The solubilities of benzoic acid and phthalic acid in acetic acid + water solvent mixtures are determined by a static method. The experimental temperature ranges from (298.3 to 367.9) K, and the mass fraction of acetic acid in the solvent mixtures ranges from 0.8 to 1.0. The experimental results show that, within the temperature range of the measurements, the solubility of benzoic acid and phthalic acid in all the mixtures shows an increasing trend as the temperature increases. The solubility of benzoic acid decreases with increasing mass fraction of water. For the solubility of phthalic acid in acetic acid + water within the solvent composition range of the measurements, below 325.2 K, the higher the mass fraction of water, the less the solubility. However, above 325.2 K the higher the mass fraction of water, the greater the solubility. A simple explanation was given for this "maximum-solubility effect". The experimental data was correlated by the Non-Random Two Liquids (NRTL) activity coefficient model, and the model parameters were regressed.

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The reaction mechanism and kinetics for the liquid-phase catalytic oxidation of p-xylene to terephthalic acid are briefly reviewed, which indicates that the available literature is not complete when one looks for the industrially applicable mechanism and kinetics. In this work, a detailed radical chain reaction mechanism for the liquid-phase catalytic oxidation of p-xylene to terephthalic acid is proposed. Using several assumptions, a simple fractional-like kinetic model is derived from the assumed reaction mechanism. Several semicontinuous oxidation experiments are carried out at different reactant feed rates and temperatures. The experimental results show that the measured concentrations of liquid-phase reactants increase approximately linearly with time, which indicates that the reaction rate for the liquid-phase reactants is approximately independent from its concentration. The derived kinetic model can explain and correlate these experimental results satisfactorily. By combining the results determined in batch oxidation experiments with the semicontinuous experimental results, the kinetic model parameters are determined by data fitting. The correlated results generally agree with both the semicontinuous and the batch experimental results satisfactorily.

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In a previous paper (Wang, Q.; Li, X.; Wang, L.; Cheng, Y.; Xie, G. Ind. Eng. Chem. Res. 2005, 44 (2), 261−266) a lumped kinetic scheme and a fractional kinetic model for the liquid-phase oxidation of p-xylene to terephthalic acid catalyzed by cobalt acetate and manganese acetate and promoted by hydrogen bromide was proposed and tested. Here, the effect of water content on the time evolution of the experimental product distribution and kinetic constants of the developed model were investigated. Experiments on four levels of initial water content were carried out in a semi-batch oxidation reactor where the gas and liquid phase were well mixed. The results show that for the first two fast steps of p-xylene and p-tolualdehyde oxidation, the rates decrease with the increase of water content, while for the latter two slower oxidation steps of p-toluic acid and 4-carboxybenzaldehyde, the rates increase with the increase of water content. There was an optimal water content for the reaction system. The mechanism was interpreted by the competition between the coordination effect, which had negative influence on the transfer rate of the electron, and the decrease of the redox potential of the cobalt ion, which had positive influence on the reaction rate.

Liquid-phase catalytic oxidation of p-xylene to terephthalic acid was performed at 150-210°C over CoMn-Br catalyst system. There was an interesting synergistic effect of cobalt and manganese catalyst. In the previous papers (Ind. Eng. Chem. Res. 2005,44, 261-266; 4518-4522; 7756-7760), a lumped kinetic scheme and a fractional kinetic model for the liquid-phase oxidation of p-xylene were proposed and tested, and the effects of catalyst concentration, water content, and guanidine catalyst additive were investigated. In this paper, the synergistic effect of cobalt and manganese on the oxidation kinetics was studied. Experiments of several levels of Co/Mn ratio and temperature were carried out in a semibatch oxidation reactor where the gas and liquid phases were well-mixed. The results showed that the variation of the Co/Mn ratio in the catalyst did affect the activity and selectivity of the catalyst system. For the main reaction, there existed an optimum Co/Mn ratio at which the rates of the latter two slower oxidation steps of p-toluic acid and 4-carboxybenzaldehyde reached the maximum, and the optimum Co/Mn ratio decreased with the increase of reaction temperature. However, the burning side reaction of reactant and solvent due to carbon dioxide and carbon monoxide formation increased remarkably with the increase of Co/Mn ratio. A possible mechanism that the optimum Co/Mn ratio presents in the oxidation was proposed eventually.

Experimental solubilities are reported for terephthalic acid (TA) in binary mixtures of N-methyl pyrrolidone (1) + water (2) and N,N-dimethyl acetamide (1) + water (2) in the temperature range of (303.2 to 363.2) K. The mole fraction of water in the N-methyl pyrrolidone + water solvent mixtures x 2 ranges from 0 to 0.5791 and in the N,N-dimethyl acetamide + water solvent mixtures x 2 ranges from 0 to 0.5477. The experimental results show that the solubility of TA increases significantly with an increase in temperature and decreases significantly with an increase in x 2. The solubility data were correlated by a modified Buchowski equation.

2,5-Furandicarboxylic acid (FDCA), mainly synthesized by the selective oxidation of 5-hydroxymethylfurfural (HMF), is a biobased monomer for high-performance polymers. In this work, we have a comprehensive investigation on the rapid and highly selective oxidation process of HMF to FDCA in acetic acid (HAc) with Co/Mn/Br catalyst and air as the oxidant. It was found that both aldehyde and hydroxymethyl functional groups of HMF could be first oxidized in the sequential oxidation of HMF to FDCA, but 2,5-diformylfuran (DFF) was the main oxidation intermediate. Apart from the side reaction of HMF overoxidation to CO x (CO and CO 2 ) and HMF condensation to polymers, a small part of HMF will be further oxidized to maleic acid (MA) and fumaric acid (FA) via the ring-opening reactions under severe conditions because of the instability of furan ring. To reduce the side reactions and maximize the FDCA yield, the effects of temperature, pressure, substrate solvent ratio, catalyst composition and concentration, and water concentration on the main reactions and side reactions of the HMF oxidation were systematically evaluated. Under the optimum conditions, the selectivity of FDCA reached 92% with the total conversion of HMF in less than 20 min at a high mass ratio of substrate and solvent (1/9), and the purity of FDCA exceeded 99.8%. The experimental results provide a great reference and inspiration for the optimization of the HMF oxidation process and the large-scale production of FDCA.