Low Temperature Glycerolysis as a High FFA Pre-Treatment Method for Biodiesel Production

Abstract

A novel low temperature glycerolysis process for lowering free fatty acid (FFA) in crude jatropha oil for alkali catalyzed transesterification has been developed. The response surface methodology (RSM) based on central composite design was used to model and optimize the glycerolysis efficiency under three reaction variables namely; reaction time, temperature and glycerol to oil mass ratio. The optimum conditions for highest glycerolysis efficiency of 98.67% were found to be temperature of 65˚C, reaction time of 73 minutes and 2.24 g/g glycerol to oil mass ratio. These conditions lower the high free fatty acid of crude jatropha oil from 4.54% to 0.0654% which is below 3% recommended for alkali catalyzed transesterification. The pre-treated crude jatropha oil was then transesterified by using homogeneous base transesterification resulting to a conversion of 97.87%. The fuel properties of jatropha biodiesel obtained were found to be comparable to those of ASTM D6751 and EN 14214 standards. The process can also utilize the crude glycerol from the transesterification reaction, hence lowering the cost of biodiesel. The glycerolysis is easier implemented than acid esterification thereby avoiding the need for neutralization and alcohol removal step.

Re-esterification of high free fatty acid oils for biodiesel production

“…The re-esterification reaction was carried out in a glass batch reactor equipped with IKA RW20 mechanical digital stirrer and Barnstead BI electrothermal heating instrument. [8] Crude castor oil was heated and maintained at a constant set temperature. NaOH catalyst 1.75% wt of oil was dissolved in glycerol before mixing with oil at 800 rpm using IKA RW20 mechanical digital stirrer.…”

“…The variables were generated using Design-Expert Ò 7 software based on the preliminary trial experiments. [8] Experiments were carried out in a random manner to minimize the effects of uncontrolled factors. The reaction product mixture was then poured into a separating funnel and allowed to settle for 3 hours.…”

“…The top layer comprised of oil, whereas the bottom layer contained glycerol, dissolved catalyst and other minor components from the oil. [8] The final amount of FFA was established and the re-esterification efficiency was determined using Equation (1).…”

“…Kombe et al [8] have summarized the works of several authors on re-esterification as a pre-treatment for high FFA as listed in Table 4. Most of the existing researchers have focused on the use of acidic catalysts which lead to high temperatures above 120 C and more than 120 minutes of reaction time.…”

“…Pre-treatment of this oil for lowering FFA prior to alkali catalysed transesterification is therefore unavoidable. In previous work by Kombe et al [8] it has been demonstrated that the new proposed pre-treatment method, i.e. low temperature re-esterification (glycerolysis), could lower effectively the FFA in Jatropha curcas prior to base catalysed transesterification.…”