Fabrication of mixed‐matrix membranes with MOF‐derived porous carbon for CO2 separation

Mixed‐matrix membranes (MMMs) have shown great advantages but still face some challenges, such as the trade‐off between permeability and selectivity, stability, and the lack of efficient ways to enhance them simultaneously. Here, the fabrication of MMMs with metal‐organic frameworks derived porous carbons (MOF‐PCs) as fillers which exhibit selective‐facilitating CO₂ transport passage originating from interactions between fillers and CO₂ is showed. With the aid of the developed multicalcination method, MOF‐PCs with variable N‐contents were prepared and incorporated into PPO‐PEG matrix for the first time to prepare MMMs, which show excellent separation performance for CO₂/CH₄ mixture with a tunable separation performance by combining different N‐contents and surface areas of MOF‐PCs. Moreover, the developed MMMs have hydrothermal and chemical stability. This work not only presents a series of MMMs with both good separation properties and stability, it also provides useful information for guiding the fabrication of high performance MMMs for practical application. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3400–3409, 2018     

CO2/N2 separation ability and structural characteristics of poly(butadiene‐co‐acrylonitrile)‐based polyurethanes and hydrogenated nitrile rubbers

Two families of rubbery polymers, commercial hydrogenated nitrile rubbers and synthesized poly(acrylonitrile‐co‐butadiene)‐based polyurethanes with different amount of nitrile groups were studied as CO₂ selective membrane materials. The polymers were characterized by the techniques of FTIR, gel permeation chromatography, WAXD, and differential scanning calorimetry. The permeabilities of pure CO₂ and N₂ were measured using constant pressure/variable volume method at a feed pressure of 6 atm. With a higher amount of polar nitrile group within a given family of polymers, the permeability coefficient (P) was found to decrease, while the permselectivity (α) of these membranes was found to increase. The trade‐off between both transport parameters was less severe for the polyurethanes, which also showed much higher permeabilites. The results obtained were also discussed with respect to the polymer structure, and some relationships were found between P and T_g values. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

CO2/CH4 separation using inside coated thin film composite hollow fiber membranes prepared by interfacial polymerization

Carbon dioxide(CO_2) is greenhouse gas which originates primarily as a main combustion product of biogas and landfill gas. To separate this gas, an inside coated thin film composite(TFC) hollow fiber membrane was developed by interfacial polymerization between 1,3–cyclohexanebis–methylamine(CHMA) and trimesoyl chloride(TMC). ATR-FTIR, SEM and AFM were used to characterize the active thin layer formed inside the PSf hollow fiber. The separation behavior of the CHMA-TMC/PSf membrane was scrutinized by studying various effects like feed gas pressure and temperature. Furthermore, the influence of CHMA concentration and TMC concentration on membrane morphology and performance were investigated. As a result, it was found that mutually the CHMA concentration and TMC concentration play key roles in determining membrane morphology and performance. Moreover, the CHMA-TMC/PSf composite membrane showed good CO_2/CH_4 separation performance. For CO_2/CH_4 mixture gas(30/70 by volume) test, the membrane(PD1 prepared by CHMA 1.0% and TMC 0.5%) showed a CO_2 permeance of 25 GPU and the best CO_2/CH_4 selectivity of 28 at stage cut of 0.1. The high CO_2/CH_4 separation performance of CHMA-TMC/PSf thin film composite membrane was mostly accredited to the thin film thickness and the properties of binary amino groups.     

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。     

Fabrication of Pebax/SAPO mixed matrix membranes for CO2/N2 separation

Mixed matrix membranes (MMMs) were prepared by solvent evaporation method using Pebax-1074 polymer as matrix and inorganic zeolite SAPO-23 as dopant. The morphology, surface functional groups, microstructure, thermal stability, and separation performance of MMMs were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and gas permeation, respectively. The effects of dopant loading amount, permeation temperature, and permeation pressure on the structure and properties of MMMs were investigated. The results showed that the introduction of SAPO zeolite reduced the crystallinity of the MMMs and improved the CO₂/N₂ selectivity. Under the conditions of 30°C and 0.15 MPa, the MMMs prepared by incorporating with 5% SAPO zeolite in content exhibited the highest CO₂/N₂ selectivity of 72.0 together with the CO₂ permeability of 98.2 Barrer.     

