Page 113 - Fundamentals of Air Pollution

III. Stationary Sources 83

8. Resins and Plastics
Resins are solid or semisolid, water-insoluble, organic substances with
little or no tendency to crystallize. They are the basic components of plastics
and are also used for coatings on paper, particleboard, and other surfaces
that require a decorative, protective, or special-purpose finish. The common
characteristic of resins is that heat is used in their manufacture and applica-
tion, and gases are exhausted from these processes. Some of the gases that
are economically recoverable may be condensed, but a large portion are
lost to the atmosphere. One operation, coating a porous paper with a resin
to form battery separators, was emitting to the atmosphere about 85% of
the resin purchased. This resin left the stacks of the plant as a blue haze,
and the odor was routinely detected more than 2 km away. Since most
resins and their by-products have low odor thresholds, disagreeable odor
is the most common complaint against any operation using them.

C. Varnish and Paints
In the manufacture of varnish, heat is necessary for formulation and
purification. The same may be true of operations preparing paints, shellac,
inks, and other protective or decorative coatings. The compounds emitted
to the atmosphere are gases, some with extremely low odor thresholds.
3
Acrolein, with an odor threshold of about 4000 /xg/m , and reduced sulfur
3
compounds, with odor thresholds of 2 ptg/m , are both possible emissions
from varnish cooking operations. The atmospheric emissions from varnish
cooking appear to have little or no recovery value, whereas some of the
solvents used in paint preparation are routinely condensed for recovery
and return to the process. If a paint finish is baked to harden the surface
by removal of organic solvents, the solvents must either be recovered,
destroyed, or emitted to the atmosphere. The last course, emission to the
atmosphere, is undesirable and may be prohibited by the air pollution
control agency.

D. Acid Manufacture
Acids are used as basic raw materials for many chemical processes and
manufacturing operations. Figure 6-8 illustrates an acid plant with its flow
diagram. Sulfuric acid is one of the major inorganic chemicals in modern
industry. The atmospheric discharges from a sulfuric acid plant can be
expected to contain gases including SO 2 and aerosol mists, containing SO 3
and H 2SO 4, in the submicron to 10-/xm size range. The aerosol mists are
particularly damaging to paint, vegetation, metal, and synthetic fibers.
Other processes producing acids, such as nitric, acetic, and phosphoric
acids, can be expected to produce acid mists from the processes themselves
as well as various toxic and nontoxic gases. The particular process must be
thoroughly studied to obtain a complete listing of all the specific emissions.