用于CO2/CH4分离的cPIM-1/ZIF-8混合基质膜的制备

自聚微孔聚合物（PIM-1）虽具有良好的CO₂渗透性能,但其气体选择性普遍较差,限制其在CO₂/CH₄分离领域的应用。本文以N,N-二甲基甲酰胺（DMF）为溶剂制备ZIF-8纳米粒子,将其引入到羧基化的PIM-1基质中,制备了cPIM-1/ZIF-8混合基质膜,用于CO₂/CH₄分离。结果表明：由于合成ZIF-8的溶剂也是cPIM-1的良溶剂,使得两者之间具有良好的界面相容性,从而使ZIF-8添加量高达质量分数45%。随着ZIF-8添加量的增加,膜的CO₂渗透速率持续增加,CO₂/CH₄选择性呈现先上升后下降的趋势。当ZIF-8添加量为质量分数25%时,膜的CO₂/CH₄分离性能最好,即CO₂渗透系数为3942 Barrer,CO₂/CH₄选择性为18.7,较cPIM-1纯膜分别提高了 84%和43%,成功地超越了Robeson分离上限。     

离子液体支撑液膜的CO2/CH4分离性能

由于离子液体对CO₂具有较好的溶解选择性,离子液体支撑液膜分离CO₂越来越受到关注。比较了含3种不同阴离子的常规离子液体([bmim][BF₄]、[bmim][PF₆]、[bmim][Tf₂N])作为支撑液膜的液膜相分离CO₂/CH₄的性能,考察了咪唑环上烷基链长对离子液体支撑液膜性能的影响。考虑向离子液体中引入胺基和羧基等亲CO₂基团,制备了1-丁基-3-甲基咪唑丙氨酸离子液体([bmim][β-Ala]),考察了 [bmim][β-Ala]支撑液膜分离CO₂/CH₄的性能,并对在CO₂渗透测试前后的支撑液膜进行了FT-IR分析,发现氨基酸离子液体中的-NH₂和CO₂的较强作用以及该离子液体的高黏性影响了CO₂的透过性,使[Bmim][β-Ala]支撑液膜的CO₂透过率低。     

基于沸石ZSM-5的CH4/N2/CO2二元体系吸附平衡

采用Rubotherm磁悬浮天平测量CH₄、N₂和CO₂在沸石ZSM-5上的单组分吸附平衡等温线,温度273～353 K,压力0～500 kPa。采用Sips模型、Toth模型和MSL模型对单组分吸附平衡实验数据进行拟合,拟合结果良好,非线性回归得到相应的模型参数。测量双组分CO₂/N₂、CO₂/CH₄和CH₄/N₂在沸石ZSM-5上的竞争吸附平衡等温线,实验温度为293 K,实验压力为0～500 kPa。采用基于Sips模型的理想吸附溶液理论和双组分MSL模型预测双组分气体在沸石ZSM-5上的竞争吸附平衡等温线,并与实验结果进行比较,预测结果良好。比较CO₂/N₂、CO₂/CH₄以及CH₄/N₂体系在沸石ZSM-5上的竞争吸附选择性系数,探究沸石ZSM-5吸附分离烟道气（CO₂/N₂体系）、垃圾填埋气（CO₂/CH₄体系）或煤层气（CH₄/N₂体系）的可行性,为将来进行工艺设计提供基础数据。     

一步法制备含氨基化合物的非对称CO2分离膜

采用一步相分离法,制备以聚醚砜（PES）为主体材料,二乙醇胺（DEA）为添加剂和氨基载体的膜,用于CO₂分离。考察了PES浓度、DEA浓度、膜厚度对CO₂/N₂分离性能的影响,同时考察了膜性能的长时间稳定性。当涂膜液中DEA/PES的质量比为12/26、刮刀与无纺布的距离为300 μm、进料气压力为0.11 MPa（表压）时,膜的CO₂渗透速率可达274 GPU,CO₂/N₂分离因子可达50。测试温度低于40℃时,DEA/PES膜的CO₂渗透速率和CO₂/N₂分离因子保持稳定。另外,对CO₂/N₂分离性能较好的DEA/PES膜（质量比为12/27）进行CO₂/CH₄分离性能测试,在1 MPa（表压）下性能优于商品膜。上述结果表明,本文研制的DEA/PES膜制备步骤简单,易于规模化制备,性能较优,在CO₂分离领域具有良好的应用前景。     

