Isobaric vapor–liquid equilibria for mixtures of tetrahydrofuran, 2-propanol, and 2,2,4-trimethylpentane at 101.3 kPa

Vapor–liquid equilibrium (VLE) at 101.3 kPa have been determined for a ternary system (tetrahydofuran + 2-propanol + 2,2,4-trimethylpentane) and its constituent binary systems (tetrahydrofuran + 2-propanol, tetrahydrofuran + 2,2,4-trimethylpentane, and 2-propanol + 2,2,4-trimethylpentane). The activity coefficients of liquid mixtures were calculated from the modified Raoult's law. Thermodynamic consistency tests were performed for all VLE data. The VLE data of the binary mixtures and ternary mixtures were correlated using the Margules, Wilson, NRTL, and UNIQUAC activity-coefficient models. The models with their best-fitted interaction parameters of the binary systems were used to predict the ternary vapor–liquid equilibrium. All VLE data are also used to calculate the reduced excess molar Gibbs free energy g^E/RT and the deviations in the boiling point ΔT. The calculated quantities of g^E/RT and ΔT were fitted to variable-degree polynomials in terms of liquid composition.     

Dry grinding kinetics of binary mixtures of ceramic raw materials by Bond milling

The kinetics of batch dry grinding of binary mixtures of ceramic raw materials, namely quartz–kaolin, quartz–potassium feldspar and kaolin–potassium feldspar, from the feed sizes of −3.350 + 2.360, −2.000 + 1.400, −0.850 + 0.600, −0.500 + 0.355 and −0.300 + 0.212 mm have been determined using a Bond mill with a mixture of ball sizes of 38.10, 31.75, 25.40, 19.05 and 12.70 mm diameter and total mass of 22.648 kg. The Bond mill used was a size of 30.5 cm diameter, 30.5 cm length, with a total volume of 22,272 cm³. The fractional ball filling was 22% of mill volume and the mill speed was 70 rpm. The breakage parameters were obtained for those mineral mixtures to predict the product size distributions. As the feed sized given above, which were ground in the mill, increase, the specific rate of breakage (S_i) values also increase, which means faster breakage with higher S_i value occurs in the order of quartz–kaolin, quartz–potassium feldspar and kaolin–potassium feldspar mixtures when comparing the characteristic values (slope of S_i versus size relationship with higher value). The cumulative breakage distribution function (B_i,j) values obtained for these mineral mixtures were slightly different in terms of the fineness factor, γ. This means that quartz–potassium feldspar mixture produced less fines with higher γ value, while kaolin–potassium feldspar gave more fines with lower γ value. The simulations of the product size distribution for these mixing were very close to the experimental data. Finally, slowing down effect, treated with false time concept, started earlier than the expected for these binary mixtures. There were some correlations found between the simulated time (θ) and experimental time (t).     

Liquid-phase methanol synthesis in apolar (squalane) and polar (tetraethylene glycol dimethylether) solvents

The kinetics of the three-phase methanol synthesis over a commercial Cu–Zn–Al₂O₃ catalyst were studied in an apolar solvent, squalane and a polar solvent, tetraethylene glycol dimethylether (TEGDME). Experimental conditions were varied as follows: P=3.0–5.3 MPa, T=488–533 K and Φ_vG/w=7.5×10⁻³–8×10⁻³ Nm³ s⁻¹kg⁻¹_cat. The nature of the slurry–liquid influences the activation energy and the kinetic rate constant by interaction between adsorbed species and solvent and by competitive adsorption of the solvent on the catalyst surface. The rate of reaction to methanol observed in TEGDME appeared to be about 10 times lower than in squalane. TEGDME reduces the reaction rate, which is a disadvantage for its use as a solvent.     

