二氧化碳/甲烷/氮气二元混合物在有序介孔碳材料CMK-3 中的吸附和分离

采用分子模拟与吸附理论研究了天然气成分在有序介孔碳材料CMK-3上的吸附和分离.巨正则系综蒙特卡罗(GCMC)模拟表明,CH4和CO2气体的较优存储条件分别为208 K、4 MPa和298 K、6 MPa,其最大超额吸附量分别为10.07和14.85 mmol· g-1.基于双位Langmuir-Freundlich (DSLF)模型,使用理想吸附溶液理论(IAST)预测了不同二元混合物在CMK-3中的分离行为,发现吸附选择性Sco2/CH4与ScH4/N2比较接近,在298 K和4 MPa下约等于3,而N2-CO2体系中的CO2吸附选择性较高,可达到7.5,说明CMK-3是一种适合吸附和分离天然气组分的碳材料.     

纤维状吸附、分离材料的进展

本文简要地阐明了纤维状吸附、分离材料,其中包括活性碳纤维(ACF)、离子交换纤维(IEF)和螫合纤维(CLF)近年来的发展,它们的基本性质、制备方法和应用。尤其是在环境保护、贵金属的分离、回收等方面的应用前景。文中扼要地介绍了本文作者近年来发现的活性碳纤维和某些螯合纤维的氧化一还原特性。这类纤维在吸附某些高价态金属离子的同时可以把它们还原成低价态或金属元素。     

用Kierlik-Rosinberg的DFT方法研究活性炭分离空气中微量CCl_4

以N_2作为空气的主要成分，利用Kierlik和Rosinberg提出的密度函数理论 (density functional theory, KR-DFT)研究了N_2/CCl_4双元混合物在活性炭内的 吸附。重点讨论了孔径、压力和温度对CCl_4吸附选择性的影响，不为同条件下吸 附回收空气中的CCl_4提供了理论参考。在KR-DFT计算中。N_2分子和CCl_4分子模 型化为单点的Lennard-Jones球；流体分子与吸附剂材料之间的作用采用平均场理 论中的10-4-3模型。在KR-DFT方法中，自由能采用标度的场粒子理论(scaled field particle theory, SPT)处理。讨论了孔径、压力和温度对吸附选择性的影 响。研究结果表明，常温下当空气中CCl_4的含量为1%时，1.39nm的孔径最有利于 CCl_4的吸附。     

离子交换及多孔材料的制备与应用

离子交换和多孔材料是一类高效的吸附剂,这类新型的高效吸附分离材料具有高的比表面积或丰富的表面官能团;显示出高的吸附容量、快的吸附或脱附速度和一定的吸附选择性;可织成束、纸、布、毡等多种集合形态.本文简要地介绍了包括离子交换纤维、螯合纤维、活性碳纤维、碳气凝胶等新型离子交换和多孔材料的制备、吸附特征研究的进展,并介绍了它们在饮用水净化、环境治理、资源回收、化学工业和医疗卫生、催化剂等方面的应用.     

基于多壁碳纳米管的人参皂苷快速分离

将多壁碳纳米管(MWCNTs)作为选择性吸附材料,用于快速分离人参提取物中的人参皂苷.人参经甲醇溶液超声提取后,提取物中主要为人参皂苷和糖类.人参中的糖类与人参皂苷的极性相近,是提取分离人参皂苷时的主要干扰物. MWCNTs可以快速吸附和脱附人参皂苷,但是对糖类无吸附作用.利用其选择性吸附性能,建立了MWCNTs快速分离人参提取物中人参皂苷和糖类的方法.在优化的分离条件下,MWCNTs对人参提取物中糖类的分离度高于90%,对8种主要人参皂苷[Rb1,Rb2,Rc,Rd,Re,Rg1,20(S)-Rf和Ro]的吸附容量为15. 0~24. 0μg/mg,回收率高于90%.进一步研究表明,人参皂苷在3 min内即可达到吸附和脱附平衡,并且人参皂苷的回收率受脱附溶剂极性的影响.相比于常规材料大孔树脂,MWCNTs可以更快速、简便地分离人参皂苷.     

