**2. Oligomers**

288 Recent Trends for Enhancing the Diversity and Quality of Soybean Products

It is noteworthy that many of the applications mentioned for the glycerol require high degree of purity, which for glycerol derived from biodiesel requires several stages of treatment, increasing its cost. The main impurities in the glycerol from biodiesel is methanol or ethanol, water, inorganic salts and catalyst residues, free fatty acids, unreacted mono, di and triglycerides and various other matter organic non-glycerol (MONG) (Pagliaro & Rossi, 2008). Thus, it is necessary to develop new routes for the consumption of glycerol from

In this chapter, will be treated the transformation of glycerol based on production of ethers from condensation of two (or more) glycerol's molecules. One of the mechanisms Favorable

other alcohol and water loss. The condensation reaction of glycerol (Scheme 2), is usually catalyzed by acids or bases producing small polymers called oligomers and water. Along the text will be described the oligomers, polymers and carbons obtained from polyglycerol

), followed by condensation of

for the formation of ethers is by alcohol protonation (ROH <sup>2</sup>

Scheme 1.

biodiesel.

Scheme 2.

and its applications.

Oligomerization of glycerol (Scheme 2) is an alternative to the use of byproduct of biodiesel, because their products have wide application. For a better understanding of oligomerization (and polymerization), was accompanied through ESI-MS (Electrospray Ionization Mass Spectrometry in the positive ion mode) a typical reaction of oligomerization - glycerol PA catalyzed by 1% H2SO4 at 280°C/2h, in reflux.

Analysis of the sample (2h) is shown in Figure 3. The presence of an intense ion of *m/z* 93 (protonated glycerol = [glycerol + H]+) is clearly noticeable indicating the subsistence of glycerol in the reaction medium even after 2 h reaction.

Fig. 3. ESI(+)-MS of the acid-catalyzed oligomerization of glycerol conducted in aqueous medium at 280 °C, 2 h. The ions marked with an asterisk (\*) refer to dehydration products.

A remarkable presence of an ion of *m/z* 167 is also noticed in Figure 3. This corresponds to the protonated form of diglycerol, i.e*.* [(glycerol)2 – H2O], formed under these reaction conditions via the condensation of two molecules of glycerol and loss of water. This condensation can occur via the primary or secondary hydroxyl groups at the glycerol molecule to yield linear (α, α -diglycerol) and branched (α, β -diglycerol; β, β -diglycerol) isomers, as displayed in Scheme 3.

Scheme 3.

Across of the fragmentation of the ion of *m/z* 167 are yield mainly product ions from losses of one or two molecules of water (*m/z* 149 and 131, respectively) besides to other product

Chemical Conversion of Glycerol from

**2c**.

Scheme 5.

Biodiesel into Products for Environmental and Technological Applications 291

such as the cyclic species **1a-c** (their formation have been reported by Barrault and coworkers (Barrault et al., 2004, 2005) that submitted glycerol to similar reaction conditions than those employed herein) besides the acyclic carbonyl compounds **2a-b** and the alkene

All the products resulting from the mono-dehydration of diglycerol, including the ones shown in Scheme 3 (**1a**-**c** and **2a**-**c**), possess the same chemical formula (C6H12O4) and bear similar functional groups (especially hydroxyl substituents). Hence, these protonated molecules lose mainly water and other small molecules, being unfeasible the unambiguous characterization of a particular product based exclusively on your fragmentation profile.

Fig. 4. Fractions of the ions of *m/z* 167, 241, 315, and 389 as a function of reaction time. Each fraction was calculated as the quotient ratio between the absolute intensity of one of such

In Figure 4, the fraction of the ions of *m/z* 93, 167, 241, 315 and 389 (protonated glycerol, di, tri, tetra and pentaglycerol, respsctively), given as a quotient ratio between the absolute

ions and the sum of the absolute intensities of the whole set of ions.

ions, such as [glycerol + H]+ (*m/z* 93), [glycerol – H2O + H]+ (*m/z* 75), and [glycerol – 2 H2O + H]+ (*m/z* 57). To illustrate the formation of such fragments, the dissociation pathways for protonated α, α-diglycerol are shown in Scheme 4.

In the Table 2, are showed ions ascribed to be the protonated forms of products formed by successive dehydrations of di, tri, tetra and pentaglycerol.