Liquid-phase hydrogenation of diethylbenzenes

Hydrogenation of diethylbenzenes in the liquid phase was studied at 358–418 K and 2–6 MPa over 16.7% Ni/Al₂O₃. The reactivity of diethylbenzene isomers was dependent on the mutual position of the substituents and decreased in the following order: 1,3- > 1,4- > 1,2-. The apparent activation energies were ca. 60 kJ/mol. The cis-to-trans ratio of the corresponding saturated products exhibited only a weak dependence on temperature and hydrogen pressure.     

Drag on ensembles of fluid spheres translating in a power-law liquid at moderate Reynolds numbers

This work elucidates the role of power-law rheology on the sedimentation velocity of an ensemble of mono-size spherical Newtonian droplets (free from surfactants) translating in a power-law continuous phase numerically by solving the momentum equations of both phases. A simple sphere-in-sphere cell model has been used to account for inter-drop interactions. In particular, in this study, the effects of the Reynolds number (Re_o), the internal to external fluid characteristic viscosity ratio (k), the volume fraction of the dispersed phase (Φ) and the power-law index of the continuous phase (n_o) on the external flow field, pressure drag (C_dp), friction drag (C_df) and total drag (C_d) coefficients have been analyzed over wide ranges of parameters as follows: 1 ≤ Re_o ≤ 200, 0.1 ≤ k ≤ 50, 0.2 ≤ Φ ≤ 0.6 and 0.6 ≤ n_o ≤ 1.6. Based on the extensive numerical results obtained in this work, a simple predictive correlation has been proposed for the total drag coefficient, which can be used to predict the rate of sedimentation of ensembles of Newtonian fluid spheres in power-law liquids in a new application.     

Isomerization of n-hexane over mono- and bimetallic Pd–Pt catalysts supported on ZrO2–Al2O3–WOx prepared by sol–gel

The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO₂ (70, 85 wt.%)–Al₂O₃ (15, 0 wt.%)–WO_x (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N₂ physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WO_x and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO₃ bulk phase. The catalysts increased their S_BET for about 15% promoted by Al₂O₃ addition. Various oxidation states of WO_x species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WO_x species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W⁶⁺ and reduced-state WO_x species (either W⁴⁺ or W⁰). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers.     

Phase transition phenomena of the adsorbed 1-dodecanol monolayer at the air–water interface

Phase transition phenomenon of the 1-dodecanol monolayer at the air/water interface was studied by the dynamic γ(t) curves and the adsorption isotherm obtained by ellipsometry at 20 °C. The surface-concentration adsorption isotherm clearly showed three abrupt increases at bulk concentration C of 1.3 × 10⁻⁹, 2 × 10⁻⁹ and 3.7 × 10⁻⁹ mol/mL, respectively. The 1st and the 3rd transitions observed herein, that were typical 2D first-order transitions, were consistent with the gas to liquid expanded (G–LE) and the liquid expanded to liquid condensed (LE–LC) phase transitions observed in a previous tensiometry study. The 2nd transition that occurred at C = 2 × 10⁻⁹ mol/mL was not identified from any previous dynamic surface-tension profiles. Judging from the substantial increase in the film thickness of the transition, it was believed that the orientation change of the adsorbed molecule was involved in the LE phase. A LE_h and a LE_v phase, that denoted the “lie-down” and “stand-up” types of adsorption, respectively, was used to describe this transition and a cusp, instead of a constant surface-tension region, was observed in the dynamic γ(t) curves for this transition. This suggested that, since the surface tension varied during the transition process, the newly identified LE_h and LE_v transition might not be the typical first-order type of phase transition.     

Producing a high-quality synthetic steamcracker feedstock from different aromatic model components of pyrolysis gasoline on bifunctional zeolite catalysts

Aromatics with 6–9 carbon atoms, i.e., model components of pyrolysis gasoline, are hydroconverted on bifunctional Pd/H-ZSM-5 zeolites into a high-quality synthetic steamcracker feedstock (consisting mainly of ethane, propane and n-butane). The yield of these desired n-alkanes with two or more carbon atoms depends strongly on the nature of the aromatic feed: at 400 °C and 6 MPa in an excess of hydrogen, a yield of 72.8% is observed with toluene, but yields higher than 90% can be achieved with benzene or ethylbenzene as feed. These pronounced differences are rationalized in terms of varying types of classical β-scission and different contributions of non-classical Haag–Dessau cracking.     

