孔活性炭储存CH4的分子模拟

吸附天然气被认为是未来最具有发展前景的CH₄储存方式之一,其中的关键是寻找合适的吸附剂,使其具有良好的CH₄吸脱附性能。以纳米多孔碳材料作为多孔活性炭的结构,采用巨正则蒙特卡洛（GCMC）和平衡分子动力学（EMD）的方法研究CH₄在纳米多孔碳材料中的吸附和扩散行为,通过考察不同因素的影响,期望获得高的CH₄吸附量和自扩散系数。其中,研究的主要因素有：构成多孔碳材料的石墨片微元的大小、多孔碳材料的不同密度、多孔碳材料的表面基团改性。结果表明：多孔碳材料对CH₄的吸附受石墨片微元种类和混合比例的影响不大;在所研究的多孔碳材料密度范围内,存在最优密度,能够获得最大的CH₄吸附量,此最优密度在0.50 g·cm^-3左右,但是多孔碳材料的表面经羟基修饰后,最佳材料密度发生了偏移,此时最优密度在0.72 g·cm^-3左右;此外,经表面改性后的多孔碳材料吸附量大小顺序为：CH₃ > OH > CO > COOH;对于CH₄在多孔碳材料中的扩散,总体规律是低的密度,并且经过COOH修饰,其CH₄自扩散系数最大。     

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。     

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。     

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.     

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。     

Effect of pore size on CH4/N2 separation using activated carbon

In this paper, a model of activated carbon was established by molecular simulation and the separation performance of N_2 and CH_4 on activated carbon was studied. In order to evaluate the adsorption selectivity and diffusion selectivity of N_2 and CH_4, Grand Canonical Monte Carlo and molecular dynamic methods were used to obtain equilibrium adsorption isotherms and mean square displacements of N_2 and CH_4 on activated carbon with different pore sizes. Research results showed that the difference in adsorption isosteric heat of N_2 and CH_4 at the pore size of 0.46 nm is the largest, which is 5.759 and 7.03 kcal·mol~(-1)(1 cal=4.184 J), respectively. Activated carbon with pore size of 0.46 nm has the best N_2 and CH_4 adsorption selectivity, while its diffusion selectivity is not obvious.     

MER型沸石吸附分离CO2/CH4的分子模拟

MER型沸石在吸附分离CO₂/CH₄方面展现出良好的工业应用前景,受到广泛关注,但还缺乏理论基础数据。本文采用巨正则蒙特卡洛（GCMC）模拟方法,以全硅MER型沸石作为对照,模拟分析了CO₂/CH₄在Na⁺、K⁺、Cs⁺和Ca²⁺交换的MER型沸石中的吸附分离行为。结果表明：不同阳离子交换的MER型沸石对CO₂和CH₄的吸附符合Langmuir-Freundlich吸附等温线模型,平衡吸附量的大小顺序为：Ca-MER＞Na-MER＞K-MER＞Cs-MER,与沸石的自由体积和比表面积大小顺序一致,且近似成线性关系,选用高价阳离子MER型沸石可以提高吸附量;CO₂和CH₄主要分布在沸石的pau笼中,在d8R笼和ste笼中也有少量分布;骨架外阳离子与CO₂的强吸附作用和独特的八元环窗口孔径是MER型沸石对CO₂/CH₄混合组分表现出超高吸附选择性的原因,吸附选择性高达1000以上。综合吸附量、吸附热和吸附选择性分析指出,Na-MER和K-MER型沸石是优良的CO₂吸附剂。本研究为MER型沸石吸附分离CO₂/CH₄提供了理论依据和实验指导。     

Adsorption and separation of CO2/N2 and CO2/CH4 by 13X zeolite

Accumulation of greenhouse gases in the atmosphere is responsible for increased global warming of our planet. The increasing concentration of carbon dioxide mainly from flue gas, automobile and landfill gas (LFG) emissions are major contributors to this problem. In this work, CO₂, CH₄ and N₂ adsorption was studied on Ceca 13X zeolite by determining pure and binary mixture isotherms using a constant volume method and a concentration pulse chromatographic technique at 40 and 100°C. The experimental data were then compared to the predicted binary behaviour by extended Langmuir model. Results showed that the extended Langmuir theoretical adsorption model can only be applied as an approximation to predict the experimental binary behaviour for the systems studied. Equilibrium phase diagrams were obtained from the experimental binary isotherms. For these systems, the integral thermodynamic consistency tests were also conducted. It was found that Ceca 13X exhibits large CO₂/CH₄ and CO₂/N₂ selectivity and could find application in landfill gas purification, CO₂ removal from natural gas and CO₂ removal from ambient air or flue gas streams. © 2011 Canadian Society for Chemical Engineering     

