Investigation Of Catalysts On The Selective Oxidation Of Methacrolein To Methacrylic Acid

Methyl methacrylate(MMA) is an important chemical raw material. The main traditional process for the production of MMA contains the conventional acetone cyanohydrine(AC H) process and IB oxidation process. The ACH process uses highly toxic hydrocyanic acid(HCN) as the substrate, uses highly caustic sulphuric acid in the process and generates solid waste of ammonium bisulfate. The price of IB rises with the shortage of petroleum. The process of BASF, which uses ethylene and syngas as raw materials, suits for the situation of China which is rich in coal. The research of selective oxidation of methacrolein(MAL) to methacrylic acid(MAA), as one of the key steps of BASF route, makes a great significance.In this study, the selective oxidation of MAL to MAA was investigated using P-Mo-V HPCs of Keggin structure as catalysts. The effect of Cs, transition metal(Fe, Co, N i, C u, Zn), V and Si on the structure, acidity, redox property and catalytic performance of HPCs were investigated. The preparation condition of catalysts and reaction temperature were also studied.The effect of Cs on the structure, acidity, redox property and catalytic performance of the H4PMo11VO40-based HPCs were investigated. Results showed that the addition of Cs can improve the stability of heteropolyanion [PMo11VO40]4- and enhance the catalytic activity due to the increase of the surface area of HPCs. The conversion rate of MAL increased, and the selectivity of MAA first increased and then decreased with the increase of Cs content. Further, the effect of transition metal(Fe, Co, Ni, Cu, Zn) as counter- ions were investigated. It is found that the addition of Co, N i had the negative influence on catalytic performance. The introduction of Zn changed the activity of catalysts slightly, while the addition of Fe could enhance the selectivity of MAA. The leading of C u significantly improved the catalytic performance with the conversion of MAL83.3% and selectivity of MAA 79.5%, respectively.The effect of V substituting for Mo on the structure, acidity, redox property and catalytic performance of the Cs2HPMo12O40-based HPCs was investigated. Results showed that the addition of vanadium into the framework of heteropolyanion reduced structural symmetry of heteropolyanion, even leading to the structural deformity. Thereby, the acidity, the redox abilities and surface areas of the catalysts changed. The substitution of optimized vanadium could increase surface area and high content of V4+ of the catalyst, which generally are beneficial to the catalytic performance. However, excessive vanadium substitution(x > 1) reduced the activity of the catalysts. Moreover, the substitution of P with Si in Keggin structure decreased the activity of the catalysts.The optimal calcination and reaction conditions were determined and summarized as the following: calcination temperature = 360°C; calcination time = 12 h, reaction temperature = 305°C. For Cs1H2P1.2Mo11V1Cu0.5O40, the best performance could be observed on the optimum condition with the conversion of MAL 86.6% and selectivity of MAA 79.0%, respectively.