Showing papers on "Methanol published in 2008"

Factors affecting the yield of oxidants from the reaction of nanoparticulate zero-valent iron and oxygen.

Abstract: The corrosion of zero-valent iron (Fe0(s)) by oxygen (O2) can lead to the oxidation of organic compounds. To gain insight into the reaction mechanism and to assess the nature of the oxidant, the oxidation of methanol, ethanol, 2-propanol, and benzoic acid by the reaction of nanoparticulate zero-valent iron (nZVI) or ferrous iron (Fe[II]) with O2 in the absence of ligands was studied. At pH values below 5, Fe0(s) nanoparticles were oxidized by O2 within 30 min with a stoichiometry of approximately two Fe0(s) oxidized per O2 consumed. The yield of methanol and ethanol oxidation products increased from 1% at acidic pH to 6% at pH 7, relative to nZVI added. Product yields from 2-propanol and benzoic acid were highest under acidic conditions, with little oxidation observed at neutral pH. At pH values below 5, product formation was attributable to hydroxyl radical (OH·) production through the Fenton reaction, involving hydrogen peroxide and Fe(II) produced during nZVI oxidation. At higher pH values, the oxidati...

Reversible interconversion of carbon dioxide and formate by an electroactive enzyme.

Abstract: Carbon dioxide (CO2) is a kinetically and thermodynamically stable molecule. It is easily formed by the oxidation of organic molecules, during combustion or respiration, but is difficult to reduce. The production of reduced carbon compounds from CO2 is an attractive proposition, because carbon-neutral energy sources could be used to generate fuel resources and sequester CO2 from the atmosphere. However, available methods for the electrochemical reduction of CO2 require excessive overpotentials (are energetically wasteful) and produce mixtures of products. Here, we show that a tungsten-containing formate dehydrogenase enzyme (FDH1) adsorbed to an electrode surface catalyzes the efficient electrochemical reduction of CO2 to formate. Electrocatalysis by FDH1 is thermodynamically reversible—only small overpotentials are required, and the point of zero net catalytic current defines the reduction potential. It occurs under thoroughly mild conditions, and formate is the only product. Both as a homogeneous catalyst and on the electrode, FDH1 catalyzes CO2 reduction with a rate more than two orders of magnitude faster than that of any known catalyst for the same reaction. Formate oxidation is more than five times faster than CO2 reduction. Thermodynamically, formate and hydrogen are oxidized at similar potentials, so formate is a viable energy source in its own right as well as an industrially important feedstock and a stable intermediate in the conversion of CO2 to methanol and methane. FDH1 demonstrates the feasibility of interconverting CO2 and formate electrochemically, and it is a template for the development of robust synthetic catalysts suitable for practical applications.

Selective degradation of wood lignin over noble-metal catalysts in a two-step process.

Abstract: Direct conversion of lignin into alkanes and methanol was carried out in a two-step process (hydrogenolysis and hydrogenation) involving initial treatment of white birch wood sawdust with H2 in dioxane/water/phosphoric acid using carbon supported Ru, Pd, Rh, or Pt as catalysts. The resulting monomers and dimers obtained by selective C-O hydrogenolysis were then hydrogenated in near-crit. water empolying Pd/C as the catalyst. The study is of interest with respect to prodn. of biofuel from lignin.

Methanol to gasoline over zeolite H-ZSM-5: Improved catalyst performance by treatment with NaOH

