【作者】 聂飞；

【导师】 贺高红；

【作者基本信息】 大连理工大学 ， 化学工程与技术， 2013， 博士

【摘要】 气体分离膜具有低耗高效的特点,在节能减排和能源利用方面具有广泛的应用前景。作为气体分离膜的核心部件,目前广泛使用的选择性涂层材料聚二甲基硅氧烷(PDMS)易被有机气体溶胀,存在选择性下降的问题。设计开发具有耐溶胀选择性涂层材料以及与之匹配的支撑膜结构是解决这一难题的关键,对拓宽气体分离膜的应用范围具有重要的理论和社会意义。聚三氟丙基甲基硅氧烷(PTFPMS)具有与PDMS类似的硅氧主链结构,其独特的三氟丙基甲基不对称结构赋予其一定的耐溶胀性。本论文选用PTFPMS作为选择层材料,在使用分子模拟研究聚硅氧烷与气体分子相互作用的基础上,制备了一系列气体分离复合膜,并考察其分离性能和耐溶胀性。首先选择具有相同的硅氧主链结构而侧基体积不同的PDMS、PPMS、PTFPMS和POMS(侧基体积从小到大)为目标涂层材料,利用分子模拟工具计算聚硅氧烷与不同溶剂、气体和聚合物的混合自由能。相比其它三种全烷基侧链的聚硅氧烷,PTFPMS与溶剂、气体的二元体系具有较高的混合自由能,说明耐溶胀性较好；PTFPMS与PEG聚合物的混合自由能较低,说明二者可能具有较好的共混相容性。进一步以PDMS和PTFPMS为代表性聚硅氧烷,采用MD方法进行小分子气体、PDMS和PTFPMS主链的均方位移模拟计算,结果表明小分子气体扩散方向与PDMS主链运动方向具有一致性,其在PTFPMS中的扩散与主链不具有一致性,导致其在PTFPMS中的扩散系数低。采用GCMC方法模拟计算CH4、CO2、C3H8三种气体在四种聚硅氧烷中的溶解度,与实验报道值吻合良好,模拟结果表明由于PTFPMS侧基扭曲严重,难以形成较大的孔体积,导致有机气体在其中的溶解度相对较低。其次,根据上述分子模拟计算确定出PTFPMS为选择层材料。通过实验确定了PTFPMS温和可控(交联温度≤80。C,交联反应时间0.5h)的加成型交联体系和室温溶液涂覆条件。将其滚涂在多孔聚醚酰亚胺(PEI)支撑膜上制备成PTFPMS/PEI复合膜,其C02渗透速率为193.7GPU,相应的O2/N2和CO2/N2的选择性分别为2.25和16.38,比PDMS/PEI复合膜分别提高了12.5%和48%。建立了基于改进Henis阻力模型预测了PTFPMS选择性涂层的最小临界厚度。理论计算表明,只有当PTFPMS涂层厚度达到15μm时,能够保证PTFPMS/PEI复合膜的性能,与实验观测到的厚度一致,表明模型具有实际指导意义。考察了涂覆次数、涂膜液中PTFPMS浓度和分子量、支撑膜预处理对PTFPMS/PEI复合膜气体分离性能的影响。以PTFPMS-Ⅲ (分子量1100K)为涂膜材料,水为预处理溶液,一次滚涂(浓度10wt.%)比其低浓度5wt.%的2次滚涂可以减轻嵌入层厚度的65%,CO2渗透速率提高43%。相同操作压差下(0.3MPa),PTFPMS/PEI复合膜C3H6/N2的理想选择性较PDMS/PEI复合膜提高了18%,经过异辛烷和正戊烷48小时连续浸泡后测试,PTFPMS复合膜对C3H6/N2的理想选择性下降变化率为1.4和2.3%,远低于PDMS复合膜的24.5%和27.8%,显示了PTFPMS复合膜良好的耐溶胀性。为进一步提高对C02的分离性能,将系列聚乙二醇(PEG)与PTFPMS共混制备了复合膜。红外谱图显示PEG和PTFPMS无明显基团偏移,DSC测试显示无新的放热峰,表明二者相容性良好。PEG-400/PTFPMS共混复合膜的CO2渗透速率为65.6GPU,高于相同共混比(0.2)下的PEG-600/PTFPMS和PEG-1000/PTFPMS共混复合膜,02/N2和CO2/N2的选择性分别为2.73和19.24,较PTFPMS/PEI复合膜分别提高22%和17%,显示了PEG的存在对提高C02分离性能的作用。气体渗透性能实验值分布在基于Maxwell’s方程得到的PEG和PTFPMS的理论计算值之间,表明气体的传质路径为PEG和PTFPMS的双连续相。最后,为提高膜对有机气体的耐溶胀性,以疏水Si02为无机相,采用先共混后交联的方法制备了疏水SiO2/PTPMFS杂化共混膜,考察了疏水Si02对共混膜形态、溶胀性能和气体分离性能的影响。当疏水SiO2/PTPMFS共混比低于0.018时,杂化膜在非极性溶剂异辛烷中的溶胀度一直保持不变,在极性溶剂乙酸乙酯中的溶胀度较PTFPMS均质膜下降了11.9%,表明疏水SiO2/PTFPMS均质膜的耐溶胀性提高。对于疏水SiO2/PTFPMS杂化复合膜,简单气体渗透速率随着Si02共混比的增加呈平缓的单调下降趋势,而C02渗透速率先增大后减小。当Si02共混比为0.012时,C02的渗透速率可达到156.1GPU, CO2/N2和C3H6/N2的选择性较PTFPMS/PEI复合膜分别提高28%和25%。更多还原

