C3H8 separation from CH4 and H2 using a synthesized PDMS membrane: Experimental and neural network modeling

A polydimethylsiloxane (PDMS) membrane was synthesized and permeation behavior of ternary gas mixtures including C₃H₈, CH₄ and H₂ through it was studied as a function of operating parameters. Mixed gas permeability values were also compared with pure gas data as well as literature to validate experimental results. The aim was to predict separation factor (SF) of C₃H₈ as a function of feed temperature, pressure, flow rate and C₃H₈ concentration with the aid of artificial neural network (ANN) technique. Multilayer perceptron (MLP), which is the most common type of feedforward neural network (FFNN), was used for prediction. The Levenberg–Marquardt training method was initially employed to train the net. Then, optimum numbers of hidden layers and nodes in each layer were determined. The selected structure (4:4:5:1) was finally used to predict SF of C₃H₈ for different inputs in the domain of training data. The modeling results showed that there is an excellent agreement between the experimental data and the predicted values, with mean absolute errors of less than 1%. Both modeling and experimental results confirmed that increasing feed temperature, feed pressure and C₃H₈ concentration in feed debilitates separation performance; however, SF increases with increasing feed flow rate. As a result, ANN can be recommended for the modeling of mixed gas transport through dense membranes such as PDMS.     

A parametric study of CO2/N2 gas separation membrane processes for post-combustion capture

Capture of CO₂ from flue gases produced by the combustion of fossil fuels and biomass in air is referred to as post-combustion capture. Chemisorbent processes are considered to be the most feasible method and are already at an advanced stage of development, but gas separation membranes are attracting more and more attention as a possible alternative. This paper describes a detailed parametric study of mass and energy balances for a simulated single membrane process. Typical operating conditions (CO₂ concentration in the flue gas, pressure and temperature, etc.) together with the influence of the membrane quality (permeability, selectivity) and membrane area on membrane performance (CO₂ separation degree and CO₂ purity) are simulated over a wide range of parameters.     

Interfacially formed poly(N,N-dimethylaminoethyl methacrylate)/polysulfone composite membranes for CO2/N2 separation

Interfacially formed poly(N,N-dimethylaminoethyl methacrylate)/polysulfone (PDMAEMA/PSF) composite membranes were developed for CO₂/N₂ separation. A layer of PDMAEMA was deposited on a microporous PSF substrate by the solution coating technique, followed by crosslinking with p-xylylene dichloride (XDC) at the interface between the PDMAEMA solid layer and the crosslinking solution. The hydrophilicity and surface free energy of the membranes were analyzed by contact angle measurements with different probe liquids. The permselectivity of the membrane was shown to be affected by the PDMAEMA deposition time, interfacial crosslinking reaction time, and the PDMAEMA and XDC concentrations in the polymer coating solution and the crosslinking solution, respectively. The composite membrane showed a CO₂ permeance of 85 GPU and a CO₂/N₂ ideal separation factor of 50 at 23 °C and 0.41 MPa of CO₂ feed pressure.     

Molecular beam chemiluminescence. VIII: Pressure dependence and kinetics of Sm + (N2O,O3, F2, Cl2) and Yb + (O3, F2, Cl2) reaction. Dissociation energies of the diatomic reaction products

The CL spectra of the title reactions and their pressure dependences have been studied over the 5 × 10^?6 ? 5 × 10^?3 torr range in a beam-gas experiment. In the Sm + N₂O, O₃ and Yb + O₃ reactions simple bimolecular formation of the short lived (radiative lifetime τ_R < 3 × 10^?6 s) MO* emitters dominates the entire pressure range. In the other systems Sm + (F₂, Cl₂), Yb + (F₂, Cl₂) the CL spectra are strongly pressure dependent, indicating extensive energy transfer from long-lived intermediates. Reaction mechanisms are suggested. The quantum yields Φ, obtained by calibrating relative quantum yields with Dickson and Zare's absolute value for Sm + N₂O [Chem. Phys. 7 (1975) 367], range from Φ = 2.3% (for Sm + F₂, the most efficient reaction) down to Φ = 0.005% for Yb + Cl₂. The following lower limit estimates were obtained for the product dissociation energies from the short wavelength CL cutoffs: D⁰₀(SmF) ? 121.3 ± 2.4 kcal/mole, D⁰₀(SmCl) ? ? 100 ± 3 kcal/mole, D⁰₀(YbO) ? 94.2 ± 1.5 kcal/moie, D⁰₀(YbF) ? 123.7 ± 2.3 kcal/mole.     

