**Materials:**

294 Biodiesel – Feedstocks and Processing Technologies

NRX

C

C

The section of the column below where the fresh feed of A is introduced (the stripping section with NS trays) separates heavy product D from all of the lighter components, so a bottom is produced that is fairly pure product D. The reflux flow rate and the reboiler heat input can be manipulated to maintain these product purities. The specific numerical case has 30 total trays, consisting of 10 stripping trays, 10 reactive trays, and 10 rectifying trays. Trays are numbered from the bottom. Note that the concentrations of the reactants peak at their respective feed trays. The purities of the two products are both 95 mol%, with B the

Reactive distillation column must be adjusted to achieve these specifications while optimizing some objective function such as total annual cost (TAC). These design degrees of freedom include pressure, reactive tray holdup, number of reactive trays, location of reactant feed streams, number of stripping trays, number of rectifying trays, reflux ratio,

Tray holdup is another design aspect of reactive distillation that is different from conventional. Holdup has no effect on the steady-state design of a conventional column. It certainly affects dynamics but not steady-state design. Column diameter is determined from maximum vapor loading correlations after vapor rates have been determined that achieve the desired separation. Typical design specifications are the concentration of the heavy key component in the distillate and the concentration of the light key component in the bottoms.

major impurity in the bottoms and A the major impurity in the distillate [7].

Fig. 4. Flow sheet of ideal reactive distillation column

NS

NR

A

B

and reboiler heat input [9].



Table 2. Physical Properties of Vegetable Oil Feed stocks Used For Transesterification

b. Methanol:

Methanol (Merck) of 99.5% purity (density: 0.785 g/mL at 30oC) was used in this transesterification process.

c. Catalyst:

In this study the catalysts used are:


The two homogeneous basic catalysts (KOH & NaOH) used for reactive distillation were purchased from local Chemical store at Amravati. M.S.The heterogeneous catalyst used for transesterification Amberlyst BD15 was purchased from Dayo Scientific Laboratory, Nashik Road, Nashik, M.S. India.

#### **Amberlyst-15:**

Amberlyst 15 wet is a macro reticular, strongly acidic, polymeric catalyst. Its continuous open pore structure makes it an excellent heterogeneous acid catalyst for a wide variety of organic reactions. Amberlyst 15 is extremely resistant to mechanical and thermal shocks. It

Transesterification by Reactive Distillation for Synthesis and Characterization of Biodiesel 297

 <sup>1</sup> 2 Triglyceride TG OH Diglycerides DG <sup>1</sup> COOR *<sup>k</sup>*

 <sup>3</sup> 4 Diglycerides DG <sup>1</sup> OH Monoglycerides MG COOR *<sup>k</sup>*

**Startup Procedures of transesterification using reactive distillation:** 

reboiler to analyze the biodiesel composition and methanol content.

∑A = the total peak area from the FAME C14:0 to C24:1 AEI = the peak area of methyl heptadecanoate

VEI = the volume, in ml of the methyl heptadecanoate solution

1.5 hours till the temperature of the top column reached 62°C.

**Steady-operation:** 

reactive distillation technique

m = the mass, in mg of the sample

**5. Experimental setup** 

**Calculations:** 

formula:

 <sup>5</sup> 6 Monoglycerides MG OH Glycerin GL COOR3 *k*

To start of each experiment, approximate 2 L of oil and 250 mL of methanol were injected into the column. The reboiler heater was set to 120°C and allowed to heat for approximately

The inputs, both oil at 55°C and methanol at 30oC, were pumped into a short tube mixer to mix the oil with the methanol/catalyst solution. Then the reactant mixture at 62°C was entered to the top of the RD column. In the RD column, triglyceride in the reactant mixture further reacted with the present methanol. The product mixture was withdrawn from the reboiler section and sent to a glycerol ester separator, where the glycerol and esters were separated by gravity in a continuous mode. Every hour, samples were collected from

In this experimentation reaction parameters has been optimized and an optimized process has been investigated for biodiesel production by transesterification of vegetable oil using

