Optimization of alkali-catalyzed transesterification of Pongamia pinnata oil for production of biodiesel

Abstract

Studies were carried out on transesterification of Karanja oil with methanol for the production of biodiesel. The reaction parameters such as catalyst concentration, alcohol/oil molar ratio, temperature, and rate of mixing were optimized for production of Karanja oil methyl ester (KOME). The fatty acid methyl esters content in the reaction mixture were quantified by HPLC and ¹H NMR method. The yield of methyl esters from Karanja oil under the optimal condition was 97–98%.

Introduction

Presently the world’s energy needs are met through non-renewable resources such as petrochemicals, natural gas and coal. Since the demand and cost of petroleum based fuel is growing rapidly, and if the present pattern of consumption continues, these resources will be depleted in few years. Hence, efforts are being made to explore for alternative source of energy. An alternative fuel must be technically feasible, economically competitive, environmentally acceptable and readily available (Srivastava and Prasad, 2000).

Fatty acid methyl esters derived from renewable sources such as vegetable oils has gained importance as an alternative fuel for diesel engines. The edible oils such as soybean oil in USA, rapeseed oil in Europe and palm oil in countries with tropical climate such as Malaysia are being used for the production of biodiesel to fuel their compression ignition engines (Knothe, 2002). In Indian context, the use of edible oils for engine fuel is not feasible; however, there are several non-edible oilseed species such as Karanja (Pongamia pinnata), Jatropha (Jatropha curcas), Neem (Azadirachta indica), Mahua (Madhuca indica), Simarouba (Simarouba indica) etc., which could be utilized as a source for production of oil. Among these, Karanja is an oil seed bearing tree, which is non-edible and does not find any suitable application with only 6% being utilized out of 200 million tons per annum (Biswas, 2002).

Karanja is a native to humid and subtropical environments having annual rainfall ranging from 500 to 2500 mm in its natural habitat. The maximum temperature ranges from 27 to 38 °C and the minimum 1 to 16 °C. It can grow on most soil types ranging from stony to sandy to clay, including verticals. It does not do well in dry sands. It is highly tolerant to salinity. It can be propagated either by seeds or by root suckers (Duke, 1983). The yield of kernels per tree is between 8 and 24 kg (Bringi and Mukerjee, 1987).

The freshly extracted Karanja oil is yellowish orange to brown and rapidly darkens on storage. It has a disagreeable odor and bitter taste. The oil contains several furanoflavones such as karanjin, pongapin, and pongaglabrin. The presence of toxic flavonoids makes the oil non-edible. At present the oil is being used as a raw material for soap, and after sulphonating and sulphation in the leather tanning industries, the main constraints for its more usage are the color and odor (Bringi and Mukerjee, 1987).

Vegetable oils and animal fats are chemically triglyceride molecules, in which three fatty acid groups are ester bound to one glycerol molecule. The triglyceride molecules differ by the nature of the alkyl chain bound to glycerol. Transesterification is the process of reacting a triglyceride such as one of the vegetable oils with alcohol in presence of a catalyst to produce fatty acid esters and glycerol. In this process, there is the displacement of alcohol part by a monohydric alcohol that yields three alkyl esters from one triglyceride molecule. The molecular weight of a typical ester molecule is roughly one-third that of a straight vegetable oil molecule and has viscosity approximately twice that of diesel fuel instead of 10–20 times as in the case of neat vegetable oils (Peterson, 1986). There is decrease in viscosity and improvement of fuel properties of product fatty acid alkyl esters in the process of transesterification.

Attempts have been made for the conversion of Karanja oil to fatty acid methyl esters (De and Bhattacharyya, 1999, Karmee et al., 2004). The latest studies by Vivek and Gupta (2004) revealed the maximum yield of methyl esters up to 89% with molar ratio of MeOH/oil 8–10, KOH 1.5% w/w of oil as catalyst when the reaction was conducted for 40 min at 68–70 °C. In the present study, the optimal reaction conditions were investigated to increase the yield of methyl esters from Karanja oil. The influence of the variables such as catalyst concentration, alcohol to oil molar ratio, reaction temperature, mixing intensity on transesterification was studied.