Ethanol production

Ethanol. Accurate projections of ethanol costs are much more difficult to make than are those for methanol. Large scale ethanol production would impact upon food costs and have important environmental consequences that are rarely cost-analyzed because of the complexity. Furthermore, for corn, the most likely large-scale feedstock, ethanol costs are strongly influenced by the credit assigned to the protein by-product remaining after the starch has been removed and converted to ethanol. 

Eig. 15. Eurfural, phenols, and ethanol production from wood in a multiproduct process biomass chemical plant (52). Wood (qv) is ca 50% cellulose (qv),... 

Table 31. Net Energy Production Ratios for Ethanol Production from Com in Integrated System ...

Fig. 42. Integrated distillation/pervaporation plant for ethanol recovery from fermentors. The distillation columns concentrate the ethanol—water mixture from 5 to 80%. The pervaporation membrane produces a 99.5% ethanol product stream and a 40—50% ethanol stream that is sent back to the distillation...

Fig. 8. Combustion turbines with process heat recovery (a) represents direct use of exhaust gas for process heating where industrial process includes refinery, chemicals, food processing, and ethanol production and (b) exhaust-to-water heat exchanger where industrial process includes material drying,...

A. J. Baker and T. W. Jeffries, Status of Wood Hydrolysisfor Ethanol Production, Report of U.S. Department of Agriculture, Porest Service, for U.S. Agency for International Development Support Bureau, Office of Energy (TMR Authorization No. 81—89), Washington, D.C., June 1981. 

A typical bourbon fermentation continues for 72 hours at a fermentation temperature within the 31—35°C range. Many fermentation vessels are equipped with agitation and/or cooling coils that facHitate temperature control. Significant increases in yeast numbers occur during the first 30 hours of fermentation. Over 75% of the carbohydrate is consumed and converted to ethanol. Within 48 hours, 95% or more of the ethanol production is complete. 

An increase in pressure causes a corresponding increase in ethanol production rate. Higher pressures also increase polymer formation hence, there is htde practical advantage to be gained above a certain limit. 

An optimum temperature exists at which the ethanol production rate is maximal. Ethylene conversion is limited by catalyst activity at lower temperatures and by equiUbrium considerations at higher temperatures. 

An optimum ethylene-to-water ratio exists that gives a maximum ethanol production rate. However, as expected, the highest ethylene conversion is obtained at the lowest ethylene-to-water mole ratio. 

An increases in space velocity increases the ethanol production rate, but at the expense of incurring higher recycling costs. 

A Guide to Commercial-Scale Ethanol Production andFinancing, Report No. SERI/SP-751-877, Solar Energy Research Institute, Golden, Colo., Mar. 1981. 

The mechanism shown in Figure 21.7 is supported by isotope-labeling studies. When ethyl propanoate labeled with lsO in the ether-like oxygen is hydrolyzed in aqueous NaOH, the l80 label shows up exclusively in the ethanol product. None of the label remains with the propanoic acid, indicating that saponification occurs by cleavage of the C-OR bond rather than the CO—R bond. 

Use of biofilm reactors for ethanol production has been investigated to improve the economics and performance of fermentation processes.8 Immobilisation of microbial cells for fermentation has been developed to eliminate inhibition caused by high concentrations of substrate and product, also to enhance productivity and yield of ethanol. Recent work on ethanol production in an immobilised cell reactor (ICR) showed that production of ethanol using Zymomonas mobilis was doubled.9 The immobilised recombinant Z. mobilis was also successfully used with high concentrations of sugar (12%-15%).10... 

Ethanol production in the fermentation process was detected with gas chromatography, HP 5890 series II (Hewlett-Packard, Avondale, PA, USA) equipped with a flame ionisation detector (FID) and GC column Porapak QS (Alltech Associates Inc., Deerfield, IL, USA) 100/120 mesh. The oven and detector temperature were 175 and 185 °C, respectively. Nitrogen gas was used as a carrier. Isopropanol was used as an internal standard. 

The inner surface of the beads before and after use was compared. The cells were initially trapped inside the beads after 72 hours the cells apparently migrated from the inner side to the surface. The micrographs of the inner sides of the beads before and after use, at magnifications of 300 and 2000, are shown in Figure 8.5. After 72 hours the cells appealed to have formed new colonies on the surface of the alginate layer. By contrast, the surfaces were completely covered with colonies after 72 hours of ethanol production in the ICR. 

Reactor productivity was obtained by dividing final ethanol concentration with respect to sugar concentration at a fixed retention time. It was found that the rates of 1.3, 2.3 and 2.8 g 1 1 h 1 for 25, 35 and 50 g 1 1 glucose concentrations were optimal. Ethanol productivities with various substrate concentrations were linearly dependent on retention time (Figure 8.12). The proportionality factor may have increased while the substrate... 

Fig. 8.12. Ethanol production versus retention time in the immobilised cell column. Reprinted from Najafpour et al. (2004).18 Copyright with permission from Elsevier.

A high glucose concentration of 150 g l 1 was used in continuous fermentation with immobilised S. cerevisiae the obtained data for sugar consumption and ethanol production with retention time are shown in Figure 8.13. As the retention time gradually increased the glucose concentration chopped, while the ethanol concentration profile showed an increase. The maximum ethanol concentration of 47 g l 1 was obtained with a retention time of 7 hours. The yield of ethanol production was approximately 38% compared with batch data, where only an 8% improvement was achieved. 

Table 8.7. Ethanol productivity from immobilised systems...

The effect of temperature on the rate of ethanol production is markedly different for free and immobilised systems. Thus while a constant increase in rate is observed with free S. cerevisiae as temperature is increased from 25 to 42 °C, a maximum occurs at 30 °C with cells immobilised in sodium alginate. The lower temperature optimum for immobilised systems may result from diffusional limitations of ethanol within the support matrix. At higher temperatures, ethanol production exceeds its rate of diffusion so that accumulation occurs within the beads. The achievement of inhibitory levels then causes the declines observed in the ethanol production rate. 

Alcoholic fermentation, ethanol production, has been best known for a few decades by S. cerevisiae. Many obligate aerobic fungi, such as common moulds of the genera Aspergillus, Fusarium and Mucor are also well known for their ability to produce ethanol.2 The benefits are ... 

---