The Role of Nitrogen in Facilitating Methylcyclohexane Aromatization on Pt/Al2O3 and Pt-Re/Al2O3 Catalysts

The kinetics of methylcyclohexane aromatization on commercial Pt/Al₂O₃ and Pt-Re/Al₂O₃ catalysts was investigated in a micro-reactor using N₂ and/or H₂ as carrier gases at temperatures ranging between 300-500°C, W/F values ranging between 0.83-3.75 mg min/mL and at a total pressure of 4.0 kg/cm². On both catalysts in N₂ atmosphere, aromatization accompanied by demethylation was observed with the formation of cracked products, benzene and toluene. However, in H₂ methane was the predominant product of methylcyclohexane reforming on PtA1₂O₃ and Pt-Re/Al₂O₃ at 500°C and 400-500°C respectively, whereas at 350°C, aromatization was predominant on Pt/Al₂O₃ but on Pt-Re/Al₂O₃, aromatization was accompanied by fragmentation to methane. In N₂-H₂ mixtures, demethylation activity was observed to decrease with H₂ content of the mixture on Pt-Re/Al₂O₃. A preliminary test of the kinetic data using Sica's method of pulse kinetic analysis suggests a first order rate in methylcyclohexane with activation energies of 3.21 kcal/gmol in N₂ and 19.70 kcal/gmol in H₂ for the Pt/Al₂O₃ catalyst and 16.66 kcal/gmol in N₂ and 34.94 kcal/gmol in H₂ for the Pt-Re/Al₂O₃ catalyst. However, a more comprehensive kinetic analysis suggested an aromatization mechanism for Pt-Re/Al₂O₃, where adsorbed H₂ was a participant. A different aromatization mechanism for the reaction in N₂ where hydrogen was not needed explained the data on Pt/Al₂O_3. In both cases, the desorption of toluene was determined as the rate determining step.     

COMPARATIVE REACTION STUDY OF METHYLCYCLOHEXANE AND 3-METHYLHEXANE IN H2 AND N2 ON Pt/Al2O3 CATALYST

ABSTRACT

The reaction of methylcyclohexane and 3-methylhexane were studied in a pulse microcatalytic reactor using H₂ and N₂ carriers on Pt/Al₂O₃ catalyst at temperatures from 350 to 500°C, contact times (W/F) of 1.25 × 10^?3–3.75 × 10^?3 g min/ml and a total pressure of 4.0 kg/cm². In N₂, there was complete conversion of methylcyclohexane to methane, benzene and toluene while similar products were produced for 3-methylhexane, albeit with diminished conversion level. In H₂, methane was produced from 3-methylhexane conversion while aromatization without demethylation was obtained in addition to some cracking for methylcyclohexane at the low temperature range (350–400°C); a higher temperature range (460–500°C) resulted in complete fragmentation for methylcyclohexane. In H₂–N₂ mixtures, the presence of N₂ of not less than 50% in the carrier gas stream yielded an aromatic catalyst at conditions where only cracking activity was previously evident. The differences in product distribution and/or product types for the two reactants in H₂ and N₂ suggest a different reaction mechanism for both reactants.     

KINETIC INVESTIGATION OF METHYLCYCLOPENTANE REFORMING ON FRESH AND DEACTIVATING Pt/Al2O3 CATALYST

ABSTRACT

The conversion of methylcyclopentane (MCP) in hydrogen on fresh and deactivating Pt/Al₂O₃ catalyst to hydrogenolysis products (2-methylpentane, 3-methylpentane and n-hexane), cyclohexane and benzene was studied in a Berty CSTR at various partial pressures of MCP and H₂, and at a total pressure of 1 atm. For the kinetic studies, temperatures between 370 – 400° and W/F values up to 0.33 g min/cm³ were used. The conversion of MCP was found to increase with increase in temperature at all the MCP partial pressures investigated. The hydrogenolysis products and benzene composition generally increased with increase in temperature and W/F. The mechanism for the reforming of MCP was similar to that proposed by Dartigues et al. (1978) except that the formation of hydrogenolysis products was accounted for in this formulation. Eleven rate models were developed and tested and six satisfied the set criteria. Since hydrogenation/dehydrogenation and desorption steps are relatively rapid, the conversion step to hydrogenolysis products was deemed the only rate determining step with an activation energy of 36.31 kcal/gmol. For the deactivation studies, the model of Corella and Asua (1982) was used for the development of two deactivation models. The only model found to predict the deactivation behavior was the step leading to the formation of the coke precursor as rate controlling.     

