Multiscale Simulation And Screening Of IL@MOF Materials For Gas Desulfurization And Decarbonization

Coke oven gas(COG)is one of the most important by-products in the coking process.The reasonable recovery and utilization of COG have important economic value and strategic significance.As cleaner energy with high combustion calorific value,natural gas(NG)has become the third-largest energy source in the world.However,before using these two gases,desulfurization and decarbonization must be carried out to avoid serious problems such as environmental pollution,safety accidents,or equipment corrosion.Considering the stringent environmental protection policies and clean production standards,traditional gas purification technologies cannot meet the needs of actual production,and it is urgent to find new alternatives.In recent years,ionic liquids(ILs)have been considered as ideal solvents for gas purification due to their extremely low saturated vapor pressure,high chemical stability,low toxicity,and tunable structure.In addition,metal-organic frameworks(MOFs)also show great potential in the field of gas adsorption and separation for their high specific surface area,high pore volume,and tunable pore structure.Since both ILs and MOFs have massive structural databases,designing or screening specific structures for gas purification is a significant and long-term research topic.In this paper,the desulfurization and decarbonization performance of ILs for coke oven gas and IL@MOF for natural gas were studied successively.The main contents are as follows:(1)The COSMO/Aspen method was used to screen ideal solvents from 1305 ILs for deep desulfurization of COG.First,the absorption-selectivity-desorption indices(ASDI)of ILs for hydrogen sulfide(H2S),carbonyl sulfide(COS),and thiophene(TS)were calculated based on the COSMO-SAC model.Afterwards,the melting point and viscosity of ILs were calculated by the group contribution method.4 ILs([C1mpyr][DMP],[C1mpyr][Oac],[C2mpyr][DMP],[C2mpyr][Oac])survived and were taken as candidates for the process simulation.Process simulations were performed on Aspen Plus.Sensitivity analysis and central combinatorial design methods were used to determine optimal operating parameters.Finally,[C1mpyr][Oac]showed the best desulfurization performance,which could remove 99.05% of the total sulfur,and the recovery ratios of methane,hydrogen,and carbon monoxide were as high as 99.96%,94.65%,and 98.71%,respectively.The total annual cost is 5k Wh/kg Sulfide and $9 million/year,respectively.(2)Based on the theory of quantum chemistry,the interactions between 4 screened ILs and H2 S,COS and TS were studied by various analytical methods,including electrostatic potential,atoms in molecules,natural valence bond orbitals,and reduced density gradient functions.The order of binding energy between ILs and solutes is ILsH2 S > ILs-TS > ILs-COS > ILs-CH4.Anions dominate the absorption performance,[DMP]-and [Oac]-bind with H2 S through strong hydrogen bonds,and bind with COS and TS mainly through van der Waals interactions.(3)The method based on geometry optimization through CP2 K software and DDEC charge calculation was adopted to design the IL@MOF composites.The desulfurization and decarbonization performance of 12 IL@MOFs on natural gas was investigated by GCMC simulation.The adsorption performance score(APS)was used for screening.[C4mim][Cl]@ZIF-8 exhibited the best acid gas removal performance,and the adsorption capacities of H2 S,CO2,and CH4 were 0.6434 mmol/g,0.8866mmol/g,and 0.3520 mmol/g,respectively.The fixed-bed breakthrough curves demonstrate the industrial application potential of [C4mim][Cl]@ZIF-8.The radial distribution function and adsorption equilibrium conformation indicated that the Cl atom in [C4mim][Cl]@ZIF-8 replaced Zn as the best adsorption site,and preferentially adsorbed H2 S and CO2 in the mixed gas.In summary,the COSMO/Aspen method and quantum chemical analysis combine molecular design and process simulation to systematically evaluate the desulfurization performance of ILs,laying a theoretical foundation for the development and screening of ideal solvents,and screening out suitable IL structures for the subsequent design of IL@MOF composites.The method based on the structure optimization through CP2 K software and DDEC charge calculation provides a direction for the molecular design of high-performance composite materials and lays a theoretical and conceptual foundation for later high-throughput screening of IL@MOF.