Ethanol, fermentation 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. 

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,... 

The same as F-T produced mixed-alcohols, low purity bio-ethanol extracted from fermentation broth must be refined into high purity fuel grade ethanol. The pervapo-ration dehydration pilot plant based on NaA zeolite membrane was set up by Mitsui Engineering Shipbuilding Co., Ltd. (MES) in 1999. Recently, a pilot-scale NaA zeolite membrane based vapor permeation dewatering installation has been setup in our group with a handling capacity of 250 L/D. This installation can continuously produce 225 L 99.7wt.% ethanol per day. Meanwhile the permeate is nearly pure water. 

An area of current interest is the purification of biofuels produced from biomass. The fermentation of sugar from starch or cellulose typically produces an aqueous mixture of 6-8% ethanol by weight. Other low molecular alcohols (e.g., butanol) may be produced at concentrations as low as 1% and the use of alcohol-resistant yeast can allow fermentation up to a concentration of 15%. Currently, fuel grade alcohol is produced by distillation of the aqueous mixture. However, membrane pervaporation [63], vapor permeation [64], and hybrid processes offer the potential for significant energy and cost savings. 

With the invention and development of the internal combustion engine as a source of mobile and stationary power, the use of energy in the U.S. increased significantly in the twentieth century. Dependence on liquid fuels also increased. Early in the century, annually renewable products were proposed as a source of liquid fuels, particularly fuel-grade ethanol as a product of fermentation of carbohydrates and, to a lesser extent, methanol as a product of destructive distillation of wood. 

Separation of alcohols, such as ethanol and butanol, from the fermentation broth is traditionally done by distillation. The higher the alcohol concentration in the fermentation broth, the lower the energy required for distillation. For ethanol fermentation, the broth usually contains 10-15% (w/w) ethanol. After distillation, ethanol concentration in the distillate is about 90% (w/w). The distillation process will not yield more than 93% (w/w) ethanol, which is the azeotropic mixture of ethanol-water. Azeotropic mixtures cannot be separated by distillation because the compositions of ethanol in the vapor and liquid phases are the same. Therefore, azeotropic distillation with benzene or dehydration with molecular sieves is usually used to remove the remaining water and produce fuel grade ethanol (99.9 wt-%). 

The simplest way to produce ethanol is from sweet juices extracted from sugarcane, sugar beet, or sweet sorghum because the juice is directly fermented and then distilled to obtain fuel-grade ethanol. The disadvantages of this process are the relatively low conversion rates (70 L/ton), the relatively low shelf life of the cut stalks, and the seasonal harvesting that impedes the utilization of the biorefinery throughout the whole year. 

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