锂离子交换ZSM-5型分子筛中水分子吸附特性的分子模拟

用巨正则系综Monte Carlo(grand canonical assemblage Monte Carlo,GCMC)模拟方法计算了水在HZSM-5型分子筛中的吸附热,计算结果与文献报道的实验结果吻合得较好.模拟了水在经锂离子(Li )交换后的ZSM-5型分子筛上的吸附等温线.在此基础上,进一步预测了水在不同硅铝摩尔(下同)比的LinZSM-5型分子筛中的吸附性质.计算结果显示:分子筛骨架上的硅铝比显著影响水的吸附量和等温吸附曲线,随着硅铝比的减小,分子筛中的自由体积减小,对水的吸附量增加.水分子的主要吸附位置是在Li 和铝原子的周围,LinZSM-5型分子筛中存在着1个主要的吸附位点.Li 等金属阳离子的交换能有效降低水的吸附热.在吸附量相同的条件下,水的吸附热随着硅铝比的升高而降低.     

锂离子交换ZSM–5型分子筛中水分子吸附特性的分子模拟

用巨正则系综 Monte Carlo(grand canonical assemblage Monte Carlo, GCMC)模拟方法计算了水在 HZSM–5 型分子筛中的吸附热,计算结果与文献报道的实验结果吻合得较好。模拟了水在经锂离子(Li )交换后的 ZSM–5 型分子筛上的吸附等温线。在此基础上,进一步预测了水在不同硅铝摩尔(下同)比的 LinZSM–5 型分子筛中的吸附性质。计算结果显示:分子筛骨架上的硅铝比显著影响水的吸附量和等温吸附曲线,随着硅铝比的减小,分子筛中的自由体积减小,对水的吸附量增加。水分子的主要吸附位置是在 Li 和铝原子的周围,LinZSM–5 型分子筛中存在着 1 个主要的吸附位点。Li 等金属阳离子的交换能有效降低水的吸附热。在吸附量相同的条件下,水的吸附热随着硅铝比的升高而降低。     

二氧化硫在HZSM-5分子筛中吸附的分子模拟

通过实验测定了二氧化硫(SO2)在HZSM-5型分子筛中的吸附性能,采用巨正则系综Monte Carlo方法建立相应的吸附模型,模拟计算相应的吸附行为。在实验与模拟结果相吻合的基础上,进一步模拟计算了SO2在HZSM-5型分子筛中的吸附等温线、吸附微观构型及吸附热等性质。结果表明:随着硅铝比(摩尔比)的增大,分子筛对SO2的吸附量降低,当硅铝比大于191时,硅铝比对SO2的吸附量影响很小。SO2分子主要吸附在氢离子和Al原子周围。在Al原子周围,SO2分子比较集中,同时发现氢离子的存在会阻碍SO2的扩散。在吸附量相同的条件下,SO2在HZSM-5型分子筛的吸附热随着硅铝比的升高而降低。     

水在ZSM-5型分子筛中吸附的Monte Carlo模拟

构建了ZSM-5型分子筛物理模型,采用Connoly表面方法和Solvent表面方法对ZSM-5型分子筛的几何结构和性质进行了模拟分析。通过巨正则系综蒙特卡罗方法(GCMC)模拟研究了水蒸气在ZSM-5型分子筛上的吸附特性。通过模拟方法看到了实验难以表征的水蒸气在分子筛中具体吸附位,研究了压力、温度和硅铝比对ZSM-5型分子筛吸附性能的影响及其吸附热的变化规律。     

ZSM-5型分子筛对二氧化硫的动态吸附性能

采用ZSM-5型分子筛吸附脱除烟气中的二氧化硫,分析了其动态吸附过程的基本特性,以及硅铝物质的量比、温度、空速等影响因素.结果表明:ZSM-5型分子筛对二氧化硫的吸附符合Langmuir吸附等温线类型,属于单分子层物理吸附.用硅铝物质的量比为38的ZSM-5型分子筛,在温度为25 ℃、空速为700 h-1、入口二氧化硫体积分数为0.3%条件下,测量吸附饱和时间为180 min,饱和二氧化硫吸附容量为0.018 g/g.温度较低、硅铝物质的量比较小、空速较低的条件下,ZSM-5型分子筛对二氧化硫的吸附性能较好.     

