**63**(2):248-250

1935;**21**:1-14

Patents. 2011

2008;**26**(2):125-135

The Journal of Chemical Physics.

storage. Renewable and Sustainable Energy Reviews. 2017;**70**:1052-1058

[23] Ohlberg SM. The stable crystal structures of pure n-Paraffins Contalmng an even number of carbon atoms in the range C30 to C36. The Journal of Physical Chemistry.

[24] Higgs P. The utilization of paraffin wax and petroleum ceresin. Journal of the Institution of Petroleum Technology.

[25] Zaky MT et al. Raising the efficiency of petrolatum deoiling process by using non-polar modifier concentrates separated from paraffin wastes to produce different petroleum products. RSC Advances. 2015;**5**(88):71932-71941

Zenhaeusern B. Hair wax products with a liquid or creamy consistency. Google

[26] Maillefer S, Rehmann A,

[27] Saleh A, Ahmed M, Zaky M. Manufacture of high softening waxy asphalt for use in road paving. Petroleum Science and Technology.

[28] Zaky M, Soliman F, Farag A.

on the formulation of wax-based binders and their debinding from green molded parts using two comparative techniques. Journal of Materials Processing Technology. 2009;**209**(18-19):5981-5989

Influence of paraffin wax characteristics

[29] El Naggar AM et al. New advances in hydrogen production via the catalytic decomposition of wax by-products using nanoparticles of SBA frameworked MoO3. Energy Conversion and Management. 2015;**106**:615-624

[30] Mohamed NH et al. Thermal conductivity enhancement of treated petroleum waxes, as phase change material, by α nano alumina: Energy

**8**

## Wax Chemical and Morphological Investigation of Brazilian Crude Oils

*Erika C.A. Nunes Chrisman, Angela C.P. Duncke, Márcia C.K. Oliveira and Márcio N. Souza*

## **Abstract**

The waxes in petroleum can precipitate and form unwanted gels and deposition when exposed to low temperatures. The idea of this chapter is to approach methods of quantification and physicochemical and morphological characterization of waxes and how this information can help in understanding this deposition. Information such as the quantity of waxes and the chemical structures in the oil is fundamental to predict the possible deposition and its ability to aggregate with other crystals. For example, the knowledge about the wax morphology may contribute to explain the nucleation and growth of the deposits. The polarized light microscopy, the most common technique to visualize wax crystals, and the brightfield microscopy, the most simple technique, able to show crystal details that have not been seen on the polarized light, was used.

**Keywords:** waxes, crude oil, quantification, characterization, microscopy, DSC

### **1. Introduction**

Petroleum is a complex mixture of hydrocarbons of varying nature and small fractions of nitrogen, oxygen, sulfur, and metal compounds. At room temperature, petroleum can be gas, liquid, and/or solid, being considered as gases and solids dispersing in a liquid phase [1]. Under high temperature and pressure, as encountered at reservoirs (e.g., 8000–15,000 psi and 70–150°C), Newtonian rheological behavior prevails, whereas at low temperatures the pseudoplastic behavior is commonly found [2].

A large portion of the Brazilian oil production comes from offshore fields, from the pre-salt layer. These oils have high levels of waxes, which are alkanes (linear or branched) encompassing carbonic chains of 15–75 carbons [3, 4]. This class of compounds has a high precipitation potential, due to the low sea temperatures (about 4–5°C) [5–7]. In temperatures below the wax appearance temperature (WAT), the wax crystallization takes place with subsequent deposition [2]. The wax deposition is dominated by the molecular diffusion mechanism [8] in which the waxes initially precipitate at the cold pipeline walls and subsequently generate a radial gradient of precipitation causing deposit [9, 10]. This can lead to a strong waxy crystal interlocking network, which causes pipeline clogs and dramatically affects the rheological fluid behavior [9, 11–13].

Gelation and deposition problems, leading to increases in yield stress and losses in production, are probably connected to wax morphology. This chapter aims to show some techniques to characterize the structure and morphology of wax crystals based on four pre-salt Brazilian crude oils, all provided by Petrobras, under different shear conditions, aging times, and temperatures. In addition, some physicochemical characterization techniques are discussed as density, viscosity, and SAP (saturated, aromatic, and polar). The wax quantification is the harder part of the study of crude oils, due to the petroleum complex matrix, which can cause complications related to the wax crude oil separation; however, through differential scanning calorimeter (DSC) measurements, it is possible to obtain a precipitated wax content as well as through some American Society for Testing and Materials (ASTM), Universal Oil Products Collection (UOP), gas chromatography (GC), and others.

the aliquots of crude oil in this chapter were observed on optical microscope Axio

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils*

The BF technique (**Figure 1a**) provides lower contrast than PL technique (**Figure 1b**); however, it can be seen that in BF micrographs the wax crystal is continuous, i.e., the structure appears and integrates, without rupture. On the other hand, PL micrographs show "dark cracks," i.e., the wax crystals do not appear entirely. These "dark cracks" can be attributed to two factors: first, amorphous or low crystallinity regions due to the presence of impurities and second, due to light extinction positions, related to the parallel orientation of polarizers and the crystal organization, i.e., no light is deflected by the sample [30]. Therefore, much attention should be taken to make length measurements in crystals observed by PL technique. According to these results, to determine the size and crystal shape (as verified by BF) can be critical to avoid erroneous measurements. In this work, the length measurements were performed on images obtained by BF, but the PL images

Another characteristic of wax crystals that can be seen in **Figure 1a** is a rough-

In order to characterize the wax morphology and crystals length in dependence of temperature and shear, a continuous cooling protocol was performed (**Figure 2**). Initially, the thermal history removal of 100 mL of each oil was carried out by heating the samples for 2 h at 80°C in a circulating oven model 400-3ND (Ethik Technology). This condition is sufficient to dissolve all wax present in the crude oil and prevent that the wax crystal formation was not influenced by pre-existing nuclei [32, 33]. Secondly, the samples were transferred to a jacketed Becker coupled to a circulation bath (Haake Phoenix II-C25P - Thermo Scientific). Then, the cooling step was carried out quiescently or in presence of shear (mechanical agitation 250 rpm on RW20 Digital IKA) for 80–5°C. The cooling rate was 0.5°C/min. **Figure 2** shows the influence of shear on waxy crystal growth of P1–P4 paraffinic oil comparing the PL micrographs of tests carried out at 5°C, on quiescent and shear

ened surface. The roughness, as well as the tortuosity of wax crystals, can be attributed to a heterogeneous nucleation and growth, by the presence of asphaltenes, resins, and different wax chain lengths or the presence of isocycle

It was verified that experiments performed with quiescent condition (**Figure 2A**–**D**) were characterized by large crystals and cluster of crystals when compared with experiments carried out with shear condition (**Figure 2E**–**H**). The

*PL micrographs of test performed at 5°C on quiescent (A–D) and shear (E–H) conditions of waxy crude oils*

Vert 40 MAT (Carl Zeiss).

