Showing papers on "Methanol published in 2001"

Electrocatalytic oxidation of aliphatic alcohols: Application to the direct alcohol fuel cell (DAFC)

Abstract: The electrooxidation of some low molecular weight alcohols, such as ethanol, ethylene glycol and n-propanol, is discussed in terms of reaction mechanisms and catalytic activity of the anode material Some examples of a single cell, using a proton exchange membrane (PEM) as electrolyte, are given to illustrate interesting results, particularly for the direct electrooxidation of ethanol This alcohol may replace methanol in a direct alcohol fuel cell

Production of biodiesel fuel from triglycerides and alcohol using immobilized lipase

Abstract: Transesterification reaction was performed using triglycerides and short-chain alcohol by immobilized lipase in non-aqueous conditions. The long-chain fatty acid ester, which is the product of this reaction, can be used as a diesel fuel that does not produce sulfur oxide and minimize the soot particulate. Immobilized Pseudomonas fluorescens lipase showed the highest activity in this reaction. Immobilization of lipase was carried out using porous kaolinite particle as a carrier. When methanol and ethanol were used as alcohol, organic solvent like 1,4-dioxane was required. The reaction could be performed in absence of solvent when 1-propanol and 1-butanol were used as short-chain alcohol. The activity of immobilized lipase was highly increased in comparison with free lipase because its activity sites became more effective. Immobilized enzyme could be repeatedly used without troublesome method of separation and the decrease in its activity was not largely observed.

Synthesis of dimethyl carbonate and glycols from carbon dioxide, epoxides, and methanol using heterogeneous basic metal oxide catalysts with high activity and selectivity

Abstract: This paper gives a comprehensive report on a two-step synthesis of dimethyl carbonate (DMC) from epoxides, carbon dioxide and methanol using various basic metal oxide catalysts. The first step is the reaction of ethylene oxide or propylene oxide with CO 2 to form the corresponding cyclic carbonates, and the second step is the transesterification reaction of the cyclic carbonates with methanol to DMC and glycols. Among the catalysts examined, MgO is the most active and selective for both these reactions. Other alcohols can be used for the second step, but the activity decreases as the carbon number of the alcohol increases. Although a one-pot synthesis of DMC, i.e. the sequential reaction of the epoxide, CO 2 and methanol, is also possible with MgO, the selectivity is low because of the alcoholysis of the epoxide. In contrast with the reactions of ethylene oxide and propylene oxide, when styrene oxide is used for the first reaction and for the one-pot synthesis, mandelic acid is produced. Basic properties of the metal oxide catalysts were measured by temperature programmed desorption of CO 2 . The relationship between the catalytic performance and the basic property is discussed.

NiO thin-film formaldehyde gas sensor

Abstract: The suitability of both pure and Li-doped NiO as a thin-film resistive gas sensor for formaldehyde has been investigated. Pure NiO had a linear formaldehyde sensitivity of 0.825 mV ppm−1 while that for 0.5 at.% Li-doped NiO was 0.488 mV ppm−1 at 600°C. These gas-sensing materials also showed similar sensitivity for methanol and acetone as well as a reduced sensitivity for toluene and ethanol. Chloroform was a poison for these gas-sensing materials. Due to resistive noise, the detection limit for formaldehyde was found to be ≈40 ppm.

Adsorption dynamics of gases and vapors on the nanoporous metal organic framework material Ni2(4,4'-bipyridine)3(NO3)4: guest modification of host sorption behavior.

Abstract: This study combines measurements of the thermodynamics and kinetics of guest sorption with powder X-ray diffraction measurements of the nanoporous metal organic framework adsorbent (host) at different adsorptive (guest) loadings. The adsorption characteristics of nitrogen, argon, carbon dioxide, nitrous oxide and ethanol and methanol vapors on Ni2(4,4'-bipyridine)3(NO3)4 were studied over a range of temperatures as a function of pressure. Isotherm steps were observed for both carbon dioxide and nitrous oxide adsorption at approximately 10-20% of the total pore volume and at approximately 70% of total pore volume for methanol adsorption. The adsorption kinetics obey a linear driving force (LDF) mass transfer model for adsorption at low surface coverage. At high surface coverage, both methanol and ethanol adsorption follow a combined barrier resistance/diffusion model. The rates of adsorption in the region of both the carbon dioxide and methanol isotherm steps were significantly slower than those observed either before or after the step. X-ray diffraction studies at various methanol loadings showed that the host structure disordered initially but underwent a structural change in the region of the isotherm step. These isotherm steps are ascribed to discrete structural changes in the host adsorbent that are induced by adsorption on different sites. Isotherm steps were not observed for ethanol adsorption, which followed a Langmuir isotherm. Previous X-ray crystallography studies have shown that all the sites are equivalent for ethanol adsorption on Ni2(4,4'-bipyridine)3(NO3)4, with the host structure undergoing a scissoring motion and the space group remaining unchanged during adsorption. The activation energies and preexponential factors for methanol and ethanol adsorption were calculated for each pressure increment at which the linear driving force model was obeyed. There was a good correlation between activation energy and ln(preexponential factor), indicating a compensation effect. The results are discussed in terms of reversible adsorbate/adsorbent (guest/host) structural changes and interactions and the adsorption mechanism. The paper contains the first evidence of specific interactions between guests and functional groups leading to structural change in flexible porous coordination polymer frameworks.

