Control of Volatile Organic Compounds Emissions from Manufacturing

Polypropylene resins are supplied in many grades for a variety of
uses. Apart from major distinctions between homopolymer, intermediate-impact
co-polymer, and high-impact co-polymer, the grades may a1 so di ffer in
speci fi c formulations. Different grades of polypropylene lend themselves
to use in di fferent applications. Molded applications include bottles
for syrups and foods, caps, auto parts, appliance parts, toys, housewares,
and furniture components. Fibers and filaments are used in carpets,
rugs, and cordage. Film uses include packaging for cigarettes, records,
and housewares. Extrusion products include pipes, prof i1 es, wi res and
cable coatings, and corrugated packing sheetsS3
Injection mol di ng accounts for 41 percent of polypropylene use;
fibers and filaments account for 31 percent; and other forms account for
28 percent.3 In terms of end uses, major sectors are shown in Table 2-1.
Production of polypropylene has grown from 981 Gg in 1973 t o 1,743-Gg
in 1979, a 10.1 percent annual growth rate. C.H. Kline projects a
9.0 percent growth rate for polypropylene from 1978 t o 1983,4 and SRI
International projects an 8 percent growth rate from 1977 to 1982.5
Currently, 24 plants produce polypropylene in the United ~tates.~ The
existing polypropylene plants known to be in the current ozone nonattainment
areas are listed in Table 2-2.
2.2.2 Model Plant
The continuous slurry process for manufacture of polypropylene is
the most widely used process commercially. Based on data from 10 existing
plants 1 ocated in nonattainment areas, a model plant capacity of 141 Gg/yr
was selected.
The polypropylene resins, characterized by havi ng a control 1 ed
content of isotactic material, are obtained through coordination polym-
erization, employing a heterogeneous Ziegler-Natta type catalyst system,
which typical ly is a combination of titanium tetrachloride and alumi num
alkyls. More recent process technology, which uses a high-yield catalyst
with improved activity, requires much less catalyst than the conventional
process. With this high-yield process, the catalyst is left in the
product. This techno1 ogy results in fewer processing steps and, thus,
less emi ssions. This new process is incorporated in the model plant by
exclusion of several processing units, and is consistent with a proportional
reduction in the total emission factor.