【Abstract】 Gas separation membranes with their low cost characteristics have broad application prospects in terms of energy conservation. As the core component of gas separation membrane, material used for selective layer and support along with their structure determine the performance of composite membrane. Nowadays, polydimethylsiloxane (PDMS) is widely used as selective layer material but it can be swollen heavily by organic gases, which leads to huge selectivity loss. Therefore, developing material of high solvent resistance is the key to fabricate composite membranes used for gas separation, which will widen their application fields also. Polyfluoropropylmethylsiloxane (PTFPMS) has similar backbone structure to PDMS and its unique trifluoropropyl group exhibits outstanding solvent resistance property. The main work of this dissertation was to fabricate a series of PTFPMS compoiste membranes and investigate their performance on simple and organic gas seperation, on the basis of molecular simulation which studies the interaction between polysiloxanes and gases.Firstly, polysiloxanes (PDMS, PPMS, PTFPMS and POMS) with same main chain but different side groups were selected as target coating materials. The interaction between polysiloxanes, solvents and gases were analyzed through free energy of mixing of the binary systems which were calculated by Materials Studio4.0software. Free energies of PTFPMS and different solvents was the largest among the four kinds of polysiloxanes, reflecting its highest resistance to non-polar solvents. Besides, the free energy of mixing between PTFPMS and PEG was low, indicating their good compatibility. Further, the diffusion coefficients of O2and N2molecules in PDMS and PTFPMS were calculated by molecular dynamic (MD) simulations. The diffusion of small molecules in PTFPMS showed inconsistency with main chains, which was different with the case of PDMS. The reason of this difference was the bulky trifluoropropyl hindered the diffusion of gases and the side groups in PTFPMS distributed asymmetrically which led to lower diffusion coefficients of gases. GCMC method was used to calculate solubilities of CH4, CO2, and C3H8in polysiloxanes and the results were in good agreement with reported experimental values. Also, the simulation revealed large pore volume can not be obtained in PTFPMS for its heavy distortion of side groups, which resulted in lower solubilities of organic gases.Secondly, PTFPMS was selected as selective coating material according to the simulation study. Cross-linking of PTFPMS was controlled in mild condition (crosslink temperature at80℃, crosslink time at0.5h) and coating parameters were determined through experiments. The CO2permeance of prepared PTFPMS/PEI composite membrane was193.7GPU. The selectivity of O2/N2and CO2/N2were2.25and16.38, respectively, which was enhanced by12.5%and48%compared with PDMS/PEI composite membrane. Based on the improved Henis transport model, the minimum thickness of coating layer was predicted. The calculation revealed that the thickness larger than15μm was necessary to guarantee a satisfied performance. For PTFPMS-Ⅲ(1100K g/mol), with water as pre-treatment solvent, one step coating at the concentration of10wt.%could decrease the thickness of insert layer by65%and increase the CO2permeance by43%compared to coating twice (5wt%). The selectivity for C3H6/N2of PTFPMS/PEI composite membrane is larger than that of PDMS/PEI composite membrane by18%. After soaking in isooctane and pentane for48h, ideal selectivities of C3He/N2for PTFPMS composite membrane decreased by1.4and2.3%, which were quite lower than that for PDMS composite membrane (24.5and27.8%), showing better solvent resistance of PTFPMS membrane.To further enhance the separation performance of CO2, polyethylene glycol (PEG) with different molecular weights were introduced into PTFPMS network to form a blend selective layer. FTIR spectrum of PEG/PTFPMS blend membrane showed no shift for functional groups and no new peak appeared in DSC result, whichmeant a good compatability between PEG and PTFPMS. The CO2permeation rate of the PEG-400/PTFPMS blend composite membrane with a blend ratio of0.2is65.6GPU, while the O2/N2and CO2/N2selectivities are improved by22%and17%, respectively. Maxwell’s model was applied to investigate the transport behavior of blend membrane and results indicated the transport path of gases consist of binary phase of PEG and PTFPMS.Finally, to improve the solvent resistance property of gas separation membrane, hydrophobic SiO2/PTFPMS hybrid composite membrane was fabricated by solution blending-crosslinking method. The effects of blend ratio of SiO2to PTFPMS in mass on the membrane morphology, solvent resistance, and gas separation performance of the hydrophobic SiO2/PTFPMS hybrid composite membrane were investigated. The swelling degree of hybrid membrane was0in isooctane and decreases by11.9%in ethyl acetate when the blend ratio is lower than0.018. Permeances of simple gases (H2, N2, O2) decrease with increased SiO2blend ratio, while permeance of CO2increases till the blend ratio of SiO2is0.012. The CO2gas permeation rate can reach as high as156.1GPU while selectivities of CO2/N2and were increased by28%and25%, respectively.更多还原