N2优先渗透ZIF-8复合膜的制备及其CO2捕集

为了获得经济节能的烟道气CO₂回收方法，制备了一种新型的N₂优先渗透ZIF-8复合膜。以柔性聚砜(PSf)多孔膜为支撑层，采用Zn²⁺与壳聚糖的交联溶液对聚砜支撑层表面改性，使Zn²⁺固定在PSf膜表面；然后与2-甲基咪唑(Hmim)配位得到ZIF-8晶种层；最后通过界面聚合法二次生长制得ZIF-8复合膜。采用FTIR、XRD及SEM对ZIF-8复合膜的形貌结构进行表征，结果显示成功制备了致密的ZIF-8复合膜。在进料气为纯气条件下，探究了二次生长时间、Zn²⁺溶液的浓度、测试时间及测试压力对ZIF-8复合膜N₂/CO₂分离性能的影响，阐明其N₂优先渗透机理；并进一步考察了混合气分离性能。结果表明：在25℃和0.1 MPa下，最优ZIF-8复合膜的N₂渗透性为523 GPU，N₂/CO₂选择性为19；同条件下混合气的N₂渗透性和N₂/CO₂选择性分别为517 GPU和18。所制备的ZIF-8复合膜可以使N₂优先渗透，实现烟道气中高浓度N₂渗透，低浓度CO₂截留在膜的上游侧。原因主要是ZIF-8复合膜含有较多的CO₂强吸附位点，使CO₂被吸附在膜内不易从膜的下游侧脱附，渗透性小，而N₂优先渗透，这为N₂优先渗透膜的制备提供了一种新思路。

Preparation of N2 selective ZIF-8 composite membrane for CO2 capture

To improve the economic benefits of CO₂ capture in flue gas, a novel N₂ selective zeolitic imidazolate framework-8 (ZIF-8) composite membrane has been designed in this work. The zinc ion (Zn²⁺) was tightly adhered to the polysulfone support by chelating crosslinked chitosan matrix. The ZIF-8 seeding layer was prepared by zinc ion coordinated with 2-methylimidazole (Hmim), and then the dense ZIF-8 composite membrane was prepared by the secondary growth method. The morphological structure of ZIF-8 composite membrane was characterized by FTIR, XRD and SEM. And the results showed that the dense ZIF-8 composite membrane has been prepared. The effects of the time of secondary growth, the concentration of Zn²⁺ solution, the continuous test time and feed gas pressure on gas separation performance of ZIF-8 composite membrane were systematically investigated by pure gas, and the gas transport mechanism was analyzed. In addition, the separation performance of membranes was investigated by CO₂/N₂ mixed gas. At testing temperature of 25℃ and feed gas pressure of 0.1 MPa, N₂ permeance and N₂/CO₂ selectivity were 523 GPU and 19 for pure gas, respectively. While N₂ permeance and N₂/CO₂ selectivity were 517 GPU and 18 for mixed gas under the same condition, respectively. The results showed that the ZIF-8 composite membrane could preferentially permeate N₂ in the flue gas. The ZIF-8 composite membrane contained many CO₂ active adsorption sites, so that CO₂ was adsorbed in the membrane and was not easily desorbed from the downstream side of the membrane, and N₂ could preferentially permeate, which provided a new idea for the preparation of N₂ selective membrane.