Thermodynamic Basis And Kinetics Mechanical Optimization Of Natural Gas Components Separation And The Related Pilot-Scale Test Study

Natural gas is a strategically important low-carbon fossil energy source and an important petrochemical material.In addition to the methane component that with high calorific value,natural gas contains about 10 mol%of C₂₊components.These C₂₊components have a high downstream industrial feedstock value.Therefore,the separation and recovery of C₂₊high-value fractions from natural gas is of great economic and strategic importance.This paper focuses on the separation of pentane isomers based on the kinetic differences,and the recovery and purification of C₂₊components from natural gas using ZIF-8 slurry.A series of optimizations based on thermodynamics and kinetics separation mechanism were carried out to verify the feasibility and superiority of the slurry method and to systematically optimize the operating conditions.Then the feasibility of practical industrial application of slurry method was evaluated by the pilot tests.The main studies are as follows:（1）The separation of pentane isomers based on the kinetic sorption differences was developed.The study was centered on the difference in n-and iso-pentane sorption speed in ZIF-8/1,3-dimethylpropyleneurea（DMPU）slurry and ZIF-8/water slurry.It was found that the formulation of ZIF-8/DMPU-water composite solvent slurry could effectively improve the separation performance of the slurry for the pentane isomers,and simultaneously maintain a high kinetic sorption performance.Furthermore,the slurry exhibits an excellent renewability in the regenerative performance examination,and the characteristic structure of ZIF-8 remains intact after reuse for over 10 times.The absorption and adsorption process of pentane isomers in different ZIF-8 slurry was restored from a microscopic molecular simulation perspective.The absorption characteristics of different ZIF-8 slurries for n-and isopentane were analyzed from a microscopic point of view,and the reasons for the kinetic sorption differences in different ZIF-8 slurries were explained.（2）The recovery and purification of the C₂₊component from natural gas were systematically investigated.The single-component sorption characteristics of natural gas components in two slurry systems,ZIF-8/DMPU and ZIF-8/iso-hexadecane,were studied.The separation and purification of the C₂₊components of natural gas by a thermodynamic equilibrium mechanism in the absence of kinetic sorption differences.It was found that the C₂H₆ sorption speed in ZIF-8/iso-hexadecane slurry was more than doubled and the viscosity of the slurry was significantly reduced compared to that in ZIF-8/DMPU slurry.The sorption isotherms of CH₄,C₂H₆ and C₃H₈ in ZIF-8/iso-hexadecane slurry were measured and the corresponding desorption heat was calculated accordingly.Under the optimal conditions,the slurry could recover up to 91.59%of the C₂₊fraction from natural gas.And it showed excellent desorption kinetics during the regeneration process.（3）Based on the recovery and purification of C₂₊fraction from natural gas in the previous section,studies on capturing NMHCs from oilfield exhaust were investigated systematically.The stability and durability of the ZIF-8 in slurry under acidic conditions containing CO₂ and water were tested.The feasibility of the study was evaluated by comparing the sorption capacity of the main components of the exhaust gas N₂,CH_4,and C₂H₆.The capture of C₂H₆,C₃H₈,and n-C₄H₁₀ was achieved to a ppm level in the capture experiment for NMHCs.The stability and durability of ZIF-8 in an aqueous and acidic environment were investigated.And it was found that the characteristic structure of ZIF-8 could be protected by retaining a small amount of 2-methylimidazole in the synthesis of ZIF-8 material.（4）The study on the kinetic breakthrough tests of the two mixed gas systems,natural gas and exhaust gas containing NMHCs,was carried out.The effects of temperature,pressure and feed gas flow rate on breakthrough results were systematically examined.The results showed that both mixture systems exhibited excellent dynamic breakthrough effect in ZIF-8/iso-hexadecane slurry,further verifying the excellent kinetic separation properties of the slurry.The effects of temperature,pressure and feed gas flow rate on the experimental results were also revealed,laying a foundation for the subsequent pilot tests.（5）The pilot-scale tests on the recovery and purification of C₂₊components from natural gas were carried out.And the separation effects of ZIF-8/DMPU slurry and ZIF-8/iso-hexadecane slurry in pilot-scale were systematically evaluated,respectively.According to the rules of the laboratory-scale tests and breakthrough tests,under the optimal conditions,the overall recoveries of the C₂₊components can reach 55.55%and86.75%,respectively,and the concentrations of the C₂₊components in the product gas can reach nearly 60 mol%and 75.61 mol%,respectively.