The Spontaneous Liquid-Gas Imbibition For Characterization Of Porous Materials

The gas adsorption capacity and gas mixture selectivity of porous materials may be mainly caused by the micropore texture and surface properties. Hence, to develop better porous materials for the gas mixture separation and evaluate whether they are appropriate for application, an accurate means for assessing the micropore texture of the porous materials is needed. N2adsorption at77K is currently employed as a standard technique for the pore size determination. However, the application of this technique to ultramicropore is limited because N2is adsorbed at unreasonably slow rates in this kind pore at cryogenic temperature. The pore size characterized by smaller gas adsorption at ambient temperature extends to samller than that by N2adsorption at77K.In this dissertation, characterization of microporous texture of porous materials by analyzing the volume or rate of gas recovered by liquid imbibition is proposed. An experimental set-up was built to measure the volume or rate of gas recovered by liquid imbibition.The volume of gas recovered by the water imbibition was measured and applied to evaluate the density of the N2adsorbed in the carbon molecular sieves. The micropore size of the carbon molecular sieves was determined by comparing the N2density from the water-N2imbibition with that calculated by Grand Canonical Monte Carlo simulation. The micropore size evaluated by the liquid-gas imbibition coincides with that obtained by N2adsorption at ambient temperature. The size-exclusion property of the carbon molecular sieves was estimated by comparing the volume of N2recovered by imbibition of liquids with varied molecular dimensions, because the liquid can probe only pores with mouth larger than the size of liquid molecules and only the gas in these pores can be replaced. The mian micropore mouth size distribution of the carbon molecular sieves for air separation dominates in0.28-0.37nm. Furthermore, the effect of chemical vapor deposition treatment on the porous texture of the carbon molecular sieves was revealed by the liquid-gas imbibition.The micropore size distribution of the activated carbons was estimated by comparing the volume CH4and N2recovered by imbibition of liquids with varied molecular dimensions, respectively, because the liquid can probe only pores with size larger than the size of liquid molecules and only the gas in these pores can be replaced. The results showed that the pore sizes characterized by spontaneous liquid-gas imbibition extend to smaller than that by N2 adsorption at77K. The influence of micropore size on their selective adsorption of CH4from CH4/N2mixture is analyzed with the CH4/N2separation factors obtained by dynamic method. The separation factor for CH4/N2on activated carbons changes with the micropore size distribution. The micropore of activated carbons plays an important role in their selective adsorption of CH4from CH4/N2mixture, particularly those pores smaller than0.48nm.The micropore size distribution of the ZSM-5was estimated by comparing the volume CH4and N2recovered by imbibition of liquids with varied molecular dimensions, respectively, because the liquid can probe only pores with mouth larger than the size of liquid molecules and only the gas in these pores can be replaced. The results showed that the dominated micropore size of the ZSM-5is about0.48nm, and the micropore size evaluated by the liquid-gas imbibition coincides with that obtained by N2adsorption at77K.The effect of temperature, the kinds of gases, particle size, liquid viscosity and polarity on the rate of gas recovered by water imbibition in carbon molecular sieves, activated carbon and ZSM-5was investigated. The experimental results showed that the rate of N2recovered by water imbibition increases with the temperature incrcasea and the particle size decreases, showing that the rate of gas recovered by water imbibition is controlled by both the macropore and the micropore. The kinds of gases play some role in the rate of gas recovered by water imbibition in carbon molecular sieves. There is a critical particle size0.250-0.180mm and0.850-1.400mm for carbon molecular sieves and ZSM-5, respectively, below which the rate of N2recovered by water imbibition is independent of the particle size, showing that the rate of N2recovered by water imbibition in carbon molecular sieves and ZSM-5is only controlled by the micropore when the particle size of carbon molecular sieves and ZSM-5below0.250-0.180mm and0.850-1.400mm, respectively. The viscosity and polarity of the liquid, can influence the rate of N2recovered by imbibition in activated carbons and13X. Furthermore, the effect of chemical vapor deposition time on the rate of N2recovered by water imbibition in micropore of carbon molecular sieves is investigated. The experimental results show that the rate of N2recovered by water imbibition in micropore of carbon molecular sieves decrease as the time of chemical vapor deposition increases and the activation energy of N2recovered by water imbibition in micropore of carbon molecular sieves increases as the time of chemical vapor deposition increases.