Recovery of By-Product Maleic Anhydride in Phthalic Anhydride Plants

In phthalic anhydride plants based on vapor phase oxidation of o-xylene, the off-gas stream after phthalic anhydride removal is vented to the atmosphere. However, this stream contains some organic compounds, principally maleic anhydride, and before the stream is vented it must be passed through a catalytic or thermal incinerator or else through a scrubber to satisfy pollution control requirements. One way to offset the cost incurred in the interest of pollution control is to use the scrubber system for pollution control and to recover maleic anhydride from the scrubber solution for use or sale. Capital and production cost estimates are presented for such a recovery operation.