Hydrotreating of heavy gas oil using CoMo/γ-Al2O3 catalyst prepared by equilibrium deposition filtration

CoMo/γ-Al₂O₃ catalyst containing 16.0 wt% MoO₃ and 3.2 wt% CoO was prepared by equilibrium deposition filtration method (EDF). The CoMo oxidic catalyst was characterized by elemental analysis, N₂ adsorption, XRD, and TPR. The sulfided catalyst was characterized by FTIR of adsorbed CO at 30 °C. Hydrodesulfurization (HDS) and hydrodearomatization activities were evaluated for heavy gas oil (HGO) in a trickle bed reaction system using the following conditions: reaction temperatures of 340, 360, 380 and 400 °C, a reaction pressure of 20, 35, 50 and 65 bar, a liquid hourly space velocity (LHSV) of 1.0, 1.5, 2.0, 2.5 and 3 h⁻¹ and a H₂/feed ratio of 400 L L⁻¹. The experimental results were used to determine apparent reaction orders and activation energies. The dispersion, nature of active sites and hydrotreating activity of this catalyst were compared with the conventionally prepared CoMo/γ-Al₂O₃ catalyst containing similar wt% of MoO₃ and CoO. The CoMo catalyst prepared by equilibrium deposition filtration method has higher HDS and HDA rate constants than the conventional catalyst due to an improved dispersion of MoS₂.     

Kinetics of Bitumen‐Derived Gas Oil Upgrading Using a Commercial NiMo/Al2O3 Catalyst

Hydrotreating (HT) kinetics of Athabasca bitumen‐derived gas oil has been studied between 340 to 420°C using a commercial NiMo/γ‐Al₂O₃ catalyst. The kinetics analyses included overall conversion of high‐boiling species into low‐boiling products, hydrodenitrogenation (HDN) of total, basic and non‐basic nitrogen compounds and hydrodesulfurization (HDS). Three temperature regimes were marked out for the kinetic analyses: low (340‐370°C), intermediate (370‐400°C) and high (400‐420°C). The mechanism for the conversion of high to low‐boiling species was observed to change from one temperature regime to the other, giving rise to different activation energies. HDS and HDN activation energies increased in the order: high < low < intermediate severity temperature regime.     

Dynamic modeling of curing process of epoxy prepreg

The dynamic curing process was studied by using differential scanning calorimetry (DSC) and modeled by two methods. One was based on the Kissinger and Ozawa approach, in which the activation energy was taken as a constant for all the heating rates. The whole curing process was modeled with two cure reactions. Reaction 1 exhibited the behavior of the autocatalytic reaction, whereas Reaction 2 was the nth order reaction. The effect of heating rate on the preexponential factor A₁ of Reaction 1 was apparent. As the heating rate increased, the A₁ decreased. There was no significant effect of heating rate on the preexponential factor A₂ of Reaction 2 and the reaction orders for both reactions. The calculated results showed that the contributions of these two reactions to the total curing process were very different and changed with the heating rate. Except in the early cure stage, the calculated total degree of cure agreed well with the experimental data. Another method was based on the Borchardt and Daniels kinetic approach, where the activation energy of the cure reaction at each heating rate was determined separately. The whole curing process was modeled with one autocatalytic reaction. The fitting results showed that both preexponential factor and activation energy increased with the increment of the heating rate. As in the first method, the effect of heating rate on the orders of reaction was very small. The calculated results agreed well with experimental values in the early cure stage. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1911–1923, 2002     

Hydrodenitrogenation and Hydrodesulphurization of Heavy Gas Oil Using NiMo/Al2O3 Catalyst Containing Phosphorus: Experimental and Kinetic Studies

