Multi-scale Modeling And Simulation Of Adsorption Performance Of Adsorption Bed

Microporous adsorbents such as zeolites,carbon molecular sieves(CMS),metal-organic frameworks(MOFs),zeolitic imidazolate framework(ZIFs),Covalent Organic Skeleton(COFs)and porous Aromatic Skeleton(PAFs),have strong separation potential and are widely used to separate gaseous mixtures.Separation performance depends on a combination of adsorption and diffusion properties,and can be controlled by appropriate selection of pore size,pore topology,connections,and interactions between guest molecules and skeleton atoms,including van der Waals forces and electrostatic forces.Only by fully understanding the theoretical model of adsorption equilibrium and diffusion process,can we accurately grasp the combination of adsorption and diffusion characteristics and provide qualitative and quantitative basis for the application of various adsorption materials.Therefore,based on the adsorption material separation and capture of carbon dioxide as the application background,multi-scale modeling method and strategy are adopted in this paper to systematically study the adsorption equilibrium and diffusion characteristics of gas in the adsorption material.First of all,we need to study the adsorption equilibrium of gas on adsorptive material.Adsorption equilibrium is the core problem of the whole adsorption process.In many cases,the ideal gas equilibrium is for mixed gases rather than pure gases.It has more practical significance to study the adsorption equilibrium of mixed gas.In this paper,the adsorption equilibrium of mixed gases is described by the ideal solution adsorption theory.The mathematical model and solution method of ideal solution adsorption theory are introduced.The selectivity of Kureha activated carbon for CO2 in N2/CO2 and CH4/CO2 mixed gases and the selectivity of MOR zeolite,LTA-5A zeolite,13X zeolite and AFX zeolite for CO2 in CH4/CO2 mixed gases were calculated respectively by using ideal solution adsorption theory.It was found that the strongest selectivity of CO2 in CH4/CO2 mixed gases was AFX zeolite.Next,the adsorption kinetics simulation of single particle size gas is introduced.First,a mathematical model of one-component gas diffusion on adsorbent particles is established,and then the mathematical model is solved by numerical calculation.It is found that the concentration dependence of the diffusion coefficient has a great influence on the diffusion process.The effect of adsorption equilibrium on diffusion process is negligible.For multi-component gas,a mathematical model describing the diffusion-adsorption of two-component gas on adsorbent particles was established,and the overshoot of mixed gas on adsorbent particle was revealed based on simulation analysis.Finally simulation of the gas in the fixed bed adsorption penetration process,by using the appropriate assumptions,established in the fixed bed adsorption mixed gases are described through the process of the model and algorithm,respectively to simulate the N2/CO2 and CH4/CO2 gas mixture in Kureha carbon fixed bed adsorption gas penetration behavior,the simulation results and experiment results have a greater agreement.Then,the gas penetration behavior of CH4/CO2 mixture on the fixed adsorption bed of AFX zeolite was simulated.From the simulation results,the ability of AFX zeolite to separate CH4/CO2 was 14.5 times that of Kureha activated carbon.Finally,the influences of mass transfer on gas penetration are investigated.