Recent advances in processes and catalysts for the production of acetic acid

Abstract: Novel acetic acid processes and catalysts have been introduced, commercialized, and improved continuously since the 1950s. The objective of the development of new acetic acid processes has been to reduce raw material consumption, energy requirements, and investment costs. At present, industrial processes for the production of acetic acid are dominated by methanol carbonylation and the oxidation of hydrocarbons such as acetaldehyde, ethylene, n-butane, and naphtha. This paper discusses advances in acetic acid processes and catalysts according to the following routes: (1) methanol carbonylation; (2) methyl formate isomerization; (3) synthesis gas to acetic acid; (4) vapor phase oxidation of ethylene, and (5) other novel technologies.

Methanol: A “Smart” Chemical Probe Molecule

Abstract: A novel chemisorption method was employed for the dissociative adsorption of methanol to surface methoxy intermediates in order to quantitatively determine the number of surface active sites on one-component metal oxide catalysts (MgO, CaO, SrO, BaO, Y2O3, La2O3, CeO2, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, Cr2O3, MoO3, WO3, Mn2O3, Fe2O3, Co3O4, Rh2O3, NiO, PdO, PtO, CuO, Ag2O, Au2O3, ZnO, Al2O3, Ga2O3, In2O3, SiO2, GeO2, SnO2, P2O5, Sb2O3, Bi2O3, SeO2 and TeO2). The number of surface active sites for methanol dissociative adsorption corresponds to ∼3 μmol/m2 on average for many of the metal oxide catalysts. Furthermore, the methanol oxidation product distribution at low conversions reflects the nature of the surface active sites on metal oxides since redox sites yield H2CO, acidic sites yield CH3OCH3 and basic sites yield CO2. The distribution of the different types of surface active sites was found to vary widely for the different metal oxide catalysts. In addition, the commonality of the surface methoxy intermediate during dissociative chemisorption of methanol and methanol oxidation on oxide catalysts also allows for the quantitative determination of the turnover frequency (TOF) values. The TOF values for the various metal oxide catalysts were found to vary over seven orders of magnitude (10−3 to 104 s−1). An inverse relationship (for metal oxide catalysts displaying high (>85%) selectivity to either redox or acidic products) was found between the methanol oxidation TOF values and the decomposition temperatures of the surface M–OCH3 intermediates reflecting that the decomposition of the surface M–OCH3 species is the rate-determining step during methanol oxidation over the metal oxide catalysts.

Evaluation of a Sol-Gel Derived Nafion/Silica Hybrid Membrane for Polymer Electrolyte Membrane Fuel Cell Applications: II. Methanol Uptake and Methanol Permeability

Abstract: Sol-gel derived Nafion/silica hybrid membranes were investigated as a potential polymer electrolyte for direct methanol fuel cell applications. Methanol uptake and methanol permeability were measured in liquid and vapor phase as a function of temperature, methanol vapor activity, and silica content. Decreased methanol uptake from liquid methanol was observed in the hybrid membranes with silica contents of 10 and 21 wt %. The hybrid membrane with silica content of ≈20 wt % showed a significant lower methanol permeation rate when immersed in a liquid methanol-water mixture at 25 and 80°C. Methanol uptake from the vapor phase by the hybrid membranes appears similar to that of unmodified Nafion. Methanol diffusion coefficients, as determined from sorption experiments, were slightly lower in the hybrid membranes than in unmodified Nafion. However, in direct permeation experiments, significantly lower methanol vapor permeability was seen only in the hybrid membrane with silica content of ≈20 wt %. Based on these results, Nafion/silica hybrid membranes with high silica content have potential as electrolytes for direct methanol fuel cells operating either on liquid or vapor-feed fuels. © 2001 The Electrochemical Society. All rights reserved.

Supramolecular origins of product selectivity for methanol-to-olefin catalysis on HSAPO-34.

