Cellulosic Fuel Production: One Step Closer to Standard Refining
The advanced renewable fuel standard (RFS2) requires aggressively increasing amounts of cellulosic biofuels to be included in the fuel pool each year, and it is likely that there will be a strong market demand from obligated parties for this type of fuel as blend requirements increase. The current federal RFS2 requires that 36 million gallons of biofuels must be used in transportation fuel by 2022, including at least 21 billion gallons of advanced biofuels such as cellulosic biofuels, creating a gigantic market.
The U.S. DOE has identified a small number of potential intermediates obtainable from cellulosic biomass resources. Levulinic acid, a breakdown product from the acid hydrolysis of cellulose, is one such intermediate and has been studied by the Energy & Environmental Research Center and other laboratories. One of the biggest challenges to utilizing levulinic acid as a biofuel intermediate is its costly separation out of the product mix. The EERC in partnership with Mercurius Biofuels has shown in the laboratory that cellulosic biomass in an alcohol medium can be catalytically converted to levulinate esters instead (ethanolysis). These chemicals are also useful for fuels and chemical intermediates. However, a major advantage of forming levulinate esters, as opposed to levulinic acid, is that the ester form is much easier to extract using a simple condensation reaction. Experiments were performed by the EERC using laboratory-scale batch reactors. Tests were done using laminated particleboard, cellulosic municipal solid waste, shredded paper and pineapple waste; all of which successfully were decomposed to ethyl levulinate. Further processing was done to create higher molecular-weight compounds.
A major push will now be made to create a pilot-scale version of a biorefinery based on this technology. The biorefinery, in very simple terms, will run in a sustainable mode using common agricultural feedstocks such as wheat straw and corn stover. The process will include three steps: 1) ethanolysis, 2) condensation, and 3) hydrotreatment to stabilize the fuel products. Final products from this biorefinery will include advanced fuel additives in the form of cyclic ethers and hydrocarbons. This technology will ultimately be used to improve engine performance using a renewable product, both in gasoline and diesel engines. In the case of diesel fuel, the additives will boost the cetane levels, improve flow properties and, most importantly, reduce particulate emissions.
Subsequent product-upgrading steps will also be conducted in continuous reactor systems, and sufficient volumes of the desired fuel products will be produced so that more extensive fuel testing can be done. The data collected from these continuous production runs will be used to further assess process economics and will also be used for the future design and construction of a larger pilot plant facility. Calculations at this time show that this type of three-step biorefinery will have a lower cost than competing technologies. Capital costs will be lower because residence times are measured in minutes compared to hours or even days for fermentation-based technologies. Also, operating conditions are moderate compared to gasification or pyrolysis. In summary, this biorefinery technology is superior to other technologies because it does not depend on enzymes and fermentation or extreme operating conditions. This technology is more in line with the petroleum refining model and will benefit from many of the same efficiencies.
The technology is patent pending for the EERC Foundation and licensed to Mercurius Biofuels on a global, exclusive basis.
Author: Ed Olson
Senior Research Advisor, EERC