Computational Study of Adsorption and Separation of CO(2), CH(4), and N(2) by an rht-Type Metal-Organic Framework

In this work, a computational study is performed to evaluate the adsorption-based separation of CO(2) from flue gas (mixtures of CO(2) and N(2)) and natural gas (mixtures of CO(2) and CH(4)) using microporous metal organic framework Cu-TDPAT as a sorbent material. The results show that electrostatic interactions can greatly enhance the separation efficiency of this MOF for gas mixtures of different components. Furthermore, the study also suggests that Cu-TDPAT is a promising material for the separation of CO(2) from N(2) and CH(4), and its macroscopic separation behavior can be elucidated on a molecular level to give insight into the underlying mechanisms. On the basis of the single-component CO(2), N(2), and CH(4) isotherms, binary mixture adsorption (CO(2)/N(2) and CO(2)/CH(4)) and ternary mixture adsorption (CO(2)/N(2)/CH(4)) were predicted using the ideal adsorbed solution theory (IAST). The effect of H(2)O vapor on the CO(2) adsorption selectivity and capacity was also examined. The applicability of IAST to this system was validated by performing GCMC simulations for both single-component and mixture adsorption processes.     

Aqueous and gaseous adsorption from montmorillonite-carbon composites and from derived carbons

Clay-carbon composites and the carbons derived from demineralization of the clay template were examined for their aqueous adsorption properties (2,4,6-trichlorophenol and methylene blue) and for their gas adsorption/separation abilities regarding CO(2), CH(4), and N(2) gases. The sorption results are discussed in relation with their structural properties (surface area, pore width and volume, and surface chemistry). It was found that the properties of the adsorbents depend highly on the synthetic route, for instance, on the use of clay or H(2)SO(4) as structure mediating and activating agents, respectively. Particularly, the simultaneous use of clay and H(2)SO(4) leads to a synergistic action, which imparts to the final solids the highest sorption capacity and the best potential for separation of CO(2) from gaseous mixtures of CH(4) and N(2).     

A modification of the Doong-Yang model for gas mixture adsorption using the lewis relationship

The Doong-Yang model, which is used for predicting gas mixture adsorption equilibrium from pure-component isotherms of the Dubinin type, is modified by incorporating the Lewis relationship. The modified model is tested against experimental data for four binary systems, including a like-component (or nearly ideal) mixture, CH(4) + C(2)H(6), a moderately nonideal mixture, CO(2) + C(2)H(4), and two highly nonideal mixtures, CO(2) + C(3)H(8) and CO(2) + H(2)O. Comparisons are made with the ideal adsorbed solution (IAS) theory and the Bering model. Results show that the proposed model is the best for the like-component mixture and the moderately nonideal mixture. In contrast, for the highly nonideal mixtures, the original Doong-Yang model is the only one among the four models that can predict CO(2) + C(3)H(8) adsorption correctly. The IAS theory and the Bering model have similar predictions and are suitable only for like-component mixtures. The new model requires a simple numerical iteration but is easy to use; no new parameters are required. Theoretical reasons are given for the fact that the original Doong-Yang model is best for nonideal mixtures, whereas the modified Doong-Yang model is best for ideal mixtures.     

The interaction of an anionic gemini surfactant with conventional anionic surfactants

The interaction in two mixtures of an anionic gemini surfactant having N ,N -dialkylamide and carboxylate groups in a molecule, (CH2)2[N(COC11H23)CH(CO2H)CH2(CO2H)]2. 2NaOH (GA), and conventional anionic surfactants have been investigated in 0.1 M NaCl at pH 5.0. The two mixtures are GA/sodium dodecylsulfate (SDS) and GA/sodium N -dodecanoylglutamate (AGS) at a molar fraction of GA, alphaGA = 0.25 . Mixtures of both GA/SDS and GA/AGS exhibit synergism in surface tension reduction effectiveness. The GA/SDS mixture also exhibits synergism in surface tension reduction efficiency and mixed micelle formation, whereas the GA/AGS mixture does not. The interaction in mixed adsorption film formation is stronger than that in mixed micelle formation for the two mixtures. The interaction in the formation of the mixed adsorption film and the mixed micelle for the GA/SDS mixture is stronger in both formations than that for the GA/AGS mixture. The stronger interaction for the GA/SDS mixture may be caused by the combination of the smaller minimum area per molecule at the air/water interface (Amin) of the head groups in the GA molecule and the larger Amin in the SDS molecule.     

