Control of Volatile Organic Compounds Emissions from Manufacturing

A1 though polymers with molecular weights in the mil 1 ions can be
made, those most useful for molding have molecular weights of about
125,000; while those used in the surface coating industry average about
35,000.
2.4.2 Model Plant
A continuous process for the manufacture of polystyrene was chosen
for developing the model plant primarily because of its significant VOC
emissions. Mass (bul k) polymerization was used as a basis for developing
the flow diagram. However, the model plant represents all liquid phase
continuous processes, In the case of suspension polymerization, because
polymerization takes place in water, dewatering, washing, centrifuge and
dryer sections are required. These sections usually are not sources of
VOC emissions. The model plant capacity is 73.5 Gg/yr. This capacity
represents an average of capacities from polystyrene plants using batch
or continuous processes in ozone nonattainment areas. The existing
polystyrene plants in ozone nonattainment areas are listed in Table 2-7.
The list includes both continuous and batch-type processes; when the
process type is unknown the process comment is left blank. The plants
with unknown process type are included for completeness of the list.
Only the continuous processes are covered by RACT.
2.4.2.1 ProcessDescription. This description is for a
fully continuous, thermal co-polymerization process for the manufacture
of pel 1 eti zed polystyrene resi n from styrene monomer and polybutadi ene.
Several grades of crystal and impact polystyrene are produced by this
process. The continuous process is represented in Figure 2-3.
Styrene, polybutadiene, mineral oi i , and small amounts of recycl e
polystyrene, anti-oxidants and other additives are introduced into the
feed dissolver tank in proportions that vary according to the grade of
resin being produced. Blended feed is pumped on a continuous basis to
the reactor where the feed is thermally polymerized to polystyrene. The
polymer melt, containing some unreacted styrene monomer and by-products