合成CFC-12替代物HFC-134a的CrF3/AlF3催化剂研究(V)——CrF3与AlF3的相互作用

由于氟氯烃(CFCs)对大气臭氧层的破坏作用,使得开发CFCs无污染替代品的研究成为热门课题.氢氟烃(HFCs,如HFC-134a)是CFCs的理想替代物.     

单壁碳纳米管上毒性苯气体净化的分子模拟(英文)

采用巨正则系综蒙特卡罗(GCMC)方法研究了空气中微量苯组分在单臂碳纳米管(SWNTs)上的吸附净化.模拟表明,具有较大孔径的(20,20)纳米管比较适合吸附纯苯蒸汽,而对于移除空气中的毒性苯物质,苯的吸附选择性分别在(12,12)纳米管及4.0 MPa时和(18,18)纳米管及0.1 MPa时出现最小值和最大值.为了解释这一异常行为,我们进一步分析了N2-O2-C6H6混合物的局部密度分布、吸附分子构型和概率密度分布,发现(18,18)纳米管内外完全被苯分子占据,而对于(12,12)纳米管,由于存在更强的吸附质-吸附剂相互作用,空气分子更倾向于吸附在管与管之间的间隙.此外,吸附分子的空间有序参数表明大多数苯分子采取"平躺"在纳米管表面的定位,而线性的N2和O2分子则多数平行于孔轴方向.最后研究了温度和苯分子主体相浓度对分离效果的影响.我们发现较大孔中的选择性随着温度的增加比小孔下降更加明显.与此对比,主体相苯浓度对小孔中的选择性起到更加重要的作用.     

CrOx-Y2O3催化剂中Cr物种对氟氯交换反应性能的影响

用沉积-沉淀法制备了CrOx-Y2O3催化剂, 考察焙烧气氛及温度对1,1,1-三氟-2-氯乙烷(HCFC-133a)气相氟化合成1,1,1,2-四氟乙烷(HFC-134a)催化性能的影响. 采用拉曼光谱、X射线粉末衍射(XRD)等表征手段观察了催化剂中铬物种价态的变化情况. 结果表明, 先氮气后空气中不同温度(T)焙烧的催化剂(NAT), 随着空气中焙烧温度的升高, Cr物种由CrO3向YCrO4、YCrO3转变. 500 ℃焙烧的NA500催化剂虽然活性低于直接在空气中350 ℃焙烧的催化剂(A350), 然而前者的反应稳定性明显高于后者. 这归因于YCrO4物种在氟化过程中生成的活性物种既不易流失并且表面不容易结炭.     

单壁碳纳米管上毒性苯气体净化的分子模拟

采用巨正则系综蒙特卡罗(GCMC)方法研究了空气中微量苯组分在单臂碳纳米管(SWNTs)上的吸附净化. 模拟表明, 具有较大孔径的(20,20)纳米管比较适合吸附纯苯蒸汽, 而对于移除空气中的毒性苯物质, 苯的吸附选择性分别在(12,12)纳米管及4.0 MPa时和(18,18)纳米管及0.1 MPa时出现最小值和最大值. 为了解释这一异常行为, 我们进一步分析了N₂-O₂-C₆H₆混合物的局部密度分布、吸附分子构型和概率密度分布, 发现(18,18)纳米管内外完全被苯分子占据, 而对于(12,12)纳米管, 由于存在更强的吸附质-吸附剂相互作用, 空气分子更倾向于吸附在管与管之间的间隙. 此外, 吸附分子的空间有序参数表明大多数苯分子采取“平躺”在纳米管表面的定位, 而线性的N₂和O₂分子则多数平行于孔轴方向. 最后研究了温度和苯分子主体相浓度对分离效果的影响. 我们发现较大孔中的选择性随着温度的增加比小孔下降更加明显. 与此对比, 主体相苯浓度对小孔中的选择性起到更加重要的作用.     