Synthesis, characterization and catalytic properties of SAPO-34 synthesized using diethylamine as a template

SAPO-34 molecular sieve was successfully synthesized using diethylamine (DEA) as a template. The influence of template concentration and silica concentration on the synthesis were investigated. Pure SAPO-34 could be obtained when n(DEA)/n(Al₂O₃)  1.5 and n(SiO₂)/n(Al₂O₃) > 0.1 in the synthesis gel. Further increase of DEA concentration in the starting gel [n(DEA)/n(Al₂O₃) > 3] has a negative effect on both crystallinity and crystal yield. The products were characterized by XRD, XRF, SEM, NMR, FT-IR, TG-DTA and nitrogen adsorption techniques. It was found that SAPO-34 synthesized with DEA as a template has the characteristic of high silicon incorporation and exhibits good thermal and hydrothermal stability. The catalytic performance of SAPO-34 was tested by methanol-to-olefin (MTO) reaction and high olefins (C₂H₄ + C₃H₆) selectivity was obtained.     

2,2-Dimethylbutane adsorption and diffusion in MFI zeolite

Adsorption rates of 2,2-dimethylbutane (DMB) from the liquid phase into MFI zeolite crystals were measured by a volumetric/gravimetric method. Desorption rates in the presence of liquid n-hexane were measured by a non-adsorbing solvent (isooctane) method. Dimethylbutane desorbed, and was replaced by n-hexane, approximately three orders of magnitude faster than it adsorbed. Adsorption was slow and reached only 40% of saturation loading in 6-μm crystals after 45 days at 295 K, but this DMB loading desorbed into n-hexane in less than 1 h. Desorption may be faster due to slight expansion of the MFI unit cell by n-hexane adsorption. Although DMB diffused slower than n-hexane in MFI crystals, its transient time through a silicalite-1 membrane was an order of magnitude shorter than the n-hexane time at 313 K because DMB diffused through defects, whereas n-hexane diffused mainly through zeolite pores. The n-hexane transient time was longer because n-hexane: (1) expanded the MFI crystal size slightly and shrank non-zeolitic pores, and (2) adsorbed in the zeolite as it moved through the remaining non-zeolitic pores. A silicalite-1 membrane saturated with DMB at 423 K was sealed so effectively, and DMB desorbed slowly enough, that the helium permeation flux at 313 K was below the detection limit.     

Optical amine sensor based on metallophthalocyanine

The spun film of zinc(II) 1,4,8,11,15,18,22,25-octabutoxy-phthalocyanine was investigated as optical sensor for amine vapors. The enhancement of the Q band absorbance at 750 nm was attributed to the coordination of amine to the central zinc ion. Effects of the amine structure on the sensing properties were investigated to elucidate the sensing mechanism. Sensitivity and response speed of the sensor are influenced by the gas phase basicity and the steric hindrance effect of the amine. Among the six-carbon amines studied, n-hexylamine shows the highest sensitivity and the fastest response, followed by dipropylamine, and then the tertiary triethylamine. For primary amines, the sensitivity and the response speed increase as length of the alkyl chain increases. The response time for 1000 ppm n-hexylamine is 11 s, and that for methylamine is 440 s. The response signal ΔA₇₅₀ is found to be proportional to the amine concentration for n-butylamine in the 5–40 ppm range, with the sensitivity S = 0.0009/ppm.     