CO2/CH4在活性炭上吸附与分离的分子模拟

Monte Carlo 模拟(GCMC)研究了CO2和CH4在活性炭中的吸附情况.氢气和二氧化碳分子被模拟作Kennard-Jones球体,活性炭用一个裂缝气孔模型代替.研究了压力、温度、孔径活性炭对CO2(以CH4为基准)的选择性的影响.结果表明,低压、低温、孔径越小,选择性越大,即对分离CO2和CH4有利;233 K、孔径为2.29 nm以及低压下选择性达到10,此时分离效果较好.     

煤基碳分子筛的制备及CH4/N2分离性能研究

以煤为原料,通过气相碳沉积法制备了CH4/N2变压吸附分离用碳分子筛,研究了苯沉积量对碳分子筛吸附性能的影响。用液氮吸附（77 K）、扫描电镜对碳分子筛孔结构及表面形貌进行了表征,结果表明：制备的碳分子筛（CMS-1）平衡分离系数大于5,比表面积SBET=251.5 m2/g,微孔孔容Vm=0.1178 mL/g,孔径主要分布在0.35~2 nm,能满足CH4/N2变压吸附分离要求。     

CH4／O2在炭分子筛上的吸附动力学

为消除低浓度煤层气对煤层开采存在的安全隐患,提出了利用甲烷和氧气在炭分子筛上的动力学差异进行脱氧的工艺。采用容积法测定了纯CH4和O2在炭分子筛颗粒上的吸附动力学数据,并利用单床变压吸附装置测定了混合气体在298．15K,各压力下的穿透曲线。研究结果显示：吸附初期,O2在CMS上的扩散速率明显大于CH4;在混合体系穿透曲线上,O2的穿透时间远大于CH4,炭分子筛固定床表现出对O。的优先吸附选择性,可以实现出口直接富集甲烷的目的。0．4MPa时,当产品气中CH4含量为92．44％时,CH4回收率为73．27％。     

不同管径碳纳米管中CO2/CH4分离的分子模拟

生物甲烷路线在CO₂减排和节能方面有很大的应用前景。而对生物沼气的分离是此路线的一个关键问题,特别是在60℃和0.1 MPa下。巨正则Monte Carlo（GCMC）和平衡分子动力学（EMD）的分子模拟方法研究CO₂和CH₄在不同管径的碳纳米管（CNT）中的吸附和扩散,可以从分子层面研究生物沼气的分离机理。分别计算了CO₂/CH₄二元混合物吸附量、吸附选择性、自扩散系数和渗透选择性等参数。模拟结果表明：由于碳管的受限空间和CO₂与碳纳米管壁面分子之间强相互作用,导致二元等物质的量的混合物CO₂/CH₄的吸附量和扩散系数的差异。CO₂的吸附量和自扩散系数都比CH₄的大。渗透选择性在碳管管径达到最接近1 nm时达到最大值,此时混合物的分离过程是吸附控制,而非扩散控制。     

Adsorption of binary CO2/CH4 mixtures using carbon nanotubes: Effects of confinement and surface functionalization

Effect of confinement and surface functionalization in carbon nanotubes (CNTs) on the competitive adsorption of a binary CO₂/CH₄ mixture has been investigated by grand canonical Monte Carlo simulations. Adsorption using CNTs with different functionalization arrangements, different diameters, different functionalization degrees, and different functional groups, such as –COOH, –CO, –OH, –CH₃, is investigated. Effects of (a) the pore textural properties, such as pore size and accessible surface area, and (b) the gas–adsorbent interaction, especially the electrostatic interaction, are discussed. From these results, we discuss the impact that variables such as confinement and surface functionalization have on the performance for CO₂ separation.     

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.     