In this work, a systematic study has been conducted to optimize the process conditions and to evaluate kinetic parameters for hydrodenitrogenation (HDN) and hydrodesulphurization (HDS) of heavy gas oil derived from Athabasca bitumen using NiMo/Al₂O₃ catalysts containing phosphorus (P). In the catalyst, the concentration of phosphorus was maintained at 2.7 wt%. Experiments were performed in a tickle‐bed reactor at the temperature, pressure and liquid hourly space velocity (LHSV) of 340‐420°C, 6.1‐10.2 MPa and 0.5‐2 h^?1, respectively. H₂ flow rate and catalyst weight were maintained constant at 50 mL/min and 4 g, respectively in all cases. Statistical analysis of all experimental data was carried out using ANOVA to optimize the process conditions for HDN and HDS reactions. Kinetic studies for HDN and HDS reactions were studied within the temperature range of 340‐400°C using the power law model as well as the Langmuir‐Hinshelhood model. The power law model showed that HDN and HDS of heavy gas oil follow first order kinetics. The activation energies for HDN and HDS reactions from the power law and Langmuir‐Hinshelwood models were 94 and 96 kJ/mol and 113 and 137 kJ/mol, respectively.     

Kinetics of dimethyl ether oxidation over Pt/ZSM-5 catalyst

A kinetic study of dimethyl ether (DME) combustion over Pt/ZSM-5 was performed below 423 K. Power law model and Langmuir-Hinshelwood model were established to predict the reaction rate. Reaction orders for DME and O₂ were 0.28 and 2.30, respectively. Activation energies for the two models were 99.35 and 109.30 kJ/mol. The reaction orders and adsorption constants suggested DME was more strongly adsorbed on Pt/ZSM-5 than O₂ at low temperatures. The reliability of the models was confirmed by the comparison between the predicted and experimental conversions of DME.     

Kinetic Reaction Models for the Selective Reduction of NO by Methane over Multifunctional Zeolite‐based Redox Catalysts

Kinetic measurements of the selective catalytic reduction (SCR) of NO by methane were performed over CeO₂/H‐ZSM‐5, In‐ZSM‐5, and CeO₂/In‐ZSM‐5 catalysts. The parameter space covered NO, CH₄, and O₂ concentrations varying from 250 to 1000 ppm, from 500 to 2000 ppm, and from 0.5 to 10 vol.‐%, respectively, space velocities between 5000 and 90000 h^–1 and temperatures between 573 and 873 K depending on the catalyst activities. With CeO₂/In‐ZSM‐5 an additional series of measurements was performed with moistened feed gas (0.5–10 vol.‐% H₂O). On the basis of a pseudo‐homogeneous, one‐dimensional fixed‐bed reactor model, the data were fitted to a kinetic model that includes power rate laws for the reduction of NO and for the unselective total oxidation of methane. From analyses of isothermal data sets, almost all reaction orders were found to vary significantly with changing temperature, which indicates that the simple kinetic model cannot reflect the complex reaction mechanism correctly. Nevertheless, the data measured with In‐ZSM‐5 could be modeled with good accuracy over a wide range of reaction temperatures (150 K) while the accuracy was less satisfactory with the remaining data sets, in particular for data with the moist feed over CeO₂/In‐ZSM‐5. With the latter catalyst it was not possible to represent the data measured in dry and in moist feed in a single model even upon confinement to fixed reaction temperatures. A comparison of the separate models established showed strong changes in the reaction orders in the presence of water, which occur apparently already at a very low water content (≤ 0.5 vol.‐%). The kinetic parameters found are in agreement with earlier conclusions about the reaction mechanisms. With In‐ZSM‐5, both reaction orders and the activation energy show a rate‐limiting influence of NO oxidation on the NO reduction path which is removed by the presence of the CeO₂ promoter. A difference in the reaction mechanism over CeO₂/In‐ZSM‐5 and CeO₂/H‐ZSM‐5 is reflected in different kinetic parameters. The differences of the kinetic parameters between dry‐feed and moist‐feed models for CeO₂/In‐ZSM‐5 reflect adsorption competition between the reactants and water.     

