Kinetics of liquid phase xylene isomerization over H-mordenite

A study of the kinetics for the liquid phase isomerization of ortho-xylene over H-mordenite has been made at 505°K, 2.76 × 10⁵ N/m², and 23 mole % toluene diluent. This is the first known study reporting kinetic data for the liquid phase isomerization of xylene over a zeolite catalyst. High activity is indicated by the 80% achievement of para-xylene equilibrium at 505°K, 2.76 × 10⁵ N/m², and 0.767 × 10⁻³ kg/s/kg. Although high selectivity has previously been reported for a specifically prepared zeolite catalyst, the 99+% selectivity of the isomerization reaction with H-mordenite as indicated by no C₉+ aromatics and less than 0.5 mole % benzene in the product is most significant. Catalyst deactivation was also significant. Reaction rate constants are reported for a first-order reversible triangular model among the xylene isomers with catalyst deactivation incorporated into the model.     

Deactivation kinetics of a HZSM‐5 zeolite catalyst treated with alkali for the transformation of bio‐ethanol into hydrocarbons

The kinetics of deactivation by coke of a HZSM‐5 zeolite catalyst in the transformation of bioethanol into hydrocarbons has been studied. To attenuate deactivation, the following treatments have been carried out: (i) the zeolite has been subjected to a treatment with alkali to reduce the acid strength of the sites and (ii) it has subsequently been agglomerated into a macro and meso‐porous matrix of bentonite and alumina. The experimental study has been conducted in a fixed bed reactor under the following conditions: temperature, between 300 and 400°C; pressure, 1 atm; space‐time, up to 1.53 (g of catalyst) h (g of ethanol)^?1; particle size of the catalyst, between 0.3 and 0.6 mm; feed flowrate, 0.16 cm³ min^?1 of ethanol+water and 30 cm³ (NC) min^?1 of N₂; water content in the feed, up to 75 wt %; time on stream, up to 31 h. The expression for deactivation kinetics is dependent on the concentration of hydrocarbons and water in the reaction medium (which attenuates the deactivation) and, together with the kinetics at zero time on stream, allows the calculation of the evolution with time on stream of the yields and distribution of products (ethylene, propylene and butenes, C₁‐C₃ paraffins, and C₄‐C₁₂). By increasing the temperature in the 300–400°C range the role of ethylene on coke deposition is more significant than that of the other hydrocarbons (propylene, butenes and C₄‐C₁₂), which contribute to a greater extent to the formation of coke at 300°C. © 2011 American Institute of Chemical Engineers AIChE J, 58: 526–537, 2012.     

Absorption of 2-butene and 2-methyl-2-butene in aqueous solutions of sulphuric acid

The kinetics of absorption of 2-butene in aqueous solutions of sulphuric acid was studied in a stirred cell in the range of acid concentration from 70·2 per cent w/w (11·5 g mole/l.) to 80·2 per cent w/w (14·56 g mole/l.). The absorption was found to conform to fast pseudo-first order mechanism. The pseudo-first order reaction rate constant at 28°C was found to vary from about 500 to 3·8 × 10⁶ sec^?1 over the above concentration range.The absorption of 2-methyl-2-butene (isoamylene) in aqueous solutions of sulphuric acid was also found to conform to fast psuedo-first order mechanism, in the range of acid concentration from 61·5 per cent w/w (9·395 g mole/l.) to 75 per cent w/w (12·845 g mole/l.). The pseudo-first order reaction rate constant at 30°C was found to vary from about 4·2 × 10⁵ to 2·2 × 10⁸ sec^?1 over the above concentration range.     

Control of urethane prepolymerization from reaction kinetics and viscosity

A theory of the kinetics of consective second-order reactions has been generalized and used to interpret observations of toluene-2,4-diisocyanate reacting with polyoxypropylene glycol without diluent or catalyst to form a urethane prepolymer. The first reaction in the sequence has a second-order rate constant of 1.2 × 10^?7 m³mole^?1 sec^?1 at 303°K with an activation energy of 3.5 × 10⁴ J mole^?1. The rate constant of the second reaction appears to be one half of this. Deviations from the theoretical kinetics and an increase in the viscosity of the prepolymer product above 1.9 kg m^?1s^?1 (measured at 313°K) when the temperature of reaction exceeds about 360°K show that above this temperature, undesirable side reactions are important.     