Abstract: This work outlines how treatment of zeolite H-ZSM-5 (Si/Al = 46) with NaOH may improve the catalytic performance in the conversion of methanol to gasoline. The zeolite was treated with 0.05 or 0.20 M NaOH solution for 2× 4 h at 75 °C. XRD confirmed the retention of crystallinity. The Si/Al ratio of the catalyst decreased as a consequence of the treatment, in particular for the more severely treated sample, but the total acidity determined by NH 3 -TPD was not altered, showing that the treated samples contain significant amounts of Al not giving rise to acidity. The BET surface area increased from 313 to 419 m 2 /g as a consequence of the desilication, and the N 2 adsorption measurements indicated mesopore generation. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated presence of Lewis acidity in the treated samples. Methanol conversion was carried out in a fixed bed reactor at 370 °C and WHSV = 8 g g −1 h −1 . The catalyst lifetime, quantified as the total conversion capacity, increased by a factor of 3.3 as a consequence of the most severe treatment. The procedure led to a moderate increase in the initial activities. Further, the product selectivities were altered dramatically. The selectivity towards the gasoline fraction (C 5+ ) was at best increased by a factor of 1.7. Hydrogen transfer reactions became faster and led to more aromatic and paraffinic compounds in the products. Increases in the propene/ethene ratios were observed at moderate conversion. The results are well rationalized by alterations of acidic properties, mesopore formation, and improved diffusivity.

Esterification of free fatty acids using sulfuric acid as catalyst in the presence of triglycerides

Abstract: Biodiesel is one of the new possible substitutes of regular fuel for engines and is produced from different vegetable oils or animal fats. The main reaction involved is the transesterification of triglycerides into esters. When an acid oil, such as spent or waste oil, is used, the amount of free fatty acids range from 3% to 40%, and another reaction takes place simultaneously with the transesterification, the direct esterification of the free fatty acid. In this work, the direct esterification reaction of triglycerides to biodiesel was studied and the effects of the main variables involved in the process, reaction temperature, amount of catalyst, initial amount of free fatty acid and the molar ratio alcohol/oil, were analyzed. For this investigation, we employed a model acid oil produced by mixing pure oleic acid with refined sunflower oil. Ethanol was used in the experiments instead of methanol since it is less toxic and safer to handle. Sulfuric acid was employed as catalyst because of its advantages compared with conventional homogeneous catalysts (NaOH). It was found that ethanol and sulfuric acid were suitable to perform not only the transesterification reaction but also the direct esterification reaction to increase biodiesel production of the process.

CaO supported on mesoporous silicas as basic catalysts for transesterification reactions

Abstract: A new group of basic catalysts supported on mesoporous solids has been prepared with the aim of being used as heterogeneous catalysis in biodiesel production. These catalysts based on calcium oxide supported on porous silica (SBA-15, MCM-41 and fumed silica) have been characterized and evaluated in transesterification processes. They were characterized by DRX, XPS, SEM, FT-IR, CO2-TPD and N2 adsorption. The catalytic activity was evaluated in the transesterification of ethyl butyrate with methanol, and different reaction parameters were optimized by a factorial design response surface methodology. Thus, a sample containing 14 wt.% of CaO supported on SBA-15 was the most active, and, unlike commercial CaO, no lixiviation of the active phase was detected in the reaction medium. The transesterification activity of vegetable oils confirms the results obtained in the reaction of ethyl butyrate with methanol, reaching conversion as high as 95% with sunflower oil (after 5 h of reaction) and 65% (after 1 h) for castor oil.

Active phase of calcium oxide used as solid base catalyst for transesterification of soybean oil with refluxing methanol

Abstract: For developing a process of biodiesel production with environmental benignity, much interest has been focused on solid base catalysts such as calcium oxide for transesterification of vegetable oils with methanol. In this paper, the active phase of calcium oxide was investigated by characterizing the catalyst collected after achieving the conversion of edible soybean oil into its methyl ester at reflux of methanol in a glass batch reactor. Calcium oxide combined with the by-produced glycerol, so that calcium diglyceroxide was a major constituent of the collected catalyst. The absence of calcium methoxide was clear from the spectrum of solid-state 13C-NMR. The chemical change of calcium oxide was not observed, when the yield of FAME reached 30%. The collected catalyst was not as active as the fresh one (calcium oxide), but was reused without any deactivation. In order to identify the active phase of the collected catalyst, we prepared calcium diglyceroxide by immersion of calcium oxide with refluxing methanol in the presence of glycerol. Calcium diglyceroxide prepared as the reference sample was as active as the collected catalyst in the transesterification, and was tolerant to air-exposure.

