Enhancement of CO2 Adsorption and CO2/N2 Selectivity on ZIF‐8 via Postsynthetic Modification

Imidazolate framework ZIF‐8 is modified via postsynthetic method using etheylenediamine to improve its adsorption performance toward CO₂. Results show that the BET surface area of the modified ZIF‐8 (ED‐ZIF‐8) increases by 39%, and its adsorption capacity of CO₂ per surface area is almost two times of that on ZIF‐8 at 298 K and 25 bar. H₂O uptake on the ED‐ZIF‐8 become obviously lower compared to the ZIF‐8. The ED‐ZIF‐8 selectivity for CO₂/N₂ adsorption gets significantly improved, and is up to 23 and 13.9 separately at 0.1 and 0.5 bar, being almost twice of those of the ZIF‐8. The isosteric heat of CO₂ adsorption (Q_st) on the ED‐ZIF‐8 becomes higher, while Q_st of N₂ gets slightly lower compared to those on the ZIF‐8 Furthermore, it suggests that the postsynthetic modification of the ZIF‐8 not only improves its adsorption capacity of CO₂ greatly, but also enhances its adsorption selectivity for CO₂/N₂/H₂O significantly. ©2013 American Institute of Chemical Engineers AIChE J, 59: 2195–2206, 2013     

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。     

一种具有高CO吸附容量和高CO/N2及CO/CO2分离选择性的CuCl@β吸附剂

研制了一种新型的CuCl@β分子筛吸附剂材料,它不仅对CO有着高吸附容量,而且对CO/N₂和CO/CO₂的二元混合气有着高吸附选择性。利用自发单层分散的原理制备了一系列的CuCl@β分子筛材料,分别应用氮气吸附以及XRD进行表征。CO在CuCl@β分子筛上吸附等温线和动态透过曲线分别通过静态吸附和固定床实验获得。依据IAST理论模型计算了CuCl@β分子筛对CO/N₂二元混合物和CO/CO₂二元混合物的吸附选择性。研究结果表明:(1)氯化亚铜的负载增强了一氧化碳在CuCl@β分子筛上的吸附容量,其最佳负载量为0.4 g·g^-1。(2)CuCl@β分子筛吸附剂在增强CO的吸附量的同时,还降低了对二氧化碳和氮气的吸附。由于Cu⁺-CO π位络合键的存在,提高了CuCl@β分子筛对二元混合物CO/N₂和CO/CO₂的吸附选择性。(3)在低压下(0～10 kPa)下0.4CuCl@β分子筛对CO/N₂和CO/CO₂的吸附选择性分别高达1600～5200和120～370,远大于原始的β分子筛。CuCl@β分子筛对CO有着超高吸附容量以及吸附选择性,将会是一种很有潜力的CO分离提纯材料。     

CO2和N2吸附的研究札记

Experiments were made for the adsorption of CO2 and N2 on typical adsorbents to investigate the effects of porous structure and surface affinity of adsorbents as well as those of adsorption temperature and pressure that might cause the variation of adsorption mechanism. It is shown that polar surface tends to enlarge the adsorption difference between CO2 and N2, and the difference is more sensitive to temperature than the adsorbents with non-polar surface. The adsorbents with non-polar surface are not much sensitive to the effect of water vapor, though the water vapor interferes the separation remarkably. The separation coefficient linearly increases with the micropore volume per unit surface area of activated carbons, but no rule is shown on mesoporous silicon materials. The function of adsorption mechanism on the separation is not as much as expected.     

改性蜂窝状活性炭吸附二氧化碳和氮气的热力学

蜂窝状活性炭具有较高的比表面积、多孔道、压降低、吸脱附速率快、不易堵塞等优点,因此被认为是捕集烟道气中CO₂重要吸附材料。选用蜂窝状煤基和椰壳两种活性炭吸附剂,采用磁悬浮热天平分别测定了CO₂和N₂的吸附等温线。采用1 mol·L^-1 K₂CO₃对蜂窝状活性炭材料进行浸渍改性,提高在低二氧化碳分压下的CO₂吸附性能。采用Langmuir、multi-site Langmuir和Virial 3种模型对吸附平衡数据进行拟合,得出热力学参数,为后续吸附工艺优化设计提供基础数据。结果表明在实验范围内3种模型均能对实验测量的等温线进行较好的拟合,Langmuir模型总体拟合效果最好。     

