High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO_(2)/N_(2) and CH_(4)/N_(2) separation

Flue gas and coal bed methane are two important sources of greenhouse gases.Pressure swing adsorption process has a wide range of application in the field of gas separation,and the selection of adsorbent is crucial.In this regard,in order to assess the better adsorbent for separating CO_(2) from flue gas and CH_(4) from coal bed methane,adsorption isotherms of CO_(2),CH_(4) and N_(2) on activated carbon and carbon molecular sieve are measured at 303.15,318.15 and 333.15 K,and up to 250 kPa.The experimental data fit better with Langmuir 2 compared to Langmuir 3 and Langmuir-Freundlich models,and Clausius-Clapeyron equation was used to calculate the isosteric heat.Both the order of the adsorbed amount and the adsorption heat on the two adsorbents are CO_(2)>CH_(4)>N_(2).The adsorption kinetics are calculated by the pseudo-first kinetic model,and the order of adsorption rates on activated carbon is N_(2)-CH_(4)>CO_(2),while on carbon molecular sieve,it is CO_(2)-N_(2)>CH_(4).It is shown that relative molecular mass and adsorption heat are the primary effect on kinetics for activated carbon,while kinetic diameter is the main resistance factor for carbon molecular sieve.Moreover,the adsorption selectivity of CH_(4)/N_(2) and CO_(2)/N_(2) were estimated with the ideal adsorption solution theory,and carbon molecular sieve performed best at 318.15 K for both CO_(2) and CH_(4) separation.The study suggested that activated carbon is a better choice for separating flue gas and carbon molecular sieve can be a strong candidate for separating coal bed methane.

Microwave irradiation-induced alterations in physicochemical properties and methane adsorption capability of coals:An experimental study using carbon molecular sieve

In order to comprehend the applicability of microwave irradiation for recovering coalbed methane,it is necessary to evaluate the microwave irradiation-induced alterations in coals with varying levels of metamorphism.In this work,the carbon molecular sieve combined with KMnO_(4)oxidation was selected to fabricate carbon molecular sieve with diverse oxidation degrees,which can serve as model substances toward coals.Afterwards,the microwave irradiation dependences of pores,functional groups,and highpressure methane adsorption characteristics of model substances were studied.The results indicated that microwave irradiation causes rearrangement of oxygen-containing functional groups,which could block the micropores with a size of 0.40-0.60 nm in carbon molecular sieve;meanwhile,naphthalene and phenanthrene generated by macro-molecular structure pyrolysis due to microwave irradiation could block the micropores with a size of 0.70-0.90 nm.These alterations in micropore structure weaken the saturated methane adsorption capacity of oxidized carbon molecular sieve by 2.91%-23.28%,suggesting that microwave irradiation could promote methane desorption.Moreover,the increased mesopores found for oxidized carbon molecular sieve after microwave irradiation could benefit CH4 diffusion.In summary,the oxidized carbon molecular sieve can act as model substances toward coals with different ranks.Additionally,microwave irradiation is a promising technology to enhance coalbed methane recovery.

Direct Synthesis of Dimethyl Carbonate from CO_2 and CH_3OH Using 0.4nm Molecular Sieve Supported Cu-Ni Bimetal Catalyst

The 0.4 nm molecular sieve supported Cu-Ni bimetal catalysts for direct synthesis of dimethyl carbonate (DMC) from CO 2 and CH 3 OH were prepared and investigated. The synthesized catalysts were fully characterized by BET, XRD (X-ray diffraction), TPR (temperature programmed reduction), IR (infra-red adsorption), NH 3-TPD (temperature programmed desorption) and CO 2-TPD (temperature programmed desorption) techniques. The results showed that the surface area of catalysts decreased with increasing metal content, and the metals as well as Cu-Ni alloy co-existed on the reduced catalyst surface. There existed interaction between metal and carrier, and moreover, metal particles affected obviously the acidity and basicity of carrier. The large amount of basic sites facilitated the activation of methanol to methoxyl species and their subsequent reaction with activated carbon dioxide. The catalysts were evaluated in a continuous tubular fixed-bed micro-gaseous reactor and the catalyst with bimetal loading of 20% (by mass) had best catalytic activities. Under the conditions of 393 K, 1.1 MPa, 5 h and gas space velocity of 510 h 1 , the selectivity and yield of DMC were higher than 86.0 % and 5.0 %, respectively.

