Analysis and Modeling of the Hydroisomerization Process for <Emphasis Type="Italic">n</Emphasis>-Hexane

A stage six-path mechanism for the reaction of n-hexane hydroisomerization on a BEA Pt-zeolite catalyst has been proposed. The mass flow rate of n-hexane in the feed stream varies in the range of 0.7?2.8 h^?1; the mole ratio of hydrogen to the n-hexane range of 2.7–14.6; the reactor temperature falls in the range from 453 to 573 K; and the gas flow pressure varies in the range of 1.0–10.0 atm. Thirty experiments have been carried out. In the product stream, the concentrations of n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, propane, C₁-alkanes, and C₂-alkanes are analyzed by gas chromatography. A kinetic model has been constructed for the six-path mechanism of the reaction of n-hexane hydroisomerization, which contains 15 kinetic constants. Based on the results of laboratory experiments, the kinetic constants of the model have been estimated by the method of nonlinear least squares. The model has been shown to correspond with the experiment in the selected field of experimentation.     

Kinetics of the low-temperature isomerization of <Emphasis Type="Italic">n</Emphasis>-hexane on the NIP-3A catalyst in an isothermal flow reactor

Low-temperature n-hexane isomerization kinetics was studied in an isothermal fixed-bed flow reactor on the chlorinated platinum-alumina catalyst NIP-3A under conditions of the coexistence of liquid and vapor phases. Optimum n-hexane isomerization conditions have been determined. Kinetic equations for the process are suggested.     

Oxidative Dehydrogenation of <Emphasis Type="Italic">n</Emphasis>-Butene to 1,3-Butadiene over Sulfated ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Catalyst

Oxidative dehydrogenation of n-butene to 1,3-butadiene over sulfated ZnFe₂O₄ catalyst was carried out in a continuous flow fixed-bed reactor. The effect of sulfation on the catalytic performance of ZnFe₂O₄ was investigated. Sulfated ZnFe₂O₄ catalyst showed a better catalytic performance than ZnFe₂O₄ catalyst in the oxidative dehydrogenation of n-butene. Acid–base property of sulfated ZnFe₂O₄ catalyst was measured by TPD experiment, with an aim of correlating the catalytic performance with the surface acid–base property of the catalyst. It was revealed that the catalytic performance of sulfated ZnFe₂O₄ catalyst was closely related to the surface weak-acid density of the catalyst. The enhanced acidity of sulfated ZnFe₂O₄ catalyst was responsible for its high catalytic performance in the oxidative dehydrogenation of n-butene. Thus, sulfation served as an efficient method for improving catalytic performance of ZnFe₂O₄ in the oxidative dehydrogenation of n-butene.     

Optimization of biodiesel production process in a continuous microchannel using response surface methodology

We assessed the biodiesel production process in a continuous microchannel through preparation of a heterogeneous catalyst (CaO/MgO) from demineralized water plant sediment. This mixed oxide catalyst was used for transesterification of rapeseed oil as feedstock by methanol to produce biodiesel fuel at various conditions. A microchannel, utilized as a novel reactor, was applied to convert rapeseed oil into biodiesel in multiple steps. The effects of the process variables, such as catalyst concentration, methanol to oil volume ratio, n-hexane to oil volume ratio, and reaction temperature on the purity of biodiesel, were carefully investigated. Box-Behnken experimental design was employed to obtain the maximum purity of biodiesel response surface methodology. The optimum condition for the production of biodiesel was the following: catalyst concentration of 7.875 wt%, methanol to oil volume ratio of 1.75: 3, n-hexane to oil volume ratio of 0.575: 1, and reaction temperature of 70 °C.     

Modeling the catalytic process of cyclohexane isomerization to methylcyclopentane

The kinetics of the isomerization of cyclohexane to methylcyclopentane on Pd-mordenite catalyst in a flow reactor has been studied. In the experiments, parameters such as the volumetric flow rate of the feedstock, the component composition of the feed gas (cyclohexane, methylcyclopentane, hydrogen), and the temperature and pressure in the reactor have been varied. The concentrations of hydrogen, cyclohexane, and methylcyclopentane in the feed gas have been determined. A stepwise reaction mechanism of cyclohexane isomerization has been suggested. A kinetic model that contains the direct constant of the limiting stage rate and the combination of equilibrium constants of the fast stages in a set for estimating the constants has been built. An additional precision (improving) experiment has shown that the model constants are estimated with a high accuracy. A predictive ability of the model under experimental conditions has been proved to be high.     

