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

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 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


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

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

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

Transesterification by Reactive Distillation for Synthesis and Characterization of Biodiesel 305

Mixed oil 1 Mixed oil 2 Mixed oil 3

Methyl esters Conversion (%), Coconut oil

> Castor oil Cottonseed oil Coconut oil

0 2 4 6 8 10 **Reaction Time(min.)**

Fig. 10. Effect of reaction time using different mixed oils on methyl ester conversion

It was observed that mixed oil 3 i.e. 50% Coconut oil + 50% Cottonseed oil showed the

5 90 92 90 6 94 96 93 7 94 95 93 Molar ratio of Methanol to Oil = 6:1, Reaction time = 6min., Catalyst (KOH) =1% (by wt. of oil),

> 345678 **Flow rate,ml/min.**

Methyl esters Conversion (%), Cottonseed oil

50

Flow rate, ml/min

Temperature = 60oC

80

Optimum flow rate = 6ml/min

85

90

**Methylester conversion(%)**

95

100

maximum methyl ester conversion.

**5.2.2 Effect of flow rates on methyl ester conversion** 

Table 11. Effect of Flow rates on methyl ester conversion

Fig. 11. Effect of Flow rates on methyl ester conversion

Methyl esters Conversion (%) , Castor oil

60

70

**Methylester conversion(%)**

80

90

100


Reaction temperature =60oC, Catalyst concentration =1 wt%, Methanol to mixed oil molar ratio = 3:1, 6:1, 9:1

Table 10. (b) Effect of methanol-to-mixed oil feed molar ratio on methyl ester conversion

Fig. 9. Effect of Methanol to Mixed oil Molar ratio on methyl ester conversion

The three vegetable oil feedstock's under consideration were mixed and three mixed feed oils were prepared for the experimental runs. The effect of Methanol to Mixed oil Molar ratio on methyl ester conversion was observed as shown in fig.9. The conversion of methyl esters was found to increase with increase in molar ratio during initial reaction time. Also the highest conversion o e 6min in RD column. Thus it can be concluded that the mixed oils can be used for synthesis of biodiesel. This would help in reduction in overall cost of biodiesel synthesis by cutting down the cost of expensive oil by replacing the portion of expensive oils by cheaper oils or the oils which are easily available in abundance.


Reaction temperature =60oC, Catalyst concentration =1 wt%, Methanol to mixed oil molar ratio = 6:1, Mixed oil 1= 50% Castor oil+50% Cottonseed oil, Mixed oil 2 = 50% Castor oil+ 50% Coconut oil, Mixed oil 3 = 50% Coconut oil + 50% Cottonseed oil

Table 10. (c) Effect of reaction time using different mixed oils on methyl ester conversion

Fig. 10. Effect of reaction time using different mixed oils on methyl ester conversion

It was observed that mixed oil 3 i.e. 50% Coconut oil + 50% Cottonseed oil showed the maximum methyl ester conversion.

#### **5.2.2 Effect of flow rates on methyl ester conversion**

304 Biodiesel – Feedstocks and Processing Technologies

2 68 72 55 6 89 96 88 8 91 94 89

Reaction temperature =60oC, Catalyst concentration =1 wt%, Methanol to mixed oil molar ratio = 3:1,

Table 10. (b) Effect of methanol-to-mixed oil feed molar ratio on methyl ester conversion

Methanol/oil molar Ratio (mol/mol)=6

Methanol/oil molar Ratio (mol/mol)=9

Methanol/Mixed oil molar

Methanol/Mixed oil molar

Methanol/Mixed oil molar

Methyl ester conversion (%) Mixed oil 3

ratio:3

ratio:6

ratio:9

Methyl ester conversion (%) Mixed oil 2

(mol/mol)=3

0 2 4 6 8 10 **Reaction Time(Min.)**

Fig. 9. Effect of Methanol to Mixed oil Molar ratio on methyl ester conversion

expensive oils by cheaper oils or the oils which are easily available in abundance.

