石墨烯基材料在CO2分离膜领域的研究进展

节能高效的CO₂分离技术的开发具有重要的现实及长远意义,膜法CO₂分离在该领域备受关注,具有优异传质特性的新型分离膜材料对膜分离过程有决定性的影响。近年来,石墨烯及其衍生材料因独特的单原子层厚度、亚纳米级别的孔道结构以及优异的机械、化学和热稳定性,成为气体分离膜领域的研究热点,膜的加工难度、技术成本、大面积制备、工作稳定性等问题是限制其实际应用的关键因素。石墨烯基CO₂分离膜主要有三种形式：纳米孔石墨烯膜、层状结构氧化石墨烯膜、基于石墨烯及其衍生材料的混合基质膜。本文综述了石墨烯基CO₂分离膜领域的突破性研究进展,重点介绍了气体的跨膜传质机理和膜的构性关系,总结了膜性能的优化思路和原理,梳理了石墨烯基CO₂分离膜发展面临的挑战,提出了潜在的研究方向。分析表明,进行系统的理论研究,采用先进的表征手段,以建立膜构性关系的理论模型,指导膜结构设计是未来研究的重点。此外,进一步降低膜加工成本,充分研究膜在实际工作环境中的稳定性也至关重要。     

Recent advances on mixed matrix membranes for CO2 separation

Recent advances on mixed matrix membrane for CO2 separation are reviewed in this paper. To improve CO2 separation performance of polymer membranes, mixedmatrixmembranes (MMMs) are developed. The concept of MMM is illustrated distinctly. Suitable polymer and inorganic or organic fillers for MMMs are summarized.Possible interface morphologies between polymer and filler, and the effect of interface morphologies on gas transport properties of MMMs are summarized. The methods to improve compatibility between polymer and filler are introduced. There are eightmethods including silane coupling, Grignard treatment, incorporation of additive,grafting, in situ polymerization, polydopamine coating, particle fusion approach and polymer functionalization. To achieve higher productivity for industrial application,mixed matrix composite membranes are developed. The recent development on hollow fiber and flat mixedmatrix composite membrane is reviewed in detail. Last, the future trend of MMM is forecasted.     

Highly selective polymeric membranes for gas separation

Polymeric membranes have gained an important place in chemical technology and are used in a broad range of applications. The key property that is exploited is the ability of a membrane to control the permeation rate of a chemical species through the membrane. The goal is to allow one component of a mixture to permeate the membrane freely, while hindering permeation of other component. To accomplish this, we proposed a novel concept of a (universal) ‘organic molecular sieve’ and experimentally proved its possibility by showing that organic polymer molecules at the interface between the permeable phase and the impermeable phase play the role of molecular sieves. This resulted in a significantly improved selectivity in gas separation, in fact going over the so-called ‘upper-bound’ sought for the past 30 years by many researchers but without much success. Since, this is not size selective like an inorganic molecular sieve but diffusion selective (the compatibilizer works like a molecular sieve to separate one gas molecules from the other), it can be used for the preparation of polymeric membranes for separation of any gas molecules pair. Because of polymer processability, this method is quite promising for the continuous mass production of polymeric membranes for real applications, especially when the polymers are insoluble to common solvents so that solution based techniques are hard to apply. This strategy can be applicable to various separation processes of many chemicals and gases.     

用于燃烧后CO2捕集系统的胺基固态吸附材料研究进展

随着工业化的发展和大量化石燃料的消耗,大量的CO₂气体排放到大气中并引发了一系列严重的环境问题,而采用燃烧后CO₂捕集技术可以有效地应对这一问题。寻找一种高效吸附、稳定、价格低廉的固态吸附材料对于开展燃烧后CO₂捕集系统的研究具有重要的实际意义。近年来,胺基固态吸附材料因其高CO₂吸附能力和高吸附选择性成为研究的热点。本文综述了近年来国内外学者对不同胺基固态吸附材料在合成方法、载体材料选择以及性能测试等方面进行的研究,重点讨论了以沸石分子筛、介孔硅分子筛、多孔碳和金属有机骨架为载体的胺基固态吸附材料对CO₂的吸附行为,并指出多孔载体材料的结构改进及有机胺和促进剂的合理选择将会成为未来胺基固态吸附材料的重点研究方向。     

Nitric oxide and carbon monoxide permeation through glassy polymeric membranes for carbon dioxide separation

Minor components present in polymeric membrane gas separation can have a significant influence on the separation performance. Carbon monoxide and nitric oxide exist in post-combustion gas streams and can therefore influence CO₂ transport through membranes designed for that application. Here, the permeability of nitric oxide (NO) through three glassy polymeric membranes (polysulfone, Matrimid 5218 and 6FDA-TMPDA) was determined and found to be less than the CO₂ but greater than the N₂ permeability in each membrane. This study also investigated the influence of 1000 ppm CO on the mixed gas permeability of CO₂ and N₂ for two glassy polymeric membranes; polysulfone and 6FDA-TMPDA. For both membranes, CO competitive sorption resulted in a reduction in the measured permeability of CO₂ and N₂ even though present at only low concentration.     