The development of kinetics model for CO2 absorption into tertiary amines containing carbonic anhydrase

CO₂ absorption into aqueous solutions of two tertiary alkanolamines, namely, MDEA and DMEA with and without carbonic anhydrase (CA) was investigated with the use of the stopped‐flow technique at temperatures in the range of 293–313 K, CA concentration varying from 0 to 100 g/m³ in aqueous MDEA solution with the amine concentration ranging from 0.1 to 0.5 kmol/m³, and CA concentration varying from 0 to 40 g/m³ in aqueous DMEA solution with the amine concentration ranging from 0.05 to 0.25 kmol/m³. The results show that the pseudofirst‐order reaction rate (k_{0, amine}; s^?1) is significantly enhanced in the presence of CA as compared with that without CA. The enhanced values of the kinetic constant in the presence of CA has been calculated and a new kinetics model for reaction of CO₂ absorption into aqueous tertiary alkanolamine solutions catalyzed by CA has been established and used to make comparisons of experimental and calculated pseudo first‐order reaction rate constant (k_{0, with CA}) in CO₂‐MDEA‐H₂O and CO₂‐DMEA‐H₂O solutions. The AADs were 15.21 and 15.17%, respectively. The effect of pKa on the CA activities has also been studied by comparison of CA activities in different tertiary amine solutions, namely, TEA, MDEA, DMEA, and DEEA. The pKa trend for amines were: DEEA > DMEA > MDEA > TEA. In contrast, the catalyst enhancement in amines was in the order: TEA> MDEA> DMEA> DEEA. Therefore, it can be seen that the catalyst enhancement in the amines decreased with their increasing pKa values. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

KINETICS OF CATALYTIC THERMAL TREATMENT (CATALYTIC THERMOLYSIS) OF BIODIGESTER EFFLUENT OF AN ALCOHOL DISTILLERY PLANT

The biodigester effluent (BDE) of a molasses-based alcohol distillery unit was taken for catalytic thermal treatment (catalytic thermolysis) in the presence of CuO catalyst in batch mode in the temperature range of 100° to 140°C and pressure range of 1–9 bar. The catalyst mass loading, C_w, varied between 2 and 5 kg m^?3. Thermal treatment at 140°C with a C_w of 3 kg m^?3 gave COD reduction of about 70% from its initial value of 34 kg m^?3. The BOD reduction was found to be 83% from its initial value of 6.3 kg m^?3. The reductions of COD and consequently BOD are due to formation of residues of organics, i.e., carbohydrates, lignin, and proteins, present in the biodigester effluent. The characterization of CuO catalyst through X-ray diffraction shows the presence of the phase of CuO only, at different 2θ values. The kinetic data show two clearly distinct steps, a fast rate process followed by a slower process, adequately described by first-order kinetics with respect to COD. The order with respect to C_w was found to be 0.744 and 0.187 for the first and second steps, respectively.     

Studies on the potential of coal fly ash as a heterogeneous catalyst in oxidation of aqueous sodium sulfide solutions with hydrogen peroxide

The potential of fly ash procured form coal-fired thermal power plants was studied as a heterogeneous catalyst in the oxidation of aqueous sodium sulfide solutions with hydrogen peroxide in the temperature range of 303–323 K. The effects of various parameters (source of fly ash, fly ash loading, initial concentrations of sodium sulfide and hydrogen peroxide, electrolyte and deactivation of catalytic effect of fly ash) were studied. For an initial sodium sulfide and hydrogen peroxide concentration of 26·98×10⁻² kmol m⁻³ and 24·28×10⁻² kmol m⁻³ respectively, only 4% (w/v) fly ash loading intensified the rate of oxidation by a factor of 4·52 over that without fly ash at 303 K. The deactivation of the catalytic effect of fly ash was found to be less than 20% even after six repeated uses. The kinetics of aqueous phase decomposition of hydrogen peroxide was also studied in the presence of fly ash in alkaline medium. ©1997 SCI     

Mesoporous aluminosilicate: efficient and reusable catalysts for esterification of <Emphasis Type="Italic">sec</Emphasis>-butanol with acetic acid

Esterification of acetic acid with sec-butanol to produce sec-butyl acetate has been systematically carried out by using mesoporous (3–9 nm size) aluminosilicate (meso-AS) catalysts (surface area 327–578 m² g^?1) derived from Na-montmorillonite by controlled HCl acid activation. High catalytic activity up to 89% conversion with nearly 100% selectivity towards sec-butyl acetate is observed. The effect of reaction temperature, mole ratio of reactants and catalyst concentration on esterification reactions were studied. The catalyst could be recycled and reused several times without significant loss of their catalytic activities. The catalysts were characterized by pyridine adsorbed FT-IR, XRD, SEM-EDX, MAS-NMR, surface area (BET) and TPD analysis.     

