Many-body effects in some thermodynamic properties of supercritical CO2, CO2–Ar,and CO2–CH4 using HFD-like potentials from molecular dynamics simulation

Molecular dynamics simulation has been performed to obtain the pressure and self-diffusion coefficient of supercritical carbon dioxide using a two-body HFD (Hartree–Fock dispersion)-like potential determined via the inversion of reduced viscosity collision integrals at zero pressure. We have also obtained pressures of CO₂–Ar and CO₂–CH₄ fluid mixtures at constant temperatures at different densities using new accurate two-body HFD-like potential functions. To take many-body forces into account, the three-body potentials of Hauschild and Prausnitz [27], Wang and Sadus [30], [38], Oakley et al. [3], and Guzman et al. [33] have been used with the two-body potentials. The significance of this work is that the modified many-body potential of Hauschild and Prausnitz (extended as a function of density, temperature, and molar fraction) has been used with the two-body HFD-like potentials of CO₂, CO₂–Ar, and CO₂–CH₄ systems to improve the prediction of the pressure values without requiring an expensive three-body calculation. The results are in good agreement with experimental values.     

Molecular beam mass spectrometry and modelling of CH4–CO2 plasmas in relation with polycrystalline and nanocrystalline diamond deposition

CH₄–CO₂ microwave plasmas have been studied by optical emission spectroscopy, microwave interferometry, Langmuir probing and molecular beam mass spectrometry. The variations of plasma parameters and the concentration variations of both stable species and radicals in the plasma had been reported previously as a function of the power density; the influence of the total inlet flow rate is reported here. While the power density influences directly the plasma kinetics, the flow rate changes the residence time in the plasma and then the degree of conversion of the chemical system that is the extent to which the gas composition moves toward its steady-state composition. This is studied by modelling of plasma kinetics taking into account the coupled fluid dynamics of the gaseous species and the gas-phase chemistry including electron dissociation and surface recombination at the reactor wall. The experimental and modelling studies are used for correlating: – the relative concentration of important hydrocarbon radicals and etching radicals in the plasma and the gradients of all these species in front of the surface; – to the deposition domain, the structure (polycrystalline or nanocrystalline) and the quality of diamond films, which is the ratio of sp³ to (sp³ + sp²)-hybridized carbon in the film. All results evidence the plasma kinetic effect on the diamond deposition domain and the diamond deposition quality and structure, due to different degrees of conversion of the chemical system. The deposition of diamond coating from CH₄–CO₂ is shown to be a versatile process that permits deposition of a great variety of diamond films. However it requires particular attention because of the variation of the deposition conditions and then diamond quality and structure of the deposits depending on the extent of conversion of the inlet species to various intermediate and finally stable species formed in the plasma chemical system.     

Modified COSMO-UNIFAC model for ionic liquid–CO2 systems and molecular dynamic simulation

A new predictive molecular thermodynamic model (i.e., modified COSMO-SAC-UNIFAC) was first proposed and extended to predict the solubility of CO₂ in pure and mixed ionic liquids (ILs) at the temperatures down to 263.2 K. It is interesting to discover that with equimolar amounts, the solubility of CO₂ in such 1:1 IL pairs, that is, [A₁][B₁] + [A₂][B₂] and [A₁][B₂] + [A₂][B₁], was consistent at the same temperature and pressure in the case of exchanging their respective cations and anions. The molecular dynamic (MD) simulation for CO₂ + mixed ILs was performed to deeply analyze and explain this intriguing phenomenon. Not only the CO₂ gas drying experiment with the ILs ([C2mim][OAc], [C2mim][dca], and [C2mim][OAc] + [C2mim][dca]) as absorbents but also the corresponding process simulation and optimization were made to stress the effectiveness and applicability of the new thermodynamic model. Thus, this work ranges from molecular level to systematic scale.     

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.     