N2和CO在5A分子筛上吸附的气相色谱研究

文中重新推导并简化了采用反相气相色谱法来测定吸附热力学参数的计算公式,并且在不同温度下,对N2和CO在4种5A分子筛上色谱保留时间进行了测定,对测定结果以推导公式为函数作线性回归,并且计算了吸附热力学参数ΔadH,ΔadS和ΔadG。结果表明,保留时间与1/T相关性很好,CO的吸附热随着分子筛Ca2+交换度的增加而增加,随着H+交换度的增加而减少,N2的吸附热则随着Ca2+交换度的增加变化不明显,随着H+交换度的增加而减少;CO和N2的吸附热在-25.36—-29.39 kJ/mol,4种分子筛对N2和CO的吸附熵在-80.01—-73.96J/(mol.K)和-72.13—-60.48 J/(mol.K),吸附G ibbs自由能变分别在-2.98—-4.77 kJ/mol和-9.82—-8.26 kJ/mol。     

Experimental Evaluation of the Adsorption,Diffusion, and Separation of CH4/N2 and CH4/CO2 Mixtures on Al-BDC MOF

Adsorption equilibrium, thermodynamics, and kinetics of CH₄, N₂, and CO₂ were investigated by volumetric-chromatographic and inverse gas chromatographic (IGC) methods on the Al-BDC MOF. The binary adsorption data from the volumetric-chromatographic experiments represents that the Al-BDC MOF has a high CO₂/CH₄ selectivity ca. 11 and a CH₄/N₂ selectivity ca. 4.3 at 303 K, and appears to be a good candidate for the CH₄ separation. The initial adsorption heats of CH₄, N₂, and CO₂ on the Al-BDC MOF were determined to be 15.3, 11.5, and 32.2 kJmol^?1 by IGC method, respectively. Moreover, the micropore diffusivities of N₂, CH₄ and CO₂ in the Al-BDC MOF at 303 K were also estimated to be 1.58 × 10^?7 cm²/s, 7.04 × 10^?8 cm²/s, and 3.95 × 10^?9 cm²/s, respectively. The results indicate that micropores play a crucial role in the adsorptive separation of the CH₄/N₂ and CH₄/CO₂ mixtures, and the IGC method is a validity manner to estimate the thermodynamic and kinetic parameters of MOF adsorbents.     

Separation of CO2/N2 Gas Mixture through Carbon Membranes: Monte Carlo Simulation

Abstract

Monte Carlo simulation method is employed to investigate separation behavior of gas mixture composed of carbon dioxide and nitrogen through a model carbon membrane under the different conditions. The simulation gives insight into the separation mechanism to a certain extent, which is based on the loading and diffusion of carbon dioxide and nitrogen in the carbon membrane with different pore size. The simulation results indicate that the carbon dioxide can be adsorbed on the surface of membrane wall more strongly, whereas the diffusion rate of nitrogen is more prominent. When the separation condition alters, the influence of the two main factors mentioned above on transport of gas molecules in membranes becomes different. Therefore, the equilibrium selectivity of nitrogen and carbon dioxide changes correspondingly.     

Interaction of gases with ablative composites. I. Ar,CO2, and N2

The sorption of argon, carbon dioxide, and nitrogen on two heat shield composites SLA-561 and SLA-561V and the SLA components was measured over the pressure range of 10^?3 to 760 torr and in the temperature range of 30° to 50°C. The sorption of the gases by both the composites and the components varied directly with pressure. The sorption of CO₂ by the phenolic spheres and the silicone elastomer and of Ar by the silicone elastomer varied inversely with temperature. The mechanism involved in the gas sorption was primarily absorption.     

Flexible two-dimensional square-grid coordination polymers: structures and functions

Coordination polymers (CPs) or metal-organic frameworks (MOFs) have attracted considerable attention because of the tunable diversity of structures and functions. A 4,4'-bipyridine molecule, which is a simple, linear, exobidentate, and rigid ligand molecule, can construct two-dimensional (2D) square grid type CPs. Only the 2D-CPs with appropriate metal cations and counter anions exhibit flexibility and adsorb gas with a gate mechanism and these 2D-CPs are called elastic layer-structured metal-organic frameworks (ELMs). Such a unique property can make it possible to overcome the dilemma of strong adsorption and easy desorption, which is one of the ideal properties for practical adsorbents.     

