Electrochemical synthesis of methoxide for transesterification of palm oil

Abstract

Sodium methoxide (NaOCH3) is commonly used as an alkaline homogeneous catalyst in transesterification to produce fatty acid methyl ester (FAME) and glycerol as a by-product. However, this conventional process requires a few steps to remove the homogeneous catalyst from the products by neutralization and washing, creating waste salts to be treated with additional cost. This study investigates the electrochemical synthesis of methoxide. Amberlite IRA402 anion exchange resin is used to adsorb the generated methoxide and subsequently as a heterogeneous catalyst for transesterification to observe its catalytic activity. In contrast to many other similar works, this synthesis was performed with anion-exchange resin as the only electrolyte in the cathode compartment where methoxide is synthesized electrochemically and stored in the resin without any other additives such as sodium chloride (NaCl) or water needed, eliminating the need for neutralization and washing. Platinized titanium fiber felt was used as electrodes. Methoxide ions can be generated with the presence of an anion-exchange membrane at a constant current density of 8.25 mA cm-2 for 4 h. The hydroxide equivalent of electrolyzed resin was 0.00039 mol cm-3, compared with that from ion exchange of 0.00029 mol cm-3. The results of the experiment suggest that hydroxide ions as base in the resin could better catalyze transesterification than methoxide ions; therefore, electrochemical regeneration did not restore its catalytic activity. The response surface methodology (RSM) from a central composite design (CCD) of experiments was conducted to analyze the effects of the catalyst loading, the methanol-to-oil molar ratio, and the reaction temperature. Statistical analysis suggested that only the catalyst loading, the reaction temperature, and the interaction between the catalyst loading and the reaction temperature affected the FAME yield significantly.