“Looking ahead, Virent is moving rapidly to prove the technology at a commercial scale,” says Randy Cortright, one of the inventors cited on the application and the company’s founder and chief technology officer. The approach already has attracted Royal Dutch Shell’s attention, which is licensing the technology and collaborating on developing it for bio-based gasoline.
Figure 1 -- Biorefinery: Teaming proprietary APR process with conventional catalytic processes can produce a variety of biofuels.
BioForming technology combines Virent’s proprietary Aqueous Phase Reforming (APR) process for converting sugars, starches or cellulosic biomass into fuels with conventional catalytic techniques such as hydrotreating and condensation — including ZSM-5 acid condensation, base-catalyzed condensation, acid-catalyzed dehydration and alkylation (Figure 1). (A white paper about BioForming can be found at www.virent.com.)
Each step can be optimized and modified depending upon the product required. For example, gasoline is produced using a zeolite (ZSM-5)-based process, jet fuel and diesel via a base-catalyzed condensation route, and a high-octane fuel through a dehydration/oligomerization scheme.
The biofuel product naturally separates from water, eliminating the energy-intensive distillation step required in ethanol processes and providing more net energy — while matching petroleum fuels in composition, functionality and performance, claims the company.
At the heart of the process is APR, which converts water-soluble carbohydrates into hydrogen, lower alkanes and high yields of condensable chemical intermediates. The latter undergo further catalytic processing to generate hydrocarbons for fuels or chemicals for use in other industrial applications.
The APR process uses heterogeneous catalysts at 450–575K and pressures of 10–90 bar in a number of series and parallel reactions to reduce the oxygen content of the carbohydrate feedstock. These reactions include: reforming to generate hydrogen, dehydrogenation of alcohols/hydrogenation of carbonyls, deoxygenation, hydrogenolysis and cyclization.
A key feature of the method is the in-situ use of generated hydrogen for de-functionalization of the highly reactive carbohydrate to a less reactive mono-oxygenated species. The company already had found that mono-oxygenated species such as alcohols, ketones and aldehydes could be converted to non-oxygenated hydrocarbons in a continuous process using conventional catalytic condensation and hydrotreating techniques.
Unlike fermentation, BioForming can effectively process complex sugars and mixed sugar streams, notes Virent. The method can handle a wide variety of feedstocks, including both food and nonfood materials. Indeed, it can transform any plant sugar once reduced to its water-soluble form, says the company. Potential carbohydrates include sucrose (from sugar cane or sugar beets), corn sugar (glucose from conversion of corn starch), sugars derived from hemicellulose and cellulose (including polysaccharides, organic acids and furfural byproducts) and water-soluble oxygenated compounds such as diols, glycerol and sugar alcohols.