REFORMING OF N-OCTANE ON A Pt/Al2O 3 CATALYST. 1. PRODUCT DISTRIBUTION AND KINETIC ANALYSIS.

ABSTRACT

The conversion of n-octane on Pt/Al₂O₃ catalyst to hydrocracked products, isooctane, ethylbenzene, o-,p-,m-xylene and toluene was investigated in hydrogen in a Berty CSTR at three different partial pressures of n-octane, 101·325 KPa total pressure, temperatures between 400°C-460°C and W/F values up to 0·33gmincm^-3. The hydrocracked products were the most predominant. Of the other products, isooctane was present in the highest yield. A sequence of elementary steps based on the suggested reaction network of Ako and Susu (1986) was found to predict the experimental conversion-W/F data with the conversion of adsorbed isooctane to adsorbed o-xylene as the rate determining step. The activation energies for the forward and backward reactions of this step were determined to be 21·2 and 14·3 Kcal/gmol, respectively.     

REFORMING OF N-OCTANE ON A Pt/Al2O3 CATALYST. II. KINETIC ANALYSIS OF HYDROGEN DEPENDENCE.

ABSTRACT

The conversion of n-octane on Pt/Al₂O₃ catalyst was found to pass through pronounced maxima with the variation of the partial pressure of hydrogen at temperatures between 420°C-460°C, P_N = 7·63 × 10^-3 atm and W/F = 0·11lg min cm_-3. The products of reaction were hydrocracked products, octane, ethylbenzene, o-.p-,m,-xylene and toluene. The order of appearance of the optimum PH for the various reactions were: Isooctane>Dehydrocyclized products>Hydrocracked products.

A sequence of elementary steps earlier postulated was found to predict the maximum in the n-octane P_H profiles for the three temperatures investigated. The rate determining steps for the two rate equations that were found suitable were conversion of adsorbed isooctane to adsorbed o-xylene and ethylbenzene.     

Desulfurization of FCC Gasoline Over Mordenite Modified with Al2O3

Abstract

Mordenite modified with Al₂O₃ (Al₂O₃/mordenite) was synthesized and used for the desulfurization of FCC gasoline. The influences of operating parameters on the results were studied for the model solution composed of dibenzothiophene (DBT) and isooctane. Al₂O₃/mordenite exhibits higher sulfur capacity than other kinds of chemisorbents. The suitable composition of the chemisorbent is 30 wt% Al₂O₃ to 70 wt% mordenite. The optimal operating parameters are: temperature 160°C; velocity 3 h^?1 (WHSV). Under the stated conditions, desulfurization was carried out for the FCC gasoline with sulfur content of 220.4 μg/g. The chemisorbent can maintain the sulfur content under 50 μg/g for 40 h and has good regeneration ability after desorption using benzene.     

Role of Mn/Al2O3 catalyst in deep oxidative desulfurization of diesel

Abstract

In this work, a series of supported manganese catalyst has been synthesized and utilized in oxidative desulfurization to remove 4,6-dimethyldibenzothiophene (4,6-DMDBT), dibenzothiophene (DBT) and thiophene. The influences of catalyst parameters were investigated including manganese precursors, manganese loading and calcination temperature in details. The synthesized catalyst was characterized by scanning electron microscopy (SEM), N₂ adsorption/desorption and X-ray diffraction (XRD) techniques. 90.2% of 4,6-DMDBT, 98.5% of DBT and 95.5% of thiophene conversion were achieved under mild operational conditions using 3Mn(NO₃)₂/Al₂O₃ at 500?°C calcination temperature. A slight decrease in desulfurization activity was observed after Mn/Al₂O₃ catalyst being used in five cycles ODS.     

Mechanistic Kinetic Models for n-Heptane Reforming on Platinum/Alumina Catalyst

Abstract

The kinetics of the reforming of n-heptane on a platinum/alumina catalyst has been studied in a pulse microcatalytic reactor at a total pressure of 391.8 kPa over a relatively wide temperature range of 420°C–500°C. The differential and integral methods were used for the kinetic analyses of the reforming reaction. Twenty-nine reaction rate equations of the Langmuir-Hinselwood-Hougen-Watson type, based on molecular and atomic adsorption of hydrogen, were developed. Parameter estimates for the n-heptane reforming reactions were obtained by application of the Nelder-Mead simplex optimization technique to the predicted and observed conversion/production rates of the reaction components. Discrimination among rival kinetic models was based upon physicochemical criteria, analysis of the residuals, and statistical and thermodynamic tests. The rate-determining step was found to be the surface reaction of adsorbed iso-heptane to adsorbed methylcyclohexane with dissociative adsorption of hydrogen on the catalyst surface during dehydrocyclization of iso-heptane to methylcyclohexane. Hence, the surface reaction on the metallic function is rate-determining for the n-heptane reforming on the Pt/Al₂O₃ catalyst.     