Scheme 4.


Table 2. Primary products (diglycerol, triglycerol, tetraglycerol and pentaglycerol) and their dehydration products formed upon acid-catalyzed oligomerization of glycerol at 280°C. All these products were observed as their protonated forms in the ESI(+)-MS (Fig. 3).

These findings thus indicate that under acidic medium and heating, olygomers can easily lose one or two molecules of water to form a myriad of isomeric products. Scheme 5 shows, for instance, products possibly formed as a result of the mono-dehydration of diglycerol, such as the cyclic species **1a-c** (their formation have been reported by Barrault and coworkers (Barrault et al., 2004, 2005) that submitted glycerol to similar reaction conditions than those employed herein) besides the acyclic carbonyl compounds **2a-b** and the alkene **2c**.

Scheme 5.

290 Recent Trends for Enhancing the Diversity and Quality of Soybean Products

ions, such as [glycerol + H]+ (*m/z* 93), [glycerol – H2O + H]+ (*m/z* 75), and [glycerol – 2 H2O + H]+ (*m/z* 57). To illustrate the formation of such fragments, the dissociation pathways for

In the Table 2, are showed ions ascribed to be the protonated forms of products formed by

diglycerol (167) [diglycerol – H2O] (149)

Table 2. Primary products (diglycerol, triglycerol, tetraglycerol and pentaglycerol) and their dehydration products formed upon acid-catalyzed oligomerization of glycerol at 280°C. All

These findings thus indicate that under acidic medium and heating, olygomers can easily lose one or two molecules of water to form a myriad of isomeric products. Scheme 5 shows, for instance, products possibly formed as a result of the mono-dehydration of diglycerol,

these products were observed as their protonated forms in the ESI(+)-MS (Fig. 3).

**Dehydration Products (m/z of the protonated forms)**

[diglycerol – 2 H2O] (131)

[triglycerol – H2O] (223) [triglycerol – 2 H2O] (205) [triglycerol – 3 H2O] (187)

[tetraglycerol – H2O] (297) [tetraglycerol – 2 H2O] (279) [tetraglycerol – 3 H2O] (261)

[pentaglycerol –H2O] (371) [pentaglycerol – 2 H2O] (353) [pentaglycerol – 3 H2O] (335)

protonated α, α-diglycerol are shown in Scheme 4.

Scheme 4.

successive dehydrations of di, tri, tetra and pentaglycerol.

**Primary Oligomers (m/z of the protonated forms)**

triglycerol (241)

tetraglycerol (315)

pentaglycerol (389)

All the products resulting from the mono-dehydration of diglycerol, including the ones shown in Scheme 3 (**1a**-**c** and **2a**-**c**), possess the same chemical formula (C6H12O4) and bear similar functional groups (especially hydroxyl substituents). Hence, these protonated molecules lose mainly water and other small molecules, being unfeasible the unambiguous characterization of a particular product based exclusively on your fragmentation profile.

Fig. 4. Fractions of the ions of *m/z* 167, 241, 315, and 389 as a function of reaction time. Each fraction was calculated as the quotient ratio between the absolute intensity of one of such ions and the sum of the absolute intensities of the whole set of ions.

In Figure 4, the fraction of the ions of *m/z* 93, 167, 241, 315 and 389 (protonated glycerol, di, tri, tetra and pentaglycerol, respsctively), given as a quotient ratio between the absolute

Chemical Conversion of Glycerol from

systems it took at least 120 minutes.

after 45 min of reaction.

did not dissolve in any solvent tested.

home utensils as well as controlled release fertilizers.