Molecular insight into the high selectivity of double-walled carbon nanotubes

Combining experimental knowledge with molecular simulations, we investigated the adsorption and separation properties of double-walled carbon nanotubes (DWNTs) against flue/synthetic gas mixture components (e.g. CO(2), CO, N(2), H(2), O(2), and CH(4)) at 300 K. Except molecular H(2), all studied nonpolar adsorbates assemble into single-file chain structures inside DWNTs at operating pressures below 1 MPa. Molecular wires of adsorbed molecules are stabilized by the strong solid-fluid potential generated from the cylindrical carbon walls. CO(2) assembly is formed at very low operating pressures in comparison to all other studied nonpolar adsorbates. The adsorption lock-and-key mechanism results from perfect fitting of rod-shaped CO(2) molecules into the cylindrical carbon pores. The enthalpy of CO(2) adsorption in DWNTs is very high and reaches 50 kJ mol(-1) at 300 K and low pore concentrations. In contrast, adsorption enthalpy at zero coverage is significantly lower for all other studied nonpolar adsorbates, for instance: 35 kJ mol(-1) for CH(4), and 14 kJ mol(-1) for H(2). Applying the ideal adsorption solution theory, we predicted that the internal pores of DWNTs have unusual ability to differentiate CO(2) molecules from other flue/synthetic gas mixture components (e.g. CO, N(2), H(2), O(2), and CH(4)) at ambient operating conditions. Computed equilibrium selectivity for equimolar CO(2)-X binary mixtures (where X: CO, N(2), H(2), O(2), and CH(4)) is very high at low mixture pressures. With an increase in binary mixture pressure, we predicted a decrease in equilibrium separation factor because of the competitive adsorption of the X binary mixture component. We showed that at 300 K and equimolar mixture pressures up to 1 MPa, the CO(2)-X equilibrium separation factor is higher than 10 for all studied binary mixtures, indicating strong preference for CO(2) adsorption. The overall selective properties of DWNTs seem to be superior, which may be beneficial for potential industrial applications of these novel carbon nanostructures.     

Unexpected adsorption behavior of nonionic surfactants from glycol solvents

Adsorption and interfacial properties of model methyl-capped nonionic surfactants C8E4OMe [C8H17O(C2H4O)4CH3] and C10E4OMe [C10H21O(C2H4O)4CH3] were studied in water and water/ethylene glycol mixtures as well as pure ethylene glycol. Critical micellar concentrations (cmc's), surface tensions, and surface excess were determined using surface tension (ST) and neutron reflection (NR) as a function of solvent type and surfactant tail length. The ST results show a strong dependence on solvent type in terms of cmc. The NR data were analyzed using a single-layer model for the adsorbed surfactant films. Surprisingly, the adsorption parameters obtained in both water and pure ethylene glycol were very similar, and variations in film thickness or area per molecule are negligible in respect of the uncertainties. Similarly, for C10E4OMe, estimates for the free energies of adsorption and micellization show only a weak solvent dependence. These results suggest that for such model nonionic surfactants dilute solution properties are dictated by solvophobicity, which is quite similar for this class of water, glycol, and water-glycol mixtures. More specifically, the nature of the adsorption layer appears to be hardly affected by the type of solvent subphase. The findings highlight the significance of solvophobicity and show that model nonionic surfactants can behave very similarly in hydrogen-bonding glycol solvents and water.     

还原剂对Au-Pd/CeO2催化剂甲醇部分氧化性能的影响

以PVP为保护剂,乙醇(ER)、乙二醇(GR)和水合肼(HR)为还原剂制备了一系列Au-Pd/CeO2催化剂,考察了还原剂对甲醇部分氧化性能的影响,并运用XRD、TPD和TPR等手段对催化剂进行了表征。结果表明,Au-Pd/CeO2(ER)催化剂具有较大的比表面积,形成的AuxPdy量较多、粒径较小、分散度较高、活性组分与载体的相互作用较强,同时对甲醇的吸附量较大和吸附温度较低。因此,该催化剂具有较高的催化活性和氢气选择性以及较低的CO质量分数。     

Oxorhenium phosphinophenolato complexes with model peptide fragments: synthesis, characterization, and stability considerations