Ultraselective carbon molecular sieve membrane for hydrogen purification

Hydrogen is a green clean fuel and chemical feedstock. Its separation and purification from hydrogencontaining mixtures is the key step in the production of hydrogen with high purity(>99.99%). In this work, carbon molecular sieve(CMS) membranes with ultrahigh permselectivity for hydrogen purification were fabricated by high-temperature(700–900 ℃) pyrolysis of polymeric precursor of phenolphthaleinbased cardo poly(arylene ether ketone)(PEK-C). The evolution of the microstructural texture and ultramicroporous structure and gas separation performance of the CMS membrane were characterized via TG-MS, FT-IR, XRD, TEM, CO2 sorption analysis and gas permeation measurements. CMS membranes prepared at 700 ℃ exhibited amorphous turbostratic carbon structures and high H2 permeability of 5260 Barrer with H2/CH4, H2/N2 and H2/CO selectivities of 311, 142, 75, respectively. When carbonized at900 ℃, the CMS membrane with ultrahigh H2/CH4 selectivity of 1859 was derived owing to the formation of the dense and ordered carbon structure. CMS membranes with ultrahigh permselectivity exhibit an attractive application prospect in hydrogen purification.

Preparation and Characterization of Stellera Chamaejasme-Based Carbon Molecular Sieves

The activation effect of boric acid as an activator is good,and we investigate the best activation conditions for the boric acid impregnation method.To represent the structural characteristics and adsorption performance of the Stellera Chamaejasme based carbon molecular sieves,we use Brunner-Emmet-Teller(BET)measurements,scan-ning electron microscope(SEM),Raman spectra(Raman),X-ray diffraction(XRD),and adsorption property measurement.When the loading ratio was 0.68:1,the specific surface area was 532.21 m^(2)/g,the total pore volume was 0.24 cm 3/g,the average pore size was 1.81 nm,the adsorption value of methylene blue was 145.28 mg/g,and the adsorption value of iodine was 713.33 mg/g,the results showed that boric acid had better activation effect.The carbon molecular sieves made from Stellera Chamaejasme and activated with boric acid produce two peaks on the aperture distribution graph that are densely distributed in the micropore range.This indicates that boric acid’s pore-forming tendency is primarily micropore.

Molecular dynamics simulations of the interaction of carbon nanotube and a carbon disulfide solvent

An analysis of the molecular dynamics (МD) of the interaction between a carbon nanotube (CNT) and a carbon disulfide active solvent (CS2) has been carried out. The aim of the present work is to estimate the dynamical and structural behavior of the CNTCS2 system at different relative atomic concentrations and under temperature changes. The structural radial distribution functions and the dynamical configurations have been built for a CNT interacting with a CS2 solvent. A nontrivial observation for the CNTCS2 system is that the solvent carbon disulfide atoms make up a patterned (layered) formation around the carbon nanotube.

Carbon Molecular Sieve Membrane(CMSM)for Industrial Gas Separation

Membrane separation is an enviroranental benign technology for 21st century, and is developing quickly to replace the conventional distillation process. Carbon raolecular sieve membrane (CMSM) was synthesized through the contndled pyrolysis of polyimide films. The CMSM is synanetric in structure and presents strong sieving effect towards gas molecules of slightly different diameters. The microstructure of CMSM was manipulated through the thermal treatment program and further modified through activation vapor/chemical depositions. It is demonstrated that CMSM can be synthesized/modified for specific gas mixtures, such as O2/N2, CO2/CH4, C3H6/C3H8, and ect. The pore size distrilmfion, relationship between the permeance & selectivity on CMSM for the separation d some gas pairs was also investigated.

Carbon dioxide reforming of methane over Ni/Mo/SBA-15-La_2O_3 catalyst:Its characterization and catalytic performance

The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 adsorption, H2-TPR, CO2-TPD, XRD, FT-IR and SEM. It was found that the major role of La2O3 additive was to improve the pore structure and inhibit carbon deposition on the catalyst surface. The La2O3 modified Ni/Mo/SBA-15 catalyst possessed a mesoporous structure and high surface area. The high surface area of the La2O3 modified catalysts resulted in strong interaction between Ni and Mo-La, which improved the dispersion of Ni, and retarded the sintering of Ni during the CO2 reforming process. The reaction evaluation results also showed that the La2O3 modified Ni/Mo/SBA-15 catalysts exhibited high stability.