单锰取代的Keggin型多酸吸附大气小分子X(X=H2O,N2,O2,NO,N2O,CO和CO2)的密度泛函理论计算研究

基于密度泛函理论（DFT） M06L方法对一系列单锰取代的Keggin型POM吸附大气小分子X（X=H₂O,N₂,O₂,NO,N₂O,CO和CO₂）配合物的分子几何,电子结构和成键性质进行了系统研究。由于POM的多阴离子性质,铯盐Cs₄[PW₁₁O₃₉Mn^ⅢH₂O]被用来考虑抗衡离子效应。DFT-M06L计算表明,当改变4个Cs抗衡阳离子的位置时,多酸阴离子的几何结构和电子结构参数几乎没有变化。当不考虑抗衡离子效应,在气相和溶液中单独优化多酸阴离子（[PW₁₁O₃₉Mn^ⅢH₂O]^4-）时,其主要几何和电子参数没有显著变化。比较不同自旋态的能量表明[PW₁₁O₃₉Mn^ⅡX]^4-（X=H₂O、N₂、N₂O、CO和CO₂）的最低能量态是高自旋五重态,[PW₁₁O₃₉Mn^ⅢO₂]^4-为三重态,而[PW₁₁O₃₉Mn^ⅢNO]^4-则为双重态。这些大气小分子在类卟啉POM配体上的吸附能量按照以下顺序增加：N₂ < N₂O < CO≈CO₂ < O₂ < H₂O < NO。POM-Mn-NO配合物具有较大的吸附能。Mulliken布居分析表明,NO配体与多酸中Mn^Ⅲ中心的相互作用主要来自于中间自旋态的Mn^Ⅲ中心与NO^·分子之间的反铁磁性耦合相互作用。     

A Suberato-Pillared Mn(II) Coordination Polymer: Hydrothermal Synthesis, Crystal Structure, and Magnetic Properties of Mn2(H2O)[O2C(CH2)6CO2]2

A suberato-pillared Mn(II) coordination polymer Mn₂(H₂O)(C₈H₁₂O₄)₂ was hydrothermally synthesized at 170°C for 3 days and characterized by single-crystal X-ray diffraction. Crystal data: monoclinic, C2/c, Z=4, a=26.544(5), b=7.617(2), c=9.187(2) Å, β=105.38(2)°, V=1791.0(7) ų, R₁=0.064 and wR₂=0.162. The compound shows a layered structure consisting of inorganic Mn oxygen polyhedral layers and organic regions. The inorganic Mn oxygen layers are generated from Mn₂O₁₀ bioctahedral units, which share corners with neighbors to form zigzag chains along the [001] direction and are, along the [010] direction, further connected by carboxylate groups of the suberato ligands and hydrogen bonds. The magnetic studies indicated that the compound becomes antiferromagnetic at low temperatures with T_Néel=12 K and follows Curie-Weiss law χ_m(T+22.429)= 4.48 cm³ mol⁻¹ K between 25 and 300 K. Upon heating in Ar stream, Mn₂(H₂O)(C₈H₁₂O₄)₂ decomposes in three steps.     

Sorption of H2, O2 and CO on bimetallic catalysts Pd?Ag/Al2O3 over a wide temperature range

Adsorption of hydrogen, oxygen and carbon monoxide on Pd–Ag/Al₂O₃ catalysts of different compositions within the temperature range from 293 to 773 K has been investigated. Adsorption measurements have been carried out by the pulse chromatographic method. The results obtained reflect interactions of the above adsorbates with the alloy surface, strongly enriched in silver atoms, as a result of surface segregation processes.

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, Pd–Ag/Al₂O₃ 293–773 K. . , , .

