Ethanol synthetic, cost

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. 

The processes for manufacturing methanol by synthesis gas reduction and ethanol by ethylene hydration and fermentation are very dissimilar and contribute to their cost differentials. The embedded raw-material cost per unit volume of alcohol has been a major cost factor. For example, assuming feedstock costs for the manufacture of methanol, synthetic ethanol, and fermentation ethanol are natural gas at 3.32/GJ ( 3.50/10 Btu), ethylene at 0.485/kg ( 0.22/lb), and corn at 0.098/kg ( 2.50/bu), respectively, the corresponding cost of the feedstock at an overall yield of 60% or 100% of the theoretical alcohol yields can be estimated as shown in Table 11.12. In nominal dollars, these feedstock costs are realistic for the mid-1990s and, with the exception of corn, have held up reasonably well for several years. The selling prices of the alcohols correlate with the embedded feedstock costs. This simple analysis ignores the value of by-products, processing differences, and the economies of scale, but it emphasizes one of the major reasons why the cost of methanol is low relative to the cost of synthetic and fermentation ethanol. The embedded feedstock cost has always been low for methanol because of the low cost of natural gas. The data in Table 11.12 also indicate that fermentation ethanol for fuel applications was quite competitive with synthetic ethanol when the data in this table were tabulated in contrast to the market years ago when synthetic ethanol had lower market prices than fermentation ethanol. Other factors also... 

Before 1945, most of the supply of ethyl alcohol for industrial solvent or feedstock uses was derived from fermentation (Table 16.13). Since this time, the reliability and low cost of petrochemical routes to the product caused a rapid displacement of fermentation sources in the U.S. Since 1975, however, subsidies for fermentation alcohol have changed this. Large new fermentation units have been constructed, and distilleries formerly used for spirits production have been converted to industrial alcohol production [56]. Increased costs of American synthetic ethanol have kept its production at two-thirds of the total. The early petrochemical sources were based on the formation and hydrolysis of ethyl sulfate, but in North America, this has been replaced by the direct gas phase hydration of ethylene (Eqs. 16.18-16.20). 

Cysewski and Wilke suggested some process design fermentation schemes for continuous cell recycle and also vacuum fermentation processes for making 75.000 gallons of 95% ethanol/day. Using a reasonable yeast byproduct credit of 0.10/lb. their net estimated production cost appeared to be 0.823/gal for the continuous cell recycle system as compared to 0.806/gal for the vacuum fermentation. This compares favorably with the current price of synthetic 95% ethanol selling around 1.40/gal. 

Figure 6 shows the projected selling price for a 15% return on investment after taxes for the 50,000.000 gal/yr Gulf cellulose alcohol plant and for fermentation corn and synthetic ethylene-alcohol plants of the same capacity (Table VI). The ethylene costs are escalated at 9%, per industry projections, cellulosics at 7%. and according to USDA projections, corn at 5%. Feedstock costs used as a basis for these graphs are (starting 1983 as in Tables V and VI) MSW 14.00/oven-dried ton (ODT), SMW 21.00/ODT, Pulp mill wastes 14.00/ODT, Ethylene 0.18/pound and corn 3.00/bushel. Thus, the total feedstock cost per gallon of ethanol produced is 0,104 in the case of cellulose. 0.75 for ethylene, and 1.20 for corn. By-product credits used escalated from prices listed in 1983 at a 7% rate. 

---