Gas-phase Hydrogenation Of Maleic Anhydride To γ-Butyrolactone At Atmospheric Pressure Over Cu-based Catalysts

y-Butyrolactone (GBL) is an important intermediate in fine chemical industry and an excellent solvent with high boiling point. With the large-scale industrialization of producing maleic anhydride (MA) by partial oxidation of n-butane, the production cost of MA is greatly lowered. Therefore, the gas-phase hydrogenation of MA to GBL at atmospheric pressure, with better atom economical efficiency, has been attracting more and more attentions.In this thesis, two novel catalyst systems, such as ZnO-containing Cu-ZnO-SiO2catalyst and ZnO-free Cu-CeO2-Al2O3catalyst, were developed for the gas-phase hydrogenation of MA to GBL at atmospheric pressure. Effects of catalyst composition, promoter, support, reaction temperature, liquid hourly space velocity (LHSV) of raw material and preparation conditions of catalyst on the catalytic performance and catalyst stability were investigated. The mechanisms of catalytic reaction and catalyst deactivation, and the reaction pathways for the gas-phase hydrogenation of MA to GBL at atmospheric pressure over Cu-based catalysts were proposed. The main research results were concluded as follows:1. Cu-ZnO-SiO2catalyst (CZS), prepared by fractional precipitation method, has better catalytic performance for the gas-phase hydrogenation of MA to GBL at atmospheric pressure. Effects of catalyst composition, reaction temperature and LHSV of raw material (20wt.%MA/GBL) on the catalytic performance of CZS catalyst were investigated. Under the reaction conditions of LHSV of raw material of0.1h-1and reaction temperature of220℃, MA conversion and GBL selectivity was99.4%and98.3%respectively, over CZS111catalyst (Cu/Zn/Si=1:1:1, molar ratio). Cu0is the active site for the gas-phase hydrogenation of MA, and the catalyst deactivation is attributed to the deposit formation on the catalyst surface. The introduction of Ba as a promoter can obviously improve the stability of CZS111catalyst due to the increases in the Cu specific surface area (SCu) and the dispersion of ZnO. The reasonable reaction pathway was proposed for the gas-phase hydrogenation of MA at atmospheric pressure over CZS111catalyst, in which the promotion effect of Ba on the catalyst stability was explained.2. Cu-REOX-Al2O3(CREA, RE=Y, La, Ce, Dy or Ho) catalysts, prepared by coprecipitation method, show excellent catalytic performance for the gas-phase hydrogenation of MA to GBL at atmospheric pressure, in which both MA conversion and GBL selectivity were100%, and Cu-CeO2-Al2O3(CCA) catalyst has the best catalyst stability. Cu0is the active site for the gas-phase hydrogenation of MA at atmospheric pressure. Higher Scu and larger pore size of catalyst are favorable to increasing the catalytic performance and stability of CREA catalysts.3. The effects of catalyst composition, LHSV of raw material and reaction temperature on the catalytic performance of CCA catalyst were investigated. Under the reaction conditions of LHSV of0.6h-1and reaction temperature of240℃, both MA conversion and GBL selectivity were100%over C112catalyst (Cu/Ce/Al=1:1:2, molar ratio). Smaller crystallite size of Cu and higher SCu are favorable to the gas-phase hydrogenation of MA to GBL at atmospheric pressure. The introduction of Ba can significantly improve the stability of C112catalyst and keep the best catalytic performance. However, the introduction of Zn increases tetrahydrofuran (THF) selectivity and results in the formation of trace amount of n-butyric acid (BA) and n-butyraldhyde (BD). The introduction of Ba decreases the crystallite size of Cu, increases SCu, and hence increases the numbers of Cu0active sites on the surface of C112catalyst. Meanwhile, the introduction of Ba results in an increase in the catalyst pore size, which is beneficial to diffusion of raw material and products, and heat transmission inside the catalyst pores. The deactivation of C112catalyst is due to the formation of surface deposit which is closely related to presence and amount of succinic anhydride (SA) in products. The deactivated C112catalyst can be regenerated by N2-air-H2regeneration method and the catalytic performance of the regenerated catalyst can be recovered completely, which indicates that CCA catalyst has better regenerable property. The reasonable reaction pathway for the gas-phase hydrogenation of MA to GBL at atmospheric pressure over C112catalyst was proposed based on the hydrogenation reaction of GBL.4. Effects of residual Na+and H2O in the catalyst precursor on the physiochemical properties, catalytic performance and stability of resultant CCA catalyst for the gas-phase hydrogenation of MA to GBL at atmospheric pressure were investigated. The residual Na+and H2O in the catalyst precursor are disadvantageous to the catalytic performance and stability of CCA catalyst. The presence of Na+as Na2CO3in CCA catalyst resulted in a decrease in the dispersion of CuO, growing up of CeO2crystallite size, coverage of the catalyst surface and plugging of the catalyst pores, and hence decreases in SBET, Scu and Cu dispersion, and CuO difficulty to reduce. The effect of residual H2O in the catalyst precursor on the physiochemical properties of CCA catalyst were attributed to the destructive hard agglomeration or sintering of CCA catalyst in the course of drying and calcination, which lead to decreases in SBET, SCu and Cu dispersion.