Showing papers on "Methanol published in 2000"

Kinetics of Palm Oil Transesterification in a Batch Reactor

Abstract: Methyl esters were produced by transesterification of palm oil with methanol in the presence of a catalyst (KOH). The rate of transesterification in a batch reactor increased with temperature up to 60°C. Higher temperatures did not reduce the time to reach maximal conversion. The conversion of triglycerides (TG), diglycerides (DG), and monoglycerides (MG) appeared to be second order up to 30 min of reaction time. Reaction rate constants for TG, DG, and MG hydrolysis reactions were 0.018–0.191 (wt%·min)−1, and were higher at higher temperatures and higher for the MG reaction than for TG hydrolysis. Activation energies were 14.7, 14.2, and 6.4 kcal/mol for the TG, DG, and MG hydrolysis reactions, respectively. The optimal catalyst concentration was 1% KOH.

Methanol transport through Nafion membranes : Electro-osmotic drag effects on potential step measurements

Abstract: This paper describes methanol flux measurements across Nafion, 1100 equivalent weight membranes under conditions of a direct methanol fuel cell but in which methanol is completely electro-oxidized on the opposite side in an inert atmosphere at sufficiently high electrode potential. Both the diffusion coefficient and the methanol concentration in the membrane were determined from the measured transient limiting current density following a potential step. Corrections for electro-osmotic drag effects are developed and found necessary even for low MeOH concentrations. The results agree well with those obtained from nuclear magnetic resonance measurements. The partition coefficient [{rho} = [MeOH]{sub membrane}/[MeOH]{sub solution}] was approximately constant for the membranes in contact with methanol solutions of various concentration and from room temperature to 90 C. The activation energy of methanol diffusion in a fully hydrated Nafion membrane between 30 and 130 C is 4.8 kcal/mol, and that for protonic conduction under the same conditions is 2.3 kcal/mol. For a membrane dried in vacuum at above 100 C, lower values of methanol permeation rate and protonic conductance were found.

Continuous production of biodiesel fuel from vegetable oil using immobilized Candida antarctica lipase

Abstract: Candida antarctica lipase is inactivated in a mixture of vegetable oil and more than 1∶2 molar equivalent of methanol against the total fatty acids. We have revealed that the inactivation was eliminated by three successive additions of 1∶3 molar equivalent of methanol and have developed a three-step methanolysis by which over 95% of the oil triacylglycerols (TAG) were converted to their corresponding methyl esters (ME). In this study, the lipase was not inactivated even though 2∶3 molar equivalent of methanol was present in a mixture of acylglycerols (AG) and 33% ME (AG/ME33). This finding led to a two-step methanolysis of the oil TAG: The first-step was conducted at 30°C for 12 h with shaking in a mixture of the oil, 1∶3 molar equivalent of methanol, and 4% immobilized lipase; the second-step reaction was done for 24 h after adding 2∶3 molar equivalent of methanol (36 h in total). The two-step methanolysis achieved more than 95% of conversion. When two-step reaction was repeated by transferring the immobilized lipase to a fresh substrate mixture, the enzyme could be used 70 cycles (105 d) without any decrease in the conversion. From the viewpoint of the industrial production of biodiesel fuel production, the two-step reaction was conducted using a reactor with impeller. However, the enzyme carrier was easily destroyed, and the lipase could be used only several times. Thus, we attempted flow reaction using a column packed with immobilized Candida lipase. Because the lipase packed in the column was drastically inactivated by feeding a mixture of AG/ME33 and 2∶3 molar equivalent of methanol, three-step flow reaction was performed using three columns packed with 3.0 g immobilized lipase. A mixture of vegetable oil and 1∶3 molar equivalent of methanol was fed into the first column at a constant flow rate of 6.0 mL/h. The eluate and 1∶3 molar equivalent of methanol were mixed and then fed into the second column at the same flow rate. The final step reaction was done by feeding a mixture of eluate from the second column and 1∶3 molar equivalent of methanol at the same flow rate. The ME content in the final-step eluate reached 93%, and the lipase could be used for 100 d without any decrease in the conversion.