The ester content (*C)* expressed as a fraction in percent, is calculated using the following

100% *EI EI EI*

The system consists of a reactive distillation column fed at the top with the initial reactive solution (oil, alcohol, catalyst). This solution slowly travels down between the plates. When the solution exits the column; the alcohol that has not reacted is recuperated by evaporation. Then, the vapors are re-circulated in the reactive distillation column in the upward direction passing through the plates. As the vapors travel through, interactions between the gaseous alcohol and the liquid solution occur. This then would increase the effective oil to alcohol ratio up to 20:1 (He, Singh et al.2006), thus shifting the reaction equilibrium to the product side and therefore increasing the reaction efficiency. Finally, once the alcohol vapors have reached the top of the reactive distillation column, they are condensed through a condenser

(4)

*EI A A C V <sup>C</sup> A m*

CEI = the concentration , in mg/ml of the methyl heptadecanoate solution

*<sup>k</sup> R R*

*<sup>k</sup> R R* (2)

*<sup>k</sup> R R* (3)

also possesses greater resistance to oxidants such as chloride, oxygen and chromates than most other polymeric catalyst. It can use directly in the aqueous system or in organic medium after conditioning with a water miscible solvent. Amberlyst 15 has optimal balance of surface area, acid capacity and pore diameter to make it the catalyst of choice for esterification reactions.


Table 3. Characteristics of Amberlyst-15 catalyst

#### **4.2 Transesterification**

Transesterification also called alcoholysis is the most common way to produce biodiesel. This involves a catalyzed chemical reaction between vegetable oil and an alcohol to yield fatty acid alkyl esters (i.e., biodiesel) and glycerol. Transesterification is the displacement of alcohol from an ester by another alcohol in a process similar to hydrolysis, except that an alcohol is employed instead of water. Triglycerides, as the main component of vegetable oil, consist of three long chain fatty acids esterified to a glycerol backbone. When triglycerides react with an alcohol (e.g., methanol), the three fatty acid chains are released from the glycerol skeleton and combine with the alcohol to yield fatty acid alkyl esters (e.g., fatty acid methyl esters or biodiesel). Glycerol is produced as a by-product.

The mechanism of transesterification can be represented as follows:

$$\begin{aligned} \text{CH}\_{2}-\text{OOC}-\text{R}\_{1} & \quad & \text{R}\_{2}-\text{OOC}-R' & \text{CH}\_{2}-\text{OH} \\ \text{CH}-\text{OOC}-\text{R}\_{2} & + 3\text{R'}\text{OH} & \underset{\text{CH}\_{2}-\text{OOC}-R'}{\text{R}\_{2}-\text{OOC}-R'} + \text{CH}\_{2}-\text{OH} & \quad \text{(1)} \\ \text{CH}\_{2}-\text{OOC}-\text{R}\_{1} & \quad & \text{R}\_{3}-\text{OOC}-R' & \text{CH}\_{2}-\text{OH} \end{aligned} \tag{1}$$

$$\begin{aligned} \text{Triglyceride} \ + & \text{Alcohol} \quad \xrightarrow{\text{Catalyst}} \text{Eters} \ + & \text{Glycerol} \end{aligned}$$

#### **4.2.1 Transesterification of vegetables oils**

In the transesterification of different types of oils, triglycerides react with an alcohol, generally methanol or ethanol, to produce esters and glycerin. To make it possible, a catalyst is added to the reaction.The overall process is normally a sequence of three consecutive steps, which are reversible reactions. In the first step, from triglycerides diglyceride is obtained, from diglyceride monoglyceride is produced and in the last step, from monoglycerides glycerin is obtained. In all these reactions esters are produced. The stoichiometric relation between alcohol and the oil is 3:1. However, an excess of alcohol is usually more appropriate to improve the reaction towards the desired product:

$$\text{Triglycine} \text{(TG)} + \text{R'OH} \xrightarrow[k\_2]{k\_1} \text{Diglycerides (DG)} + \text{ R'COOR}\_1$$

$$\text{Diglyceries (DG)} \,+\,\text{R'OH} \xrightarrow[k\_4]{k\_3} \text{ Monoglyceries (MG)} + \,\text{R'COOR}\_1 \tag{2}$$

$$\text{Monoglyerides (MG)} + \text{R'OH} \xrightarrow[k\_b]{k\_i} \text{Glycerol (GL)} + \text{R'COOR}\_3 \tag{3}$$

