Eco-efficient processes for biodiesel production from waste lipids

The paper proposes innovative eco-efficient processes for converting waste lipid feedstock with up to 35% free fatty acids into biodiesel. Free fatty acids pre-treatment is a key issue, which can be handled by esterification with methanol or glycerol, using hetero- or homogeneous catalyst. The integration with the transesterification stage is possible using methods based on process intensification and heterogeneous catalysis. Three integrated continuous processes are investigated. The first performs the esterification with methanol by reactive absorption and superacid solid catalyst, followed by transesterification by reactive distillation with alkali catalyst. The second method applies the esterification with glycerol at high temperature, coupled with transesterification by heterogeneous catalyst in a variable residence-time plug-flow reactor. The third alternative replaces the second reaction stage with vacuum distillation. In all cases, biodiesel fulfills the specifications of D6751 and EN14214 norms. This result is obtained by kinetic simulation of reactors including free fatty acids esterification and glycerides transesterification. A techno-economic analysis pinpoints the pros and cons of each process. The first process is suited for low free fatty acids content, as used cooking oils. The second and third processes can be applied for higher content of free fatty acids, such as animal fats and greases. Particularly the third process can deliver biodiesel of highest quality, conforming to the cold soak filtration test.