How To Make Electrocatalysts More Active for Direct Methanol OxidationAvoid PtRu Bimetallic Alloys

Abstract: Contrary to the current understanding of Pt−Ru electrocatalyzed oxidation of methanol, the bimetallic alloy is not the most desired form of the catalyst. In the nanoscale Pt−Ru blacks used to electrooxidize methanol in direct methanol fuel cells, Pt0Ru0 has orders of magnitude less activity for methanol oxidation than does a mixed-phase electrocatalyst containing Pt metal and hydrous ruthenium oxides (RuOxHy). Bulk, rather than near-surface, quantities of electron−proton conducting RuOxHy are required to achieve high activity for methanol oxidation. The active catalyst forms a nanoscopic, phase-separated hydrons oxide-on-metal structure that retains the Pt metal−RuOxHy boundaries required to oxidize methanol fully to carbon dioxide and water.

Roles for Cyclopentenyl Cations in the Synthesis of Hydrocarbons from Methanol on Zeolite Catalyst HZSM-5

Abstract: In situ 13C NMR measurements on samples prepared using a pulse-quench catalytic reactor show that the 1,3-dimethylcyclopentenyl carbenium ion (1) is an intermediate in the synthesis of toluene from ethylene on zeolite catalyst HZSM-5. Cation 1 forms in less than 0.5 s when ethylene is pulsed onto the catalyst bed at 623 K, and its presence obviates the kinetic induction period for conversion of a subsequent pulse of dimethyl ether, or methanol, into olefins (MTO chemistry). The kinetic induction period returns when the interval between pulses is many times the half-life of 1 in the catalyst bed. Density functional theory calculations (B3LYP/ 6-311G**) on a cluster model of the zeolite confirm that 1 is stable in the zeolite as a free cation and suggest why the alternative framework alkoxy is not observed. A π complex of the neutral cyclic diene is only 2.2 kcal/mol higher in energy than that of the ion pair. Theoretical (GIAO-MP2/tzp) 13C isotropic shifts of isolated 1 are in good agreement with the exper...

The chemical modification seen in the Cu/ZnO methanol synthesis catalysts

Abstract: We have carried out a project to clarify the active site and the role of ZnO in Cu/ZnO-based catalysts for methanol synthesis from CO 2 and H 2 using both classical catalytic and surface science techniques. The active site model in which Zn species present on the Cu surface promote the methanol synthesis had been initially proposed based on the results of the powder catalysts such as a physical mixture of Cu/SiO 2 and ZnO/SiO 2 . The promotion of Zn has then been proved by a model catalyst of a Zn-deposited Cu(1 1 1) surface. The mechanism and kinetics of the methanol synthesis over Zn/Cu(1 1 1) as well as the structure of the active site have been studied on the atomic level by surface science techniques, such as XPS, AES, LEED, IRAS, and STM. A metallic Cu–Zn surface alloy is a catalytically active species for the methanol synthesis from CO 2 and H 2 .

Methanol plant retrofit for acetic acid manufacture

Abstract: The retrofitting of an existing methanol or methanol/ammonia plant to make acetic acid is disclosed. The existing plant has a reformer to which natural gas or another hydrocarbon and steam (water) are fed. Syngas is formed in the reformer. All or part of the syngas is processed to separate out carbon dioxide, carbon monoxide and hydrogen, and the separated carbon dioxide is fed either to the existing methanol synthesis loop for methanol synthesis, or back into the feed to the reformer to enhance carbon monoxide formation in the syngas. Any remaining syngas not fed to the carbon dioxide separator can be converted to methanol in the existing methanol synthesis loop along with carbon dioxide from the separator and/or imported carbon dioxide, and hydrogen from the separator. The separated carbon monoxide is then reacted with the methanol to produce acetic acid or an acetic acid precursor by a conventional process. Also disclosed is the reaction of separated hydrogen with nitrogen, in a conventional manner, to produce ammonia. Also disclosed is the reaction of a portion of the acetic acid in a conventional manner with oxygen and ethylene to form vinyl acetate monomer. The nitrogen for the added ammonia capacity in a retrofit of an original methanol plant comprising an ammonia synthesis loop, and the oxygen for the vinyl acetate monomer process, are obtained from a new air separation unit.