自支撑石墨烯炭膜的制备及气体分离性能

通过溶剂蒸发法得到聚酰胺酸（PAA）与氧化石墨烯（GO）的复合石墨烯膜,并经600℃炭化制备了具有良好柔韧性的仿贝壳珍珠层结构的自支撑石墨烯炭膜。通过X射线衍射和场发射扫描电镜对薄膜微观结构进行表征,并测试不同PAA固含量制备的石墨烯炭膜对CO₂和CH₄的分离性能。结果表明,炭化后,GO被还原成石墨烯,呈层状堆叠,堆叠的层间填充了空穴和残炭;石墨烯炭膜的CO₂渗透通量和CO₂/CH₄分离理想选择性随PAA加入量增加,CO₂通量最高可达824 barrer,此时CO₂/CH₄理想选择性达38.9。石墨烯层骨架和碳分子筛构成石墨烯炭膜的气体传输通道,本研究成果为柔性自支撑气体分离炭膜的制备开辟了新思路。     

炭膜分离CO2/CH4混合气的分子模拟

针对炭膜分离CO₂/CH₄混合气体的过程,分别采用Materials Studio和Lammps软件进行分子模拟,建立与炭膜孔结构相近的Z字形孔模型,通过实验数据验证了模型的可靠性,通过对CO₂/CH₄纯组分及混合气体在膜孔内的吸附和扩散过程的模拟得到分离系数并探讨气体分离机理。综合吸附与扩散过程的模拟结果表明:适当的低温和较小的孔径有利于实现CO₂/CH₄混合气体的分离;随着温度的升高,CO₂/CH₄的分离系数减小,而且膜孔径对分离系数的排序为0.670nm>1.005nm>1.340nm;在温度为298K、膜孔径为0.670nm的操作条件下CO₂/CH₄的分离系数为20.1,与实验数据较吻合。研究结果可为优化炭膜制备提供指导,并为探讨分离过程机理提供依据。     

机械化学法合成小尺寸MOF填料助力高性能CO2分离

利用金属-有机骨架UTSA-280具有特定刚性尺寸的一维孔道可以筛分CO₂、CH₄、N₂的特性,采用机械化学研磨法减小其颗粒尺寸,将UTSA-280掺入聚砜（PSf）中制备MOF基混合基质膜,用于天然气提纯和烟道气CO₂捕获。结果表明,在PSf中掺入UTSA-280不仅可以增加聚合物的CO₂渗透通量而且提高了气体分离选择性。当UTSA-280掺杂量为30%（质量）时,混合基质膜对CO₂/CH₄、CO₂/N₂的分离因子分别为56.39和53.17,CO₂的渗透通量为18.61 Barrer,相对于PSf纯膜,选择性分别提高了47.3%和63.5%,CO₂渗透通量提高了128.9%,打破了“trade-off”效应。该工作通过引进具有分子筛分效应的MOF填料,能够增加气体通量的同时提高混合基质膜对含CO₂气体的分离性能,对天然气的提纯以及烟道气的CO₂的捕获有重要意义。     

铁基氧载体化学链CO2重整CH4方法制备合成气

提出一种铁基氧载体（Fe₃O₄/FeO）化学链CO₂重整CH₄方法制备合成气。为评价该系统的性能,采用Aspen Plus软件对其进行过程模拟和热力学分析。以CH₄转化率、CO₂转化率、能源利用效率和产气氢碳比（H₂/CO）为评价指标,得到系统的优化运行条件,并研究各操作参数（包括各反应器的温度和压力、氧载体甲烷比和CO₂甲烷比）对系统性能的影响。结果表明：当系统处于优化工况时,得到CH₄转化率为97.91%、CO₂转化率为32.76%、能源利用效率为93.77%及产气氢碳比为0.93。该系统能有效利用CO₂和CH₄这两种温室气体获得较低氢碳比的合成气,利于二甲醚的高效合成。     

