Poly Ether Block Amide (PEBA) membranes are considered in the gas separation industry due to their permeability and appropriate selectivity, film-making ability and desirable mechanical properties. Low flue gas pressure and low concentration of carbon dioxide are two major problems in the use of polymer membranes in carbon dioxide separation, which has necessitated for high selectivity membranes. In the present study, the surface of poly ether block amide membrane is modified by immersion method using the mediocrity size of carbon dioxide adsorbent. Membrane modification is performed with three types of amine substances at different lengths and also in two steps. In the first step, isocyanate was bonded on the surface in the presence of a catalyst for one hour at 25 C^°, which was confirmed by ATR test. In the second stage, the modified membrane and isocyanate were exposed to a solution of carbon dioxide adsorbent amine groups for one hour at 25 C^° in order to form a bond between the amine groups and isocyanate. ATR, static and dynamic contact angle, XRD and pure gas separation tests were used to eva‎luate the properties of the modified membranes. In order to investigate the effect of toluene solvent on the membrane, the poly ether block amide membrane was exposed to toluene solvent for 3 hours (including washing time) at 25 C^° in similar times during the modification process. Permeability of CH_4, O_2, N_2, He and CO_2 are increased by 18.19%, 20.75%, 21.63%, 13.35% and 23.09% in toluene-modified membrane compared to pure membrane, respectively. Besides, CO_2 selectivity to He, N_2, O_2and CH_4 are increased by 4.15%, 1.93%, 1.20% and 8.59% in toluene-modified membrane compared to pure membrane, respectively, which is consistent with the ATR and XRD results. ATR results show an increase in the ratio of bonded carbonyl to free carbonyl and XRD results indicate a decrease in the distance of crystals in the hard section. Increment of the ratio of bonded carbonyls to free carbonyls and decrement of the distance of crystals in the hard section indicates more phase separation, which justifies the increase in permeability. On the other hand, ATR results show the migration of amine groups to the surface in toluene-modified membranes, which was confirmed by the relative increase in hydrophilicity of the membrane surface by static and dynamic contact angle tests. Therefore, the increment of the selectivity of carbon dioxide in comparison other gases can be explained due to the high condensability and polarizability of carbon dioxide gas. All modified membranes with amine groups reduced permeability and increased membrane selectivity. The decrease in CO_2 permeability in modified membranes with TETA, TEPA and PEHA compared to pure membrane is 32.31%, 40.52% and 0.39%, respectively, and the increase in CO_2 selectivity to N_2 is 68.80%, 54.93% and 63.82%, respectively. The decrement of in permeability is consistent with the ATR results, which show a decrease in free-bonded carbonyls, as well as the XRD results indicate an increase in the distance of the crystals in the hard section. In addition, the phase interference and inhibition that amine groups are created on the surface of these membranes led to a reduction in the diffusion coefficient of gases. However, the presence of amine groups on the surface and the hydrophilicity of the membrane surface leads to an increase in the solubility coefficient of carbon dioxide, while the solubility coefficient of other gases has not changed much, and hence, the increase in selectivity of carbon dioxide can be explained by high polarizability of carbon dioxide.

مرتضي صادقي، احمد اسدي نژاد

محمد ديناري

احمد محب،افسانه فخار