气相氟化合成1,1,1,2-四氟乙烷的CrOx-Y2O3催化剂的表征与性能

制备了一系列CrOx-Y2O3催化剂用于气相氟化1,1,1-三氟-2-氯乙烷(HCFC-133a)合成1,1,1,2-四氟乙烷(HFC-134a), 并考察了Y(OH)3、YCl3和Y(NO3)3前躯体对催化剂性能的影响. XRD和UV-Vis光谱实验结果表明, Y前躯体对催化剂表面Cr物种有影响, 其中采用Y(OH)3前躯体的催化剂有利于以高分散的Cr6+形式存在. 研究表明CrOx-Y2O3催化剂在预处理和反应过程中, 部分高价CrOx可转化为CrF3. 催化剂中CrF3含量增加, 导致其转化为活性物种的含量相对减少, 所以其催化活性下降.     

Adsorptive behavior of CO2, CH4 and their mixtures in carbon nanospace: a molecular simulation study

Using molecular simulation, four types of nanoporous carbons are examined as adsorbents for the separation of CO(2)/CH(4) mixtures at ambient temperature and pressures up to 10 MPa. First, the adsorption selectivity of CO(2) is investigated in carbon slit pores and single-walled carbon nanotube bundles in order to find the optimal pore dimensions for CO(2) separation. Then, the adsorptive properties of the optimized slit pore and nanotube bundle are compared with two realistic nanoporous carbon models: a carbon replica of zeolite Y and an amorphous carbon. For the four carbon models, adsorption isotherms and isosteric heats of adsorption are presented for both pure components and mixtures. Special attention is given to the calculation of excess isotherms and isosteric heats, which are necessary to assess the performance of model nanoporous materials in the context of experimental measurements. From these results, we discuss the impact that variables such as pore size, pore morphology, pressure and mixture composition have on the performance of nanoporous carbons for CO(2) separation.     

Hydrogen confinement in carbon nanopores: extreme densification at ambient temperature

In-situ small-angle neutron scattering studies of H(2) confined in small pores of polyfurfuryl alcohol-derived activated carbon at room temperature have provided for the first time its phase behavior in equilibrium with external H(2) at pressures up to 200 bar. The data were used to evaluate the density of the adsorbed fluid, which appears to be a function of both pore size and pressure and is comparable to the density of liquid H(2) in narrow nanopores at ～200 bar. The surface-molecule interactions responsible for densification of H(2) within the pores create internal pressures that exceed the external gas pressure by a factor of up to ～50, confirming the benefits of adsorptive storage over compressive storage. These results can be used to guide the development of new carbon adsorbents tailored for maximum H(2) storage capacities at near-ambient temperatures.     

Hydrogen storage in pure and Li-doped carbon nanopores: combined effects of concavity and doping

Density functional calculations are reported for the adsorption of molecular hydrogen on carbon nanopores. Two models for the pores have been considered: (i) The inner walls of (7,7) carbon nanotubes and (ii) the highly curved inner surface of nanotubes capped on one end. The effect of Li doping is investigated in all cases. The hydrogen physisorption energies increase due to the concavity effect inside the clean nanotubes and on the bottom of the capped nanotubes. Li doping also enhances the physisorption energies. The sum of those two effects leads to an increase by a factor of almost 3 with respect to the physisorption in the outer wall of undoped nanotubes and in flat graphene. Application of a quantum-thermodynamical model to clean cylindrical pores of diameter 9.5 A, the diameter of the (7,7) tube, indicates that cylindrical pores of this size can store enough hydrogen to reach the volumetric and gravimetric goals of the Department of Energy at 77 K and low pressures, although not at 300 K. The results are useful to explain the experiments on porous carbons. Optimizations of the pore size, concavity, and doping appear as promising alternatives for achieving the goals at room temperature.     

