Experimental Optimization on a Continuous-flow Reactive Distillation Reactor System for Biodiesel Production via Transesterification

A comprehensive study of biodiesel (canola methyl ester) synthesis was performed on a continuous reactive distillation system. The transesterification reaction of vegetable oil and methanol is reversible in nature with an equilibrium ester yield of about 75%. The reactive distillation, a process unit that enables reaction and distillation in a single unit, is an excellent option for the biodiesel production and ideally can achieve 100% reaction conversion. Effects of six process variables were evaluated on the reaction conversion, productivity and soap formation. An inline static-mixer type pre-reactor was used prior to the RD column that achieved a substantial portion of the reaction duty. Potassium methoxide is found to be significantly better catalyst than KOH for achieving high conversion while low reboiler temperatures were favorable for lower soap formation. The condenser in total reflux mode was found to be better than in total recycle mode. Surprisingly the feed molar ratio and overall flow rate was not highly correlated to overall product conversion or soap formation. Wide range of different quality parameters have been obtained with the 16 experiments performed on the RD reactor system setup. The reaction conversion achieved on the RD reactor ranges from 41.46 - 94.94% with an average of 76.32%. Similarly, the productivity varies from 16–55.8 kmol/ m3 reactor-h with an average of 32 kmol/ m3 reactor-h, which are equivalent to 5.6–19.5 m3/ m3 reactor-h with an average of 13.1 m3/ m3 reactor-h, respectively. The optimum conditions predicted through statistics software would lead to reaction conversion rate >98%, productivity > 50 kmol esters/ m3 reactor-h, or 17.5 m3/ m3 reactor-h, and soap formation of less than 7 moles per 100 moles of feed triglyceride. Experimental verification of such optimum operating conditions is under investigation.