Other lignocellulosic feedstocks

Many polymers conventionally derived from petrochonicals can be produced from renewable resources such as lignocellulosic biomass. Tremendous efforts have been made to produce biological substitutes for petrochemical feedstocks. Many technically feasible approaches are available to convert biomass to biopolymers. However, no large-scale conunercial facility is operating to date. This situation can be attributed to a combination of the following three factors technical inadequacy, lack of economic competitiveness, and lack of understanding of the industrial need. 

The market potential for bio-based products is very promising. The Roadmap for Biomass Technologies in the United States (USDOE, 2007) forecasts a large increase in bio-based products. Production of chemicals and materials from biomass increases substantially from approximately 5.67 bilUon kg or 5% of the current production of target United States chemical commodities in 2001, to 12% in 2010,18% in 2020 and 25% in 2030. 

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A unique pilot plant for ethanol production from lignocellulose feedstock was inaugurated in O-vik, Sweden in May 2004. The aim of the pilot plant was to develop efficient continuous technologies for the various process steps in ethanol production from forest raw material and other lignocellulosic feedstock. Different raw materials require different conditions during the production process and the process also needs to be optimised for every raw material. Further it was important to demonstrate that large-scale lignocellulose ethanol production was possible... 

The current ethanol supply is, in the large part, derived from starch. Nevertheless, vast amounts of agricultural residues and other lignocellulosic biomass can serve as the feedstock for ethanol production. Theoretically, enough ethanol can be produced from cellulosic biomass to meet most of the liquid fuel requirements in the US. The expanded utilization of lignocellulosic biomass for ethanol production can also free starchy crops for food and other uses. In addition, less carbon dioxide emission can be realized if more ethanol can be produced from lignocellulosic biomass and if the market for ethanol as a transportation fuel can be expanded beyond the current level. 

Notwithstanding recent progress, it remains to be demonstrated that ther-mophiles can produce economically viable titers under industrial conditions - for example, an affordable lignocellulosic feedstock, inexpensive growth media, and in the presence of potential inhibitors. It has been shown that thermophiles can be adapted to manifest increased resistance to inhibitors other than ethanol, in particular in the case of by-products resulting from Populus pretreatment [85]. We speculate that it may be difficult and perhaps not feasible to develop strains of thermophiles that are as resistant to chemical inhibition as yeast, and that the merits of thermophiles may be best realized in the context of processes that minimize formation of inhibitors in the first place. 

In other areas of the world, waste from the sugar industry (molasses), starch, waste lipids, alcohols such as methanol (Bourque et al. 1995) and especially lignocellulosic feedstocks are available in quantities that are appropriate for industrial process demands. 

Second-generation biofuel technologies make use of a much wider range of biomass feedstock (e.g., forest residues, biomass waste, wood, woodchips, grasses and short rotation crops, etc.) for the production of ethanol biofuels based on the fermentation of lignocellulosic material, while other routes include thermo-chemical processes such as biomass gasification followed by a transformation from gas to liquid (e.g., synthesis) to obtain synthetic fuels similar to diesel. The conversion processes for these routes have been available for decades, but none of them have yet reached a high scale commercial level. 

Both in the USA and the EU, the introduction of renewable fuels standards is likely to increase considerably the consumption of bioethanol. Lignocelluloses from agricultural and forest industry residues and/or the carbohydrate fraction of municipal solid waste (MSW) will be the future source of biomass, but starch-rich sources such as corn grain (the major raw material for ethanol in USA) and sugar cane (in Brazil) are currently used. Although land devoted to fuel could reduce land available for food production, this is at present not a serious problem, but could become progressively more important with increasing use of bioethanol. For this reason, it is important to utilize other crops that could be cultivated in unused land (an important social factor to preserve rural populations) and, especially, start to use cellulose-based feedstocks and waste materials as raw material. 

It may be estimated that ethanol yields from lignocellulosics will range between 0.12 and 0.32 L kg-1 undried feedstock, depending upon the efficiency of five-carbon sugar conversion [26]. Other types of fermentation, including bacterial fermentation under aerobic and anaerobic conditions, can produce various other products from the sugar stream, including lactic acid. 

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