Hydroisomerization of benzene-containing gasoline fractions on a Pt/SO 42? -ZrO2-Al2O3 catalyst: II. Effect of chemical composition on acidic and hydrogenating and the occurrence of model isomerization reactions

The acidic and hydrogenating of Pt/SO₄²⁻-ZrO₂-Al₂O₃ samples containing from 18.8 to 67.8 wt % Al₂O₃ as a support constituent were studied by the IR spectroscopy of adsorbed CO and pyridine, and the model reactions of n-heptane and cyclohexane isomerization on these catalysts were examined. The total catalyst activity in the conversion of n-heptane decreased with the concentration of Al₂O₃; this manifested itself in an increase in the temperature of 50% n-heptane conversion from 112 to 266°C and in an increase in the selectivity of isomerization to 94.2%. In this case, the maximum yield of isoheptanes was 47.1 wt %, which was reached on a sample whose support contained 67.8 wt % Al₂O₃. A maximum yield (69.6 wt %) and selectivity (93.7%) for methylcyclopentane formation from cyclohexane were also reached on the above catalyst sample. This can be explained by lower concentrations of Lewis and Br?nsted acid sites in the Pt/SO₄²⁻-ZrO₂-Al₂O₃ system, as compared with those in Pt/SO₄²⁻-ZrO₂. The experimental results allowed us to make a preliminary conclusion that the Pt/SO₄²⁻-ZrO₂-Al₂O₃ catalyst whose support contains 67.8 wt % Al₂O₃ is promising for use in the selective hydroisomerization of benzene-containing gasoline fractions in the thermodynamically favorable process temperature range of 250–300°C.     

Hydroisomerization of n-heptane over bimetal-bearing H3PW12O40 catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H₃PW₁₂O₄₀ (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H₂-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250°C and WHSV of 1.4 h^?1, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%.     

The transformations of toluene on alumina and bifunctional catalysts

The activity of Pt, Rh, and Ni catalysts deposited on Al₂O₃ and tungsten-containing catalysts 20% H₄SiW₁₂O₄₀/ZrO₂ and 15% WO_x/ZrO₂ in the hydrogenation of toluene and toluene ring opening and isomerization in the presence of hydrogen was studied. Under experimental conditions (160–360°C, 2.2 MPa), the main reactions on Rh/Al₂O₃ were the hydrogenation of toluene into methylcyclohexane, hydrogenolysis into isoheptanes, and hydrocracking into alkanes C₁–C₆. On Pt, Rh, and Ni catalysts on carriers with strong acid properties, the isomerization of the six-membered into five-membered ring followed by hydrogenolysis (hydrocracking) of alkylcyclopentanes occurred. The yield of heptane isomers, however, did not exceed 13%. The activity of Pt and Rh catalysts on a high-acidity carrier (WO_x/ZrO₂) in hydrocracking was much higher than that of catalysts based on deposited heteropoly acid. The yields of hydrogenolysis (hydrocracking) products on Ni/WO_x/ZrO₂ were much lower than on Pt(Rh)/WO_x/ZrO₂. The highest yield of ring opening products (isoheptanes and n-heptane) was obtained with layered loading of two catalysts; it reached 58 wt % at 300°C and a 2.2 MPa pressure, which was 4.5 and 2 times higher than the yield obtained on Ni-Pt/WO_x/ZrO₂ and 2% Rh/Al₂O₃ catalysts. Hydrodemethylation was not the main direction of toluene transformations on any of the catalysts studied.     

Ethylene/1-hexene copolymerization with TiCl4/MgCl2/AlCl3 catalyst in the presence of hydrogen

A TiCl₄/AlCl₃/MgCl₂ (Cat-B) catalyst containing 5.2 wt.% Al was prepared by the reaction of TiCl₄ with ethanol adduct of AlCl₃/MgCl₂ mixture. A TiCl₄/MgCl₂ catalyst (Cat-A) without doped AlCl₃ was also prepared by the same method. Ethylene-1-hexene copolymerization catalyzed by Cat-B in the presence of hydrogen showed slightly higher efficiency and higher 1-hexene incorporation than Cat-A. Comonomer incorporation was markedly increased when the cocatalyst AlEt₃ was replaced by Al(i-Bu)₃. Adding Ph₂Si(OMe)₂ as external donor in the catalyst system caused decrease in polymerization activity and 1-hexene incorporation. Each copolymer sample was fractionated into three fractions: n-heptane insoluble fraction (fraction A), n-heptane soluble and n-hexane insoluble fraction (fraction B) and n-hexane soluble fraction (fraction C). In most cases the amount of intermediate fraction (fraction B) was smaller than the other fractions and did not increase as the total 1-hexene content increase, indicating the presence of two classes of copolymer fractions with greatly different comonomer content and clear bimodality of the copolymer composition distribution. Doping AlCl₃ in the catalyst, changing cocatalyst and adding external donor mainly changed the weight ratio of fraction A to fraction C, but exerted little influences on their composition. According to the sequence distribution data of the fractions, doping AlCl₃ in the catalyst resulted in slight decrease of product of reactivity ratios (r₁r₂) in both fraction A and fraction C.     