*DOI: http://dx.doi.org/10.5772/intechopen.83736*

are shown due to easy observation.

[24, 31].

cooling conditions.

**Figure 2.**

*P1–P4.*

**11**

## **2. Morphological characterizations**

Due to the petroleum multicomponent nature, the wax precipitation occurs heterogeneously, and resins and asphaltene molecules, inorganic solids, and corrosion products, among others, can behave as nuclei for the phenomenon, enhancing the flow assurance issue [14].

Waxes crystallize into basically orthorhombic and hexagonal shapes. The orthorhombic form is needle-shaped, and it is found in crudes with high waxy content [15, 16]. Crystallization kinetics and crystal morphology can be highly affected by some recognized factors, such as cooling rate [13, 17–23], carbonic chain nature (branched or linear and average length) [21], resins and asphaltene content [2, 7, 24, 25], and shear rate [16, 26–28].

The polarized light (PL) optical microscopy is the fundamental technique for wax crystal examination [24]. According to [29] it allows verifying the anisotropic optical behavior of crystalline materials, named birefringence. This technique uses two cross polarizers. When the light beam passes through crystalline structures, as wax crystals, the polarized light plane is altered generating a visible image pattern. On the other hand, isotropic structures, which do not exhibit the same level of organization, are not able to modify the light plane. Apart from PL microscopy, the bright-field (BF) microscopy regards another important technique for wax crystal visualization. The procedure is very simple, and no artifacts are employed in the optical path.

**Figure 1** shows BF and PL micrographs of P1 Brazilian crude oil, for the same point of the coverslip, at 25°C, as received, i.e., without any thermal treatment. All

**Figure 1.** *(A) BF and (B) PL micrograph of P1, for the same point of cover slip at 25°C, as received.*

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils DOI: http://dx.doi.org/10.5772/intechopen.83736*

the aliquots of crude oil in this chapter were observed on optical microscope Axio Vert 40 MAT (Carl Zeiss).

The BF technique (**Figure 1a**) provides lower contrast than PL technique (**Figure 1b**); however, it can be seen that in BF micrographs the wax crystal is continuous, i.e., the structure appears and integrates, without rupture. On the other hand, PL micrographs show "dark cracks," i.e., the wax crystals do not appear entirely. These "dark cracks" can be attributed to two factors: first, amorphous or low crystallinity regions due to the presence of impurities and second, due to light extinction positions, related to the parallel orientation of polarizers and the crystal organization, i.e., no light is deflected by the sample [30]. Therefore, much attention should be taken to make length measurements in crystals observed by PL technique. According to these results, to determine the size and crystal shape (as verified by BF) can be critical to avoid erroneous measurements. In this work, the length measurements were performed on images obtained by BF, but the PL images are shown due to easy observation.

Another characteristic of wax crystals that can be seen in **Figure 1a** is a roughened surface. The roughness, as well as the tortuosity of wax crystals, can be attributed to a heterogeneous nucleation and growth, by the presence of asphaltenes, resins, and different wax chain lengths or the presence of isocycle [24, 31].

In order to characterize the wax morphology and crystals length in dependence of temperature and shear, a continuous cooling protocol was performed (**Figure 2**). Initially, the thermal history removal of 100 mL of each oil was carried out by heating the samples for 2 h at 80°C in a circulating oven model 400-3ND (Ethik Technology). This condition is sufficient to dissolve all wax present in the crude oil and prevent that the wax crystal formation was not influenced by pre-existing nuclei [32, 33]. Secondly, the samples were transferred to a jacketed Becker coupled to a circulation bath (Haake Phoenix II-C25P - Thermo Scientific). Then, the cooling step was carried out quiescently or in presence of shear (mechanical agitation 250 rpm on RW20 Digital IKA) for 80–5°C. The cooling rate was 0.5°C/min. **Figure 2** shows the influence of shear on waxy crystal growth of P1–P4 paraffinic oil comparing the PL micrographs of tests carried out at 5°C, on quiescent and shear cooling conditions.

It was verified that experiments performed with quiescent condition (**Figure 2A**–**D**) were characterized by large crystals and cluster of crystals when compared with experiments carried out with shear condition (**Figure 2E**–**H**). The

#### **Figure 2.**

*PL micrographs of test performed at 5°C on quiescent (A–D) and shear (E–H) conditions of waxy crude oils P1–P4.*

Gelation and deposition problems, leading to increases in yield stress and losses in production, are probably connected to wax morphology. This chapter aims to show some techniques to characterize the structure and morphology of wax crystals based on four pre-salt Brazilian crude oils, all provided by Petrobras, under different shear conditions, aging times, and temperatures. In addition, some physicochemical characterization techniques are discussed as density, viscosity, and SAP (saturated, aromatic, and polar). The wax quantification is the harder part of the study of crude oils, due to the petroleum complex matrix, which can cause complications related to the wax crude oil separation; however, through differential scanning calorimeter (DSC) measurements, it is possible to obtain a precipitated wax content as well as through some American Society for Testing and Materials (ASTM), Universal Oil Products Collection (UOP), gas chromatography (GC), and

Due to the petroleum multicomponent nature, the wax precipitation occurs heterogeneously, and resins and asphaltene molecules, inorganic solids, and corrosion products, among others, can behave as nuclei for the phenomenon, enhancing

Waxes crystallize into basically orthorhombic and hexagonal shapes. The orthorhombic form is needle-shaped, and it is found in crudes with high waxy content [15, 16]. Crystallization kinetics and crystal morphology can be highly affected by some recognized factors, such as cooling rate [13, 17–23], carbonic chain nature (branched or linear and average length) [21], resins and asphaltene content

The polarized light (PL) optical microscopy is the fundamental technique for wax crystal examination [24]. According to [29] it allows verifying the anisotropic optical behavior of crystalline materials, named birefringence. This technique uses two cross polarizers. When the light beam passes through crystalline structures, as wax crystals, the polarized light plane is altered generating a visible image pattern. On the other hand, isotropic structures, which do not exhibit the same level of organization, are not able to modify the light plane. Apart from PL microscopy, the bright-field (BF) microscopy regards another important technique for wax crystal visualization. The procedure is very simple, and no artifacts are employed in the

**Figure 1** shows BF and PL micrographs of P1 Brazilian crude oil, for the same point of the coverslip, at 25°C, as received, i.e., without any thermal treatment. All

*(A) BF and (B) PL micrograph of P1, for the same point of cover slip at 25°C, as received.*

others.

*Paraffin - an Overview*

optical path.

**Figure 1.**

**10**

**2. Morphological characterizations**

[2, 7, 24, 25], and shear rate [16, 26–28].

the flow assurance issue [14].

researchers carried out by [2, 16, 34] show that under quiescent conditions, the waxy crystals were characterized by extended and continuous particles. The formation of extended and continuous particles allowed a colloidal network that embodies the oil itself. Probably, the gel would have a high shear modulus, in order to the side-by-side interactions between particles. Under the shear condition, the lateral growth of the individual crystals is constricted. However, extended particles are not observed, and consequently, these particles lost their interconnectivity.

