Ethanol, manufacture

Because most fuel ethanol manufactured ia the United States is made from com, price plays a cmcial role ia determining the competitive position of ethanol ia an open market. With com priced at about 2.50/bu, the embedded feedstock cost of product ethanol is about 0.14—0.23/L ( 0.52—0.87 gal), depending on over-all yield and by-products ignored (125). Euel ethanol plants may have contingency plans to close if com prices rise to a certain level, eg, 3.50/bu or above (126). 

In 1975, Bra2il embarked upon the ambitious ProAlcohol program for fermentation ethanol manufacture (198,199) from sugar cane to reduce the... 

The predominant method of ethanol manufacture, at one time, was by fermentation of sugars this method went out of use in the 1930s. However, com fermentation is now a source of 92% of all ethanol and is used for gasohol, a 10% alcohol 90% gasoline blend used for automobile fuel. 

A subsequent case-control study nested in an expanded cohort at the aforementioned isopropanol and ethanol manufacturing plant in the United States indicated that the increased risk of laryngeal cancer was related to exposure to sulfuric acid the risk persisted even after exclusion of workers in the ethanol and isopropanol units (lARC, 1992a). 

As described in the monograph on diethyl sulfate (see this volume), a cohort study at an isopropanol and ethanol manufacturing plant in the United States revealed an increased risk for laryngeal cancer. As also mentioned in the same monograph, a cohort study at a plant producing ethanol and isopropanol in the United States suggested an increased risk for cancers of the larynx, buccal cavity and pharynx in strong-acid workers (lARC, 1992). 

During corn dry mill ethanol manufacturing, the most common method for ethanol production in North America, the primary byproduct is dried distiller s grain (DDG). As production increases to meet demand, the supply of DDG will significantly increase. Thus, ethanol producers need to modify their processes for the sake of profitability. Technological... 

Figure 15.10 Block-diagram scheme for ethanol manufacturing from lignocellulosic biomass.

The hydrolysis of polysaccharides into monomeric sugars is a well-studied process its mechanism is still believed to be accurately described by the work of Saeman in 1945.432 Its significance is linked to the production of fermentable sugars for ethanol manufacture. Many of these processes are based on acid catalysis and overlap closely the pretreatment methods described earlier.363,364,373 Treatments with both concentrated and dilute acids are well known as methods for the hydrolysis of cellulose and hemicellulose, as is the use of organic dicarboxylic acids as alternative catalysts to mineral acids.433... 

TABLE 14.13 Net Energy Analysis of Ethanol Manufacture in a Modem Integrated Com Production-Fermentation System with and without Co-product Energy Content Credit ... 

The resulting fermentation broth is quite dilute, 2% ethanol or less. The ethanol can be recovered from the broth using distillation schemes developed for the existing com to ethanol manufacturing process (Spath and Dayton, 2003). 

Margihdt L B., Reid, A. J, O Sullivan. T. J., Ethanol manufacture and applications , ACS I79tk National Meeting, Houston, Texas (23/26 March 1980). 

Hundreds of millions of gallons of ethanol are produced annually by this procedure. Operating in competition with other methods, this process accounts for about two-thirds of all the ethanol manufactured in the United States. The success of this process has been made possible by good yields, continuous operation on a large scale, an efficient procedure for reconcentrating the spent sulfuric acid for recycle, and, of course, a cheap source of ethylene. It will be noted that both the mono- and disulfates are converted to alcohol. A detailed description of a commercial operation, using 97.5 per cent acid, is given on p. 385. 

FIGURE 26.9 Direct hydration process for ethanol manufacture. (Direct hydration of ethylene for the production of ethanol is carried out at high pressure (75 kg/cm ) and high temperature (300°C). The major by-product is diethyl ether, which is recycled back to the reactor to form ethanol.)... 

Alcoholic fermentation is by far the most common technology for ethanol manufacture, accounting for more than 90% of all ethanol production the residual amount being made by acid catalyzed hydration of ethylene in the gas phase at 300 °C and 60-70 atm in the presence of a catalyst consisting of solid silicon dioxide coated with phosphoric acid. ... 

In 1855, the ethanol manufactured in this process of fermentation and distillation was exempted from excise duty, provided it was first denatured with methanol. Only then was the resulting product (industrial methylated spirit) able to develop as an industrial solvent. Nor was it the last occasion on which a biological process needed the assistance of chemical technology (continuous distillation) and government intervention (exemption from duty) in order to become established. 

Then, as now, petrol distilled from oil was thought unlikely to supply the burgeoning need for a liquid fuel the known reserves of crude oil were too small. Benzol distilled from coal would not fill the gap, but ethanol produced by fermentation seemed, if not an alternative, at least a supplement which would conserve petrol supplies. Such a scheme was considered particularly attractive where the input sugar could be derived from waste cellulose. To divert ever-increasing areas of good agricultural land to the supply of starch for ethanol manufacture was not thought practical. 

Table 6.4 Estimated proportion of ethanol manufactured by fermentation in the USA between 1920 and 1990...

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