Preparation and characterization of novel carbon molecular sieve membrane/PSSF composite by pyrolysis method for toluene adsorption

Carbon molecular sieve membrane(CMSM)/paper-like stainless steel fibers(PSSF)has been manufactured by pyrolyzing poly(fiirfuryl alcohol)(PFA)coated on the metal fibers.PFA was synthesized using oxalic acid dihydrate as a catalyst and coated on microfibers by dip coating method.For the purpose of investigating the effects of final carbonization temperature,the composites were carbonized between 400℃ and 800℃ under flowing nitrogen.The morphology and microstructure were examined by X-ray diffraction,Fourier transforms infrared spectroscopy,scanning electron microscopy,thermogravimetric analysis,N2 adsorption and desorption,Raman spectra and X-ray photoelectron spectra.The consequences of characterization showed that the CMSM containing mesopores o f 3.9 nm were manufactured.The specific surface area of the CMSM/PSSF fabricated in different pyrolysis temperature varies from 26.5 to 169.1 m^2·g^-1 and pore volume varies from 0.06 to 0.23 cm^3·g^-1.When pyrolysis temperature exceeds 600℃,the specific surface,pore diameter and pore volume decreased as carbonization temperature increased.Besides,the degree of graphitization in carbon matrix increased with rising pyrolysis temperature.Toluene adsorption experiments on different structured fixed bed that was padded by CMSM/PSSF and granular activated carbon(GAC)were conducted.For the sake of comparison,adsorption test was also performed on fixed bed packed with GAC.The experimental results indicated that the rate constant κ′ was dramatically increased as the proportion of CMCM/PSSF composites increased on the basis of Yoon-Nelson model,which suggested that structured fixed bed padded with CMSM/PSSF composite offered higher adsorption rate and mass transfer efficiency.

Design and experiment of high-productivity two-stage vacuum pressure swing adsorption process for carbon capturing from dry flue gas

A two-stage vacuum pressure swing adsorption(VPSA)process that coupled kinetically controlled and equilibrium controlled separation process with reflux has been investigated for capturing carbon dioxide from dry flue gas(85%N_(2)/15%CO_(2)).In the first enriching stage,carbon molecular sieve(CMS),which shows kinetic selectivity for CO_(2)/N_(2),is adopted as the adsorbent to remove most N_(2)in feed gas,thereby upgrading CO_(2)and significantly reducing the amount for further refinement.The second stage loads zeolite 13X as adsorbent to purify the CO_(2)-rich flow from the first stage for meeting the requirements of National Energy Technology Laboratory.Series of experiments have been conducted for adsorption isotherms measuring and lab-scale experimental validation as well as analysis.The effect of feed composition on the separation performance of the PSA system was studied experimentally and theoretically here.The optimal results achieved 95.1%purity and 92.9%recovery with a high CO_(2)productivity(1.89 mol CO_(2)·h^(-1)·kg^(-1))and an appropriate energy consumption of 1.07 MJ·(kg CO_(2))^(-1).Further analysis has been carried out by simulation for explicating the temperature,pressure,and concentration distribution at cyclic steady state.

Modification of pore size in activated carbon by benzene deposition and its effects on CH4/N2 separation

Anthracite coal was used as raw material to prepare activated carbons as the carbon support in the carbonization-activation process. Modification of the pore size of the activated carbon by chemical vapor deposition of carbon from benzene was examined. These samples were characterized by adsorption of N2 at 77 K and CH4 and N2 at 303 K. The microporosity of these samples was evaluated by the Dubinin-Astakhov Equation. The pore size distribution was obtained by the DFT method applied to the N2 adsorption data at 77 K. The separation selectivity was obtained by the Langmuir Equation. The surface morphology was characterized by an environmental scanning electron microscope. It was observed that all samples of carbon molecular sieves studied were microporous carbonaceous materials. CMS-2 prepared in the present study has a better N2/CH4 separation performance; it can satisfy the requirements of the pressure swing adsorption for concentrating CH4 from the N2/CH4 mixture gas.