Acid-Catalyzed Homogeneous Esterification Reaction for Biodiesel Production from Palm Fatty Acids

Abstract: This work deals with esterification of palm fatty acids to produce biodiesel in a batch reactor, using homogeneous acid catalysts, evaluating the effect of the alcohol used, presence of water, type and concentration of catalysts. Methanesulfonic and sulfuric acid were the best catalysts. Reaction with methanol showed greater yields. It was showed very clearly that the presence of water in the reaction medium showed a negative effect in the reaction velocity. Kinetic parameters were estimated and molecular modeling was performed. Protonation of the carboxylic moiety of the fatty acid were defined as rate determinant step for the reaction.

Electrochemical Processing of Carbon Dioxide

Abstract: With respect to the negative role of carbon dioxide on our climate, it is clear that the time is ripe for the development of processes that convert CO(2) into useful products. The electroreduction of CO(2) is a prime candidate here, as the reaction at near-ambient conditions can yield organics such as formic acid, methanol, and methane. Recent laboratory work on the 100 A scale has shown that reduction of CO(2) to formate (HCO(2)(-)) may be carried out in a trickle-bed continuous electrochemical reactor under industrially viable conditions. Presuming the problems of cathode stability and formate crossover can be overcome, this type of reactor is proposed as the basis for a commercial operation. The viability of corresponding processes for electrosynthesis of formate salts and/or formic acid from CO(2) is examined here through conceptual flowsheets for two process options, each converting CO(2) at the rate of 100 tonnes per day.

Ca and Zn mixed oxide as a heterogeneous base catalyst for transesterification of palm kernel oil

Abstract: Transesterification of palm kernel oil with methanol over mixed oxides of Ca and Zn has been investigated batchwise at 60 °C and 1 atm. CaO·ZnO catalysts were prepared via a conventional co-precipitation of the corresponding mixed metal nitrate solution in the presence of a soluble carbonate salt at near neutral conditions. The catalysts were characterized by using techniques of X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). The results indicated that the mixed oxides possess relatively small particle sizes and high surface areas, compared to pure CaO and ZnO. Moreover, the combination of Ca and Zn reduced the calcination temperature required for decomposition of metal carbonate precipitates to active oxides. Influences of Ca/Zn atomic ratio in the mixed oxide catalyst, catalyst amount, methanol/oil molar ratio, reaction time, and water amount on the methyl ester (ME) content were studied. Under the suitable transesterification conditions at 60 °C (catalyst amount = 10 wt.%, methanol/oil molar ratio = 30, reaction time = 1 h), the ME content of >94% can be achieved over CaO·ZnO catalyst with the Ca/Zn ratio of 0.25. The mixed oxide can be also applied to transesterification of palm olein, soybean, and sunflower oils. Furthermore, the effects of different regeneration methods on the reusability of CaO·ZnO catalyst were investigated.

Production of sunflower oil methyl esters by optimized alkali-catalyzed methanolysis.

Abstract: We report the optimization of sunflower oil methyl esters (SOME/biodiesel) production via alkaline catalyzed transesterification of crude sunflower oil and subsequent physical and chemical characterization. The optimum conditions elucidated for the methanolysis of sunflower oil were found to be: methanol/sunflower oil molar ratio, 6:1; reaction temperature, 60 °C; and NaOH catalyst concentration, 1.00% (w/w). An optimum SOME yield of 97.1% was achieved. SOME were analyzed by gas–liquid chromatography (GLC). A number of fuel properties of SOME as measured according to accepted methods were found to satisfy nearly all prescribed ASTM D 6751 specifications, where applicable. The results of the present study indicated that SOME could be a potential alternative to other common biodiesels and petrodiesel.