The synthesis and characterization of a series of mixed-ligand oxorhenium(V) complexes containing the o-diphenylphosphinophenolato ligand (HL) and model peptide fragments acting as the tridentate coligand are reported. Thus, by reacting equimolar amounts of tiopronin, Gly-Gly, Gly-L-Phe, or glutathione (GSH) peptides on the [(n-C4H9)4N][ReOCl3(L)] precursor in refluxing MeCN/MeOH or aqueous MeCN/MeOH mixtures, the following complexes were obtained: ReO([SC(CH3)CONCH2COO][L])[(n-C4H9)4N], 1, ReO([H2NCH2CONCH2COO][L]), 2, ReO)[H2NCH2CONCH(CH2C6H5)COO][L]), 3, and ReO([SCH2CH(NHCOCH2CH2CHNH2COOH)CONCH2COO][L])Na, 4. The compounds are closed-shell 18-electron oxorhenium species adopting a distorted octahedral geometry, as demonstrated by classical spectroscopical methods including multinuclear NMR. X-ray diffraction analyses for 1 and 2 are also reported. By comparative stability studies of complexes 1-3 against excess GSH it was shown that complex 3 containing the bulky C6H5CH2 substituent adjacent to the coordinated carboxylate group of Phe is the most stable complex.     

沸石的孔口改性与气体吸附分离

沸石由干具有独特的微孔结构和表面性质，对物质的吸附表现出高度的选择性，已被广泛用于许多工业吸附分离过程．在气体分离方面，最常见的是利用沸石制造纯净的稀有气体和富氧空气．Niwa等［‘－‘］和本实验室［‘’］已成功地采用出（OCH小化学气相沉积方法对HM和Hi8M七沸石进行孔径精细调变，改善了沸石的择形吸附分离和催化性能．本文试图进一步研究沸石孔口改性在气体吸附分离方面的应用潜力．我们选择的H元气体混合物体系是NZ／OZ和CH。川。，因为O。，NZ和CH。三种分子的动力学直径分别为0．346O．364和0．380urn，相差甚…     

透氧膜反应器内NiO/MgO催化焦炉煤气重整反应途径

对透氧膜反应器内焦炉煤气(COG)重整反应模型进行分析.通过H2+N2、CH4+N2、CO+N2和H2+CH4+N2混合气在透氧膜反应器内重整反应,以及有无催化剂下重整反应和催化剂床层厚度重整反应实验,推测焦炉煤气重整反应模型:首先焦炉煤气中H2在催化剂活性金属镍颗粒上吸附解离,解离后的氢向高活性位迁移"(三相界面")并与膜表面侧晶格氧(或O2-)反应生成H2O.同时CH4也可能在活性镍颗粒上裂解生成CH3*和H*,反应生成的H2O与膜表面催化剂上裂解的碳反应生成H2和CO.未反应完的H2O在催化剂床层内与剩余CH4反应生成H2和CO.     

m-4-m型Gemini表面活性剂对铂电极上亚甲蓝吸附溶出伏安行为的影响

在0.050 mol·L-1磷酸盐缓冲溶液(PBS)中(pH=6.4), 亚甲蓝(MB)在铂电极上于-0.2 V产生一对不明显的伏安峰. 当向溶液中加入阳离子型Gemini表面活性剂Br-C16H33N+(CH3)2-C4H8-N+(CH3)2C16H33Br-, Br-C12H25N+(CH3)2-C4H8-N+(CH3)2C12H25Br-或Br-C8H17N+(CH3)2-C4H8-N+(CH3)2C8H17Br-后, 亚甲蓝的氧化峰显著增高, 还原峰降低, 氧化还原峰峰电位均正移, 这和表面活性剂与MB在电极表面的协同吸附有关. 联接基团相同的Gemini表面活性剂, 其影响程度随烷基链的增长而逐渐增强. 增大表面活性剂的浓度, MB的氧化峰先升高后缓慢降低. 如当Br-C16H33N+(CH3)2-C4H8-N+(CH3)2C16H33Br-的浓度为15 μmol·L-1 时, 5 μmol·L-1 MB的氧化峰峰电流达到最大值. 此外,溶液pH值和富集电位等对MB及表面活性剂的吸附亦有影响.     

Correlation of Solution and Gas Phase Complexation Assessed by Electrospray Ionization Mass Spectrometry: Application to One-, Two-, and Three-Ring Macrocycles

Electrospray ionization mass spectrometry (ESI-MS) was used to probe multiple cation complexation by C(12)H(25)(CH(2))(12)(CH(2))(12)C(12)H(25), 2, and <18N>CH(2)C(6)H(4)CH(2), 3. Complexation of two cations (2Na(+), 2 K(+), or Na(+) and K(+)) by 3 and three cations by 2 (3 Na(+), 3 K(+), and mixtures) as well as mixed proton-metallic cation complexes of both were observed. The K(+)/Na(+) cation-binding selectivity of 18-crown-6 was studied by ESI-MS of a methanol solution, and the selectivity profile was favorably compared with data obtained previously by ion-selective electrode techniques in the same solvent.     

