Boosting C2H6/C2H4 separation in scalable metal-organic frameworks through pore engineering

The development of ethane (C₂H₆)-selective adsorbents for ethylene (C₂H₄) purification, although challenging, is of prime industrial importance. Pillared-layer metal-organic frameworks (MOFs) possess facilely tunable pore structure and functionality, which means they have excellent potential for high-performance C₂H₆/C₂H₄ separation applications. Herein, we report a family of isostructural pillared-layer MOFs with various metal centers M and co-ligands L, M₂(D-cam)₄L₂ (denoted M-cam-L; M = Cu, Co, Ni; L = pyz, apyz, dabco), with a variety of pore surface properties. All of the M-cam-L materials exhibit preferential adsorption for C₂H₆ over C₂H₄. In particular, Ni-cam-pyz exhibits the highest C₂H₆ capture capacity (68.75 cm³ g⁻¹ at 1 bar and 298 K), Cu-cam-dabco possesses the greatest C₂H₆/C₂H₄ adsorption selectivity (2.3), and the lowest isosteric heat of adsorption is demonstrated for Cu-cam-pyz (20.1 kJ mol⁻¹). Dynamic column breakthrough experiments also confirmed the excellent separation performance of M-cam-pyz and M-cam-dabco materials. The synthesis route of the M-cam-L materials is easily scaled-up under laboratory conditions, and hence this class of MOFs is promising for practical C₂H₄ purification.     

Study of the preparation of bulk tungsten carbide catalysts with C2H6/H2 and C2H4/H2 carburizing mixtures

The influence of the preparation procedure of tungsten carbide on the mechanism of carburization is discussed. This work is focused on the reduction and the carburization of tungsten trioxide by a mixture of hydrocarbon and H₂ to form WC. Temperature-programmed reaction spectra obtained with CH₄, C₂H₆ and C₂H₄ have been measured. In presence of the CH₄-H₂ mixture, H₂ is the reducing agent and the hydrocarbon is consumed for the carburization whereas C₂H₆ or C₂H₄ participates in the reduction of the tungsten oxide. The temperatures of reduction and carburization are lower by about 150 K using C₂H₆ or C₂H₄ instead of CH₄. Such a decrease of the temperature of reduction of tungsten oxide is needed to avoid the formation of poorly reducible compounds that can occur during the preparation of supported tungsten carbide. Furthermore, the surface area of the resulting carbide is 25 m²/g with C₂H₆ and C₂H₄ and 10 m²/g with CH₄. During the carburization, the deposit of excess carbon on the WC surface is larger with the C₂ hydrocarbons than with CH₄, but it protects the carbide and can be removed by hydrogen treatment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ethane‐selective carbon composites CPDA@A‐ACs with high uptake and its enhanced ethane/ethylene adsorption selectivity

Novel composites (CPDA@A‐ACs) of carbonized polydopamine (CPDA) and asphalt‐based activated carbons (A‐ACs) were successfully synthesized, and characterized for adsorption separation of ethane/ethylene. The resulting CPDA@A‐ACs exhibited high Brunauer–Emmett–Teller surface area of 1971 m²/g. The O and N contents on CPDA@A‐ACs are higher than those on A‐ACs due to the introduction of CPDA. Interestingly, CPDA@A‐ACs exhibited great preferential adsorption of ethane over ethylene. Its ethane capacity reached as high as 7.12 mmol/g at 100 kPa and 25°C, and its ethane/ethylene adsorption selectivity became higher compared to A‐ACs, reaching as high as 3.0～20.6 below 100 kPa, significantly superior to the reported ethane‐selective adsorbents. Simulation results revealed the mechanism of enhanced selectivity toward C₂H₆/C₂H₄, and suggested that the surface oxygen functionalities of the composites play predominant role in enhancing ethane/ethylene adsorption selectivity. Fixed‐bed experiments showed that C₂H₆/C₂H₄ mixtures can be well separated at room temperature, suggesting great potential for industrial C₂H₆/C₂H₄ separation. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3390–3399, 2018     

A stable metal–organic framework with well-matched pore cavity for efficient acetylene separation

