Chemistry Reference
In-Depth Information
Chapter 9: Biocatalysis
HERBERT L. HOLLAND
1 Introduction
alytic method for this conversion replaced a chemi-
cal process involving acid catalysis and eliminated
the formation of acrylic acid as a side product [2].
Biocatalytic nitrile hydrolysis also has been
employed systematically by the Lonza group as a
method for the production of substituted nicotinic
acids and nicotinamide, as illustrated in Fig. 9.2 [3].
The largest scale industrial biotransformation is
currently the conversion of glucose to fructose by the
enzyme glucose isomerase, which accounts for the
production of approximately 10 million tonnes of
high-fructose syrup annually (Fig. 9.3) [4].
The food industry also uses the enzyme b-
galactosidase for the conversion of lactose into
glucose and galactose (Fig. 9.4), a key process in the
production of low-lactose milk products on a large
scale, with up to 250 000 litres of milk being
processed on a daily basis [5].
In the pharmaceutical industry, the largest scale
biocatalytic process is the conversion of the fermen-
tation product penicillin G into 6-aminopenicillanic
acid by the enzyme penicillin acylase (Fig. 9.5) [5].
The latter is used as the starting point for the pro-
duction of chemically modified penicillins, and is
produced on scales approaching 16 000 tonnes per
year. This biotransformation is carried out under
neutral conditions and without the need for elevated
temperatures; the chemical process that it super-
seded required the use of low temperatures, anhy-
drous conditions and organic solvents to avoid
decomposition of the reactive product.
The above examples of large-scale chemical pro-
duction using biocatalysts do not constitute a com-
prehensive list. Other examples that are carried out
on smaller but still impressive scales are considered
in Sections 2.2-2.6, but the examples outlined above
illustrate the scope of biocatalysis for the production
of bulk chemicals, ranging from commodity chemi-
cals and pharmaceutical products to the products of
the food industry.
The factors that are involved in selecting a biocat-
alytic process for industrial chemical production
Biological reagents are used in chemistry both for the
production of defined products (biocatalysis) and for
the removal of specific toxic materials by conversion
to benign products (biodegradation). Biocatalysis—
the use of a biological system to catalyse the con-
version of a single material (the substrate) to a
defined product—has a long history in organic
chemistry, and specific biocatalytic steps have been
used in the industrial production of both bulk and
fine chemicals for many years [1]. The ability of
enzymes to catalyse organic reactions in the moder-
ate pH range of 4-9 at reasonable temperatures
(usually 10-50°C) and without extremes of pressure
or the addition of metals can provide an environ-
mentally acceptable method of performing many
reactions that otherwise may require highly acidic or
alkaline environments, high energy input for heating
or toxic metal catalysts. Biodegradation is a natural
process but can be applied consciously for the
removal of specific target waste products from in-
dustrial processes. This chapter will cover aspects of
both biocatalysis and biodegradation, focusing on
processes that have application or potential applica-
tion for the replacement of traditional chemical
methods in industrial processes.
2 Chemical Production by Biocatalysis
2.1 Bulk chemicals
Although the production of acetic acid from ethanol
using a strain of
Acetobacter
has been carried out for
almost 200 years, it was not until comparatively
recently that biocatalysis was used for the produc-
tion of other bulk chemicals. A milestone in this area
was the commercialisation in 1985 of the use of a
nitrile hydratase enzyme from
Rhodococcus
to convert
acrylonitrile into acrylamide (Fig. 9.1), a process cur-
rently used for the production of the latter on a
multi-thousand-tonne scale annually. The biocat-
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