Equation of state for hydrofluorocarbon refrigerant mixtures of HFC-125/143a,HFC-125/134a,HFC-134a/143a and HFC-125/134a/143a

Equations of state (EOSs) in the form of dimensionless Helmholtz free energy have been developed for the binary hydrofluorocarbon (HFC) refrigerant mixtures HFC-125/143a, HFC-125/134a, HFC-134a/143a and for the ternary refrigerant mixture HFC-125/134a/143a in the present work. These EOSs are effective in the temperature and pressure ranges where the experimental measurements covered, i.e., 200 K⩽T⩽413 K, P⩽35 MPa for HFC-125/143a and HFC-125/134a; 243 K⩽T⩽413 K, P⩽17 MPa for HFC-134a/143a and HFC-125/134a/143a. Experimental measurements in both single-phase and two-phase regions are represented by the present EOSs within their estimated uncertainties.     

Destruction of Freon HFC-134a Using a Nozzleless Microwave Plasma Source

In this paper, results of the pyrolysis of Freon HFC-134a (tetrafluoroethane C₂H₂F₄) in an atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to produce plasma for the destruction of Freon HFC-134a. The processed gaseous Freon HFC-134a at a flow rate of 50–212 l min⁻¹ was introduced to the plasma by four gas ducts which formed a swirl flow in the plasma reactor (a quartz cylinder). The absorbed microwave power was 0.6–3 kW. The experimental results showed that the Freon was converted into carbon black, hydrogen and fluorine. The total conversion degree of HFC-134a was up to 84% with selectivity of 100% towards H₂, F₂ and C₂, which means that there was no conversion of HFC-134a into other hydrocarbons. The Freon destruction mass rate and corresponding energetic mass yield were up to 34.5 kg h⁻¹ and 34.4 kg per kWh of microwave energy absorbed by the plasma, respectively.     

Structurally designed synthesis of mechanically stable poly(benzoxazine-co-resol)-based porous carbon monoliths and their application as high-performance CO2 capture sorbents

Porous carbon monoliths with defined multilength scale pore structures, a nitrogen-containing framework, and high mechanical strength were synthesized through a self-assembly of poly(benzoxazine-co-resol) and a carbonization process. Importantly, this synthesis can be easily scaled up to prepare carbon monoliths with identical pore structures. By controlling the reaction conditions, porous carbon monoliths exhibit fully interconnected macroporosity and mesoporosity with cubic Im3m symmetry and can withstand a press pressure of up to 15.6 MPa. The use of amines in the synthesis results in a nitrogen-containing framework of the carbon monolith, as evidenced by the cross-polarization magic-angle-spinning NMR characterization. With such designed structures, the carbon monoliths show outstanding CO(2) capture and separation capacities, high selectivity, and facile regeneration at room temperature. At ~1 bar, the equilibrium capacities of the monoliths are in the range of 3.3-4.9 mmol g(-1) at 0 °C and of 2.6-3.3 mmol g(-1) at 25 °C, while the dynamic capacities are in the range of 2.7-4.1 wt % at 25 °C using 14% (v/v) CO(2) in N(2). The carbon monoliths exhibit high selectivity for the capture of CO(2) over N(2) from a CO(2)/N(2) mixture, with a separation factor ranging from 13 to 28. Meanwhile, they undergo a facile CO(2) release in an argon stream at 25 °C, indicating a good regeneration capacity.     

Catalytic properties of Ru nanoparticles embedded on ordered mesoporous carbon with different pore size in Fischer-Tropsch synthesis