Acetylene, an important petrochemical feedstock, is the starting chemical to produce many polymer products. Separating C₂H₂ from its by-product mixtures is still an energy-consuming process and remains challenging. Here, we present a metal–organic framework[Zn₂(bpy)(btec)], with a desirable pore geometry and stable framework, which demonstrated a high separation performance of C₂H₂ from simulated mixtures. With the desirable pore dimension and hydrogen bonding sites, Zn₂(bpy)(btec) shows by far the both highest C₂H₂/C₂H₄ and C₂H₂/CO₂ uptake ratios, very high adsorption selectivities and moderately C₂H₂ uptake of 93.5 cm³/cm³ under 298 K and 1 atm. Not only straightforwardly produced high purity of C₂H₄, but also recovered high purity of C₂H₂ (>98%) in the regeneration process (>92% recovery). More notably, Zn₂(bpy)(btec) can be straightforwardly synthesized at a large scale under environmentally friendly conditions, and its good water/chemical stability, thermostability, and cyclic stability highlight the promise of this molecular sieving material for industrial C₂H₂ separation.     

Separation of C6H6 and C6H12 from H2 using ionic liquid/PVDF composite membrane

Ionic liquid/polyvinylidene fluoride composite membrane was successfully prepared by impregnation method and used for the separation on organic chemical hydride process. The separation factors of C₆H₆/H₂ and C₆H₁₂/H₂ in the ternary mixture system were 7500 and 300, respectively. The ionic liquid membrane showed an excellent possibility as a technology of H₂ purification in the organic chemical hydride process by removing aromatic hydrocarbon and cycloalkane simultaneously from the ternary system. © 2015 American Institute of Chemical Engineers AIChE J, 62: 624–628, 2016     

Design and screening of ionic liquids for C2H2/C2H4 separation by COSMO‐RS and experiments

Ionic liquids (ILs) have been proposed as promising solvents for separating C₂H₂ and C₂H₄, but screening an industrially attractive IL with high capacity from numerous available ILs remains challenging. In this work, a rapid screening method based on COSMO‐RS was developed. We also present an efficient strategy to improve the C₂H₂ capacity in ILs together with adequate C₂H₂/C₂H₄ selectivity with the aid of COSMO‐RS. The essence of this strategy is to increase molecular free volume of ILs and simultaneously enhance hydrogen‐bond basicity of anions by introducing flexible and highly asymmetric structures, which is validated by a new class of tetraalkylphosphonium ILs featuring long‐chain carboxylate anions. At 298.1 K and 1 bar, the solubility of C₂H₂ in ILs reaches 0.476 mol/mol IL, very high for a physical absorption, with a selectivity of up to 21.4. The separation performance of tetraalkylphosphonium ILs to the mixture of C₂H₂/C₂H₄ was also evaluated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2016–2027, 2015     

Permeation of H2, N2, CH4, C2H6, and C3H8 through asymmetric polyetherimide hollow‐fiber membranes

Permeation properties of pure H₂, N₂, CH₄, C₂H₆, and C₃H₈ through asymmetric polyetherimide (PEI) hollow‐fiber membranes were studied as a function of pressure and temperature. The PEI asymmetric hollow‐fiber membrane was spun from a N‐methyl‐2‐pyrrolidone/ethanol solvent system via a dry‐wet phase‐inversion method, with water as the external coagulant and 50 wt % ethanol in water as the internal coagulant. The prepared asymmetric membrane exhibited sufficiently high selectivity (H₂/N₂ selectivity >50 at 25°C). H₂ permeation through the PEI hollow fiber was dominated by the solution‐diffusion mechanism in the nonporous part. For CH₄ and N₂, the transport mechanism for gas permeation was a combination of Knudsen flow and viscous flow in the porous part and solution diffusion in the nonporous part. In our analysis, operating pressure had little effect on the permeation of H₂, CH₄, and N₂. For C₂H₆ and C₃H₈, however, capillary condensation may have occurred at higher pressures, resulting in an increase in gas permeability. As far as the effect of operating temperature was concerned, H₂ permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N₂ and CH₄, whereas the permeability of C₂H₆ and C₃H₈ decreased with increasing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 698–702, 2002     

