High-throughput Screening And Pressure Swing Adsorption Process Simulation Of Cofs For CO₂ Capture In Humid Environments

CO₂ is one of the main greenhouse gases.Excessive CO₂ emissions from the combustion of fossil fuels have caused a series of environmental problems.The post-combustion carbon capture technology is currently the most economically feasible CO₂ capture technology.However,the water vapor in the flue gas have a negative impact on CO₂ adsorption.Covalent organic frameworks（COFs）have been widely used in the field of gas storage and separation due to their low framework density,large specific surface area,stable and adjustable structure,and are also potential materials for efficiently capturing CO₂ in humid environments.Molecular simulation method is a commonly used research method in the field of materials chemistry,and its systematic analysis can provide guidance for experiments and accelerate the process of experiments.Pressure swing adsorption（PSA）is an important method of gas separation,and it is commonly used for post-combustion CO₂ capture.Process simulation of PSA can reduce the costs for actual process design.Combining molecular simulation methods and chemical unit process simulation,high-throughput screening and PSA process simulation for CO₂/H2O separation applications were carried out on 517 COFs that have been reported.The main research work is outlined below:（1）Under the condition of 298K and relative humidity（RH）of 40%,using molecular simulation method,14 high-performance COFs with CO₂ working capacity>0.3 mol/kg and CO₂/H2O selectivity>7 were screened out.The structure-activity analysis shows that CO₂/H2O separation performance of COFs is excellent in the range of 0.3～1.6 cm3/g for Vpore and 9～20 ? for LCD.Further research shows that the change of water content has little effect on the CO₂ adsorption of high-performance COFs.（2）Adopting the ideal mathematical model of equilibrium adsorption and isothermal,design transient breakthrough simulation with Top 14 COFs as the adsorbent.By comparing the breakthrough curves,the material with the best dynamic adsorption performance was screened out to be TpOMe-Pal.Based on the separation of CO₂/H2O by TpOMe-Pal,a single-tower four-step PSA process and a dual-tower six-step PSA process were designed.Use purity and recovery rate of CO₂ as evaluation indicators to optimize operating parameters.The optimization results of single-tower PSA process are:the adsorption time is 150 s,the desorption pressure is 0.015 bar,the purity of CO₂ is 98.88%,and the recovery rate of CO₂ is 95.11%,which meets the requirements of CCS.Substituting the optimized parameters into the dual-tower PSA process,the optimization results of dual-tower are:the tower top outlet flow rate is 4E-06 kmol/s,the adsorption time is 150 s,the pressure rise and fall time is 176 s,the pressure equalization time is 200 s,the purity of CO₂ is 99.39%,the recovery rate of CO₂ is 96.78%.The CO₂ capture effect of dual-tower PSA process is better than that of a single tower.（3）Adopting the LDF-mass transfer and non-isothermal complex mathematical model,design the breakthroough experiment.By comparing the breakthrough curve of the complex mathematical model with the breakthrough curve of the ideal mathematical model,it is found that the breakthrough curve of the complex model that considers mass transfer and heat transfer is smoother and closer to the actual situation.Design a four-tower eight-step PSA process,and optimize the operating parameters with CO₂ purity,recovery rate and productivity as evaluation indicators.After optimization,when the single cycle time is 520 s,tRp/tAD=110 s/20 s,and the end pressure of the average pressure drop stage is between 0.125 bar and 0.145 bar,the CO₂ in the product gas satisfies:99.8%<Purity≦ 99.97%,95.5%<Recovery≦ 96.7%,0.869 mol/（kg·h）<Productivity≦ 1 mol/（kg·h）.