| Using propane instead of propylene to produce acrylonitrile by ammoxidation is of great significance for the efficient and reasonable utilization of light alkanes resources,which is one of the hot topics in the field of hydrocarbon conversion and utilization.This dissertation firstly presents an overview of acrylonitrile production technology at home and abroad,the process characteristics of ammonia oxidation of propane to acrylonitrile are analyzed.The reaction networks of ammonia oxidation of propane to acrylonitrile are introduced in detail.The reaction processes are simulated by Matlab software based on the current existing kinetics of propylene ammoxidation to acrylonitrile,the main research contents and results are as follows:There are five kinds of substances and ten reactions in the reaction network proposed by Hou etal,including propane,propylene,acrylonitrile,acetonitrile and COx.Based on the propane ammoxidation reaction kinetics data obtained over V-Sb-O catalyst,the product concentration distribution exhibits the characteristics of cascade reaction accrroding to the Matlab simulation under 500 ?.The concentration of propane and COx shows a monotone increasing or a decresing property,there are an optimum reaction concentration for the intermediate products of propylene,acrylonitrile and acetonitrile.In the initial stage of the reaction,the yield of propylene has a maximum of 0.8992,and the net production rate of propylene increases very fast,while the yield of acrylonitrile is only 0.0374 and the yield of acetonitrile is only 0.0614.The yield of propylene in the catalyst bed quickly decreases,and the yield of acrylonitrile and acetonitrile can reach 0.0890 and 0.3740 respectively.Besides,it can be known that the ethylene transformation to acrylonitrile has obvious advantage based on the content distribution of acetonitrile and acrylonitrile.The simulation reslut shows that the increasing reaction temperature can increase the outlet conversion rate of propane and improve the inlet instantaneous yield of acrylonitrile.Overall,however,the increase of reation temperature is not conducive to the yield of acrylonitrile;the maximum yield of acrylonitrile at 470 0C is 0.4185,only 0.3300 under 530 ?,which decreases nearly 21.1%.But the yield of acetonitrile is opposite to that of acrylonitrile,the maximum yield of acrylonitrile at 470 ?is 0.0627,but 0.1210 under 530 ?,which increases nearly 90.3%.It is closely related to the reaction rate constants of ethylene tranformation to acrylonitrile and acetonitrile at different temperatures,the ratio of reaction rate constant for acrylonitrile and acetonitrile is 0.0627 under 470 ?;the ratios are 8.30and 6.86 under 485 ? ? 500 ?.However,the effect of reactant concentration on the product distribution can not be studied for based on the reaction kinetics proposed by Hou etal.There are seven kinds of substances and fourteen reactions in the reaction network proposed by Catani etal,including propane,propylene,acrylonitrile,acetonitrile,formonitrile,C2 and COx.Based on the propane ammoxidation reaction kinetics data obtained over V-Sb-Al catalyst,the product concentration distribution exhibits the characteristics of cascade reaction too accrroding to the Matlab simulation under 500 ?.The concentration of propane,HN3 and O2 shows a monotone decresing and that of COx shows an increasing property,there is an optimum reaction concentration for the intermediate products of propylene,acrylonitrile,acetonitrile and C2.In the initial stage of the reaction,the yield of propylene has a maximum of 0.7876.The yield of propylene in the catalyst bed quickly decreases,while the yield of acrylonitrile and acetonitrile can reach a maximum of 0.0158 and 0.7668 respectively.Besides,ethylene transformation to acrylonitrile has obvious advantage too based on the content distribution of acetonitrile and acrylonitrile.In addation,the simulation reslut shows that the increasing reaction temperature can increase the outlet conversion rate of propane and improve the inlet instantaneous yield of acrylonitrile.Overall,the increase of reation temperature is conducive to the yield of acrylonitrile.The maximum yield of acrylonitrile at 470 ? is 0.7416,it can reach 0.7871 under 530 ?.Meanwhile,the yield of acetonitrile and hydrocyanic acid decrease with the increase of reaction temperature,the maximum yiled of of acetonitrile and hydrocyanic acid are 0.0213and 0.0708 under 470 ?,which decrease to 0.0120and 0.0444 under 530 ?.The above phenomenon is related to the relative reaction rate constant of acrylonitrile,acetonitrile,hydrocyanic acid from propylene and propane under different temperatures.Finally,the effect of reactant concentration on the product distribution is investigated based on the reaction kinetics proposed by Catani etal.Based on the above the dynamics,acrylonitrile generated from ethylene occupies obvious advantages,which shows the good feasibility for the acrylonitrile production using propane ammoxidation method.The simulation result exhihts the concentration of ammonia and oxygen has a significant influence on the distribution of the product.Improving the propane conversion rate and the product concentration distribution can be achieved by regulation the import concentration of ammonia and oxygen.The propane conversion rate can be improved by increasing the the import concentration of ammonia,but exsits the best feed concentration.The conversion rate of propane can reach 91.94%when the concentration of ammonia is 2.21×10-3 mol/L.Besides,there is an optimum concentration of ammonia for the yields of propylene and acrylonitrile.The yields of acetonitrile and hydrocyanic acid obviously effects by the concentration of ammonia,the instantaneous yields of acetonitrile and hydrocyanic acid increases from 0.0050 and 0.0172 to 0.0285 and 0.1234 when the concentration of ammonia changes from 0.21 ×10-3 mol/L to 5.21 ×10-3 mol/L,they increase 4.7 and 6.3 times respectively.However,the concentration of ammonia has little effect on the yield of C2 component.The propane conversion rate can be improved by increasing the the import concentration of oxygen,but the increasment is not obviously when the concentration of oxygen is at a high level.Oxygen feeding concentration is not good for improvement the yields of propylene and acrylonitrile,which are 0.8071 and 0.7868 under 0.92×10-3 mol/L of Oxygen concentration,however decreases to 0.7287 and 0.7375 under 5.92×10-3 mol/L of Oxygen concentration.Besides,the yields of acetonitrile,hydrocyanic acid and C2 component obviously effects by the concentration of oxygen,the instantaneous yields of acetonitrile,hydrocyanic acid and C2 component increases from 0.0091,0.0335 and 0.0033 to 0.0217,0.0925 and 0.0092 when the concentration of oxygen changes from 0.92×10-3 mol/L to 5.92×10-3 mol/L,they increase 1.4,1.8 and 1.8 times respectively. |
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