OPTIMIZATION OF BIODIESEL PRODUCTION USING RESPONSE SURFACE METHODOLOGY

Abstract

Energy security has become a key issue for all the nations of the world. The increasing industrialization and modernization of the world has led to an increase in the demand of petroleum products of which 83% is met by import. It is, therefore, necessary to look forward for alternative fuels to meet the ever growing consumption of petroleum products. Biodiesel, an eco-friendly and renewable fuel, a promising substitute for diesel is getting the attention of researchers from all over the world. Biodiesel is defined as a fuel comprised of monoalkyl esters of long chain fatty acids derived from vegetable oils or animal fats, either in pure form or mixed in any combination with petroleum-based diesel fuel. Jatropha curcas oil (JCO) is a plant based feedstock that is unsuitable for human consumption and can serve as a potential feedstock for biodiesel production in India. However, its properties are not suitable to use it directly in engines and are therefore, modified by transesterification process. For high Free Fatty Acid (FFA) (14.6%) JCO, two step acid-base catalyzed transesterification process is adopted. This process involves many parameters that effect the reaction and optimizing so many reaction factors require large number of experiments, which is laborious, time consuming, and economically non-viable. Response surface methodology (RSM) is a useful statistical technique for the evaluation or optimization of complex processes, as it reduces the number of experiments required to achieve ample data for a statistically pertinent result. Literature has revealed that little work is done on the optimization of biodiesel production using RSM and no work is reported on the optimization of four reaction variables using RSM for esterification and transesterification of Jatropha curcas oil to produce biodiesel. The present study has, therefore, dealt with the optimization of biodiesel production from high FFA JCO using Central Composite Design (CCD) based on RSM and provided the optimum route for the production of biodiesel from JCO having high FFA content of 14.6%. Optimization studies for reduction of FFA of JCO and maximization of yield of Jatropha curcas Biodiesel (JCB) (%) were carried out using Desirability function based on RSM. A five-level-four-factorial CCD with 54 assays was employed to study the effect of catalyst (H2SO4) concentration, reaction temperature, reaction time .and methanol quantity on the Free Fatty Acid (FFA) content of JCO during its esterification for making biodiesel. Using RSM, a quadratic polynomial equation was obtained for FFA by regression analysis. Verification experiments confirmed the validity of the predicted model. The high FFA (14.6%) of JCO could be reduced to 0.34% by its pre-treatment with methanol (6.5:1 w/w) using H2SO4 as catalyst (1.5% v/v) in 125 min time at 50°C temperature. On the basis of ANOVA results; all the four reaction variables had a significant effect on FFA content. High reaction temperature, long reaction time and excess quantity of methanol/oil ratio were found to be the limiting factors for reduction of FFA content to a low value. This study opens up avenues for researchers to predict the FFA of JCO under given operating parameters. Industrial scale up of this novel work can boost the oil industry by saving time on optimization of process parameters. The effect of catalyst concentration (NaOH), reaction temperature, reaction time and methanol/oil molar ratio on the methyl esters yield from esterified JCO during its transesterification was studied by using a five-level-four-factorial CCD with 54 experimental runs. A model equation for predicting the yield of Jatropha curcas Biodiesel (JCB) yield was obtained by using RSM. The high FFA (14.6%) of JCO could be reduced to 0.34% by acid catalyzed esterification and a JCB yield of 98.3% was obtained with methanol/oil ratio (11:1 w/w) using NaOH as catalyst (1% w/w) in 110 min time at 55°C temperature. The predicted value of JCB yield was found to be in good agreement with the experimental value at the optimum level of input parameters. ANOVA results revealed that catalyst (NaOH) concentration, reaction time and methanol/oil molar ratio had a significant effect on JCB yield. High concentration of NaOH catalyst was found to have inhibiting effect on the conversion of triglycerides to biodiesel, thereby, decreasing the biodiesel yield. The properties of the JCB, thus, produced conformed to the ASTM and IS specifications, making it an ideal alternative fuel for diesel engines. The JCB prepared by using the optimum combination of parameters can be effectively used as a substitute of diesel fuel and reduce the harmful effects on the environment. The models can be successfully adopted in fuel industry to reduce the FFA content of JCO without wasting time on optimization of process parameters and maximize the yield of methyl esters, thereby, improving the economy of the process.