Roger Ruan in the lab.

MN Impact: University of Minnesota researchers develop new technology that helps with the conversion of bio-oil

November 2, 2019


Research will investigate and help develop novel sources of bioenergy.


Bioenergy is a valuable alternative to fossil energy. Despite decades' efforts, commercial production of bioenergy is facing many barriers, including issues with biomass production and logistics, bio-conversion processes and bio-refining processes.

What has been done

Microwave-assisted pyrolysis (MAP) is a new thermochemical process that converts biomass and recycled wastes to bio-oil and fuels. Specifically, MAP maximizes yields by recovering methyl ester from biodiesel vacuum distillation bottoms (VDBs). Compared with the conventional electrical heating pyrolysis, MAP is more rapid, efficient, selective, controllable and flexible. However, biodiesel distillation, the most significant and primary purification process, produces a waste stream of VDBs that represents approximately 5 to 15 percent of the crude biodiesel.

Roger Ruan and his team developed a MAP reactor with a fixed-bed microwave susceptor silicon carbide catalyst that absorbs microwave radiation and quickly achieves a high temperature allowing rapid heating of VDBs, and attaining targeted catalytic reforming while avoiding unwanted dimerization and derivatization.


This new MAP technology recovers valuable methyl esters from VDBs, solving the waste formation problem by recovering a significant amount (approximately 85 percent wt/wt) of the VDBs as a transparent bio-oil composed mostly of methyl esters. 
Testing shows the bio-oil can be blended back into the initial distillate stream and that it passes all ASTM D6751 tests required for commercial biodiesel. The process is easily integrated into existing biodiesel processes and can increase biodiesel yield up to 10 percent, resulting in more biodiesel sold than low grade heating fuel. Estimated net economic value of the system is $1.4 million per year with a payback period of about 2 years for a 10 million gallon biodiesel plant.