|Overview of the process. Cai et al. (2014) Click to enlarge.|
A team of researchers, led by Professor Charles E. Wyman, the Ford Motor Company Chair in Environmental Engineering at the University of California, Riverside’s Bourns College of Engineering, has developed a versatile, relatively non-toxic, and efficient way to convert lignocellulosic biomass into biofuels and chemicals.
The method couples the use of a metal halide selective catalyst with a highly tunable co-solvent—renewable tetrahydrofuran (THF)—to enhance co-production of the fuel precursors furfural and 5-HMF from biomass in a single-phase reaction strategy capable of integrating biomass deconstruction with catalytic dehydration of sugars. Those fuel precursors can then be converted into ethanol, chemicals or drop-in fuels.
Metal halides are are suitable for production of furfural and 5-HMF from sugars derived from lignocellulosic biomass; however, the researchers note, metal halides do not perform nearly as well when applied to biomass even in combination with immiscible extracting solvents or expensive ionic co-solvents.
Co-solvent Enhanced Lignocellulosic Fractionation (CELF), also developed by Wyman and his colleagues, uses THF as a co-solvent to aid in the breakdown of raw biomass feedstocks. CELF is unique in that it can consolidate multiple processing steps—such as pretreatment, sugar hydrolysis, and sugar catalysis—into one step. This reduces the water content of the reaction to maximize the amount of actual solids that can be loaded and also conserve heat and energy. The process is also tunable so that different end products can be made by changing the configurations.
Compared to other available biomass solvents, THF is well-suited for this application because it mixes homogeneously with water, has a low boiling point (66 ˚C) to allow for easy recovery, and can be regenerated as an end product of the process, said Charles M. Cai, a Ph.D. student working with Wyman.
Successful commercialization of biofuels technology is about yield, yield, yield, and we obtained great yields with this novel technology.—Charles Wyman
In a recently published paper in the RSC journal Green Chemistry, the UC Riverside researchers showed that combining CELF with metal halides was particularly effective at simultaneously producing the fuel precursors furfural and 5-hydroxymethylfurfural (5-HMF) directly from raw maple wood.
Lignocellulosic biomass, which is the only sufficiently prevalent sustainable resource for conversion into liquid transportation fuels, is the most abundant organic material on Earth. It is composed of three major components: cellulose, hemicellulose and lignin.
To create precursors for drop-in biofuels, the cellulose is broken down into hydroxymethylfurfural (5-HMF) and most of the hemicellulose is broken down into furfural. The lignin is generally considered a waste product and burnt to produce energy, although that thought is changing.
Furfural and 5-HMF are widely recognized renewable chemicals for their conversion into gasoline, jet, and diesel range liquid fuels. Furfural and 5-HMF further can be further chemo-catalytically upgraded to drop-in fuels including 2-methylfuran (MF) and 2,5- dimethylfuran (DMF).
Using the combination of THF and the metal halide iron chloride, Cai and the research team obtained yields of 95% of the theoretical maximum for and 51% for 5-HMF in a single pot reaction. This presents an improvement in yield rates of almost 50% over current commercial technologies and can thereby potentially reduce the cost of furfural production to within the range of current price of crude oil.
In addition to the high yield rates, more than 90% of the lignin was dissolved and extracted by CELF and recovered as a fine powdered product.
Lignin is often unused or burned. However, lignin is actually a promising resource for making additional high value chemicals and fuels once it is extracted and depolymerized with CELF. Because THF is easily recovered at low temperatures, its removal after the reaction allows the dissolved lignin particles to reform as solids that precipitate out of solution.
In addition to Cai and Wyman, co-authors of the paper are Nikhil Nagane, a graduate student in Wyman’s lab who performed studies on reaction kinetics with CELF, and Rajeev Kumar, an assistant research engineer in Wyman’s group who advises the graduate students along with Wyman.
In previous work, outlined in a 2013 paper published in Green Chemistry, Cai introduced the use of CELF with simple acids as a method to produce sugars for biological processes such as fermentation.
In this case, the technology is being employed in ongoing project at UC Riverside to combine CELF technology with microbial production of fuels, such as ethanol and butanol, by using CELF to produce highly reactive sugar-rich materials from lignocellulosic biomass that can be easily broken down to simple sugars using zero or very low levels of added enzymes.
This research is supported by the BioEnergy Science Center (BESC), Oak Ridge National Laboratory, a US Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science.
The drop-in fuels research was supported by a grant from the Sun Grant Initiative, the UC Riverside Research and Economic Development Office of Technology Commercialization, and the University of California Transportation Center.
The UCR Office of Technology Commercialization has worked with the inventors to file a patent on the invention. CELF is licensed by partners from Cognitek in Northbrook, Ill., who will be working with Cai and Wyman to create a new spin-off company to commercialize the technology.
Charles M. Cai, Nikhil Nagane, Rajeev Kumar and Charles E. Wyman (2014) “Coupling metal halides with a co-solvent to produce furfural and 5-HMF at high yields directly from lignocellulosic biomass as an integrated biofuels strategy,” Green Chem. 16, 3819-3829 doi: 10.1039/C4GC00747F
Charles M. Cai, Taiying Zhang, Rajeev Kumar and Charles E. Wyman (2013) “THF co-solvent enhances hydrocarbon fuel precursor yields from lignocellulosic biomass,” Green Chem. 15, 3140-3145 doi: 10.1039/C3GC41214H