CH4/CO2混合气置换强化含氮低品质甲烷的浓缩

针对CO₂置换吸附分离CH₄/N₂过程中CO₂再生困难的问题,采用少量产品气CH₄真空吹扫以提高CO₂的解吸效果,并以解吸得到的CH₄/CO₂混合气为置换步骤的置换气,通过置换来强化含氮低品质甲烷的浓缩过程。以自制椰壳活性炭为吸附剂,对CH₄/CO₂混合气置换强化吸附回收含氮低品质甲烷工艺过程进行了实验与模拟研究。在gPROMS软件中建立并求解固定床吸附分离模型方程,预测了CH₄、N₂ 和CO₂在自制椰壳活性炭上的竞争吸附穿透曲线,通过预测结果和实验的对比,验证了数学模型方程的准确性。对比了不同置换气强化吸附分离低品质甲烷的效果,结果表明CH₄/CO₂混合气置换强化相对于CO₂置换强化可获得更高纯度产品。进行了CH₄/CO₂混合气置换强化真空变压吸附循环实验,可以将14%的CH₄/N₂和53%的CH₄/CO₂联合富集到98.8%,同时获得77.8%的回收率。     

不同管径碳纳米管中CO2/CH4分离的分子模拟

生物甲烷路线在CO₂减排和节能方面有很大的应用前景。而对生物沼气的分离是此路线的一个关键问题,特别是在60℃和0.1 MPa下。巨正则Monte Carlo（GCMC）和平衡分子动力学（EMD）的分子模拟方法研究CO₂和CH₄在不同管径的碳纳米管（CNT）中的吸附和扩散,可以从分子层面研究生物沼气的分离机理。分别计算了CO₂/CH₄二元混合物吸附量、吸附选择性、自扩散系数和渗透选择性等参数。模拟结果表明：由于碳管的受限空间和CO₂与碳纳米管壁面分子之间强相互作用,导致二元等物质的量的混合物CO₂/CH₄的吸附量和扩散系数的差异。CO₂的吸附量和自扩散系数都比CH₄的大。渗透选择性在碳管管径达到最接近1 nm时达到最大值,此时混合物的分离过程是吸附控制,而非扩散控制。     

Enhanced mechanical properties of PDMS/PMMA composite membrane using MWCNTs and its application in phenol separation from saline wastewater

This work describes the enhanced mechanical properties of composite polydimethylsiloxane/poly(methyl methacrylate) (PDMS/PMMA)/multi-walled carbon nanotubes (MWCNTs) nanofiber membrane and its application in the phenol separation from saline wastewater. MWNCTs with varied content were immobilized in the membrane matrix using electric field of electrospinning. The neat PDMS/PMMA and composite PDMS/PMMA/MWCNTs membranes were characterized by scanning electron microscopy, universal testing machine, contact angle measurement, 3D automatic optical profiler, and pore size analyzer. Results indicated that tensile strength of composite PDMS/PMMA/MWNCTs membrane was drastically increased six times with a water contact angle (WCA) of 163.3° due to increased roughness parameters compared to neat membrane. However, porosity and fiber diameter of PDMS/PMMA/MWCTs membrane decreased with the increase of MWCNTs content. Moreover, phenol extraction efficiency of PDMS/PMMA/MWNCTs membrane was found to be 34.5% higher than neat one with similar salt rejection efficiency of 99.97%. The stability of MWCNTs in the membrane matrix was confirmed by the cross-sectional morphology, which indicated the robust and novel design of membrane. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47123.     