Adsorption of H2, CO2, CH4, CO,N2 and H2O in Activated Carbon and Zeolite for Hydrogen Production

Abstract

The design of a layered pressure swing adsorption unit to treat a specified off-gas stream is based on the properties of the adsorbent materials. In this work we provide adsorption equilibrium and kinetics of the pure gases in a SMR off-gas: H₂O, CO₂, CH₄, CO, N₂, and H₂ on two different adsorbents: activated carbon and zeolite. Data were measured gravimetrically at 303–343 K and 0–7 bar. Water adsorption was only measured in the activated carbon at 303 K and kinetics was evaluated by measuring a breakthrough curve with high relative humidity.     

应用于烟气中CO2捕集的固体吸附材料研究进展

固体吸附法捕集二氧化碳技术具有吸/脱附性能优良、设备轻便灵活、环保和低成本的优势，被认为是实现电厂烟气中碳捕集最具前景的技术之一。国内外学者对于可应用于电厂烟气中二氧化碳捕集的固体吸附材料开展了大量的研究并取得一定进展。该文综述了近些年沸石分子筛、金属有机框架材料（MOFs）和活性炭（ACs）等吸附材料的研究现状；归纳并分析了各类吸附材料的应用优势和在工程应用中存在的问题；总结了各类材料吸附性能的主要影响因素和吸附机理等。最后，展望了固体吸附材料的发展方向。     

MIL-53 and its Isoreticular Analogues: a Review of the Chemistry and Structure of a Prototypical Flexible Metal-Organic Framework

We present a review of the structural chemistry of metal-organic framework materials with the MIL-53 type structure. This family of materials is well-known for its structural flexibility, and also the wide variety of metal cations and functional ligands that can be included. This gives rise to a set of multivariate materials and isoreticular analogues, to which isoreticular functionalisation can also be applied. Starting from the parent structure, containing infinite chains of octahedral trivalent metal cations cross-linked by benzene-1,4-dicarboxylate, we illustrate the compositional variety possible: this includes materials that contain tetravalent and divalent cations, mixtures of metal cations, functionalised ligands, expanded structures from extended linkers and inclusion of pendant ligands. We emphasise the crystal chemistry of this group of materials, but will give some examples of properties, particularly those associated with the structural breathing effect of relevance to molecular sieving, and also discuss emerging practical applications.     

修饰的COF-102吸附和分离CO2/CH4的计算机模拟（英文）

Covalent organic framework (COF) is a porous material with low density and large BET (Brun-auer-Emmett-Teller) surface area. They have great potential in gas adsorption and separation. In this work, the ad-sorption of pure CO2 and CO2/CH4 mixture on modified COF-102 was simulated by using GCMC (grand canonical Monte Carlo). Metal Li was incorporated into COF-102 through three doping methods, including charge exchange, O--Li+ dipolar interaction and O--Li+ chemical bonding. The influence of Li doping on the adsorption of CO2 was studied. The results showed that among the three methods, the dipole doping is the best way to improve CO2 ad-sorption performance. Further, the ligands of COF-102 were replaced by extended aromatic moieties, such as di-phenyl and pyrene. The adsorption capacity of CO2 and CH4, and the selectivity of CO2/CH4 on the ligand-replaced COF-102 were studied. The capacity of CO2 and CH4 on the ligand-replaced COF-102 had obvious changes; hence the selectivity of CO2/CH4 can be adjusted accordingly.     

Binary and ternary mixtures of liquid crystals with CO2

Liquid crystals, elongated molecules with a structured liquid phase, may be used as new solvents for CO₂ capture. However, no molecule has been found yet with optimal properties. Therefore, mixtures of two liquid crystals and CO₂ are investigated. Also, the phase behavior of some binary subsystems of the investigated ternary systems is studied for comparison. In the mixtures investigated, 4,4′‐pentyloxycyanobiphenyl + 4,4′‐heptyloxycyanobiphenyl + CO₂ and 4,4′‐propylcyclohexylbenzonitrile + 4,4′‐heptylcyclohexylbenzonitrile + CO₂, the nematic phases form a nematic homogeneous solution and the solid phases form an eutectic system, leading to a material with improved properties for CO₂ capture. Moreover, the ternary mixture of 4,4′‐propylcyclohexylbenzonitrile + 4,4′‐heptylcyclohexylbenzonitrile + CO₂ showed an increased solubility of CO₂ compared with the binary subsystems. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2977–2984, 2015     

