Sustainable Production of Liquid Fuels

Sustainable energy is the key to long term, global energy stability, which includes the need for a sustainable liquid transportation fuel. Ethanol and butanol are options to fill this energy need if they can be produced in an economical and sustainable fashion. This paper looks at various processes designed for the continuous production of ethanol and butanol via the biochemical conversion of lignocellulosic biomass. Processes designed for ethanol production include conventional separate hydrolysis and fermentation (SHF) as well as consolidated bioprocessing (CBP) with options for various biomass feedstocks and corresponding pretreatment technologies are optimized to determine the minimum breakeven selling price of the ethanol produced. The production of butanol via acetone-butanol-ethanol (ABE) fermentation and a gas stripping recovery process is also analyzed. It is found that both SHF and CBP processes give favourable economic outlooks, with SHF being favoured without energy generation and CBP being favoured when the waste is used for energy production. In addition, it has been shown that using continuous ABE fermentation with gas stripping is capable of producing a product stream with