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Hydrogen Pressure (hydrogen + pressure)
Selected AbstractsCatalytic Reductive Etherification of Ketones with Alcohols at Ambient Hydrogen Pressure: A Practical, Waste-Minimized Synthesis of Dialkyl Ethers.CHEMINFORM, Issue 16 2007Lukas J. Goossen Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Effects of hydrogenation parameters on trans isomer formation, selectivity and melting properties of fatEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 3 2008Anar Musavi Abstract Effects of hydrogenation conditions (temperature, hydrogen pressure, stirring rate) on trans fatty acid formation, selectivity and melting behavior of fat were investigated. To this aim, soybean oil was hydrogenated under various conditions and fatty acid composition, trans isomer formation, slip melting point (SMP), solid fat content (SFC) and iodine number (IV) of the samples withdrawn at certain intervals of the reactions were monitored. A constant ratio (0.03%) of Nysosel 222 was used in the various combinations of temperature (150, 165 and 180,°C), stirring speed (500, 750 and 1000,rpm) and hydrogen pressure (1, 2 and 3,bar). Raising the temperature increased the formation of fatty acid isomers, whereas higher stirring rates decreased this formation, while changes in hydrogen pressure had no effect or slightly reduced it, depending on other parameters. Results also indicated that the trans fatty acid ratio increased with IV reduction, reached the highest value when the IV was about 70 and decreased at IV < 70 due to saturation. Selectivity values (S21) at that point ranged between 5.78 and 11.59. Lower temperatures and higher stirring rates decreased not only the trans isomer content but also the S21 values at significant levels. However, same effects were not observed with the changes in hydrogen pressure. It was determined that a high SMP does not necessarily mean a high SFC. Selective conditions produced samples with higher SFC but lower SMP, which is possibly because of higher trans isomer formation as well as lower saturation. [source] Enantioselective Synthesis of Chiral Tetrahydroisoquinolines by Iridium-Catalyzed Asymmetric Hydrogenation of EnaminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Pu-Cha Yan Abstract Chiral iridium complexes based on spiro phosphoramidite ligands are demonstrated to be highly efficient catalysts for the asymmetric hydrogenation of unfunctionalized enamines with an exocyclic double bond. In combination with excess iodine or potassium iodide and under hydrogen pressure, the complex Ir/(Sa,R,R)- 3a provides chiral N -alkyltetrahydroisoquinolines in high yields with up to 98% ee. The L/Ir ratio of 2:1 is crucial for obtaining a high reaction rate and enantioselectivity. A deuterium labeling experiment showed that an inverse isotope effect exists in this reaction. A possible catalytic cycle including an iridium(III) species bearing two monophosphoramidite ligands is also proposed. [source] Hydrogenation of Phenol in Supercritical Carbon Dioxide Catalyzed by Palladium Supported on Al-MCM-41: A Facile Route for One-Pot Cyclohexanone FormationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009M. Chatterjee Abstract The hydrogenation of phenol has been carried out in supercritical carbon dioxide (scCO2) under very mild reaction conditions at the temperature of 50,°C over palladium supported Al-MCM-41 (metal loading ,1%). This palladium catalyst is shown to be highly active and promotes the selective formation of cyclohexanone (,98%), an industrially important compound, in a "one-pot" way. The effects of different variables like carbon dioxide and hydrogen pressure, reaction time and also silica/alumina ratio of the MCM-41 support along with palladium dispersion are presented and discussed. The pressure effect of carbon dioxide is significantly prominent in terms of conversion and cyclohexanone selectivity. Moreover, the silica/alumina ratio was also found to be an important parameter to enhance the effectiveness of the catalyst as it exhibits a remarkable increase in phenol conversion from 20.6% to 98.4% as the support changes from only silica MCM-41 to Al-MCM-41. A plausible mechanism for the hydrogenation of phenol to cyclohexanone over the palladium catalyst has been proposed. The proposition is validated by transition state calculations using density functional theory (DFT), which reveal that cyclohexanone is a favorable product and stabilized by <19,kcal,mol,1 over cyclohexanol in scCO2 medium. Under similar reaction conditions, phenol hydrogenation was also carried out with rhodium, supported on Al-MCM-41. In contrast to the palladium catalyst, a mixture of cyclohexanone (57.8%) and cyclohexanol (42.2%) was