Increasing Hydrogen Partial Pressure Research Articles

Influence of hydrogen partial pressure on hydrodenitrogenation of pyridine, aniline and quinoline

Influence of hydrogen partial pressure on hydrodenitrogenation (HDN) of pyridine, aniline and quinoline was examined over Ni–Mo–P/alumina catalyst. Pyridine, aniline and quinoline are representative nitrogen compounds found in coal-derived liquids. HDN of aniline was more enhanced by increasing hydrogen partial pressure than HDN of pyridine. The greater the adsorption strength of nitrogen compounds onto catalyst surface, the lesser is the effect of partial pressure of hydrogen. When the hydrogen partial pressure increased, quinoline HDN improved further with hydrogen sulfide than without hydrogen sulfide. The differences in the influence of hydrogen partial pressure on the quinoline HDN reactions were also interpreted in terms of the differences in the adsorption strengths of nitrogen compounds produced in HDN reactions onto catalysts.

Hydroconversion of n-heptane over [formula omitted] containing HZSM5

Ni and Co containing HZSM5 zeolites were compared in the hydroconversion of n-heptane at 460–710 K and a pressure of up to 2 bar. Hydrocracking and hydrogenolysis were observed to be competing reaction pathways over CoHZSM5 and NiHZSM5. n-Heptane reacted directly to methane and small amounts of ethane over CoHZSM5, i.e., hydrogenolysis prevailed, over NiHZSM5 the main reaction products were propane and i-butane i.e., hydrocracking was dominant. With increasing hydrogen partial pressure hydrogenolysis decreased while hydrocracking increased over both metal containing ZSM5 zeolites.

Propionic acid accumulation and controlling factors in anaerobic treatment of carbohydrate: effects of H2 and pH

Propionic acid is believed to be the most retardative volatile acid appearing in the anaerobic treatment process. However, the mechanisms by which propionic acid accumulates have not been well understood. Several studies and thermodynamical calculations suggest that an increased hydrogen partial pressure in the system is the cause for the accumulation of propionic acid. However, recent findings by the authors and a few other researchers indicated that artificially elevated or reduced hydrogen partial pressure had no discernible effect. Hence, the consensus on the inhibitory effects of hydrogen is lacking. This study was done to test the hypothesis that propionic acid accumulation during start-up or overloading is not caused by high hydrogen partial pressure, rather it is a result of a shift in the dominant species of acidogenic populations. Hydrogen partial pressure and pH were chosen as controlled system parameters. The type of the reactors used was completely stirred tank reactor (CSTR). The results have indicated that hydrogen partial pressure has no discernible effect while low pH around 5 is effective for preventing propionic acid production from decomposition of glucose.

Influence of Hydrogen Partial Pressure on Hydrodenitrogenation of Coal-derived Liquid.

The influence of hydrogen partial pressure on hydrodenitrogenation (HDN) of nitrogen compounds, found in the coal-derived naphtha fraction, was examined using a continuous flow reactor. The HDN reaction of coal-derived naphtha was not enhanced by increasing the hydrogen partial pressure from 2.4 to 5.3 MPa. The influence of hydrogen partial pressure on HDN of pyridine, pyrrole, and aniline was also investigated. Although HDN of pyridine was not improved by increasing hydrogen partial pressure, HDN of aniline was improved. The HDN rate of pyridine was constant during the experiment, however, the HDN rate of aniline gradually decreased with increasing space time. Properties of pyrrole HDN were somewhat between those of pyridine and aniline. The difference in the HDN properties was interpreted in terms of the difference in the adsorption strengths of nitrogen compounds on the catalyst surface.

Methylamine hydrogenolysis on a rhodium catalyst: kinetics at high hydrogen partial pressures

The kinetics of hydrogenolysis of methylamine to methane and ammonia on a rhodium catalyst were investigated at hydrogen partial pressures in the range of 2–10 atm at temperatures of 368, 383, and 408 K. At a fixed methylamine partial pressure, the rate decreased with increasing hydrogen partial pressure. When the hydrogen pressure was held constant, the rate increased with increasing methylamine pressure. Results of a previous investigation by our group at lower hydrogen partial pressures (0.01–1 atm) indicated that the hydrogenolysis rate passed through a maximum with increasing hydrogen pressure. Moreover, at the lower hydrogen pressures, there was an inverse rather than positive dependence of the rate on methylamine partial pressure. With the aid of the present results, there is a much clearer definition of the maximum in the experimental data relating the reaction rate to hydrogen partial pressure. The inversion of the effect of methylamine pressure on the rate as the hydrogen pressure is varied over a sufficiently wide range is also firmly established. With regard to the interpretation of the many interesting features of the kinetics, we retain the suggestion from our earlier work that the rate limiting step at the highest hydrogen pressures is the scission of the carbon-nitrogen bond in a partially dehydrogenated methylamine intermediate chemisorbed on the rhodium, with no direct participation of hydrogen as a reactant in this step. At the lowest hydrogen pressures, however, there is a different rate limiting step in which hydrogen does participate directly as a reactant.

