Reactive distillation versus conventional biodiesel production using enzymatic catalysis – When process intensification becomes questionable

Abstract

Enzymatic biodiesel production offers advantages in overcoming the limitations of base-catalyzed process that is sensitive to free fatty acid contents and acid-catalyzed process that requires high operating conditions. The present study is the first to explore the techno-economic viability of enzymatic biodiesel production from castor oil considering both conventional reactor-distillation and enzymatic reactive distillation (ERD) technologies. The ERD technology was assessed by previous studies for other chemical systems, while the ERD prospect for biodiesel process currently remains unknown. This work proposes a reliable thermodynamic model and a new power-law kinetic expression for the specific assessed system. The realistic approach of reactor and enzymatic reactive distillation design in this study suggests that compared to the ERD scheme, the conventional process achieves slightly higher conversion (99.65% vs 97.61%) at substantially lower specific energy use (1.50 vs 3.93 GJ/tonne FAME) and lower specific CO₂ emissions (0.12 vs 0.31 kg CO₂/tonne FAME), with comparable production costs (2.05 vs 2.11 USD/kg). Due to the inherent slow reaction in enzymatic systems and an unfavorable components’ volatility order in the biodiesel system, a standalone ERD without pre-reactors is not practically viable. Despite the fact that the reactive distillation scheme offers advantages of process integration in some chemical reaction systems, this study reveals that sometimes process intensification fails to outperform conventional processes, particularly in enzymatic biodiesel production.