Effect of the property of solid acid upon syngas-to-dimethyl ether conversion on the hybrid catalysts composed of Cu–Zn–Ga and solid acids

Abstract: Syngas-to-dimethyl ether (STD) conversion was examined on various hybrid catalysts. The catalyst composed of a methanol-synthesis catalyst and a silica-rich silica–alumina showed high dimethyl ether (DME) yield (55.5%) with a good selectivity (93.5%). The effects of water on the acid property and on the reaction were examined. At atmospheric pressure, Lewis acid–base pairs were major active sites for methanol dehydration. At higher pressures, however, water formed by methanol dehydration was strongly adsorbed on Lewis acid sites, suppressing the DME formation. The solid-acid catalyst having Bronsted acid sites with moderate acid strength was the best catalyst for the STD process. Modification of the methanol-synthesis catalysts with Pd was effective to enhance the STD activity at low temperatures.

Bio-oils obtained by vacuum pyrolysis of softwood bark as a liquid fuel for gas turbines. Part I: Properties of bio-oil and its blends with methanol and a pyrolytic aqueous phase

Abstract: The objective of this study was to provide background information on biomass pyrolysis oils (bio-oils) regarding their use as a liquid fuel for gas turbine applications. The bio-oil was obtained by vacuum pyrolysis of softwood bark residues. Alkali metal content, viscosity, solid content, heating value, surface tension, moisture content and density of the bio-oil were investigated. The effect of the addition of methanol and/or a pyrolytic aqueous phase on the physicochemical properties of the bio-oils was also investigated. The pyrolytic aqueous phase is the sum of the water contained in form of moisture in the feedstock plus the water formed during biomass pyrolysis reactions. The results indicated that the bio-oil sample investigated is a valuable gas turbine fuel: it has a relatively low Na+K+Ca content (21 ppm), a low viscosity ( 5.3 cSt @90° C ), a high net heating value (32 MJ/kg, as-received basis) and a low solid content (0.34 wt%). The addition of methanol to the oil was beneficial. It was also found that the pyrolytic aqueous phase addition had no significant effect on the viscosity, but that its “flowability” effect was beneficial for other properties. A concentration of 10–15% of the aqueous phase in the bio-oil seemed to be optimal. The second phase of this study investigated the storage and thermal stability of bio-oils and their mixtures. This was carried out using a method performed in our laboratory. The results are presented in Part II of this study.

Oxygen Reduction on Ru1.92Mo0.08SeO4, Ru/Carbon, and Pt/Carbon in Pure and Methanol‐Containing Electrolytes

Abstract: The oxygen reduction reaction (ORR) activity of a Ru 1.92 Mo 0.08 SeO 4 catalyst, a Vulcan XC72-supported Ru catalyst and, for comparison, a Vulcan XC72-supported Pt catalyst was studied with a rotating ring-disk electrode. The very similar reaction characteristics of the two Ru catalysts in pure and CH 3 OH-containing H 2 SO 4 electrolyte, which differ markedly from those of the Pt catalyst, indicate that the reactive centers in both Ru catalysts must be identical. They are highly selective (>95%) toward reduction to H 2 O (four electron pathway), independent of the presence of methanol. In the latter case, they are 100% selective toward the ORR, i.e., completely methanol tolerant, while the ORR on Pt catalysts is accompanied by significant CH 3 OH oxidation. Based on mass specific current densities, however, the Ru catalysts are significantly less active than the standard Pt catalysts. Only at methanol concentrations above 10-30 mM does their methanol tolerance make them more active than Pt/Vulcan. Implications for their use as cathode catalysts in a direct methanol fuel cell are discussed.

Bio-oils obtained by vacuum pyrolysis of softwood bark as a liquid fuel for gas turbines. Part II: Stability and ageing of bio-oil and its blends with methanol and a pyrolytic aqueous phase