淀粉基多孔碳材料的制备及其吸附CO2/CH4性能

以淀粉为原料,使用水热法将其碳化后用活化剂KOH对其活化,制备了淀粉基多孔碳材料,并对其进行结构表征和CO₂/CH₄的吸附性能测试,计算吸附热以及材料对CO₂/CH₄的吸附选择性,讨论了碳材料结构对其吸附性能的影响。结果表明：在制备过程中,随着活化剂KOH用量比例的增大,所制得的材料其比表面积和孔容增大,其孔径分布也就越宽。所制得的碳材料其比表面积可达2972 m²·g^-1。这些淀粉基多孔碳材料对水蒸气的吸附等温线呈现出Ⅳ类等温线。所制备材料对CO₂吸附容量主要取决于其孔径小于0.8 nm的累积孔容（Vd < 0.8 nm）。材料的超微孔的孔容越大,其对CO₂吸附容量也越大。所制备的C-KOH-1材料在101325 Pa和298 K条件下,对CO₂的吸附量达到4.2 mmol·g^-1,其对CO₂的吸附热明显高于其对CH₄吸附热,其对CO₂/CH₄吸附选择性为3.7～4.26,同时本文通过对材料的水蒸气吸附等温线进行测试,结果表明所得材料主要表现为中等憎水性,这对材料在实际工况的应用奠定了基础。     

Composite mixed matrix membranes incorporating microporous carbon molecular sieve as filler in polyethersulfone for CO2/CH4 separation

Membrane technology has been considered a key factor for sustainable growth in high-efficiency gas separation. Current mixed matrix membranes (MMMs) technology is rising, but these membranes in the dense structure are having difficulties in operating at high pressures and scale up for commercialization. The purpose of this research is to synthesize composite MMMs (CMMMs) consisting of polyethersulfone (PES), carbon molecular sieve (CMS 1–5 wt %), and Novatex 2471 nonwoven fabric (support layer). The membranes' physical, chemical, and thermal properties were evaluated by different analytical equipment. The morphology of both PES and PES-CMS composite membranes had a porous and asymmetric structure, in which CMS was uniformly distributed in the polymer matrix. The thermal properties showed that the membranes were stable up to 350 °C with a single glass transition temperature. The functional groups in the membrane were confirmed by spectral analysis. The gas performance results showed that carbon dioxide permeance increased with increased CMS concentration and methane permeance decreased due to the hindering effect of CMS under similar operating conditions. The highest selectivity achieved was 12.774 using CMMM of 5 wt % of CMS at 10 bar, which on average was 137.80%, improved selectivity compared to pure PES membrane. The support layer was able to withstand high operating pressures and showed the ability to scale up. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48476.     

聚丙烯中空纤维膜组件分离烟气中的CO2

膜吸收法在大型工业燃煤电厂二氧化碳（CO2）捕集方面具有很好的应用前景,但烟气组分对该技术效果影响还有待进一步研究。本文以单乙醇胺（MEA）为吸收剂,开展了疏水性聚丙烯（PP）中空纤维膜组件分离模拟烟气中的CO2的实验研究,考察了吸收操作条件以及燃煤烟气中水汽和SO2对膜组件吸收效率的影响。结果表明,试验的最佳液气比为24 L/m3;MEA的浓度为0.6 mol/L;膜组件进口的温度变化对吸收效率基本没有影响;CO2的浓度在10%～20%内变动对吸收效率影响不大。与CO2相比,SO2会优先发生吸收作用,而水汽则会吸附在聚丙烯中空纤维膜组件的孔壁上,产生毛细管凝聚现象,阻塞CO2的渗透吸收。     

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。     

PBI/Clinoptilolite mixed-matrix membranes for binary (N2/CH4) and ternary (CO2/N2/CH4) mixed gas separation

