Gasoline with ethanol, economic

One example of an industrial system with excess reactant is the ETBE system. A 10-20% excess of ethanol is fed to the column. If the excess ethanol can be included in the ETBE bottoms product from the column and blended into gasoline with the ETBE, there may be no economic penalty and no need for recovering the excess ethanol. However, in other systems, the excess reactant must be removed from the product and recycled. This involves an additional separation step, so capital investment and energy costs are increased. 

Ethers, such as MTBE and methyl / fZ-amyl ether (TAME) are made by a catalytic process from methanol (qv) and the corresponding isomeric olefin. These ethers have excellent octane values and compete on an economic basis with alkylation for inclusion in gasoline. Another ether, ethyl tert-huty ether (ETBE) is made from ethanol (qv) and isobutylene (see Butylenes). The cost and economic driving forces to use ETBE vs MTBE or TAME ate a function of the raw material costs and any tax incentives that may be provided because of the ethanol that is used to produce it. 

The above rough economics suggest a significant advantage for the enzymatic process, about 10% in capital costs and 6% in product "cost", or, since it includes an allowance for adequate return on investment, price. The price per gallon would make this ethanol competitive with industrial alcohol today, but it is too expensive to be considered for motor fuel at present gasoline prices. 

Iogen, a Canadian biotechnology company, makes just such an enzyme and has been operating a test plant to determine how economical the process may be. The company hopes to construct a 300-million, large-scale biorefinery with a potential output of 50 million gallons per year. Its pilot plant in Ottawa utilizes wheat straw and com stalks. In mid-2009, a Shell gasoline station in Ottawa, Canada became the first retail outlet in that nation to sell a blend of gasoline that features 10% cellulosic ethanol. 

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