Fabrication and thermoelectric properties of heavily rare-earth metal-doped SrO(SrTiO3)n (n = 1, 2) ceramics

To clarify the effect of substitutional electron doping on the thermoelectric figure of merit (ZT = S²σTκ⁻¹) of Ruddlesden–Popper phase SrO(SrTiO₃)_n (or Sr_n+1Ti_nO_3n+1), measurements were conducted for several thermoelectric parameters, e.g. electrical conductivity (σ), Seebeck coefficient (S) and thermal conductivity (κ), of (Sr_1−xRE_x)_n+1Ti_nO_3n+1 (n = 1 or 2, RE (rare earth): La or Nd, x = 0.05 and 0.1) dense ceramics prepared by a conventional solid-state reaction and hot-pressing technique. Crystal structures of the resultant ceramics were represented as (Sr_1−xRE_x)_n+1 Ti_nO_3n+1 evaluated by powder X-ray diffraction followed by the Rietveld analysis. All the ceramics exhibited electrical conductivity and the σ values simply depended on the dopant concentration, indicating that both La³⁺ and Nd³⁺ ions act as electron donors. The |S| values increased with temperature due to decrease in the chemical potential. Significant reduction of the κ values was observed as compared to cubic-perovskite SrTiO₃. The ZT value increased with temperature and reached 0.15 at 1000 K for (Sr_0.95La_0.05)₃Ti₂O₇.     

Support effects on structure and activity of molybdenum oxide catalysts for the oxidative dehydrogenation of ethane

The structural and catalytic properties of MoO₃ catalysts supported on ZrO₂, Al₂O₃, TiO₂ and SiO₂ with Mo surface densities, n_s, in the range of 0.5–18.5 Mo/nm² were studied for the oxidative dehydrogenation (ODH) of ethane by in situ Raman spectroscopy and catalytic activity measurements at temperatures of 400–540 °C. The molecular structure of the dispersed surface species evolves from isolated monomolybdates (MoO₄ and MoO₅, depending on the support) at low loadings to associated MoO_x units in polymolybdate chains at high loadings and ultimately to bulk crystalline phases for loadings exceeding the monolayer coverage of the supports used. The nature of the oxide support material and of the Mo–O–support bond has a significant influence on the catalytic behaviour of the molybdena catalysts with monolayer coverage. The dependence of reactivity on the support follows the order ZrO₂ > Al₂O₃ > TiO₂ > SiO₂. The oxygen site involved in the anchoring Mo–O–support is of relevance for the catalytic activity.     

Vanadomolybdophosphoric acid/fluorapatite solid-phase system for aerobic oxidative dehydrogenation

We developed a solid-phase-oxidation-system using FAp disperse phase and vanadomolybdophosphoric acid (H_3+nPV_nMo_12−nO₄₀: PVn) catalysts with molecular oxygen as a new green reaction system. The PV4/FAp system was an efficient and recyclable solid–catalyst system for solvent-free oxidative dehydrogenation of -terpinene to p-cymene under 1 atm of molecular oxygen at 50 °C. The catalytic activity in the solid-phase system was comparable to that in the homogeneous liquid-phase system with acetonitrile. Even if under air conditions, PV4/FAp system was able to promote the catalytic dehydrogenation at room temperature sufficiently.     

Effect of ammonium polyacrylate on rheology of anatase TiO2 nanoparticles dispersed in silicon alkoxide sols

