Ethanol, fermentation potential yields

ABE (acetone, butanol, and ethanol) fermentation has a long history of commercial use and perhaps the greatest potential for an industrial comeback. Acetone, butanol, and ethanol can all be isolated from this remarkable metabolic system carbon dioxide and hydrogen are additional products. The solvents were used as paint solvents in the expanding automobile industry. Ultimately these processes proved uncompetitive because of poor yields, low product... 

The potential of Jerusalem artichoke as a feedstock for ethanol production has been assessed in many countries in recent years. In New Zealand, for instance, Jerusalem artichoke gave the highest potential ethanol yield (calculated from known crop yields and fermentable content) of a range of crops assessed. From three harvests of the tops a year, estimated ethanol production was 78 It-1 and 11,230 1-ha-1. Although fodder beet (Beta vulgaris L.) remains a favored feedstock for ethanol production in New Zealand, Jerusalem artichoke has been recommended for further study (Judd, 2003). 

Wood is about 65—75% carbohydrate and has been considered as a potential source of ethanol for fuel. The carbohydrate material can be hydrolyzed to monomer sugars, which in turn can be fermented to produce ethanol. However, wood carbohydrates are expensive to hydrolyze. Hydrolysis with acids and enzymes is impeded by the crystalline structure of cellulose. Lignin interferes with processing, and hydrolytic by-products such as furfural, acetic acid, and derivatives of lignin and extractives can inhibit fermentation. Research is still being conducted on wood hydrolysis to develop a process that is economically sound. Furfural is a useful chemical feedstock and results from the dehydration of pentose sugars. It can be obtained in 9 to 10% yield from the dilute acid hydrolysis of hardwoods (75). 

TABLE 11.8 Potential Fermentation Ethanol Yields from Various Biomass Feedstocks ... 

Another potentially adverse impact on fermentation ethanol markets is presented by the options available for the manufacture of mixed alcohols from synthesis gas. Sufficient experimental data have been accumulated to show how the alcohol yields and distributions can be manipulated and what catalysts and conditions are effective. Some of these data have established the utility of mixed alcohols as motor fuels and motor fuel components. 

Production of bulk chemicals. The production of solvents is normally characterized by a general inhibition phenomenon which has been mainly attributed to the changes in membrane permeability, or to the toxic effects on the metabolic pathway. Aqueous two-phase systems have been shown to be effective as media for the extractive fermentation of a number of solvents which include ethanol, acetone-butanol and acetic acid (3). Improved productivity has been achieved in most of the cases as compared to the conventional fermentations, which is significantly due to the elimination of product inhibition. However, there is an indication that changes in the microenvironment of the microbial cells due to the presence of non-metabolizable polymers could also contribute, in the initial phases, to the increased production. The addition of PEG and dextran to a growth medium, for instance, was shown to give increased initial ethanol yields, as a result of decrease in the chemical potential of water (8). 

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