Effects of alkali metals on the liquid phase oxidation of p-xylene

Effects of Guanidine on the Liquid-Phase Catalytic Oxidation of p-Xylene to Terephthalic Acid

“…[3][4][5][6] Recently, increasing attention has been paid to improvement of the Co-Mn-Br catalyst system by adding a fourth active catalyst component such as transition, alkali, and lanthanide metals, which can enhance the reaction activity greatly and ameliorate the selectivity in some instances. 2,[9][10][11][12][13][14] As Partenheimer had shown, the reaction was profoundly accelerated by Zr 4+ and Hf 4+ contained in the catalyst system. [9][10][11] However, Cheng observed that the side reaction rates increase more evidently than the main reactions with the addition of Zr and Hf.…”

“…The reaction mechanism is a typical catalyst-modified free-radical chain mechanism, and its kinetics has been investigated in detail for the last several years. − In previous papers a lumped kinetic scheme and a fractional kinetic model for the liquid-phase oxidation of PX catalyzed by Co−Mn−Br was proposed and tested and the effect of water on the oxidation reaction kinetics was investigated. , By accounting for the most important intermediates and final products of the oxidation process, i.e., p -tolualdehyde (TALD), p -toluic acid (PT), 4-carboxybenzaldehyde (4-CBA), and TA, a lumped kinetic model (Figure ) for the liquid-phase oxidation of PX to TA was widely adopted, where the reaction of PX to TALD and PT to 4-CBA involves addition of 1 O 2 and reaction of TALD to PT and 4-CBA to TA involve the addition of 1 / 2 O 2 . Wang and Cheng developed the kinetic model as shown in eq 1 from the radical chain reaction mechanisms. − Recently, increasing attention has been paid to improvement of the Co−Mn−Br catalyst system by adding a fourth active catalyst component such as transition, alkali, and lanthanide metals, which can enhance the reaction activity greatly and ameliorate the selectivity in some instances. ,− As Partenheimer had shown, the reaction was profoundly accelerated by Zr 4+ and Hf 4+ contained in the catalyst system. − However, Cheng observed that the side reaction rates increase more evidently than the main reactions with the addition of Zr and Hf . Jhung reported the effects of alkali metals on the liquid-phase oxidation of xylenes. , The reaction rate can be eventually accelerated, even though the rate is decelerated a bit initially, with the addition of a suitable composition of alkali metal.…”

Liquid Phase Oxidation of Xylenes: Effects of Water Concentration and Alkali Metals

“…The effects of alkali metal on the oxidation of xylene isomers will be explained in detail elsewhere. 26 Potassium can be used not only for increasing reaction rates but also for overcoming the retardation of reaction in its later stage when the water concentration is equal to about 5.0%. If the water concentration is too low the rate of reaction, even with and without the additional potassium, decreases quite sharply, even though the rate is high in the earlier stage of the reaction.…”

Production of Isophthalic Acid from m-Xylene Catalyzed by Co(II) and HPW@C Modified with Acetic Acid

“…Many scholars have paid attention to optimizing the Co–Mn–Br system to improve IPA and TPA selectivity or yield. Some experts attempted to add a fourth active catalyst constituent, such as lanthanide or alkali metal, to accelerate the oxidation of PX and upgrade the selectivity of TPA. − Partenheimer , reported that the oxidation of PX to TPA was improved by the addition of Zr 4+ and Hf 4+ into the Co–Mn–Br system. Cheng et al reported that the introduction of Zr and Hf accelerated the side reactions more conspicuously than the main reactions.…”

“…Cheng et al reported that the introduction of Zr and Hf accelerated the side reactions more conspicuously than the main reactions. Jhung et al , investigated the role of alkali metals in the oxidation of xylenes. Replacement of acetic acid with water or utilization of carbon dioxide as a co-oxidant has been tried in the Co–Mn–Br system for the oxidation PX to TPA.…”