Exhaust Gas Recovery Technology Of Butane Oxidation To MA Process And Side-Stream Test Of VPO Catalyst

Maleic anhydride(MA)is produced commercially from n-butane oxidation because of its light environmental pollution and low raw material costs.MA yield is 53 mol%-65 mol%,which is far from being optimised.So improvements in the yield of MA have been the focus of scholars.In this paper,exhaust gas recovery technology was put forward to improve MA yield.In addition,China has no ability to produce industrial VPO catalyst.So there is an urgent need to develop domestic VPO catalyst,which is of great significance to China.VPO catalyst developed by Sinopec was tested in the industrial side-stream unit.In this paper,to improve MA yield and develop domestic VPO catalyst,the main research work as follows:(1)The effect of exhaust gas composition on n-butane oxidation reaction was studied in the industrial single-tube reactor with molten salt heating system.With the decrease of oxygen concentration,n-butane conversion rate decreases and MA selectivity increases.The lower oxygen concentration,the higher molten salt temperature in which MA yield is the highest.Increasing CO2 concentration can improve MA selectivity,which is mainly because CO2 atmosphere reduces the number of nonselective V3+ species on catalyst surface,thus decreasing the decomposition rate of MA.CO atmosphere has no effect on VPO catalyst.The influence of the amount of exhaust gas recovery on the lower explosion limit of n-butane mixture was studied by Le Chatelier’s Principle.It’s found that the lower explosion limit of n-butane mixture is gradually increased with the amount of exhaust gas recovery.(2)A high-throughput exhaust gas recovery technology is proposed for MA production unit with air as oxidant and high butane conversion rate,and the amount of exhaust gas recovery depends on the sensitivity of the catalyst to temperature.This exhaust gas recovery technology was applied to MA plant with capacity of 80 kilo ton annual.The deacidification process of exhaust gas was designed and two schemes were proposed.The exhaust gas recovery process was simulated by Aspen Plus V8.6.Simulation result shows that this recovery technology significantly reduces n-butane consumption per ton MA and MA yield increases from 56.0 mol%to 59.5 mol%,which saves raw material’s cost of annual 35.88 million and reduces annual 16.75 million tons CO2 emissions.(3)The composition,morphology and active site of three industrail catalysts were characterized by XRD,FT-IR,XRF,SEM,BET,Raman,H2-TPR and XPS,and their catalytic performance was studied in the exhaust gas recovery process.The effect of P/V and V5+ species on catalyst performance was discussed.By correlating catalytic performance with characterization results,it is concluded that VPO catalyst has following structural characteristics to better match exhaust gas recovery process:firstly,catalyst surface should has low P/V;secondly,catalyst surface should have isolated V5+ species.(4)The process and device of side-stream test were designed.Start-up scheme of side-stream test and regulatory means of catalyst activity were also established.The industrial side-stream test of VPO catalyst was carried out.At present,the side-stream test has stably run for 1925 h.Run result shows that side-stream process,start-up program and controlling scheme are reasonable.The induction period of VPO catalyst was studied,and it was found that the activity of VPO catalyst activated in air/N2/H2O mixed atmosphere decreases and MA selectivtiy increases with time during the induction period,which is due to structural rearrangement of V-P mica phase and gradual reduction of V5+ species.