Propionic acid accumulation and controlling factors in anaerobic treatment of carbohydrate: Effects of H2 and pH

Propionic acid is believed to be the most retardative volatile acid appearing in the anaerobic treatment process. However, the mechanisms by which propionic acid accumulates have not been well understood. Several studies and thermodynamical calculations suggest that an increased hydrogen partial pressure in the system is the cause for the accumulation of propionic acid. However, recent findings by the authors and a few other researchers indicated that artificially elevated or reduced hydrogen partial pressure had no discernible effect. Hence, the consensus on the inhibitory effects of hydrogen is lacking. This study was done to test the hypothesis that propionic acid accumulation during start-up or overloading is not caused by high hydrogen partial pressure, rather it is a result of a shift in the dominant species of acidogenic populations. Hydrogen partial pressure and pH were chosen as controlled system parameters. The type of the reactors used was completely stirred tank reactor (CSTR). The results have indicated that hydrogen partial pressure has no discernible effect while low pH around 5 is effective for preventing propionic acid production from decomposition of glucose.

Activation of Hydrogen on Zeolites: Kinetics and Mechanism of n-Heptane Cracking on H-ZSM-5 Zeolites Under High Hydrogen Pressure

The cracking of n-heptane on H-ZSM-5 zeolite was studied using a tubular reactor at 543 K, 2.4 MPa total pressure and varying hydrogen and n-heptane partial pressures. The rate of reaction was determined at times on stream ranging from 0.5 to 62 min. Under the above experimental conditions H-ZSM-5 deactivates rapidly during the first 10 min of reaction time. The initial rate of n-heptane cracking is independent of the n-heptane partial pressure between 0.25 and 0.47 MPa, while it increases linearly with increasing hydrogen partial pressure. This is interpreted with the assumption that under these reaction conditions the desorption of adsorbed intermediates is the rate determining step and that the rate of desorption can be increased by hydrogen via hydride transfer from molecular hydrogen, producing a high paraffin/olefin ratio in the reaction products. In addition to this effect, hydrogen diminishes the rate of catalyst coking.

Cracking of n-Heptane on Metal-Free H-ZSM-5 Zeolite at High Hydrogen Pressure

The cracking of n-heptane in the presence of hydrogen on metal-free H-ZSM-5 was investigated. Under certain conditions it was possible to combine the processes of cracking and hydrogenation. The product distribution was attributed to the bimolecular cracking mechanism whether hydrogen was present or not. However, the relative amount of saturated reaction products depended on the hydrogen partial pressure. This was interpreted by hydrogen transfer reactions and direct hydrogenation. ′rhe hydrogenation of alkenes counteracts the coke formation and/or controls the number of vacant acid sites. The rate of cracking increases with increasing hydrogen partial pressure according to be apparent first order kinetics. The apparent activation energy (70 ± 2 kJ/mol) of n-heptane cracking was found to be independent of hydrogen partial pressure.

IRON FISCHER-TROPSCH CATALYSIS — PROPERTIES OF AN ULTRAFINE IRON OXIDE CATALYST

ABSTRACT ABSTRACT Slurry phase Fischer-Tropsch synthesis has been conducted starting with an ultrafine iron oxide catalyst with an average particle size of 30A. Catalyst activity gradually increased during the first 400 hour of synthesis and then remained stable for 250 days. Potassium promotion greatly increased the initial activity of the catalyst; however, the stability decreased. The CO conversion of the unpromoted catalyst was found to vary linearly with the reciprocal of the space velocity up to 60% conversion. Alkene selectivity increased with increasing space velocity but remained constant above GHSV = 2,0. Secondary reactions are believed to account for the higher alkane content at low space velocity. Methane, ethane and alkane formation increased with increasing hydrogen partial pressure up to a H2/CO ratio of 1. CO conversion is highest at lowest CO partial pressure and likewise for hydrogen. In general it is observed that this ultrafine catalyst is not as active as precipitated catalysts and h...

Comparison of cracking and hydrocraking of n‐heptane on H‐ZSM‐5 catalysts

AbstractAcid catalyzed cracking and bifunctional cracking of n‐heptane were investigated on HZSM‐5 catalysts. At a reaction temperature of 543 K, the cracking on metal‐free zeolite was found to be directly proportional to hydrogen partial pressure. Hydrogen influences the hydrogenation of product olefins and carbon deposits and therefore enhances the overall activity. Under the same conditions, in the presence of platinum, the hydrocracking rate reaches a maximum with increasing hydrogen partial pressure. The reaction can be formally described by a Langmuir Hinshewood mechanism: hydrogen is adsorbed on Pt in competition with hydrocarbons. The maximum reaction rate depends on a favourable ratio of the two adsorbed reactants. The energy of activation of hydrocracking was over 100 kJ/mol higher than that of acid cracking.

