The CO₂Adsorption And Diffusion Performances In Carbon Membrane

Carbon membrane as a novel inorganic porous membrane material has quickly developed in recent two decades. It can be applied in the separation and recovery of carbon dioxide from flue gas, hydrogen/carbon dioxide separation and the natural gas purification owing to its perfect thermal stability, good chemical stability and no plasticizing phenomenon to carbon dioxide.Carbon membrane has the developed extremely microporous structure which is match to the size of gas molecules.The separation of gas mixture by carbon membrane was based on the adsorption and diffusion performance of the gas molecules..Investigation of the adsorption and diffusion performance of gas across carbon membrane is very important for study the gas separation performance of the materials.The adsorption and diffusion performances of CO2in carbon membranes were investigated by means of the volumetric method. Pore structure parameters of carbon menbranes prepared under different conditions were calculated by the data of adsorption. XRD and gas permeability were used to characterize the micro structure of membranes which were prepared at different pyrolysis temperatures. The adsorption equilibrium of CO2was investigated. Four isothermal models were used to fit the experimental data of adsorption. Fick diffusion model was utilized to calculate the diffusion coefficients of carbon dioxide in carbon membrane. The concentration dependence of diffusion coefficients was investigated and calculated diffusion activation energy. In order to improve the diffusion properties of carbon membranes, inorganic nanoparticles of TiO2was introduced into the precursor. The interface between the inorganic particles and carbon matrix improve the diffusion capacity of the gas molecules in carbon membranes. To further improve the diffusion properties of the carbon membranes owing to TiO2itself does not have the porous channel, we introduced zeolite NaY with ordered microporous channels into the precursor. The ordered channels of the zeolite and the interfacial pores between carbon and zeolite can promote the gas diffusion.Results show that the pore structures of carbon membranes are affected by the pyrolytic temperature. The pore sizes of carbon membrane are reduced along with the pyrolytic temperature rising. The pore volume of carbon membrane increases with the increasing of pyrolytic temperature from600to800℃, and then decreases when the temperature is higher than800℃. The isosteric heat slightly decreased with the increase of the adsorption amounts. The energy distribution is nearly uniform for the surface of carbon membrane. The CO2diffusion coefficients in carbon membrane prepared at different pyrolytic temperatures are between1.04×10-13m2·s-1and8.56×10-12m2·s-1. The change of pore structure characteristics of carbon membrane leads to various diffusion performances. The diffusion activation energy increases and the diffusion coefficients decrease as the pyrolytic temperature rising The diffusion coefficient increased first and then decreased as the equilibrium pressure rising at the given pressure in this work. The introduction of TiO2and NaY changes the pore structure characteristics reduces the diffusion activation energy and the diffusion coefficients of the CO2are notably improved.