Both technologies are based on a process developed by Dumesic and Cortright at the University of Wisconsin called aqueous phase reforming (APR). (Earlier post.) Virent has exclusive worldwide license to the basic APR process from Wisconsin Alumni Research Foundation (WARF), multiple independent patent applications, and a significant trade secret position.

In passing a watery slurry of plant-derived sugar and carbohydrates over a series of catalysts in several flow reactors integrated in a cascade mode, carbon-rich organic molecules split apart into component elements that recombine to form many of the chemicals that are extracted from non-renewable petroleum.

As part of a suite of second-generation biofuel alternatives, renewable bio-hydrocarbon approaches like aqueous phase reforming are generating interest across the academic and industrial communities because they yield a product that is compatible with existing infrastructure, closer than many other alternatives in their net energy yield, and that can be crafted from plants grown in marginal soils, like switchgrass, or from agricultural waste.

This is the same fuel we’re currently using, just from a different source. It’s not something that burns like it—it is it.

—James Dumesic

While several years of further development will be needed to refine the process and scale it for production, the promise of gasoline and other petrochemicals from renewable plants has led to broad industrial interest. Virent, for example, has formed key strategic alliances with Royal Dutch Shell as a commercial collaborator for bio-gasoline, and has attracted leading industrial companies as investors, including Cargill and Honda. (Earlier post.)

To convert biomass-derived carbohydrates to drop-in replacement liquid hydrocarbon fuels requires the removal of the oxygen atoms.

To produce non-oxygenated liquid fuels, this removal of oxygen must be accompanied by isomerization to form branched hydrocarbons for gasoline, and/or by C-C coupling reactions to increase the molecular weight for diesel and jet fuels.

—Kunkes et al. (2008)

On 23 September, the National Science Foundation, which supported both research efforts, will host an expert panel session featuring experts from academia and industry, including Randy Cortright and George Huber (earlier post), to highlight how far researchers have come, and how far they still need to go, to bring plant-derived gasoline to market.

Virent’s BioForming process. Click to enlarge.

Virent’s BioForming. Virent’s APR methods uses heterogeneous catalysts at moderate temperatures (450-575 K) and pressures (10 to 90 bar) in a number of series and parallel reaction to reduce the oxygen content of carbohydrate feedstock. The reactions include:

1. Reforming to generate hydrogen;

2. Dehydrogenation of alcohols/hydrogenation of carbonyls;

3. Deoxygenation reactions;

4. Hydrogenolysis; and

5. Cyclization.

A key feature of the method is the use of hydrogen generated within the process. Virent found that mono-oxygenated species such as alcohols, ketones and aldehydes can be converted to hydrocarbons in a continuous process using conventional catalytic condensation and hydrotreating techniques. BioForming is essentially the integration of APR with these conventional catalytic processes—such as catalytic hydrotreating and catalytic condensation processes, including ZSM-5 acid condensation, base catalyzed condensation, acid catalyzed dehydration, and alkylation.

As in a petroleum refinery, each of these process steps can be optimized and modified to produce a particular slate of product. For example, Virent says, a gasoline product can be produced using a zeolite (ZSM-5) based process, jet fuel and diesel can be produced using a base catalyzed condensation route, and a high octane fuel can be produced using a dehydration/oligomerization route.

The key step is APR, which converts water-soluble carbohydrates into hydrogen, lower alkanes, and high yields of condensable chemical intermediates. These intermediates undergo further processing to generate the end hydrocarbons. The hydrogen is used in the production of the condensable intermediates, with excess recycled for upgrading use. The lighter alkanes, such as C₁-C₄ fuel gases, can provide process heat.

Dumesic process. Dumesic and his team had earlier developed a process to produce furan derivatives (e.g., hydroxymethylfurfural, HMF) involving dehydration of sugars (e.g., fructose) that can subsequently undergo aldol-condensation with ketones (e.g., acetone), followed by hydrodeoxygenation to form C₉ to C₁₅ alkanes for use in diesel and jet fuels. (Earlier post.)

The new process uses a different approach, beginning the oxygen removal process by converting sugars and polyols over a Pt-Re catalyst to form primarily hydrophobic alcohols, ketones, carboxylic acids, and heterocyclic compounds.

This process can be used to produce ketones for C-C coupling with HMF, thereby replacing the acetone in our previous process with ketones derived directly from biomass. This alternative process does not require the separate formation of HMF, because we demonstrate that the ketones produced can undergo self-coupling reactions. In addition, this process provides a route to highly branched alkanes and olefins, as well as alkylated aromatics, these compounds being high-octane components of gasoline. Moreover, intermediate compounds formed during the conversion of biomass-derived carbohydrates to liquid transportation fuels can serve as valuable compounds for the chemical and polymer industries.

—Kunkes et al. (2008)

According to Dumesic, a key feature of the approach is that between the sugar or starch starter materials and the bio-hydrocarbon end products, the chemicals go through an intermediate stage as an organic liquid composed of functional compounds.

The intermediate compounds retain 95 percent of the energy of the biomass but only about 40 percent of the mass, and can be upgraded into different types of transportation fuels, such as gasoline, jet and diesel fuels. Importantly, the formation of this functional intermediate oil does not require the need for an external source of hydrogen.

—James Dumesic

In the initial step of the process, a fraction of the feed is reformed over Pt-Re/C to supply the hydrogen required to partially de-oxygenate the remainder of the feed to mono-functional hydrocarbons. Endothermic reforming reactions are balanced with exothermic de-oxygenated reactions in the same reactor, such that the overall conversion is mildly exothermic and more than 90% of the energy content of the polyol or sugar feed is retained in the reaction products.

Resources

• Production of Conventional Liquid Fuels from Sugars (Virent white paper)

• Edward L. Kunkes, Dante A. Simonetti, Ryan M. West, Juan Carlos Serrano-Ruiz, Christian A. Gärtner, James A. Dumesic (2008) Catalytic Conversion of Biomass to Monofunctional Hydrocarbons and Targeted Liquid-Fuel Classes. Science DOI: 10.1126/science.1159210