COMPARATIVE REACTION STUDY OF METHYLCYCLOHEXANE AND 3-METHYLHEXANE IN H2 AND N2 ON Pt/Al2O3 CATALYST

The reaction of methylcyclohexane and 3-methylhexane were studied in a pulse microcatalytic reactor using H₂ and N₂ carriers on Pt/Al₂O₃ catalyst at temperatures from 350 to 500°C, contact times (W/F) of 1.25 × 10^-3-3.75 × 10^-3 g min/ml and a total pressure of 4.0 kg/cm². In N₂, there was complete conversion of methylcyclohexane to methane, benzene and toluene while similar products were produced for 3-methylhexane, albeit with diminished conversion level. In H₂, methane was produced from 3-methylhexane conversion while aromatization without demethylation was obtained in addition to some cracking for methylcyclohexane at the low temperature range (350-400°C); a higher temperature range (460-500°C) resulted in complete fragmentation for methylcyclohexane. In H₂-N₂ mixtures, the presence of N₂ of not less than 50% in the carrier gas stream yielded an aromatic catalyst at conditions where only cracking activity was previously evident. The differences in product distribution and/or product types for the two reactants in H₂ and N₂ suggest a different reaction mechanism for both reactants.     

Desulfurization using an oxidation/catalysis/adsorption scheme over H3PW12O40/SiO2−Al2O3 1

A desulfurization experiment was performed with tert-butyl hydroperoxide (t-BuOOH) as the oxidant in the presence of H₃PW₁₂O₄₀/SiO₂₋Al₂O₃ as the catalyst prepared by the sol-gel method, by using dibenzothiphene (DBT) in petroleum ether as the model compound. This work presents the results for the desulfurization by an oxidation/catalysis/adsorption scheme. The effects of catalyst amounts, t-BuOOH amounts, reaction temperature, and reaction time on the desulfurization efficiency and regeneration performance of the catalyst were studied. It was found that the H₃PW₁₂O₄₀/SiO₂-Al₂O₃ catalyst presented a higher maximum desulfurization conversion than SiO₂-Al₂O₃ solids also prepared by the sol-gel method. In addition, the H₃PW₁₂O₄₀/SiO₂-Al₂O₃ catalyst showed a higher desulfurization conversion after regeneration with N,N-dimethylamide. It was also found that the oxidation agent t-BuOOH resulted in a higher desulfurization conversion than hydrogen peroxide (H₂O₂). The text was submitted by the authors in English.     

Study on flame propagation of premixed N2O–NH3/N2O–NH3–C3H8 in cylindrical vessels

The flame propagation behavior of premixed N₂O–NH₃/N₂O–NH₃–C₃H₈ was experimentally investigated in elongated vented cylindrical vessels with central ignition. The effect of vessel diameter and propane concentration ([C₃H₈] = 1.96–7.41 wt.%) on the process of flame acceleration was studied and discussed. The results revealed that the maximum value of flame acceleration rate was found in the cylindrical vessel with an inner diameter of 7 mm, followed by 5 mm, 10 mm, and 15 mm. At a constant vessel diameter, the rate of flame acceleration was noticeably improved by adding propane ([C₃H₈] = 1.96–3.85 wt.%) to the premixed N₂O–NH₃. However, a further increase in the propane fraction up to 5.66%, caused a decline in the flame acceleration rate, probably as a consequence of a combined effect between the reduction of oxygen and greater dilution of the ammonia in the total concentration.     

Preparation and characterization of FeNi/Al2O3 catalysts for production of light olefins

The 24%Fe-36%Ni/Al₂O₃ catalyst was prepared using sol-gel method. This research investigated many variable factors for conversion synthesis gas to C₂?CC₄ light olefins by using Fisher-Tropsch synthesis. The effects of calcination atmospheres and calcination heating rates and also operation conditions such as the H₂/CO molar feed ratios, gas hourly space velocity (GHSV), temperatures and total reaction pressure on the catalytic performance of 24%Fe-36%Ni/Al₂O₃ catalyst was investigated. The stability of the catalyst for 240 h has been tested at optimal operating conditions (T = 260°C, H₂/CO = 2/1, GHSV = 3200 h^?1 and P = 3 bar). The results indicated that this catalyst was highly stable for production C₂?CC₄ light olefins. Characterization of precursors and calcined catalysts were carried out by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area measurement, temperature program reduction (TPR) and thermal analysis methods such as thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).     

