Investigation Of Single-event Micro-Kinetic Modeling For Ethene Oligomerization To Gasoline Components Process

The process of converting small molecular olefins into hydrocarbons with a relatively large molecular weight through the oligomerization reaction is an extension of the domestic coal and methanol to olefins industry.The oligomerization reaction results in a high purity of gasoline components compared to the liquid obtained from direct crude oil refining.The fuel contains a large amount of nitrogen and sulfur-containing impurities,and has a high degree of cleanliness as a fuel.The process of developing olefin oligomerization into gasoline components is of great significance for improving the international competitiveness and resource utilization of liquid fuel energy alternative technologies in China,and for the development of coal-to-gasoline new coal chemical industry.The study of the oligomerization mechanism and kinetics of low-carbon olefins is an important theoretical and practical basis for optimizing the process conditions of olefin oligomerization,the development and design of industrial reactors,and the development and design of catalysts.The process belongs to hydrocarbon complex reaction system,and it is difficult to solve the problem using traditional kinetic theory research methods.The single event micro-kinetic concept could greatly reduce the number of parameters of the intrinsic kinetic equation of the complex reaction system.At the same time,the kinetic equation retained detailed information of the reaction network,to ensurethat the kinetic parameters involved do not change with the feed composition of the reaction system and is the recognized frontier field for solving the kinetic of complex reaction systems in the petrochemical process.In this work,the process of synthesis of gasoline components by ZSM-5molecular sieve catalyst was studied by means of single event micro-kinetic.A continuous flow fixed bed constant temperature reactor was used to study the interchanges of olefins at a temperature range of 350⁴50℃,and an empty time range of 4.15¹8.67 gcat·h/mol Ethene,with nitrogen as the carrier gas mixture.The catalyst was calcined,pressed,ground and then sieved to 60-80 mesh to avoid heat transfer and eliminate the influence of internal diffusion.The catalyst was placed in the constant temperature section of the reactor and filled with quartz sand up and down to make the reactor flow into a plug flow with a reaction pressure of 1 bar and an ethylene partial pressure of 0.2 bar.After qualitative analysis of the product by gas chromatography-mass spectrometry（GC-MS）,the peak sequence of the product was determined and the product was analyzed online by gas chromatography（GC）.With the method of the Back-lumped product being collected aggregate,the product was assembled into a packet 13 Back-lumped:methane,ethane,propane,propylene,butene,cyclopentene,pentene,benzene,cyclohexene,Hexene,toluene,1-methylcyclohexene,xylene.A set of data was selected from the collected experimental data to test the carbon balance.The test results showed that the experimental carbon balance fit well during the reaction.The establishment of the reaction network and the calculation of the corresponding thermodynamic parameters were realized by computer algorithm.For an olefin oligomerization process with a maximum carbon number of 8 and considering every possible type of elementary step of carbenium ion chemistry,about 3000 hydrocarbon molecules/ions are generated,When the total carbon number in the reaction network is up to 8,there were 3,059hydrocarbons involved,and there were 10,669 elementary steps involved.The transition theory and the thermodynamic constraints between elementary steps were applied to construct the rate equation.The kinetic parameters of ethylene oligomerization kinetics were simplified by the single event method.By comparing the computational efficiency of different algorithms,it is found that hybrid genetic algorithm is more effective and reliable in finding the global optimal solution than the pure genetic algorithm in parameter estimation process.The penalty function method is used to limit the physical and chemical relations of the parameters,so that the calculated parameters are satisfied with the corresponding physical and chemical constraints.In the course of gradually expanding the C₁-C₅ olefin oligomerization reaction model to the C₁-C₈ olefin oligomerization reaction model,the reaction kinetics model was discussed and analyzed through experimental results,fitting results and reaction mechanisms.The result is as follows::It was found that the protonation heat of the reaction subtypes involved in the reaction is divided into three types according to the types of carbenium ion involved;There are three kinds ofβ-scission involved in the reaction:aliphatic,exocyclic and endocyclicβ-scission,and all are completely different reactions,so the correspondingβ-scission frequency factor also needs to be treated as different parameters;In the ethylene oligomerization reaction,there is no hydride transfer elementary step between the carbenium ion and the aromatic hydrocarbon,so the elementary step need not be considered in the entire reaction network;In ethylene-based reactions,the first ethylene reaction should be ethylene dimerization,which needs to be considered in the reaction network.Through the corresponding test（F,t test）of the improved model parameters,the applicability of the model and the reliability of the parameter fitting results are judged.The calculated results showed that the obtained kinetic model can predict the results of oligomerization of C₁-C₈ olefins on the catalyst well under the conditions of reaction temperatures of 350,400,and 450℃,a reaction pressure of 1 bar,and reaction space time of 4.15,5.33,7.47,12.44,18.67 gcat·h/mol ethene.By comparing the calculated parameters of the model,it is found that the variation law of the experimental products is consistent with the model calculation result,and the reliability of the model is verified again.This result can provide reference for further extrapolation to the calculation of kinetic parameters of model compounds with high carbon number.