C1-C7直链烷烃在MFI沸石内吸附行为的分子模拟

本文用巨正则系综蒙特卡罗（GCMC）及构型偏移蒙特卡罗（CBMC）的方法模拟了300K时C1—C7直链烷烃分子在MFI沸石分子筛中的吸附行为，并用目前常用的几种吸附理论对之进行拟和。包括单双点Langmuir吸附等温式、拟化学近似吸附等温式及Gibbs吸附等温式。双点Langmuir吸附等温式取得了最好的拟和效果。模拟及拟和结果说明了MFI沸石内通道吸附性能具有非均一性，也说明了吸附分子间相互作用对分子在沸石中的吸附行为的影响不能忽略，所以若要建立描述的客体分子在沸石内的吸附行为的较好模型，推导模型时必需考虑沸石的这种非均一性及吸附分子之间的相互作用。     

用于高湿度废气中甲苯吸附净化的疏水型ZSM-5分子筛的合成及其吸附性能研究

采用水热原位法合成了不同硅铝比的ZSM-5分子筛，研究了硅铝比对ZSM-5分子筛结构和疏水性的影响。以典型的挥发性有机物甲苯为对象，在动态吸附实验装置上评价了ZSM-5分子筛吸附有机物的性能，并拟合了甲苯在疏水ZSM-5上的吸附等温线方程。结果表明，高硅铝比ZSM-5具有良好的疏水性，其静态水吸附容量为0.014 g·g^-1，在高湿度条件下，甲苯浓度为1800 mg·m^-3，GHSV为25000 ml·h^-1·g^-1，温度为35℃，甲苯穿透吸附容量为0.041 g·g^-1，甲苯饱和吸附容量为0.075 g·g^-1。吸附等温线的拟合显示，甲苯在疏水ZSM-5分子筛上的吸附符合Langmuir-Freundlich复合模型。     

煤矸石碱熔—水热法制备NaX型分子筛及其对Pb2+的吸附特性研究

为实现煤矸石中硅铝组分的高值利用,以煤矸石为原料,采用碱熔水热法合成NaX型分子筛,通过X射线衍射(XRD)、红外光谱(FT-IR)、扫描电镜(SEM)等对产物进行表征,同时采用静态饱和吸水量和钙离子交换量对所制备分子筛进行性能评价。结果表明：硅铝比为3,碱灰比1.2,陈化温度40℃,陈化30 min,水热温度100℃,水热时间5 h, NaOH浓度为2.73 mol/L时合成分子筛的钙离子交换量为283.37 mg/g。将所合成的NaX型分子筛用于吸附液相中的Pb²⁺。在分子筛投加量1 g/L、吸附温度25℃、吸附时间2 h时,吸附容量(Q_e)最高可达483.05 mg/g;分子筛的吸附等温线符合Langmuir模型,饱和吸附容量(Q_m)可达528.31 mg/g。     

改性5A分子筛对水中As(Ⅴ)的吸附作用研究

改性5A分子筛是一种高效吸附材料。实验用5A分子筛作为载体,制备了该吸附剂,并表征了其基本性质。结果表明,改性5A分子筛对As(Ⅴ)具有很高的吸附率和选择性;室温下,pH=7时,改性5A分子筛吸附As(Ⅴ)的吸附等温线符合Langmuir型和Freundlich型。     

CO_2和CO在分子筛与活性炭上的吸附平衡

本文分别用静态称重法测定了CO_2和CO在5A,13X,NaY分子筛与活性炭上的吸附等温线,用流动法测定了CO_2-N_2体系中CO_2在13X分子筛与活性炭上25℃时的吸附等温线以及透过曲线（break-through curve）。吸附等温线分别用Langmuir方程和Freundlich方程回归。     

Comparative study of pure component adsorption of linear alkanes in zeolites MFI, BEA and MOR

Grand canonical Monte Carlo (GCMC) simulations and configurational-bias Monte Carlo simulations (CBMC) have been performed to compute and compare the pure component adsorption isotherms of C1–C7 linear alkanes in MFI, BEA, and MOR zeolites at 300 K. It is demonstrated that generally, the surfaces of the three zeolites available for adsorption are not energetically homogeneous; adsorption of the alkanes in the three zeolites can be divided into two steps, in the first step of which molecules are adsorbed in the strong sites and on the later of which on the weak sites; all isotherms obtained can be well described by the dual-site Langmuir equation, though the saturation loadings and the adsorption strengths are different for the three different topologic zeolites. A quantitative analysis of the isotherms shows that the Henry’s law constants in the three zeolites obey a similar linear relation to the number of carbon atoms of the alkanes.     