Flow Modes of Non-Newtonian Fluids with Power-Law Rheology in a T-Shaped Micromixer

The flow and mixing modes of non-Newtonian fluids in a T-shaped micromixer were studied by numerical simulation in the range of Reynolds numbers 1–250. The non-Newtonian fluid was described using the power-law model. The exponent n was varied: 0.3, 0.5, and 0.8. The mixing efficiency and pressure drop in the channel were correlated with the exponent n and Reynolds number. The exponent n was shown to significantly affect the flow structure before and especially after the transition from symmetric to asymmetric flow modes.     

Evaluation of different kinetics for bioethanol production with emphasis to analytical solution of substrate equation

Fermentation is typically modelled by kinetic equations giving the time evolutions for biomass, substrate, and product concentrations. In the present study, production of bioethanol from glucose, substrate and Saccharomyces cerevisiae (S. cerevisiae) as a biomass was investigated through a batch fermentation process. Time variation of the S. cerevisiae growth, glucose utilization and ethanol productivity was described using different kinetic models and analytically solution. The kinetic constants were determined through the fitting of experimental data with the kinetic model equations. The results demonstrated that the Monod, Logistic, and Luedeking-Piret served as the best describing models for S. cerevisiae growth, glucose, and ethanol concentrations, respectively. Moreover, determination of substrate concentration in according to time via analytical solution of equation was hallmark result of this research.     

Structure of an <Emphasis Type="Italic">n</Emphasis>-heptane/toluene flame: Molecular beam mass spectrometry and computer simulation investigations

Molecular beam mass spectrometry was used to measure mole fraction profiles of the reactants, major reaction products and intermediates, including precursors of polycyclic aromatic hydrocarbons, in a premixed fuel-rich (equivalence ratio of 1.75) n-heptane/toluene/O₂/Ar flame stabilized on a flat burner at atmospheric pressure. The ratio of the liquid volumes in the n-heptane/toluene mixture was 7: 3. The chemical structure of the flame was modeled using a detailed mechanism of chemical reactions tested against experimental data of other authors on n-heptane/toluene flames and comprising the reactions of formation of polycyclic aromatic hydrocarbons. The mechanism was extended with cross-reactions involving derivatives of n-heptane and toluene. Overall, the new experimental data are in satisfactory agreement with the numerical simulation results; however, there are differences between the measured and calculated mole fraction profiles of some species. Analysis shows that in the n-heptane/toluene flame, the main reactions leading to the formation of low-aromatic compounds (benzene and phenyl) are reactions typical of the pure toluene flame.     

Adsorptive removal of fluoride from water samples using <Emphasis Type="Italic">Azospirillum</Emphasis> biofertilizer and lignite

The present study involves a comparison of Azospirillum biofertilizer and lignite for removal of fluoride from aqueous solution. Batch experiments were performed to remove fluoride by the use of Azospirillum biofertilizer and lignite. Fluoride adsorption capacity was found by varying different parameters such as adsorbent dose, pH, initial concentration, temperature and contact time. The adsorption capacity for fluoride by using Azospirillum biofertilizer was 0.456 mg/g and for lignite 0.16 mg/g. Pseudo-second-order kinetic model best fit the experimental data. Field water samples were tested for fluoride removal by Azospirillum biofertilizer and lignite. The fluoride concentration was reduced to the permissible limit.     

Pilot tests of the microspherical aluminochromium KDI-M catalyst for <Emphasis Type="Italic">iso</Emphasis>-butane dehydrogenation

Results from pilot tests of microspherical aluminochromium KDI-M catalyst mixed with IM-2201 in a large-scale unit (Nizhnekamskneftekhim) for iso-butane dehydrogenation are discussed. Compared to KDI catalyst, its modified analogue KDI-M is more active and selective; the optimized grain-size composition and mechanical strength ensures higher yields of iso-butylene and longer nonstop operation (up to 400 days) of the reactor unit.     

