New Process For P-xylene Liquid-phase Catalytic Oxidation

Terephthalic acid?PTA?, one of the most important raw materials of polyester industry, is widely applied to all aspects of national economy such as fiber, electronics and building etc. P-xylene as raw material, Co-Mn-Br as catalyst system, acetic acid as solvent, p-xylene liquid-phase oxidation by air is the most representative method forwards. The reaction conditions are harsh and the presence of bromide icon may lead severe corrosion. New process for p-xylene liquid-phase oxidation is proposed and the mechanism of the reaction is speculated in this thesis.Ozone-air mixture as new oxidant for p-xylene oxidation, cobalt acetate as catalyst, glacial acetic acid as solvent, temperature ranging from 60? to 110?, process of p-xylene catalytic oxidation to terephthalic acid at atmosphere pressure was studied and the crude terephthalic acid was refined using NMP crystallization purifying method. Effect of different aspects such as catalyst, temperature, ozone concentration, reaction time and bromide on PX conversion and product selectivity was investigated. Results showed that p-xylene was oxidized with 76.5% conversion and 83.7% selectivity for terephthalic acid at 80? under 63.0mg/L of ozone concentration for 6h at the gas flow rate of 0.8L/min when the mole ratio of p-xylene and cobalt acetate was 10:1. And the conversion of p-xylene and the selective of terephthalic acid can reach 95.5% and 84.5% when 1.09mmol ?mole ratio of p-xylene and potassium bromide was 18.4:1? potassium bromide was employed. The composition of TA can reach 99.07% when employing NMP as selective recrystallization solvent to purify CTA two times. If cobalt acetate, ozone and bromide were used at the same time, there existed obvious synergistic effect on the PX oxidation reaction. But this effect was gradually weakened by increasing the temperature because the decomposition rate of ozone was accelerated.A new process of p-xylene catalytic oxidation was proposed. Nano particle CeO₂ as novel catalyst, ozone-air mixture as new oxidant, water or glacial acetic acid as solvent, process of p-xylene oxidation at 85? was studied. Effect of different factors such as temperature, catalyst, ozone concentration, reaction time on the reaction was investigated. Results showed that p-xylene was oxidized with 13.6% conversion and 86.3% selectivity for p-toluic acid at 85? under 65mg/L of ozone concentration for 8h at the gas flow rate of 0.4L/min when the mole ratio of p-xylene and nano particle CeO₂ was 590.1:1. If the solvent was changed from water to glacial acetic acid, the oxidation depth could increase significantly so that the methyl in p-toluic acid could be further oxidized to aldehyde group.The mechanism of p-xylene liquid-phase catalytic oxidation is researched. The contribution to the reaction of p-xylene catalytic oxidation and the interaction reaction mechanism are studied in the presence of cobalt, ozone and bromide.