formed. Detailed characterization by X-ray diffraction and transmission electron microscopy confirmed the presence of metal nanoparticles (palladium and rhodium) between 10,20,nm. Both the catalysts exhibit strikingly different product distributions in solventless conditions compared to scCO2. This method can also be successfully applied to the other hydroxylated aromatic compounds. [source] Kinetic Study of the Asymmetric Hydrogenation of Methyl Acetoacetate in the Presence of a Ruthenium Binaphthophosphepine ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Eva Öchsner Abstract The asymmetric hydrogenation of methyl acetoacetate (MAA) in methanol using dibromobis{(S)-4-phenyl-4,5-dihydro-3H -dinaphtho[2,1- c: 1,,2,- e]phosphepine}-ruthenium was studied in detail. For the determination of the reaction network, data from kinetic experiments were compared to different possible reaction networks using the kinetic software Presto Kinetics. The simulation was optimised to describe the reaction accurately with a minimal set of process parameters and reaction equations. For the best model the reaction orders, collision factors and activation energy of all reaction steps were determined. Additionally, the influence of reaction temperature and hydrogen pressure on the enantiomeric excess (ee) of the reaction was studied. It was found that high reaction temperatures and high hydrogen pressures result in increasing enantioselectivities. [source] Convenient General Asymmetric Synthesis of Roche Ester Derivatives through Catalytic Asymmetric Hydrogenation: Steric and Electronic Effects of LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2008Cyrielle Pautigny Abstract An efficient and concise asymmetric hydrogenation of acrylate esters promoted by the cationic ruthenium monohydride complex [Ru(H)(,6 -cot)SYNPHOS]+BF4, is reported. A full investigation of the effects of catalyst precursors, solvents, temperature, hydrogen pressure, substrates as well as steric and electronic properties of ligands was carried out. The corresponding valuable Roche ester derivatives were obtained in good to excellent isolated yields and high enantioselectivities under mild conditions. The robustness and practicability of this highly enantioselective hydrogenation was demonstrated by the synthesis of the 3-hydroxy-2-methylpropanoic acid tert -butyl ester on a multigram scale, resulting in excellent yield and ee up to 94%. [source] Enantioselective Hydrogenation of N -Acetyldehydroamino Acids over Supported Palladium CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2007György Szöll Abstract The enantioselective hydrogenation of two N -acetyldehydroamino acids over Cinchona alkaloid-modified, supported palladium catalysts has been studied. Moderate enantioselectivities, up to 36,%, were obtained in the hydrogenation of 2-acetamidocinnamic acid over cinchonidine-modified Pd/TiO2 under low hydrogen pressure. Increase in the pressure or use of benzylamine as additive led to a gradual decrease in the enantiomeric excess and eventually inversion of the sense of the enantioselectivity. On the contrary, the optical purity of the product resulting from the hydrogenation of 2-acetamidoacrylic acid was significantly increased by addition of benzylamine to the reaction mixture. Enantiomeric excess values up to 58,% and 60,% were obtained over Pd/Al2O3 modified by cinchonidine and cinchonine, respectively. These optical purities are the best obtained in the hydrogenation of dehydroamino acid derivatives over chirally modified heterogeneous metal catalysts. [source] Dramatic Pressure Effects on the Selectivity of the Aqueous/Organic Biphasic Hydrogenation of trans -Cinnamaldehyde Catalyzed by Water-Soluble Ru(II)-Tertiary Phosphane ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2003Gábor Papp Abstract In a water/chlorobenzene biphasic reaction, the hydrogenation of trans- cinnamaldehyde, catalyzed by water-soluble Ru(II)-phosphane complexes at pH,3.04 (phosphate buffer), produces a 61:39 mixture of cinnamyl alcohol and dihydrocinnamaldehyde at 1,bar H2; however, the selectivity is increased to 93:7 by increasing the hydrogen pressure to 8,bar. [source] Synthesis and characterization of low relative molecular weight trans -1,4-poly(isoprene)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Huafeng Shao Abstract Low relative molecular weight trans-1,4-polyisoprene oligomers were synthesized successfully by bulk precipitation and solution polymerization with supported titanium catalyst using hydrogen as relative molecular weight modifier. The effects of polymerization conditions on intrinsic viscosity ([,]), catalyst efficiency (CE) and structure of polymer were studied. Increasing the hydrogen pressure resulted