Measuring and modeling the competitive adsorption of CO2, CH4, and N2 on a dry coal

Data on the adsorption behavior of CO 2, CH 4, and N 2 on coal are needed to develop enhanced coalbed methane (ECBM) recovery processes, a technology where the recovery of CH 4 is enhanced by injection of a gas stream consisting of either pure CO 2, pure N 2, or a mixture of both. The pure, binary, and ternary adsorption of these gases on a dry coal from the Sulcis Coal Province in Italy has been measured at pressures up to 180 bar and temperatures of 45 and 70 degrees C for the pure gases and of 45 degrees C for the mixtures. The experiments were performed in a system consisting of a magnetic suspension balance using a gravimetric-chromatographic technique. The excess adsorption isotherms are successfully described using a lattice density functional theory model based on the Ono-Kondo equations exploiting information about the structure of the coal, the adsorbed gases, and the interaction between them. The results clearly show preferential adsorption of CO 2 over CH 4 and N 2, which therefore indicate that ECBM may be a viable option for the permanent storage of CO 2.     

Hydrogen and methane sorption in dry and water-loaded multiwall carbon nanotubes

Both H2 and CH4 are clean energy sources. Adsorption was considered a measure to enhance their storage, and many efforts have been dedicated to creating novel materials including carbon nanotubes as efficient carriers for them. In order to understand the uptake mechanism and the viability of practical application, eight adsorption isotherms of H2 on a sample of multiwall carbon nanotubes were collected. The heat of adsorption was determined and an isotherm model was presented. Isotherms of CH4 on the same sample were also collected. While the adsorption on dry samples behaves similarly to that of H2, the sorption behavior of CH4 in the water-loaded sample is quite different and five times higher uptake capacity was observed in the wet sample due to the formation of methane hydrates. However, carbon nanotubes are unlikely to be used as an energy carrier due to its limited surface area and pore volume.     

In silico screening of metal-organic frameworks in separation applications

Porous materials such as metal-organic frameworks (MOFs) and zeolitic imidazolate frameworks (ZIFs) offer considerable potential for separating a variety of mixtures such as those relevant for CO(2) capture (CO(2)/H(2), CO(2)/CH(4), CO(2)/N(2)), CH(4)/H(2), alkanes/alkenes, and hydrocarbon isomers. There are basically two different separation technologies that can be employed: (1) a pressure swing adsorption (PSA) unit with a fixed bed of adsorbent particles, and (2) a membrane device, wherein the mixture is allowed to permeate through a micro-porous crystalline layer. In view of the vast number of MOFs, and ZIFs that have been synthesized there is a need for a systematic screening of potential candidates for any given separation task. Also of importance is to investigate how MOFs and ZIFs stack up against the more traditional zeolites such as NaX and NaY with regard to their separation characteristics. This perspective highlights the potency of molecular simulations in determining the choice of the best MOF or ZIF for a given separation task. A variety of metrics that quantify the separation performance, such as adsorption selectivity, working capacity, diffusion selectivity, and membrane permeability, are determined from a combination of Configurational-Bias Monte Carlo (CBMC) and Molecular Dynamics (MD) simulations. The practical utility of the suggested screening methodology is demonstrated by comparison with available experimental data.     

Plasma chemistry of NO in complex gas mixtures excited with a surfatron launcher

The plasma chemistry of NO has been investigated in gas mixtures with oxygen and/or hydrocarbon and Ar as carrier gas. Surface wave discharges operating at microwave frequencies have been used for this study. The different plasma reactions have been analyzed for a pressure range between 30 and 75 Torr. Differences in product concentration and/or reaction yields smaller than 10% were found as a function of this parameter. The following gas mixtures have been considered for investigation: Ar/NO, Ar/NO/O2, Ar/NO/CH4, Ar/CH4/O2, Ar/NO/CH4/O2. It is found that NO decomposes into N2 and O2, whereas other products such as CO, H2, and H2O are also formed when CH4 and O2 are present in the reaction mixture. Depending on the working conditions, other minority products such as HCN, CO2, and C2 or higher hydrocarbons have been also detected. The reaction of an Ar/NO plasma with deposits of solid carbon has also been studied. The experiments have provided useful information with respect to the possible removal of soot particles by this type of plasma. It has been shown that carbon deposits are progressively burned off by interaction with the plasma, and practically 100% decomposition of NO was found. Plasma intermediate species have been studied by optical emission spectroscopy (OES). Bands and/or peaks due to N2*, NO*, OH*, C2*, CN*, CH*, or H* were detected with different relative intensities depending on the gas mixture. From the analysis of both the reaction products and efficiency and the type of intermediate species detected by OES, different plasma reactions and processes are proposed to describe the plasma chemistry of NO in each particular mixture of gases. The results obtained provide interesting insights about the plasma removal of NO in real gas exhausts.     