The wax crystals presented in waxy crude oils (**Figure 2**) are elongated. According to [16], waxes precipitated in crude oil tend to crystallize in an orthorhombic structure, which is characterized by an elongated structure. Evidently, the crystals of **Figure 2** (and in detail in **Figure 1**) are not linear (needle-like). The sinuosity and tortuosity are probably due to the presence of impurities during nucleation and crystal growth processes [2, 21]. [2] analyzed the aspect ratio, which is the ratio between the length and the width of a crystal. Based on aspect ratio value, it is possible to verify how the structure is elongated. The values of average aspect ratio, at 5°C, of samples P1, P2, and P3, are 5.5, 6.2, and 5.0, respectively, legitimizing the elongated characteristic. P4 sample has a 4.0 aspect ratio value, which indicates that the crystals are less elongated than other samples.

Another common factor studied on precipitation and morphology of waxy crystals is the aging time, which represents the influence of the time at a certainly constant temperature on the crystal wax. PL micrographs in **Figure 4** show the influence of 1 h aging time at temperatures 40, 20, and 5°C, for P4. To study the aging time influence, first, the thermal history was removed. The samples were transferred to the jacketed Becker coupled to a circulation bath at 80°C and then started the cooling steps (80–40°C; 80–20°C or 80–5°C). When the temperature arrives 40, 20, or 5°C, the samples were kept cool for 1 h at this temperature. The

*PL micrographs of P3 obtained at (A) 30°C, (B) 10°C, (C) 5°C and during quiescent cooling.*

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils*

*DOI: http://dx.doi.org/10.5772/intechopen.83736*

It was verified that the aging time favored the increase of crystal length and appearance of large clusters. This result can be attributed to the Ostwald ripening of wax crystals, a mechanism by which the large crystals grew at the expenses of smaller crystals of higher energy. Furthermore, oil uptake can also change the wax crystal distribution, leading to larger and softer wax crystals that can interpenetrate

**Table 2** shows the wax crystal's average length at t = 0 h and after 1 h (t = 1 h) at temperatures 40, 20, and 5°C, as well as the crystal growth percentage in function

Analyzing **Table 2**, at 40°C the oils P1 and P3 show an increase of about 26.3% in

the length of the crystal after 1 h in an isothermal condition. Under these same conditions, P2 shows a growth of almost 80.0%. P2 has the WAT at 42.1°C (see 4. Wax quantification), and consequently, there is no visible crystal on microscope when the temperature just arrives at 40°C. For this reason, the crystal size, in this

*PL micrographs of tests carried out with P4, at t = 0 h for 40°C (A), 20°C (B) and 5°C (C); and after 1 h at*

increasing intermolecular interactions between crystals [11, 37, 38].

cooling rate was 0.5°C/min.

of aging time.

**Figure 4.**

**13**

*40°C (D), 20°C (E) and 5°C (F).*

**Figure 3.**

**Table 1** shows the average length and width of crystals to waxy crude oils P1–P4 in function of temperature for 30, 10, and 5°C, for quiescent and shear conditions, and shows the average percentage of crystal growth between both cooling conditions.

For quiescent conditions, it is possible to note the crystal length increases between 10 and 5°C; however, for shear conditions, the length becomes basically stationary at these temperatures. This behavior could be attributed to a possible crystal breakage by the shear, which prevents the crystals from becoming large. The average percentage of growth between quiescent and shear conditions increases with the temperature decrease. For 30°C the crystals obtained in quiescent cooling are about 12.4% higher than that obtained by shear conditions. At 5°C this difference reaches 25.1%. On the other hand, the crystal width underwent an effective action of the shear, being about 22.3% less wide than those obtained in quiescent conditions.

To illustrate the **Table 1**, **Figure 3** shows PL micrographs of P3 obtained at 30, 10, and 5°C during quiescent cooling. This condition resembles the operational shutdowns when crude oil is cooled. As expected and discussed above, the concentration and size of wax crystals increase with the decrease in temperature. Since the solubility of high molecular weight waxes decreases sharply with the decrease in temperature, they precipitate out and crystallize. This result indicates that in low temperatures, it is more probably to have problems of flow assurance due to pipeline blockage occasioned by wax crystal depositions and to the formation of a highstrength gel, characterized by yield stress [35–37].


**Table 1.** *Length and width of crystal's average and growth percentage.*

#### **Figure 3.**

researchers carried out by [2, 16, 34] show that under quiescent conditions, the waxy crystals were characterized by extended and continuous particles. The formation of extended and continuous particles allowed a colloidal network that embodies the oil itself. Probably, the gel would have a high shear modulus, in order to the side-by-side interactions between particles. Under the shear condition, the lateral growth of the individual crystals is constricted. However, extended particles are not observed, and consequently, these particles lost their interconnectivity. The wax crystals presented in waxy crude oils (**Figure 2**) are elongated. According to [16], waxes precipitated in crude oil tend to crystallize in an orthorhombic structure, which is characterized by an elongated structure. Evidently, the crystals of **Figure 2** (and in detail in **Figure 1**) are not linear (needle-like). The sinuosity and tortuosity are probably due to the presence of impurities during nucleation and crystal growth processes [2, 21]. [2] analyzed the aspect ratio, which is the ratio between the length and the width of a crystal. Based on aspect ratio value, it is possible to verify how the structure is elongated. The values of average aspect ratio, at 5°C, of samples P1, P2, and P3, are 5.5, 6.2, and 5.0, respectively, legitimizing the elongated characteristic. P4 sample has a 4.0 aspect ratio value,

which indicates that the crystals are less elongated than other samples.

conditions.

*Paraffin - an Overview*

conditions.

**Table 1.**

**12**

and shows the average percentage of crystal growth between both cooling

For quiescent conditions, it is possible to note the crystal length increases between 10 and 5°C; however, for shear conditions, the length becomes basically stationary at these temperatures. This behavior could be attributed to a possible crystal breakage by the shear, which prevents the crystals from becoming large. The average percentage of growth between quiescent and shear conditions increases with the temperature decrease. For 30°C the crystals obtained in quiescent cooling are about 12.4% higher than that obtained by shear conditions. At 5°C this difference reaches 25.1%. On the other hand, the crystal width underwent an effective action of the shear, being about 22.3% less wide than those obtained in quiescent

To illustrate the **Table 1**, **Figure 3** shows PL micrographs of P3 obtained at 30, 10, and 5°C during quiescent cooling. This condition resembles the operational shutdowns when crude oil is cooled. As expected and discussed above, the concentration and size of wax crystals increase with the decrease in temperature. Since the solubility of high molecular weight waxes decreases sharply with the decrease in temperature, they precipitate out and crystallize. This result indicates that in low temperatures, it is more probably to have problems of flow assurance due to pipeline blockage occasioned by wax crystal depositions and to the formation of a high-

strength gel, characterized by yield stress [35–37].

