Ethanol by fermentation

Because oil and gas ate not renewable resources, at some point in time alternative feedstocks will become attractive however, this point appears to be fat in the future. Of the alternatives, only biomass is a renewable resource (see Fuels frombiomass). The only chemical produced from biomass in commercial quantities at the present time is ethanol by fermentation. The cost of ethanol from biomass is not yet competitive with synthetically produced ethanol from ethylene. Ethanol (qv) can be converted into a number of petrochemical derivatives and could become a significant source. 

As discussed in previous sections, sugars, starch and (ligno)cellulose can be converted into ethanol by fermentation, the latter via preliminary chemical and physical pretreatment followed by enzymatic breakdown of the biopolymers. Pure ethanol can be added to gasoline or diesel. However, this requires an energy-intensive distillation step. This and the energy used in fertilizers, transportation... 

What are some disadvantages of producing ethanol by fermenting food biomass ... 

Some countries have already experimented with ethanol as a fuel for cars. Up to 20% of ethanol can be added to petrol without the need to adjust the carburettor. Brazil, which has few oil reserves, produces ethanol by fermentation (breakdown by enzymes) of sugar cane and grain, and uses it as a petrol additive (Figure 6.16). The Brazilian government has cut down its petrol imports by up to 60% through using this alcohol/petrol mixture. 

Ethanol Alcohol made by converting carbohydrates to sugar, which is then converted to ethanol by fermentation. Formula ... 

Hydrolysate B from corn stover contained 4 g/L of glucose, 17.9 g/L of xylose, 5 g/L of arabinose, and 2.5 g/L of acetic acid. Glucose was readily fermented eighty-three percent of xylose was fermented in 23 h. The production of ethanol by fermentation of the com stover hydrolysate was 9 g/L (Fig. 3). The yield of ethanol from consumed sugars reached 93% of theoretical yield. We did not observe xylitol production and acetic acid consumption. 

When production volume is sufficient, it is economical to build one plant for one product. Batch production in a single unit may be limited by maximum reactor size. Holdups of greater than 20,000 gal are handled in separate parallel reactors. To use common upstream and downstream facilities, the reactors may not be operated simultaneously but on overlapping schedules. When long reaction times cannot be avoided, the reaction sections operate batch wise however, feeding reactants and recovering products may be continuous for economic reasons. This practice is typical of many processes, such as the saponification of natural fats in intermediate quantities. In the production of ethanol by fermentation, two reactions (saccharification and fermentation) are operated on a batch basis, while hydrolysis (conversion of starch to dextrin) and product recovery by distillation are continuous. 

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. 

Thibault et al [14] investigated experimentally the production of ethanol by fermentation under CO2 pressure, but they were not successful due to the negative effect of pressure on the microorganisms used. L ltalien et al [15] attempted to improve the ethanol fermentation under hyperbaric conditions with limited success. The separation of ethanol from fermentation broth, however, was not investigated thoroughly. 

One can envisage the future production of liquid fuels and commodity chemicals in a biorefinery Biomass is first subjected to extraction to remove waxes and essential oils. Various options are possible for conversion of the remaining biofeedstock, which consists primarily of lignocellulose. It can be converted to synthesis gas (CO + H2) by gasification, for example, and subsequently to methanol. Alternatively, it can be subjected to hydrothermal upgrading (HTU), affording liquid biofuels from which known transport fuels and bulk chemicals can be produced. An appealing option is bioconversion to ethanol by fermentation. The ethanol can be used directly as a liquid fuel and/or converted to ethylene as a base chemical. Such a hiorefinery is depicted in Fig. 8.1. 

The production of ethanol by fermentation of grains and sugars is one of the oldest known organic reactions, going back at least 8()()0 years in the Middle East and perhaps as many as 9000 years in China. Fermentation is carried out by adding yeast to an aqueous sugar solution, wlicic cnz.yines break down carbohydrates into ethanol and CO2. As noted in the chapter introduction, approximately 4 billion gallons of ethanol is produced each year in the United States by fermentation, with essentially the entire amount used to make E85 automobile fuel. 

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 production of ethanol by fermentation of grains and sugars is one of the oldest known organic reactions, going back at least 2500 years. Fermentation is carried out by adding yeast to an aqueous sugar solution, where enzymes break down carbohydrates into ethanol and CO2 ... 

The rate of production of ethanol by fermentation is slowed by the increasing concentrations of ethanol formed in the process. A method is being investigated in which the ethanol is to be separated continuously in situ with solvent. The solvent is then pumped off and the ethanol recovered. How many moles/hr of ethanol are recycled in the solvent for the system shown in Fig. P2.72 ... 

The hexose sugars, glucose and mannose, are subsequently converted to ethanol by fermentation with a yeast such as Saccharomyces cerevisiae within the first 12 hours at 35°C ... 

Abstract A commercial strain of Saccharomyces cerevisiae was used for the production of ethanol by fermentation of cashew apple juice. Growth kinetics and ethanol productivity were calculated for batch fermentation with different initial sugar (glucose + fructose) concentrations. Maximal ethanol, cell, and glycerol concentrations were obtained when... 

Resources that contain sugars can be used as a feedstock for ethanol fermentation. There are many biomass resources in the world that can be used to produce ethanol by fermentation. According to the traditional approach, they can be divided into three categories - starch, sugar, and cellulose materials-... 

G2. [Note This problem is quite extensive.] Biorefineries producing ethanol by fermentation have several distillation columns to separate the ethanol from the water. The first column, the beer still, is a stripping column that takes the dilute liquid fermenter product containing up to 15% solids and produces a clean vapor product that is sent to the main distillation column. The main column produces a distillate product between about 65 mole % and the ethanol azeotrope, and a bottoms product with very litde ethanol. The calculated diameter of the main distillation column is much greater at the top than elsewhere. To reduce the size and hence the cost of the main column, one can use a two-enthalpy feed system split the vapor feed into two parts and condense one part, then feed both parts to the main column at their optimum feed locations. This method reduces the vapor velocity in the top of the column, which reduces the calculated diameter however, a few additional stages may be required to obtain the desired purity. 

These preliminary calculations indicate that ethanol by fermentation of sugarcane juice is close to equivalence with ethanol derived from petrole mi or natural gas liquids at 1.15/gal. As described above, the competitiveness of sugarcane with the nonrenewable resources depends heavily on the cost of the fermentable sugars. If one had to purchase molasses on the open market, the venture could be in deep trouble during times of high molasses prices, occasioned, perhaps, by a corn crop failure. 

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