Study On Spontaneous Liquid-gas Imbibition Method In The Structural Characterization Of Porous Materials

Porous materials are widely used in many fields because of their advantages of large specific surface area,controllable pore structure,and adjustable pore size.Accurate characterization of the structure of porous materials is the basis of their applications.The low-temperature nitrogen adsorption method is one of the standard methods to determine the pore structure of porous materials.However,when the gas adsorption method obtains the adsorption isotherm of the ultra-micropore at low temperature,it takes a long time to reach the adsorption equilibrium,and it is difficult to obtain the real adsorption isotherm.Therefore,it is impossible to obtain accurate ultra-micropore structure information.The spontaneous liquid-gas imbibition method can quickly characterize the structure of porous materials at room temperature and pressure,and is a promising characterization technique,but it cannot characterize powder materials due to the limitation of material morphology,and current research has insufficient understanding of the process of liquid imbibition and gas displacement.In this paper,the experiment of spontaneous liquid-gas imbibition was carried out on different porous materials,different liquid probes and different gas probes using a constant volume device.A characterization method for spontaneous liquid-gas imbibition of powder porous materials was established,the application range of the spontaneous liquid-gas imbibition method was expanded,and the liquid-gas imbibition process of porous materials was studied.Two methods are used to characterize the powder activated carbon by spontaneous liquidgas imbibition.One method is to bond the powder activated carbon into particles and use polyvinylidene fluoride as a binder.When the amount of binder is small enough,after high temperature after-treatment,particles with a certain strength are obtained,and the bonding process does not affect the microporous structure of the powder activated carbon.Another method is to reduce the surface tension of the liquid probe so that small powder particles can overcome the surface tension and immerse into the liquid probe.The use of ethanol,isopropanol,and the surfactant polyethylene glycol can effectively reduce the surface tension of the liquid.The equilibrium displacement of spontaneous liquid-gas imbibition is determined by the liquid probe with the smallest molecular size.The addition of larger molecular surfactant does not affect the volume of gas recovery.The research on the process of spontaneous liquid-gas imbibition of different porous materials shows that the rate of gas recovered by liquid imbibition is affected by the macroscopic fluid flow process,but also by the micropore structure.When the surface tension of the used liquid probe is reduced,the rate of gas recovered by liquid imbibition increases for the porous material with poor wettability,while the rate of increase for the material with strong wettability is not obvious or even decreased.When adding oxygen-containing functional groups on the surface of the porous material to enhance its hydrophilicity,the rate of gas recovered by liquid imbibition increases.The reduction of the particle size of the porous material allows the liquid probe to enter the interior of the particle faster and contact more micropores to absorb the liquid and accelerate the gas removal rate.The pore size of the porous material has a great influence on the rate of gas recovered by liquid imbibition.The micropores with larger pore size can absorb gas at supercritical temperature and be displaced by the liquid probe with almost no resistance.When it is wide,the adsorbed gas in the larger pore size is displaced faster,and the adsorbed gas in the small pore size is discharged at a slower speed due to the effect of the micropore resistance.