*Length and width of crystal's average and growth percentage.*

**Table 1** shows the average length and width of crystals to waxy crude oils P1–P4 in function of temperature for 30, 10, and 5°C, for quiescent and shear conditions,

*PL micrographs of P3 obtained at (A) 30°C, (B) 10°C, (C) 5°C and during quiescent cooling.*

Another common factor studied on precipitation and morphology of waxy crystals is the aging time, which represents the influence of the time at a certainly constant temperature on the crystal wax. PL micrographs in **Figure 4** show the influence of 1 h aging time at temperatures 40, 20, and 5°C, for P4. To study the aging time influence, first, the thermal history was removed. The samples were transferred to the jacketed Becker coupled to a circulation bath at 80°C and then started the cooling steps (80–40°C; 80–20°C or 80–5°C). When the temperature arrives 40, 20, or 5°C, the samples were kept cool for 1 h at this temperature. The cooling rate was 0.5°C/min.

It was verified that the aging time favored the increase of crystal length and appearance of large clusters. This result can be attributed to the Ostwald ripening of wax crystals, a mechanism by which the large crystals grew at the expenses of smaller crystals of higher energy. Furthermore, oil uptake can also change the wax crystal distribution, leading to larger and softer wax crystals that can interpenetrate increasing intermolecular interactions between crystals [11, 37, 38].

**Table 2** shows the wax crystal's average length at t = 0 h and after 1 h (t = 1 h) at temperatures 40, 20, and 5°C, as well as the crystal growth percentage in function of aging time.

Analyzing **Table 2**, at 40°C the oils P1 and P3 show an increase of about 26.3% in the length of the crystal after 1 h in an isothermal condition. Under these same conditions, P2 shows a growth of almost 80.0%. P2 has the WAT at 42.1°C (see 4. Wax quantification), and consequently, there is no visible crystal on microscope when the temperature just arrives at 40°C. For this reason, the crystal size, in this

#### **Figure 4.**

*PL micrographs of tests carried out with P4, at t = 0 h for 40°C (A), 20°C (B) and 5°C (C); and after 1 h at 40°C (D), 20°C (E) and 5°C (F).*


• SAP: this characterization is less specific than SARA because resins and asphaltenes are considered together as polars. The SAP contents were determined by a liquid chromatography separation composed by silica gel column 60 (2.5 g silica, 0.063–0.200 mm) from Merck, which was used to determine the SAP content. The column was heated for 10 hrs at 120°C for activation. Fractions were eluted with 10 mL n-hexane for saturated, 10 mL of n-hexane/dichloromethane (8:2) for aromatic, and dichloromethane/methanol

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils*

*DOI: http://dx.doi.org/10.5772/intechopen.83736*

(9:1) for polar fractions. Residual solvents were submitted to a rotary evaporation. This technique was employed only for non-paraffinic (NP).

• WAT: this is one of the main characterizations when working with waxy crudes, because it gives an idea of the precipitation potential of the oil and ideas about the wax type. A wide range of techniques can be used to determine WAT, as microscopy, rheology, and near-infrared spectroscopy (NIR), but the most used is DSC. In this work, measurements were performed using Nano DSC differential scanning calorimeter (TA Instruments). The samples were heated from room temperature to 80°C, at 2°C/min. Then they were held for 15 min at 80°C, following by a cooling step from 80–4°C, at 0.5°C/min. Kerosene was used as the reference. Before measurements, samples were homogenized and kept under vacuum for degasification for at least 30 min. A

• Gas chromatography: this technique is employed to characterize the carbon number distribution of petroleum waxes and the normal and non-normal hydrocarbons. It is oriented by ASTM D5442-17. In this work the GC evaluated

**Table 3** presents some physicochemical characterization of the four paraffinic P1–P4 and NP oils used as reference of wax absence, also provided by Petrobras. All crude oils have relatively similar values of density. The paraffinic samples are considered medium oils, while NP is classified as heavy oil according to the °API scale. The viscosity varies greatly between samples, with P1 and P3 being the less viscous. P4 exhibits the highest viscosity at 20°C, being 100 times greater than the lower one (P3). Non-paraffinic petroleum classified as heavy oil also has high

WAT is defined as the onset temperature, that is, the intersection point of the

baseline and the tangent line of the inflection point of the exothermic peak [4, 39, 40]. In crude oils, it is common to observe two exothermic events (peaks). WAT depends on the concentration and molecular weight of waxes and the chemical characterization of hydrocarbon matrix [41]. Due to the oil complexity, the

volume of 300.0 μL of crude was used.

the carbon distribution up to C36.

viscosity (896.8 mPa.s).

**Table 3.**

**15**

*Physicochemical characterizations.*

**Table 2.**

*Average wax crystal length at t = 0 h and t = 1 h at 40, 20, and 5°C and crystal's growth percentage.*

case, was considered 1.0 μm, the microscope detection limit. However, after 1 h at 40°C, this sample presents small crystals of about 4.8 μm. Evaluating a percentage of growth at 20 and 5°C, a reduction is noticed. The wax crystals seem to grow more significantly at elevated temperatures. In t = 0 at 5°C, the wax crystal has a large size due to the temperature decrease, and after 1 h in an isothermal condition, the wax crystal grows little, i.e., its sizes do not "double" as at 40°C. A smaller variation was noted between the sample growth percentages at 5°C. This temperature is close to that observed in the production fields. After 1 h at 5°C, the wax crystals are 10.3 � 2.8% higher than when the temperature just arrives 5°C. Generalizing this information and transferring it to offshore production fields, after a 1-h stop with the oil at 5°C, the crystals can grow about 10%. Of course, this is a hypothetical condition because it is impossible to happen, since the cooling rate in the fields is smaller than that used in this study, which can result in greater wax crystals.

## **3. Physicochemical characterization**

Due to the complex matrix that is the petroleum itself, the physicochemical characterization is very relevant in order to address a proper comparison between the microscopic images, which is a very useful tool in the wax crystal morphology study. The most common physicochemical characterization techniques are:

• Density: measured mainly by ASTM-D7042. By density (at 60°F = 15.6°C) it is possible to obtain the °API following Eq. (1). °API is the most general classification at petroleum industry:

$$^\*API = \frac{141.5}{\rho} - 131.5\tag{1}$$


*Wax Chemical and Morphological Investigation of Brazilian Crude Oils DOI: http://dx.doi.org/10.5772/intechopen.83736*


**Table 3** presents some physicochemical characterization of the four paraffinic P1–P4 and NP oils used as reference of wax absence, also provided by Petrobras. All crude oils have relatively similar values of density. The paraffinic samples are considered medium oils, while NP is classified as heavy oil according to the °API scale. The viscosity varies greatly between samples, with P1 and P3 being the less viscous. P4 exhibits the highest viscosity at 20°C, being 100 times greater than the lower one (P3). Non-paraffinic petroleum classified as heavy oil also has high viscosity (896.8 mPa.s).