H2, CO2, and CH4 Adsorption Potential of Kerogen as a Function of Pressure,Temperature, and Maturity

We performed molecular dynamics simulation to elucidate the adsorption behavior of hydrogen (H₂), carbon dioxide (CO₂), and methane (CH₄) on four sub-models of type II kerogens (organic matter) of varying thermal maturities over a wide range of pressures (2.75 to 20 MPa) and temperatures (323 to 423 K). The adsorption capacity was directly correlated with pressure but indirectly correlated with temperature, regardless of the kerogen or gas type. The maximum adsorption capacity was 10.6 mmol/g for the CO₂, 7.5 mmol/g for CH₄, and 3.7 mmol/g for the H₂ in overmature kerogen at 20 MPa and 323 K. In all kerogens, adsorption followed the trend CO₂ > CH₄ > H₂ attributed to the larger molecular size of CO₂, which increased its affinity toward the kerogen. In addition, the adsorption capacity was directly associated with maturity and carbon content. This behavior can be attributed to a specific functional group, i.e., H, O, N, or S, and an increase in the effective pore volume, as both are correlated with organic matter maturity, which is directly proportional to the adsorption capacity. With the increase in carbon content from 40% to 80%, the adsorption capacity increased from 2.4 to 3.0 mmol/g for H₂, 7.7 to 9.5 mmol/g for CO₂, and 4.7 to 6.3 mmol/g for CH₄ at 15 MPa and 323 K. With the increase in micropores, the porosity increased, and thus II-D offered the maximum adsorption capacity and the minimum II-A kerogen. For example, at a fixed pressure (20 MPa) and temperature (373 K), the CO₂ adsorption capacity for type II-A kerogen was 7.3 mmol/g, while type II-D adsorbed 8.9 mmol/g at the same conditions. Kerogen porosity and the respective adsorption capacities of all gases followed the order II-D > II-C > II-B > II-A, suggesting a direct correlation between the adsorption capacity and kerogen porosity. These findings thus serve as a preliminary dataset on the gas adsorption affinity of the organic-rich shale reservoirs and have potential implications for CO₂ and H₂ storage in organic-rich formations.     

CO2/CH4/N2在沸石13X-APG上的吸附平衡

采用磁悬浮热天平测量了CO₂、CH₄与N₂在沸石13X-APG上的吸附等温线,温度为293、303、333和363 K,压力为0～500 kPa。对吸附平衡实验数据采用multi-site Langmuir模型和Sips模型进行拟合,均得到良好的拟合效果,非线性回归得到吸附热等模型参数,可为变压吸附工艺过程的开发提供基础热力学数据。将沸石13X-APG吸附分离性能与文献中报道的吸附材料(如沸石分子筛、活性炭、金属有机骨架材料和介孔硅分子筛)性能相比较。通过比较CO₂、CH₄与N₂吸附容量以及相对分离系数,探讨CO₂/CH₄(垃圾填埋气或者CO₂强化煤层甲烷回收气)体系、CO₂/N₂(燃煤电厂、水泥厂以及焦炭厂烟道气)体系以及CH₄/N₂(煤层气)体系吸附分离的高效材料,为未来二氧化碳吸附捕集和甲烷吸附回收提供基础数据。     

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。     

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Abstract

Pure component adsorption equilibrium of CH₄ and CO₂ on activated carbon have been studied at three different temperatures, 298, 323, and 348?K within a pressure range of 10–2000?kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO₂/CH₄ (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800?kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO₂/CH₄, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800?kPa, extended Sips model underestimated significantly the CO₂ adsorbed amount and overestimated the CH₄ adsorbed amount.     

用于吸附分离CH4/CO2的碳分子筛的制备研究

以碳分子筛(CMS)作为吸附剂,探索其对CH4/CO2混合气的分离纯化性能。采用化学气相炭沉积法,以价格便宜的商品椰壳基活性炭为原料,以苯为沉积剂,制备碳分子筛。研究了沉积时间和沉积温度对CMS的吸附性质的影响。采用容量法对CMS吸附CH4和CO2性能进行测定。结果表明,在沉积温度为700℃,沉积时间为40min时制备的CMS平衡吸附选择性系数为58.03,远高于活性炭的5.124,对CH4/CO2有良好的分离效果。     

Equilibrium Adsorption Studies of CO2, CH4, and N2 on Amine Functionalized Polystyrene

Adsorption of CO₂, CH₄, and N₂ has been investigated using amine functionalized polymeric resins having diethanolamine, imidazole, dimethylamine, and N-methyl piperazine covalently attached to the styrene-divinyl benzene copolymer (PS) matrix. The equilibrium adsorption of CO₂, CH₄, and N₂ was examined on these functionalized polymers at pressures from atmospheric to 40 atm for CO₂ and N₂ while up to 10 atm for CH₄ at 303 K. PS-Imidazole showed the highest adsorption capacity for CO₂ as compared to other functionalized polymers. No significant uptake of CH₄ and N₂ was observed at low pressures by any of the functionalized polymers. The adsorption isotherms were analyzed using dual mode sorption model and Ideal Adsorbed Solution Theory (IAST).