Ethanol fermentation route

Manufactured by the liquid-phase oxidation of ethanal at 60 C by oxygen or air under pressure in the presence of manganese(ii) ethanoate, the latter preventing the formation of perelhanoic acid. Another important route is the liquid-phase oxidation of butane by air at 50 atm. and 150-250 C in the presence of a metal ethanoate. Some ethanoic acid is produced by the catalytic oxidation of ethanol. Fermentation processes are used only for the production of vinegar. 

Other Methods of Preparation. In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have been suggested. These include the hydration of ethylene by dilute acids, the hydrolysis of ethyl esters other than sulfates, the hydrogenation of acetaldehyde, and the use of synthesis gas. None of these methods has been successfilUy implemented on a commercial scale, but the route from synthesis gas has received a great deal of attention since the 1974 oil embargo. 

Different routes for converting biomass into chemicals are possible. Fermentation of starches or sugars yields ethanol, which can be converted into ethylene. Other chemicals that can be produced from ethanol are acetaldehyde and butadiene. Other fermentation routes yield acetone/butanol (e.g., in South Africa). Submerged aerobic fermentation leads to citric acid, gluconic acid and special polysaccharides, giving access to new biopolymers such as polyester from poly-lactic acid, or polyester with a bio-based polyol and fossil acid, e.g., biopolymers . 

The homologation reaction was first reported nearly 40 years ago (2). The catalyst precursor was Co (CO). Subsequent workers utilized cobalt catalysts but also employed iodide promoters (, 4 ), a Ru co-catalyst ( ), and trivalent phosphines ( ) to increase the yield. The reaction is carried out at 180-200 °C and 4000-8000 psig. In the better cases, the ethanol rate and selectivity are 1-6 M/hr and 50-80 %. Unsatisfactory conversion, selectivity, and the required high operating pressure have prevented commercialization of the current homologation technology. Additionally, fermentation routes to ethanol have now... 

Acetic acid (CH3COOH) is a bulk commodity chemical with a world production of about 3.1 x 106 Mg/year, a demand increasing at a rate of +2.6% per year and a market price of US 0.44-0.47 per kg (Anon., 2001a). It is obtained primarily by the Monsanto or methanol carbonylation process, in which carbon monoxide reacts with methanol under the influence of a rhodium complex catalyst at 180°C and pressures of 30-40 bar, and secondarily by the oxidation of ethanol (Backus et al., 2003). The acetic fermentation route is limited to the food market and leads to vinegar production from several raw materials (e.g., apples, malt, grapes, grain, wines, and so on). 

In 1999, the domestic demand for butanol was 841,000 metric t and it is projected to increase 3% per year (49). During the early twentieth century, the primary method of butanol production was anaerobic fermentation with Clostridium acetobutylicum to produce a mixture of acetone, butanol, and ethanol. The butanol yields were low, and as oil prices declined after World War II, petrochemical routes to butanol displaced the fermentation route (50). The primary petrochemical route used today involves the hydrogenation of n-butyraldehyde (49), and production costs hover around 0.66/kg (24). 

Ethanol is made by both ethylene hydration and fermentation of starches and sugars. In this section the synthetic route will be discussed. The fermentation route is covered in Chapters 32 and 33. 

Acetic acid is produced by oxidation of ethanol by Acetobacter organisms. It is either used in diluted form as vinegar or distilled to give neat (100 percent pure) acetic acid. For many centuries, acetic acid was produced only via the fermentation route. Since the advancement of the petrochemical industry, it is also produced synthetically, at least for industrial use. 

Of the 760/1061 of industrial ethanol (excluding fuels) produced in the United States in 1981, less than 2% was made by fermentation. Carbohydrate feedstock sources normally used for fermentation are prone to continually changing costs and cause major distortions to the price of the end product. While cheap Cuban molasses were available the fermentation route was attractive, and fermentation may be attractive again if there are petroleum shortages in future. The process is based on the direct hydration of ethylene ... 

In S. cerevisiae, the major flux of pjnuvate metabolism is to ethanol, by way of pyruvate decarboxylase and alcohol dehydrogenase. Providing an alternative route for regenerating NAD through lactate dehydrogenase, which catalyzes the reduction of pymvate to lactate, can theoretically replace ethanolic fermentation [6]. 

The biochemistry of this redirection of the ethanol fermentation is quite simple. The sulphite forms a condensation product with acetaldehyde, which is normally the immediate precursor of ethanol. This cannot be reduced by alcohol dehydrogenase, and the cell must find an alternative route to reoxidize NADH. It does this by reducing dihydroxyacetone phosphate, and after hydrolysis of the phosphate ester, glycerol is excreted (Figure 6.2). This manipulation of the yeast s metabolism, the details of which were not then understood, allowed a minor fermentation product to become the major one. 

If the necessary g° values are known, the computation of the equilibrium K is worthwhile, giving some idea of the feasibility of the reaction. But for most industrial biochemistry (e.g., the fermentation route to ethanol) other factors, like the life story of the yeasts, play a much more important role in deciding what can be done and how to do it than does the equilibrium K. 

Ethanol fermentation within lichens under oxygen-deprived conditions has been shown by PTR-MS to emit acetaldehyde and ethanol. The researchers concluded that ethanol fermentation represents both a source of atmospheric VOC emissions and a so far unconsidered carbon loss route for lichens [114]. 

Only a small number of chemicals have been produced from renewable biomass via fermentation. Europe and the United States have planned to produce lactic acid, acetic acid, and ethanol on a commercial scale. Moreover, only these products are currently produced on an industrial scale competing with the petrochemical industry (Danner and Braim, 1999). While the fermentation routes can produce a range of platform chemicals, this process suffers due to the complex and often undesired metabolic pathways of microorganisms. A wide-ranging chemical tfxat can be produced by the fermentation of forest-based biomass is displayed in Fig. 16.2. 

Industrial ethyl alcohol can be produced synthetically from ethylene [74-85-17, as a by-product of certain industrial operations, or by the fermentation of sugar, starch, or cellulose. The synthetic route suppHes most of the industrial market in the United States. The first synthesis of ethanol from ethylene occurred in 1828 in Michael Faraday s lab in Cambridge (40). 

Ethylene. Where ethylene is ia short supply and fermentation ethanol is made economically feasible, such as ia India and Bra2il, ethylene is manufactured by the vapor-phase dehydration of ethanol. The production of ethylene [74-85-1] from ethanol usiag naturally renewable resources is an active and useful alternative to the pyrolysis process based on nonrenewable petroleum. This route may make ethanol a significant raw material source for produciag other chemicals. 

Second-generation biofuel technologies make use of a much wider range of biomass feedstock (e.g., forest residues, biomass waste, wood, woodchips, grasses and short rotation crops, etc.) for the production of ethanol biofuels based on the fermentation of lignocellulosic material, while other routes include thermo-chemical processes such as biomass gasification followed by a transformation from gas to liquid (e.g., synthesis) to obtain synthetic fuels similar to diesel. The conversion processes for these routes have been available for decades, but none of them have yet reached a high scale commercial level. 

The alternative pathway is the biochemical route. It processes starches/sugars into ethanol, a standard technology with installations world-wide, but in a biorefinery the start is the whole-plant material or biomass residues containing hemicel-lulose, which is broken into sugars that then can be fermented to ethanol and/or other alcohols such as butanol. As mentioned before, there is the need to develop novel and/or improved biocatalysts for alternative organic fuels, such as biobutanol, by fermentation processes. 

---