Fundamental Study Of Cu₃（BTC）₂to Improve PDMS/PEI Composite Membrane For Gas Separation

Gas membrane separation technology has lots of advantages, such as simple technology, low investment cost, little cover area, and so on. Thus, this separation technology stands out in the field of gas mixtures separation. Metal-Organic Frameworks (MOFs), as a new type of material, which has a large specific surface area and porosity, shows better than traditional materials in the aspect of gas storage and separation. Cu3(BTC)2, one of Metal-Organic Frameworks, showed high adsorption affinity for CO2, and owned great research value. This article added Cu3(BTC)2into polydimethylsiloxane (PDMS) to prepare modified PDMS/polyetherimide (PEI) composite membrane, and use the diffusivity, solubility, permability and separation factors as evaluation parameters, then study the effects and the reasons of Cu3(BTC)2for gas separation performance of PDMS/PEI composite membrane.In this paper, PDMS/PEI composite membrane was prepared, and measured out the membrane separation performance relationship with the changes of temperature and pressure. Experimental reults indicated that the diffusivity of CO2, CH4, O2, N2and the solubility of O2, N2and the permeability of CH4, O2, N2increased with the increasing of temprtute, while the separation factors of O2/N2, CO2/N2and CO2/CH4delined. In addition, when the feed gas pressure increased, the membrane’s compression effect was stronger than the swelling effect, due to the rising of solubility and permeability, and the decline of diffusivity.Cu3(BTC)2was filled into PDMS to preparing modified PDMS/PEI membrane. And found out the effect of temperature, pressure and Cu3(BTC)2filling quantity to the modified membrane separation performance. The results showed that, adding Cu3(BTC)2could reduce compression effect, due to free volume for gas passed through increased, and also could reduce activation energy of diffusion and permeation. Under a certain feed pressure, with the increasing of temperature, the solubility, permeability and separation factors declined, while the diffusivity increased. Under a certain tempreture, with the increasing of feed pressure, both the diffusivity and permeability increased, and separation factors changed a little. Composite membrane modified by Cu3(BTC)2could get higher gas diffusivity, permeability and separation factors than the composite membrane whithout modified. The membrane achieved best separation performance when Cu3(BTC)2filling quantity was25%. Compared with the unmodified composite membrane, the diffusivity of best separation performance membrane for CO2, CH4, O2and N2were increased120%,117%,109%and120%respectively; while the permeability of those gases increased33%,17%,27%,17%respectively; and the separation factors of O2/N2, CO2/N2and CO2/CH4also improved.Then, the theoretical calculation of separation process of CO2/CH4mixtures was made. The results showed that under a certain temperature, pressure of feed gas and mixture gas composition, both the permeability and recovery rate of CO2were increased with the rising of feed flowrate, while the separation factors were decline. Under a certain temperature, feeding pressure and flow rate the permeability, recovery rate of CO2and the separation factors were increased along with the rising concentration of CO2in CO2/CH4mixtures. It also showed that Cu3(BTC)2modified PDMS/PEI membrane was suitable for the separation of CO2/CH4mixtures with low flow, high CO2concent.