in the decrease of [,] of the polymer. With the increasing of hydrogen pressure and reaction temperature, CE decreased but still maintained above 2500 g polymer/g Ti. The percentage composition of (trans-1, 4-unit) in the polymer was over 90% in all results. The crystallinity of polymer was about 50,60% with Tm being about 60°C. The relative molecular weight distribution index (MWD) was quite difference according to the polymerization method. While number average molecular weight (Mn) exceeded 860, polymer turned from viscous materials to fragile wax materials, and then to toughness materials at 1800. Dynamic property testing showed that the additional of this oligomer could increase the wet-skid resistance of the rubber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Comparative study of hydrogen, argon, and xenon uptake into a propane hydrateAICHE JOURNAL, Issue 10 2010Joanne A. Abbondondola Abstract The rate of absorption of hydrogen, argon, and xenon into a Type II propane clathrate hydrate has been studied. The propane hydrate is synthesized from 250-,m ice grains, is estimated to have a porosity of 65% and has roughly the consistency of chalk. Hydrogen is rapidly absorbed by the hydrate sample and approaches the equilibrium vapor pressure in an hour before a very slow residual absorption process ensues. For an initial hydrogen pressure of 1.5 MPa, about 4.5% of the available 512 cages are occupied by hydrogen after 1 h, and 4.9% after 18 h. In contrast, for both argon and xenon significantly more gas is absorbed by the hydrate but at a much slower rate: about 5% as fast for xenon and 1% as fast for argon. We conclude that hydrogen readily diffuses through the propane hydrate microcrystal structure, while argon and xenon are probably absorbed by growing new double hydrate while consuming the propane hydrate. Although considerably higher pressures would be required to store significant quantities of hydrogen in propane hydrate, it appears that the crystal can be loaded and emptied in relatively short times. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Corrosion monitoring of hydrogen by HUP probe in the presence of sulphide and thioureaMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2010A. Abbassi Abstract The effect of sulphide and thiourea on hydrogen uptake during the corrosion of steel in deaerated pH3 has been studied using an electrochemical hydrogen probe incorporating a solid electrolyte (HUP) and lead dioxide (PbO2) as a reference electrode. This probe has been used for the quantitative determination of the hydrogen activity generated during the corrosion of steel. The sensor voltage implies an average equivalent hydrogen pressure in uncharged steel of 2,×,10,18 atmospheres. During the corrosion of steel, this value increases by very large amounts; thus in deaerated pH3, the equivalent pressure rose by 1024.5 in the presence of 200 ppm sulphide and by 102 in the presence of 100 ppm thiourea. Weight loss and AC impedance methods were also performed under the same conditions as the hydrogen measurements. The hydrogen probe data were correlated with a.c impedance and weight loss results in order to understand the effect of S2, and thiourea on hydrogen uptake. [source] Catalytic behavior of wool,Rh complex in asymmetric hydrogenation of 2-methyl furan,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3-5 2003Man He Abstract A Wool,Rh complex was prepared by the reaction of wool with RhCl3·3H2O in ethanol solution, and was found to be useful as a chiral catalyst for the asymmetric hydrogenation of 2-methyl furan to (S)-(+)-2-methyl tetrahydrofuran at 28,°C and under atmospheric hydrogen pressure. When an appropriate Rh content in the Wool,Rh complex was selected, the yield and optical yield amounted to 53.7 and 76.9%, respectively, and the Wool,Rh complex catalyst could be reused several times without any noticeable loss in its optical catalytic activity. Wool is a very cheap natural biopolymer ligand, and Wool,Rh complex is very easy to prepare, and it is a very active, enantioselective and stable chiral catalyst for asymmetric hydrogenation of 2-methyl furan. Copyright © 2003 John Wiley & Sons, Ltd. [source] Catalytic behaviors of silica-supported methylcellulose- L -phenyl alanine,platinum complexes in asymmetric hydrogenation of diacetone alcoholPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3-4 2002Kai Huang Abstract A new chiral natural bio-polymer,metal complexe, silica-supported methylcellulose- L -phenyl alanine,platinum complex (SiO2 -MC- L -Phe,Pt) has been prepared by a very simple method, and the Pt complex has been found to be able to catalyze the asymmetric hydrogenation of diacetone alcohol to give (R)-(,)-2-methyl-2,4-pentandiol at