Biodiesel production using Aspergillus niger as a whole-cell biocatalyst in a packed-bed reactor

Abstract

Enzymatic lipase transesterification of palm oil to biodiesel in a packed-bed reactor (PBR) using a novel strain of the fungus Aspergillus niger, immobilized within polyurethane biomass support particles (BSPs), was investigated. A three-step addition of methanol was used to reduce lipase inhibition by immiscible methanol. The influence of water content and PBR flow rate was investigated. FAME yield was enhanced with an increase of PBR flow rate in the range of 0.15–30 L h−1, where inefficient mixing of the reaction mixture at lower flow rates resulted in low conversion rates i.e. 69% after 72-h reaction. Adding the third mole equivalent of methanol resulted in lipase inhibition due to methanol migration into the accumulated glycerol layer. Glutaraldehyde (GA) solution (0.5 vol.%) was used to stabilize lipase activity, which led to a high FAME yield (>90%) in the PBR after 72-h of reaction time at a flow rate of 15 L h−1, and a water content of 15%. Moreover, a high conversion rate (>85%) was maintained after four palm oil batch conversion cycles in the PBR. In contrast, lipase activity of non-GA-treated cells decreased with each PBR batch cycle, where only 70% FAME was produced after the forth PBR cycle. Transesterification of palm oil in a PBR system using BSPs-immobilized A. niger as a whole-cell biocatalyst is a viable process for enzymatic biodiesel production.