Preparation and Characterization of Thermal Conductive Composite Membranes of Aligned Esterified Carbon Nanotubes/Poly(vinylidene fluoride)

Esterified carbon nanotubes (MWCNT-COOC₁₆H₃₃) were prepared. Composite membranes were fabricated. An alternating current (AC) electric field was applied to the membrane structure orientation. The structures and properties of composite membranes were investigated. The fillers induced the β phase of PVDF; the electric field further enhanced the β phase and made more orderly structures. The fillers arranged along with the electric field and formed a thermal channel. The thermal conductivities of composite membranes were improved by MWCNT-COOC₁₆H₃₃. When the MWCNT-COOC₁₆H₃₃ content reached 5%, the thermal conductivity of composite membrane was 56.05% higher than pure PVDF and even 57.18% higher after alignment.     

Improvement of H2/CH4 Separation Performance of PES Hollow Fiber Membranes by Addition of MWCNTs into Polymeric Matrix

Carboxylated multiwalled carbon nanotubes (MWCNTs) were added to polyethersulfone hollow fiber membranes to improve their H₂/CH₄ separation properties. The addition of MWCNTs up to 1 wt% increased macrovoids formation in cross-section, while in 2 wt% loading, decreased due to increase in dope viscosity. The best gas separation performance for the mixed-matrix hollow fiber membranes was achieved at 1 wt% MWCNTs loading with hydrogen permeance of 69 GPU and H₂/CH₄ selectivity of 44.1 at 5 bar(g). Tensile test results showed that incorporation of MWCNTs into the polymeric matrix affected the mechanical properties of the fabricated membranes.     

Preparation and properties of polyvinyl chloride ultrafiltration membranes blended with functionalized multi‐walled carbon nanotubes and MWCNTs/Fe3O4 hybrids

To investigate the influence of magnetic materials combined with carbon nanotubes (CNTs) as fillers on the membrane properties, multi‐walled carbon nanotubes (MWCNTs) functionalized by mixed acids (V_H2SO4:V_HNO3=3:1) were loaded by Fe₃O₄ through a hydrothermal method. The obtained MWCNTs/Fe₃O₄ hybrids were characterized by X‐ray diffraction (XRD), Infrared spectroscopy (IR) spectrum, and scanning electron microscope (SEM) and then blended with polyvinyl chloride (PVC) to prepare ultrafiltration (UF) membranes through a phase inversion process. Simultaneously, two other UF membranes, PVC blended with acid‐treated MWCNTs and PVC blended with nothing, were also prepared. The results showed that the membrane porosity and mean pore size increased slightly with the addition of fillers. Static contact angle showed that MWCNTs/Fe₃O₄ hybrids improved the hydrophilicity of membrane surface better than the acid‐treated MWCNTs. Pure water flux increased consistently with the hydrophilicity of the membrane surface. SEM and atomic force microscope (AFM) images showed that the MWCNTs/Fe₃O₄ blended membrane formed a relatively complete pore structure throughout the cross‐section and had a rougher top surface. However, the mechanical properties of membranes with fillers were reduced compared with the pristine PVC membrane. The rejections of membranes for Bovine serum albumin (BSA), Bisphenol A (BPA), and Norfloxacin (NOR) showed that MWCNTs/Fe₃O₄ played an important role in trapping pollutants in membrane filtration. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43417.     

Fabrication and modification of cellulose acetate based mixed matrix membrane: Gas separation and physical properties