Ammonium polyacrylate (NH₄PA) was introduced into powdered mixtures consisting of anatase-structured TiO₂ nanoparticles and silicon alkoxide precursors at the sol level, and the rheological behavior of the mixtures was examined under various solid loadings (φ=0.05–0.13 in volumetric ratios), shear rates (  s⁻¹) and NH₄PA concentrations. The alkoxide precursors were mixtures of tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄), ethyl alcohol (C₂H₅OH), H₂O and HCl in a constant [H₂O]/[TEOS] ratio of 11. The nanoparticle–sol mixtures generally exhibited a pseudoplastic flow behavior over the shear-rate regime examined. The NH₄PA appeared to serve as an effective surfactant which facilitates the suspension flow by reducing the flow resistance at low NH₄PA concentrations. At φ=0.10, a viscosity reduction ca. 85% was found at  s⁻¹ when the NH₄PA concentration was held at 2.5 wt.% of the solids. As the NH₄PA exceeded a critical level, e.g., [NH₄PA]≥3.0 wt.%, the NH₄PA acted as a catalyst which quickly turned the TiO₂–silica sol mixtures (φ=0.10) into a gelled structure, resulted in a pronounced increase of mixture viscosity. The maximum solids concentration (φ_m) of the mixtures was experimentally determined from a derivative of relative viscosity, i.e., (1−η_r^−1/2)–φ dependence. The estimated φ_m increased from 0.127 to 0.165 when NH₄PA of 0.5 wt.% was introduced into the TiO₂–silica sol mixtures.     

H4SiW12O40-catalyzed oxidation of nitrobenzene in supercritical water: kinetic and mechanistic aspects

The catalytic effect of a heteropolyacid, H₄SiW₁₂O_40, on nitrobenzene (20 and 30 μM) oxidation in supercritical water was investigated. A capillary flow-through reactor was operated at varying temperatures (T=400–500 °C; P=30.7 MPa) and H₄SiW₁₂O₄₀ concentrations (3.5–34.8 μM) in an attempt to establish global power-law rate expressions for homogenous H₄SiW₁₂O₄₀-catalyzed and uncatalyzed supercritical water oxidation. Oxidation pathways and reaction mechanisms were further examined via primary oxidation product identification and the addition of various hydroxyl radical scavengers (2-propanol, acetone, acetone-d₆, bromide and iodide) to the reaction medium. Under our experimental conditions, nitrobenzene degradation rates were significantly enhanced in the presence of H₄SiW₁₂O₄₀. The major differences in temperature dependence observed between catalyzed and uncatalyzed nitrobenzene oxidation kinetics strongly suggest that the reaction path of H₄SiW₁₂O₄₀-catalyzed supercritical water oxidation (average activation E_a=218 kJ/mol; k=0.015–0.806 s⁻¹ energy for T=440–500 °C; E_a=134 kJ/mol for the temperature range T=470–490 °C) apparently differs from that of uncatalyzed supercritical water oxidation (E_a=212 kJ/mol; k=0.37–6.6 μM s⁻¹). Similar primary oxidation products (i.e. phenol and 2-, 3-, and 4-nitrophenol) were identified for both treatment systems. H₄SiW₁₂O₄₀-catalyzed homogenous nitrobenzene oxidation kinetics was not sensitive to the presence of OH√ scavengers.     

Halogen-free acylation of toluene over FeSBA-1 molecular sieves

Three-dimensional cage type iron substituted mesoporous silica with different iron contents (FeSBA-1) was synthesized in a highly acidic media using cetyltriethylammonium bromide and tetraethylorthosilicate as a template and a silica source, respectively. Acylation of toluene with acetic anhydride (AA) was carried out over FeSBA-1 mesoporous catalysts with different n_Si/n_Fe ratios in the temperature range 80–180 °C for a time-on-stream of 1–6 h under liquid phase conditions. The important factors affecting the conversion and the selectivity of the reaction, such as the reaction temperature, feed ratio, catalyst weight and time-on-stream were studied and the results are discussed in detail. The reaction conditions were optimized and the n_AA/n_Toluene ratio of 2 and catalyst weight of 0.1 g (3.3 wt% of total reaction mixture) were maintained for all catalytic runs. It was found that the catalytic activity is strongly influenced by the amount of tetrahedral iron in the catalysts. Among the catalysts used in the present study, FeSBA-1(36) showed a high toluene conversion and selectivity to p-methylacetophenone (p-MAP) under the optimized reaction conditions. It was also found that the selectivity for p-MAP was always higher than m-MAP and o-MAP for all the catalysts and the activity of the catalysts changes in the following order: FeSBA-1(36) > FeSBA-1(90) > FeSBA-1(120).     