A series of 3 wt% Ru embedded on ordered mesoporous carbon (OMC) catalysts with different pore sizes were prepared by autoreduction between ruthenium precursors and carbon sources at 1123 K. Ru nanoparticles were embedded on the carbon walls of OMC. Characterization technologies including power X-ray diffraction (XRD), nitrogen adsorption-desorption, transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H₂-TPR) were used to scrutinize the catalysts. The catalyst activity for Fischer-Tropsch synthesis (FTS) was measured in a fixed bed reactor. It was revealed that 3 wt% Ru-OMC catalysts exhibited highly ordered mesoporous structure and large surface area. Compared with the catalysts with smaller pores, the catalysts with larger pores were inclined to form larger Ru particles. These 3 wt% Ru-OMC catalysts with different pore sizes were more stable than 3 wt% Ru/AC catalyst during the FTS reactions because Ru particles were embedded on the carbon walls, suppressing particles aggregation, movement and oxidation. The catalytic activity and C₅₊ selectivity were found to increase with the increasing pore size, however, CH₄ selectivity showed the opposite trend. These changes may be explained in terms of the special environment of the active Ru sites and the diffusion of products in the pores of the catalysts, suggesting that the activity and hydrocarbon selectivity are more dependent on the pore size of OMC than on the Ru particle size.     

Isothermal phase equilibria for the (HFC-32 + HFC-134a) mixed-gas hydrate system

Isothermal phase equilibria (pressure-composition relations in hydrate, gas, and aqueous phases) in the {difluoromethane (HFC-32) + 1,1,1,2-tetrafluoroethane (HFC-134a)} mixed-gas hydrate system were measured at the temperatures 274.15 K, 279.15 K, and 283.15 K. The heterogeneous azeotropic-like behaviour derived from the structural phase transition of (HFC-32 + HFC-134a) mixed-gas hydrates appears over the whole temperature range of the present study. In addition to the heterogeneous azeotropic-like behaviour, the isothermal phase equilibrium curves of the (HFC-32 + HFC-134a) mixed-gas hydrate system exhibit the negative homogeneous azeotropic-like behaviour at temperatures 279.15 K and 283.15 K. The negative azeotropic-like behaviour, which becomes more remarkable at higher temperatures, results in the lower equilibrium pressure of (HFC-32 + HFC-134a) mixed-gas hydrates than those of both simple HFC-32 and HFC-134a hydrates. Although the HFC-134a molecule forms the simple structure-II hydrate at the temperatures, the present findings reveal that HFC-134a molecules occupy a part of the large cages of the structure-I mixed-gas hydrate.     

Ni/Al2O3 catalysts for syngas methanation: Effect of Mn promoter

Ni/Al2O3 catalysts with different amounts of manganese ranging from 1 to 3 wt% as promoter were prepared by co-impregnation method. The catalysts were characterized by N2 physisorption, XRD, TPR, SEM and TEM. Their catalytic activity towards syngas methanation reaction was also investigated using a fixed-bed integral reactor. It was demonstrated that the addition of manganese to Ni/Al2O3 catalysts can increase the catalyst surface area and average pore volume, but decrease NiO crystallite size, leading to higher activity and stability. The effects of reaction temperature, pressure and weight hourly space velocity (WHSV) on carbon oxides conversion and CH4 formation rate were also studied. High carbon oxides conversion, CH4 selectivity and formation rate were achieved at the reaction temperature range of 280 300℃.     

Shear viscosity of Stockmayer fluid: Application of integral equations method to Vesovic–Wakeham scheme

In our previous works, we applied the integral equations method to calculate transport properties of nonpolar fluids such as Lennard–Jones (12-6) fluid [R. Khordad, Physica A 387 (2008) 4519, M.M. Papari, R. Khordad, Z. Akbari, Physica A 388 (2009) 585]. The present work is a continuation of our studies on transport properties of polar fluids. We use the Stockmayer potential and examine theoretically the viscosity and pressure of several refrigerant mixtures such as R125 + R143a, HFC-125 + HFC-134a, HFC-125 + HFC-32, and HFC-134a + HFC-32. We solve numerically the Ornstein–Zernike (OZ) equation using the hypernetted-chain approximation (HNC) for binary fluid mixtures and obtain the pair correlation functions. Finally, the density and temperature dependence of shear viscosity and pressure are studied using Vesovic–Wakeham method and compared with experimental results. According to the results obtained from the present work reveals that the integral equations method is suitable for predicting the pressure and shear viscosity of this class of fluids.