부산대학교 도서관

Kineticinvestigations of the liquid phase oxidation of p-xylene (pX) to terephthalic acid (TPA)with Co/Mn/Br catalyst were performed in a stirred 50 mL Parr reactorat 200 °C and 15 bar pressure under conditions wherein productprecipitation is avoided. The oxidant (O2) was introducedby sparging into the liquid phase at constant gas-phase O2partial pressure. Apparent kinetic rate constants, estimated byregressing experimental conversion data to a pseudo-first order lumpedkinetic model, are at least an order of magnitude greater than thosereported in the literaturefor similar catalytic reactions. We attribute this difference to thepresence of gas–solid and liquid–solid mass transferresistances in the previous studies wherein the TPA product precipitatesas it forms, trapping intermediate products and slowing down theiroxidation rates. Our results also indicate that it is not possibleto completely eliminate the gas–liquid mass transfer limitationsassociated with the fast intermediate oxidation steps, even when operatingwithout solids formation and at high stirrer speeds. Other types ofreactor configurations are therefore needed to better overcome gas–liquidmass transfer limitations. Systematic studies of bromide concentrationeffects show that the observed reaction rates become zero order inbromide concentration at sufficiently high bromide levels where theelimination of intermediate 4-(bromomethyl)benzoic acid by oxidationis favored. Further, the rate constants do not show any statisticallysignificant dependence on pX concentration as suggestedin other reports involving the traditional three-phase gas–liquid–solidreaction system. This again confirms that the formation of a solidphase hinders the overall oxidation rate, resulting in much smallerapparent rate constants. [ABSTRACT FROM AUTHOR]