Study On The Reaction Of Selective Oxidation Of Toluene In Supercritical Carbon Dioxide

Benzaldehyde is an important chemical intermediate, and it was used widely. However, the application of products was limited, because of the lower purity and the lower yield. Supercritical fluids could improve the reaction process, because of the higher selectivity, faster reaction rate, and products could be separated easily. Therefore, it was studied widely, to improve the traditional process, using the special properties of supercritical fluids. To explore a new synthesis of benzaldehyde, the process of oxidation of toluene was studied in supercritical carbon dioxide.Firstly, we studied the solubility of toluene, benzyl alcohol, benzaldehyde, and benzoic acid in supercritical carbon dioxide, with visual equilibrium devices. The results showed that, the toluene has an high solubility of in supercritical carbon dioxide, and toluene-CO2 system could form single phase,under the reaction condition. And the solubility of benzyl alcohol, benzaldehyde, and benzoic acid in supercritical carbon dioxide reduced with the polarity enhanced. So, the synthesis of benzaldehyde could be realized in higher selectivity, because of the different solubility of the oxidation products. In addition, the phase behavior of heterogeneous catalysts in toluene-supercritical carbon dioxide system was also explored. And the catalysts could be dispersed in supercritical carbon dioxide uniformly.Secondly, the effects of time, pressure, temperature, and molar ratio on the selectivity and conversion were investigated, in the reaction system without catalyst in supercritical carbon dioxide. And the appropriate reaction conditions were determined. In addition, contrast experiments were investigated in pure oxygen system and nitrogen system, in order to explore the advantages in supercritical carbon dioxide. The results showed that, the over-oxidation could be inhibited, and the total selectivity of benzyl alcohol, benzaldehyde, and benzoic acid was about 3 times than in the pure oxygen system.To improve the reaction, catalytic oxidation of toluene was studied in super- critical carbon dioxide. When catalysts added, the conversion of toluene increased 2-3 times, compared with non-catalyst system in supercritical carbon dioxide. And when the temperature was 150℃, the reaction of catalytic oxidation of toluene still remaina higher activity in supercritical carbon dioxide.