Simulation Studies On The Separation And Purification Of Cracked Gas In The Partial Oxidation Of Natural Gas To Acetylene Process

Natural gas,mainly composed of methane,is an important part of the world’s energy supply and has been playing an increasingly important role as a chemical feedstock in recent years.There are various ways to process and utilize natural gas as a chemical feedstock,and one of the important ways is partial oxidation to produce acetylene.However,the partial oxidation of natural gas to acetylene has a high reaction temperature and very short reaction time,and while acetylene is produced by this method,the cracked gas also contains by-products such as synthesis gas,ethylene,and higher alkyne.To obtain products with application or commercial value such as acetylene and hydrogen from the gas mixture,separation operations must be performed.The process of separation and purification of products usually requires a large amount of energy,which is a major obstacle to energy saving and economic feasibility of the process.Therefore,it is of great practical importance to study the separation and purification of products and to obtain optimized process parameters for separation and purification.Industrial-scale experiments are labor-intensive and almost difficult to conduct;due to the amplification effect,the results of laboratory or pilot tests have limited guidance when applied to the plant.At the same time,the macroscopic information usually obtained from experiments cannot provide a microscopic understanding of the separation and purification process,and cannot provide effective guidance for solvent preferences and method improvements.In this paper,the separation and purification of the main product acetylene and the separation and purification of the by-product syngas by pressure swing adsorption in the process of partial oxidation of natural gas to produce acetylene are investigated by density function theory（DFT）calculations、molecular dynamics（MD）simulations and computational fluid dynamics（CFD）simulations.The main research contents and conclusions are as follows:（1）Theoretical studies on the separation and purification of acetylene in the partial oxidation of natural gas to acetyleneIn this study,the absorption ability of 1-methyl-2-pyrrolidone（NMP）to ethylene,acetylene and butadiyne and the ability to separate acetylene from ethylene or butadiyne were investigated by DFT calculation and MD simulation system.DFT calculations show that each gas molecule can easily form hydrogen bonds with NMP and H₂O,and the order of the strength of the generated hydrogen bonds is C₄H₂>C₂H₂>C₂H₄.MD simulations show that the viscosity of the NMP solution gradually decreases with increasing temperature,while the self-diffusion coefficient gradually increases.The calculation results show that the optimum water content for separating the C₂H₂/C₄H₂ gas group（3:1）lies around 18%;the separation efficiency reaches the highest at a temperature of 338 K.The results also show that the gas will form a gas film on the solvent surface first when diffusing into the NMP solvent,and the rate of gas film formation is much higher for the more soluble gases than for the less soluble gases.These results are in good agreement with the process parameters of industrial production and deepen the understanding of the separation and purification of cracked gas.（2）Simulation study on the separation and purification of syngas in the partial oxidation of natural gas to acetylene processThe linear driving force（LDF）equation and Langmuir-Freundlich equation were used as the adsorption driving force equation and adsorption equilibrium equation of the pressure swing adsorption process to establish a two-dimensional adsorption bed model respectively,and the computational fluid dynamics software FLUENT was used to numerically simulate the common four-step pressure swing adsorption of syngas to hydrogen production process,analyze the gas and temperature changes in the bed during the pressure swing adsorption cycle,and explore the intrinsic mechanism of pressure swing adsorption.The simulation results show that the adsorption process can be carried out at lower pressure.The simulation results show that the breakthrough point can still occur at low pressure（6 atm）for about 900 s,which indicates the validity of the adsorbent and adsorption model.In the simulation,the purity of hydrogen obtained from the adsorption step in one pressure swing adsorption cycle is high and can reach 99%.During the pressure swing adsorption process,the hydrogen concentration varies little,but the temperature varies outstanding.During adsorption,the head temperature is 360 K and the tail temperature is 365 K.During desorption,the head temperature is 280 K and the tail temperature is 150 K.The simulation results show that increasing the temperature and lengthening the adsorption time can improve the purity and yield of hydrogen,but its recovery rate will be reduced;increasing the adsorption pressure can increase the recovery rate of hydrogen,but its yield will be decrease.In summary,a computational study of the absorption separation of acetylene from cracked gas was carried out to obtain optimized parameters,and simulations of the pressure swing adsorption process was carried out to optimize the parameters of the pressure swing adsorption process.These results deepen the understanding of the gas separation section of the partial oxidation of natural gas to acetylene and provide a reference for enterprises to optimize the process parameters.