甲烷、乙烷、丙烷和丁烷在中孔活性炭上的吸附平衡

以活性炭AC1为吸附剂,在体积法实验装置上分别测定了其对甲烷、乙烷、丙烷和丁烷4种气体的吸附等温线,吸附温度分别为283、293、303和313 K。利用77 K吸附氮气数据表征AC1,得到其比表面积为956 m²·g^-1,孔体积为1.36 mL·g^-1,孔径分布在1~5 nm,中孔的比例达到了61%。AC1对4种气体的吸附等温线均为I型等温线,分别采用Langmuir方程和Langmuir-Freundlich方程(简称L-F方程)对吸附平衡数据进行拟合,结果表明,L-F方程具有更好的拟合效果,为后序的多组分吸附平衡研究提供了基础数据。AC1对乙烷/丙烷的吸附平衡选择性系数在1.7~2.5,吸附选择性随吸附压力的增大而减小,吸附温度对吸附选择性无明显影响。     

分子筛对丙烷和丙烯的吸附脱附性能

碳氢化合物(HC)捕获器是解决汽车冷启动问题的有效途径,分子筛作为碳氢化合物捕获剂的应用越来越受到重视。以丙烷和丙烯混合气为探针分子,利用瞬态应答(TSR)和程序升温脱附(TPD)技术,对4种类型分子筛的HC吸附脱附能力进行研究。结果表明,β-2分子筛的丙烷和丙烯脱附温度较高,分别为422℃和450℃,吸附量3.24 mL·g~(-1),ZSM-5-3分子筛的丙烷和丙烯脱附温度为130℃和127℃,碳氢化合物吸附量为7.87 mL·g~(-1)。     

A comparative study of the sorption of benzene and phenol in silicalite, HAlZSM-5 and NaAlZSM-5 by computer simulation

The sorption of benzene and phenol in silicalite, HAlZSM-5 and NaAlZSM-5 has been studied comparatively with the Cerius² software from MSI using Monte Carlo simulations. As a test of the simulation method, the well-studied system of benzene–silicalite was simulated first. The results show that the Henry constant and the isosteric heat of adsorption of benzene in silicalite are in good agreement with experimental data from the literature obtained by different methods. The open force field “Burchart–Dreiding” is proved to be suitable for simulation of the adsorption of aromatics in ZSM-5 type zeolites. The Henry constants of the systems mentioned above between 273 and 673 K, the isotherms at temperatures of 473 and 673 K, the sorption sites as well as the interaction energies between the guest molecules and the host zeolite frameworks have been obtained. The differences in the adsorption behavior between benzene and phenol in silicalite, HAlZSM-5 and NaAlZSM-5 are attributed to the differences in Coulomb interactions.     

Hydrogen sorption in transition metal exchanged zeolite Y: volumetric measurements and simulation study

Hydrogen adsorption capacities in zeolite Y and its nickel, palladium, rhodium and ruthenium exchanged forms were investigated at 77?K up to 101.3?kPa and 303?K up to 4,000?kPa using a static volumetric adsorption system. Hydrogen adsorption at 77?K for NaY and for Ni, Pd, Rh and Ru exchanged zeolite Y was found to be reversible with pressure. The chemisorption of hydrogen was observed at 303?K for Ni, Pd, Rh and Ru exchanged zeolite Y. Rhodium exchange zeolite Y showed the highest hydrogen adsorption capacity of 1.19 and 0.51 wt% at 77 and 303?K up to 101.3?kpa and 4,000?kpa, respectively. Grand canonical Monte Carlo simulations were also performed to study the adsorption of hydrogen in these zeolites at 77?K as well as 303?K. The simulated adsorption isotherms at 77?K are comparable to experimentally measured isotherms.     

Extra-framework charge and impurities effect,Grand Canonical Monte Carlo and volumetric measurements of CO2/CH4/N2 uptake on NaX molecular sieve

In this work, Monte Carlo simulation of CO₂, N₂, and CH₄ adsorption on zeolite 13X is carried out in grand canonical ensemble. FAU framework was used to reproduce the structure of zeolite 13X. Universal force field was used to calculate the interactions between adsorbates and 13X. Metropolis method was used for calculating adsorption isotherm. Volumetric measurements were carried out to confirm the simulation results. The simulation results using Universal force field showed good agreement with experimental results. Highest CO₂ uptake for this zeolite was found as 5.67 mol/kg from GCMC. Isosteric heat of adsorption was investigated to find the heat released during adsorption of each gas. The simulation result of isosteric heat of adsorption for CO₂, N₂, and CH₄ was utmost 17.00, 4.37, and 6.14 kcal/mole, respectively. Radial distribution graphs were used to find affinity of constituents of zeolite for CO₂. Henry’s constant evaluation was also performed at low pressure to find the selectivity of the structure. Henry’s constant of CO₂ in an equimolar mixture of N₂ and CH₄ was calculated 3.49 and 1.49 mol/kg.kPa, respectively. Finally, simulation results were fitted to Toth and dual-site Langmuir isotherms to find the best fit that belongs to dual-site Langmuir.     

