Equilibrium analysis of CH4, CO,CO2, H2O,H2, C mixtures in C–H–O atom space using Gibbs free energy global minimization

Gibbs free energy minimization is employed to carry out thermodynamic equilibrium analysis studies of mixtures containing methane, carbon monoxide, carbon dioxide, water, and hydrogen ideal gases, and possibly solid carbon. The employed global minimization approach represents a general, unifying, conceptual framework that allows reaction and phase equilibrium analysis to be simultaneously carried out in the atom-mol fraction space (a_H, a_O) , thus capturing in a comprehensive manner the equilibrium behavior of a number of industrially important processes, such as methane reforming (steam, dry, energetically enhanced), and methanation. Two theorems are presented, establishing necessary and sufficient (necessary) feasibility and regularity (optimality) conditions for the aforementioned minimization problem. The equilibrium results obtained through application of these theorems are guaranteed to be globally optimal. They quantify in (a_H, a_O) space, the feasible region, the carbon formation region, and all species mole over total atom-mol normalized ratios, for a range of temperatures and pressures.     

高浓度CO2气中H2和CH4的测定

在对高浓度二氧化碳气测定氢气、甲烷时,需用40％NaOH吸收二氧化碳后,再用奥氏仪可测定出低含量的氢气、甲烷含量。     

一维直孔道MOFs对CH4/N2和CO2/CH4的分离

非常规天然气未来可以作为常规天然气的有效补充,其中低浓度煤层气和生物质燃气分别需要脱除大量的N₂ 和CO₂以达到富集和纯化CH₄的目的。本研究针对CH₄/N₂这一对较难分离的气体组合,选取了具有一维菱形孔道的MOFs材料Cu(INA)₂作为吸附剂,将合成的样品做了XRD和TG表征,测试了纯气体CO₂、CH₄和N₂的吸附曲线,利用巨正则系综蒙特卡罗(GCMC)分子模拟和理想吸附溶液理论(IAST)计算了气体的吸附热和该材料对于CH₄/N₂和CO₂/CH₄的吸附选择性系数;3 MPa压力下制备的颗粒样品填装吸附分离装置,进行了混合气体CH₄/N₂ (50%/50%)和CO₂/CH₄ (50%/50%)的穿透试验,分离的结果显示,Cu(INA)₂不仅高选择性地吸附CH₄/N₂混合物中的CH₄(S_CH4/N2=10),而且对CH₄/N₂的分离效果优于CO₂/CH₄。     

CO2,H2,N2在MDEA水溶液中的溶解 度

ＣＯ２、Ｈ２、Ｎ２在ＭＤＥＡ水溶液中的溶解度徐国文张成芳钦淑均（华东理工大学无机化工研究所，上海２００２３７）关键词：ＣＯ２Ｈ２Ｎ２溶解度ＭＤＥＡ１前言国外报道的ＣＯ２溶解度数据［１～９］，布点稀疏，无法满足工程计算及动力学研究之需。王挹薇等采...     

Adsorption of Off‐Gases from Steam Methane Reforming (H2, CO2, CH4, CO and N2) on Activated Carbon

Abstract

Hydrogen is the energy carrier of the future and could be employed in stationary sources for energy production. Commercial sources of hydrogen are actually operating employing the steam reforming of hydrocarbons, normally methane. Separation of hydrogen from other gases is performed by Pressure Swing Adsorption (PSA) units where recovery of high‐purity hydrogen does not exceed 80%.

In this work we report adsorption equilibrium and kinetics of five pure gases present in off‐gases from steam reforming of methane for hydrogen production (H₂, CO₂, CH₄, CO and N₂). Adsorption equilibrium data were collected in activated carbon at 303, 323, and 343 K between 0‐22 bar and was fitted to a Virial isotherm model. Carbon dioxide is the most adsorbed gas followed by methane, carbon monoxide, nitrogen, and hydrogen. This adsorbent is suitable for selective removal of CO₂ and CH₄. Diffusion of all the gases studied was controlled by micropore resistances. Binary (H₂‐CO₂) and ternary (H₂‐CO₂‐CH₄) breakthrough curves are also reported to describe the behavior of the mixtures in a fixed‐bed column. With the data reported it is possible to completely design a PSA unit for hydrogen purification from steam reforming natural gas in a wide range of pressures.     

