Chap. 12. Feedstocks 309In this process, the solvents are distilled off from the extract and recirculated through
the process.
The hydrocarbon terpenes that occur in rubber trees can be tapped from the trees
as a latex suspension in tree sap. Steam treatment and distillation can be employed to
extract terpenes from sources such as pine or citrus tree biomass.
Grain seeds are rich sources of protein, almost always used for food, but potentially
useful as chemical feedstocks for specialty applications. An exciting possibility just now
coming to fruition in a practical sense is to transplant genes into plants so that they will
make specialty proteins, such as medicinal agents.
12.4. Fermentation and Plant Sources of Chemicals
In the provision of specialty and commodity chemicals and feedstocks, there are
two main biological sources of materials. One of these consists of plants, which make
huge quantities of cellulose and lesser quantities of other materials by photosynthesis.
The other source is microorganisms, especially bacteria and yeasts.
Fermentation
Fermentation refers to the action of microorganisms on nutrients under controlled
conditions to produce desired products. Fermentation for some products is anaerobic
(absence of air) and for others aerobic fermentation is used. Fermentation processes have
been used for thousands of years to produce alcoholic beverages, sauerkraut, vinegar,
pickles, cheese, yogurt, and other foods. Ethanol, the alcohol in alcoholic beverages, is
the most widely produced chemical made by fermentation. Lactic acid,
Lactic acidH
H
H
C
HO
H
C
O
HO C
has also been produced by fermentation processes for many years. More recently,
fermentation has been applied to the production of a wide variety of organic acids,
antibiotics, enzymes, and vitamins.
Starting in the 1940s, one of the major products of industrial fermentation has been
penicillin, of which there are several forms. Figure 12.2 shows a simplified diagram of
a facility for production of this life-saving antibiotic. Following penicillin, fermentation
processes were developed for the production of several other significant antibiotics.
Selection of the appropriate microorganism is the most important consideration
of a successful fermentation production process. The microorganisms have to have the
proper nutrients, the choice of which can affect the kind and yield of the product. Sterile
conditions must be maintained, and sterilization of equipment and media is accomplished
by heating to 125–150 ̊C for appropriate lengths of time. Air entering the fermenter must
be filtered and sterilized. The temperature of fermentation is important, with fermentation
rates increasing up to an optimum temperature, after which they decrease sharply with