WAT is defined as the onset temperature, that is, the intersection point of the baseline and the tangent line of the inflection point of the exothermic peak [4, 39, 40]. In crude oils, it is common to observe two exothermic events (peaks). WAT depends on the concentration and molecular weight of waxes and the chemical characterization of hydrocarbon matrix [41]. Due to the oil complexity, the


#### **Table 3.** *Physicochemical characterizations.*

case, was considered 1.0 μm, the microscope detection limit. However, after 1 h at 40°C, this sample presents small crystals of about 4.8 μm. Evaluating a percentage of growth at 20 and 5°C, a reduction is noticed. The wax crystals seem to grow more significantly at elevated temperatures. In t = 0 at 5°C, the wax crystal has a large size due to the temperature decrease, and after 1 h in an isothermal condition, the wax crystal grows little, i.e., its sizes do not "double" as at 40°C. A smaller variation was noted between the sample growth percentages at 5°C. This temperature is close to that observed in the production fields. After 1 h at 5°C, the wax crystals are 10.3 � 2.8% higher than when the temperature just arrives 5°C. Generalizing this information and transferring it to offshore production fields, after a 1-h stop with the oil at 5°C, the crystals can grow about 10%. Of course, this is a hypothetical condition because it is impossible to happen, since the cooling rate in the fields is smaller than that used in this study, which can result in greater

*Average wax crystal length at t = 0 h and t = 1 h at 40, 20, and 5°C and crystal's growth percentage.*

Due to the complex matrix that is the petroleum itself, the physicochemical characterization is very relevant in order to address a proper comparison between the microscopic images, which is a very useful tool in the wax crystal morphology study. The most common physicochemical characterization techniques are:

• Density: measured mainly by ASTM-D7042. By density (at 60°F = 15.6°C) it is possible to obtain the °API following Eq. (1). °API is the most general

*<sup>ρ</sup>* � <sup>131</sup>*:*<sup>5</sup> (1)

wax crystals.

**Table 2.**

*Paraffin - an Overview*

**3. Physicochemical characterization**

classification at petroleum industry:

International), for all paraffinic crude oils.

rheological tests.

**14**

°

*API* <sup>¼</sup> <sup>141</sup>*:*<sup>5</sup>

• Viscosity: can be also determined by ASTM-D7042 on a viscometer or by

• Saturated, aromatic, resin, and asphaltene (SARA): can be determined mainly by Clay-Gel, according to ASTM D2007, thin layer chromatography with flame ionization detection (TLC-FID) according to IP-469, or by high-performance liquid chromatography (HPLC) according to IP-368. In this work, SARA content was obtained by TLC-FID using the IATROSCAN MK-6 (NTS

values of the peaks are around 50°C for the first exothermic event and 25°C for the second; [16, 42] assign the first peak to a liquid-liquid transition and the second to liquid-solid transition. However, in this paper, the authors believe that each exothermic event refers to a different group of waxes according to the chain length. [43, 44] declare that n-alkanes with similar carbon numbers can co-crystallize with the longer n-alkane chains.

sufficiently sensitive to identify WAT for samples with low wax contents; however, the Nano DSC shows two slight baseline variations for NP sample, even in a low cooling rate (0.5°C/min). These peaks are very low if compared to other oils due to the non-paraffinic characteristic of NP, but their presence confirms the sensitivity

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils*

*DOI: http://dx.doi.org/10.5772/intechopen.83736*

**Figure 6** shows the GC graphs of the crude oils P1–P4 and their respective extracted waxes through the UOP46–85 method (see Section 4). It is possible to note that the values obtained for the GC of the crude oil (white bars) are dispersed

of the equipment.

**Figure 6.**

**Figure 7.**

**17**

*P1-P4 crystal length versus temperature.*

*Carbon number distribution for P1-P4 crude oil.*

**Figure 5** shows the thermal curves for all samples obtained by Nano DSC. All oils have at least two well-defined exothermic peaks. It is possible to note a great similarity between the WAT values and the intensity of the exothermic peaks in the curves of the oils P1 and P3. However, the saturated values are quite different (**Table 3**). P1 has the 54.0 wt% and P3 has the 63.1 wt%, the highest values between the samples. Nevertheless, we must keep in mind that not all saturated content refers to wax; thus, these differences between saturated content among the oils do not represent the real wax content.

Continuing the analysis of **Figure 5**, it is noted that P2 was characterized by the lower WAT values and P4 shows the higher (**Table 3**), which may be an evidence that the P2 is composed by short waxy chains and P4 has the longest. According to [36] the larger the carbon chain size, the higher the crystallization temperature. Moreover, the first peak of P2 is barely evident which can be a sign of less wax content. P4 has a second peak very evident, that is, this oil may contain the higher wax content. However, P4 has the smallest crystals, as discussed before, being on average 35% smaller than the others are. According to the P4 higher WAT value, large crystals were expected. Senra et al. [45] suggest a co-crystallization between chains with different carbon numbers and with other compounds, affecting the crystal morphology. According to [46] the co-crystallization weakens the crystal structure and disfavors large crystal formation. This is a plausible hypothesis, since according to SARA, P4 has 42.7 wt% of resins and the higher content of asphaltenes (0.65 wt%).

Another curious fact is a possible third peak at temperatures just below the second, especially for P2 and P4. This peak may represent a third population of waxes, and as far as we know, it was never reported in conventional DSC analyses. Possibly this third peak is related to a group of very-short-chain waxes. Based on this observation, it is verified that the Nano DSC technique presents greater sensitivity to enthalpy variations. In the conventional DSC technique, this third peak may be masked with the second. According to [19] the conventional DSC is not

**Figure 5.** *P1-P4 and NP thermal curves behavior.*

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils DOI: http://dx.doi.org/10.5772/intechopen.83736*

sufficiently sensitive to identify WAT for samples with low wax contents; however, the Nano DSC shows two slight baseline variations for NP sample, even in a low cooling rate (0.5°C/min). These peaks are very low if compared to other oils due to the non-paraffinic characteristic of NP, but their presence confirms the sensitivity of the equipment.