     

Novel measurements of refractive index, density and mid-infrared integrated band strengths for solid O2, N2O and NO2:N2O4 mixtures

We present novel measurements of the refractive index, density and integrated band strengths of mid-infrared features of solid N₂O at 16 K and of NO₂ and N₂O₄ in two frozen NO₂:N₂O₄ mixtures deposited at 16 and 60 K. The refractive index and density measurements were performed also for frozen O₂ deposited at 16 K. In this case, the integrated band strength values could not be determined since O₂ is a homonuclear molecule and therefore its fundamental mode is not infrared active. The solid samples were analysed by infrared spectroscopy in the 8000÷800 cm⁻¹ range. The sample thickness was measured by the interference curve obtained using a He–Ne laser operating at 543 nm. The refractive index at this laser wavelength was obtained, by numerical methods, from the measured amplitude of the interference curve. The density values were obtained using the Lorentz–Lorenz relation. Integrated band strength values were then obtained by a linear fit of the integrated band intensities plotted versus column density values. The astrophysical relevance of these novel measurements is briefly discussed.     

Vibrations and dissociation of molecules in strong electric fields: N2, NACl, H2O and SF6

The static deformations and vibrations of the title compounds with an applied static electric field have been studied by density functional theory calculations. It is found that for diatomic molecules, bond length and vibrational frequency as a function of the field can be fit very well all the way up to the dissociation limit by an analytical formula derived from a Morse potential model including an additional external field term. Polyatomic molecules show more complex behaviour with a single mode becoming soft at the dissociation limit. The frequency of the soft mode near the critical field is again described well by the analytical model. The vibrational analysis shows that in polyatomic molecules dissociation proceeds as a heterolytic fragmentation process, which can break the symmetry of the molecule in the applied field.     

Coordination of water to organolead(IV) nitrates: The examples of [PbPh2(NO3)2(H2O)2] and [PbMe3(NO3)(H2O)]

The compound [PbPh₂(NO₃)₂(H₂O)₂] was synthesized and characterized by spectroscopic methods (IR; ¹H, ¹³C and ²⁰⁷Pb NMR) and mass spectrometry. An X-ray diffraction study showed that the crystal is a supramolecular tridimensional network of hydrogen-bonded PbPh₂(NO₃)₂(H₂O)₂ units in which the Pb atom is octacoordinated and adopts a distorted hexagonal bipyramidal geometry, with four O (bidentate nitrate) and two O (water) atoms in equatorial positions and two C-phenyl atoms in axial positions. The crystal of [PbMe₃(NO₃)(H₂O)], obtained as a byproduct in the synthesis of PbMe₂(NO₃)₂, contains chains of hydrogen-bonded PbMe₃(NO₃)(H₂O) units in which the Pb atom is pentacoordinated with a slightly distorted trigonal bipyramidal environment. In this arrangement the three C-methyl atoms are equatorial and the O atoms from the monodentate nitrate and the water molecule are axial.     

Diamine incorporated compounds derived from polymeric nickel(II) fumarates and oxalates: Crystal structure, spectral and thermal properties of [Ni(en)3](O2CCHCHCO2)·3H2O and [Ni(en)3](O2CCO2)

Lewis-base mediated fragmentation of polymeric nickel(II) fumarate and oxalate are attempted using chelating σ-donor diamines like ethylenediamine (en) and 1,3-diaminopropane (dap) in various conditions which yielded [Ni(en)₃](fum)·3H₂O (1), [Ni(en)₃](ox) (2), [Ni(dap)₂(fum)] (3) and [Ni(dap)(ox)]·2H₂O (4). While 1 and 2 are molecular products each containing octahedral [Ni(en)₃]²⁺ moieties and the anionic dicarboxylate species, 3 and 4 are dap-incorporated polymeric products. The fumarate derivative 1 containing [Ni(en)₃]²⁺ moieties crystallizes in the monoclinic space group C2/c with a = 17.899(4) Å, b = 11.747(2) Å, c = 10.748(2) Å, β = 125.59(3)°, V = 1837.7(6) ų, Z = 4, while the oxalate analogue 2 is seen to be in the trigonal space group P−31c with a = 8.8770(13) Å, b = 8.8770(13) Å, c = 10.482(2) Å, γ = 120°, V = 715.3(2) ų, Z = 2. The octahedral [Ni(en)₃] units in both 1 and 2 are seen to be strongly H-bonded to the dicarboxylate moieties through the coordinated en units leading to a three-dimensional network. However, in 1 the water molecules also take part in the H-bonding and contribute to the overall 3D structure. In both 1 and 2 the crystal packing is done with the [Ni(en)₃]²⁺ units with absolute configuration Λ(δδδ) and its mirror conformer with Δ configuration in exactly equal numbers. Spectral (IR and UV–Visible) and magnetic measurements were carried out and some of the ligand-field parameters like D_q, B and β were evaluated for all the four compounds. These values suggest the presence of octahedrally coordinated nickel(II) in all the four complexes. Spectral data suggest that 3 has the two chelating dap moieties and the fumarate coordinated in η¹ form through both its carboxylate moieties while 4 has one chelating dap and the oxalate moiety coordinated in η⁴-bis-chelating form. Though both 1 and 2 are made of the same type of [Ni(en)₃]²⁺ units their thermograms give entirely different thermal features; 1 showing three clearly successive and step-wise dissociation of each en unit while 2 having a combined loss of two en units in the first thermal step. The relevant thermodynamic and kinetic parameters like E_a and ΔS also could be evaluated for various thermal steps for the compounds 1–4 using Coats–Redfern equation.     

