Ethanol synthesis, commercial fermentation

Other Methods of Preparation. In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have been suggested. These include the hydration of ethylene by dilute acids, the hydrolysis of ethyl esters other than sulfates, the hydrogenation of acetaldehyde, and the use of synthesis gas. None of these methods has been successfilUy implemented on a commercial scale, but the route from synthesis gas has received a great deal of attention since the 1974 oil embargo. 

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. 

Ethanol is the only renewable liquid fuel made in commercial quantities and supplies about 1% of the gasoline type transport fuels used in the USA. Approximately 95% of the commercial production of ethanol in the USA is currently by direct fermentation of com-sourced carbohydrates. However, fermentation of synthesis gas has the advantage over direct fermentation of sugars from cellulose and the hemicelluloses in that all wood components, including lignin and bark, are suitable feedstocks. 

One of the most convincing arguments against the further development of fermentation ethanol plants is the advent of synthetic ethanol. As far back as 1921 plants were erected in Germany for the synthesis of ethanol from hydrocarbons but were not at that time very successful. Processes for the production of the synthetic product have been developed in Europe to a commercial scale while at least two American chemical companies have carried the process beyond the experimental stage. A pennit was recently granted by the Commissioner of Prohibition to conduct an experi-... 

This is the commercial method for this preparation. Ethanol in various concentrations is produced either by fermenting sugar, starch, or cellulose or by the hydration of ethylene. The products then are concentrated to the 95% azeotrope by regular distillation. In 1982, 816 x 10 L of 190 proof ethanol were produced, 10% by fermentation, and the rest by synthesis. The synthetic method is less expensive ( 0.50/L) in that 1 kg of ethanol requires 2 kg of sugar,... 

The organic chemicals that fall into this category and can be produced by fermentation include ethanol, butanol, acetone, 2,3-butane-diol, and glycerol. 2.3-Butanediol and glycerol fermentations have been developed at laboratory and pilot-plant scales, but have not been commercialized. Ethanol, butanol, and acetone have been produced industrially by fermentation, but chemical synthesis is the manufacturing practice of choice for economic reasons. However, as price and availability of ethylene and propylene as feedstocks for the synthetic processes become subjects of concern, there is renewed interest in examining the fermentation pocesses as means of producing all or a portion of the future needs of ethanol, butanol, and acetone. 

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