Showing papers on "Methanol published in 1987"

Chemical Kinetic Data Base for Combustion Chemistry. Part 2. Methanol

Abstract: This publication contains evaluated and estimated data on the kinetics of reactions involving methanol and hydroxymethyl radicals and various small inorganic and organic species which are of importance for the proper understanding of methanol combustion and pyrolysis. It is meant to be used in conjunction with the kinetic data given in an earlier publication pertaining to methane pyrolysis and combustion, but which also contains a large volume of data that are applicable to the methanol system. The temperature range covered is 300–2500 K and the density range 1×1016 to 1×1021 molecules cm−3.

In situ FTIR studies of methanol and dimethyl ether in ZSM-5

Abstract: In situ infrared spectra are reported of methanol and dimethyl ether in H-ZSM-5 and Na-ZSM-5. Methanol reacts with internal acidic hydroxyl groups at 523 K to form a methoxy species, the appearance of which correlated with the onset of hydrocarbon formation. Dimethyl ether is protonated is lower temperatures but forms the same methoxy species at 473 K. The methoxy species methylates benzene and alkenes at 523 K. The implications of these observations for the mechanism of hydrocarbon formation are discussed.

Promotion of methanol synthesis and the water-gas shift reactions by adsorbed oxygen on supported copper catalysts

Abstract: The surfaces of the copper metal crystallites of working Cu/ZuO/Al2O3 and other copper catalysts are partially oxidised in reaction mixtures for methanol synthesis and the water-gas shift reaction. Work with unsupported polycrystalline copper has confirmed earlier results that copper metal is the active phase in supported copper catalysts. The coverage of adsorbed oxygen, O(a), up to half-monolayer, was determined by reaction with N2O and it was found to be controlled by the overall reaction CO2(g)= CO(g)+ O(a). The free energy of formation of O(a) was calculated to be –240 kJ mol–1 at 513 K. The induction period found in methanol synthesis from CO–CO2–H2 mixtures is consistent with the calculated rate of formation of O(a). The role of O(a) in the methanol synthesis and water-gas shift reactions is both as promoter and reaction intermediate. The dissociative chemisorption of hydrogen on copper is promoted by O(a) but this is not necessary for the reactions. Experiments with unsupported polycrystalline copper have shown that O(a) both increases the extent of physisorption of CO2 and creates new chemisorbed states of CO2, with desorption energies of 109, 113 and 125 kJ mol–1. O(a) is also essential for the dissociative chemisorption of water on copper. A regenerative mechanism for the water-gas shift reaction on copper [involving the formation and reaction of O(a)] has been established by observation of the separate stages. The adsorbed formate intermediate, pivotal in methanol synthesis from carbon dioxide, is irrelevant to the water-gas shift reaction.

Mechanism of selective methanol oxidation over vanadium oxide-titanium oxide catalysts: a FT-IR and flow reactor study

Abstract: The mechanism of the selective oxidation of methanol on two V-Ti oxide catalyst samples, prepared by impregnation and coprecipitation techniques, respectively is investigated. The interaction of methanol and its oxidation products (i.e., formaldehyde, dimethoxymethane, formic acid, and methyl formate) is studied by FR-IR spectroscopy and compares with the results of flow reactor measurements performed at different temperatures, contact times, and methanol/oxygen molar feed ratios. The data are interpreted on the basis of a reaction mechanism which involved the following steps: (i) condensation of methanol with surface VOH groups; (ii) H abstraction from methoxy groups leading to coordinated formaldehyde; (iii) formation of dioxymethylene species by interaction of adsorbed formaldehyde with nucelophilic sites; (iv) reaction of dioxymethylene species with methanol to give dimethoxymethane; (v) successive oxidation of dioxymethylene groups to formate ions; (vi) reaction of these ions either with methanol to produce methyl formate or with water to give formic acid; (vii) decomposition of formate species to produce carbon monoxide; (viii) parallel oxidation of methanol to carbon dioxide. The behaviors of the surface species are compared with those monitored on other systems and the catalyst requirements for the title reaction are discussed.

Stable Carbon Isotope Fractionation by Methanosarcina barkeri during Methanogenesis from Acetate, Methanol, or Carbon Dioxide-Hydrogen.