Chemical equilibrium and liquid-phase splitting in acetic acid + <Emphasis Type="Italic">n</Emphasis>-propanol + <Emphasis Type="Italic">n</Emphasis>-propyl acetate + water system at 293.15 and 353.15 K

The paper presents new experimental data on the chemical equilibrium in the system n-propanol + acetic acid + n-propyl acetate + water at 293.15 and 353.15 K, and the data on liquid–liquid equilibrium at 353.15 K. Based on the experimental and literature data, the possibilities that chemical equilibrium exists in a homogeneous or heterogeneous region of compositions has been analyzed. The temperature shift of chemical and phase equilibria and the values of the thermodynamic constants of chemical equilibrium are discussed.     

Optimization of controlled ring-opening polymerization of <Emphasis Type="SmallCaps">l</Emphasis>-lactide to hydroxyl terminated polylactides using zinc acetate catalyst

Hydroxyl terminated polylactide polymers with number of average molecular weights (M _n ) varying from 1625 to 3459 g mol^?1 were synthesized by ring opening bulk polymerization of lactide in the presence of zinc acetate being a potent catalyst. The use of 1,4 butanediol (BDO) initiator leads to hydroxyl terminated polylactides, thus excellent precursors for shape-memory biodegradable polyurethanes. Different reaction conditions employed for the synthesis of hydroxyl terminated polylactide polymers via activated monomer mechanism may result in differences in M _n , percentage mass conversion and percentage degree of crystallinity (%χ _c ) of the product. Influence of process parameters, i.e. catalyst concentration, initiator concentration, reaction temperature and time on characteristics of hydroxyl terminated polylactides was studied. These polymers were characterized by Nuclear Magnetic Resonance (¹H-NMR) spectroscopy, Fourier transforms infrared (FTIR) spectroscopy, gel permeation chromatography (GPC) and X-ray diffraction (XRD) techniques. FTIR and ¹H-NMR confirmed the formation of hydroxyl terminated polylactides. M _n was determined by ¹H-NMR, GPC and end group analysis. %χ _c was calculated from XRD spectra. Maximum mass conversion, M _n and %χ _c were observed at 5 mol% SnOct₂ and 5 mol% BDO concentration. At optimum temperature of 145 °C, these characteristics improved linearly with polymerization time up to 6 h and declined thereafter.     

Détermination de constantes cinétiques du craquage catalytique par la modélisation du test de microactivité (MAT)

The microactivity test (MAT) for cracking catalyst test works with an approximately plug flow isothermal reactor. The yields at the outlet of such a reactor is numerically computed in the case of lumped kinetic with large molecular expansion and rapid catalyst deactivation expressed versus poison concentration. The poison (coke in cracking reaction) is considered as a product formed by several reaction routes. The results are applied to catalytic cracking kinetic with a four lump model (feedstock, gasoline, gas, coke). The comparison between experimental and computed yields, permits the adjustment of kinetic constants with a set of experimental results obtained from a laboratory scale reactor derived from the MAT. The simulation of concentration profile in the reactor permits a better understanding of the reaction courses.     

Kinetics of growth on dual substrates,production of novel glutaminase-free L-asparaginase and substrates utilization by <Emphasis Type="Italic">Pectobacterium carotovorum</Emphasis> MTCC 1428 in a batch bioreactor

Bacterial L-asparaginase has been widely used as a potential therapeutic agent in the treatment of various lymphoblastic leukemia diseases. We studied product and dual substrates utilization kinetics by P. carotovorum MTCC 1428 in batch bioreactor. The kinetic study revealed that the maximum growth of P. carotovorum MTCC 1428 was achieved at 2 g l ^?1 and 5 g l ^?1 of glucose and L-asparagine, respectively. Different substrate inhibition models were fitted to the growth kinetic data and the additive form of double Luong model was found to best explain the growth kinetics of P. carotovorum MTCC 1428. The kinetic parameters of growth studies showed that the predicted maximum inhibition concentration of glucose (S _mg ) and L-asparagine (S _ma ) was close to the experimentally observed value 15.0 and 10 g l ^?1, respectively. Modified form of the Luedeking-Piret model was used to describe the kinetics of L-asparaginase production, and the system seems to be mixed growth associated. Kinetic models of dual substrate growth, L-asparaginase production and substrate(s) utilization by P. carotovorum MTCC 1428 well fitted with experimental data with regression coefficients (R²) value of 0.97, 0.96 and 0.93, respectively.     

