Showing papers on "Methanol published in 1998"

Platinum Catalysts for the High-Yield Oxidation of Methane to a Methanol Derivative

Abstract: Platinum catalysts are reported for the direct, low-temperature, oxidative conversion of methane to a methanol derivative at greater than 70 percent one-pass yield based on methane. The catalysts are platinum complexes derived from the bidiazine ligand family that are stable, active, and selective for the oxidation of a carbon-hydrogen bond of methane to produce methyl esters. Mechanistic studies show that platinum(II) is the most active oxidation state of platinum for reaction with methane, and are consistent with reaction proceeding through carbon-hydrogen bond activation of methane to generate a platinum-methyl intermediate that is oxidized to generate the methyl ester product.

Surface Structure Effects in Platinum/Ruthenium Methanol Oxidation Electrocatalysis

Abstract: Catalytic activity of low-index platinum single-crystal faces, Pt(111), Pt(100), and Pt(110), and polycrystalline platinum toward methanol electrooxidation was enhanced by controlled amounts of electrodeposited ruthenium. Platinum surface structure affects all factors involved in the oxidation process: (i) ruthenium coverage corresponding to the highest methanol oxidation rate, (ii) rate of oxidation current decay, (iii) Tafel slopes and reaction turnovers, and (iv) apparent activation energy. We found a unique methanol oxidation reactivity at the Pt(111) surface covered by 0.2 monolayer of ruthenium. The turnover number from such a surface at 80 °C is approximately 1 order of magnitude higher than that from the industrial platinum/ruthenium catalyst. Therefore, the Pt(111)/Ru electrode is the best laboratory scale fuel cell anode for methanol oxidation. We conclude that crystallographic variables should be exploited in syntheses of novel metal-alloy catalysts for fuel cell use.

Fast formation of high-purity methyl esters from vegetable oils

Abstract: Experiments have confirmed that the base-catalyzed methanolysis of vegetable oils occurs much slower than butanolysis because of the two liquid phases initially present in the former reaction. For the same reason, second-order kinetics are not followed. The use of a cosolvent such as tetrahydrofuran or methyl tertiary butyl ether speeds up methanolysis considerably. However, like one-phase butanolysis, one-phase methanolysis initially exhibits a rapid formation of ester, but then slows drastically. Experiments show that the half-life of the hydroxide catalyst is too long to explain the sudden slowing of the reaction. Similarly, lower rate constants for the methylation of the mono- and diglycerides are not a reasonable explanation. Instead the cause has been identified as the fall in polarity which results from the mixing of the nonpolar oil with the methanol. This lowers the effectiveness of both hydroxide and alkoxide catalysts. Increasing the methanol/oil molar ratio to 27 in the one-phase system raises the polarity such that the methyl ester content of the ester product exceeds 99.4 wt% in 7 min. This has obvious implications for the size of new methyl ester plants as well as the capacity of existing facilities.

Proton and Methanol Transport in Poly(perfluorosulfonate) Membranes Containing Cs + and H + Cations

Abstract: Poly(perfluorosulfonate acid) membranes were doped with cesium ions to several degrees. These, along with the H{sup +}-form membrane, were investigated in relation to methanol permeability as well as hydrogen ion conductivity. While retaining considerable conductivity, the cesium-doped membranes are highly impermeable to methanol. The author found that methanol permeability in the membrane reduced by over one order of magnitude, owing to the presence of cesium ions. These findings are discussed on the basis of alterations produced by cesium in the membrane microstructure. Also discussed is the potential implication of these results in the direct methanol fuel cell technology.

Biodiesel Fuel from Animal Fat. Ancillary Studies on Transesterification of Beef Tallow

Abstract: Transesterification of beef tallow was investigated. The solubility of ethanol in beef tallow was much higher than that of methanol. At 100 °C the solubility of methanol was 19% (w/w). The solubility of ethanol in beef tallow reached 100% (w/w) at about 68 °C. For the distribution of methanol between beef tallow methyl esters (BTME) and glycerol, the percentage of total methanol in the glycerol phase was higher than that in the fatty acid methyl ester (FAME) phase in a simulated system at room temperature. At 65-80 °C, however, the percentage of total methanol in FAME (60% (w/w)) was higher than that in glycerol (40% (w/w)) in a 90:10 (w/w) blend of FAME and glycerol. This coincided with the methanol distribution in the transesterified product. The process for making beef tallow methyl esters should recover methanol using vacuum distillation, separate the ester and glycerol phases, and then wash the beef tallow methyl esters with warm water. At neutral pH, the separation of ester and glycerol and water washing was easier because it reduced emulsion formation.