Curing kinetics of a rigid polyurethane foam formulation

The curing kinetics of a typical commercial formulation used in the manufacture of rigid polyurethane foams has been studied. The adiabatic temperature rise method was used, taking into account corrections for heat losses. A polymeric isocyanate was reacted with a stoichiometric amount of a polyether polyol, using dibutyltin dilaurate (DBTDL) as catalyst. For DBTDL < 2.6 mol m^?3, a strong inhibition of the catalyst took place, and the uncatalysed reaction played a major role. Second order kinetics gave a good fit for the whole conversion range. For DBTDL > 2.6 mol m^?3, the catalysed reaction took place. Second order kinetics were applicable up to the gel point, but then the rate slowed down severely. A first order dependence on the initial catalyst concentration was observed in the pre-gel region. The kinetics are discussed in terms of a modified version of the Van der Weij's mechanism. The heat of reaction was 17.6 kcal/NCO equivalent.     

Phenomenological‐based kinetics modelling of dehydrogenation of ethylbenzene to styrene over a Mg3Fe0.25Mn0.25Al0.5 hydrotalcite catalyst

This communication reports a mechanism‐based kinetics modelling for the dehydrogenation of ethylbenzene to styrene (ST) using Mg₃Fe_0.25Mn_0.25Al_0.5 catalyst. Physicochemical characterisation of the catalyst indicates that the presence of basic sites Mg²⁺O^2? on the catalysts along with Fe³⁺ is responsible for the catalytic activity. The kinetics experiments are developed using a CREC Fluidised Riser Simulator. Based on the experimental observations and the possible mechanism of the various elementary steps, Langmuir–Hinshelwood type kinetics model are developed. To take into account of the possible catalyst deactivation a reactant conversion‐based deactivation function is also introduced into the model. Parameters are estimated by fitting of the experimental data implemented in MATLAB. Results show that one site type Langmuir–Hinshelwood model appropriately describes the experimental data, with adequate statistical fitting indicators and also satisfied the thermodynamic restraints. The estimated heat of adsorptions of EB (64 kJ/mole) is comparable to the values available in the literature. The activation energy for the formation of ST (85.5 kJ/mole) found to be significantly lower than that of the cracking product benzene (136.6 kJ/mole). These results are highly desirable in order to achieve high selectivity of the desired product ST. © 2012 Canadian Society for Chemical Engineering     

Mathematical modelling of the alcoholic fermentation of glucose by Zymomonas mobilis mobilis

The kinetics of alcoholic fermentation of a strain of Zymomonas mobilis, isolated from sugarcane juice, has been studied with the objective of determining the constansts of a non-structured mathematical model that represents the fermentation process. Assays in batch and in continuous culture have been carried out with different initial concentrations of glucose. The final concentrations of glucose, ethanol and biomass were determined. The following kinetic parameters were obtained: μ_max, 0·5 h^?1; K_s, 4·64 g dm^?3; P_max, 106 g dm^?3; Y_x/s, 0·0265 g g^?1; m, 1·4 g g^?1 h^?1; α, 17·38 g g^?1; β, 0·69 g g^?1 h^?1.     

Microreactor technology for synthesis of ethyl methyl oxalate from diethyl oxalate with methanol and its kinectics

This study focused on the performances and kinetics of the transesterification reaction of diethyl oxalate with methanol to prepare ethyl methyl oxalate via microreactor technology. The conversion of 79.8% of diethyl oxalate (DEO) and the selectivity of 65.9% of ethyl methyl oxalate (EMO) was obtained under the following optimized conditions: the mole ratio of methanol to diethyl oxalate was 3.3:1, the temperature was 35°C, the K₂CO₃ catalyst concentration was 15 mg/mL, and the residence time was 2.30 minutes. In the temperature range of 25°C to 38°C, the simplified dynamic model was found to obtain the reaction order (α = 2.30), frequency factor (k₀ = 2.377 × 10⁵), and apparent activation energy (E = 31.86 kJ/mol). The macroscopic dynamic equation was derived from the experimental result of the transesterification reaction of two feedstocks, which can be obtained through a series of calculations.     

PERFORMANCE OF ACIDIC MCM-LIKE ALUMINOSILICATE CATALYSTS IN PYROLYSIS OF POLYPROPYLENE

Mesoporous aluminosilicate catalysts having different Al/Si ratios were synthesized following a hydrothermal synthesis route and using different aluminum sources, such as aluminum nitrate and aluminum isopropoxide. These mesoporous materials have high surface areas, in the range of 520–1001 m²/g, and exhibit Type IV nitrogen adsorption isotherms. EDS and ²⁷Al MAS NMR results showed that aluminum was incorporated more effectively into the structure of the catalyst forming a tetrahedral framework when aluminum nitrate was used as the aluminum source. The activities of these catalysts in the polypropylene pyrolysis reaction were tested in a TGA apparatus. Results showed a marked reduction in the degradation temperature in the presence of aluminosilicate catalysts. The activation energy of degradation was 172 kJ/mole without any catalyst. However, using the mesoporous aluminosilicate catalysts synthesized by using aluminum nitrate as the aluminum source, activation energy of the degradation reaction decreased to values of about 24–28 kJ/mole.     