In this work, polybenzimidazole (PBI)-based mixed matrix membranes (MMMs) with natural zeolite were prepared and their transport properties for binary (N₂/CH₄) and ternary (CO₂/N₂/CH₄) mixed-gas separation were studied. The MMMs, were prepared with PBI as polymeric matrix and Mexican natural zeolite clinoptilolite enriched with cations of Ca²⁺ as filler. The thermal properties analysis of the PBI and MMMs studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicates that the MMMs membranes have Tg higher than 350°C and decomposition temperatures above 600°C compared with the pristine membranes. PBI membrane and MMMs were analyzed by X-Ray Diffraction (XRD) and the diffraction patterns showed the zeolite signals combine with the amorphous dome from the polymeric matrix. In addition, the perm-selectivity properties of the polymeric membranes and MMMs were tested with binary (N₂/CH₄; 10/90 mol%) and ternary (CO₂/N₂/CH₄; 5/10/85 mol%) gas mixtures at different pressure rates (50, 150 and 300 psi). The perm-selectivity properties of the MMMs membranes show an improvement in their values about 30% higher compared to the PBI polymeric membranes, favoring the permeation of CO₂ and N₂.     

A cobalt metal‐organic framework with small pore size for adsorptive separation of CO2 over N2 and CH4

In this study, a new cobalt‐based metal‐organic framework (MOF), [ (μ₃‐OH)₂(ipa)₅(C₃O₂)(DMF)₂] (CoIPA) was synthesized. The crystal structure analysis shows that CoIPA is constructed by Co₆(μ₃‐OH)₂ units linked by isophthalic acid forming a sxb topology and it possesses a small pore size of about 4 Å. The new MOF has been characterized using multiple experimental methods. Monte Carlo and Molecular Dynamic simulations were employed to investigate adsorption equilibrium and kinetics in terms of capacity and diffusivity of CO₂, N₂, and CH₄ on CoIPA. The gas adsorption isotherms collected experimentally were used to verify the simulation results. The activated CoIPA sample exhibits great gas separation ability at ambient conditions for CO₂/N₂ and CO₂/CH₄ with selectivity of around 61.4 and 11.7, respectively. The calculated self‐diffusion coefficients show a strong direction dependent diffusion behavior of target molecules. This high adsorption selectivity for both CO₂/N₂ and CO₂/CH₄ makes CoIPA a potential candidate for adsorptive CO₂ separation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4532–4540, 2017     

CO_2/CH_4分离膜研究进展

介绍ＣＯ２／ＣＨ４分离膜的开发背景及发展历史;ＣＯ２／ＣＨ４分离膜材料及相应的成膜技术,并提出ＣＯ２／ＣＨ４分离膜的发展方向。     

具有缺陷孔结构的炭膜分离CO2/CH4混合气的分子模拟

基于炭膜无缺陷Z字形孔模型研究结果,建立随机缺陷、均匀缺陷与局部缺陷3种不同缺陷方式的炭膜微孔模型,研究等摩尔CO₂/CH₄混合气在缺陷膜孔中的吸附和扩散过程,探讨缺陷对炭膜气体分离的影响。结果表明,在273~348 K的温度范围内,CO₂与CH₄在缺陷炭膜孔模型内的平衡吸附量与扩散系数均低于无缺陷炭膜孔模型;与无缺陷、均匀缺陷和随机缺陷孔模型相比,局部缺陷孔模型的CO₂/CH₄总分离系数最低;温度低于298 K时,随机缺陷和均匀缺陷孔模型的总分离系数均大于无缺陷孔模型;随机缺陷孔模型的总分离系数大于均匀缺陷孔模型,说明随机删除碳原子的方式比均匀删除和局部删除更加合理。研究结果可为炭膜气体渗透机理的深入研究提供依据。     

A study on natural clinoptilolite for CO2/N2 gas separation

Based on its low cost and low water adsorption capacity, compared to synthetic zeolites (A-type, X-type and Y-type), natural, untreated clinoptilolite was examined as a potential adsorbent for a separation process targeting on removal of CO₂ from flue gas. Taking into consideration typical flue gas composition and temperature, adsorptive properties of binary CO₂/N₂ mixtures were tested in the temperature range of 268 to 403 K and compared with literature data. The results showed that CO₂ concentration, total pressure, and temperature strongly affect selectivity and working capacity, restricting the conditions under which the material could be used as an efficient adsorbent.     