Hydrogen production by catalytic methane decomposition over Ni,Co, and Ni-Co/Al2O3 catalyst

Hydrogen is a chief source of energy. Catalytic decomposition produces hydrogen and carbon. In this work, x%M/Al₂O₃ (where M is Ni, Co and combined Ni-Co, and x is 10%, 15%, and 30%) has been successfully employed as a catalyst. The effect of activation temperature and active metal type and loading on catalyst perfomance was investigated. The catalysts were characterized with BET, XRD, TPO, TPR, TEM, XPS, and Raman. The results displayed that the 30%Co/Al₂O₃ catalyst activated at 500°C provided the greatest catalytic performance toward methane conversion. 30%Co/Al₂O₃ catalyst activated at 500°C formed amorphous carbon.     

The Effect of Metal Dispersion on Ni/Al2O3 Wax Hydrofining Catalyst

Abstract

Positron annihilation spectroscopy for chemical analysis (PASCA), powder x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) were used to study the effect of calcination temperature on active metal dispersion of wax hydrofining catalyst. The experimental results showed that, with the increase of calcination temperature, the metal Ni and the support Al₂O₃ interaction became weaker. When calcination temperature reached 280°C, Ni(NO₃)₂ began to decompose and the inhibition effect of NO₃ ^? began to diminish. At 380°C, Ni(NO₃)₂ was almost decomposed, and NiO still had a high dispersion on the catalyst surface. At 440°C or higher, Ni(NO₃)₂ was completely decomposed, and to some extent, NiO aggregated on the catalyst surface in the form of noncrystalline clusters (atomic clusters). The most suitable calcination temperature in the experiment for the catalyst Ni/Al₂O₃ was 440°C or a little higher.     

Selective Oxidation of Cyclohexane Using a Co-M/Al2O3 Catalyst without Additives

Abstract

Without any organic solvent or activator, the selective oxidation of cyclohexane with air to afford cyclohexanol and cyclohexanone was investigated over Co/Al₂O₃ and Co-M/Al₂O₃ (M = Cu, Zn, and Ni) catalysts prepared by sol-gel method. The activity of the catalysts decreases in the following order: Co-Ni/Al₂O₃ > Co/Al₂O₃ > Co-Zn/Al₂O₃ > Co-Cu/Al₂O₃. The optimum contents of cobalt and nickel are 4.0 wt% and 3.0 wt% in Co-Ni/Al₂O₃ catalyst, respectively. The best result was obtained over Co-Ni/Al₂O₃ catalyst with a conversion of 9.9% and a selectivity of 94.6% and the ratio of cyclohexanone to cyclohexanol of 2.8 when the reaction was carried out at 443 K for 120 min under 4.5 MPa, and catalytic activity did not change after five consecutive reactions.     

An in situ study of dimethyl ether conversion over HZSM-5/Al2O3 zeolite catalysts by high-temperature diffuse reflectance infrared fourier transform spectroscopy

Isolated and associated OH groups have been in situ identified by high-temperature diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of the surface of zeolites calcined until complete removal of water. It has been shown that the Brønsted acid sites (BASs) involved in dimethyl ether (DME) conversion on the zeolite surface exhibit two characteristic bands in the DRIFT spectra. It has been found that the composition of DME conversion products on HZSM-5 zeolite catalysts modified with Mg or Rh is temperature-dependent. Ethanol and a small amount of methanol were detected on an Rh-HZSM-5/Al₂O₃ zeolite catalyst at T = 270°C and were not observed on Mg-HZSM-5/Al₂O₃ under the same conditions. Spectral features of ketene were detected in the DRIFT spectra of the surface of Mg-HZSM-5/Al₂O₃ in a stream of DME. The spectrum of Rh-HZSM-5/Al₂O₃ calcined at 200°C exhibited spectral features of ethyl alcohol and bands characterizing a strong Lewis acid site (LAS) capable of hydrogenating ketene to ethyl alcohol. The spectra of the surface of all the zeolite catalysts tested in a DME stream at 320°C contain bands characterizing olefins and alkanes and do not exhibit the spectral features of alcohols and ketene.     