Triterpene Glycosides from Cussonia paniculata. I. Isolation and Structure Determination of Glycosides A, B1, B2, C, D, G2, H1, and H2 from Leaves of Cussonia paniculata

The 3-O-β-D-glucopyranoside of β-sitosterol (1) and the known triterpene glycosides 3-O-α-L-arabinopyranosides of oleanolic (2a) and ursolic (2b) acids and hederagenin (3), 3-O-β-D-glucopyranosyl-(1→2)-α-L-arabinopyranosideofoleanolic acid (4), 3-O-α-L-arabinopyranosyl-28-O-α-L-rhamnopyranosyl-(1→4)-O-β-D-glucopyranosyl-(1→6)-O-β-D-glucopyranosides of oleanolic (5a) and ursolic (5b) acids and the newglycoside 28-O-α-L-rhamnopyranosyl-(1→4)-O-β-D-glucopyranosyl-(1→6)-O-β-D-glucopyranoside of 23-hydroxyursolic acid (6) were isolated from leaves of Cussonia paniculata (Araliaceae). Their structures were established using chemical methods and NMR spectroscopy.__________Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 160–163, March–April, 2005.     

Syntheses, crystal structures and optical properties of the first strontium selenium(IV) and tellurium(IV) oxychlorides: Sr3(SeO3)(Se2O5)Cl2 and Sr4(Te3O8)Cl4

Two new quaternary strontium selenium(IV) and tellurium(IV) oxychlorides, namely, Sr₃(SeO₃)(Se₂O₅)Cl₂ and Sr₄(Te₃O₈)Cl₄, have been prepared by solid-state reaction. Sr₃(SeO₃)(Se₂O₅)Cl₂ features a three-dimensional (3D) network structure constructed from strontium(II) interconnected by Cl⁻, SeO₃²⁻ as well as Se₂O₅²⁻ anions. The structure of Sr₄(Te₃O₈)Cl₄ features a 3D network in which the strontium tellurium oxide slabs are interconnected by bridging Cl⁻ anions. The diffuse reflectance spectrum measurements and results of the electronic band structure calculations indicate that both compounds are wide band-gap semiconductors.     

Oxidative versus reductive additions: A 13C NMR study of H2, HX (X = Cl,Br, OR I), and Cl2 additions to some iridium(I) complexes

The ¹³C NMR spectra of a number of iridium complexes and of their adducts with H₂, HX, and Cl₂ (X = Cl, Br, I) are used to estimate the redox character of these additions. Rather than having the oxidative character expected, H₂ addition seems to be reductive. HX and Cl₂ additions are oxidative. Some of these complexes appear to have Lewis acid, rather than the expected Lewis base character.     

Photo-injected electron current in cryogenic liquids: a comparison of liquid Ar, Ne, He, N2, and H2 near their boiling points

The steady-state photoelectron currents J_L arising from a cathode irradiated by a deuterium lamp in liquid Ar, Ne, He, H₂ and N₂ near their boiling points were measured for external field strengths of up to 10⁵ V/cm. The current attenuation in the liquids compared to that available from the same light intensity into vacuum J_v, J (J_L/J_v), is in reverse order to the dielectric strength of the liquids. This may suggest that the facility of electron injection from the cathode plays an important role in determining the dielectric strength.     