Influence of the surface structure on the kinetics of ethane hydrogenolysis over Ni/SiO2 catalysts

The rate of ethane hydrogenolysis, which was shown previously to be a structure-sensitive reaction, is studied in a large range of pressure and temperature over Ni/SiO₂ catalysts of different morphology. It is observed that the partial reaction order with respect to ethane is unity at low hydrocarbon pressures, and that the partial reaction order with respect to hydrogen and the apparent activation energies vary with hydrogen pressure and temperature. Moreover, orders and apparent activation energies are independent of the nature and of the activity of the catalyst, indicating that the previously reported variations of reaction rate with nickel particle size do not depend on the standard conditions which were chosen. Furthermore, on less active samples, there is no simple relation between the reaction rate, r, and the resulting hydrogen coverage, θ_H (as was the case for a very active sample), from which it is concluded that only a small fraction of the nickel surface is active, (111) planes probably being inactive. On the most active sample, it is supposed that most of the nickel atoms are nearly equivalent from the viewpoint of catalytic activity.     

Rationalizing the catalytic performance of γ-alumina-supported Co(Ni)–Mo(W) HDS catalysts prepared by urea-matrix combustion synthesis

A comparative study of the influence of Co (or Ni) promoter loadings and the effect of different sulfurizing agents and sulfurizing temperatures on the structure, morphology and catalytic performance of Mo- or W-based hydrodesulfurization (HDS) catalysts was carried out. Catalyst performance using a tubular fixed-bed reactor and the HDS of thiophene as a model reaction was evaluated. The oxidic and sulfurized states of the HDS catalysts were characterized by laser Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and high resolution transmission electron microscopy (HRTEM). It has been found that the urea-matrix combustion (UMxC) synthesis is a simple tool for preparing supported catalysts in a short period of thermal treatment. Several consecutive stages such as urea melting, metal precursor dissolution and chemical reactions take place before and upon combustion process. The C₄H₄S/H₂-activated Co- (or Ni-) promoted MoS₂ (or WS₂) catalysts present a strong synergistic effect (SE) when the Co (or Ni)/Mo (or W) molar ratio is near to 0.5, whereas the C₄/C ₄ ⁼ molar ratios display a weak antagonistic effect. Alumina-supported Ni–W catalyst showed an optimal SE 2.5 times higher than those for Co (or Ni)-promoted Mo HDS catalysts. The kinetic parameters for thiophene-HDS reaction were also determined, suggesting that the C–S bond cleavage reaction for alumina-supported Co(Ni)–Mo HDS catalysts and H₂ activation reaction for Ni-promoted WS₂catalysts play an important role in the rate-limiting step.     

Effect of supercritical deposition synthesis on dibenzothiophene hydrodesulfurization over NiMo/Al2O3 nanocatalyst

The synthesis of two NiMo/Al₂O₃ catalysts by the supercritical carbon dioxide/methanol deposition (NiMo‐SCF) and the conventional method of wet coimpregnation (NiMo‐IMP) were conducted. The results of the physical and chemical characterization techniques (adsorption–desorption of nitrogen, oxygen chemisorption, XRD, TPR, TEM, and EDAX) for the NiMo‐SCF and NiMo‐IMP demonstrated high and uniform dispersed deposition of Ni and Mo on the Al₂O₃ support for the newly developed catalyst. The hydrodesulfurization (HDS) of fuel model compound, dibenzothiophene, was used in the evaluation of the NiMo‐SCF catalyst vs. the commercial catalyst (NiMo‐COM). Higher conversion for the NiMo‐SCF catalyst was obtained. The kinetic analysis of the reaction data was carried out to calculate the reaction rate constant of the synthesized and commercial catalysts in the temperature rang of 543–603 K. Analysis of the experimental data using Arrhenius' law resulted in the calculation of frequency factor and activation energy of the HDS for the two catalysts. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Control of the product distribution in the hydrogenation of vegetable oils over nickel on silica catalysts

