Existing gasoline, jet and diesel fuels are composed of mixtures of hydrocarbon molecules. Efforts to make hydrocarbon fuels, the so called ‘drop-in fuels,' from renewable resources has escalated over the past few years. However, the process options available to make the fuels aren't well developed for policy makers and even the scientific and engineering community pursuing the fuels. The importance of drop-in fuels is their fit into gasoline, jet and diesel fuels without changes to the fuel or vehicle infrastructure. Meanwhile ethanol is by far the largest renewable fuel today and has provided an excellent start to sustainable, domestically produced renewable fuels. Additionally ethanol has provided an infrastructure, including technical expertise that is extremely valuable to support the development and commercialization of advanced biofuels. Longer term the desire is to continue to improve the sustainability profile for biofuels production and to convert plant matter into fuels and blend stocks that fit exactly, without special rules, into the existing infrastructure for crude oil derived transportation fuels and vehicles.
This contribution will focus on making drop-in hydrocarbon fuels and make the case that much of the technology required already exists. Additionally the ethanol industry infrastructure provides a platform to launch the drop-in fuels and blend stocks. There are multiple ways possible to produce hydrocarbon fuels from biomass a sampling of which will be described. The importance of conserving the energy content of the feed stock converted will be emphasized as this leads to the lowest cost, most efficient processes for production. Initially the technology for drop-in fuels is likely to be built on the backs of the existing ethanol infrastructure, migrating to cellulosic biomass as the technology and markets mature.
One route to drop-in hydrocarbons is the fermentative conversion of biomass to isobutanol followed by catalytic chemistry to yield a variety of chemicals, materials and fuels. Isobutanol from carbohydrates by fermentation has been enabled by pioneering biotechnology utilizing a novel five step pathway for the conversion of pyruvate to isobutanol. Additionally novel recovery technology has been developed providing for low cost purification of the isobutanol. Isobutanol is easily converted to isobutylene and a wide variety of ‘drop-in' hydrocarbon chemicals and materials including isobutylene, para-xylene, isooctane, terephthalic acid, propylene, PET plastic, and polypropylene. The catalytic chemistry required has been previously developed and can be used to convert isobutanol to whole gasoline, jet and diesel fuels that meet all specifications for the fuels.
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