A Study of White‐Spirit Vapor Combustion on Pt/Al2O3 Catalyst

The objective of the work is to investigate the catalytic combustion of white spirit solvent vapors at low concentration in air, typical for depollution applications, on a commercial catalyst, Pt/γ‐Al₂O₃ (0.5 wt‐% Pt). To study the influence of the main variables on the process kinetics, experiments were performed under various operating conditions (temperature domain: 150–350 °C; flow rates: 125–250 mL min^–1; white spirit concentrations: 220–260 ppmv). The stoichiometry and kinetics of the vapor combustion was described globally by using a pseudo‐compound, representing the average molecular weight and the carbon/hydrogen ratio of the mixture. Experimental data were reasonably well correlated by a first order rate expression with respect to the apparent concentration of the lumping pseudo‐component.     

Combined biological and chemical oxidation of ferrous sulfate using immobilised Thiobacillus ferrooxidans

Thiobacillus ferrooxidans immobilised in biomass support particles with activated carbon coating were used in a packed‐bed bioreactor to study the combined effects of chemical and biological catalysis on the oxidation of ferrous iron. The effect of ferrous iron concentration (in the range 5–30 kg m⁻³) and of its volumetric loading on the kinetics of reaction were investigated. With low concentrations of ferrous iron, 5–10 kg m⁻³, the combined catalysis did not offer a significant advantage to oxidation of ferrous iron and the kinetics of reaction were slightly faster than those achieved with just the biological catalyst. With ferrous iron at a concentration of 20 kg m⁻³, the combination of chemical and biological catalysis resulted in a remarkable enhancement of the reaction rate. The maximum oxidation rate of ferrous iron in the presence of combined catalysts, 21.9 kg m⁻³ h⁻¹, was twice as high as that achieved with just the biological catalyst. © 1999 Society of Chemical Industry     

Sodium bisulfite-initiated polymerization of methyl methacrylate in aqueous medium in the presence of the metal oxides CuO and MnO2

Sodium bisulfite-initiated polymerization of methyl methacrylate (MMA) in water medium was carried out in the absence and in the presence of cupric oxide and manganese dioxide using various initiator concentrations at various temperatures ranging from 30° to 60°C. It seems that the metal oxide–water interface plays an important role, as it has been found that both oxides accelerate the rate of polymerization. Cupric oxide was found to be more effective than manganese dioxide. The cupric oxide was found to have nearly the same catalytic effect as the cuprous oxide, and manganese dioxide was found to be somewhat more effective than titanium dioxide. The initial rate of polymerization increased from 2.3 × 10^?5 mole/(l.sec) to 3.4 × 10^?4 mole/(l.sec) and to 6.6 × 10^?5 mole/(l.sec) when the metal oxide concentration increased from 0 to 3 g/l. in case of cupric oxide and manganese dioxide, respectively. The initial rate of polymerization increased from 3.7 × 10^?4 mole/(l.sec) to 4.2 × 10^?4 mole/(l.sec) and from 7.2 × 10^?5 to 2.2 × 10^?4 mole/(l.sec) when the temperature was raised from 30° to 60°C in the presence of cupric oxide and manganese dioxide, (9 g/l.), respectively. Both the rate of polymerization and the number-average molecular weights were found to increase with increase the monomer concentration; the rate values were higher while the number-average molecular weights were lower in case of cupric oxide than in case of manganese dioxide. For example, the rate of polymerization increased from 2 × 10^?5 mole/(l.sec) to 8.1 × 10^?5 mole/(l.sec) and from 1.9 × 10^?5 mole/(l.sec) to 6.9 × 10^?5 mole/(l.sec); and the number-average molecular weight increased from 0.7 × 10⁵ to 2.2 × 10⁵ and from 1.5 × 10⁵ to 4.9 × 10⁵ in the presence of cupric oxide and manganese dioxide (10 g/l.), respectively, when the monomer concentration was increased from 23.5 g to 94 g/1. water. The apparent energy of activation for the polymerization of methyl methacrylate in water medium between 40° and 50°C was found to be 0.8 and 4.3 kcal/mole when using cupric oxide and manganese dioxide (9 g/l.), respectively.     