Formation of defect‐free polyetherimide/PIM‐1 hollow fiber membranes for gas separation

Dual‐layer hollow fiber membranes were produced from blends of Ultem and polymer of intrinsic microporosity (PIM‐1) with enhanced gas permeance. The effects of spinning parameters (take‐up speed and air gap distance) on gas separation performance were investigated based on the pristine Ultem. Selected spinning conditions were further adopted for the blend system, achieving defect‐free and almost defect‐free hollow fibers. Adding PIM results in a higher fractional free volume, 50% increments in gas permeance were observed for Ultem/PIM‐1 (95/5) and more than 100% increments for Ultem/PIM‐1 (85/15). Both O₂/N₂ and CO₂/CH₄ selectivities remained the same for Ultem/PIM‐1 (95/5) and above 80% of their respective intrinsic values for Ultem/PIM‐1 (85/15). The selective layer thickness ranges from 70 to 120 nm, indicating the successful formation of ultrathin dense layers. Moreover, minimum amounts of the expensive material were consumed, that is, 0.88, 1.7, and 2.3 wt % PIM‐1 for Ultem/PIM‐1 (95/5), (90/10), and (85/15), respectively. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3848–3858, 2014     

炭分子筛CH4/N2吸附分离

煤层气(CBM)是一种非常规天然气。在中国,煤层气在抽采出来时常混有空气。考虑到安全因素,氧气首先应该被去除。之后,煤层气利用的最重要步骤则是甲烷-氮气混合气体的甲烷高效提浓。本文搭建了双床变压吸附(PSA)装置,选择特定的炭分子筛(CMS)进行CH₄/N₂混合物分离实验研究。由于CMS的动力学吸附特性,氮被吸附在CMS上,带有一定压力的甲烷则连续输出。研究了吸附压力、进气速度和循环周期等因素对吸附过程整体性能的影响。从50% CH₄/50% N₂的原料气可以获得95.45%纯度的甲烷产品,而从30% CH₄/70% N₂的原料气可以获得94.89%纯度的甲烷产品。研究表明,以上3个参数都对分离性能有影响,其中后两者的影响更大。在较低吸附压力和较低进气速度时更容易获得纯度90%以上的甲烷产品。另外,循环周期越短,获得的甲烷纯度越高。     

沸石分子筛对CO_2/CH_4混合气的分离效果研究

选取5A沸石分子筛作为脱碳吸附材料,考察了其对CO2及CH4单组份的吸附效果。结果表明,5A分子筛真空解吸在1 h 50 min即可达到解吸、脱碳、再生的目的,且经8次重复吸附-解吸后仍具有较高及较稳定的脱碳效率。将5A分子筛应用到沼气实际分离实验中,在沼气中n(CO2)∶n(CH4)=40∶60的条件下,经单塔处理可达0.17 m3/kg处理量,甲烷纯度可达97%以上,且连续处理速率为0.60 m3/(h·kg),该研究为今后的沼气分离工程提供了技术参数。     

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。     

离子液体膜材料分离二氧化碳的研究进展

离子液体由于具有不易挥发、结构可调、对CO₂有良好的吸收性能等特点而成为当前CO₂分离领域的研究热点,但因高黏度和高成本问题而限制了其工业化应用。将离子液体与气体分离膜材料结合,得到的新型分离膜材料兼具离子液体和膜的优势,成为当前离子液体研究领域的趋势之一。针对这一热点问题,综述了离子液体支撑液膜、聚离子液体膜和离子液体共混/杂化膜在CO₂分离方面的研究现状和进展,讨论了离子液体结构和含量对膜分离性能、稳定性等的影响。相关研究表明,离子液体共混/杂化膜具有较高的分离性能和稳定性,是一种很有应用前景的CO₂分离材料。提出该领域的重点发展方向,即开发新的功能化离子液体共混/杂化膜材料是解决高渗透通量与高稳定性之间矛盾、强化CO₂分离性能的有效途径,深入研究离子液体共混/杂化膜的形成机制、气体在膜中的渗透行为以及CO₂分离机理。