Study On Catalyst Of Liquid-Phase Oxidation For Aromatic Acids

Toluene and xylene were the typical single methyl and double methyl aromatic hydrocarbons, as well as the industrial important organic chemical raw materials. Liquid-phase catalytic oxidation of aromatic hydrocarbons for synthesizing aromatic carboxylic acid, was the most important industrial process of aromatic carboxylic acid production, especially in petrochemical industry. The process normally used cobalt acetate, manganese acetate as the catalyst, bromide compound as the initiator, oxygen or oxygen-enriched air as the oxidant, oxidation under high temperature and pressure. However this process has some disadvantages, such as difficulty in catalyst recycling, severe equipment corrosion, environment pollution and other issues, therefore developing a new catalyst system, or exploring a new technology is imminent.In this paper, the experiment was conducted in a stainless steel high pressure autoclave, using toluene and xylene as the substrates, and oxygen as oxidant, exploring improvement of the traditional MC catalyst (Co-Mn-Br) and a novel gas-liquid-solid three-phases catalyst systems.The influence of initiator and metal ions additives on performance of Co-Mn/Br catalyst system in selective oxidation of p-xylene to terephthalic acid was investigated for improvement of reaction rate at low temperature. The results show that the introduction of N-Hydroxyphthalimides (NHPI) and butanone (MEK) into MC catalyst as the second initiator improves the activity of the MC-catalyst, while Zr4+ has little impact on activity, Cu2+ has adverse effect on activity. Comparing with traditional MC catalytic system, the dual initiators’ catalyst, containing NHPI and Br, shows better performance of higher catalytic activity at low reaction temperature.In order to further improve reaction rate of toluene and the selectivity of benzoic acid, and simplify the separation and recycle of the catalyst, V2O5/TiO2、MnO2�'� Mn0.15Ce0.85O2 have been developed as catalysts for the solvent-free catalytic oxidation of toluene. It was investigated systematically how catalyst dosage, reaction temperature, reaction time and oxygen pressure influenced the performance of the catalytic oxidation of toluene. The results showed that V2O5/TiO2 and Mn0.15Ce0.85O2 would dissolve in liquid solution and result in loss of catalyst. But MnO2 is very stable in the reaction and proposed to be the most suitable catalyst for liquid phase catalytic oxidation of toluene to benzoic acid. The conversion of toluene reached 21.9%, and the selectivity of benzoic acid reached 83.9%, when the reaction was conducted at 200℃ in 1 MPa initial O2 pressure for 4 h. Oxidizing toluene under liquid-phase solvent-free condition, the majority of product was benzoic acid, the by-products were Benz aldehyde and benzyl alcohol. The catalyst could be separated by filtration, and the product by cooling crystallization, so the process has a good industrial application prospect with simple operation.