Abstract: Ethylene selectivity in methanol-to-olefin (MTO) catalysis is related to the number of methyl groups on benzene rings trapped in the nanocages of the preferred catalyst HSAPO-34. By correlating the time evolutions of the catalysts' 13C NMR spectra and the volatile product distribution following abrupt cessation of methanol flow, we discovered that (in the absence of other adsorbates) propene is favored by methylbenzenes with four to six methyl groups but ethylene is predominant from those with two or three methyl groups. We substantially increased ethylene selectivity by operating at lower methanol partial pressures or higher temperatures, either of which reduces the steady-state average methyl substitution. As a step toward a kinetic analysis of the MTO reaction on HSAPO-34, we treated each nanocage with a methylbenzene molecule as a supramolecule capable of unimolecular dissociation into ethylene or propene and a less highly substituted methylbenzene. Addition of a water molecule to a nanocage containin...

The stability of Cu/ZnO-based catalysts in methanol synthesis from a CO2-rich feed and from a CO-rich feed

Abstract: Water produced during methanol synthesis from a CO 2 -rich feed (CO 2 /CO/H 2 ) accelerated the crystallization of Cu and ZnO contained in a Cu/ZnO-based catalyst to lead to the deactivation of the catalyst. A small amount of silica added to the catalyst greatly improved the catalyst stability by suppressing the crystallization of Cu and ZnO. On the other hand, the catalysts both with and without silica were only slightly deactivated during methanol synthesis from a CO-rich feed containing a higher concentration of CO, because only a small amount of water was produced during the reaction, so no remarkable crystallization of Cu and ZnO contained in the catalyst occurred.

Highly effective conversion of CO2 to methanol over supported and promoted copper-based catalysts: influence of support and promoter

Abstract: In this study, gallium-promoted copper-based catalysts prepared by impregnation methods on silica and ZnO supports, were examined for the hydrogenation of CO 2 to methanol. The surface characteristics of catalysts depended on the support and were related to their catalytic performance. Silica-supported catalysts tested at reaction temperatures between 523 and 543 K were highly selective and stable. The selectivity to methanol was around 99%, the conversion to CO was very low and negligible amounts of hydrocarbons were formed. The use of hydrophobic silica enhanced the performance of the catalyst in terms of activity, selectivity and stability. The modification of properties of copper particles is related to the presence of very small particles of Ga 2 O 3 on the surface.

Methanol Oxidation on a Carbon-Supported Pt Fuel Cell CatalystA Kinetic and Mechanistic Study by Differential Electrochemical Mass Spectrometry

Abstract: Methanol oxidation on a supported Pt fuel cell catalyst was investigated by on-line differential electrochemical mass spectrometry (DEMS) at continuous electrolyte flow and defined catalyst utilization, employing a thin-film electrode setup and a thin-layer flow-through cell. The active surface of the Pt/Vulcan (E-TEK) high surface area catalyst was characterized quantitatively by Hupd and preadsorbed CO monolayer stripping. Methanol stripping DEMS experiments, oxidizing the adsorbed dehydrogenation products formed upon methanol adsorption at potentials in the hydrogen adsorption region, show that the coverage of these products and hence the methanol uptake depend on the electrode potential, in contrast to the potential-independent COad coverage. The dehydrogenation products cannot be displaced by Hupd. The number of close to two electrons used per oxidation of one adsorbed dehydrogenation product identifies this as COad species. Further methanol dehydrogenation is hindered when the CO adlayer reaches a d...

Transesterification of rapeseed oil in the presence of basic zeolites and related solid catalysts

Abstract: The transesterification of rapeseed oil with methanol was performed by reflux of methanol over cesium-exchanged NaX faujasites, mixed magnesium-aluminum oxides, magnesium oxide, and barium hydroxide for different methanol-to-oil ratios. Over cesium-exchanged NaX faujasites and mixed magnesium-aluminum oxides, a long reaction time and a high methanol-to-oil ratio are required to achieve both high oil conversion and high yields in methyl esters. However, over a 300 m2/g magnesium oxide, methanol-to-oil ratios and reaction times are significantly reduced to obtain both high oil conversion and high yield in the methyl esters, particularly when the hydroxide precursor is calcined at 823 K. Finally, preliminary results with other basic solids such as barium hydroxide have shown a very high activity and a very high yield in esters. This catalyst is particularly effective since, for a methanol-to-oil ratio of 6, at reflux of methanol and after a reaction time of only 1 h, the oil conversion is about 80% with a nearly quantitative ester molar fraction.