Biodiesel into Products for Environmental and Technological Applications 293

The curves shown in Figure 4 indicate a significant increase in viscosity of the solution, by varying the mole percentage of catalyst of 0.5-5%. However, this increase is gradual, as it rises the concentration of H2SO4. It is interesting to note that the system promoted by 5 mol% of catalyst is very active, because it took only 45 minutes to produce a solid polymer (unable to measure the viscosity, since the material solidified, Figure 5), whereas in other

Fig. 6. Images of scanning electron microscopy (SEM) of polyglicerol with 5 mol% of H2SO4,

The system promoted by 0.5, 1 and 3 mol% H2SO4 show similar viscosity curves (Figure 4) but with varying slopes (the higher the catalyst concentration, greater the slope of the viscosity). With the increase of H2SO4 concentration (0.5-3%) is expected larger number of simultaneous condensation, therefore, the selectivity of the catalyst to reactive hydroxyl groups of glycerol decreases, leading to complex structures, which offer increased viscosity of the solution (in 60 minutes: system promoted by 0.5 mol% relative viscosity of 4,1%; 1 mol% relative viscosity of 51 e 3 mol% relative viscosity of 169 times that of glycerol. In the first 15 minutes of reaction, the viscosity of the medium practically does not change. It is believed that during this period, is occurring the formation of linear oligomers and products of dehydration. However, as the polymerization reaction progresses, the ethers formed formed become larger and more complex, mainly due to the formation of branches and some bonds between parallel chains of oligomers and/or polymers. And this is the increase size and complexity of structures of the ethers formed which increased the solution viscosity, reaching 169 times the viscosity of glycerol in just 60 minutes (system promoted by 3 mol% H2SO4), because the move of the structures is becoming increasingly difficult. To confirm the nature (thermoplastic or thermosetting) polymeric material formed by polymerization of glycerol, are carried out two separate tests: heating in the direct flame of a Bunsen burner, to ensure that it is malleable (suffers fusion) or undergo thermal decomposition, and washing the polymer in solvents with different polarities (hexane, THF and ethanol). The results of these tests showed that all the polymers (0.5, 1, 3 and 5 mol% H2SO4) are thermosets, because not suffers fusion, but rather, thermal decomposition and

The polyglycerol may be used as a substitute for thermosetting phenolic resins, used in

intensity of one of such ions and the sum of the absolute intensities of the whole set of ions, are plotted against the reaction time. These results show that after 2 h reaction more than 90% of glycerol is consumed. Furthermore, during the first 30 min a relatively high concentration of diglycerol is formed. At longer reaction times, however, its concentration decreases whereas the amount of the heavier oligomers (tri, tetra and pentaglycerol) concomitantly increases. The result shows that glycerol is continuously converted into the heavier oligomeric compounds.

#### **3. Polymerization of glycerol**

In open system, the polycondensation (condensation of many molecules to create larger molecules - polymers) that the glycerol suffers in the presence of H2SO4 at 150 ° C, is a type of polymerization in which mingle the three stages: initiation, propagation and termination, which are characteristic of polymerization reactions (Mano & Mendes, 1999). The condensation polymerization, when employ monomers (molecules susceptible to undergo polymerization) with more than two functional groups (glycerol has three OH groups), tends to form crosslinked or branched polymers (structures with crosslinks between chains). In this case, the polymerization is complex because it is formed gel (polymer molecular weight too large), in the same setting of the sol (the fraction that remains soluble and can be extracted from the middle). As the sol will turn into gel, the mixture becomes increasingly viscous until elastic consistency, and finally rigid. In this transformation of glycerol in hard polymer, the catalyst concentration has an important role. An example of the participation of the catalyst in the polymerization of glycerol is shown in Figure 5, in which the viscosities of solution reaction is monitored by 60 minutes, with different concentrations of catalyst (0.5, 1, 3 and 5 mol%) .

Fig. 5. Variation of relative viscosity of the solution for the polymerization of glycerol, with 0.5,1, 3 and 5 mol% H2SO4 (viscosity values are relative to the glycerol).

intensity of one of such ions and the sum of the absolute intensities of the whole set of ions, are plotted against the reaction time. These results show that after 2 h reaction more than 90% of glycerol is consumed. Furthermore, during the first 30 min a relatively high concentration of diglycerol is formed. At longer reaction times, however, its concentration decreases whereas the amount of the heavier oligomers (tri, tetra and pentaglycerol) concomitantly increases. The result shows that glycerol is continuously converted into the