Boosting xenon adsorption with record capacity in microporous carbon molecular sieves

Xenon/krypton(Xe/Kr)separation is an important task in industry,yet it remains challenging to develop adsorbents with high Xe/Kr selectivity and adsorption capacity of Xe,especially at low partial pressures.Herein,we report a series of microporous carbon molecular sieves(CMSs)for Xe/Kr separation.Those materials have ideal bimodal pore size distributions that not only provide substantial space for the accommodation of gas molecules,but also allow selective diffusion of gas molecules.Additionally,the carbon frameworks decorated with polar oxygen-containing functional groups afford higher affinity for Xe than Kr,which is proven by density functional theory(DFT)calculations and charge density difference analysis.The optimal CPVDC-700 exhibits a high selectivity of Xe/Kr and,more importantly,a record-high uptake of Xe(2.93 mmol g^(-1))at 0.2 bar and298 K,which is the highest among all the reported carbon adsorbents.Breakthrough experiments confirm the excellent performance of such CMSs for Xe/Kr separation,and the dynamic adsorption uptake of Xe and productivity of high-purity Kr are calculated to be 2.91 mmol g^(-1)and 208 m L g^(-1)(9.29 mmol g^(-1)),respectively,which also set up a new benchmark for Xe/Kr separation of carbon adsorbents.

Adsorption behaviour of molecular sieve and activated carbon for CO_(2) adsorption at cold temperatures

At present,insufficient works have provided insights into the application of adsorption to remove CO_(2) in flue gas below room temperatures under ambient pressure.In this work,the effects of temperature,CO_(2) partial pressure and moisture on dynamic adsorption characteristics for CO_(2) are conducted for various adsorbents.Based on our findings,lower the adsorbing temperature can drastically enhance the adsorption of carbon dioxide over molecular sieves and activated carbon.Among various adsorbents,13X molecular sieve shows highest adsorption capacity.With a concentration of 10%CO_(2) in flue gas,the specific adsorption capacity of CO_(2) over 13X molecular sieve is 0.11,2.54 and 5.38 mmol/g at 80℃,0℃ and -80℃,respectively.In addition,the partial pressure of CO_(2) also has a significant impact on the adsorption capacity.With the increment of the concentration of CO_(2) from 1%to 10% under 0℃,the specific capacity of 13X molecular sieve increases from 1.212 mmol/g to 2.538 mmol/g.Water vapor in flue gas can not only reduce the specific adsorption capacity of CO_(2) due to competing adsorption,but also increase the heat penalty of molecular sieve regeneration due to the water adsorption.An overall analysis is conducted on the energy penalty of capture 1 ton CO_(2) at various adsorption temperatures between -80℃ and 80℃,considering both the heat penalty of molecular sieve regeneration as well as the energy penalty for cooling the adsorber.It is found that the lowest energy penalty is about 2.01 GJ/ton CO_(2) when the adsorption is conducted at 0℃.

甲醇对于PEI-SBA固态胺制备及其性能的影响

固态胺材料具有优异的二氧化碳(CO_(2))选择吸附性能,是一类潜在的CO_(2)捕集材料。作为一种重要的固态胺材料,SBA-15负载聚乙烯亚胺(PEI-SBA-15)由于原材料较为廉价且性能优异受到了大量的关注。PEI-SBA-15的制备过程需要采用甲醇溶剂,而溶剂使用量对于其CO_(2)吸附性能的影响尚无系统研究。系统研究了溶剂使用量对SBA-15负载聚乙烯亚胺的CO_(2)吸附性能的影响。研究结果表明,可以同时实现提升CO_(2)吸附性能和CO_(2)/N_(2)选择性和大幅降低甲醇的使用量。对于降低PEI-SBA-15的制备成本以及提升制备过程环保性具有重要意义。

