Published October 1998
Worldwide consumption of phthalic anhydride (PA) reached 6.6 billion lb/yr in 1996, and is projected to reach 7.9 billion lb/yr by 2001. About 90% of consumption is concentrated in 3 major uses: (1) PA esters are widely used as plasticizers for polyvinyl chloride resins; (2) unsaturated (thermosetting) polyesters find major uses to fabricate fiberglass-reinforced parts such as boats and bath tubs; and (3) glycerol-phthalate alkyd resins are a widely used base for paints.
Since our first PA reports, PEP Report 34 (March 1968) and PEP Report 34A (June 1974), respectively, several aspects of PA production have changed: o-Xylene is now the major feedstock, whereas naphthalene's use as a feedstock has diminished to about 16% of the total. Catalyst improvements allow smaller reactors. Improvements in equipment and safety release device designs provide for safe operation within the explosive limits of the higher o-xylene loadings desired. And environmental concerns now require the addition of an exhaust gas incinerator.
Currently, almost all PA is manufactured by the single fixed bed oxidation reactor process with conventional switch condensers that collect PA as a solid, and fully developed technology is available for licensing from several sources.
No commercial liquid recovery systems have been announced, but the dual reactor system has been, in part, commercialized by BASF and plans to commercialize a similar system have recently been announced by Nesté. We show that fluidized bed technology offers promise, and we quantify the additional catalyst improvements required to realize this potential.
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