**Figure 6** shows the GC graphs of the crude oils P1–P4 and their respective extracted waxes through the UOP46–85 method (see Section 4). It is possible to note that the values obtained for the GC of the crude oil (white bars) are dispersed

**Figure 6.** *Carbon number distribution for P1-P4 crude oil.*

**Figure 7.** *P1-P4 crystal length versus temperature.*

values of the peaks are around 50°C for the first exothermic event and 25°C for the second; [16, 42] assign the first peak to a liquid-liquid transition and the second to liquid-solid transition. However, in this paper, the authors believe that each exothermic event refers to a different group of waxes according to the chain length. [43, 44] declare that n-alkanes with similar carbon numbers can co-crystallize with

**Figure 5** shows the thermal curves for all samples obtained by Nano DSC. All oils

Continuing the analysis of **Figure 5**, it is noted that P2 was characterized by the lower WAT values and P4 shows the higher (**Table 3**), which may be an evidence that the P2 is composed by short waxy chains and P4 has the longest. According to [36] the larger the carbon chain size, the higher the crystallization temperature. Moreover, the first peak of P2 is barely evident which can be a sign of less wax content. P4 has a second peak very evident, that is, this oil may contain the higher wax content. However, P4 has the smallest crystals, as discussed before, being on average 35% smaller than the others are. According to the P4 higher WAT value, large crystals were expected. Senra et al. [45] suggest a co-crystallization between chains with different carbon numbers and with other compounds, affecting the crystal morphology. According to [46] the co-crystallization weakens the crystal structure and disfavors large crystal formation. This is a plausible hypothesis, since according to SARA, P4 has 42.7 wt% of resins and the higher content of asphaltenes

Another curious fact is a possible third peak at temperatures just below the second, especially for P2 and P4. This peak may represent a third population of waxes, and as far as we know, it was never reported in conventional DSC analyses. Possibly this third peak is related to a group of very-short-chain waxes. Based on this observation, it is verified that the Nano DSC technique presents greater sensitivity to enthalpy variations. In the conventional DSC technique, this third peak may be masked with the second. According to [19] the conventional DSC is not

have at least two well-defined exothermic peaks. It is possible to note a great similarity between the WAT values and the intensity of the exothermic peaks in the curves of the oils P1 and P3. However, the saturated values are quite different (**Table 3**). P1 has the 54.0 wt% and P3 has the 63.1 wt%, the highest values between the samples. Nevertheless, we must keep in mind that not all saturated content refers to wax; thus, these differences between saturated content among the oils do

the longer n-alkane chains.

*Paraffin - an Overview*

not represent the real wax content.

(0.65 wt%).

**Figure 5.**

**16**

*P1-P4 and NP thermal curves behavior.*

and have a tendency of decrease after around C30. This behavior can be attributed to the complex matrix of the oil itself. However, the carbon distribution number obtained from the extracted wax fraction from each oil (dark bars) has a more plausible chain distribution. For all oils, there is a chain predominance around C30.

**Figure 7** shows the crystal length versus temperature for P1–P4. The first experimental point of the curves is the respective WAT values. This graph is presented in order to analyze the growth tendency of the wax crystals as a function of the temperature reduction, as a way to summarize the information previously discussed.

## **4. Wax quantification**

The wax quantification is more difficult to develop than the other characterizations. However, some techniques are available:


$$\mathcal{L}\_w = \frac{\int\_{T\_f}^{WAT} dQ}{\overline{Q}} = \frac{Q}{\overline{Q}} \tag{2}$$

obtained by DSC integration baseline, but they are not in agreement with the values obtained by this same technique. The UOP 46‒85 method is a traditional way of wax estimation by very steps extractions, as well as time-consuming, lots of chemicals and solvents. These many delicate steps have great chances to produce erroneous

**Figure 8** shows the carbon number distribution, obtained through GC, only for the extracted waxes by means of UOP method. As determined by DSC integration baseline, P2 has the lowest percentage of waxes, and P4 has the highest. This can be observed again on the GC graph. According to [50] the GC and DSC analyses can be used to quantify wax content of crude oils showing reasonable agreement, but wax precipitation technique, as UOP method, must be corrected due to the presence of

The polarized light microscope is the most used technique to visualize wax crystals; however, bright-field microscopy shows crystal details that are not seen on the polarized light. The wax crystals observed have elongated structure, but they are not linear, i.e., not needle-shaped. They have superficial roughness attributed to the presence of crystallization interferers such as asphaltenes, resins, organic solids, and different carbon chain sizes. The gradual temperature decrease favors the length crystal increases, as well as the increase in the quantity and size of the agglomerates. Under shear conditions, crystals were observed around 25% smaller and in less quantity than under quiescent conditions. In addition, shearing promotes crystal breakage at very low temperatures. The aging time of the oil favors the crystal growth more drastically at higher temperatures (around 45% after 1 h at 40° C) than in low temperatures (around 10% after 1 h at 5°C), as well as the formation of agglomerates. P4 shows the higher content of precipitated waxes by means of DSC integration baseline and GC analysis, but their crystals were smaller, possibly due to the higher polar content. The DSC integration baseline is in accordance to the GC result to wax content determination; however, the UOP method is in disagreement. Another characteristic observed about Nano DSC was the great sensitivity to obtain WAT values. This technique can identify a possibly third peak precipitation

This chapter looks at some techniques of wax characterization and quantification; however, there are many other techniques that can be used and that present satisfactory results. The use of combined techniques may assist in the more accurate

results if not done properly [47].

*Carbon number distribution for P1-P4 crude oil.*

*DOI: http://dx.doi.org/10.5772/intechopen.83736*

and two peaks for the NP sample.

analysis of sample characteristics.

**19**

**5. Conclusions**

**Figure 8.**

trapped crude oil in the precipitated solid wax crystal.

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils*

By means of simple math, it is possible to calculate the mass content of precipitated waxes (*w*) as shown in Eq. (3), where *ρ* is the specific mass and *Ve* is the experimental volume used to the DSC measurement:

$$w = \frac{c\_w}{\rho.V\_\varepsilon}.\mathbf{100}\tag{3}$$

The percentages by mass of precipitated wax obtained by the DSC integration baseline show 3.1 and 2.9 wt% for P1 and P3, respectively. As cited before these oils have many similarities. P2 has the lowest value (2.2 wt%) and P4 has 4.7 wt% of precipitated waxes. However, by the UOP 46–85 method, the wax contents in mass percentage obtained were 3.7 � 0.3 for P1, 5.7 � 0.4 for P2, 5.0 � 0.1 for P3, and 3.6 � 0.2 for P4. In general, these values are at the same range of the values

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils DOI: http://dx.doi.org/10.5772/intechopen.83736*

**Figure 8.**

and have a tendency of decrease after around C30. This behavior can be attributed to the complex matrix of the oil itself. However, the carbon distribution number obtained from the extracted wax fraction from each oil (dark bars) has a more plausible chain distribution. For all oils, there is a chain predominance around C30. **Figure 7** shows the crystal length versus temperature for P1–P4. The first experimental point of the curves is the respective WAT values. This graph is presented in order to analyze the growth tendency of the wax crystals as a function of the temperature reduction, as a way to summarize the information previously

The wax quantification is more difficult to develop than the other characteriza-

• GC: as mentioned on 3. Physicochemical characterization, this technique is employed to characterize the carbon number distribution. In this work the GC

• Nuclear magnetic resonance (NMR) correlation: presented by [47], estimates the wax content of crude oil and their fractions by H NMR spectroscopy. The

