Selective Oxidation Of Propane To Acrylic Acid Over Mo-v-sb-o Catalysts

Light alkanes now mainly used for fuel are cheap chemicals existed in natural gas, coal bed gas, liquid petroleum gas and petroleum refinery processes. Since light alkanes are very cheap chemicals, the conversion of light alkanes to high valued oxygenates and olefins such as corresponding alcohols, aldehydes, acids and propene has attracted much attentions in the past decades. The economic importance of this possibility and the successful manufacture of maleic anhydride by selective oxidation of n-butane over VPO catalysts have stimulated various researches, one of which is the selective oxidation of propane to acrylic acid because propane could be activated more easily than methane and ethane.Acrylic acid is an ideal monomer widely used in chemical industry due to itsα,β-unsaturated double bond. Up to now acrylic acid is commercially produced in a two-step process using propene as the raw material, which now limited by the climbing price of petroleum. Selective oxidation of propane to acrylic acid is one of promising methods to replace the commercial two-step method for producing acrylic acid.Various methods have been employed to prepare multiply metal oxides catalysts for selective oxidation of propane to acrylic acid, including solid state reaction method, solution method and hydrothermal synthesis method. some catalyst precursors and most of catalysts used in the present work were characterised by XRD, SEM, EDS,BET and FT-IR et al. Activity testing experiments were also carried out over as-prepared catalysts. Results can be listed as follows:(1) Mo-V-Sb-O catalysts prepared by hydrothermal method possess higher activity compared to those specimens prepared by other two methods.(2) Uncalcined precursors of Mo-V-Sb-O catalyst prepared by hydrothermal synthesis method show poor activity though possess orthorhombic structure for the adsorption of ammonium cation and water over their surface, so calcination is needed to drive off adsorbed specimens and to obtain catalytic activity.(3) Calcination conditions including calcination temperature, calcination atmosphere and calcination time have effective impacts over catalytic performance. An Effective Mo-V-Sb-O catalyst were obtained after as-synthesized orthorhombic-structured precousor were calcined for 2 hours in a 40ml/min flowing Argon atmosphere under 600℃. (4) Effects of molar ratio of different metal atoms in mother suspension over catalyst performance was investigated, preferred molar ratio of metal atoms is Mo:V:Sb=6:2:0.5. 28.7% of C3H8 conversion and 11.7% of acrylic acid yield was obtained when activity testing experiment was performed over as-prepared Mo6V2Sb0.5Ox catalyst under the following conditions: reaction temperature of 390℃, the space velocity of 2760ml/(g·h) and the feedstock composition(C3H8/O2/CO2/H2O volume ratio) of 6/12/24/75.(5) Effects of reaction conditions such as balance gas, reaction temperature, steam content and space velocity were investigated and discussed. Results showed that yield of acrylic acid was slightly promoted when nitrogen and carbon dioxide was introduced as balance gas respectively, which indicated that over oxidation was prevented to some extent. Acrylic acid selectivity and yield were strongly effected by reaction temperature, steam content and space velocity. The temperature of 390℃, the space velocity of 3680ml/(g·h) and the feedstock compositon (C3H8/O2/CO2/H2O volume ratio) of 6/12/24/50 were suitable for acrylic acid production. The acrylic acid yield could reach 13.8% when the optimal reaction experiment was tested.