炭膜的二氧化碳吸附扩散性能的研究

以商业化的Kapton型聚酰亚胺为前驱体制备炭膜,采用容量法研究了不同炭化温度制备的炭膜CO2吸附和扩散行为,并利用Sips模型对实验数据进行拟合,DA方程计算炭膜的孔结构参数,Fick扩散模型求取CO2在炭膜内的扩散系数,采用XRD分析探讨了炭膜的炭结构。结果表明,炭膜孔结构随着热解炭化温度的提高,孔径收缩,且当炭化温度从600℃升高到800℃,炭膜的微孔体积随炭化温度的升高而增大,而800℃以后,微孔体积随炭化温度的升高而下降。CO2在不同炭膜中的扩散系数约为1.04×10-13~8.56×10-12m2·s-1,在实验测定的压力范围内扩散系数随着平衡压力的增大呈现出先增大后减小的规律。     

Separation of He/N2/CH4 ternary mixtures by a triple-reflux pressure swing adsorption process

Conventional pressure swing adsorption (PSA) processes can only produce one high purity product in a single stage, whereas the state-of-art dual-reflux PSA (DR-PSA) can produce two high purity products simultaneously. However, multicomponent gas separation is often required in the industry, targeting at recovering several valued products at the same time. In this study, we propose a novel adsorption process, namely triple-reflux PSA (TR-PSA), to separate three components simultaneously. A middle product outlet and a middle reflux stream were introduced to the adsorption columns of a conventional DR-PSA process to separate ternary mixtures of nitrogen, methane, and helium. Nonisothermal dynamic models were built to investigate the impacts of operating parameters particularly the location of the middle reflux/product stream and the middle reflux flow rates. Results showed that the TR-PSA process successfully separated ternary mixtures obtaining three enriched products simultaneously in a single stage, yielding a separation performance comparable to that of the double-stage DR-PSA with significantly lower capital and energy cost.     

Amine‐functionalized mesoporous silica: A material capable of CO2 adsorption and fast regeneration by microwave heating

The surface of ordered mesoporous (MCM‐48) silica has been subjected to covalent grafting with silane molecules containing one to three amino groups. The dielectric properties of the materials were studied in detail, and the functionalized materials were used for CO₂ adsorption at room temperature, followed by regeneration under either conventional heating or microwave irradiation. It has been found that, as the intensity of functionalization with amino groups increases (from mono‐ to tri‐amino silanes) both the CO₂ load and the dielectric response at microwave frequencies increase. In particular, functionalization with a tri‐amino silane derivative gave the highest CO₂ adsorption and the fastest microwave heating, resulting in a fourfold acceleration of adsorbent regeneration. The grafted material was fully stable for at least 20 adsorption‐regeneration cycles, making it an ideal candidate for microwave‐swing adsorption (MWSA) processes. © 2015 American Institute of Chemical Engineers AIChE J, 62: 547–555, 2016     

Equilibrium Analysis of Cyclic Adsorption Processes: CO2 Working Capacities with NaY

Abstract

The most common application of adsorption is via pressure swing adsorption. In this type of design, the feed and regeneration temperatures are kept approximately equal, whereas the feed pressure is higher than the regeneration pressure. By exploiting the difference in the amount adsorbed at a higher pressure to the amount adsorbed at a lower pressure, a working capacity is realized. Therefore, by examining the expected (ideal) working capacity of an adsorbent, a performance characteristic can be analyzed for a pressure swing adsorption process (PSA). For this work, feed pressures up to 2.0 atm CO₂ and feed temperatures from 20°C to 200°C were investigated. These limits were chosen due to the nature of the target process: CO₂ removal from flue gas.

Carbon dioxide adsorption isotherms were determined in a constant volume system at 23°C, 45°C, 65°C, 104°C, 146°C, and 198°C, for pressures between 0.001 and 2.5 atm CO₂ with NaY zeolite. These data were fit with the temperature dependent form of the Toth isotherm. Henry's Law constants and the heat of adsorption at the limit of zero coverage were also determined using the concentration pulse method. Comparison of the Henry's Law constants derived from the Toth isotherm, and those obtained with the concentration pulse method provided excellent agreement.

By using the Toth isotherm, expected working capacity contour plots were constructed for PSA (Pressure Swing Adsorption), TSA (Temperature Swing Adsorption), and PTSA (Pressure Temperature Swing Adsorption) cycles. The largest expected working capacities were obtained when the bed was operated under a high‐pressure gradient PSA cycle, or a high thermal and pressure gradient PTSA cycle. The results also showed that certain TSA and PSA cycle conditions would result with higher expected working capacities as the feed temperature increases.