FAU zeolite membranes for dewatering of amine-based post-combustion CO2 capture solutions

In amine-based CO₂ capture processes, aqueous amine solvent is circulated between absorber (CO₂ absorption) and stripping (solvent regeneration) columns. To reduce solvent regeneration energy demand, a selective membrane can dewater and enrich the CO₂ concentration in solution prior to the stripper, lowering steam requirements for solution heating. In this work, a facile synthesis strategy was developed to prepare faujasite (FAU) zeolite membranes built upon polydopamine (PDA) modified α-Al₂O₃ substrates. PDA facilitated the attachment of zeolite phases onto the substrate surface to form a 3 μm membrane layer. Membrane permeation flux of 4.45 kg m⁻² h⁻¹ and 95% rejection rate calculated by either CO₂ loading or total alkalinity was achieved in dewatering of CO₂ loaded 30 wt% monoethanolamine (MEA) solution. The effects of temperature on membrane dewatering performance and stability were investigated. This study highlights the potential for process integration of membrane technology in amine-based post-combustion CO₂ capture operations.     

Nano-silica/polysulfone asymmetric mixed-matrix membranes (MMMs) with high CO2 permeance in the application of CO2/N2 separation

Nano-sized silica/polysulfone (PSf) flat sheet asymmetric MMMs with high CO₂ permeance for CO₂/N₂ separation were fabricated by dry/wet phase inversion method using N, N-dimethylacetamide (DMAc) and tetrahydrofuran (THF) as solvents and ethanol as additives. The results indicated that the addition of nano-silica on the polymer matrix resulted on reduced membrane performance due to void formation and particle agglomeration. Optimum membrane performance was obtained at the following fabrication parameters: 22 wt.% PSf, 31.8 wt.% DMAc, 31.8 wt.% THF, 14.4 wt.% ethanol, 20 s evaporation time, and 0 wt.% silica loading, with CO₂/N₂ selectivity of 15.6 and CO₂ permeance of 14.2 GPU.     

Impregnation of carbonaceous nanofibers into glassy polymer-based composite membrane for CO2 separation

The development of defect-free composite membrane (CM) is often challenging due to poor dispersion and distribution of filler particles in the polymer matrix. Despite the attractive physicochemical properties and gas separation performance of carbon nanotube (CNT) based CM, CNT displayed poor dispersion characteristics in most polymer matrix domain. Instead of incorporating CNT, a viable alternative, carbon nanofiber (CNF) which exhibits similar properties as CNT, but improved dispersion quality in the polymer matrix is found. In this work, CNF particles were incorporated in poly(2,6-dimethyl-1,4-phenylene oxide) (PPO_dm) polymer continuous phase for CM development. The optimum gas separation performance of the PPO_dm-CNF CM (11.25 at 197.02 barrer of CO₂ permeability) was obtained at 3 wt% of CNF loading. Compared to pristine PPO_dm membrane, CO₂ permeability and CO₂/CH₄ selectivity of PPO_dm-3 wt% CNF CM were enhanced by 180% and 55%, respectively. At 3 wt% CNF loading, the filler particles were dispersed and distributed more homogenously, in which no obvious CNF agglomeration was observed. In addition, the incorporation of CNF particles also enhanced the mechanical and thermal properties of the resultant CM.     