Transformations of cyclohexane and benzene on the bimetallic Ru-Pt oxide catalysts

The bimetallic Ru-Pt/Al₂O₃ catalysts with an overall metal content of 1 wt. % and Pt: Ru weight ratios from 1: 3 to 3: 1 were studied. The catalytic activity for cyclohexane and benzene transformations, including hydrogenation, hydrogenolysis, and skeletal isomerization of the initial substrates and products of intermediate transformations, was studied at temperatures 180–350 °C and H₂ pressures from 1.0 to 5.0 MPa. The maximum yield of n-hexane from cyclohexane and benzene was obtained on the catalysts with a ruthenium content of 0.75–1.0%, being ∼29–30 wt.% at 40% selectivity. The selectivity to form n-hexane decreases with an increase in the cyclohexane conversion and is almost independent of the composition of the Ru-Pt system. On the catalysts under study, benzene is converted to the same products but at temperatures by 60 °C lower as compared to cyclohexane conversion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 633–637, April, 2006.     

Liquid-liquid equilibria for ternary acetonitrile-ethanol-saturated hydrocarbon and acetonitrile-1-propanol-saturated hydrocarbon mixtures

Isothermal vapour-liquid equilibrium data for acetonitrile-1-propanol at 45° C were measured by use of a recirculating still. The liquid-liquid equilibria of (acetonitrile-etha-nol)-(n-hexane or n-heptane or n-octane) and those of (acetonitrile-1-propanol)-(cyclohexane or n-hexane or n-heptane) were obtained from measurements of tie-lines. The experimental results were compared with those calculated from the UNIQUAC associated-solution model.     

Hydroisomerization of n-heptane over bimetal-bearing H3PW12O40 catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H₃PW₁₂O₄₀ (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H₂-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250°C and WHSV of 1.4 h⁻¹, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%. Supported by the Natural Science Foundation of China (Nos. 20306011 and 20476046), the Ph. D. Program Foundation of Chinese University (20040291002), and the Ph. D. innovation Program Foundation of Nanjing University of Technology (BSCX200506)     

Alkane oxidation by the H2O2-NaVO3-H2SO4 system in acetonitrile and water

A simple system is described, which oxidizes saturated hydrocarbons either in acetonitrile or (less efficiently) in water. The system consists of 50% aqueous hydrogen peroxide as an oxidant, sodium metavanadate, NaVO₃, as a catalyst and sulfuric (or oxalic) acid as a co-catalyst. The reactions were carried out at 20-50 °C. In the oxidation of cyclohexane in acetonitrile, the highest yield (37% based on cyclohexane) and turnover number (TON=1700) were attained after 3 h at 50 °C. The corresponding parameters were 16% and 1090 for n-heptane oxidation under the same conditions. The oxidation of higher alkanes, RH, in acetonitrile gives almost exclusively the corresponding alkyl hydroperoxides, ROOH. Light alkanes (n-butane, propane, ethane, and methane) have been also oxygenated by the system under consideration. The highest TON (200) was attained for ethane and the highest yield (19%) was obtained in the case of n-butane. The selectivity parameters measured for the oxidation of linear and branched alkanes are low, the reaction with cis- and trans-1,2-dimethylcyclohexanes is not stereoselective. These facts lead us to conclude that the oxidation occurs with the formation of hydroxyl radicals in the crucial step.     