Cure kinetics of cyanate ester resin using microencapsulated dibutyltin dilaurate as catalyst

Dibutyltin dilaurate (DBTDL) catalyst-filled microcapsules (MCs) were used to catalyze the reaction of thermosetting cyanate ester (CE) resins. Dynamic differential scanning calorimetry (DSC) experiments were performed at multiple heating rates (β) to investigate the effects of the MC content (0.125, 0.25, and 0.5 %) on the cure kinetics of CE resins. The kinetic parameters of CE/MC systems, including activation energy (E _a), preexponential factor (A), and reaction order (n), were analyzed using the Flynn–Wall–Ozawa method, Kissinger method, Crane method, Ozawa isoconversional method, and Coats–Redfern method. The results indicate that, as the MC content increases, the reaction temperature of CE/MC system gradually shifts to low temperature owing to the increase of the DBTDL catalyst released from MCs under heating conditions. Compared to the unencapsulated DBTDL, the encapsulated DBTDL can decrease the E _a, A, and the reaction rate constant of CE resins due to the gradual release of DBTDL from MCs and the homogeneous dispersion of the released DBTDL in CE resins. The E _a, A, and the reaction rate constant of CE/MC systems are effectively adjusted by the MC content and heating process. The reaction orders for all CE/MC systems are close to 1. The reaction model of CE/MCs is considered as a two-dimensional nucleation (A ₂).     

Numerical Analysis of Hydrogen Sulphide Conversion to Hydrogen during Its Pyrolysis and Partial Oxidation

Production of hydrogen during pyrolysis and partial oxidation of hydrogen sulphide is analyzed on the basis of a detailed kinetic model of H₂S oxidation. It is shown that the H₂ yield in the case of H₂S pyrolysis in an adiabatic flow reactor with a residence time of ≈1 s is rather small. Even for the initial temperature of the mixture T₀ = 1400 K, the molar fraction of H₂ is only 12%, though the equilibrium value is reached within the reactor in this case. At T₀< 1200 K, there is no enough time for the chemical equilibrium inside the reactor to be established, and the H₂ concentration is lower than the equilibrium value. At T₀ < 1000 K, the pyrolysis reaction in the reactor practically does not occur. Addition of a small amount of air to H₂S leads to energy release, to an increase in temperature, and, as a consequence, to acceleration of H₂S conversion. The relative yield of H₂ can be increased by several times. For each value of T₀, there exists an optimal value of the fuel-to-air equivalence ratio φ that ensures the maximum H₂ yield in the H₂S–air mixture. The process of partial oxidation at high values of φ > φb and low values of T₀ is essentially nonequilibrium; as a result, the H₂ concentration at the exit from a finite-length reactor can be higher than its equilibrium value, e.g., the relative yield of H₂ can exceed the equilibrium value by 30–40% at T₀ = 800 K and φ = 6–10. The reasons responsible for reaching a “superequilibrium” concentration of H₂ at the flow reactor exit are determined.     

Two-step hydrothermal synthesis of β-MCM-41 composite molecular sieves as supports of bifunctional catalysts for hydroisomerization of <Emphasis Type="Italic">n</Emphasis>-heptane

β-MCM-41 composite molecular sieves were hydrothermally synthesized via two-step method. All the catalysts were characterized by XRD, FT-IR, BET and ICP. The catalysts were evaluated in hydroisomerization of n-heptane in a fixed bed flow reactor. Under the same condition, Pt/Hβ-MCM-41 was demonstrated to be a more mono-iso selectivity catalyst because the connection between mesopores and micropores accelerates the diffusion. Under optimal conditions, (precursor7.5d) Pt/Hβ-MCM-41 provided a very high selectivity to isomerization 90.0 % coupling with a considerable high conversion of n-heptane 59.9 % at 250 °C.     