Several nickel on silica catalysts, prepared by impregnation or precipitation/deposition, and a commercial catalyst were tested for activity and selectivity in the sunflower seed oil hydrogenation. An average turn-over frequency of 2.57 s^?1 was found for the catalysts, assuming inaccessibility of nickel in pores smaller than 2 nm and a constant nickel surface concentration poisoned by the reaction mixture. After studying the mass-transfer steps, the effect of temperature (373-453 K) and pressure (101-608 kPa) on reaction rates in the kinetic regime was analyzed, and the corresponding apparent activation energies and reaction orders were obtained. Conclusions on the effect of temperature and pressure on the selectivity to the preferential hydrogenation of polyunsaturates (S_o) and to the formation of trans-isomers ((S_trans)₀) in the kinetic regime were derived from the results. Finally, a similar analysis was carried out when diffusion limitations were known to be present.     

Upgrading of gas oils: the HDS kinetics of dibenzothiophene and its derivatives in real gas oil

The hydrodesulphurization (HDS) of dibenzothiophene (DBT), 4-methyl dibenzothiophene (4 M-DBT), 4,6-dimethyl dibenzothiophene (4,6 DM-DBT) and 4,6-diethyl dibenzothiophene (4,6 DE-DBT) as real gas oil components on NiMo/Al₂O₃ catalyst was investigated. On the basis of the first order rate constants of HDS of the individual sulphur compounds reactivities of the investigated compounds decreased in the order DBT ≫ 4 M-DBT > 4,6 DE-DBT ≈ 4,6 DM-DBT. Apparent activation energies of HDS of above sulphur compounds increased from 80.0 to 120.5 kJ/mol.     

Kinetics studies of nano-structured cobalt–manganese oxide catalysts in Fischer–Tropsch synthesis

The nano-structured cobalt/manganese oxide catalyst was prepared by thermal decomposition of [Co(NH₃)₄CO₃]MnO₄ precursor, and was tested for the Fischer–Tropsch reaction (hydrocarbon forming) in a fixed-bed micro-reactor. Experimental conditions were varied as follow: reaction pressure 1–10 bar, H₂/CO feed ratio of 1–2 and space velocity of 3600 h^?1 at the temperature range of 463.15–523.15 K. On the basis of carbide and/or enolic mechanisms and Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equations, 30 kinetic expressions for CO consumption were tested and interaction between adsorption HCO and dissociated adsorption hydrogen as the controlling step gave the most plausible kinetic model. The kinetic parameters were estimated with non-linear regression method and the activation energy was 80.63 kJ/mol for optimal kinetic model. Kinetic results indicated that in Fischer–Tropsch synthesis (FTS) rate expression, the rate constant (k) has been increased by decreasing the catalyst particle size. The catalyst characterization was carried out using different methods including powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area measurements.     

Upgrading Siberian (Russia) crude oil by hydrodesulfurization in a slurry reactor: A kinetic study

Hydrodesulfurization (HDS) of sour crude oil is an effective way to address the corrosion problems in refineries, and is an economic way to process sour crude oil in an existing refinery built for sweet oil. In the current study, the HDS of Siberian crude oil was carried out in a slurry reactor. The Co–Mo, Ni–Mo, and Ni–W catalysts supported on γ-Al₂O₃ were compared at the temperature of 340 °C and the pressure of 4.5 MPa. The HDS activity follows the order of Co–Mo > Ni–Mo > Ni–W at a high concentration of H₂S, and the difference between Co–Mo and Ni–Mo becomes insignificant at a low concentration of H₂S. The influence of reaction temperature 320–360 °C and reaction pressure 3–5.5 MPa was investigated, and both play a positive role in the HDS reaction. A kinetic model over Ni–Mo/Al₂O₃ in the slurry reactor was established. The activation energy is estimated as 60.34 kJ·mol⁻¹; the orders of sulfur components and hydrogen partial pressure are 1.43 and 1.30, respectively. The kinetic parameters are compared with those in a trickle-bed reactor, implying that the mass transfer is greatly enhanced in the slurry reactor. The back mixing effect is present in the slurry reactor and can be reduced by a multi-stage design, which would lead to higher reactor efficiency in industrial application.     