[Cellulose acetate (CA)-blend-multi walled carbon nano tubes (MWCNTs)] mixed matrix membranes (MMMs), [CA/polyethylene glycol (PEG)/MWCNTs] and [CA/styrene butadiene rubber (SBR)/MWCNTs] blend MMMs were prepared by solution casting method for gas separation applications using Tetrahydrofuran (THF) as solvent. Both raw-MWCNTs (R-MWCNTs) and functionalized carboxylic-MWCNTs (C-MWCNTs) were used in membrane preparation. The MWCNTs loading ratio and pressure effects on the gas separation performance of prepared membranes were investigated for pure He, N₂, CH₄ and CO₂ gases. Results indicated that utilizing C-MWCNT instead of R-MWCNTs in membrane fabrication has better performance and (CO₂/CH₄) and (CO₂/N₂) selectivity reached to 21.81 and 13.74 from 13.41 and 9.33 at 0.65 wt% of MWCNTs loading respectively. The effects of PEG and SBR on the gas transport performance and mechanical properties were also investigated. The highest CO₂/CH₄ selectivity at 2 bar pressure was reached to 53.98 for [CA/PEG/C-MWCNT] and 43.91 for [CA/SBR/C-MWCNT] blend MMMs at 0.5 wt% and 2 wt% MWCNTs loading ratio respectively. Moreover, increase of feed pressure led to membrane gas permeability and gas pair selectivity improvement for almost all prepared membranes. The mechanical properties analysis exhibited tensile modules improvement with increasing MWCNTs loading ratio and utilizing polymer blending.     

Dispersions of carbon nanotubes in sulfonated poly[bis(benzimidazobenzisoquinolinones)] and their proton-conducting composite membranes

A sulfonated poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI) possessing a conjugated pyridinone ring was shown to be effective for dispersing multiwalled carbon nanotubes (MWCNTs) in DMSO. The dispersions in which the SPBIBI to MWCNTs mass ratio was 4:1 demonstrated the highest MWCNTs concentrations, i.e., 1.5-2.0 mg mL⁻¹, and were found to be stable for more than six months at room temperature. Through casting of these dispersions, MWCNTs/SPBIBI composite membranes were successfully fabricated on substrates as proton exchange membranes for fuel cell applications and showed no signs of macroscopic aggregation. The properties of composite membranes were investigated, and it was found that the homogeneous dispersion of the MWCNTs in the SPBIBI matrix altered the morphology structures of the composite membranes, which lead to the formation of more regular and smaller cluster-like ion domains. As a result, and in comparison to a pristine SPBIBI membrane, the composite membranes displayed more significant proton conductivities, especially at low relative humidity, without sacrificing other excellent properties, such as thermal, dimensional and oxidative stabilities. For instance, the composite membranes with an MWCNTs content only of 0.5 wt% exhibited proton conductivities of 0.021 S cm⁻¹ at 50 RH% and 70 °C, a value almost fourfold as high as that of the pristine SPBIBI membranes under identical conditions (0.005 S cm⁻¹). The result was comparable to Nafion 117 (0.021 S cm⁻¹). The homogenous dispersion of the MWCNTs and the efficient enhancement the SPBIBI performance were attributed to the π-π interaction between the pyridinone ring and the sidewalls of the MWCNTs which changed the morphological structure of composite membranes as revealed by TEM. A combination of a low methanol crossover with excellent thermo-oxidative and water stabilities indicated that the SPBIBI composite membranes were good candidate materials for proton exchange membranes in fuel cell applications.     

Synthesis and characterization of poly(ether-<Emphasis Type="Italic">block</Emphasis>-amide) copolymers/multi-walled carbon nanotube nanocomposite membranes for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation

One of the effective techniques for improving separation properties of polymeric membranes is incorporation of suitable nanoparticles into their matrices. This study presents the preparation of three types of nanocomposite membranes comprising three grades of poly (ether-block-amide) (Pebax 1074, Pebax 1657 and Pebax 2533) and modified multi-walled carbon nanotubes (MWCNTs) with different loadings (1, 1.5, 2 and 2.5 wt%). The prepared membranes were characterized by field emission scanning electron microscopy (FESEM), attenuated total reflection-Fourier transfer infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD). Permeation of CO₂ and CH₄ gases through the prepared membranes was measured at the pressure range of 2-8 bars and 25 °C. The results showed that the incorporation of MWCNTs into the polymers matrices improves CO₂/CH₄ selectivity. Further, Pebax 1074/MWCNT nanocomposite membrane exhibits better performance for CO₂/CH₄ separation compared to the neat Pebax and the two other nanocomposite membranes.     

