50KT Phthalic Anhydride Plant
This role supports the Phthalic Anhydride (PA) plant, a BASF process unit commissioned in 1971. The facility has undergone multiple upgrades, including increased orthoxylene loading capacity (from 40 g/nm³ to 80 g/nm³) and enhanced safety systems. Currently derated to 110 Mlbs./year, the plant operates with two reactors and associated equipment.
About the Plant
The Phthalic Anhydride Unit consists of three primary areas:
- Oxidation: Produces crude Phthalic Anhydride using compressors, reactors, switch condensers, a circulating oil system, and tail gas incinerators.
- Purification: Refines crude PA to 99.8% assay via decomposers, distillation columns, a separate hot oil system, and a distillation incinerator.
- Utilities: Includes heat exchangers, steam drums, and boiler feed water equipment generating 650#, 450#, 150#, and 30# steam.
Process Overview
The exothermic reaction of orthoxylene to Phthalic Anhydride removes heat through:
- 450# steam generation at the reactor.
- Temperature increase of the air stream passing through the reactor.
Post-reaction, the product gas is pre-cooled in a gas cooler (producing 150# steam) and further cooled in switch condensers, where crude PA crystallizes on tube bundles. Waste gas is incinerated in tail gas incinerators, generating 650# steam. Crude PA is melted off condenser tubes, drained, and pumped to storage for purification.
The circulating oil system alternates hot and cold oil to switch condensers for crystallization and melting cycles. Crude PA contains impurities (phthalic acid, benzoic acid, o-/p-toluic acid, maleic anhydride, and trace compounds), which are thermally treated under vacuum to remove water and low-boiling materials. The treated crude undergoes two-stage vacuum distillation:
- First column: Removes low-boiling impurities (maleic anhydride, benzoic acid, toluic acid) and some PA as overheads.
- Second column: Separates high boilers from pure PA overhead.