Molecular Simulation Study On The Separation Of CO₂ By Graphene Oxide Ionic Liquid Composite Membran

With the rapid development of social economy,the massive exploitation and use of fossil energy,excessive greenhouse gas carbon dioxide emissions have led to further global warming.In order to ensure the sustainable development of the ecological environment,the capture and storage of carbon dioxide has become a very important topic.Among many technologies of carbon dioxide capture,membrane separation technology has lower investment cost and higher energy efficiency and its development prospect is broad.In recent years,how to improve the performance of separation membranes has been widely concerned by experts and scholars in the industry.With the deepening of research,a variety of separation membranes have been discovered,among which the supported ionic liquid membranes(SILM)can break through the traditional separation restrictions and provide a platform for the efficient separation of small molecular gases.In this paper,molecular dynamics simulation method was used to explored the membrane separation process represented by the GO based supported ionic liquid membrane from the microscopic scale,revealing the microscopic transport mechanism of carbon dioxide in the separation membrane.At the same time,in-depth studies were conducted on the effects of carrier structural characteristics such as the rigidity and flexibility of membrane carriers,carrier pleat morphology,and membrane internal structural characteristics such as the amount of filler and membrane interlayer spacing on the separation results.The specific research contents are as follows:(1)Study on the rigidity and flexibility of separation membranes and its response mechanism to environment.Based on the deformation characteristics of the membrane carrier affected by the environment,the mechanism of carbon dioxide dissolution and separation in the membrane were investigated.In the absorption system,the gas separation performance of membrane is determined by the upper saturation limit of carbon dioxide in ionic liquid.Influenced by structural deformation,the gas retention capacity of the flexible membrane makes it closer to the saturation value,while the gas retention time of the rigid membrane is short,which leads to the weak absorption capacity.In the separation system,the transmembrane pressure difference as the main driving force makes the carbon dioxide in the membrane always in an unsaturated state.The dense ionic liquid in the flexible membrane has higher selectivity.While the rigid membrane is relatively loose,and the selectivity is weak.This rule is explained by the concentration gradient and energy analysis of the components in the membrane.Finally,external force induction is performed on the membrane,and it is found that the selectivity can be improved by adjusting external force.(2)Study on the influence mechanism of membrane carrier strcture on gas separation.The effect of graphene oxide wrinkle morphology on gas transport and retention in the separation membrane was investigated.By analyzing of density and energy barrier of the component,the relationship between the density selectivity of the interface is revealed.Subsequently,the relationship between the permeability of carbon dioxide and the change of the layer spacing is discovered by the regional statistics of the gas transmembrane time.In addition,through the analysis of carbon dioxide migration path,the existence of an independent cavities in the membrane was found,which revealed the reason why the permeation time of gas molecules in narrow pores increased sharply.Finally,in the later stage of simulation,it was found that the main driving force of separation membrane changes from transmembrane differential pressure to the affinity between gas and components.(3)Study on the mechanism of the effect of internal structure of separation membrane on the separation mechanism on gas separation.The influence of the heterogeneity in the separation membrane on the separation of gas mixture was investigated.The filler dosage of ionic liquid and the number of graphene oxide layers are two aspects.In the exploration of solvent filling volume,based on the rigid and flexible carrier structure,we made statistics on the selective permeability of gases under different filling volumes,and found that high filling volume brought strong selectivity and low permeability,in which the change of the properties of the two-phase interface and the difference of the free volume in the membrane played a key role.In the exploration of bilayer membrane,60% of the filling volume of ionic liquid is taken as an example.It is found that the selective permeation law of the bilayer membrane is similar to that of the monolayer membrane,and the system with good selectivity is usually accompanied by low permeability.However,the difference between rigidity and flexibility is significantly reduced,and the narrow hole brought by the bilayer membrane weakens the effect of liquid membrane deformation on selectivity.