Methyl ester conversion (%) Mixed oil 1

The three vegetable oil feedstock's under consideration were mixed and three mixed feed oils were prepared for the experimental runs. The effect of Methanol to Mixed oil Molar ratio on methyl ester conversion was observed as shown in fig.9. The conversion of methyl esters was found to increase with increase in molar ratio during initial reaction time. Also the highest conversion o e 6min in RD column. Thus it can be concluded that the mixed oils can be used for synthesis of biodiesel. This would help in reduction in overall cost of biodiesel synthesis by cutting down the cost of expensive oil by replacing the portion of

2 65 77 78 6 89 92 95 8 90 93 95 Reaction temperature =60oC, Catalyst concentration =1 wt%, Methanol to mixed oil molar ratio = 6:1, Mixed oil 1= 50% Castor oil+50% Cottonseed oil, Mixed oil 2 = 50% Castor oil+ 50% Coconut oil, Mixed

Table 10. (c) Effect of reaction time using different mixed oils on methyl ester conversion

Reaction Time(min.) Methanol/oil molar Ratio

6:1, 9:1

**Methylester Conversion(%)**

Reaction Time(min.)

oil 3 = 50% Coconut oil + 50% Cottonseed oil


Molar ratio of Methanol to Oil = 6:1, Reaction time = 6min., Catalyst (KOH) =1% (by wt. of oil), Temperature = 60oC

Table 11. Effect of Flow rates on methyl ester conversion

Optimum flow rate = 6ml/min

Fig. 11. Effect of Flow rates on methyl ester conversion

Transesterification by Reactive Distillation for Synthesis and Characterization of Biodiesel 307

The rate of transesterification depends on the time of reaction as shown in fig.12 The reaction was slow during the first few minutes due to time taken for mixing and dispersion of methanol with the triglycerides in the oil. However the rate of reaction increased steadily from 6 min of the reaction. The residence time of the reactants in the RD Column was 6min. at which the highest ME conversion was achieved. Thus the reaction time clearly influences

The type of catalyst and the amount of catalyst has a great impact on formation of biodiesel. The adequate catalyst loading is necessary to obtain the maximum conversion of triglycerides to methyl esters. In the above experimentation, different types of catalysts with different catalyst loadings were utilized for transesterification reaction and their effects were studied. In the course of the tests, it is observed that addition of excess amount of catalyst, give rise to the formation of an emulsion, which has increased the viscosity and led to the

1 80 92 95 1.5 78 93 96 2 60 93 96 Methanol to oil molar ratio = 6, Temperature =60oC, Catalyst loadings used for experimentation = 1% ,

> 1 1.5 2 **Catalyst, KOH(wt.%)**

Fig. 13. Effect of catalyst (KOH) loading on Methyl ester Conversion

b. Effect of catalyst(NaOH) loading on methyl ester conversion

Methyl esters Conversion (%), Cottonseed oil

Methyl esters Conversion (%), Coconut oil

> Castor oil Cottonseed oil Coconut oil

the conversion rate of methyl esters.

formation of gel.

KOH Catalyst loading (wt.%)

1.5% and 2% KOH by wt of oil

50

60

70

**Methylester(% conversion)**

80

90

100

**5.2.4 Effect of catalyst loading on methyl esters conversion** 

a. Effect of catalyst (KOH) loading on methyl ester conversion

Methyl esters Conversion (%), Castor oil

Table 13. Effect of catalysts loadings on methyl ester conversion

The feed stream flow rates for the test run were chosen carefully in order to avoid any column flooding problem. The flow rate, which is inversely related to retention time, is used as an experimental factor to interpret the reaction conversion with the liquid retention time. The flow rate achieved in the experimental runs varied from 5 to 7 mL/min. The retention time varied from about 4 to 8 min. These values may not be the actual reaction time because of some reaction that takes place in the reboiler. Since the concentrations of methanol and catalyst were very small in the liquid phase of the reboiler, it was not possible to determine the actual retention time of reactants and catalyst in the reboiler. The effect of flow rate was mainly on the production of methyl ester of the reactor. The % weight of methyl ester decreased while the flow rate increased since the retention time is less. For the RD operation of setup in this study, the feed flow rate should not be higher 6mL/min in order to avoid flooding in column and this rate were considered as optimum range of operation.


### **5.2.3 Effect of reaction time on methyl ester conversion**

Molar ratio of Methanol to Oil = 6:1, Catalyst (KOH) = 1% (by wt. of oil), Flow rate = 6ml/min, Temperature = 60oC

Table 12. Effect of Reaction time on methyl ester conversion

Optimum Reaction time = 6min.

Fig. 12. Effect of reaction time on methyl ester conversion

The rate of transesterification depends on the time of reaction as shown in fig.12 The reaction was slow during the first few minutes due to time taken for mixing and dispersion of methanol with the triglycerides in the oil. However the rate of reaction increased steadily from 6 min of the reaction. The residence time of the reactants in the RD Column was 6min. at which the highest ME conversion was achieved. Thus the reaction time clearly influences the conversion rate of methyl esters.