• UOP 46–85 method: estimates the wax content of the crude oil and is defined as the mass percentage of precipitated material when an asphaltene-free

• DSC integration baseline: is possible to obtain the total thermal effect of the wax precipitation (*Q*) by integrating the area of the exothermic peaks. With this value, the wax precipitated concentration (*cw*) can be determined following Eq. 2 [48]. *Q* is defined as 210 J/g, a constant thermal value of wax precipitation for crude oils with an unknown molecular structure [49]. WAT is the WAT temperature itself, and *Tf* is the final temperature, in this work, 4°C:

> Ð *WAT Tf dQ <sup>Q</sup>* <sup>¼</sup> *<sup>Q</sup>*

By means of simple math, it is possible to calculate the mass content of precipitated

The percentages by mass of precipitated wax obtained by the DSC integration baseline show 3.1 and 2.9 wt% for P1 and P3, respectively. As cited before these oils have many similarities. P2 has the lowest value (2.2 wt%) and P4 has 4.7 wt% of precipitated waxes. However, by the UOP 46–85 method, the wax contents in mass percentage obtained were 3.7 � 0.3 for P1, 5.7 � 0.4 for P2, 5.0 � 0.1 for P3, and 3.6 � 0.2 for P4. In general, these values are at the same range of the values

*<sup>Q</sup>* (2)

*:*100 (3)

*cw* ¼

waxes (*w*) as shown in Eq. (3), where *ρ* is the specific mass and *Ve* is the

*<sup>w</sup>* <sup>¼</sup> *cw ρ:Ve*

experimental volume used to the DSC measurement:

method shows good fit for oils with boiling range from 340 to 550°C.

discussed.

**18**

**4. Wax quantification**

*Paraffin - an Overview*

tions. However, some techniques are available:

sample solution is cooled to �30°C.

evaluated the carbon distribution up to C36.

*Carbon number distribution for P1-P4 crude oil.*

obtained by DSC integration baseline, but they are not in agreement with the values obtained by this same technique. The UOP 46‒85 method is a traditional way of wax estimation by very steps extractions, as well as time-consuming, lots of chemicals and solvents. These many delicate steps have great chances to produce erroneous results if not done properly [47].

**Figure 8** shows the carbon number distribution, obtained through GC, only for the extracted waxes by means of UOP method. As determined by DSC integration baseline, P2 has the lowest percentage of waxes, and P4 has the highest. This can be observed again on the GC graph. According to [50] the GC and DSC analyses can be used to quantify wax content of crude oils showing reasonable agreement, but wax precipitation technique, as UOP method, must be corrected due to the presence of trapped crude oil in the precipitated solid wax crystal.

## **5. Conclusions**

The polarized light microscope is the most used technique to visualize wax crystals; however, bright-field microscopy shows crystal details that are not seen on the polarized light. The wax crystals observed have elongated structure, but they are not linear, i.e., not needle-shaped. They have superficial roughness attributed to the presence of crystallization interferers such as asphaltenes, resins, organic solids, and different carbon chain sizes. The gradual temperature decrease favors the length crystal increases, as well as the increase in the quantity and size of the agglomerates. Under shear conditions, crystals were observed around 25% smaller and in less quantity than under quiescent conditions. In addition, shearing promotes crystal breakage at very low temperatures. The aging time of the oil favors the crystal growth more drastically at higher temperatures (around 45% after 1 h at 40° C) than in low temperatures (around 10% after 1 h at 5°C), as well as the formation of agglomerates. P4 shows the higher content of precipitated waxes by means of DSC integration baseline and GC analysis, but their crystals were smaller, possibly due to the higher polar content. The DSC integration baseline is in accordance to the GC result to wax content determination; however, the UOP method is in disagreement. Another characteristic observed about Nano DSC was the great sensitivity to obtain WAT values. This technique can identify a possibly third peak precipitation and two peaks for the NP sample.

This chapter looks at some techniques of wax characterization and quantification; however, there are many other techniques that can be used and that present satisfactory results. The use of combined techniques may assist in the more accurate analysis of sample characteristics.

## **Acknowledgements**

The authors thank Conselho Nacional de Pesquisa e Desenvolvimento (CNPq), Fundação Carlos Chagas de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), and Petrobras for supporting this work.

## **Conflict of interest**

The authors declare no competing financial interest.

## **Nomenclatures**


**Author details**

**21**

Erika C.A. Nunes Chrisman<sup>1</sup>

2 Cenpes, Petrobras, Rio de Janeiro, Brazil

provided the original work is properly cited.

\*Address all correspondence to: enunes@eq.ufrj.br

and Márcio N. Souza<sup>1</sup>

\*, Angela C.P. Duncke<sup>1</sup>

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils*

*DOI: http://dx.doi.org/10.5772/intechopen.83736*

, Márcia C.K. Oliveira<sup>2</sup>

*Wax Chemical and Morphological Investigation of Brazilian Crude Oils DOI: http://dx.doi.org/10.5772/intechopen.83736*

## **Author details**

**Acknowledgements**

*Paraffin - an Overview*

**Conflict of interest**

**Nomenclatures**

BF brightfield

GC gas chromatography

NP non-paraffinic P1–<sup>4</sup> paraffinic petroleum PL polarized light

NIR near-infrared spectroscopy NMR nuclear magnetic resonance

SAP saturated, aromatic and polar

UOP universal oil products collection WAT wax appearance temperature

*cw* wax precipitated concentration

*w* mass content of precipitated waxes

*Tf* final DSC temperature

*ρ* specific mass

**20**

The authors thank Conselho Nacional de Pesquisa e Desenvolvimento (CNPq),

Fundação Carlos Chagas de Amparo à Pesquisa do Estado do Rio de Janeiro

(FAPERJ), and Petrobras for supporting this work.

API American Petroleum Institute

DSC differential scanning calorimeter

The authors declare no competing financial interest.

ASTM American Society for Testing and Materials

HPLC high performance liquid chromatography

SARA saturated, aromatic, resins and asphaltenes

*Q* total thermal effect of wax precipitation

*Q* constant thermal value of wax precipitation

*Ve* experimental volume used to the DSC measurement

TLC-FID thin layer chromatography with flame ionization detection

Erika C.A. Nunes Chrisman<sup>1</sup> \*, Angela C.P. Duncke<sup>1</sup> , Márcia C.K. Oliveira<sup>2</sup> and Márcio N. Souza<sup>1</sup>

1 Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

2 Cenpes, Petrobras, Rio de Janeiro, Brazil

\*Address all correspondence to: enunes@eq.ufrj.br

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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2018:1-8. DOI: 10.1080/ 10916466.2018.1536713

ef200059p

ef301190s

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[40] Ruwoldt J, Kurniawan M,

[39] Oliveira MCK, Texeira A, Vieira LC, Carvalho RM, Carvalho ABM, Couto BC. Flow assurance study for waxy crude oils. Energy & Fuels. 2012;**26**: 2688-2695. DOI: 10.1021/ef201407j