Synthesis and characterization of six-coordinate "3 + 2" mixed-ligand oxorhenium complexes with the o-diphenylphosphinophenolato ligand and tridentate coligands of different N and S donor atom combinations

A series of octahedral six-coordinate oxorhenium(V) mixed ligand complexes containing the common [ReO(L)]2+ fragment (L = o-OC6H4P(C6H5)2] have been synthesized and characterized. Hence, it was shown that the [ReO(L)]2+ moiety can accommodate a variety of tridentate ligands containing a central amine group amenable to deprotonation and different combinations of lateral groups, such as ethylamine, substituted ethylamine, ethylthiol, and ethylthioether arms. In particular, by reaction of equimolar amounts of the pertinent HLn ligands with the [(n-C4H9)4N][ReOCl3(L)] precursor in refluxing acetonitrile/methanol or dichloromethane/methanol mixtures, the following series of [ReO(Ln)(L)]+/0 oxorhenium(V) complexes has been generated: ReO[[N(CH2CH2NH2)2][o-OC6H4P(C6H5)2]]Cl (1); ReO[[C2H5)2NCH2CH2NCH2CH2S][o-OC6H4P5)2]] (2); ReO[[(CH2)4NCH2CH2NCH2CH2S][o-OC6H4P(C6H4P(C6H5)2]] (3); and ReO[[C2H5SCH2CH2NCH2CH2S][o-OC6H4P(C6H5)2]] (4). The complexes are closed-shell 18-electron oxorhenium species, which adopt octahedral geometries both in solution and in the solid state, as established by conventional physicochemical techniques including multinuclear NMR and single-crystal X-ray diffraction analyses.     

Polymer-supported and free-standing metal-organic framework membrane

Thrive on a polymer: A polymer-supported method is developed and used to prepare well-intergrown and free-standing metal-organic framework (MOF) membranes. By using this method, a stainless steel net/PMMA-PMAA-supported HKUST-1 membrane was fabricated and applied in gas separation. Results indicated that such a membrane has a high separation factor to H(2) /N(2) , H(2) /CH(4) , H(2) /CO(2) gas mixtures.     

Preparation and gas separation properties of zeolite T membrane

Zeolite T membranes were synthesized on tubular porous mullite tubes by hydrothermal synthesis. The membranes selectively permeated carbon dioxide from CO2/CH4 and CO2/N2 mixtures with high separation performances, which were due to combined effects of molecular sieving and competitive adsorption.     

Experimental study and detailed modeling of toluene degradation in a low-pressure stoichiometric premixed CH4/O2/N2 flame

Temperature and mole fraction profiles have been measured in laminar stoichiometric premixed CH4/O2/N2 and CH4/1.5%C6H5CH3/O2/N2 flames at low pressure (0.0519 bar) by using thermocouple, molecular beam/mass spectrometry (MB/MS), and gas chromatography/mass spectrometry (GC/MS) techniques. The present study completes our previous work performed on the thermal degradation of benzene in CH4/O2/N2 operating at similar conditions. Mole fraction profiles of reactants, final products, and reactive and stable intermediate species have been analyzed. The main intermediate aromatic species analyzed in the methane-toluene flame were benzene, phenol, ethylbenzene, benzylalcohol, styrene, and benzaldehyde. These new experimental results have been modeled with our previous model including submechanisms for aromatics (benzene up to p-xylene) and aliphatic (C1 up to C7) oxidation. Good agreement has been observed for the main species analyzed. The main reaction paths governing the degradation of toluene in the methane flame were identified, and it occurs mainly via the formation of benzene (C6H5CH3 + H = C6H6 + CH3) and benzyl radical (C6H5CH3 + H = C6H5CH2 + H2). Due to the abundance of methyl radicals, it was observed that recombination of benzyl and methyl is responsible for main monosubstitute aromatic species analyzed in the methane-toluene flame. The oxidation of these substitute species led to cyclopentadienyl radical as observed in a methane-benzene flame.