Facile construction of C3N4-TE@TiO2/UiO-66 with double Z-scheme structure as high performance photocatalyst for degradation of tetracycline

In the current research, a double Z-scheme photocatalyst C₃N₄-TE@TiO₂/UiO-66 (CNTU) is fabricated via a two-steps facile solvothermal method from Z-scheme C₃N₄-TE@TiO₂ (CNT). This double Z-scheme photocatalyst reveals greater performance for the removal of tetracycline (TC) than pristine C₃N₄-TE, TiO₂, UiO-66 (U66), and their binary compounds. The optimized composite 35C₃N₄-TE@TiO₂/35UiO-66 (35CNTU), exhibitions photocatalytic performance for antibiotic removal (TC) more than 5,4 and 2 times higher than that pure TiO₂, UiO-66, and C₃N₄-TE, respectively. The physical and chemical features of synthesized samples were described via FTIR, XRD, SEM-EDX, TEM, BET, UV–Vis DRS, and PL. The key parameters on photocatalytic performances of 35CNTU such as pH, the amount of catalyst, and the primary concentration of TC were clari?ed. The advancement of the photocatalytic process for 35CNTU is due to the increase in the surface area and structure of double Z-scheme in this compound, which growths the active sites of the reaction as well as better separation of the photo-induced electron and hole pairs. Furthermore, 35CNTU can be recycled with superior stability for 5 cycles. The photocatalytic removal proficiency of TC over 35CNTU under visible light achieves 96% in 40 min. The findings of this study could inspire various novel plans for fabricating practical double Z-scheme photocatalyst for great performance and extensive useful applications.     

Thermodynamic-kinetic synergistic separation of CH4/N2 on a robust aluminum-based metal-organic framework

A robust aluminum-based metal–organic framework (Al-MOF) MIL-120Al with 1D rhombic ultra-microporous was reported. The nonpolar porous walls composed of para-benzene rings with a comparable pore size to the kinetic diameter of methane allow it to exhibit a novel thermodynamic-kinetic synergistic separation of CH₄/N₂ mixtures. The CH₄ adsorption capacity was as high as 33.7 cm³/g (298 K, 1 bar), which is the highest uptake value among the Al-MOFs reported to date. The diffusion rates of CH₄ were faster than N₂ in this structure as confirmed by time-dependent kinetic adsorption profiles. Breakthrough experiments confirm that this MOF can completely separate the CH₄/N₂ mixture and the separation performance is not affected in the presence of H₂O. Theoretical calculations reveal that pore centers with more energetically-favorable binding sites for CH₄ than N₂. The results of pressure swing adsorption (PSA) simulations indicate that MIL-120Al is a potential candidate for selective capture coal-mine methane.     

Mechanochemically synthesized ZIF-8 nanoparticles blended into 6FDA-TrMPD membranes for C3H6/C3H8 separation

The mixed matrix membranes (MMMs) consisting zeolitic-imidazolate framework-8 (ZIF-8) nanoparticles in a polymer have been of considerable interest in separation applications. The fillers used are mostly synthesized using the solvothermal method. In this study, the ZIF-8 nanoparticles were synthesized using a solvent-less and salt-free mechanochemical method and were added to 6FDA-TrMPD polyimide to prepare MMMs. The single gas permeation of C₃H₆ and C₃H₈ through the MMMs was investigated. The C₃H₆ permeability and C₃H₆/C₃H₈ ideal selectivity of a 20 wt% mechano-synthesized ZIF-8/6FDA-TrMPD MMM were 70% and 32% higher than those of the neat polymer membrane at 0.1 MPa and 308 K, respectively. The C₃H₆/C₃H₈ separation performance of the mechano-synthesized ZIF-8 MMM was similar to that of the conventional solvothermal-synthesized ZIF-8 MMM. This separation performance was in good agreement with the Maxwell model. Temperature and pressure dependence analyses confirmed that the mechano-synthesized ZIF-8 nanoparticles acted as molecular sieves in the MMMs for the C₃H₆ and C₃H₈ permeation.     