Pseudopeptide bioconjugate additives for CO2 separation membranes

1:1[α/α‐N^α‐Bn‐hydrazino] pseudopeptide?polymer bioconjugates were synthesized and investigated as additives in a reference gas separation membrane (Pebax®) for CO₂ capture. Pebax® is a polyether block amide thermoplastic elastomer provided by Arkema and is already well known for its good performance for CO₂ separations. First, dimer and tetramer pseudopeptides were synthesized and their terminal amine was modified into a ‘clickable’ alkyne group in view of coupling. Second, an α‐azido acrylic poly(ethylene glycol)‐based oligomer was obtained by single‐electron transfer living radical polymerization and the two partners were coupled using copper(I) catalyzed alkyne‐azide cycloaddition (CuAAC) ‘click’ chemistry. The pseudopeptides and their bioconjugates were then assessed as original additives in Pebax® membranes for CO₂/CH₄ and CO₂/N₂ separations. The permeation data were analyzed according to the solution‐diffusion model. Compared to pseudopeptides, the pseudopeptide?polymer bioconjugates enabled the membrane properties to be greatly improved with better permeability (×1.5) and a good constant selectivity for CO₂ capture. The best membrane properties were obtained with 3 eq. wt% of the tetramer‐based bioconjugate with a CO₂ permeability of 194 Barrer (+46% compared to that of Pebax®) and constant selectivity (αCO₂/N₂ = 44 and αCO₂/CH₄ = 13). © 2016 Society of Chemical Industry     

Amine-functionalized polycarbosilane hybrids for CO2-selective membranes

Commercially available polycarbosilane has been chemically modified with primary and secondary amino silane derivatives in order to provide amine-functionalized polycarbosilane as hydrophobic solid sorbent capable of reversibly capturing CO₂ from flue gas streams. CO₂ uptake by the samples was investigated at the molecular level using thermogravimetric analysis under CO₂ atmosphere, in situ DRIFTS analysis, and CO₂ sorption isotherm. The reaction paths and sorption mechanisms were examined by comparing with the CO₂ adsorbing behaviors previously studied for amine-functionalized SiO₂, and proven to be related to the presence of adsorbed water, as well as the nature of the grafted amino silanes. With effective CO₂ adsorption rate, regeneration capacity at 40–50 °C, and lesser sensitivity to moist due to its hydrophobic Si-C backbone, secondary amine-functionalized polycarbosilane hybrids have potential applications in membrane gas separation through facilitated transport of CO₂.     

界面聚合制备含丙烯氧基团的复合膜用于CO2分离

含有醚氧基团的膜与CO₂分子具有较强的极性作用,可以实现对CO₂/N₂物系的高效分离.其中,含丙烯氧(PO)基团的聚合物链段自由体积较大且不易结晶,是一类具有发展潜力的溶解选择性膜材料.以均苯三甲酰氯为油相单体,含PO基团的多胺为水相单体,通过界面聚合,成功制备了含PO基团的复合膜.分别采用聚醚胺D400、D230及T403为多胺水相单体,考察了膜内PO基团数量和交联度对复合膜分离性能的影响.结果表明,采用D400所制的复合膜由于具有最高的PO基团含量及较低的交联度,因此具有最高的CO₂渗透速率和CO₂/N₂分离因子.之后,考察了单体浓度、酸吸收剂种类以及水相溶液pH对复合膜分离性能的影响.通过优化这些制膜条件,制备出了CO₂/N₂分离性能较好的复合膜.     

Mixed oxygen ionic-carbonate ionic conductor membrane reactor for coupling CO2 capture with in situ methanation

CO₂ methanation is one of the vital reactions to utilize CO₂ and realize power to gas process. To decrease the CO₂ capture cost and alleviate the hot spots during the strong exothermic methanation reaction, here, we report a coupling of CO₂ capture process with in situ CO₂ methanation process through a ceramic-molten carbonate (MC) dual phase membrane reactor over the Ni-based catalyst. The performance of the membrane reactor was systematically investigated and compared with the traditional fixed-bed reactor. The results show that the performance of the membrane reactor is higher than that of the fixed-bed reactor, since the produced steam through the methanation process can be partially removed through the dual-phase membrane, which promotes the reaction shift to right side. A stability test shows no obvious degradation within 32 h. These results indicate that the membrane reactor is promising for coupling CO₂ capture with in situ methanation process.     

多孔液体在CO2捕集与利用领域的研究进展

为助力中国早日实现“双碳目标”,深入落实化工领域绿色低碳可持续发展的重要举措,吸附-吸收耦合有望成为气体分离的绿色变革性分离技术,其关键是高性能吸附（收）材料的开发。多孔液体（PLs）作为一类具有永久孔隙的液体材料,兼具了液体吸收剂的易于管道输送、传质传热效果好等优点和固体吸附剂的高比表面积、高孔隙率等优点,有望成为新一代CO2捕集的绿色变革性介质。该文首先简单介绍了多孔液体发展脉络;然后,重点聚焦于多孔液体在CO2的吸附/吸收、膜分离、催化转化等领域的应用展开探讨,并对多孔液体性能和优缺点进行分析归纳。最后,对多孔液体目前面临的挑战和未来发展趋势进行了展望。     

Understanding the performance of membrane for direct air capture of CO2

Direct air capture (DAC) of CO₂ is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO₂ from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single-stage separation process with the co-current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO₂ in permeate, and power requirement. Additionally, three levels of CO₂ reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade-off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate.     