Effects of hydrogen and formate on the degradation of propionate and butyrate in thermophilic granules from an upflow anaerobic sludge blanket reactor

Degradation of propionate and butyrate in whole and disintegrated granules from a thermophilic (55 degrees C) upflow anaerobic sludge blanket reactor fed with acetate, propionate, and butyrate as substrates was examined. The propionate and butyrate degradation rates in whole granules were 1.16 and 4.0 mumol/min/g of volatile solids, respectively, and the rates decreased 35 and 25%, respectively, after disintegration of the granules. The effect of adding different hydrogen-oxidizing bacteria (both sulfate reducers and methanogens), some of which used formate in addition to hydrogen, to disintegrated granules was tested. Addition of either Methanobacterium thermoautotrophicum delta H, a hydrogen-utilizing methanogen that does not use formate, or Methanobacterium sp. strain CB12, a hydrogen- and formate-utilizing methanogen, to disintegrated granules increased the degradation rate of both propionate and butyrate. Furthermore, addition of a thermophilic sulfate-reducing bacterium (a Desulfotomaculum sp. isolated in our laboratory) to disintegrated granules improved the degradation of both substrates even more than the addition of methanogens. By monitoring the hydrogen partial pressure in the cultures, a correlation between the hydrogen partial pressure and the degradation rate of propionate and butyrate was observed, showing a decrease in the degradation rate with increased hydrogen partial pressure. No significant differences in the stimulation of the degradation rates were observed when the disintegrated granules were supplied with methanogens that utilized hydrogen only or hydrogen and formate. This indicated that interspecies formate transfer was not important for stimulation of propionate and butyrate degradation.

Hydrogen doping effects in the sulfidation of molybdenum

The kinetics of molybdenum sulfidation have been studied in H2S/H2 gas mixtures at 1173 K. Sulphur partial pressures were controlled by the equilibrium reaction between H2S, H2, and S2. Pure molybdenum metal was sulfidized at a fixed\(p{_S} _{_2 } \) value of 133 Pa with varying H2S and H2 partial pressures, and at fixed H2S partial pressures of 5.06×10 pa4 and 5.06×103 Pa with varying hydrogen and sulfur partial pressures. The gravimetric sulfidation kinetics were parabolic under all conditions. X-ray diffraction analysis of the reaction product scale revealed the presence of MoS2 only. The sulfide scales were of uniform thickness, had a compact morphology, and were tightly adherent to the metal. The sulfidation rates at a fixed sulfur partial pressure increased with increasing hydrogen partial pressure. At fixed\(p{_H} _{_2} {_S} \) values, the rate was almost constant at high\(p{_H} _{_2 } \) values, but increased substantially as\(p{_H} _{_2 } \) was decreased. Defect models for hydrogen dissolution in MoS2 are developed and compared with the experimental results. It is concluded that the sulfidation rate effects are due to hydride anion occupation of interlayer sites in MoS2.

Acetofilamentum rigidum gen, nov., sp. nov., a Strictly Anaerobic Bacterium from Sewage Sludge

Summary A new, strictly anaerobic, non-sporeforming, non-motile, rigid, long filaments forming bacterium, strain MN, was isolated from a sewage sludge fermenter. Cells stained Gram-negative. Single cells were extremely thin, 0.18–0.3 × 2–3μm in size. Filaments of more than 100 μm in length were frequently formed. Optimum growth was between 35–38°C, optimum pH between 7.3–8.5. Growth was dependent on the presence of yeast extract. Acetate and H2 in a molar ratio of 1:2 as well as CO2 were formed from hexoses. Increasing hydrogen partial pressure inhibited growth, while elevated acetate concentration did not affect growth of strain MN. The G+C content of the DNA was 47 mol%. The new mesophilic isolate was named Acetofilamentum rigidum gen. nov., sp. nov. with isolate MN, deposited in the Deutsche Sammlung fur Mikroorganismen under DSM 20769, as the type strain.

