New Biorefining Process Makes Use of Biorefinery Waste Product

Research conducted by Purdue University's Center for Direct Catalytic Conversion of Biomass to Biofuels, also known as C3Bio, has developed a process that turns the lignin in cell walls of plants into lignin-free cellulose and that also produces two phenols. The cellulose can be used to produce ethanol, while the phenols can be used to create fragrances for household products, flavorings, and a high-octane hydrocarbon fuel that could be used by racecars and jets. The biomass for the research came from untreated chipped and milled wood from sustainable poplar, eucalyptus, or birch trees. Currently, artificially produced fragrances and flavorings, such as artificial vanilla, come from petroleum.

In a one-step process, the research team, led by Mahdi Abu-Omar, Purdue's R.B. Wetherill Professor of Chemistry, adds a catalyst and solvent to the biomass. The catalyst initiates and speeds up the chemical reactions that produce the two phenols, and the solvent dissolves and loosens the materials produced by the chemical reactions. The materials are then heated in a pressurized reactor for several hours. The heating process breaks up the lignin into lignin-free cellulose and a liquid stream that contains the catalyst and the phenols. The catalyst, which is expensive, is then evaporated from the stream, recycled, and reused.

The lignin-free cellulose created by the process can be used as the basis of liquid fuels such as ethanol. In addition, a second catalyst can be used to convert the phenols into a hydrocarbon fuel with an octane rating of over 100. This hydrocarbon fuel could be used as a drop-in gasoline. Currently, gasoline has octane ratings in the 80s.

 Lignin is a tough, complex molecule that provides the rigid structure of plant cell walls, and most biorefineries treat lignin as waste, a physical and chemical barrier to extracting sugars from biomass. In most biorefining processes, the extracted sugar is fed to yeast, which produces ethanol. However, lignin poisons the yeast enzymes. So, some biorefineries use harsh pretreatments to remove lignin from the biomass, but most simply burn it for heat.

The team continues to look for ways both to scale up their process and to increase their efficiency in recovering and reusing the catalyst. These improvements are needed to make the new process feasible for existing biorefineries. Abu-Omar says, "A biorefinery that focuses not only on ethanol but also on other products that can be made from biomass is more efficient and profitable overall." He believes that lignin could become more valuable than cellulose and even subsidize the production of ethanol because lignin produces both the two phenols and cellulose for ethanol in a single step. Purdue's Research Foundation has filed patent applications on the new process and launched Spero Energy, a startup company founded by Abu-Omar.

 

C3Bio is an Energy Frontier Research Center that is part of Discovery Park's Energy Center and Purdue's Bindley Bioscience Center. It receives funding from the U.S. Department of Energy.