Various characteristics of Ni and Pt–Al2O3 nanocatalysts prepared by microwave method to be applied in some petrochemical processes

Alumina-supported metal nanocatalysts were prepared via the microwave method, by loading nano Ni particles (at 1, 3 and 5 wt%) or nano Pt particles (at 0.3, 0.6 and 0.9 wt%). Structural and adsorption features of the nano catalysts were revealed through XRD, DSC-DTA, TEM, H₂-chemisorption and N₂-physisorption. N₂-adsorption–desorption isotherms of type IV were related typically to mesoporous materials with H₂ class of hysteresis loops characterizing ink bottle type of pores. The well dispersed nano-sized metal particles were evidenced in the studied catalytic systems, exhibiting marked thermal stability up to 800 °C. The catalytic performances of different catalyst samples were assessed during cyclohexane, normal hexane and ethanol conversions, using the micro-catalytic pulse technique at different operating conditions. The 5% Ni–γ–Al₂O₃ sample was found to be the most active in dehydration of ethanol to produce ethylene, as well as in n-hexane cracking. However, the 1% Ni–Al₂O₃ sample showed the highest dehydrogenation activity for selective production of benzene from cyclohexane. On the other hand, the 0.9% Pt–γ–Al₂O₃ sample exhibited the highest activity in the dehydration of ethanol and in the dehydrogenation of cyclohexane. The 0.3% Pt–γ–Al₂O₃ sample was the most active in the dehydrocyclization of normal hexane, as compared to the other catalyst samples under study.     

Recovery of precious metals from spent Mo–Co–Ni/Al2O3 catalyst in organic acid medium: Process optimization and kinetic studies

In present study, the leaching kinetics of the spent Mo–Co–Ni/Al₂O₃ catalyst was investigated in the presence of formic acid as an organic leaching agent. Firstly, the spent catalyst was roasted in different roasting temperature (200–700?°C) and time (15–240?min), the maximum metal extraction was achieved that at 500?°C with 90?min. Then, the leaching experiments were carried out to determine the influences of process parameters following; particle size, liquid/solid ratio, formic acid concentration, leaching temperature, leaching time and stirring speed. According to the experimental results, the highest dissolution rates of molybdenum (Mo, 75.82%), cobalt (Co, 96.81%), nickel (Ni, 93.44%) and aluminum (Al, 19.46%) were reached under optimum experimental conditions; particle size +75???30?µm; liquid/solid ratio 10?ml/g; formic acid concentration 0.6?M; leaching temperature 80?°C; leaching time 90?min and stirring speed 300 r/min. Moreover, the leaching kinetics clearly reveal that the leaching reaction is controlled by liquid film diffusion and that the activation energy values (E_a) of Co, Ni, Mo and Al were to be 24.49, 25.98, 32.36 and 33.47?kJ/mol, respectively. In conclusion, the leaching process can be conducted in the presence of formic acid for the various industrial wastes in similar structure and composition to Mo–Co–Ni/Al₂O₃ spent catalyst.     

Catalytic Performance of Modified HZSM-5/Al2O3 Catalysts for Nonhydrodewaxing

The HZSM-5/Al₂O₃ molecular sieve catalyst was modified by phosphoric acid, tetraeth-oxysilane, tetrabutyl titanate, and boric acid, respectively. Properties of modified catalysts are characterized. The results show that the specific surface area declines and the acid density increases after modification of the catalysts, and the strong acid strength of Si/HZSM-5/Al₂O₃ catalyst enhanced. Modified catalysts performances are evaluated on fixed bed reactor using hydrocracking tail oil from a refinery as raw material. Results show that the Si/HZSM-5/Al₂O₃ catalyst has better catalytic dewaxing effect and stability than the other modified catalysts.     

Stability of La-Zr-HZSM-5/Al2O3 zeolite catalysts in the conversion of dimethyl ether to lower olefins

The stability of the zeolite component and a La-Zr-HZSM-5/Al₂O₃ catalyst synthesized on its basis in the synthesis of lower olefins from dimethyl ether (DME) has been studied. It has been shown that both the zeolite component and the catalyst based on it exhibit highly stable catalytic properties. A high-temperature treatment of the zeolite component and the finished La-Zr-HZSM-5/Al₂O₃ catalyst with air and steam, respectively, leads to a significant increase in the catalyst selectivity for olefins, particularly propylene, while the activity in the DME conversion slightly decreases as the steaming temperature increases from 500 to 750°C.