二氧化碳在CH4+CO2+N2/C2H6三元系中的结霜温度计算

含CO₂的天然气体系在历经低温工艺时,由于CO₂的三相点温度(216.55 K)较高,容易凝华结霜产生固体CO₂,因而有必要对CO₂在天然气中的结霜温度进行计算。根据气固相平衡原理,分别采用道尔顿分压定律、PR状态方程对CO₂在CH₄-CO₂-N₂和CH₄-CO₂-C₂H₆三元系中的结霜温度进行了计算。此外,还采用HYSYS软件对CO₂的结霜温度做了相应的计算。将3种方法的计算结果和实验结果进行了比较,结果表明3种方法在预测三元系中CO₂的结霜温度时,都具有良好的精度。其中,PR状态方程法和HYSYS法的精度略高于道尔顿分压定律法;道尔顿分压定律法虽精度最低,但计算最简单,且也能获得满意的精度,可做工程快速估算使用。     

CO2/CH4 and CH4/N2 separation on isomeric metal organic frameworks☆

Two isomeric metal-organic frameworks(MOFs) with 2-dimensional(2D) and 3-dimensional(3D) topologies both comprised of Cu(Ⅱ) and OTf(OTf = trifluoromethanesulfonate) ions were synthesized and characterized.The CO_2,CH_4 and N_2 adsorption properties of the two isomeric MOFs were investigated from 263 K to 298 K at0.1 MPa.The results showed that the 2D MOF exhibited a higher selectivity for CO_2 from CO_2/CH_4 and CH_4from CH_4/N_2 compared to the 3D MOF,even though it possessed a lower surface area and pore volume.The higher adsorption heats of gases on the 2D MOF inferred the strong adsorption potential energy in the layered MOFs.Dynamic separation experiments using CO_2/CH_4 and CH_4/N_2 mixtures on the two MOFs proved that the2 D MOF had a longer elution time than the 3D MOF as well as better separation abilities.     

H2, CO, N2, O2和CH4在碳膜中的扩散

Diffusion of pure H2, CO, N2,O2 and CH4 gases through nanoporous carbon membrane is investigated by carrying out non-equilibrium molecular dynamics （NEMD） simulations. The flux, transport diffusivity and activation energy for the pure gases diffusing through carbon membranes with various pore widths were investigated. The simulation results reveal that transport diffusivity increases with temperature and pore width, and its values have a magnitude of 10^-7 m^2·s^-1 for pore widths of about 0.80 to 1.21 nm at 273 to 300 K. The activation energies for the gases diffusion through the membrane with various pore widths are about 1-5 kJ·mol^-1, The results of transport diffusivities are comparable with that of Rao and Sircar （J. Membr. Sci., 1996）, indicating the NEMD simulation method is a good tool for predicting the transport diffusivities for gases in porous materials, which is always difficult to be accurately measured by experiments.     

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.     

气体透过碳膜的非平衡动力学模拟研究

The permeation of various pure gas （H2, He, Ne, CH4 and At） through carbon membranes is investigated using a dual control volume grand canonical molecular dynamics method. A two-dimensional slit pore is employed instead of the one-dimensional pore. Compared with the experiments, simulation results show that the improvement of pore model is very necessary. The effects of membrane thickness, pore width and temperature on gas permeance and ideal separation factor are also discussed. Results show that gas permeates through membrane according to Knudsen diffusion in large pore, while Knudsen diffusion is accompanied by molecular sieving in small pore. Moreover, methane is easily adsorbed on the membrane surface due to strong attractive interactions of membrane and shows higher permeance than that of Knudsen flow. In addition, it is noted that when membrane thickness is thin enough the permeance of gas does not decrease with the increase of membrane thickness due to the strong adsorption until membrane resistance becomes dominant.     

