Commercial production of ethanol in the San Luis Valley, Colorado. Final Report Page: 37 of 222
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form a binary constant-boiling mixture (azeotrope) of this composition which boils at a
slightly lower temperature than absolute or anhydrous alcohol.
In order to remove the remaining 4-5 percent water present in this azeotrope,
a third component is normally used to break the azeotrope. The normal dehydration
process steps are shown in Figure 2-3. A hydrocarbon is commonly used in industrial
ethanol operations to form a ternary minimum boiling azeotrope with water and etha-
nol. Anhydrous alcohol is obtained from the bottom of the distilling column because its
vapor pressure is relatively lower than that of the constant-boiling mixture of ethanol,
hydrocarbon and water. The ternary azeotrope is stripped of its hydrocarbon and etha-
nol content and these components are returned to the dehydration column.
2.4 ALTERNATIVES TO CONVENTIONAL PRODUCTION TECHNIQUES
The production of industrial alcohol by fermentation has evolved from the
manufacturing processes of the beverage distilleries. These plants are concerned pri-
marily with taste, and efforts have not been directed towards optimizing heat conserva-
tion and production rates, but have been focused primarily on manufacturing a palatable
product. The key to improving the economics of industrial ethanol plants is to.concen-
trate on techniques that are specifically geared towards the formation of 200 proof
The subjective criterion of taste is eliminated from consideration in anhy-
drous ethanol production. The aldehydes and ketones which give beverage grade alcohol
its flavor are considered contaminants in producing 200 proof ethanol and must be
removed, which requires additional process steps and increased operating costs. The
yeast and enzymes currently used could be modified to accommodate the requirements
of a fuel grade ethanol plant. Recent laboratory research has discovered that the
bacterium zymomonas mobilis used in the fermentation cycle can produce fuel grade
alcohol two to three times faster than the same amount of yeast (University of New
South Wales, Australia, 1981). These microorganisms could be tailored to increase
alcohol production rates, minimize by-product formation and function in an environ-
ment conducive to the overall, ethanol process. Applicability to industrial scale plants
has not been demonstrated.
Several techniques have been put forward to improve fermentation char-
acteristics. Yeast growth and sugar conversion are inhibited by alcohol formation, and
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Hewlett, E.M.; Erickson, M.V.; Ferguson, C.D.; Sherwood, P.B.; Boswell, B.S.; Walter, K.M. et al. Commercial production of ethanol in the San Luis Valley, Colorado. Final Report, report, July 1, 1983; United States. (digital.library.unt.edu/ark:/67531/metadc874948/m1/37/: accessed July 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.