In open system, the polycondensation (condensation of many molecules to create larger molecules - polymers) that the glycerol suffers in the presence of H2SO4 at 150 ° C, is a type of polymerization in which mingle the three stages: initiation, propagation and termination, which are characteristic of polymerization reactions (Mano & Mendes, 1999). The condensation polymerization, when employ monomers (molecules susceptible to undergo polymerization) with more than two functional groups (glycerol has three OH groups), tends to form crosslinked or branched polymers (structures with crosslinks between chains). In this case, the polymerization is complex because it is formed gel (polymer molecular weight too large), in the same setting of the sol (the fraction that remains soluble and can be extracted from the middle). As the sol will turn into gel, the mixture becomes increasingly viscous until elastic consistency, and finally rigid. In this transformation of glycerol in hard polymer, the catalyst concentration has an important role. An example of the participation of the catalyst in the polymerization of glycerol is shown in Figure 5, in which the viscosities of solution reaction is monitored by 60 minutes, with different concentrations of catalyst

Fig. 5. Variation of relative viscosity of the solution for the polymerization of glycerol, with

0.5,1, 3 and 5 mol% H2SO4 (viscosity values are relative to the glycerol).

heavier oligomeric compounds.

**3. Polymerization of glycerol** 

(0.5, 1, 3 and 5 mol%) .

The curves shown in Figure 4 indicate a significant increase in viscosity of the solution, by varying the mole percentage of catalyst of 0.5-5%. However, this increase is gradual, as it rises the concentration of H2SO4. It is interesting to note that the system promoted by 5 mol% of catalyst is very active, because it took only 45 minutes to produce a solid polymer (unable to measure the viscosity, since the material solidified, Figure 5), whereas in other systems it took at least 120 minutes.

Fig. 6. Images of scanning electron microscopy (SEM) of polyglicerol with 5 mol% of H2SO4, after 45 min of reaction.

The system promoted by 0.5, 1 and 3 mol% H2SO4 show similar viscosity curves (Figure 4) but with varying slopes (the higher the catalyst concentration, greater the slope of the viscosity). With the increase of H2SO4 concentration (0.5-3%) is expected larger number of simultaneous condensation, therefore, the selectivity of the catalyst to reactive hydroxyl groups of glycerol decreases, leading to complex structures, which offer increased viscosity of the solution (in 60 minutes: system promoted by 0.5 mol% relative viscosity of 4,1%; 1 mol% relative viscosity of 51 e 3 mol% relative viscosity of 169 times that of glycerol.

In the first 15 minutes of reaction, the viscosity of the medium practically does not change. It is believed that during this period, is occurring the formation of linear oligomers and products of dehydration. However, as the polymerization reaction progresses, the ethers formed formed become larger and more complex, mainly due to the formation of branches and some bonds between parallel chains of oligomers and/or polymers. And this is the increase size and complexity of structures of the ethers formed which increased the solution viscosity, reaching 169 times the viscosity of glycerol in just 60 minutes (system promoted by 3 mol% H2SO4), because the move of the structures is becoming increasingly difficult.

To confirm the nature (thermoplastic or thermosetting) polymeric material formed by polymerization of glycerol, are carried out two separate tests: heating in the direct flame of a Bunsen burner, to ensure that it is malleable (suffers fusion) or undergo thermal decomposition, and washing the polymer in solvents with different polarities (hexane, THF and ethanol). The results of these tests showed that all the polymers (0.5, 1, 3 and 5 mol% H2SO4) are thermosets, because not suffers fusion, but rather, thermal decomposition and did not dissolve in any solvent tested.

The polyglycerol may be used as a substitute for thermosetting phenolic resins, used in home utensils as well as controlled release fertilizers.

Chemical Conversion of Glycerol from

minutes to obtain the same results).

**5. Vermiculite composites/activated carbon** 

of the composite in case of water application, requiring only one net.

Fig. 9. Adsorption of methylene blue by carbonaceous material derived from the

polyglycerol at different activation times (0, 3, 5, 10 and 15 h).

in Figure 9.

(internal diameter of less than 2 nm) (Figure 8).