The kinetic study of the curing reaction of mono- and di-epoxides obtained during the reaction of divinylbenzene and hydrogen peroxide with acid anhydrides

In this paper, the non-isothermal differential scanning calorimetry (DSC) was employed to investigate the cure process and to determine the kinetic parameters of the curing reactions of mono- and di-epoxides with maleic and glutaric anhydrides. The epoxides were obtained during the epoxidation process of commercially available divinylbenzene by using 60% hydrogen peroxide as the oxidant in the presence of organic solvents and magnesium oxide as the catalyst. It was found that the cure process of epoxides with maleic anhydride was described through higher values of enthalpy of polymerization (ΔH_R) and lower temperatures of the cure initiation (T_onset), the peak maximum temperature (T_max) and the final cure temperature (T_end). It can be considered to accelerate the rate of reaction and lead to an excellent network structure when maleic anhydride was used as curing agent. The kinetic analysis was firstly computed using a model free-estimation of the activation energy (Friedman, Ozawa-Flynn-Wall methods) and then the multivariate non-linear regression with a 6th degree Runge-Kutta process in a modified Marquardt procedure was employed to calculate the corresponding kinetic parameters (E_i, n_i, A_i) using the nth-order reaction f(α). The unbranched three-step process of the nth-order reaction f(α) for each step was the best to describe the cure process of mono- and di-epoxide with acid anhydrides. The determined values of the activation energies were in the range 64.7-105.2 kJ/mol for epoxides/glutaric anhydride system and 64.7-82.7 kJ/mol when maleic anhydride was used as hardening agent.     

The Effect of Operational Parameters on the Catalytic Combustion of n-Butane/Air Mixtures on Platinum Wire

The effect of mixture composition, total pressure and catalyst temperature on the kinetics of the catalytic combustion of n-butane/air or n-butane/oxygen mixtures on isothermally heated platinum wire is reported. The catalyst temperature was changed from 680 to 1,130 K for mixtures containing n-butane between 1 and 4.5% at total pressures between 10 and 100 kPa. The measurements allowed the determination of different kinetic properties like reaction rate, turnover frequency, overall and partial reaction orders and activation energy. The pressure dependence of the reaction rate offered the possibility to make a critical analysis of the kinetic equations frequently utilized in the literature.     

Simulation of hydrodesulfurization using artificial neural network

Artificial neural network (ANN) is applied to investigate the hydrodesulfurization (HDS) process with light‐cycle oil as feed and NiMo/Al₂O₃ as catalyst. ANN models frequently work as a “black box” which makes the model invisible to users and always need significant data for training. In this work, a new ANN is proposed. The Langmuir–Hinshelwood kinetic mechanism is incorporated into the model so that the proposed ANN model is forced to follow the given reaction mechanisms. Both advantages of self‐learning ability of ANN and the existing knowledge of HDS were taken into account. Lengthy training process is minimised. Effects of operating temperature, pressure, and LHSV on the sulfur removal rate are studied. The inhibition of nitrogen compounds is also investigated. It is shown that the presence of nitrogen can significantly reduce the conversion rate of sulfur components, in particularly, hard sulfur such as 4,6‐DMDBT.     

The functionalities of Pt/γ-Al2O3 catalysts in simultaneous HDS and HDA reactions

A Pt/γ-Al₂O₃ catalyst was tested in simultaneous hydrodesulfurization (HDS) of dibenzothiophene and hydrodearomatization (HDA) of naphthalene reactions. Samples of it were subjected to different pretreatments: reduction, reduction–sulfidation, sulfidation with pure H₂S and non-activation. The reduced catalyst presented the best performance, even comparable to that of Co(Ni)Mo catalysts. All catalyst samples were selective to the HDS reaction over HDA, and to the direct desulfurization pathway of dibenzothiophene HDS over the hydrogenation reaction pathway of HDS. The effect of H₂S partial pressure on the functionalities of the reduced Pt/γ-Al₂O₃ catalyst was studied. The results showed that an increase in H₂S partial pressure does not cause poisoning, but an inhibition effect, without changing the catalyst selectivity. Accordingly, the activity trends were ascribed to adsorption differences between the different reactive molecules over the same catalytic active site. TPR characterization along with a thermodynamics analysis showed that the active phase of reduced Pt/γ-Al₂O₃ is constituted by Pt⁰ particles. However, presulfidation of the catalyst leads to a mixture of PtS and Pt⁰ which has a negative effect on the catalytic performance without changing catalyst functionalities.     