#### **Startup Procedures of transesterification using reactive distillation:**

To start of each experiment, approximate 2 L of oil and 250 mL of methanol were injected into the column. The reboiler heater was set to 120°C and allowed to heat for approximately 1.5 hours till the temperature of the top column reached 62°C.

#### **Steady-operation:**

296 Biodiesel – Feedstocks and Processing Technologies

also possesses greater resistance to oxidants such as chloride, oxygen and chromates than most other polymeric catalyst. It can use directly in the aqueous system or in organic medium after conditioning with a water miscible solvent. Amberlyst 15 has optimal balance of surface area, acid capacity and pore diameter to make it the catalyst of choice for

Transesterification also called alcoholysis is the most common way to produce biodiesel. This involves a catalyzed chemical reaction between vegetable oil and an alcohol to yield fatty acid alkyl esters (i.e., biodiesel) and glycerol. Transesterification is the displacement of alcohol from an ester by another alcohol in a process similar to hydrolysis, except that an alcohol is employed instead of water. Triglycerides, as the main component of vegetable oil, consist of three long chain fatty acids esterified to a glycerol backbone. When triglycerides react with an alcohol (e.g., methanol), the three fatty acid chains are released from the glycerol skeleton and combine with the alcohol to yield fatty acid alkyl esters (e.g., fatty acid

2 1 2 2

CH OOC R R OOC CH OH CH OOC R 3 OH R OOC CH OH CH OOC R R OOC CH OH

 

2 1 3 2

2 22

*R R*

 **Catalyst Triglyceride Alcohol Esters Glycerol**

In the transesterification of different types of oils, triglycerides react with an alcohol, generally methanol or ethanol, to produce esters and glycerin. To make it possible, a catalyst is added to the reaction.The overall process is normally a sequence of three consecutive steps, which are reversible reactions. In the first step, from triglycerides diglyceride is obtained, from diglyceride monoglyceride is produced and in the last step, from monoglycerides glycerin is obtained. In all these reactions esters are produced. The stoichiometric relation between alcohol and the oil is 3:1. However, an excess of alcohol is usually more appropriate to improve the reaction towards the desired product:

*R*

*R*

(1)

Physical forms Opaque beads Ionic form as shipped Hydrogen Total exchange capacity ≥1.7 eq /L Moisture holding capacity 52-57% Harmonic mean size 600-850 μm Fine contents < 0.355 mm :1.0% Coarse beads > 1.180 mm :5.0%

Average pore diameter 24 nm Surface area 45 m2 / gm Shrinkage water to methanol 4.0%

methyl esters or biodiesel). Glycerol is produced as a by-product. The mechanism of transesterification can be represented as follows:

Table 3. Characteristics of Amberlyst-15 catalyst

**4.2.1 Transesterification of vegetables oils** 

esterification reactions.

**4.2 Transesterification** 

The inputs, both oil at 55°C and methanol at 30oC, were pumped into a short tube mixer to mix the oil with the methanol/catalyst solution. Then the reactant mixture at 62°C was entered to the top of the RD column. In the RD column, triglyceride in the reactant mixture further reacted with the present methanol. The product mixture was withdrawn from the reboiler section and sent to a glycerol ester separator, where the glycerol and esters were separated by gravity in a continuous mode. Every hour, samples were collected from reboiler to analyze the biodiesel composition and methanol content.

