Pyrolytic carbon membranes containing silica derived from poly(imide siloxane): the effect of siloxane chain length on gas transport behavior and a study on the separation of mixed gases
Pyrolytic carbon membranes containing silica derived from poly(imide siloxane): the effect of siloxane chain length on gas transport behavior and a study on the separation of mixed gases
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DOI：
10.1016/j.memsci.2004.01.025
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发表时间：
2004-06
影响因子：
9.5
通讯作者：
H. Park;C. Jung;Youn Kook Kim;S. Nam;S. Lee;Y. Lee
中科院分区：
文献类型：
--
作者：
H. Park;C. Jung;Youn Kook Kim;S. Nam;S. Lee;Y. Lee
合成了不同组成的聚酰亚胺硅氧烷（PIS）前体，并对其形成含二氧化硅（C-SiO2）碳膜的能力进行了评价。在惰性热解过程中，PIS中的酰亚胺结构域转化为富碳相，从而赋予小气体分子对（例如H2/N2、He/N2、CO2/N2和O2/N2）的分子筛能力。PIS中的硅氧烷域被转化为富含二氧化硅的相，这提供了进一步的气体通路。PIS中的硅氧烷链长影响C-SiO2膜的气体渗透性能。PIS前驱体中聚二甲基硅氧烷（PDMS）链段的硅氧烷链长变化直接影响C-SiO2膜的气体渗透和分离性能。当PDMS体积分数一定时，PIS中的硅氧烷链越长，C-SiO2膜的气体渗透性越大，气体选择性越低。此外，所选择的气体的扩散系数也受到二氧化硅相，这是嵌入在连续的碳基体。迁移率（扩散）的选择性的整体选择性的贡献减少与PIS前体中的PDMS部分的体积分数。混合气体分离实验在25°C和5atm（Iatm = 101325 Pa）的进料压力下使用进料气体混合物，例如O2/N2（71%/29%）和CO2/N2（15%/85%）进行。对于混合气体分离，通过将氧化铝管浸涂到含戊烷的聚酰胺酸（SPA）溶液中，然后在高达600°C的温度下热解来制造碳涂覆的微孔氧化铝管。复合膜的分离性能与单一纯气体渗透实验结果吻合较好。
Poly(imide siloxane) (PIS) precursors have been synthesized in different compositions and appraised in their ability to form carbon membranes containing silica (C–SiO2). During inert pyrolysis, the imide domains in the PIS were transformed into a carbon-rich phase conferring a molecular sieving capability for molecular pairs of small gases, such as H2/N2, He/N2, CO2/N2, and O2/N2. The siloxane domains in the PIS were converted into a silica-rich phase, which provided further gas pathways. The siloxane chain length in the PIS influenced the gas permeation characteristics of the C–SiO2membranes. A change in the siloxane chain length of the polydimethylsiloxane (PDMS) segment in the PIS precursor directly influenced the gas permeation and separation properties of the C–SiO2membranes. For a constant volume fraction of PDMS moieties, a longer siloxane chain in the PIS led to a drastic increase in gas permeability and a reduction in gas selectivity of the C–SiO2membranes. Moreover, the diffusion coefficients of selected gases were also affected by the silica phase, which was embedded in the continuous carbon matrix. The contribution of mobility (diffusion) selectivity to the overall selectivity decreased with volume fraction of PDMS moieties in the PIS precursor. Mixed gas separation experiments were conducted at 25°C and at a feed pressure of 5atm (1atm = 101325Pa) using feed gas mixtures, such as O2/N2(71%/29%) and CO2/N2(15%/85%). For mixed gas separation, carbon-coated microporous alumina tubes were fabricated by dip-coating alumina tubes into siloxane-containing poly(amic acid) (SPA) solutions followed by pyrolysis at temperatures up to 600°C. The separation properties of the composite membranes showed good agreement with the results obtained from single pure gas permeation experiments.