Synthesis, crystal structure and thermal behavior of two hydrated forms of lanthanide phthalates Ln2(O2+C6H4-CO2)3(H2O) (Ln=Ce, Nd) and Nd2(O2C-C6H4-CO2)3(H2O)3

New hydrated lanthanide phthalates have been hydrothermally prepared with cerium and neodymium in different reaction media involving water or mixed water-ethanol solvent. The monohydrated Ln₂(1,2-bdc)₃(H₂O) (Ln=Ce or Nd) and dihydrated Nd₂(1,2-bdc)₃(H₂O)₂ forms have been characterized by single-crystal analysis. Their structures consist of infinite inorganic chains of lanthanide-centered polyhedra linked to each other through the phthalate ligands in order to generate mixed organic-inorganic layered structure. The two hydrated structures differ by the number of terminal water species attached to the lanthanide cations, which induce symmetry change from a triclinic (Nd₂(1,2-bdc)₃(H₂O)₂) to an orthorhombic (Nd₂(1,2-bdc)₃(H₂O)₂) cell for neodymium whereas the cerium-based phase only exists in the monohydrated form, with two distinct symmetries (orthorhombic or triclinic). Structural comparisons with the other members of the lanthanide phthalate series with identical chemical formula are also discussed. Thermal X-ray diffraction experiment indicates that the transformation from dihydrate form into the monohydrated form does not occur during a heating process.     

[Ni(phen)2(3,5-DMBA)](m-MBA)2(H2O)2配合物的合成、晶体结构及电化学分析

The title complex of nickel (II) with 3,5-dimethylbenzoic acid, m-methylbenzoic acid and 1,10- phenanthroline was synthesized and characterized. Crystal data for this complex: triclinic, space group P1, a=1.198 5(2) nm, b=1.315 3(2) nm, c=1.531 8(3) nm, α=92.602(3)°, β=103.292(3)°, γ=114.849(3)°, V=2.104 7(6) nm³, D_c=1.361 g·cm^-3, Z=2, F(000)=902, final GooF=1.071, R₁=0.067 2, wR₂=0.155 5. The crystal structure shows that the nickel ion is coordinated with four nitrogen atoms of two 1,10-phenanthroline molecules and two oxygen atoms of one 3,5-dimethyl benzoic acid molecule, forming a distorted octahedral coordination geometry. The cyclic voltametric behavior of the complex was also investigated. CCDC: 286966.     

Chemistry of polyfunctional molecules-123. Reactions of BiBr3, SbI3 and AsI3 with LiN(PPh2)2; X-ray structure of a cyclophosphazene salt containing arsenic(I)

BiBr₃ or SbI₃ react at 20°C with LiN(PPh₂)₂ (1) to give elementary Bi or Sb and the P---P coupled phosphazene ligand Ph₂P---N=PPh₂---PPh₂=N---PPh₂ (2). The reaction of AsI₃ with 1 at room temperature formed yellow needles of the eight-membered heterocycle (3), whereas AsI₃ interacted at 80°C with 1 in the molar ratio of 1:3 to give elementary arsenic and 2. Treatment of AsI₃ and 1 at 20°C in a 1:2 stoichiometry yielded the seven-membered, cyclic arsenium(I) salt

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I·4THF (5·4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis.     

NO、CO和O2在铜离子分子筛上吸附的理论研究

以Cu-ZSM-5离子交换分子筛为例,利用Hartree-Fock和DFT理论,对小分子（NO,CO和O2）在CU+上吸附的空间立体模型进行了优化计算,结果表明,Cu+与小分子之间形成直线形吸附最为稳定,也存在其他成一定角度的吸附,但是不稳定,计算了吸附过程的势能曲线和温度对吸附的影响,在500-800K的反应温度下,温度越低吸附越稳定,NO在Cu表面能够形成Cu+(NO)(ON)双分子吸附,最后,比较了价态的变化对金属吸附性能的影响。