Reversible interaction of hydrogen with thin layers of thermally grown silicon dioxide

Some effects of hydrogen on the electrical properties of Pd-metal-thin (≊10 nm) oxide-silicon capacitors are reported. High-frequency (1 MHz) and quasistatic capacitance voltage curves are measured at 100 °C as a function of hydrogen partial pressure in a background atmosphere of 20% O2/Ar. Besides the standard hydrogen-induced shift of the capacitance-voltage characteristics we find: (1) an increase in the accumulation capacitance with increasing hydrogen partial pressure, and (2) a nonmonotonic increase in the quasistatic capacitance minimum with increasing hydrogen pressure. The relative increase in the accumulation capacitance is shown to be related to the square of the hydrogen-induced voltage shift (and hence to the square of the concentration of hydrogen atoms at the Pd-SiO2 interface). We discuss our findings, based on existing hydrogen-silicon dioxide models, to interpret the effects of hydrogen on the high-frequency and quasistatic capacitance characteristics.

Cyclohexane dehydrogenation on a nickel catalyst: Kinetics and catalyst fouling

AbstractThe main reaction and deactivation kinetics of cyclohexane dehydrogenation in the presence of hydrogen has been investigated at atmospheric pressure over a nickel kieselguhr catalyst in the temperature range 583–623 K. The rate of reaction for the fresh catalyst increased with increasing temperature, cyclohexane and hydrogen partial pressures whereas it decreased with an increase in the benzene partial pressure. The experimental data could be adequately modelled by a power law rate expression. The catalyst activity decreased with run time due to catalyst fouling by coke deposition. The rate of deactivation was independent of cyclohexane partial pressure, increased with increasing benzene concentration and decreased with increasing hydrogen partial pressure. It is postulated that coke is most likely formed by the successive dehydrogenation of benzene.

Properties of magnetron sputtered hydrogenated amorphous and microcrystalline silicon films alloyed with germanium

The dependence of hydrogen partial pressure on the structural, optical, electrical and optoelectronic properties of hydrogenated amorphous and microcrystalline Si 1− x Ge x ( x = about 0.1) films prepared by the magnetron sputtering method has been investigated, in comparison with that of amorphous and microcrystalline Si. The photoconductivity and the photosensitivity of amorphous films increase by up to one order of magnitude, while the optical band gap decreases by about 0.2 eV, compared with amorphous Si films. Microcrystallization with increasing hydrogen partial pressure is less observable in the Ge alloyed films compared to Si films.

Effect of increased hydrogen partial pressure on the acetone-butanol fermentation by Clostridium acetobutylicum

Elevated H2 partial pressure in the acetone-butanol fermentation increased the butanol and ethanol yields on glucose by an average of 18% and 13%, respectively, while the respective yields of acetone and of the endogenous H2 decreased by an average of 40% and 30%, and almost no effect was observed on the growth of the culture. The butanol to acetone ratio and the fraction of butanol in the total solvents were also increased with the H2 pressure. There were no major differences in the observed pattern of change with pressurization at either t=0 or t=18 h. The results demonstrate the importance of H2 partial pressure in the regulation of the C. acetobutylicum metabolism.

Microcrystalline formation in sputtered a-Si: H films

Microcrystalline formation in hydrogenated silicon films deposited under high hydrogen partial pressures by reactive r.f. sputtering method has been studied by means of small angle scattering of X-ray. The existence of microcrystalline regions are detected in samples deposited under high hydrogen partial pressure above 40% at the total gas pressure of H 2 and Ar mixture of 2 × 10 -2 torr. The mean radius of microcrystalline regions increases with increasing hydrogen partial pressure. Relation between the presence of microcrystalline state and the electric properties of films is briefly discussed.

Low-temperature hydropyrolysis of coal under pressure of H 2-CH 4 mixtures

Hydropyrolysis of a Beringen bituminous coal (VM, 32.8wt%) has been studied in a fixed bed reactor with different gas flows of H 2-CH 4 and H 2-N 2 mixtures. At 580 °C, various hydrogen partial pressures between 0 and 1 MPa were used with a total pressure of 1 and 4 MPa. Oil yield increased significantly with increasing hydrogen partial pressure. However, if the difference between partial and total pressure is too large, the oil yield is affected more by the total than the hydrogen partial pressure. Similar effects are observed for the yields of BTX, PCX and naphthalenes except that for the latter the total pressure does not have a significant effect. In the conditions investigated the methane is chemically inert. Thus it is possible to recycle the gas during coal hydropyrolysis with only a slight decrease of the yields.

Effect of hydrogen on the density of gap states in reactively sputtered amorphous silicon

The density of states near midgap and the hydrogen content have been measured on a number of reactively sputtered $a\ensuremath{-}\mathrm{Si}{\mathrm{H}}_{x}$ films prepared at different hydrogen partial pressures. The density of states near midgap is observed to decrease exponentially with increasing hydrogen partial pressure to less than ${10}^{15}$ states ${\mathrm{cm}}^{\ensuremath{-}3}$ e${\mathrm{V}}^{\ensuremath{-}1}$. The data are interpreted in terms of a simple kinetic model of the H incorporation in the $a\ensuremath{-}\mathrm{S}\mathrm{i}$ network.