Partition of <Emphasis Type="Italic">n</Emphasis>-Butanol Among Phases and Solubilization Ability of Winsor type III Microemulsions

The partition of n-butanol in Winsor type III (W-III) microemulsions was investigated in this work. Three kinds of anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (DSS), and sodium dodecyl benzene sulfonate (SDBS)) and two kinds of anionic/cationic surfactant mixtures (SDS/octadecyl trimethyl ammonium chloride (OTAC) mixtures and DSS/OTAC mixtures) were studied. Internal standard gas chromatography was employed in n-butanol content analysis. The results showed that no water exists in the excess oil (EO) phase and no oil exists in the excess water (EW) phase. For the W-III microemulsions obtained by salinity scanning, relatively constant n-butanol content in the EO (11–12 v%) and EW (1–4 v%) was found under different salinities. Accurate measurement of n-butanol content in each phase is important for those systems having low solubilization ability. For the W-III microemulsions prepared using SDS/OTAC surfactant mixture, the percentage of n-butanol distributed into the interfacial layer decreased while the fraction of n-butanol in the interfacial layer first increased sharply and then tended to be stable with the addition of n-butanol. For the different optimum W-III microemulsion systems tested, most of the surfactant-to-alcohol molar ratio data are near 1:3, but obvious deviation could be observed for some data. On the basis of the accurate measurement of n-butanol content in the EO and EW phases, the standard free energy, ΔG _o→in ^* (T = 298.15 K) of n-butanol transferring from the EO phase to the interfacial region was calculated. The results show negative ΔG _o→in ^* values. For microemulsions with the same components, n-butanol content is an important factor influencing the ΔG _o→in ^* value, and a high absolute value of ΔG _o→in ^* leads to high solubilization ability.     

Effect of Cu promoter and alumina phases on Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for propane dehydrogenation

We investigated the effects of different Cu weight ratio on θ or γ-Al₂O₃ which were impregnated with platinum in terms of catalytic activity for propane dehydrogenation and physicochemical properties. 1.5 wt% Pt, 0-10 wt% Cu catalyst supported on θ-Al₂O₃ or γ-Al₂O₃ was prepared by incipient wetness co-impregnation. Enhanced Pt dispersion by increasing Cu contents in γ-Al₂O₃ supported catalyst was confirmed via XRD and XPS. Pt and CuO was separated in Pt-Cu/θ-Al₂O₃, but Pt-Cu alloy was identified after reduction treatment. Also, adding Cu in Pt/Al₂O₃ makes catalyst’s acidity lower and this property led to increased propylene yield in propane dehydrogenation. However, Pt₃Cu was not good for yield of PDH, which was confirmed in Pt-10Cu/θ-Al₂O₃ through XRD.     

Catalyst Screening through Quantum Chemical Calculations and Microkinetic Modeling: Hydrolysis of Carbon Dioxide

Quantum chemical calculations are emerging as an effective way to screen catalysts for particular applications. In this contribution, we demonstrate the power of density functional theory to study CO₂ hydrolysisby six carbonic anhydrase mimics, evaluating thermodynamic and kinetic parameters at the mechanistic level. A microkinetic model was then built based on the kinetics and thermodynamics calculated from first principles. The intrinsic reaction rate constant was calculated from the results of the microkinetic model and compared with experimental data. Overall, the rate constants were in good agreement with experimental values, except for zinc-tri and complex b, which were overestimated. This was ascribed to their ineffective complexation with Zn²⁺. How the reaction rate constants vary with time was also investigated. From 0 to 12 ms, the rate constants of complexes a and d decreased to 50 and 67% of their initial values, respectively; the rate constants of complexes b and f2 were almost invariant with time; the rate constant of complex f1 showed an unusual double sigmoidal shape. The pK_a values of these six carbonic anhydrase mimics as well as three additional mimics were calculated. A correlation between pK_a values and the binding free energy of OH-was obtained by fitting data from five zinc(II) aza-macrocyclic complexes. The reaction rate constants were found to increase linearly with the pK_a value, indicating CO₂ adsorption is the rate-limiting step.