Oschmann H-J. Non-linear dependency of wax appearance temperature on cooling rate. Journal of Petroleum Science and Engineering. 2018;**165**: 114-126. DOI: 10.1016/j.petrol.2018.0 10.1016/j.petrol.2018.02.011 2.011

[41] Kok KM, Létoffé J-M, Claudy P, Martin D, Garcin M, Volle J-L. Comparison of wax appearance temperatures of crude oils by differential scanning calorimetry, thermomicroscopy and viscometry. Fuel. 1996;**75**(7):787-790. DOI: 10.1016/

[42] Srivastava SP, Handoo J, Agrawal KM, Joshi GC. Phase-transition studies in n-alkanes and petroleum-related waxes: A review. Journal of Physics and Chemistry of Solids. 1993;**54**:639-670. DOI: 10.1016/0022-3697(93)90126-C

[43] Guo X, Pethica BA, Huang JS, Prud'homme RK, Adamson DH, Fetters LJ. Crystallization of mixed paraffin from model waxy oils and the influence of micro-crystalline poly(ethylenebutene) random copolymers. Energy & Fuels. 2004;**18**(4):930-937. DOI:

[44] Senra M, Panacharoensawad E, Kraiwattanawong K, Singh P, Fogler HS. Role of n-alkane polydispersity on the crystallization of n-alkanes from solution. Energy & Fuels. 2008;**22**: 545-555. DOI: 10.1021/ef700490k

[45] Senra M, Scholand T, Maxey C, Fogler HS. Role of polydispersity and co-crystallization on the gelation of long-chained n-alkanes in solution.

0016-2361(96)00046-4

10.1021/ef034098p

[31] Speight JG. The Chemistry and Technology of Petroleum. 3rd ed. New York: Marcel-Dekker; 1999. 918 p

[32] Pedersen KS, Rønningsen HP. Effect of precipitated wax on viscosity: A model for predicting non-Newtonian viscosity of crude oils. Energy & Fuels. 2000;**14**:43-51. DOI: 10.1021/ef9901185

[33] Li H, Zhang J. A generalized model for predicting non-Newtonian viscosity

temperature and precipitated wax. Fuel. 2003;**82**:1387-1397. DOI: 10.1016/

[34] Lee HS, Singh P, Thomason WH, Fogler HS. Waxy oil gel breaking mechanisms: Adhesive versus cohesive failure. Energy & Fuels. 2008;**22**(1): 480-487. DOI: 10.1021/ef700212v

[35] Chang C, Boger DV, Nguyen QD. Influence of thermal history on the waxy structure of statically cooled waxy crude oil. SPE Journal. 2000;**5**:148-157.

characteristics of wax deposits in fields pipelines. Energy & Fuels. 2013;**27**:

[37] Barbato C, Nogueira B, Khalil M, Fonseca R, Gonçalves M, Pinto JC, et al. Contribution to a more reproducible method for measuring yield stress of waxy crude oils emulsions. Energy & Fuels. 2014;**28**(3):1717-1725. DOI:

[38] Silva JAL, Coutinho JAP. Dynamic rheological analysis of the gelation behavior of waxy crude oils. Rheologica

of waxy crude as a function of

S0016-2361(03)00035-8

DOI: 10.2118/57959-PA

752-759

**24**

10.1021/ef401976r

[36] Bai C, Zhang J. Thermal, macroscopic and microscopic

New York; 2011. pp. 7-64. DOI: 10.1007/978-1-4419-8831-7

*Paraffin - an Overview*

[46] Dirand M, Bouroukba M, Chevallier V, Petitjean D, Behar E, Ruffier-Meray V. Normal alkanes, multialkane synthetic model mixtures, and real petroleum waxes: Crystallographic structures, thermodynamic properties, and crystallization. Journal of Chemical & Engineering Data. 2002;**47**(2): 115-143. DOI: 10.1021/je0100084

[47] Saxena H, Majhi A, Behera B. Prediction of wax content in crude oil and petroleum fraction by proton NMR. Petroleum Science and Technology. 2018:1-8. DOI: 10.1080/ 10916466.2018.1536713

[48] Yi S, Zhang J. Relationship between waxy crude oil composition and change in the morphology and structure of wax crystals induced by pour-pointdepressant beneficiation. Energy & Fuels. 2011;**25**:1686-1696. DOI: 10.1021/ ef200059p

[49] Chen J, Zhang J, Li H. Determining the wax content of crude oils by using differential scanning calorimetry. Thermochimica Acta. 2004;**410**:23-26. DOI: 10.1016/S0040-6031(03)00367-8

[50] Robustillo MD, Coto B, Martos C, Espada JJ. Assessment of different methods to determine the total wax content of crude oils. Energy & Fuels. 2012;**26**:6352-6357. DOI: 10.1021/ ef301190s

**Chapter 3**

**Abstract**

Managing Paraffin/Wax

*Keshawa Shukla and Mayank Vishal Labh*

in Deepwater Hydrocarbon

The prevention of solids formation and their deposition are major challenges to design and operate any subsea hydrocarbon production systems. One of the most challenging issues is the management of paraffin/wax. As the water depth increases, at the low temperatures of subsea conditions, hydrocarbons may precipitate as wax, which can solidify and restrict the flow. During shutdown of a subsea production system wax gel may form and solidify when a crude oil cools below its pour point causing operational problems from downhole to the processing facilities. The purpose of this chapter is to address the paraffin/wax formation and deposition issues to properly design a subsea production system consisting of pipe-in-pipe flowline and flexible riser under deepwater environment. A field specific example is presented to manage the wax formation/deposition and prevent paraffin/wax deposition risks in an effective way during the normal and the shut-in operations of the subsea production system. This study illustrates that the subsea hardware, such as water stop and equipment valves, along with the flowline, riser and jumper should be sufficiently insulated in order to prevent any cold spots in the production

system, and achieve sufficient cooldown time for the shut-in operations.

The major flow assurance challenges in the design and operation of a subsea hydrocarbon production system arise mainly due to the reservoir fluid properties,

multiphase fluid flow, and solid formation such as paraffin/wax, hydrate, asphaltene, scale, corrosion, emulsion and foam. In particular, the formations of paraffin/wax and hydrate at low temperature and high pressure conditions in a deep water production system are critical to manage when transporting fluids from the reservoirs to the host facilities. The wax present in hydrocarbon fluids is mainly comprised of high molecular weight paraffinic compounds that are crystalline in nature. The wax can drop out of the crude oil at the wax appearance temperature (WAT) and deposit in the subsea systems during the production operations when the fluid temperature is lower than WAT. Below the pour point, the wax can gel and

**Keywords:** paraffin/wax, subsea production system, hydrocarbons,

pipe-in-pipe flowline, flexible riser

**1. Introduction**

**27**

Deposition Challenges

Production Systems

## **Chapter 3**