Carbon–Al2O3–Ag composite molecular sieve membranes for gas separation

Phenolic resins loaded with two different inorganic fillers (boehmite (γ-AlO(OH)) and silver (Ag)) were used to prepare composite carbon membranes. Polymer solutions containing γ-AlO(OH) and AgNO₃ were prepared and the effect of Ag on the transport properties of the composite membrane was evaluated. The polymer solutions were coated on α-Al₂O₃ tubes and carbonized in a single dipping-drying-pyrolysis step. After pyrolysis at 550 °C, γ-AlO(OH) yielded γ-Al₂O₃, and Ag agglomerated forming spherical nanoparticles of 30 nm in diameter. Ag loading enhanced the carbon membrane performance for several gas pairs of interest, especially for C₃H₆/C₃H₈ separation, where the C₃H₆/C₃H₈ permselectivity increased from a maximum of 15 to 38.     

Use of molecular simulation for evaluating adsorption equilibrium of inhalation anaesthetic agents on metal–organic frameworks

Metal–organic frameworks (MOFs) were studied as alternatives to zeolites and activated carbon for adsorptive removal of wasted inhalation anaesthetic agents (IAA). Monte Carlo simulation was used to predict equilibrium adsorption isotherms of IAA on selected MOFs. Rather than generic forcefields (FFs), the all-atom FF parameters published by Arcario were used for IAA modelling. Continuous fractional component Monte Carlo (CFCMC) proved crucial for speedy simulation of large molecules. We found that allocating 70% probability to the CFlambdaSwap move gave optimum fits between simulation and experiment. The simulations provided us with an insight into the adsorption mechanisms of IAA in these structures. Heats of adsorption, Brauner-Emmet-Teller (BET) surface area, and total pore volume were deduced to be the crucial parameters for low, medium, and high range of relative pressures in the isotherm. Therefore, the chromium atoms in MIL-101-Cr are better adsorbers of IAA than MIL-100-Al at lower pressures despite the similarities in terms of the type of linkers and topology. Our simulation results corroborated the earlier published studies on the self-association behaviour of sevoflurane molecules based on the experimental isotherms reported for MOF-177-Zn. Finally, the high polarity of IAA is thought to explain good low-pressure simulation/experiment data agreement for the MOFs possessing coordinatively unsaturated sites (CUS) despite using generic DREIDING FF for the framework atoms. Our in-house parsing code helped realize that the grand-canonical Monte-Carlo simulation speed is not the same for all pressure points but decreases for higher pressure points. This can be explained by increased density of the adsorbates making successful trial moves less probable.     

A highly thermal stable microporous lanthanide–organic framework for CO2 sorption and separation

A new lanthanide–organic framework formulated as TbL 1 (H₃L = 9-(4-carboxy-phenyl)-9H-carbazole-3,6-dicarboxylic acid), was synthesized under hydrothermal reaction condition. Single-crystal X-ray diffraction analysis shows that 1 crystallizes in a hexagonal P6₅ space group with three-dimensional network and microporous structure. The desolventized framework of 1 shows much higher uptake of CO₂ (43.7 cm³ g^− 1) than that of CH₄ (15.1 cm³ g^− 1) at 1 atm and 273 K, which makes it a potential candidate for CO₂/CH₄ separation.     

Sol–Gel-Generated La2NiO4 for CH4/CO2 Reforming

A stable La₂NiO₄ catalyst active in CH₄/CO₂ reforming has been prepared by a sol–gel method. The catalyst was characterized by techniques such as XRD, BET, TPR and TG/DTG. The results show that the conversions of CH₄ and CO₂ in CH₄/CO₂ reforming over this catalyst are significantly higher than those over a Ni/La₂O₃ catalyst prepared by wet impregnation and those over a La₂NiO₄/-Al₂O₃ catalyst. The TG/DTG outcome confirmed that the amount of carbon deposition observed in the former case was less than that observed in the latter two cases, a phenomenon attributable to the uniform dispersion of nanoscale Ni particles in the sol–gel-generated La₂NiO₄ catalyst.     