Adsorption of methane, nitrogen, carbon dioxide and their mixtures on wet Tiffany coal

Gas adsorption was measured for methane, nitrogen, CO₂ and their binary and ternary mixtures on a wet Tiffany coal sample. The measurements were conducted at 327.6 K (130.0 F) at pressures to 13.8 MPa (2000 psia). The expected uncertainties in the amounts adsorbed vary with pressure and composition. In general, average uncertainties are about 5% (0.01–0.08 mmol/g) for the total adsorption; however, the expected percentage uncertainties in the amount of individual-component adsorption are significantly higher for the lesser-adsorbed gas at lower molar feed concentrations (e.g. nitrogen in the 20/80 nitrogen/CO₂ system).

The Langmuir/loading ratio correlation (LRC) and the Zhou–Gasem–Robinson (ZGR) two-dimensional equation of state (EOS) are capable of representing the total adsorption for the pure, binary and ternary systems within their expected experimental uncertainties. However, the quality of fit for the individual-component adsorption varies significantly, ranging from 3% (0.01 mmol/g) for the more-adsorbed methane or CO₂ to 32% (0.01 mmol/g) for the lesser-adsorbed nitrogen. Further, the LRC and ZGR EOS predict binary adsorption isotherms, based solely on pure-fluid adsorption parameters, within twice their experimental uncertainties.     

In situ ellipsometric study of the growth and electrochemical cycling of polypyrrole films on platinum

The growth and potential cycling of polypyrrole films on platinum has been examined using time-resolved in situ ellipsometry. The optical properties of the films produced depend critically on the experimental conditions used to grow the films. Films grown from “wet” acetonitrile, or acidic ( n (1.25–1.35) at 633 nm, indicating the presence of a very strong absorption band in the near-infra-red (Lorentz oscillator model). Films grown in less optimal conditions (neutral aqueous solution, or with Fe(CN)³⁻₆-containing electrolyte) have higher n values (1.45–1.5). Comparison of calculated (from charge per unit area data) and measured (ellipsometric) film thickness shows that films grown in aqueous media are somewhat denser than those grown in acetonitrile. On reduction, the film thickness increases for films grown under all conditions, but the change is greater for films grown from aqueous solution. Changes in n and absorbance, k, are, as expected, wavelength-dependent, but in general n greatly increases (to 1.65–1.80); this is also rationalized using the Lorentz oscillator model, since the wavelengths employed are to low energy of a strong absorption in neutral polypyrrole at ca 390 nm. On potential cycling from the reduced to the oxidized form, the film thickness decreases between ca −0.6 and −0.2 V, but thereafter, although charge is still being passed, changes much more slowly.     

Modelling a catalytic membrane reactor with plug flow pattern and a hypothetical equilibrium gas-phase reaction with Δn ≠ 0

The scope of this paper is to present a theoretical study of a catalytic polymeric dense membrane reactor (CPDMR) assuming isothermal conditions, plug flow pattern without pressure drop in both retentate and permeate sides, shell side feed and cocurrent operation. The conversion enhancement over the thermodynamic equilibrium value is studied for a gas-phase reaction of the type aAbB, considering two different stoichiometric ratios: Δn > 0 and Δn < 0, where Δn = b − a. For each of these cases, the influence of the relative sorption and diffusivity of the reaction species is studied. It is concluded that the conversion of a reversible reaction can be significantly enhanced when the diffusivity of the reaction products is higher than that of the reactants and/or the sorption is lower. It is also concluded that, even for equal sorption and diffusion coefficients, the conversion could also be improved for reactions with Δn ≠ 0. The extension of this enhancement depends on the reaction stoichiometry, the overall concentration inside the membrane, the Thiele modulus, and the contact time.