Investigations on supercritical transesterification of chicken fat for biodiesel production from low-cost lipid feedstocks

Batch experiments on chicken fat reactions with methanol were performed at supercritical conditions to answer basic questions regarding the transesterification characteristics such as reactant ratios, lipid and reaction product thermal stability, reaction reversibility, nature of the intermediates, and glycerol consumption. The experiments were conducted at temperatures of 300-400 °C, pressures up to 41.1 MPa, methanol to triglyceride molar ratios of 3:1 and 6:1, and reaction times from 2 to 6 min. The results show that the transesterification process to produce biodiesel from low-cost lipid feedstocks with low excess of methanol and without glycerol generation is technically feasible. Since thermal decomposition of chicken fat at these temperatures is an important issue to be considered, batch experiments with emphasis on this aspect were also carried out. It was found that the thermal decomposition of chicken fat was not significant if heated up to 350 °C which will permit preheating the feedstock up to this temperature in a more practical flow process. Additional experiments showed that the overall transesterification at these conditions is not reversible and that the byproduct glycerol thermally decomposed and reacted with methanol to form ethers and other fuel components. The use of low-cost lipid feedstocks and moderate excess of methanol, associated with glycerol in situ consumption, has the potential to increase biodiesel profitability for continuous flow processes that are coupled with power generation.