Page 17 - Chemical process engineering design and economics

4 Chapter 1

Over a period of many years polymeric materials have gradually replaced
metals in many applications. Among the five leading thermoplastics; low and
high density polyethylene, polyvinyl chloride, polypropylene, and polystyrene;
polyethylene is the largest volume plastic in the world. Polyethylene was initially
made in the United States in 1943. In 1997, the estimated combined worldwide
10
production of both low and high-density polyethylene was 1.230 x 10 kg (2.712
x 10 10 Ib) [10]. Low density polyethylene is produced at pressures of 1030 to
3450 bar (1020 to 3400 arm) whereas high density polyethylene is produced at
pressures of 103 to 345 bar (102 to 340 arm) [11].
Explosives are most noted for their military, rather than civilian uses, but
they are also a valuable tool for man in construction and mining. Interestingly, as
described by Mark [12], the first synthetic polymer, although it is only partially
synthetic, was nitrocellulose or guncotton, a base for smokeless powder. Nitrocel-
lulose was discovered accidentally in 1846 when a Swiss chemist, Christian
Schoenbein, wiped a spilled mixture of sulfuric and nitric acids using his wife's
cotton apron. After washing the apron, he attempted to dry it in front of a strove,
but instead the apron burst into flames. Although the first application of modified
cellulose was in explosives, it was subsequently found that cellulose could be
chemically modified to make it soluble, moldable, and also castable into film,
which was important in the development of photography. Nitrocellulose is still
used today as an ingredient in gunpowder and solid propellants for rockets.
Nitrogen is an essential element for life, required for synthesizing proteins
and other biological molecules. Although the earth's atmosphere contains 79%
nitrogen, it is a relatively inert gas and therefore not readily available to plants and
animals. Nitrogen must be "fixed", i.e., combined in some compound that can be
more readily absorbed by plants. The natural supply of fixed nitrogen is limited,
and it is consumed faster than it is produced. This led to a prediction of an even-
tual world famine until 1909 in Germany, when Badische Anilin and Soda Fabrik
(BASF) initiated the development of a process for ammonia synthesis [13]. In
1910, the United States issued a patent to Haber and Le Rossignol of BASF for
their process [14]. The first plant was started up in 1913 in Ludwigshafen, Ger-
many, expanded in the 1960's, and only shut down in 1982 after seventy years of
production [15]. This is certainly an outstanding engineering achievement. Al-
though the fixed nitrogen supply is no longer limited by production from natural
sources, they are still major sources. Agricultural land produces 38%; forested or
unused land, 25%; combustion, resulting in air pollution, 9%; lightning, 4%; and
industrial fixation, 24% [16]. The oceans produce an unknown amount.
Processes could be subdivided according to the type of reaction occurring,
as illustrated by bread making and the activated sludge process, by also classifying
them as biochemical processes. Similarly, we could also have electrochemical,
photochemical, and thermochemical processes and so on, but this subclassification
could lead to difficulties because in some processes more than one type of reaction
occurs, such as in the vitamin C process.

Copyright © 2003 by Taylor & Francis Group LLC