CO2通过合成聚合物膜的促进传递

Two kinds of fixed carrier membrane materials containing secondary amine and carboxyl groups which can be used as carriers of CO2 were prepared. One was poly(N-vinyl-7-sodium aminobutyrate)(PVSA), which was obtained through the hydrolysis of polyvinylpyrrolidone (PVP) synthesized with N-vinylpyrrolidone(NVP) by radical polymerization. The other was poly(N-vinyl-7-sodium aminobutyrate-co-sodium acrylate)(VSA-SA), which was obtained through the hydrolysis of copolymer of N-vinylpyrrolidone and acrylamide(AAm) (NVP-AAm). The composite membranes were developed with PVSA or VSA-SA as active layer and polysulfone (PS) as support membranes. The permeation rates of pure CO2 and CH4 gas as well as binary mixtures of CO2/CH4 through the composite membranes were measured. The results show that the composite membranes present better CO2 permeation rates than other fixed carrier membranes do reported in literature. For example, at 26℃, 1330 Pa of CO2 pressure, the PVSA/PS composite membrane displays a CO2 permeation     

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.     

Diffusivity of CO2, CH4, C2H6 and N2 in athabasca bitumen

Experimental data for the diffusivity of carbon dioxide, methane, ethane and nitrogen in Athabasca bitumen are presented in the range 25–90°C at 4 and 8 MPa. The diffusivity of these gases has been determined as a function of gas concentration in bitumen using a non‐intrusive experim?ental method. The diffusivity of gas in general is found to increase with temperature and pressure, and is a unimodal function of concentration. A correlation is provided for the average diffusivity of these gases as a function of temperature.     

Membranes for CO2 /CH4 and CO2/N2 Gas Separation

Membrane technology has emerged as a leading tool worldwide for effective CO₂ separation because of its well-known advantages, including high surface area, compact design, ease of maintenance, environmentally friendly nature, and cost-effectiveness. Polymeric and inorganic membranes are generally utilized for the separation of gas mixtures. The mixed-matrix membrane (MMM) utilizes the advantages of both polymeric and inorganic membranes to surpass the trade-off limits. The high permeability and selectivity of MMMs by incorporating different types of fillers exhibit the best performance for CO₂ separation from natural gas and other flue gases. The recent progress made in the field of MMMs having different types of fillers is emphasized. Specifically, CO₂/CH₄ and CO₂/N₂ separation from various types of MMMs are comprehensively reviewed that are closely relevant to natural gas purification and compositional flue gas treatment     

Adsorption of CO2, CH4, CO2/N2 and CO2/CH4 in novel activated carbon beads: Preparation,measurements and simulation

A series of high performance carbonaceous mesoporous materials: activated carbon beads (ACBs), have been prepared in this work. Among the samples, ACB‐5 possesses the BET specific surface area of 3537 m² g^?1 and ACB‐2 has the pore volume of 3.18 cm³ g^?1. Experimental measurements were carried out on the intelligent gravimetric analyzer (IGA‐003, Hiden). Carbon dioxide adsorption capacity of 909 mg g^?1 has been achieved in ACB‐5 at 298 K and 18 bar, which is superior to the existing carbonaceous porous materials and comparable to metal‐organic framework (MOF)‐177 (1232 mg g^?1, at 298 K and 20 bar) and covalent‐organic framework (COF)‐102 (1050 mg g^?1 at 298 K and 20 bar) reported in the literature. Moreover, methane uptake reaches 15.23 wt % in ACB‐5 at 298 K and 18 bar, which is better than MOF‐5. To predict the performances of the samples ACB‐2 and ACB‐5 at high pressures, modeling of the samples and grand canonical Monte Carlo simulation have been conducted, as is presented in our previous work. The adsorption isotherms of CO₂/N₂ and CO₂/CH₄ in our samples ACB‐2 and 5 have been measured at 298 and 348 K and different compositions, corresponding to the pre‐ and postcombustion conditions for CO₂ capture. The Dual‐Site Langmuir‐Freundlich (DSLF) model‐based ideal‐adsorbed solution theory (IAST) was also used to solve the selectivity of CO₂ over N₂ and CH₄. The selectivities of ACBs for CO₂/CH₄ are in the range of 2–2.5, while they remain in the range of 6.0–8.0 for CO₂/N₂ at T = 298 K. In summary, this work presents a new type of adsorbent‐ACBs, which are not only good candidates for CO₂ and CH₄ storage but also for the capture of carbon dioxide in pre‐ and postcombustion processes. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

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。