Unexpected reactions of dichloro(ethyl)silane with DMSO in organic solvents

The effect of the solvent nature on the composition of the products formed upon the reaction between EtSi(H)Cl₂ and DMSO (molar ratio 1: 1, 0 °C) was revealed. This reaction in non-polar and low polar solvents (toluene, chloroform) gives oligoethyl(hydro)cyclo-siloxanes ((EtSi(H)O) _n , n = 3—8) as the major products in the yields up to 77%. In MeCN, oligoethyl(hydro)cyclosiloxanes are formed along with cyclic monochlorinated siloxanes ((EtSi(H)O) _n (EtSi(Cl)O), n = 2—7) in a ratio of ~7: 3 (68: 29 wt.%). In excess diethyl ether, the overall yield of oligoethyl(hydro)cyclosiloxanes does not exceed 25% and the major products are linear α,ω-diethoxyoligoethyl(hydro)siloxanes (EtO(EtSi(H)O) _n Et, n = 2—7) formed in 70—75% yields. A plausible reaction mechanism leading to the final products was suggested. Apparently, the reaction proceeds via ethyl(hydro)-and chloro(ethyl)silanones as intermediates.     

Regioselective alkane oxygenation with H2O2 catalyzed by titanosilicalite TS-1

Titanosilicalite TS-1 catalyses oxidation of light (methane, ethane, propane and n-butane) and normal higher (hexane, heptane, octane and nonane) alkanes to give the corresponding isomeric alcohols and ketones. The oxidation of higher alkanes proceeds in many cases with a unique regioselectivity. Thus, in the reaction with n-heptane the CH₂ groups in position 3 exhibited a reactivity 2.5 times higher than those of the other methylene groups. This selectivity can be enhanced if hexan-3-ol is added to the reaction mixture, the 3-CH₂/2-CH₂ ratio becoming 10. It is assumed that the unusual selectivity in the oxidation of n-heptane (and other higher alkanes) is due to steric hindrance in the catalyst cavity. As a result, the catalytically active species situated on the catalyst walls can only easily react with certain methylenes of the alkane, which is adsorbed in the cavity taking U-shape (hairpin) conformations.     

Experimental and theoretical study of surface tension of n-pentane,n-heptane,and some of their mixtures at different temperatures

The surface tension of n-pentane, n-heptane and some of their mixtures were measured at 91.3 kPa and T = (283.15 to 323.15) K by the maximum bubble pressure method. The surface tension results were correlated by a new model obtained from coupling scaled particle theory (SPT) and the MMM equation of state. The parameters of the model (SPTM3) for n-pentane and n-heptane were calculated and reported. The pure component parameters obtained for the model were used for calculating the surface tension of n-pentane and n-heptane binary mixtures at different temperatures. The comparison between the mixture surface tension results and those calculated by the model indicate that the new proposed model can be satisfactorily used for calculating the surface tension of n-pentane, n-heptane and their mixtures.     

A practical chemoenzymatic process to access (R)-quinuclidin-3-ol on scale

(±)-3-Butyryloxyquinuclidinium butyrate 6 (2 M, 571 g/L), prepared from (±)-quinuclidin-3-ol 1 and butyric anhydride, undergoes enantioselective hydrolysis by an Aspergillus melleus protease {1.0% (w/v)} in water in the presence of Ca(OH)₂ to keep the reaction at pH 7 and trap butyric acid that is introduced as part of (±)-6 and generated by the enzymatic hydrolysis. After a 24 h period, extraction with n-heptane provides (R)-quinuclidin-3-yl butyrate 5a, which, on methanolysis with Na₂CO₃, is converted into (R)-1, a common pharmacophore of neuromodulators acting on muscarinic receptors, in 96% ee and 42% overall yield from (±)-1. The unwanted antipode (S)-1, which is extracted into n-butanol and purified via its hydrochloride salt in 89% ee and 40% overall yield from (±)-1, can be racemized by the catalysis of Raney Co at 140°C under an atmosphere of H₂ (5 kg/cm²) to regenerate (±)-1 in 97% yield.     

Dynamics of the isomerization of trans-stilbene in n-alcohols studied by ultraviolet picosecond absorption recovery

We have used a simple At⁺ synchronously pumped and cavity-dumped dye-laser system to generate UV picosecond pulses with energies sufficiently high for absorption recovery experiments. With these pulses, we have studied the dynamics of the isomerization of trans-stilbene in n-alcohols as a function of viscosity and temperature. It is concluded that the excited-state barrier of trans-stilbene in n-alcohols is less than 1 kcal mol^?1 and that the trans → cis isomerization yield is 0-54 ± 0.05.     

Photochemical Reactions of Linear Alkane Radical Cations in Low-Temperature Matrices

The radical cations of linear alkanes (n-pentane, n-heptane) trapped in various matrices (Freon-11, Freon-113, Freon-113a, mixture of Freon-11 and Freon-114B2, and sulfur hexafluoride) were found to undergo the following types of photochemical reactions: (1) charge transfer to the matrix followed by neutralization, (2) isomerization and unimolecular decomposition, and (3) deprotonation. The absorption spectra of the radical cations were characterized, and the quantum yields of reactions occurring in different matrices at 77 K were determined. It was shown that the reaction pathway and efficiency of the photochemical processes observed for a given radical cation in different matrices with similar physical and chemical characteristics could considerably differ.     