Preparation of molecular sieving carbon from waste resin by chemical vapor deposition

Molecular sieving carbons (MSCs) were prepared from carbonized phenol-formaldehyde resin wastes by the chemical vapor deposition (CVD) of the pyrolyzed carbon from hydrocarbon species. The pore size of the MSCs could be controlled in the range 0.37-0.42 nm by changing the hydrocarbon species pyrolyzed, the pyrolyzing temperature, and the processing time. It is shown that some of the MSCs have an excellent selectivity for separating CO₂ and CH₄, and others for separating C₃H₈ and C₃H₆. As the mechanism for controlling the pore size during CVD processing, we elucidated that the adsorption of hydrocarbon molecules first takes place on the pore surface and then the adsorbed hydrocarbons pyrolyze into carbon. Therefore, the pore size of the MSC can be adjusted by controlling the amount hydrocarbon adsorbed on the phenol-formaldehyde resin char.     

Synergetic thermodynamic/kinetic separation of C3H8/CH3F on carbon adsorbents for ultrapure fluoromethane electronic gas

Atomic layer etching (ALE) using the environmentally friendly electronic gas fluoromethane (CH₃F) is guided for fabricating nanoscale electronic components. The adsorptive purification of CH₃F provide a viable direction to remove trace amounts of impurities to produce highly pure CH₃F (>99.9999%) for the ALE process. Herein, to remove trace propane (~100 ppm) in CH₃F, we report synergetic thermodynamic and kinetic separation of C₃H₈/CH₃F over glucose-derived carbon molecular sieve CMS-T, (T as pyrolysis temperature). With pore size slightly larger than the kinetic diameter of C₃H₈, CMS-600 allows both strong confined adsorption of C₃H₈ and a higher diffusion rate of C₃H₈ over CH₃F, resulting in a remarkable separation factor of 51.1. Breakthrough experiment demonstrates a high dynamic production capacity of 457 L kg⁻¹ of 7 N CH₃F (<100 ppb of C₃H₈) over CMS-600 with excellent cycling stability. Adsorption purification over carbon provides a feasible approach for industrial hyperpurification of electronic gas.     

Synthese und Reaktivität von tert-Butyl-(2-aryl-3-methyl-but-2-yl)-peroxiden

Synthesis and Reactivity of tert-Butyl-(2-aryl-3-methyl-but-2-yl) Peroxides tert-Butyl-(2-aryl-3-methyl-but-2-yl) peroxides (2a–d) were prepared from t-BuOOH and corresponding 2-aryl-methyl-butan-2-ols (1a–d) (Ar:p-MeO C₆H₄ (a) ; Ph (b) ; p-Cl C₆H₄ (c) ; m-CF₃ C₆H₄ (d) ) and characterized by NMR, MS and elemental analysis. Kinetic data for the thermolysis of 2a–d in cumene as the solvent were determined at 110–140 °C and the products analyzed. The rate constants satisfy the Hammett equation with σ giving a ρ-value of −0.73. Oxidation of 2a–d at 80 °C gives the corresponding acetophenones 4 , epoxides 6 and hydroperoxides 8 . The products of the oxidation of 2a–2d were analysed after reduction of the reaction mixtures with LiAlH₄. Relative reactivities of the tertiary C H bonds of peroxides 2 were determined by competitive oxidations. They amount to 0.115–0.275 (with respect to the tertiary C H bond of cumene)     

The effects of titania overlayers on C2H4/CO/H2 reactions over a Rh foil

The effects of submonolayer deposits of titania on the activity and selectivity of a Rh foil catalyst for C₂H₄/CO/H₂ reactions have been investigated. Reactions were carried out at 1 atm total pressure and at temperature of 488 K and 523 K. The addition of titania to the catalyst enhances the total rate of C₃-oxygenate formation. This rate enhancement is due entirely to an increase in the rate of 1-propanol formation, which reaches a maximum at a TiO _x . coverage of 0.2 ML. The rate of propanal formation, by contrast, is not enhanced. The rates of formation of methane, ethane, and C₃-hydrocarbons also exhibit rate maxima at a TiO _x . coverage of 0.2 ML. The rates of formation of C₄- and C₅-hydrocarbons, on the other hand, are suppressed by titania addition. The higher rate of 1-propanol production in the presence of titania is attributed to an interaction between Ti³⁺ ions at the edge of TiO _x . islands and the carbonyl bond of adsorbed C₃-oxygenated species. Such interactions are envisioned to facilitate hydrogenation of the carbonyl bond.     