Adsorption separation of CO2, CH4 and N2 on β-zeolite with different SiO2/Al2O3 ratios

采用体积法在273 K和303 K温度下对CO2、CH4和N2在不同硅/铝比的β沸石上的吸附分离性能进行了研究。实验结果表明,Langmuir-Freundlich模型能够较好地拟合吸附实验数据;同一样品上,CO2的吸附量要大于CH4和N2的吸附量;随着硅铝比的减小CO2的吸附量增加,而硅/铝比对CH4和N2的吸附量的影响较小。通过结合Virial方程计算CO2、CH4和N2在不同硅/铝比β沸石上的亨利定律常数和吸附选择性,发现所研究样品对CO2/CH4和CO2/N2均具有很高的吸附选择性,随着样品硅/铝比的减小,CO2/CH4和CO2/N2的吸附选择性显著增加,说明较低硅/铝比β沸石有利于分离CO2。用Clausius-Clapeyron方程求得CO2、CH4和N2在不同硅/铝比的β沸石上的吸附热与吸附量无关,表明β沸石是一种表面势场均匀的吸附剂。     

Al–Fe PILC preparation,characterization and its potential adsorption capacity for aflatoxin B1

Montmorillonite (Mt) was used as the precursor material for synthesis of aluminum–iron–pillared montmorillonite (AlFePMt) and the adsorption of aflatoxin B1 (AFB1) by Mt and AlFePMt was investigated. Different forms of polycations were prepared and used to modify Mt, when the molar ratio of Al^3 + to Fe^3 + was 8.0, AlFePMt obtained the maximum adsorption capacity of AFB1 (660.0 μg/g) which was much higher than that of Mt (30.4 μg/g). The adsorbents were characterized by XRD, SEM and FTIR, and the effects of adsorbent amount, pH and interaction time on the adsorption of AFB1 onto Mt and AlFePMt were also studied. Adsorption isotherm parameters were obtained from Langmuir and Freundlich and the adsorption data fitted better to Langmuir. The obtained results show that the great difference of adsorption capacity between Mt and AlFePMt mainly lies in their microstructure and chemical composition, and it suggests that AlFePMt is suitable to be used as a potential adsorbent to remove AFB1 from the contaminated products.     

Improving CH4 uptake and CH4/N2 separation in pillar-layered metal–organic frameworks using a regulating strategy of interlayer channels

A pore engineering strategy involving the regulation of pillars in a series of pillar-layered metal–organic frameworks was presented to promote pore size adjustment and pore environment optimization for efficient separation of CH₄ from coal-mine methane. Compared with the original Ni(BTC)(BPY) and Ni(BTC)(TED), the suitable pore size and rich supply of carboxylate oxygens in the newly constructed Ni(BTC)(PIZ) resulted in the strongest recognition of CH₄, leading to both high CH₄ uptake (1.62 mmol/g) and CH₄/N₂ (50/50) selectivity (7.32) at 298 K and 1 bar. Its optimal balance performance between uptake and selectivity was better than most reported adsorbents, which further led to the most efficient separation of CH₄ from CH₄/N₂ mixtures. The stability of the structure and performance was verified by repeated cycle tests. Overall, it is believed the structure constructed based on the regulation strategy of the interlayer channel would enable the application of promising metal–organic frameworks in industrial gas separation processes.     

Mechanistic studies of CO2/CH4 reforming over Ni–La2O2/5A

The mechanism of CO₂/CH₄ reforming over Ni–La₂O₃/5A has been studied. The results of the CO₂‐pulsing experiments indicated that the amount of CO₂ converted was roughly proportional to the amount of H present on the catalyst, implying that CO₂ activation could be H‐assisted. Pulsing CH₄ onto a H₂‐reduced sample and a similar sample pretreated with CO₂, we found that CH₄ conversion was higher in the latter case. Hence, the idea of oxygen‐assisted CH₄ dissociation is plausible. The fact that the amount of CO produced in 10 pulses of CO₂/CH₄ was larger than that produced in 5 pulses of CO₂ followed by 5 pulses of CH₄, indicated that CO₂ and CH₄ could activate each other synergistically. In the chemical trapping experiments, following the introduction of CD₃I onto a Ni–La₂O₃/5A sample pretreated with CH₄/CO₂, we observed CD₃COOH, CD₃CHO, and CD₃OCD₃. In the in situ DRIFT experiments, IR bands attributable to formate and formyl were observed under working conditions. These results indicate that formate and formyl are intermediates for syngas generation in CO₂/CH₄ reforming, and active O is generated in the breaking of a C–O bond. Based on these results, we suggest that during CO₂/CH₄ reforming, CO₂ activation is H‐promoted and surface O species generated in CO₂ dissociation reacts with CH_x to give CO. A reaction scheme has been proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Numerical simulation and experimental study of gas cyclone–liquid jet separator for fine particle separation

To address the shortcomings of existing particulate matter trapping technology, especially the low separation efficiency of fine particles, herein, a novel gas cyclone–liquid jet separator was developed to research fine particle trapping. First, numerical simulation methods were used to investigate the flow field characteristics and dust removal efficiency of the separator under different working conditions,and to determined suitable experimental conditions for subsequent dust removal experiment...     

