Ethanol fuel-grade

Bioethanol is the largest biofuel today and is used in low 5%—10% blends with gasoline (E5, E10), but also as E85 in flexible-fuel vehicles. Conventional production is a well known process, based on the enzymatic conversion of starchy biomass (cereals) into sugars, and fermentation of 6-carbon sugars with final distillation of ethanol to fuel grade. 

Enzymes are also added to catalyze the hydrolysis or saccharification of starch. Malt produced by the germination of barley grain contains the enzymes that catalyze this hydrolysis. Sometimes called diastase, the enzymes are primarily a- and 6-amylase. Glucoamylase is a pure enzyme that can now be used. Both diastase and glucoamylase hydrolyze starch polysaccharide to the disaccharide, maltose. For fuel grade ethanol production, hydrolysis takes place at temperatures ranging from about 120°F to 140°F (50°C to 60°C) for about 1 hour. The final product of hydrolysis is called a wort. Solids can be filtered from the wort before continuing. 

The world energy crisis of the 1970s, however, spurred interest once again in ethanol as a transportation fuel source. Brazil adopted the widespread production and use of Alcool, hydrated ethanol, and Gasolina a 78 22 ratio blend of gasoline ethanol as a motor fuel. Other countries developed policies to maintain a fuel grade ethanol industry by conversion of biomass. Also, clean air and reformulated fuel policies have helped to promote the use of ethanol as a viable alternative fuel. 

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... 

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,... 

Tawfik, W.V., Optimization of Fuel Grade Ethanol Recovery System Using Solvent Extraction, PhD Thesis, Georgia Institute of Technology, Atlanta, GA, 1986. 

Optimisation of both design and operation variables of a bio-ethanol purification plant intended to produce fuel grade ethanol is a challenge to make the bio-fuel a realistic alternative in the energy market. 

Shleser, R. Ethanol Production in Hawaii Processes, Feedstocks and Current Economic Feasibility of Fuel Grade Ethanol Production in Hawaii, HD9502.5.B54.S4 Hawaii State Department of Business, Economic Development and Tourism Honolulu, HI, 1994. 

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