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.
Bibliographical noteFunding Information:
The authors are grateful to New Leaf Biodiesel for their help supplying commercially produced VDBs. This project was supported in part by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR), the Metropolitan Council for Environmental Services (MCES), the University of Minnesota MNDrive program, the Grand Challenge program, and the Center for Biorefining. R.R. is Distinguished Guest Professor, Nanchang University, and Professor and Director, University of Minnesota.
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