room temperature and under atmospheric hydrogen pressure. The product and optical yields of 2-methyl-2,4-pentandiol amounted to 67.0 and 92.7%, respectively. The product and optical yields were remarkably affected by the Pt content in the complex, the kind of solvent and the reaction temperature. This catalyst was very stable and could be reused several times without any remarkable change in optical catalytic activity. Copyright © 2002 John Wiley & Sons, Ltd. [source] Asymmetric hydrogenation ofo -Cresol andm -Cresol catalyzed by silica-supported methylcellulose,L-alanine,Pd complexPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2001Kai Huang Abstract Silica-supported methylcellulose,L-alanine,palladium complex (SiO2 -MC,LA,Pd) has been prepared and found to be a high optically active catalyst for asymmetric hydrogenation of o -cresol and m -cresol to give (S)-2-methylcyclohexanone and (R)-3-methylcyclohexanone, respectively, at 25,°C and under an atmospheric hydrogen pressure. The optical yields of (S)-2-methylcyclohexanone and (R)-3-methylcyclohexanone amounted to 91.5 and 68.5%, respectively, when optimum Pd content in SiO2 -MC,LA,Pd complex, reaction temperature and solvent were selected. SiO2 -MC,LA,Pd catalyst also has shown high stability. The optical yields for (S)-2-methylcyclohexanone and (R)-3-methylcyclohexanone were kept over 90 and 60%, respectively, when the catalyst was reused several times. Moreover, SiO2 -MC,LA,Pd complex is an economical catalyst. The methylcellulose is an abundant natural biopolymer and the procedure for preparation of the complex is very simple. Copyright © 2001 John Wiley & Sons, Ltd. [source] Hydrogenolysis of glycerol with FeCo macrocyclic complex bonded to Raney Nickel support under mild reaction conditionsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010K. A. Anand Abstract The hydrogenolysis of dilute glycerol solution to 1,2-propanediol was studied in the presence of heterogeneous catalyst (FeCoL/Raney Nickel) having a heterodinuclear FeCo macrocyclic complex ionically bonded to Raney Nickel. Studies on the stability of the complex bonded to the support were carried out at different temperature as well as the effect of solvent to confirm that it was stable up to 600°C and 100,h of refluxing. In the hydrogenolysis of glycerol, the temperature has been varied from 165 to 220°C with an initial hydrogen pressure 0.35,MPa and the conversion increases from 1% to 36% with no gases evolving in this temperature range. The major product is 1,2-propanediol which is formed with 80% selectivity. The initial water content (20,60%) in the feed was also varied and it was found that the conversion and yield of 1,2-propanediol increases when the water content increases. Based on literature, a kinetic model was proposed and optimal rate constants determined using Genetic Algorithm (GA). On a étudié l'hydrogénolyse d'une solution diluée de glycérol solution en 1,2-propanediol, en présence d'un catalyseur hétérogène (FeCoL/nickel de Raney) ayant un complexe macrocyclique hétérodinucléaire de FeCo ioniquement lié au nickel de Raney. Des études sur la stabilité du complexe lié au soutien ont été effectuées à différentes températures et on a étudié aussi l'effet du solvant pour confirmer qu'il était stable jusqu'à 600 °C et 100 h de reflux. Dans l'hydrogénolyse du glycérol, la température variait de 165 à 220°C avec une pression initiale d'hydrogène de 0,35 MPa et la conversion augmente de 1% à to 36% sans évolution des gaz dans cet intervalle de température. Le produit majeur est le 1,2-propanediol, lequel est formé avec une sélectivité de 80%. Le contenu d'eau initial (20% à 60%) dans l'alimentation variait également et on a conclu que la conversion et le rendement de 1,2-propanediol augmentait avec les augmentations de contenu d'eau. En se basant sur la littérature, un modèle cinétique a été proposé et des constantes de taux optimal ont été déterminées en utilisant un algorithme génétique. [source] Selectivity, Hydrodynamics and Solvent Effects in a Monolith Cocurrent Downflow Contactor (CDC) ReactorTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Mike Winterbottoma Abstract The liquid phase hydrogenation of 2-butyne-1,4-diol (B) to cis-2-butene-1,4,-diol (C) was studied in a Monolith (CDC) Reactor. The effect of temperature, pressure, different solvents and gas and liquid feed rates on reaction rate and selectivity was determined. RTD measurements were made under different hydrodynamic conditions. The liquid flow was largely laminar with evidence of a stagnant wall film. Selectivity to C was observed to increase with hydrogen pressure and approaches 1 at high superficial gas velocities and conversion of B (>95%) as plug flow is approached. The