Doping of Potassium Hydroxide and Calcium Oxide on Synthesized High Surface Area Activated Carbon for Transesterification of Waste Cooking Oil

Abstract

Transesterification is a process where triglyceride is converted to fatty acid methyl esters or biodiesel.  High surface area activated carbon was successfully prepared from palm kernel shells (PKS) to act as the catalyst support via chemical activation with potassium hydroxide (KOH) as an activating agent and later doped with calcium oxide (CaO).  Thermal gravimetry analysis (TGA) proved that the optimum activation temperature of PKS is 600 ºC.  The optimization of the concentration of potassium hydroxide was done according to four different concentrations at 15%, 20%, 25% and 30%.  Under FTIR analysis, the missing of O-H bond and sp³ carbon bond stretching in the activated char suggested that the activated carbon was successfully produced.  At potassium hydroxide concentration of 25%, it was found that the BET surface area was the highest, in which it achieved 443.83 m²/g. Field emission scanning electron microscopy (FESEM) analysis also proved the formation of porous structure with high surface area. The prepared activated carbon is doped with potassium hydroxide and calcium oxide (KOH-CaO-Catalyst).  The FTIR analysis show the missing of sp² carbon bond stretching, C=C bond and C-H bond bending, which deviated from the activated carbon.  FESEM analysis also proved that the surface of the activated carbon was impregnated with KOH and CaO.  The catalyst was then used for the transesterification reaction of waste cooking oil with excess methanol.  The ratio of methanol to waste cooking oil used was 20:1. The fatty acid methyl ester (FAME) yield from transesterification was 99.5%.  In this study, the optimum parameters to prepare high surface area activated carbon for transesterification of waste cooking oil was at 600ºC activation temperature with 25% of KOH concentration.