A combined coagulation–ultrafiltration method for enhanced separation of proteins and polyphenols

This work aimed to separate proteins and polyphenols from rapeseed stem extracts. The results showed that coagulation with 40% w/w ethanol and ultra-filtration with 10 kDa membrane were two efficient methods for polyphenols purification. The purity of polyphenols increased from 80.3% to 97.0% after separation. The combination of ethanol coagulation with ultrafiltration permitted decreased the ethanol consumption from 40% to 10% w/w while maintaining high polyphenols purity. Significant protein loss at room temperature was observed during the stability test, which emphasizes the importance of elaborating a fast and effective separation method for rapeseed stem extracts.     

A novel Ni–Mg–Al-LDHs/γ-Al2O3 Catalyst Prepared by in-situ synthesis method for CO2 reforming of CH4

A novel Ni–Mg–Al catalyst derived from layered double hydroxides (LDHs) which was prepared on γ-Al₂O₃ by in-situ synthesis method. The catalyst was evaluated by CO₂ reforming of CH₄ and a better catalytic performance was obtained compared with a reference catalyst of Ni/MgO/γ-Al₂O₃ prepared by impregnation. The novel catalyst was also characterized by XRD, N₂-adsorption-stripping, TEM, TG and AAS (atomic absorption spectrum). The results showed that the excellent performance of the catalyst benefited from its larger specific surface area and smaller active-crystal grain which is due to the molecular-order dispersion of active components over the LDHs precursor.     

Preparation and CO2 adsorption of amine modified Mg–Al LDH via exfoliation route

In response to the recent focus on reducing carbon dioxide emission, the preparation and characterization of organically functionalized materials for use in carbon capture have received considerable attention. In this paper the synthesis of amine modified layered double hydroxides (LDHs) via an exfoliation and grafting synthetic route is reported. The materials were characterized by elemental analysis (EA), powder x-ray diffraction (PXRD), diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) and thermogravimetric analysis (TGA). Adsorption of carbon dioxide on modified layered double hydroxides was investigated by TGA at 25–80 °C. 3-[2-(2-Aminoethylamino) ethylamino]propyl-trimethoxysilane modified MgAl LDH showed a maximum CO₂ adsorption capacity of 1.76 mmol g^?1 at 80 °C. The influence of primary and secondary amines on carbon dioxide adsorption is discussed. The carbon dioxide adsorption isotherms presented were closely fitted to the Avrami kinetic model.     

A new yttrium-based metal–organic framework for molecular sieving of propane from propylene with high propylene capacity

Developing energy-efficient alternatives for propylene (C₃H₆) and propane (C₃H₈) separation is of great significance and challenge in the petrochemical industry. Herein, we report the rational design of a new yttrium-based ultramicroporous metal–organic framework (MOF) comprised of 12-connected hexanuclear [Y₆(OH)₈(COO)₁₂]²⁻ cluster and 5-(3,5-dicarboxybenzoylamino)isophthalic acid (H₄dbai) with ftw topology. It possesses a suitable pore window size and a relatively large pore volume for molecular sieving separation of C₃H₈ from C₃H₆ with a high C₃H₆ capacity. At 298 K and 100 kPa, the adsorption capacity of C₃H₆ was 2.57 mmol/g, which is the highest among the reported C₃H₆/C₃H₈ molecular sieving MOF adsorbents. The molecular simulation revealed that the steric hindrance effect together with the electrostatic interaction of the oxygen sites in the window resulted in the molecular sieving separation of C₃H₆/C₃H₈. The breakthrough experiments confirmed its excellent separation performance under dynamic conditions to produce high purity (97.1%) of C₃H₆ with a working adsorption capacity of 1.75 mmol/g.     

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.