TECHNOLOGY AREAS: Air Platform, Information Systems, Materials/Processes

OBJECTIVE: Develop an efficient process for the conversion of biomass to short chain alkenes.

DESCRIPTION: A variety of approaches are currently under investigation for the conversion of biomass to fuels. The two most commonly explored methods are based on hydrolysis/fermentation, and pyrolysis. In the first method, acid hydrolysis followed by fermentation can directly produce alcohols such as ethanol and butanol. However, the conversion of cellulose to sugars suitable for fermentation is complex and expensive, and the product alcohols are unsuitable for applications as jet fuels due to their low net heats of combustion and high volatilities. The second method employs pyrolysis of biomass which typically produces complex oxygenated mixtures that require energy intensive post processing to remove oxygen, decrease acidity, and allow for their use in conventional engines. Biomass can also be pyrolyzed to produce synthesis gas, followed by Fischer-Tropsch catalysis to produce saturated hydrocarbon fuels, but this process typically produces a broad distribution, is energy intensive, and can require significant reforming to produce military relevant fuels.

Innovative methods are sought for the production of short chain olefins directly from biomass. Successful approaches will allow for the use of abundant renewable feedstocks for the production of saturated branched chain hydrocarbon mixtures that can be tailored to military specifications. Anticipated technical challenges include overcoming the recalcitrance of cellulose to hydrolysis, the difficulty in bioengineering microorganisms to produce specific short chain olefins, and the challenge of producing an efficient, continuous, and high throughput system.

The proposed approach should utilize a low energy, bioconversion route (microorganisms or yeast) to efficiently produce a specific short chain olefin or mixture of olefins (e.g. ethylene, propylene, butylenes, pentenes) from cellulosic or lignocellulosic feedstocks. Other approaches such as catalyzed pyrolysis or multistage catalytic processes will also be considered. The distribution of olefins can vary over a wide range, however, propylene and butylenes are the preferred products. Particular attention should be paid to the efficiency of the process, taking into account energy inputs and biomass treatment steps. The product stream should primarily consist of short chain olefins, although significant amounts of saturated hydrocarbons can be tolerated. Product streams with considerable amounts of oxygenated compounds (alcohols, carboxylic acids, ethers, etc.) are unsuitable for further applications.

PHASE I: Demonstrate the feasibility of an efficient process for the conversion of waste biomass or biomass surrogates to a short chain alkene or mixture of alkenes. Provide samples (ca. 1 g) for the Navy to confirm that the product stream is suitable for conversion to jet fuel.

PHASE II: Scale-up laboratory process to pilot plant scale (50-250 kg) and extend the approach to conventional waste biomass. Tailor the process to produce a preferred distribution of alkenes. In collaboration with the Navy, produce sample fuels from the product stream and confirm that these fuels meet specifications for JP-5.

PHASE III: Develop a commercial process for the conversion of waste biomass to a JP-5 equivalent fuel.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: In addition to its military market, there is an enormous commercial market for short chain olefins as precursors to fuels, polymers, commodity chemicals, and pharmaceuticals.

REFERENCES:
1. Wright, M. E., Harvey, B. G., & Quintana, R. L. (2008). "Highly Efficient Zirconium-Catalyzed Batch Conversion of 1-Butene: A New Route to Jet Fuels." Energy Fuels 22 (5) 3299-3302.

2. Sardesai, A., Lee, S. (2005, March 6). "Alternative Sources of Propylene." Energy Sources. 27(6), 489-500.

3. Mentzel, U. V., Shunmugavel, S., Hruby, S. L., Christensen, C. H., & Holm, M. S. (2009). "High Yield of Liquid Range Olefins Obtained by Converting i-Propanol over Zeolite H-ZSM-5." J. Am. Chem. Soc. 131(46) 17009-17013.

KEYWORDS: Alternative Fuels; Renewable Fuels; Biomass Conversion; Catalysis; Olefin Production; Alkene Production

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