Preparation and Characterization of Polycarbonate-Blend-Raw/Functionalized Multi-Walled Carbon Nano Tubes Mixed Matrix Membrane for CO2 Separation

Membrane composed of PC as base of polymer matrix with different ratio of multiwall carbon nano tubes (MWCNTs) as nanofillers and poly ethylene glycol (PEG) as second polymer was prepared by solution casting method. Both raw-MWCNTs (R-MWCNTs) and functionalized carboxyle-MWCNTs (C-MWCNTs) were used in membrane preparation. The MWCNTs loading ratio and pressure effects on the gas transport properties of membranes were examined in relation to pure He, N₂, CH₄, and CO₂ gases. Results showed that the use of C-MWCNT instead of R-MWCNTs in mixed matrix membranes (MMMs) fabrication with base of PC provides better performance and also it increases (CO₂/CH₄) and (CO₂/N₂) selectivities to 27.38 and 25.42 from 25.45 and 19.24, respectively (at 5 wt% of MWCNTs). PEG as the second rubbery polymer was utilized to improve the separation performance and mechanical properties. In blend MMMs, highest (CO₂/CH₄) selectivity at 2 bar pressure increased to 35.64 for PC/PEG/C-MWCNT blend MMMs which was 27.28 for PC/MWCNTs MMMs at 10 wt%. Increase of feed pressure led to gas permeability and gas pair selectivity improvement in approximately all of membranes. Analysis of mechanical properties showed improvement in tensile modules with the increase of MWCNTs loading ratio and use of PEG in prepared MMMs.     

Effect of Raw Multi-Wall Carbon Nanotubes on Morphology and Separation Properties of Polyimide Membranes

Raw multi wall carbon nanotubes (r-MWCNTs) were embedded as fillers inside the polyimide (PI) matrix and PI/r-MWCNTs mixed matrix membranes were fabricated by the phase inversion method. The TEM images and permeation results using helium as test gas showed that r-MWCNTs were generally closed ended and acted as impermeable nano particles. Gas permeation tests using CO₂ and CH₄ showed that the addition of r-MWCNTs into the dope solution increased the CO₂/CH₄ separation factor while decreasing the carbon dioxide and methane permeances. When the r-MWCNTs content was increased from 0% to 6 wt.%, permeance of CO₂ in the flat sheet mixed matrix membranes decreased from 9.15 GPU to 5.49 GPU and CO₂/CH₄ separation factor increased from 19.05 to 45.75. Identical to flat sheet mixed matrix membranes, the addition of 2 wt.% r-MWCNTs into a spinning dope increased the CO₂/CH₄ separation factor from 46.61 to 72.20. The glass transition temperature of the mixed matrix flat sheet membranes increased with an increase in the r-MWCNTs content. This implies a good segmental-level attachment between the two phases that forms a rigidified polymer region at the polymer/r–MWCNTs interface. FESEM images showed well dispersed r-MWCNTs in the polymer matrix at a loading of 2 wt% r-MWCNTs.     

Preparation and characterization of polyvinylchloride based mixed matrix membrane filled with multi walled carbon nano tubes for carbon dioxide separation

Poly vinyl chloride/multi wall carbon nano tubes (PVC/MWCNTs) mixed matrix membranes (MMMs) were prepared for gas separation. Raw and functionalized MWCNTs (R-MWCNTs and C-MWCNTs) were utilized in membranes preparation. The C-MWCNT shows better performance compared to raw ones. Membrane (CO₂/CH₄) selectivity was increased from 39.21 to 52.18 at 2 bar pressure by MWCNT loading ratio. The modified membranes with styrene butadiene rubber (SBR-MMMs) showed 63.52 and 34.70 selectivity for (CO₂/CH₄) and (CO₂/N₂) at 2 bar pressure. Mechanical properties analysis exhibited tensile module improvement utilizing blending modification. Increase of feed pressure led to membrane gas permeability decreasing. But gas pair selectivity follows a nearly constant behavior for MMMs and increasing behavior for blend MMMs.