이산화탄소 포집용 고투과성 열전환 고분자 중공사막 제조 및 성능평가

Abstract

This thesis is concerned with thermally rearranged (TR) hollow fiber membranes, which have been investigated for membrane gas separation, especially carbon capture and sequestration (CCS). High gas permeable TR hollow fiber membranes were fabricated under optimized spinning conditions. Pure and mixed-gas permeation test were performed to evaluate the hollow fiber membrane gas permeation properties. This thesis is organized into five chapters. The first chapter is introduction of thermally rearranged (TR) polymer membranes for CO2 capture from flue gas. TR polymers have received much attention for application in CCS field due to their exceptional gas permeation properties. The change of membrane configuration from dense flat sheet to hollow fiber is required for separation of bulk CO2 separation process. The fabrication conditions, characterization, gas permeation test were reviewed in chapter 1. In chapter 2, thermally rearranged polybenzoxazole (TR-PBO) hollow fiber membranes were fabricated from a poly(amic acid) (HPAAc) precursor through a non-solvent induced phase separation technique (NIPS). All the major fabrication conditions (e.g. dope composition, the use of additional inorganic salt, dope and bore flow rates, and coagulation bath temperature) were systematically evaluated and optimized, in order to produce defect-free hollow fiber membranes with an ultra-thin skin layer. The hollow fiber membranes fabricated with the optimized spinning conditions exhibited superior pure gas permeation behavior (CO2 permeance of 2,500 GPU and CO2/N2 ideal separation factor of 16). Slow beam positron annihilation lifetime spectroscopy (slow beam PALs) measurements revealed that such an exceptional separation performance was mainly attributed to the ideal cavity radius (3.584 Å) and ultra-thin skin layer thickness (193 nm) obtained using the optimal fabrication conditions. In addition, mixed-gas permeation tests were also performed to demonstrate the feasibility of using such membranes for post-combustion CO2 capture. In chapter 3, thermally rearranged poly(benzoxazole-co-imide) (TR-PBOI) hollow fiber membranes were fabricated from a hydroxyl polyimide-co-polyimide (HD5) precursor containing equal molar amounts of non-TR-able DAM and TR-able HAB. A wide variety of spinning conditions were optimized in order to improve the gas permeation properties. A high bore flow rate (DI water) led to lowered gas permeation properties due to the generation of a dense, thick skin layer. The shear rate contributed significantly to manipulate the polymer chain packing density during spinning, therefore, CO2 permeance was critically enhanced in low shear rate. The addition of co-solvent (propionic acid) and pore forming agent (PEG 200) was shown to improve the gas permeation properties. The TR-PBOI hollow fiber membrane fabricated under optimal spinning conditions exhibited an excellent CO2 permeance of 560 GPU and CO2/N2 ideal separation factor of 16.8. A TR-PBOI hollow fiber module was successfully fabricated with an effective area of 106 cm2 for the mixed-gas permeation tests with a ternary gas mixture containing 14 % CO2, 6 % O2, and 80 % N2. The results showed a permeate CO2 concentration around 50 % and CO2 permeance of 400 GPU at a pressure ratio of 10. In chapter 4, a comprehensive study was carried out on the mixed-gas separation performance (CO2/N2/O2) of in-house fabricated thermally rearranged polybenzoxazole-co-imide (TR-PBOI-AD5) hollow fiber membranes (pure-gas CO2 permeance of 481 GPU and ideal CO2/N2 separation factor of 17.7). The criteria for the determination of two major operating conditions (pressure ratio and feed flow rate) were identified in order to deliver the optimal separation performance with low process energy consumption. By varying the feed CO2 concentrations, it was found that a single stage operation using TR-PBOI-AD5 (produced by bis-APAF and DAM as the TR-able and non-TR-able diamines, respectively based on 6FDA) hollow fiber membranes was not sufficient to meet the required 90% permeate CO2 purity target, whilst a 2nd stage operation using the same membranes led to a permeate CO2 purity (81%) closer to the target value. The comparison study among the TR polymer membranes and three other polymer membranes highlighted the significance of an appropriate choice of mixed-gas separation operating scheme to fully utilize the exceptional permeation properties of the recently developed high performance membranes such as TR polymeric membranes. In chapter 5, the conclusions, evaluations, and directions for future work were presented regarding the study on development of TR hollow fiber membranes and the effect of water vapor, SOx and NOx in the post-combustion flue gas. Optimized TR hollow fiber membrane module can be designed via analysis of CFD simulation and productivity. Finally, process design of TR hollow fiber membrane for CO2 separation process was presented to approach the requirement of CO2 purity as recommendations for future works.