Synthesis and nanostructure of [Mo(C6H4O2)3]·2(C4H8N2O) and the synthesis from 1,2-PDA to (C4H8N2O)

Continuing our work on the synthesis of MoO₂L₂ and MoO₃L_AL_B that show excellent anti-cancer activities in vitro, the MoL₃ have been synthesized by the solvothermal reaction of Na₂MoO₄ with catechols and 1,2-DPA in the mixed solvent of MeCN/MeOH. X-ray diffraction revealed that Mo in chiral octahedral geometry coordinate with three catechol ligands formed three five-membered rings, and the [Mo(C₆H₄O₂)₃] are linked by hydrogen bonds Mo(OC₆H₄)O…H–N(C₄H₈O)N–H…O(C₆H₄O)Mo through the by-product (C₄H₈N₂O) that are formed by one 1,2-DPA with one CO₂ on the catalysis of Mo-complex. Also, we have disassembled bulk crystal into nano-aggregates, and under TEM mono-lamella morphology of nanostructures was observed, which agrees well with the previous conclusion that the morphologies of the nano-aggregates are associated with the quantum motifs in their crystal lattices. [Mo(C₆H₄O₂)₃] have also been characterized by UV–vis spectra, cyclic voltammogram and thermogravimetric analysis.     

Thermodynamic adsorption data of CH4, C2H6, C2H4 as the OCM process hydrocarbons on SAPO-34 molecular sieve

Adsorption of CH₄, C₂H₆ and C₂H₄, the feed and main products of oxidative coupling process of methane (OCM) has been studied on silicoalumina-phosphate molecular sieve (SAPO-34) in mild conditions. The experiments were conducted in a batch system based on volumetric adsorption measurement technique for determination equilibrium adsorption capacity in the absolute pressure range of 100–1000 kPa and at the isothermal temperatures of 303, 313 and 323 K. Various isotherm equations were fitted on the adsorption equilibrium data and the model parameters were predicted as a function of temperature. Isosteric heats of adsorption were determined using Clausius–Clapeyron equation at different surface coverage. Maximum capacity of SAPO-34 was observed at 303 K and 880–900 kPa equilibrium pressure with 1.25, 2.02 and 4.67 mmol/g adsorbed amount for methane, ethane and ethylene adsorption, respectively. The adsorption selectivity of ethane and ethylene against methane were determined and the appropriate potential of SAPO-34 was observed for separation of OCM products from methane. The isotherm models and enthalpy of adsorption can be efficiently used for the simulation of the adsorption process constructed at the downstream of the OCM process for separation of ethane and ethylene from methane.     

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.     

Separation of propylene and propane with a microporous metal–organic framework via equilibrium-kinetic synergetic effect

Adsorption separation of olefin and paraffin can greatly lower the energy consumption associated with the currently utilized distillation technique but remains a great challenge. Herein, we report the efficient separation of propylene (C₃H₆) and propane (C₃H₈) in a phosphate anion-functionalized metal–organic framework (MOF) ZnAtzPO₄ by synergetic effect of equilibrium and kinetics. The material features periodically expanded and contracted apertures decorated with electronegative groups, offering eligible pore shape and pore chemistry to effectively trap C₃H₆ under moderate isosteric heat of adsorption (27.5 kJ mol⁻¹) while obstruct the diffusion of C₃H₈. It simultaneously combines excellent thermodynamic selectivity (uptake ratio of 1.71) and kinetic selectivity (~31) for C₃H₆/C₃H₈ separation, meanwhile can be easily regenerated. Breakthrough experiment for C₃H₆/C₃H₈ gas mixture was conducted and confirmed the outstanding separation capability of ZnAtzPO₄. The equilibrium and kinetics cooperative C₃H₆/C₃H₈ adsorption separation was for the first time found in anion-functionalized MOFs, and further confirmed by computational studies.