Fuel fermentation ethanol

Capacity Limitations and Biofuels Markets. Large biofuels markets exist (130—133), eg, production of fermentation ethanol for use as a gasoline extender (see Alcohol fuels). Even with existing (1987) and planned additions to ethanol plant capacities, less than 10% of gasoline sales could be satisfied with ethanol—gasoline blends of 10 vol % ethanol the maximum volumetric displacement of gasoline possible is about 1%. The same condition apphes to methanol and alcohol derivatives, ie, methyl-/-butyl ether [1634-04-4] and ethyl-/-butyl ether. 

Growth of Renewable Resources. There are already large industries, associated with corn processing and food manufacture that utilize enzymes and microbial fermentation on an extremely large scale, In these cases, production and substrate costs can be 70% of the total product costs, and cost efficient engineering becomes paramount. The development of the industry that produces fuel grade ethanol, used as a nonleaded octane... 

In some European countries (eg, Belgium, France, Italy, and the Netherlands) fermentation is still important in producing industrial ethanol. In others (eg, England and Germany) synthetic ethanol predominates (191). In Japan the synthetic capacity has been shut down except for refining imported cmde, while the fermentation capacity continues to operate. Fuel ethanol programs in other countries, such as Brazil, have spurred the growth of worldwide fermentation ethanol capacity. 

Continuous fermentation processes are primarily used in the research and development stage. However, more chemostat operations are being used at the production level as the understanding of this reactor increases. Examples include ethanol fermentation for the production of fuel grade ethanol and single-cell protein production from methanol substrates. 

Glucose syrups are easily fermented by yeast to ethanol. While beverage ethanol has been produced from many sources of sugar and starch for countless centuries, large-scale production of fuel-grade ethanol by fermentation is attributed to a demand for combustible motor fuel additives. 

Today, most ethanol is made from corn starch. After separation from com by wet milling, starch slurry is thinned with alpha-amylase and saccharified with amyloglu-cosidase. The resulting sugar solution is fermented by Sacchammyces yeast. Modem US ethanol plants use simultaneous scarification, yeast propagation and fermentation. The major portion of fuel-grade ethanol is now produced by continuous fermentation,... 

In the World War II era, 72 percent of U.S. ethanol was derived from molasses fermentation. By 1978 the balance was 90 percent from direct catalytic hydration and the rest from fermentation. In 1998 the balance had returned to the dominance of fermentation, with 83 percent of the 10 billion lb of U.S. ethanol made in this way. The recent swing toward fermentation is due to the use of 90 percent of the fermentation ethanol as motor fuel, as a result of post-oil-embargo U.S. government policy. 

Because of high oil prices, Brazil (most of whose sugars are produced from sugarcane) took the dramatic step of shifting to a much greater use of fuel alcohol. One wood hydrolysis plant was constructed, but it was uneconomical to operate and was shut down. However, Brazilian experience has demonstrated that fermentation ethanol (95 percent ethanol and 5 percent water) is a perfectly satisfactory motor fuel. At least 500,000 Brazilian automobiles operate on undried alcohol continuously, and most of the rest of their fleet operates on this fuel on weekends when only alcohol is available at the gas stations.36 A number of methods can be used for the production of ethanol from wood, as described below. 

The production of ethanol by fermentation and its use as a car fuel may serve as an example to demonstrate the social benefits and risks of fermentation. Ethanol is an efficient fuel, it can be produced from carbohydrates (sugar cane, maize, and so on), that means from renewable resources. This seems to be a plus, and it is one, as long as agricultural by-products are used. However, there is a different point of view When farmers can make a better profit with raw materials for fuel, they will produce it. But who will produce our food, when the arable land is used to make car fuel With a growing world population we can hardly afford this. 

The processes for manufacturing methanol by synthesis gas reduction and ethanol by ethylene hydration and fermentation are very dissimilar and contribute to their cost differentials. The embedded raw-material cost per unit volume of alcohol has been a major cost factor. For example, assuming feedstock costs for the manufacture of methanol, synthetic ethanol, and fermentation ethanol are natural gas at 3.32/GJ ( 3.50/10 Btu), ethylene at 0.485/kg ( 0.22/lb), and corn at 0.098/kg ( 2.50/bu), respectively, the corresponding cost of the feedstock at an overall yield of 60% or 100% of the theoretical alcohol yields can be estimated as shown in Table 11.12. In nominal dollars, these feedstock costs are realistic for the mid-1990s and, with the exception of corn, have held up reasonably well for several years. The selling prices of the alcohols correlate with the embedded feedstock costs. This simple analysis ignores the value of by-products, processing differences, and the economies of scale, but it emphasizes one of the major reasons why the cost of methanol is low relative to the cost of synthetic and fermentation ethanol. The embedded feedstock cost has always been low for methanol because of the low cost of natural gas. The data in Table 11.12 also indicate that fermentation ethanol for fuel applications was quite competitive with synthetic ethanol when the data in this table were tabulated in contrast to the market years ago when synthetic ethanol had lower market prices than fermentation ethanol. Other factors also... 

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. 

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