The Calculation Of The Feature Size Of Petroleum Model Compounds And The Calculation Of Diffusion Behavior

The depletion of conventional oil and the urgent demand for energy have promoted the development and utilization of heavy oil.The catalytic conversion of heavy oil has become an important issue for major oil companies.It is well known that diffusion and mass transfer of heavy oil molecules in catalysts have significant effect on the reactions.At present,three experimental methods are mainly used in the study of the diffusion of heavy oil: diaphragm cell,adsorption diffusion and reaction kinetics.The process is not only time-consuming and laborious,but the results of different methods are controversial.In this dissertation,the diffusion process of model compounds was studied in detail using computer simulation methods,and the diffusion of model compounds in the pore channel is obtained by comparison with results of diaphragm cell experiment.In this study,the following three aspects are mainly carried out: Selecting four types of model compound molecules with different structures,and performing configuration optimization and size calculation;using Performing the simulation calculation of free diffusion of four types of model compound in toluene solution;Performing the simulation of the hindrance diffusion of the toluene solution of the four types of model compounds in the 3 nm channel.In this dissertation,we calculated the size of various model compounds and compared with the results by the diffusion experiments.We found that the calculation result of the equivalent sphere size is consistent with the experimental results.Therefore,for the model compounds of different configurations,the equivalent sphere size is most accurately used to describe their diffusion in the channel.In this dissertation,the model compounds were divided into four groups according to the configuration.The free diffusion coefficients of various types of molecules were calculated and corrected according to different molecular configurations.The relative error between the simulation results and the experimental values was less than 10%.It shows that the molecular simulation method is not only suitable for the diffusion simulation of small molecules,but also has certain reliability for the study of the diffusion coefficient of macromolecules.For the study of restrictive diffusion in the pore,we construct the molecular diffusion model.According to the experimental diffusion results of the model compound in the 15 nm channel and the 200 nm channel,we obtained the diffusion coefficient at 3 nm pore size by extrapolation,and compared with the simulation results.The results shows that the diffusion coefficient will reduces with the aperture decrease.The simulation results are basically consistent with the experimental results.Therefore,in this dissertation,the diffusion behavior of macromolecule organics in pores was explored using simulation methods.The free diffusion coefficient of the compound and the effective diffusion coefficient in the 3 nm pore channel were obtained for the heavy oil molecules in the microspores.The in-depth study of blocked diffusion provides new means.