In this experimentation reaction parameters has been optimized and an optimized process has been investigated for biodiesel production by transesterification of vegetable oil using reactive distillation technique

#### **Calculations:**

The ester content (*C)* expressed as a fraction in percent, is calculated using the following formula:

$$C = \frac{\left(\sum A\right) - A\_{EI}}{A\_{EI}} \times \frac{C\_{EI} \times V\_{EI}}{m} \times 100\,\%\tag{4}$$

∑A = the total peak area from the FAME C14:0 to C24:1 AEI = the peak area of methyl heptadecanoate CEI = the concentration , in mg/ml of the methyl heptadecanoate solution VEI = the volume, in ml of the methyl heptadecanoate solution m = the mass, in mg of the sample

#### **5. Experimental setup**

The system consists of a reactive distillation column fed at the top with the initial reactive solution (oil, alcohol, catalyst). This solution slowly travels down between the plates. When the solution exits the column; the alcohol that has not reacted is recuperated by evaporation. Then, the vapors are re-circulated in the reactive distillation column in the upward direction passing through the plates. As the vapors travel through, interactions between the gaseous alcohol and the liquid solution occur. This then would increase the effective oil to alcohol ratio up to 20:1 (He, Singh et al.2006), thus shifting the reaction equilibrium to the product side and therefore increasing the reaction efficiency. Finally, once the alcohol vapors have reached the top of the reactive distillation column, they are condensed through a condenser

Transesterification by Reactive Distillation for Synthesis and Characterization of Biodiesel 299

Fig. 7. a) View of experimental lab apparatus of Reactive distillation

allowing the remaining alcohol fraction to re-enter the system. The experimental setup is shown in fig.5 below.

Fig. 5. Schematic of Reactive distillation column for biodiesel

Singh, Thompson Et Al. 2004; Thompson and He 2007 Fig. 6. Operation in Reactive Distillation column

allowing the remaining alcohol fraction to re-enter the system. The experimental setup is

Fig. 5. Schematic of Reactive distillation column for biodiesel

Singh, Thompson Et Al. 2004; Thompson and He 2007 Fig. 6. Operation in Reactive Distillation column

shown in fig.5 below.

Fig. 7. a) View of experimental lab apparatus of Reactive distillation

Transesterification by Reactive Distillation for Synthesis and Characterization of Biodiesel 301

alcohol is vaporized from the reboiler, flows upward constantly, and bubbles through the liquid in the packing, which provides a uniform mixing. The thru-vapor is condensed at the top of the RD column and refluxes partially back to the column and the rest combines with

In this study, three non edible vegetable oils namely, castor seed oil, coconut oil and

**5.1 Physical and chemical characteristics of the feedstock vegetable oils used for the** 

Stearic acid(18:0)

Castor oila 1.1 0 3.1 4.9 1.3 0 89.6 Cottonseed oil 28.7 0 0.9 13.0 57.4 0 0 Coconut oil 9.7 0.1 3.0 6.9 2.2 0 65.7

Table 5. Table Fatty acids composition of vegetable oils samples under consideration

1 Appearance Pale dark yellow 2 Density (at 15oC) 938.8 kg/m3 3 Iodine value 82 -90 4 Saponification value 182 5 Flash Point 229 oC 6 Pour point -33 oC 7 Acid value 2.0 max 8 Moisture and Volatiles 0.50% max 9 Specific gravity at 20oC 0.954 – 0.967 10 Kinematic Viscosity ,cst(mm2/s) 115 (at 60oC)

Sr no. Parameters Values

Flash point oC

Oleic acid (18:1)

Pour point oC

Linoleic acid (18:2) Saponification value

Linolenic acid (18:3) Other

Density (Kg/m3 at 288K)

Castor oil 115 (at 60oC) 938.8 229 -33 182 Cottonseed oil 35.42 (at 40 oC) 904 15 -15.5 192 Coconut oil 24.85 (at 40 oC) 907 225 20 191.1 Table 4. Physical Properties of Vegetable Oil Feed stocks Used for Transesterification:

cottonseed oil were used one by one for transesterification.