Abstract: Methanosarcina barkeri was cultured on methanol, H2-CO2, and acetate, and the 13C/12C ratios of the substrates and the methane produced from them were determined. The discrimination against 13C in methane relative to substrate decreased in the order methanol > CO2 > acetate. The isotopic fractionation for methane derived from acetate was only one-third of that observed with methanol as the substrate. The data presented indicate that the last enzyme of methanogenesis, methylreductase, is not the primary site of isotopic discrimination during methanogenesis from methanol or CO2. These results also support biogeochemical interpretations that gas produced in environments in which acetate is the primary methane precursor will have higher 13C/12C ratios than those from environments where other substrates predominate.

Broensted basicity of atomic oxygen on the gold(110) surface: reactions with methanol, acetylene, water, and ethylene

Abstract: The adsorption and reactions of methanol, acetylene, water, and ethylene were investigated on clean and oxidized Au(110) surfaces by temperature-programmed reaction spectroscopy. All of these molecules are only weakly and molecularly adsorbed on the clean Au(110) surface. Methanol, acetylene, and water, however, react with the oxidized surface. Methanol, activated by 0.25 monolayer of oxygen adatoms, reacts to form water, methyl formate, hydrogen, and carbon dioxide. A stable methoxy intermediate is identified in these reactions. Acetylene reacts to form water and carbon dioxide, and water is more strongly bonded to the Au(110) surface in the presence of oxygen adatoms. Ethylene is the only one of these molecules which does not react with oxygen adatoms on Au(110). This pattern of reactivity parallels that associated with the acidity of these molecules as measured in the gas phase which has been observed on Cu(110) and Ag(110) surfaces. These results complete the studies necessary to demonstrate the Broensted base character of oxygen adatoms on all of the group 1B metals.

Additional characteristics of one-carbon-compound utilization by Eubacterium limosum and Acetobacterium woodii

Abstract: Growth characteristics of Eubacterium limosum and Acetobacterium woodii during one-carbon-compound utilization were investigated E limosum RF grew with formate as the sole energy source Formate also replaced a requirement for CO2 during growth with methanol Growth with methanol required either rumen fluid, yeast extract, or acetate, but their effects were not additive Cultures were adapted to grow in concentrations of methanol of up to 494 mM Growth occurred with methanol in the presence of elevated levels of Na+ (576 mM) The pH optima for growth with methanol, H2-CO2, and carbon monoxide were similar (70 to 72) Growth occurred with glucose at a pH of 47, but not at 40 The apparent Km values for methanol and hydrogen were 27 and 034 mM, respectively The apparent Vmax values for methanol and hydrogen were 17 and 011 mumol/mg of protein X min-1, respectively The Ks value for CO was estimated to be less than 75 microM Cellular growth yields were 705, 71, 338, and 084 g (dry weight) per mol utilized for glucose, methanol, CO, and hydrogen (in H2-CO2), respectively E limosum was also able to grow with methoxylated aromatic compounds as energy sources Glucose apparently repressed the ability of E limosum to use methanol, hydrogen, or isoleucine but not CO Growth with mixtures of methanol, H2, CO, or isoleucine was not diauxic The results, especially the relatively high apparent Km values for H2 and methanol, may indicate why E limosum does not usually compete with rumen methanogens for these energy sources(ABSTRACT TRUNCATED AT 250 WORDS)

Fluidized bed upgrading of wood pyrolysis liquids and related compounds

Abstract: The effective hydrogen index (EHI) is a calculated indicator of the ''net'' hydrogen/carbon ratio of a pure or mixed heteroatom-containing feed, after debiting the feed's hydrogen content for complete conversion of heteroatoms to NH/sub 3/, H/sub 2/S, and H/sub 2/O. Compounds with EHI's <--1 are difficult to upgrade to premium products over ZSM-5 catalyst due to rapid catalyst aging in continuous fixed bed processing. However, high conversions of such feeds (acetic acid, methyl acetate, and wood pyrolysis liquids) can be maintained in a fluidized bed system operating under methanol-to-gasoline conditions and employing frequent catalyst regeneration.

Chemical and Physical Properties of Copper-Based Catalysts for CO Shift Reaction and Methanol Synthesis

Abstract: The modern low-pressure methanol synthesis catalysts are based on copper-containing systems such as Cu/ZnO/Al2O3 and Cu/ZnO/Cr2O3 with various compositions. These catalysts are also highly active for the low-temperature CO shift reaction. For both reactions the nature of the active sites is still an open question.

Photocatalytic activities of layered titanium compounds and their derivatives for H2 evolution from aqueous methanol solution

Abstract: The photocatalyst prepared from H+-exchanged K2Ti2O5 with a layered structure exhibited a high activity (quantum yield = ca 10%) for H2 evolution from aqueous methanol solution without any assistance of other materials such as Pt