A new apparatus for the determination of P–x–y diagrams and Henry's constants in high pressure alcohols with critical carbon dioxide

Abstract: P–x–y diagrams and Henry's constants for carbon dioxide+methanol, ethanol, acetone, octanol, nonanol and decanol were determined by a novel technique of density measurement at different temperatures and pressures up to 8 MPa. Solubilities of carbon dioxide in these six binary mixtures were found to increase with applied pressure, but to decrease with increasing temperature. Also, Henry's constants for CO2 in these six systems decreased with ascending pressure but increased with elevated temperature. The Peng–Robinson equation of state and the Patel–Teja equation of state, with two adjustable parameters, were able to correlate equilibrium data successfully.

Are There Hydrogen Bonds in Supercritical Methanol and Ethanol

Abstract: We report chemical shift measurements of the hydroxyl protons in methanol and ethanol up to 450 °C and over a wide range of pressures. The extent of hydrogen bonding compared to room temperature co...

Methanol Tolerant Oxygen Reduction Catalysts Based on Transition Metal Sulfides

Abstract: The oxygen reduction activity and methanol tolerance of a range of transition metal sulfide electrocatalysts have been evaluated in half-cell experiments and in a liquid-feed solid polymer electrolyte direct methanol fuel cell. These catalysts were prepared in high surface area form by direct synthesis onto various surface-functionalized carbon blacks. Of the materials tested, mixed-metal catalysts based on ReRuS and MoRuS were observed to give the best oxygen reduction activities. In addition, significant increases in performance were observed when employing sulfur-functionalized carbon black, which were attributed to the preferential deposition of active Ru sites in the catalyst-preparation process. Although the intrinsic activity of the best material tested, namely, Mo{sub 2}Ru{sub 5}S{sub 5} on sulfur-treated XC-72, was lower than Pt (by ca. 1545 mV throughout the entire polarization curve), its activity relative to Pt increased significantly in methanol-contaminated electrolytes. This was due to methanol oxidation side reactions reducing the net activity of the Pt, especially at low overpotentials.

Hydrogenation of Carbon Dioxide to Methanol with a Discharge-Activated Catalyst

Abstract: To mitigate greenhouse gas CO2 emissions and recycle its carbon source, one possible approach would be to separate CO2 from the flue gases of power plants and to convert it to a liquid fuel, e.g., methanol. Hydrogenation of CO2 to methanol is investigated in a dielectric-barrier discharge (DBD) with and without the presence of a catalyst. Comparison of experiments shows that this nonequilibrium discharge can effectively lower the temperature range of optimum catalyst performance. The simultaneous presence of the discharge shifts the temperature region of maximum catalyst activity from 220 to 100 °C, a much more desirable temperature range. The presence of the catalyst, on the other hand, increases the methanol yield and selectivity by more than a factor of 10 in the discharge. Experiment and numerical simulation show that methane formation is the major competitive reaction for methanol formation in the discharge. In the case of low electric power and high pressure, methanol formation can surpass methanati...

Strategies for the analysis of polar solvents in liquid matrixes.

Abstract: Various approaches to the analysis of polar compounds in different matrixes by solid-phase microextraction (SPME) were studied. The analysis of polar analytes in nonpolar matrixes was performed with custom-made SPME fibers coated with Nafion perfluorinated resin. The sensitivity of this fiber in this type of analysis was better by 1 order of magnitude on average as compared to those of any of the commercially available fibers. The fiber was the most sensitive for the most polar of the compounds studied, i.e., methanol. Determination of methanol, ethanol, and 2-propanol in unleaded gasoline was illustrated. Except for methanol, the fiber did not perform very well in the analysis of alcohols in water. The fiber was capable of extracting water from benzene. SPME analysis of polar compounds in water was studied using aqueous solutions of acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), 2-propanol, 2-methyl-2-propanol, and tetrahydrofuran. Fibers coated with poly(dimethylsiloxane)/divinylbenzene yi...

Performance of a direct methanol fuel cell

Abstract: The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of the fuel cell with Nafion® proton conducting membranes is that of methanol crossover from the anode to the cathode through the polymer membrane. This causes a mixed potential at the cathode, can result in cathode flooding and represents a loss in fuel efficiency. To evaluate cell performance mathematical models are developed to predict the cell voltage, current density response of the fuel cell.

Catalytic methanol decomposition at low temperatures over palladium supported on metal oxides

Abstract: Palladium catalysts supported on metal oxides have been prepared by a coprecipitation method for the selective decomposition of methanol to CO and H 2 . The catalysts whose supports are ZrO 2 , Pr 2 O 3 , and CeO 2 are significantly active at 200–300°C. Turnover frequency determined from the activity of the catalysts containing 15 wt% of Pd at 200°C, increased with an increase in the binding energy of Pd 3d 5/2 for the catalysts, indicating that a positively charged Pd species, most likely Pd + , is preferable for the low-temperature decomposition of methanol. The coprecipitation method is advantageous in the preparation of catalysts containing a large amount of Pd over an impregnation method because smaller Pd particles interacting strongly with the support can be produced by the former technique.