Kinematic Viscosity, cst(mm2/s)

> 16:1 (Palmitoleic)

the feeding stream

Sample

**production of biodiesel** 

Oil Sample Palmitic

acid(16:0)

**Physical and chemical characteristics of castor oil** 

*Fatty acids content (%)*

Table 6. Physical and chemical characteristics of castor oil

11 Ricinoleic acid 89.6 12 Linoleic acid 4.2% 13 Oleic acid 3% 14 Stearic acid 1% 15 Palmitic acid 1% 16 Linolenic acid 0.3%

Castor oil contains 89.6% ricinoloic acid

Fig. 7. b) Schematic Diagram of Experimental Setup of Continuous Reactive Distillation Column for biodiesel

In the present experimental study, packed bed Lab-scale reactive distillation column is designed and constructed. This column made up of glass (Inner dia: 30mm, Height of column: 210mm) has been used. The RD column packings used were glass packing. The feed reactants entering into the column were distributed over the packings by the use of distributor plates. The process parameters studied here are alcohol-to-oil ratio.{3:1, 4:1 and 9:1, Optimum methanol-to-oil molar ratio = 4:1},Flow rates of reactants {2, 4, 6 ml/min, Optimum flow rate = 4ml/min},Reaction time {Residence time of 2min, 3min., 6min, optimum residence time = 3min},Temperature {55, 60, 65 oC, Optimum temperature = 65 oC}.

The RD reactor consists of perforated plates or packed sections. For packed columns the packing holds certain amount of reacting liquid in it, forming mini-reactors. Un-reacted alcohol is vaporized from the reboiler, flows upward constantly, and bubbles through the liquid in the packing, which provides a uniform mixing. The thru-vapor is condensed at the top of the RD column and refluxes partially back to the column and the rest combines with the feeding stream

In this study, three non edible vegetable oils namely, castor seed oil, coconut oil and cottonseed oil were used one by one for transesterification.

#### **5.1 Physical and chemical characteristics of the feedstock vegetable oils used for the production of biodiesel**


Table 4. Physical Properties of Vegetable Oil Feed stocks Used for Transesterification:


Castor oil contains 89.6% ricinoloic acid

300 Biodiesel – Feedstocks and Processing Technologies

Fig. 7. b) Schematic Diagram of Experimental Setup of Continuous Reactive Distillation

time = 3min},Temperature {55, 60, 65 oC, Optimum temperature = 65 oC}.

In the present experimental study, packed bed Lab-scale reactive distillation column is designed and constructed. This column made up of glass (Inner dia: 30mm, Height of column: 210mm) has been used. The RD column packings used were glass packing. The feed reactants entering into the column were distributed over the packings by the use of distributor plates. The process parameters studied here are alcohol-to-oil ratio.{3:1, 4:1 and 9:1, Optimum methanol-to-oil molar ratio = 4:1},Flow rates of reactants {2, 4, 6 ml/min, Optimum flow rate = 4ml/min},Reaction time {Residence time of 2min, 3min., 6min, optimum residence

The RD reactor consists of perforated plates or packed sections. For packed columns the packing holds certain amount of reacting liquid in it, forming mini-reactors. Un-reacted

Column for biodiesel

Table 5. Table Fatty acids composition of vegetable oils samples under consideration

**Physical and chemical characteristics of castor oil** 


Table 6. Physical and chemical characteristics of castor oil

Transesterification by Reactive Distillation for Synthesis and Characterization of Biodiesel 303

Feedstock oil was held in a separate heated reservoir maintained at 50oC.The methanol-to-oil molar ratios used were 3.0, 6.0 and 9.0. From several trials, it was found that an overall flow rate of 5-6 ml/min with the column temperature at 64°C provided residence time of about 6min without any significant operational difficulties. The column temperature was maintained by controlling the reboiler heat input. Temperatures above 64°C caused excessive entrainment and a reduction in methanol concentrations in the liquid phase. In preparation for each trial, stock alcoholic KOH was prepared on a stirring plate at a ratio that corresponded to 1, 1.5 and 2 % KOH w/w of oil for each given methanol-to-oil molar ratio, and placed in a holding reservoir next to the RD column. Optimum reaction time in biodiesel formation (1min in prereactor +5min in RD column=6min.). Reaction time by using RD column is 20 times shorter than that in typical batch processes. Also productivity of RD reactor system is 6 to 10 times

