Dynamic Kinetics And Reaction Network Of N-Butane Selective Oxidation To MA

Up to date, the partial oxidation of n-butane to Maleic Anhydride (MA) over vanadium phosphorus oxide (VPO) catalyst is still an unique alkane selective oxidation reaction industrialized. It is an important one of hydrocarbon selective oxidation reactions over composite metal oxide catalyst and proceeds according to the REDOX mechanism with the participation of lattice oxygen of the catalyst. It is generally accepted that only surface lattice oxygen is responsible for selective reaction, while gas phase and adsorbed oxygen provides for complete oxidation of the hydrocarbon to COX and H2O.In general, oxidation processes of hydrocarbon can be made more environmentally benign by improving selectivity and decreasing the amount of byproducts and excess heat. Strategies for improving selectivity have traditionally focused on developing new catalytic materials or reducing product loss by improving heat removal. Another approach, which is considered in this work, is to organize catalytic cycle effectively by utilizing unsteady state operation. That is, splitting up of the overall reaction in space or time domain to two steps, hydrocarbon selective oxidation and re-oxidation of catalyst reduced, and matching each step with suitable reaction conditions. It's significative for both economic profit and environment protection.This dissertation concerns with the reaction of n-butane selective oxidation to Maleic Anhydride (MA) over a commercial VPO catalyst. The structure of reaction network of n-butane selective oxidation to Maleic Anhydride (MA) was systematically probed by in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). The effects of re-oxidation conditions of the VPO catalyst on n-butane selective oxidation and the roles of adsorbed oxygen and lattice oxygenon the surface of the VPO catalyst for n-butane selective oxidation were experimentally studied and identified using on-line mass spectroscopy (MS) transient response measurements in a fixed bed micro-reactor. Re-oxidation of the VPO catalyst was investigated by temperature programmed oxidation (TPO) and by weight gain measurement in a TGA unit. The re-oxidation kinetic parameters of the catalyst were estimated and the mechanism of the reaction-diffusion process was deduced. A transient kinetic model taking account of the oxygen storage and diffusion in the bulk-phase of the VPO catalyst was introduced and its parameters were estimated. The model was examined with the data obtained in previous transient response experimental and time-average concentrations of butane and Maleic Anhydride under forced unsteady state operation.At first, the experimental setup was built for in situ steady-state and transient diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) measurement. Based on IR observations of three C4 hydrocarbons (n-butane, 1-butene and 1,3-butadiene) over the VPO catalyst placed in High Temperature/High Pressure (HTHP) chamber, The structure of reaction network of n-butane selective oxidation to Maleic Anhydride was systematically probed.Under steady-state conditions, gaseous n-butane, 1-butene and 1,3-butadiene react with oxygen species on the surface of the VPO catalyst according to Rideal mechanism. They react directly with the oxygen species on the catalyst surface, without a proceeding adsorption step. Adsorbed selective oxidation products (MA) and combustion products (CO, CO2 and H2O) could be confirmed on the catalyst surfaces. In addition, 1-butene, 1,3-butadiene and maleic acid adsorbed were detected as surface intermediates in n-butane selective oxidation.Under transient conditions, unsaturated and saturated noncyclic carbonyl species were determined to be intermediates in n-butane selective oxidation to MA. Furan was detected on the surface of the VPO catalyst in 1-butene, 1,3-butadiene selectiveoxidation. It was deduced that furan ring was cleavaged to form unsaturatednoncyclic carbonyl species before conversion of furan to MA. Based on these results and in comparison with the literat...