Enzymatic conversion of waste edible oil to biodiesel fuel in a fixed-bed bioreactor

Abstract: The conversion of waste edible oil to biodiesel fuel in a fixed-bed bioreactor was investigated. Three-step methanolysis of waste oil was conducted using three columns packed with 3 g of immobilized Candida antarctica lipase. A mixture of waste oil and 1/3 molar equivalent of methanol against total fatty acids in the oil was used as substrate for the first-step reaction, and mixtures of the first- and second-step eluates and 1/3 molar equivalent of methanol were used for the second- and third-step reactions, respectively. Ninety percent of waste oil was converted to the corresponding methyl esters (ME) by feeding substrate mixtures into the first, second, and third reactors at flow rates of 6, 6 and 4 mL/h, respectively. We also attempted one-step methanolysis of waste oil. When a mixture of waste oil and 90% ME-containing eluate (1∶3, wt/wt) and an equimolar amount of methanol against total fatty acids in the waste oil was fed into a reactor packed with 3 g of immobilized C. antarctica lipase at a flow rate of 4 mL/h, the ME content in the eluate reached 90%. The immobilized biocatalyst could be used for 100 d in the two reaction systems without significant decrease in its activity. Waste oil contained 1980 ppm water and 2.5% free fatty acids, but these contaminants had little influence on enzymatic production of biodiesel fuel.

Formation of intermediates during methanol oxidation : A quantitative DEMS study

Abstract: Current efficiencies for the formation of CO2 during methanol oxidation at smooth polycrystalline platinum electrodes were determined by differential electrochemical mass spectrometry in a thin layer flow through cell In all cases, the current efficiencies are below 60%; in particular, values as low as 16% were found in 01 M methanol solution at 06 V, which shows that a large amount of soluble intermediates (formaldehyde and/or formic acid) are formed The extent to which these soluble intermediates are further oxidized to CO2 depends on the diffusion conditions For methanol oxidation a parallel oxidation path via COad is also active The influence of the surface crystal structure and, in particular, of steps was also studied Step decoration by foreign metals allowed examination of the effect of cocatalytic metals on well defined model surfaces

Methyl Esterification of Free Fatty Acids of Rapeseed Oil as Treated in Supercritical Methanol

Abstract: Commercially available crude oils and fats contain on average 0.5-3% free fatty acids. These free fatty acids are known to react with the alkaline catalyst and form saponified products during transesterification reactions for biodiesel fuel production in the conventional commercial process. Purification of the products therefore becomes necessary after the reaction. In addition, it causes a longer production process and increases the production costs. For this aspect, supercritical methanol method without using any catalyst is evaluated in this work for reaction of free fatty acids. As a result, complete conversion is achieved for saturated fatty acids to methyl esters at temperatures above 400°C, whereas for unsaturated fatty acids, lower temperature of 350°C is appropriate, and higher temperature resulted in a degradation of the products. Consequently, a conversion of free fatty acids to methyl esters is highest, over 95%, when treated at 350°C. Fortunately, this temperature treatment is also most appropriate for transesterification of triglycerides. Thus, the overall conversion process of rapeseed oil to methyl esters is concluded to be adequate at 350°C. This finding supports the superiority of supercritical methanol method on biodiesel fuel production, compared with the conventional method, in which the production process becomes much simpler and increases the total yield due to the methyl esters produced from free fatty acids.

Methanol-to-hydrocarbons reaction over SAPO-34. Molecules confined in the catalyst cavities at short time on stream

Abstract: In order to obtain more insight into the methanol-to-hydrocarbons (MTH) reaction the organic molecules confined in a working SAPO-34 catalyst have been studied. The reaction was run for varying times, 30 s to 30 min. At a predetermined time the reaction was stopped and the catalyst dissolved in 1 M HCl. The gas phase above the solution as well as a CCl4 extract were analyzed by gas chromatography (MS detector). The gas phase consists mainly of isoalkanes C4–6. The less volatile organic molecules were concentrated in the CCl4 extract. More than 200 different species are present, but polymethylbenzenes, with one to six methyl groups, are always dominating. They constitute 30–50% of the samples. Penta- and hexamethylbenzene easily split off small hydrocarbons and turn into di- and trimethylbenzenes. It is speculated that methylations of arenes which thereupon split off small alkenes and then are remethylated again may be an essential part of the catalytic activity in the MTH reaction.

Production of hydrogen from dimethyl ether

Abstract: Catalytic reaction of steam reforming of dimethyl ether (DME) to hydrogen-rich gas was studied in a fixed-bed continuous-flow reactor at a temperature of 200–360°C under atmospheric pressure over a mechanical mixture of catalysts for DME hydration and for methanol steam reforming. It was found that the mechanical mixture of 12-tungstosilicoheteropolyacid deposited on γ-Al 2 O 3 (DME hydration catalyst) and copper deposited on SiO 2 (methanol steam reforming catalyst) provided a 100% DME conversion and hydrogen outlet concentration of ∼71 vol.% at 290°C and GHSV ∼1200 h −1 .