Accelerated synthesis of all-silica DD3R and its performance in the separation of propylene/propane mixtures

Synthesis of the all-silica Deca-Dodecasil 3 Rhombohedral (DD3R) zeolite was accelerated 10 times by seeding with small amount of crystals (0.02 wt%) with yields approaching 100%. The effects of other synthesis variables, like silica source, the presence of methanol or the synthesis pH on the final product distribution have been studied. The adsorption and separation of propylene and propane mixtures on this material are presented. The improved synthesis may form the basis to scale-up production of DD3R for selective separation processes. The single component adsorption isotherms could be well described with a dual-site Langmuir model. The binary mixture adsorption was determined from breakthrough/desorption experiments at 323, 358 and 383 K. By modelling the adsorptive column, diffusion coefficients at infinite dilution for single component and the effect of propane over propylene adsorption were determined. Cylindrical geometry describes the pore topology of DDR type materials well. Propane decreases the uptake rate of propylene by adsorption in the surface of the crystals. Propylene diffusion is best described by the “strong confinement” model inside the zeolite cages. Separation is due to only propylene adsorption with diffusion as rate determining step.Results revealed DD3R as a very effective molecular sieve for the separation or purification of propane–propylene mixtures.     

A multi-scale approach to the physical adsorption in slit pores

Adsorption isotherms are the foundation of gas storage and separation operations. The isotherm models are classified into three scale levels with empiricisms in macroscopic level, requirements of long computing time and idealized conditions in microscopic level, as well as gaps in knowledge between these two levels. A multi-scale modeling methodology is developed in this paper in order to reduce the identified limitations. Microscopic molecular simulations (MS) based on the grand canonical Monte Carlo (GCMC) method are carried out followed by the development of the localized adsorption isotherms defined as the intermediate level models. They are represented by the Boltzmann factor and the local Langmuir equations. The macroscopic models are then formulated through the integration of small scale models. The following three contributions are achieved in the paper. First of all, guidelines for the validity of the Boltzmann factor are established, showing its practical significance, and the local Langmuir isotherm is justified as a good approximation to the results from microscopic simulations. Secondly, it is demonstrated that the pore size distributions can be determined using GCMC simulations coupled with the measured adsorption isotherms as exemplified by a case study on a coal specimen. Finally, using the measurement data reported by Bae and Bhatia (2006) for carbon dioxide adsorption on coal, we show that the overall adsorption isotherms can be determined from the multi-scale approach through the integration of smaller scale models with pore size distributions without the empiricism, indicating the success of the methodology. Further work is needed to improve the prediction accuracy for methane adsorption on coal specimens.     

Adsorption of propane, propylene and isobutane on a metal-organic framework: Molecular simulation and experiment

The separation of propane/propylene mixtures is the most energy-intensive operation practiced in the petrochemical industry. Adsorptive processes are currently viewed as a promising alternative to cryogenic distillation for the separation of these mixtures. In this paper, we explore the possibility of using a new metal-organic framework material, CuBTC, in adsorptive separation processes, particularly in a simulated moving bed (SMB) context using isobutane as a potential desorbent. A gravimetric method has been used to measure the adsorption equilibrium isotherms of propylene, propane and isobutane onto a commercial CuBTC powder over a temperature range from 323 to 423 K and pressures up to 100 kPa. These were complemented by a detailed experimental characterization of the structure of CuBTC using XRD and SEM techniques. Comparison of experimental isotherms with grand canonical Monte Carlo simulations in CuBTC showed that propane adsorption occurs preferentially in small octahedral pockets, while isobutane is excluded from these pockets due to its bulky structure. Propylene was seen to interact strongly with unsaturated metal sites, due to specific π‐Cu bonds. These interactions significantly enhance the affinity of this MOF for unsaturated hydrocarbons. Furthermore, in a range of temperatures and pressures, the affinity of CuBTC for isobutane is intermediate to that of propane and propylene. Our results suggest that CuBTC-isobutane is a very promising adsorbent-desorbent pair for use in SMB processes for propane/propylene separations.     

Grand canonical Monte Carlo simulation and volumetric equilibrium studies for adsorption of nitrogen, oxygen, and argon in cadmium (II) exchanged zeolite A

The adsorption of nitrogen, oxygen and argon has been studied in cadmium (II) ions exchanged zeolite A at 288.0 and 303.0?K. Experimentally measured adsorption isotherms are compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Nitrogen showed higher adsorption capacity and selectivity than oxygen and argon in these zeolite samples. The cadmium exchanged zeolite A showed increased adsorption capacity for nitrogen, oxygen, and argon with increase in cadmium (II) exchange levels. Isosteric heat of adsorption data showed stronger interactions of nitrogen molecules with cadmium (II) cations in zeolite samples. These observations have been explained in terms of higher electrostatic interaction of nitrogen with extra framework zeolite cations. The selectivity of oxygen over argon is explained in terms of its higher interaction of oxygen with cadmium exchanged zeolites than argon molecules. Heats of adsorption and adsorption isotherms were also calculated using grand canonical Monte Carlo simulation algorithm. Simulation studies expectedly show the proximity of nitrogen molecules to the locations of extra framework sodium and cadmium cations.