The Control of Phthalic Anhydride Emissions
CHARLES W. MOORES, Pollution Control Coordinator
The Badger Company, Inc.
Cambridge, Massachusetts 02142
INTRODUCTION
Although the title and subject matter of this article may appear to be somewhat esoteric
and of little general interest, it should be pointed out that phthalic anhydride is produced by
a partial oxidation process using air as a source of oxygen. Many petrochemicals, such as
maleic anhydride, teraphthalic acid, formaldehyde, acrylic acid, etc., are also produced by
partial oxidation processes and have similar types of emission problems. Additionally,
systems for the control of hydrocarbon emissions, odors, and carbon monoxide emissions
from processes such as solvent coating, pharmaceuticals and FCC catalyst regeneration are
similar to the control systems discussed herein.
Phthalic Anhydride (PA) is a petrochemical like many commercially important
commodity petrochemicals which have experienced a significant growth in demand over
the past forty years. This demand has caused changes in production technology, feed stocks
and plant sizes. Over the past fifteen years, the environmental legislation has become an
additional significant factor in plant design and operation.
The historical evolution of the control of PA emissions which follows demonstrates
two concepts common to most, if not all, industrial emissions: 1) Plant production capacity
is added periodically in progressively larger steps while smaller, obsolete plants are phased
out. (Due to increasing environmental concern, the emission control concepts must be reassessed with each periodic expansion of the industry); and 2) The basic laws of matter
allow the plant designer to choose the physical state (solid, liquid or gas) of industrial
emissions. The final physical state of the emission is usually dictated by the control system
selected, which is a function of environmental legislation and economics.
Before tracing the history of PA emission control techniques, it may be useful to recall
some of the basic chemistry involved in its production. Mention will also be made of uses,
physical-chemical properties, and by-products.
WHAT IS PHTHALIC ANHYDRIDE?
PA is the anhydride of an ortho-dicarboxy aromatic acid. The physical-chemical
properties of phthalic anhydride are given in Table I.
Before World War I, PA was produced almost exclusively in Germany and was used
for the production of dyes, principally indigo (1). Since that time, PA has found uses in
plasticizers, alkyd resins, polyesters, and other miscellaneous products. The percentage
breakdown by uses of PA is shown in Table II.
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