> 3 56 68 55 6 68 72 88 9 72 74 89

> > **369 Methanol Oil molar ratio (mol/mol)**

**Castor Oil Cotton seed Oil Coconut Oil**

Temperature = 64oC, Flow rate =6ml/min, Reaction time = 6min., Catalyst (KOH) =1% by wt. of oil)

Table 10. (a) Effect of Methanol to oil Molar ratio on methyl esters conversion

Fig. 8. Effect of Methanol to oil Molar ratio on methyl ester conversion

Methyl esters Conversion (%), Cottonseed oil

Methyl esters Conversion (%), Coconut oil

**5.2 Continuous transesterification by reactive distillation for synthesis of biodiesel**  The process parameters studied here are alcohol-to-oil ratio.{3:1, 6:1 and 9:1 ,Optimum methanol-to-oil molar ratio =6:1},Reaction time {Residence time of 2min, 3min., 6min, optimum residence time = 3min},Temperature {55, 60, 65oC, Optimum temperature = 65oC },

**5.2.1 Effect of methanol to oil molar ratio on methyl ester conversion** 

higher than that of batch and existing continuous flow processes.

The main process parameters examined in this study were as shown below: For individual oils (Castor, Cottonseed and Coconut oil) under consideration

> Methyl esters Conversion (%), Castor oil

catalyst loading (1,1.5 and 2 % by wt of oil).

Methanol/oil molar Ratio (mol/mol)

Optimum Molar ratio of Methanol- to- oil= 6:1

**Conversion of Methyl Esters (%)**

#### **Physical and chemical characteristics of cottonseed oil**

Its fatty acid profile generally consists of 70% unsaturated fatty acids including 18% monounsaturated (oleic), 52% polyunsaturated (linoleic) and 26% saturated (primarily palmitic and stearic).


Table 7. Physical and chemical characteristics of cottonseed oil


Table 8. Fatty acids composition of cottonseed oil

#### **Physical and chemical characteristics of coconut oil**


Table 9. Physical and chemical characteristics of coconut oil

Its fatty acid profile generally consists of 70% unsaturated fatty acids including 18% monounsaturated (oleic), 52% polyunsaturated (linoleic) and 26% saturated (primarily

7 Acid value 0.6518 mg of KOH/gm of oil

**Physical and chemical characteristics of cottonseed oil** 

Sr. no. Parameters Values

8 Free fatty acids 0.3258% 9 Molecular weight 863

Table 7. Physical and chemical characteristics of cottonseed oil

Table 8. Fatty acids composition of cottonseed oil **Physical and chemical characteristics of coconut oil** 

*Fatty acids content (%)*

10 Specific gravity at 20oC 0.9406 gm/ml

Sr no. Parameters Values 1 Palmitic acid 23% 2 Oleic acid 18% 3 Linoleic acid 52% 4 Aleic acid 19% 5 Alpha lenoleic acid 1% 6 Stearic acid 3%

Sr no. Parameters Values 1 Melting point(oC) 24 2 Moisture % <0.1

9 Saturates 92.0 10 Monosaturates 6.0 11 Polyunsaturates 2.0

Table 9. Physical and chemical characteristics of coconut oil

3 Kinematic viscosity(mm2/s) 24.85 (at 40 oC) 4 Density (at 15oC) 907 kg/m3) 3 Iodine value(cgI2/g) 12-15 5 Saponification value 191.1 6 Flash Point 225 oC 7 Pour point 20 oC 8 Total phenolics(mg/kg) 620

2 Density 904 3 Kinematic viscosity(at 40oC) 35.42 cSt 4 Saponification value 192 5 Flash point 15oC 6 Pour point -15.5 oC

1 Appearance Golden yellow

palmitic and stearic).