Biodiesel into Products for Environmental and Technological Applications 295

The Figure 7 shows a gradual increase in surface area of carbonaceous material up to 1830 m2 g-1, 15 h of activation. After that time, the surface area begins to decrease, reaching a value of 1275 m2 g-1 at 18 h. A similar behavior, but not linear is observed for the surface area as a function of burn off (mass loss of carbon during activation) (detail of Figure 7). The analysis of distribution of pores indicates that the materials are essentially microporous

As the surface area of carbonaceous material derived from polyglycerol increased with activation time by 15 hours, tests were made to adsorb organic contaminants (methylene blue) during the activation process (0, 3, 5, 10 and 15 h ). The results of these tests are shown

It is evident the relationship between the activation time of the carbonaceous material (surface area) and the adsorption of organic contaminant. During the activation process of the carbonaceous material, there was a gradual increase of its surface area, which is intimately related to the growth of its adsorption capacity. The sample of the material that was activated for 15 hours showed better results in the removal of organic contaminant (in 20 minutes, the removal of contaminant was 90%, while others samples took at least 60

In order to facilitate the application of carbonaceous material in environmental problems, was produced a composite based in vermiculite clay and activated carbon, derived from the polyglycerol. This composite was designed, considering (i) some properties of the expanded vermiculite clay (Figure 10), which has low cost and ability to float in water, (ii) large adsorption capacity of Activated carbon derived from polyglycerol and (iii) facility removal

#### **4. High surface area carbons**

The thermosetting polymers have the property that thermally decomposes, producing carbon in quantities that can vary with the degree of crosslinking of the polymer. As previously discussed, the degree of crosslinking (polymerization in all directions, linking parallel chains of the polymer) is influenced by the concentration of the catalyst. Hence, a polymer obtained with 5 mol% H2SO4 is more reticulated and produces more carbon than a polymer with only 1 mol% catalyst.

The thermal decomposition of polyglycerol (obtained with 5 mol% H2SO4) yields 16% of carbon (relative to initial mass of polymer), which has extremely low surface area (2 m2g-1). For environmental applications, are typically used carbonaceous materials with high surface area. Thus, it was necessary to increase the surface area of carbons derived from polyglycerol, performing physical activation (850°C) with a flow of CO2 by 3, 5, 10, 15 and 18 h (Figure 7).

Fig. 7. Surface area of carbons derived from polyglycerol. Detail: surface area as a function of burn off.

Fig. 8. Distribution of pores in activated carbonaceous material for 3, 5, 10, 15 and 18 h.

The thermosetting polymers have the property that thermally decomposes, producing carbon in quantities that can vary with the degree of crosslinking of the polymer. As previously discussed, the degree of crosslinking (polymerization in all directions, linking parallel chains of the polymer) is influenced by the concentration of the catalyst. Hence, a polymer obtained with 5 mol% H2SO4 is more reticulated and produces more carbon than a

The thermal decomposition of polyglycerol (obtained with 5 mol% H2SO4) yields 16% of carbon (relative to initial mass of polymer), which has extremely low surface area (2 m2g-1). For environmental applications, are typically used carbonaceous materials with high surface area. Thus, it was necessary to increase the surface area of carbons derived from polyglycerol, performing physical activation (850°C) with a flow of CO2 by 3, 5, 10, 15 and

Fig. 7. Surface area of carbons derived from polyglycerol. Detail: surface area as a function

Fig. 8. Distribution of pores in activated carbonaceous material for 3, 5, 10, 15 and 18 h.

**4. High surface area carbons** 

polymer with only 1 mol% catalyst.

18 h (Figure 7).

of burn off.

The Figure 7 shows a gradual increase in surface area of carbonaceous material up to 1830 m2 g-1, 15 h of activation. After that time, the surface area begins to decrease, reaching a value of 1275 m2 g-1 at 18 h. A similar behavior, but not linear is observed for the surface area as a function of burn off (mass loss of carbon during activation) (detail of Figure 7). The analysis of distribution of pores indicates that the materials are essentially microporous (internal diameter of less than 2 nm) (Figure 8).

As the surface area of carbonaceous material derived from polyglycerol increased with activation time by 15 hours, tests were made to adsorb organic contaminants (methylene blue) during the activation process (0, 3, 5, 10 and 15 h ). The results of these tests are shown in Figure 9.

It is evident the relationship between the activation time of the carbonaceous material (surface area) and the adsorption of organic contaminant. During the activation process of the carbonaceous material, there was a gradual increase of its surface area, which is intimately related to the growth of its adsorption capacity. The sample of the material that was activated for 15 hours showed better results in the removal of organic contaminant (in 20 minutes, the removal of contaminant was 90%, while others samples took at least 60 minutes to obtain the same results).
