Research On The Effect Of Different Feedstocks On Olefin Metathesis

Propylene is a very important basic material in the chemical industry.It can be used to produce a variety of important downstream chemicals,such as polypropylene,acrylonitrile,and propylene oxide.In recent years,China’s demand for propylene has expanded year after year,making the technology used for propylene production increasingly favored.Olefin metathesis technology can be complementary to other propylene production enhancement technologies except the propane dehydrogenation process.Olefin metathesis technology can effectively use butene resources,and flexibly adjust the output ratio according to market demand,which has considerable advantages.Among them,the OCT technology using WO3/SiO2 and MgO catalysts is the only technology to achieve industrialization.The preparation of WO3/SiO2 catalyst and the conditions for olefin metathesis reactions has been studied before by our laboratory.Based on this,the effect of composition of feedstock on olefin metathesis reactions has been explored in this thesis to meet the needs in the industry.First,the effect of impurities(H2 and CO2)in the ethylene feedstock on the reaction of ethylene and 1-butene were explored.By studying the reactions with H2 content of 0,1000ppm,1500ppm and 2000ppm,it was found that all three levels of H2 had a promoting effect on the reaction,which can shorten the reaction induction period and enhance the stability of the reaction.After that,the reactions with CO2 content of 0,100ppm and 1500ppm were explored.It was found that the presence of CO2 significantly reduced the life of the catalyst.And the more its content,the faster the catalyst deactivation.Second,the process conditions of the reaction of dilute ethylene and mixed C4 were explored.In the reaction of 60vol%dilute ethylene and mixed C4,by exploring the effects of three heavy hourly space velocities(all calculated as n-butene)of 4h-1,2h-1 and 1.5h-1,it was found that the best space velocity was 2h-1.By exploring the effect of the three feed ratios of ethylene to n-butene of 1:1,2:1 and 3:1,it was found that the best feed molar ratio was ethylene:n-butene=2:1.By exploring the influence of three pressures of 2.5MPa,2.0MPa and 1.5MPa,it was found that the best reaction pressure is 2.0MPa.In the reaction of 40vol%dilute ethylene and mixed C4,by exploring the influence of the reaction pressure of 2.5MPa and 2.0MPa,it was found that the reaction was significantly affected by the pressure.Increasing the pressure can improve the conversion of n-butene.Third,the effect of isobutene on the metathesis reaction was studied.The effects of isobutene on 1-butene self-metathesis reaction or 1-butene and ethylene cross-metathesis reaction were explored.Isobutene and 1-butene were fed at the same time.The molar ratio of the two is isobutene:1-butene=2:8.The results showed that isobutene can easily produce heavy components in the reaction,and even polymerize itself to produce oil phase products.Overall,isobutene has no positive contribution to the metathesis reaction.In the end,a preliminary investigation of the catalyst regeneration process was conducted from the perspective of the regeneration gas atmosphere.It was found that the regeneration methods of pure nitrogen and pure air atmosphere had no obvious effect.Then the regeneration effect of the mixed gas of nitrogen and air was investigated.And the air mole fractions of 3%,6%and 21%were explored.The results showed that only an air content of 6%could regenerate the catalyst,but it did not completely restore the activity of the catalyst.