Design And Simulation Of Reaction-Separation Coupling Process For Ethylene Trimerization

Linear alpha-olefins（LAOs）are important chemical intermediates and can be used as copolymer monomers for high density polyethylene and linear low density polyethylene,as well as for the synthesis of surfactants,lubricant base oils,additives for lubricants,etc.Among them,1-hexene is the fastest growing demand among these copolymer monomers,and the linear low density polyethylene produced with it has the advantages of high strength,good toughness,rigidity,heat and cold resistance.The conventional non-selective ethylene oligomerization method yields alpha-olefins with a wide carbon number distribution and low 1-hexene content.The selective ethylene trimerization provides a new route for the production of 1-hexene,with the advantages of higher selectivity of 1-hexene,higher catalytic activity,simple process flow and easy operation of the whole plant.However,the selective ethylene trimerization process is accompanied by a number of side reactions,generating a small amount of ethylene polymer,which makes it difficult to handle the resulting polymer and makes the removal of reaction heat more difficult.This paper addresses these issues by designing a new ethylene trimer reaction separation coupling process and simulating it using Aspen Plus process simulation software.The main findings are as follows:（1）The binary interaction parameters of each component of the system were determined by fitting the open experimental data in NIST database;The vapor-liquid equilibrium between the solvent and the product involved in the ethylene trimerization system was calculated by PENG-ROB equation of state.Under the condition of 5 MPa and 120℃,the solvent and 1hexene with a certain molar fraction in the vapor phase could be partially condensed after vapor phase heat exchange,which was beneficial to remove the oligomerization heat by condensation heat and partially separate 1-hexene.The concentration of ethylene in pentane,cyclopentane and cyclohexane solvents is higher,which is more favorable for ethylene trimerization from the perspective of reaction kinetics.（2）According to the literature data,the reaction kinetics equation for the simulation of ethylene trimerization process was determined:K₁=5.19×10⁹e-91.78/RT,K₂=2.48×10⁸e-89.1/RT（3）According to the characteristics of ethylene trimerization,a tower process of ethylene trimerization separation and coupling to produce 1-hexene was designed.The process has the advantages of improving the mass transfer efficiency of ethylene trimerization process,using the solvent and partial condensation of 1-hexene to remove the reaction heat,the heat exchange coil will not have polymer adhesion,and 1-hexene can be separated in the reaction unit part.（4）Using Aspen Plus chemical process simulation software to simulate and optimize the coupling process of ethylene trimerization reaction separation,the influences of plate number,ethylene feed amount,inter-stage condensation temperature,reaction temperature and reaction pressure on the process were investigated,and the most suitable operating conditions were determined as follows:The number of trays is 3,the ethylene feed amount is 350 Kg/h,and the condensation temperature between stages is 55℃,The optimum reaction temperature is 95℃ and the optimum reaction pressure is 5 MPa.The traditional continuous ethylene trimerization production process was compared with the new reaction separation and coupling process.It is found that the new process increased the yield of 1-hexene by 11.3%and the selectivity of 1-hexene by 2%compared with the traditional process under the same dynamic parameters and operating parameters.