Process design of continuous biodiesel production by reactive distillation: Comparison between homogeneous and heterogeneous catalysts

• Process design and simulation of continuous biodiesel production.
• Four processes: conventional/RD catalyzed by homo-/heterogeneous catalysts.
• Energy requirements are ordered as RD Hetero < RD Homo < Conv. Homo < Conv. Hetero.
• Energy required for RD Hetero is 139 kWh/t biodiesel with glycerol byproduct.

Biodiesel production by reactive distillation processing is an attractive option to overcome the thermodynamic limitations inherently associated with conventional processes. Process simulations of transesterification of soybean oil and methanol were performed using the commercial package Aspen Plus®. Four different continuous processes were designed and simulated by using homogeneous alkali-based catalysts and heterogeneous acid-based catalysts in both conventional reactor/distillation and reactive distillation. Effects of important operating and design parameters on performance of each process were analyzed and optimum conditions were determined. The proposed homogeneous alkali-catalyzed RD for biodiesel production did not only eliminate the requirement of separation and purification of the products but also improved the biodiesel yield at reduced methanol in the feed and at lower energy consumption in comparison with the conventional approach of sequential reaction and distillation. It was demonstrated that the heterogeneous magnesium methoxide, instead of homogeneous catalyst, offered significant benefits such as reaching less number of unit operations, reducing energy consumption, and not requiring neutralization, waste water disposal or salt waste processing. The energy requirement of the reactive distillation process catalyzed by magnesium methoxide was about 153 kWh/t biodiesel or 139.2 kWh/t biodiesel with an allocated purity of 98 wt% to glycerol by-product.