Absorption of oxygen by 2-ethylhexaldehyde

The kinetics of absorption of oxygen by 2-ethylhexaldehyde dissolved in 2-ethylhexanoic acid at concentrations up to 1.38 × 10^?3 mole/cm³ (20 wt.-%), in the presence of manganese acetate, was studied in a stirred cell and in bubble and packed bubble columns. Diffusion of oxygen was found to play a major role. The reaction was first order in oxygen and second order with respect to the aldehyde, and the overall third-order rate constant was found to be 2.98 × 10⁷ cm⁶ mole^?2 sec^?1 at 30°. The effect of cobaltous acetate on the specific rate of absorption of oxygen was also studied and manganese acetate was found to be the better catalyst.     

The iron salt-catalyzed autoxidation of atactic polypropylene

The iron-catalyzed autoxidation of atactic polypropylene has been studied in the solid phase using infrared spectroscopy. The reaction temperature ranged from 110° to 130°C, the ferric acetylacetonate concentration varied from 0.3 × 10^?7 to 90.0 × 10^?7 mole per 7.5 mg atactic polypropylene, and the oxygen concentration varied from 5 to 100 vol-%. In the region of relatively low catalyst concentrations, the maximum steady rate varied approximately first order in respect to the catalyst concentration and about zero order at relatively high values of the catalyst concentration. Linear relationships between the maximum steady rate and the oxygen concentration, for both low and high concentrations, were obtained. A general scheme and kinetic expressions derived there-from previously reported for the uncatalyzed autoxidation of polyolefins and recently modified to account for cobalt-catalyzed autoxidation of actactic polypropylene has been successfully applied to the experimental results.     

Comparison of a new immobilized Fe3+ catalyst with homogeneous Fe3+–H2O2 system for degradation of 2,4‐dinitrophenol

BACKGROUND: Heterogeneous Fenton catalysts have been used to treat various organic pollutants in an aqueous environment. The present study has investigated the degradation of 2,4‐dinitrophenol (2,4‐DNP), a priority pollutant generated by such industries as pharmaceuticals, pesticides, pigments and dyes. Degradation of 2,4‐DNP (100 mg L^?1) was studied using Fe³⁺ loaded on Al₂O₃ as a heterogeneous catalyst in the presence of H₂O₂, and the efficiency compared with the homogeneous Fe³⁺/H₂O₂ based Fenton‐like process. The effect of different parameters for both processes, such as catalyst loading, H₂O₂ concentration, initial solution pH, initial substrate concentration and temperature were investigated and the optimum operating conditions determined. RESULTS: Under optimal operating conditions of the homogeneous system ([Fe³⁺] 125 mg L^?1; [H₂O₂] 250 mg L^?1; pH 3; room temperature), 92.5% degradation was achieved in 35 min for an initial 2,4‐DNP concentration of 100 mg L^?1. In the case of immobilized Fe (Fe³⁺–Al₂O₃ catalyst), degradation improved to 98.7% under the condition 10 wt% [Fe³⁺–Al₂O₃] 1 g L^?1 catalyst loading; [H₂O₂] 250 mg L^?1; pH 3; at room temperature for the same duration. CONCLUSIONS: This study demonstrated the stability and reusability of the prepared heterogeneous catalyst. This process is a viable technique for treatment of aqueous solutions containing contaminants. Copyright © 2012 Society of Chemical Industry     

The synthesis of high molecular weight polybutene‐1 catalyzed by Cp★ Ti(OBz)3/MAO

A new stereoregular polybutene‐1 was synthesized with a novel catalyst precursor η⁵‐pentamethyl cyclopentadienyl titanium tribenzyloxide (CpTi(OBz)₃) and methylaluminoxane (MAO). The effects of polymerization conditions on the catalytic activity, molecular weight and stereoregularity of the products were investigated in detail. It was found the catalyst exhibited highest activity of 91.2 kgPB mol Ti⁻¹ h⁻¹ at T = 30 °C, Al/Ti = 200. The catalytic activity and molecular weight were sensitive to the Al/Ti (mole/mole), polymerization temperature; they also depended on the Ti concentration. The molecular weight of the products increased with decreasing temperature. The structure and properties of the polybutene‐1 were characterized by ¹³C NMR, GPC, DSC and WAXD. The result showed the microstructure of polybutene‐1 extracted by boiling heptane was stereoregular, whereas the ether‐soluble fraction was atactic. The molecular weight of polybutene‐1 was over one million g mol⁻¹ and its molecular weight distribution ( M _w/ M _n) was from 1.1 to 1.2. © 2001 Society of Chemical Industry