flow regime was of influence on selectivity and kinetics, which was described by a dual site Langmuir-Hinshelwood mechanism. L'hydrogénation en phase liquide du butyne-2-diol-1,4 B en cis-butène-2-diol-1,4 C a été étudiée dans un réacteur à monolithe (CDC). On a déterminé l'effet de la température, de la pression, des différents solvants et des vitesses d'alimentation de gaz et de liquide sur la vitesse de réaction et la sélectivité. Des mesures de distribution de temps de séjour ont été effectuées pour différentes conditions hydrodynamiques. L'écoulement du liquide est largement laminaire avec un film de paroi stagnant évident. On a observé que la sélectivité pour C augmentait avec la pression de l'hydrogène et s'approchait de 1 à des vitesses de gaz superficielles élevées et à conversion de B élevée (>95%) quand l'écoulement piston devient piston. Le régime d'écoulement a une influence sur la sélectivité et la cinétique, et celle-ci est bien décrite par un mécanisme à site double de Langmuir-Hinshelwood. [source] Dynamic simulation of kinetics, heat and mass transfer during hydrogen sorption by LaNi5ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010Dr Tarek Moustafa Abstract A two-dimensional transient heat and mass transfer models have been developed to investigate the dynamic phenomena of hydrogen absorption and desorption in metal hydride bed. LaNi5 has been chosen as the alloy used for hydrogen storage. The numerical simulation has been conducted to simulate the time,space evolution of temperature, fractional conversion, hydrogen pressure and velocity, in addition to metal density. A correlation for the volumetric reaction rate has been deduced. Also, comparisons have been done between various bed geometries and their influence on the average hydrogen desorbed mass. The simulation results showed that heat transfer controls the overall rate of absorption and desorption processes, and because the driving force for the hydrogen flow is the axial pressure difference; the challenge to get optimum bed geometry is in compromising between heat transfer and pressure drop limitations. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Evaluation of porous catalytic membranes operated in pore-flow-through mode for hydrogenation of ,-methylstyreneASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Daniel Urbanczyk Abstract A study of the catalytic membrane contactor operated in pore-flow-through (PFT) mode was carried out for hydrogenation of ,-methylstyrene (AMS) to cumene over palladium as a test reaction. By applying a metalorganic chemical vapour deposition method, the catalyst was deposited as nanoparticles on the pore walls of porous alumina capillaries. Experiments were performed with up to six individual Pd-activated capillaries in a laboratory-scale reactor set-up and with capillary bundles in a small pilot plant. The influence of the operating parameters on the reactor performance such as temperature (303,333 K), hydrogen pressure (5,10 bar), transmembrane flux (up to 200 l·m,2·min,1), pore size of the capillaries (0.6,3.0 µm) and concentration of AMS in n-heptane used as solvent was investigated. Moreover, the performance of the PFT-system was compared to that of conventional reactors (e.g. fixed bed, trickle bed, bubble column, stirred tank) and novel reactor designs (catalytic membrane contactor in diffuser mode, monolith reactor) based on published data. It is shown that the PFT principle enables very high activity, comparable with a suspended powder catalyst in a stirred tank reactor and, at the same time, an excellent space time yield. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Kinetic Study of the Asymmetric Hydrogenation of Methyl Acetoacetate in the Presence of a Ruthenium Binaphthophosphepine ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Eva Öchsner Abstract The asymmetric hydrogenation of methyl acetoacetate (MAA) in methanol using dibromobis{(S)-4-phenyl-4,5-dihydro-3H -dinaphtho[2,1- c: 1,,2,- e]phosphepine}-ruthenium was studied in detail. For the determination of the reaction network, data from kinetic experiments were compared to different possible reaction networks using the kinetic software Presto Kinetics. The simulation was optimised to describe the reaction accurately with a minimal set of process parameters and reaction equations. For the best model the reaction orders, collision factors and activation energy of all reaction steps were determined. Additionally, the influence of reaction temperature and hydrogen pressure on the enantiomeric excess (ee) of the reaction was studied. It was found that high reaction temperatures and high hydrogen pressures result in increasing enantioselectivities. [source] | |||||||||||||||||||||||||