生物基呋喃催化热解耦合CO_(2)还原制取芳烃和合成气

针对生物基呋喃单独芳构化过程中通常伴随着脱氢反应,并且考虑到CO_(2)单独还原成CO需要消耗大量H_(2),提出一种生物基呋喃催化热解耦合CO_(2)还原定向制取碳负性芳烃和合成气新工艺。通过构筑分子筛负载的复合金属催化剂来同步实现2-甲基呋喃(2-MF)的高效芳构化和CO_(2)的活化。研究表明,HZSM-5负载Mo-Ni可以显著提高CO_(2)的转化率以及气体产物中合成气的选择性,分别从−4.56%(CO_(2)生成速率大于其转化速率)和46.78%大幅提高至24.68%和72.28%,这归因于双金属的配位结构引入了更多氧空位,同时通过引入路易斯酸位点有效提高了催化剂的芳构化能力。研究结果可为生物质催化热解新工艺发展和催化剂设计提供理论指导。

掺氢天然气的氢气分离提纯技术浅析

针对掺氢天然气的氢气分离提纯技术,重点调研了变压吸附、膜分离及电化学氢分离技术的各自特点,提出了应用于掺氢天然气的氢气分离提纯技术方案:具有占地和成本优势的快速变压吸附提纯技术,适宜处理小规模掺氢天然气,在氢能产业发展近中期阶段可以成为研究重点;碳分子筛膜分离技术具有分离成本低和产品氢纯度高的优势,针对氢能产业发展远期阶段的大规模应用开展布局研究具有重要意义;掺氢天然气在分离提纯前的预处理,需重点关注低碳烃和硫的脱除,应分别考虑对后续工艺稳定运行的影响和能耗大小;分离提纯后的非氢气体回注管网,应重点关注气源管线的压力和避免非氢气体压缩以降低氢气分离提纯成本。

ZSM-5基复合分子筛催化裂解制低碳烯烃研究进展

系统介绍了ZSM-5基复合分子筛的合成方法;针对典型的核-壳结构和微-介孔结构,阐述了复合结构对其孔隙结构、酸性质和水热稳定性等的调控方法和规律。在此基础上,详细综述了复合分子筛在甲醇、轻烃、生物质及其混合原料催化裂解制低碳烯烃领域的应用,提出复合分子筛催化材料未来发展前景。

有序介孔硅材料的微量碳层修饰及VOCs吸附性能

以孔道规整的介孔分子筛SBA-15和MCM-41作为硅基材料前驱体,以蔗糖作为生物质碳源,通过化学刻蚀方法将生物质碳引入两种介孔分子筛孔道中,从而制备获得碳-介孔分子筛复合材料.通过对蔗糖浓度条件的优化,可以获得比表面积、碳含量和甲苯吸附性能最佳的碳-介孔分子筛复合材料.经由TEM-EDS图谱可以证明,碳元素均匀存在于上述两种介孔硅材料的孔道.进一步通过孔径分析,发现碳层修饰后的介孔分子筛(C@MCM和C@SBA)中微孔比例显著提升,因而其甲苯吸附容量明显高于其对应的介孔分子筛(MCM-41和SBA-15).其中,C@SBA在5次吸脱附循环中容量基本保持不变,循环吸附性能相比C@MCM更为优越.此外,碳层修饰后的介孔分子筛具有良好的耐水性,其吸附容量不会随相对湿度的提高而大幅降低.最后,上述复合材料对其他含氧VOCs物种也具有较好的吸附性能,但对甲苯等弱极性分子的吸附效果更显著.

基于不同原料的碳分子筛制备技术及其应用研究进展

碳分子筛(CMS)具有孔隙结构发达、孔径分布均匀、热稳定性高等优点,可用于吸附、催化等领域。本文从CMS制备技术及其应用入手,介绍了煤、有机高分子聚合物和生物质作为CMS制备原料的性能差异,比较了活化法、沉积法、热缩聚法和模板法等方法制备CMS的优缺点,其中,炭化法、活化法及热缩聚法操作简单,但炭化法对原料要求高,活化法使用KOH等活化剂易产生有毒废水,热缩聚法则能耗较高;苯沉积法和模板法都可调节孔径结构,但苯沉积受沉积温度、流速等因数影响,而模板法与活化法一样,易产生有毒废水。重点阐述KOH活化法和苯类气相沉积法制备CMS的原理,以及可以利用减少CMS晶粒尺寸、引入空心或多级孔结构、保留微孔提供的催化活性中心等CMS改性方式来提高CMS性能。总结了CMS在吸附分离、催化等领域的应用现状,对CMS的发展方向进行了展望。