Synergism and kinetics in CO oxidation over palladium-rhodium bimetallic catalysts

The activity and kinetics of CO oxidation over alumina-supported Pd-Rh bimetallic catalysts were investigated. One bimetallic catalyst, Pd-Rh(2), was prepared by two-step impregnation and another, Pd-Rh(l), by simultaneous impregnation. Monometallic catalysts as well as a physical mixture of them were also prepared. The catalysts were characterized by selective chemisorption of both H₂ and CO, and an attempt was made to determine the surface compositions of the bimetallic catalysts. The bimetallic catalysts showed different kinetic behavior, such as higher turnover frequencies (TOFs), lower apparent activation energies and/or negative reaction orders for CO which were smaller in the absolute value, from that of the monometallic catalysts as well as a physical mixture of them. It is suggested that this Pd-Rh synergism is due to an interaction on the catalyst surface, such that adsorbed CO or oxygen on one metal migrates to the other metal site so that the reaction rate is facilitated and also that the particles of Pd and Rh are located close enough to each other for the interaction to occur. On the surface of Pd-Rh (2) most of the Pd and Rh particles existed as separate entities, while a great portion of the particles on Pd-Rh(l) exhibited the surface enrichment of Pd. This explains the higher TOF and the negative reaction orders for CO over Pd-Rh(2) which were smaller in the absolute value than those over Pd-Rh(l).     

Effect of the fluorine-addition order on the hydrodesulfurization activity of fluorinated NiW/Al2O3 catalysts

Fluorinated NiW/Al₂O₃ catalysts with different orders of fluorine addition have been prepared, tested for hydrodesulfurization (HDS) of thiophene, and characterized using nitric oxide chemisorption and temperature-programmed sulfidation. The catalyst surface area has been affected by fluorine addition but not by the order of fluorination. The fluorine addition-order does not affect the amount of fluorine retained in the catalysts after the calcination and the reaction steps, either. On the other hand, the order of fluorine addition changes the dispersion of the nickel and the tungsten species, incorporation of nickel with the tungsten edge sites, and consequently the HDS activity of the catalysts. The catalyst fluorinated in the last step, i.e., after addition of both tungsten and nickel, shows the highest activity in thiophene HDS, which is supported by other experimental results indicating the most nitric oxide chemisorption and the largest incorporation of nickel with the tungsten species. Accordingly, enhancement of the catalyst activity by fluorination is due to the repartition of the metal species rather than to partial solubilization of alumina in the fluorine-addition step.     

Kinetics of the Selective Hydrogenation of Pyrolysis Gasoline

The kinetics of the selective hydrogenation of pyrolysis gasoline (pygas) over commercial Pd/Al₂O₃ catalyst particles were investigated using a stirred semi‐batch reactor in the absence of transport limitations. The effects of reaction temperature and pressure on the conversion of styrene, cyclopentadiene, cyclopentene and 1‐hexene were obtained over ranges of temperature (313–343 K) and total pressure (2–5 MPa). Competitive hydrogenation between monoolefins and diolefins was extensive, and the reaction rates of diolefins were much faster than those of the monoolefins. A Langmuir‐Hinshelwood type model was proposed and successfully fitted to the experimental data. The kinetic and adsorption parameters were estimated by using the fourth‐order Runge‐Kutta method together with the Levenberg‐Marquardt algorithm, which minimized the residual sum of squares between the experimental concentrations and the calculated values. The orders of the estimated activation energies and the adsorption parameters were consistent with the order of the reaction rates of monoolefins and diolefins.