笼型水合物膜分离和捕获二氧化碳研究进展

开发一种低碳、高效的分离和捕获二氧化碳方法一直是缓解温室效应的关键技术。本文首先比较了现有的5种碳捕获技术,发现相较于化学吸收、深冷分离和变压吸附,水合物法和膜分离技术具有绿色环保、操作简单的优势。随后,本文以水合物法为切入点,阐述了其分离机理和强化手段。为进一步研究更加有效的新技术,通过利用水合物法的技术优势,结合膜分离的结构,提出一种更加具有发展潜力的水合物膜分离技术。然后,根据水合物膜的成膜方式将水合物膜技术分为第一、二、三代,并重点分析了每代水合物膜技术的改进手段。最后指出未来第三代水合物膜分离技术应从以下3个方面寻求突破与创新:探索合适膜载体材料;寻找合适的添加剂;优化温度、压力、流速水合分离条件。     

有机多孔聚合物CO2捕集及分离性能的研究进展

有机多孔聚合物（porous organic polymers,POPs）是一类由有机构建单元连接而形成的新型多孔材料。由于其优异的物理化学稳定性以及CO₂吸附能力,近年来有关POPs在CO₂捕集和分离的研究成为一大研究热点。大量具有优异孔性质（比表面积和孔容）的POPs通过不同有机合成反应被成功地开发出来应用于CO₂吸附分离过程。本文介绍了POPs材料的CO₂捕集与分离性能的研究现状,总结了提高POPs材料CO₂分离性能的合成策略,重点分析了可以通过功能化增强吸附剂与二氧化碳分子之间的相互作用,来提高材料的CO₂分离能力的方法。     

Tubular MXene/SS membranes for highly efficient H2/CO2 separation

Accurately constructing membranes based on two-dimensional (2D) materials on commercial porous substrates remains a significant challenge for H₂ purification. In this work, a series of tubular 2D MXene membranes are prepared on commercial porous stainless steel substrates via fast electrophoretic deposition. Compared with other methods, such as filtration or drop coating, and so on. such preparation route shows the advantages of simple operation, high efficiency for membrane assembly (within 5 min) with attractive reproducibility, and ease for scale-up. The tubular MXene membranes present excellent gas separation performance with hydrogen permeance of 1290 GPU and H₂/CO₂ selectivity of 55. Furthermore, the membrane displays extremely stable performance during the long-term test for more than 1250 h, and about 93% of the membranes from one batch have exceeded the DOE target for CO₂ capture. Most importantly, this work provides valuable referential significance for other 2D materials-based membranes for future application development.     

燃煤净烟气中共存杂质对膜法捕集CO2影响现状

膜法捕集CO₂是现役燃煤电厂碳减排的重要手段之一，在实际应用中膜法捕集系统通常适合安装在湿法脱硫系统下游，鉴于脱硫净烟气中的颗粒物及气态污染物难以完全脱除，同时水汽接近饱和状态，气相中的共存杂质以及吸收液组分与膜及膜材料相互作用，会对膜法捕集CO₂性能造成严重影响。本文综述了烟气中共存气态、颗粒物组分及液相吸收剂对膜分离、膜吸收宏观性能、膜微结构及材质的影响，以及燃煤脱硫净烟气环境下膜法捕集CO₂长期运行性能及变化规律的研究现状，指出了抑制膜失效的技术方法，以期为突破膜法捕集CO₂技术发展的瓶颈，实现膜的稳定高效运行提供参考。     

Recent developments in aqueous ammonia-based post-combustion CO2 capture technologies

Aqueous ammonia (NH₃) is a promising alternative solvent for the capture of industrial CO₂ emissions, given its high chemical stability and CO₂ removal capacity, and low material costs and regeneration energy. NH₃ also has potential for capturing multiple flue gas components, including NO_x, SO_x and CO₂, and producing value-added chemicals. However, its high volatility and low reactivity towards CO₂ limit its economic viability. Considerable efforts have been made to advance aqueous NH₃-based post-combustion capture technologies in the last few years: in particular, General Electric's chilled NH₃ process, CSIRO's mild-temperature aqueous NH₃ process and SRI International's mixed-salts (NH₃ and potassium carbonate) technology. Here, we review these research activities and other developments in the field, and outline future research needed to further improve aqueous NH₃-based CO₂ capture technologies.