Selective hydroisomerization of n-dodecane over platinum supported on zeolites

In this study, in order to develop catalysts for the selective isomerization of higher paraffin, the hydroisomerization reaction of n-dodecane was performed as a model reaction. Pt/ZSM-48, Pt/HZSM-5, Pt/HY, and Pt/SAPO-11 were examined for the selective hydroisomerization of n-dodecane. The catalysts were characterized via X-ray powder diffraction, N₂ adsorption, and the temperature-programmed desorption of ammonia. Among the catalysts studied, the Pt/HZSM-48 catalyst exhibited the best isomerization selectivity in the hydroisomerization reaction of n-dodecane, which is attributed to the moderate acid sites and medium-sized pores present in the HZSM-48. The highest iso-dodecane yield was obtained at a reaction temperature of 280 °C in the Pt/HZSM-48 catalyst. The optimal selectivity of the n-dodecane hydroisomerization over the Pt/SAPO-11 catalyst was obtained at approximately 300 °C, which was slightly higher than that of the Pt/HZSM-48 catalyst.     

Excess molar heat capacities for (decan-1-ol + n-heptane) at temperatures from (290 to 318) K. Experimental results and theoretical description using the ERAS model

The isobaric specific heat capacities were measured for (decan-1-ol + n-heptane) mixtures within the temperature range from (290.91 to 318.39) K by means of a differential scanning calorimeter. The results are explained in terms of self-association of alkanols and non-specific interactions between decan-1-ol and n-heptane. The experimental excess molar heat capacities were compared with those calculated with the aid of the ERAS model.     

Isothermal measurements of vapor-liquid equilibria for three n-alkane-chloroalkane mixtures

Results of isothermal vapor-liquid equilibrium (VLE) measurements for 1-chlorobutane with n-hexane and n-heptane at three temperatures and for 1,2-dichloroethane with n-heptane at two temperatures are reported.New constants of the Antoine vapor pressure equation for 1,2-dichloroethane are presented. The consistency of the new vapor-pressure data with published experimental data of heat of vaporization is checked.The VLE data are used for the determination of group interaction parameters of UNIFAC and of the quasichemical group surface interaction model (QUAGSIM).     

Synthesis of 3-oxatricyclo[4.4.0.02,7]decene derivatives

Unsaturated haloethers of norpinane structure were prepared by reaction of N-iodo-and N-bromosuccinimides with 1-phenyltricyclo[4.1.0.0^2,7]-heptane in the presence of unsaturated propargyl or allyl alcohol. The iodopropargyloxy derivative underwent reductive 6-exo-cyclization when treated with tributyltin hydride resulting in 5-methylene-3-oxa-2-phenyltricyclo[4.4.0.0^2,7]decane, and the iodoallyloxy derivative on heating in the presence of benzoyl peroxide suffered isomerization into 5-iodomethyl-3-oxa-2-phenyltricyclo[4.4.0.0^2,7]decene. Bromopropargyloxy and bromoallyloxy derivatives failed to undergo the reductive cyclization under the treatment with a system cobaloxime(III)-sodium borohydride, but suffered hydrogenetion at the multiple carbon-carbon bond.     

Vapor–liquid equilibrium of octane-enhancing additives in gasolines: 4. Total pressure data and GE for ternary mixtures containing isopropyl ether or benzene and n-heptane + 1-hexene at 313.15 K

The experimental isothermal P–x data at T=313.15 K for the two ternary systems (isopropyl ether+n-heptane+1-hexene) and (1-hexene+n-heptane+benzene) are reported. Data reduction by Barker’s method provides correlation for G^E. The Wohl expansion, also Wilson, NRTL and UNIQUAC models have been applied successfully to the ternary systems. The experimental data, in this work are not available in the literature.     

Photochemical transformations—I : Reactions of some terpene iodides

Photo-irradiation of longibornyl iodide in n-heptane containing some triethylamine as scavenger for hydrogen iodide, furnished rearranged hydrocarbons (longifolene, longicyclene and longiborn-8-ene). Citronellyl iodide, under similar conditions, led to simple elimination (to furnish 2,6-dimethylocta-2,7-diene) and π-participation (to yield trans-p-menth-8-ene) to almost equal extent. A possible mechanism for these reactions is discussed.