Influences of the [Co2+]/[Co3+] Ratio on the Process of Liquid-phase Oxidation of Toluene by Air

Liquid phase oxidation of toluene is an environmental benign route for the production of benzoic acid. In a phi 48 mm bubble column reactor, the commercial process of toluene liquid phase oxidation was conducted with Co(CH3COO)(2)center dot 4H(2)O as catalyst. The Co2+ concentration [Co2+] was determined by extraction spectrophotometry and hereby the Co3+ concentration [Co3+] was obtained by mass balance. The results showed that [Co3+] reached the maximum at about 25-30 min. [Co3+] increased with increasing Co catalyst amount at total Co concentration <150 mg.L-1 of toluene. The conversion of toluene, yield and selectivity of benzoic acid increased with the increasing [Co3+/Co2+](max). A high [Co3+] and a high [Co3+]/[Co2+] ratio are beneficial to the reaction.