Microwave-Assisted Pyrolysis as an Alternative to Vacuum Distillation for Methyl Ester Recovery from Biodiesel Vacuum Distillation Bottoms

The use of vacuum distillation for commercial biodiesel production has become a reliable post-treatment method for removing multiple impurity types, consistently producing high-grade biodiesel. During biodiesel distillation two streams are formed, a purified vapor stream and a liquid waste stream or "bottoms". Vacuum distillation bottoms (VDB) are a mixture of higher molecular weight methyl esters (84%) and derivatives. Microwave-assisted pyrolysis (MAP) has been researched as a methyl ester recovery process for VDBs leaving vacuum distillation. Two types of MAP processing, distillation microwave-assisted pyrolysis (dMAP) and flash microwave-assisted pyrolysis (fMAP), were developed and tested to determine the optimal reaction conditions for producing a biodiesel analogue. After dMAP, 85.9 wt %/wt of the VDBs was recovered as a transparent bio-oil and then blended back into B100 biodiesel and certified for sale using ASTM D6751. Blending dMAP bio-oil (10 wt %/wt) with B100 biodiesel met all certification requirements and demonstrated that MAP processing could be a significant yield improvement technology for any commercial biodiesel producer utilizing vacuum distillation.