Abstract: This paper completes a study the ultimate objective of which was to provide background information on biomass pyrolysis oils (bio-oils) regarding their use as a gas turbine liquid fuel. The bio-oil was obtained by vacuum pyrolysis of softwood bark residues. The stability and ageing of the bio-oil and mixtures thereof were evaluated. The samples were stored at 40, 50 and 80°C for up to 168 h and at room temperature for up to one year, period after which the phase separation time, viscosity, solid and water content and average molecular weight were measured. The results indicated that the properties of the bio-oil were significantly altered when the bio-oil was heated at 80°C, but that the variations after heating at 40 and 50°C were not critical. It was found that the molecular weight increase after heating the bio-oil for one week at 80°C was equivalent to keeping the sample for one year at room temperature. The addition of aqueous phase to the bio-oil lowered its thermal stability significantly. A rapid phase separation occurred after heating at 80°C and, therefore, the total aqueous phase concentration in the bio-oil must be limited to 15%. Ageing of the raw bio-oil at room temperature resulted in a dramatic viscosity increase during the first 65 days, period after which a plateau was reached. The addition of methanol to the bio-oil was beneficial for the bio-oil properties as well as for the stability of the bio-oil and its mixtures. Methanol dissolved some structured components of the bio-oil and thus reduced the viscosity increase rate. Moreover, the addition of methanol to the bio-oil/pyrolytic aqueous phase mixtures delayed the phase separation process.

Powerful solvent effect of water in radical reaction: Triethylborane-induced atom-transfer radical cyclization in water

Abstract: Triethylborane-induced atom-transfer radical cyclization of iodo acetals and iodoacetates in water is described. Radical cyclization of iodo acetal proceeded smoothly both in aqueous methanol and in water. Atom-transfer radical cyclization of allyl iodoacetate (3a) is much more efficient in water than in benzene or hexane. For instance, treatment of 3a with triethylborane in benzene or hexane at room temperature did not yield the desired lactone. In contrast, 3a cyclized much more smoothly in water and yielded the corresponding γ-lactone in high yield. The remarkable solvent effect of water was observed in this reaction, although the medium effect is believed to be small in radical reactions. Powerful solvent effects also operate in the preparation of medium- and large-ring lactones. Water as a reaction solvent strikingly promoted the cyclization reaction of large-membered rings. Stirring a solution of 3,6-dioxa-8-nonenyl iodoacetate in water in the presence of triethylborane at 25 °C for 10 h provided a ...

Production of nanotubes by the catalytic decomposition of different carbon-containing compounds

Abstract: Carbon nanotubes were prepared in the catalytic decomposition of different carbon containing compounds over supported transition metal catalysts. Besides acetylene, ethylene, propylene, acetone, n-pentane, methanol, toluene, and methane were tested and each resulted in carbon nanotube formation. The quality of as-made nanotubes was investigated by TEM and was found to be at least as good as obtained in acetylene decomposition. Ethylene and propylene showed somewhat lower reactivity in the buckytube formation with respect to acetylene, simultaneously suppressed formation of amorphous carbon on the outer surface was found.

Lipase-catalysed production of biodiesel fuel from some Nigerian lauric oils.

Abstract: Fatty acids esters were produced from two Nigerian lauric oils, palm kernel oil and coconut oil, by transesterification of the oils with different alcohols using PS30 lipase as a catalyst. In the conversion of palm kernel oil to alkyl esters (biodiesel), ethanol gave the highest conversion of 72%, t-butanol 62%, 1-butanol 42%, n-propanol 42% and iso-propanol 24%, while only 15% methyl ester was observed with methanol. With coconut oil, 1-butanol and iso-butanol achieved 40% conversion, 1-propanol 16% and ethanol 35%, while only traces of methyl esters were observed using methanol. Studies on some fuel properties of palm kernel oil and its biodiesel showed that palm kernel oil had a viscosity of 32.40 mm2/s, a cloud point of 28 degrees C and a pour point of 22 degrees C, while its biodiesel fuel had a viscosity of 9.33 mm2/s, a cloud point of 12 degrees C and a pour point of 8 degrees C. Coconut oil had a viscosity of 28.58 mm(2)/s, a cloud point of 27 degrees C and a pour point of 20 degrees C, while its biodiesel fuel had a viscosity of 7.34 mm2/s, a cloud point of 5 degrees C and a pour point of -8 degrees C. Some of the fuel properties compared favourably with international biodiesel specifications.

Polyaniline and its substituted derivatives as sensor for aliphatic alcohols

Abstract: Polyaniline (PAni) as well as its substituted derivatives such as poly( o -toluidine) (Po-Tol), poly( o -anisidine) (Po-Anis), poly( N -methyl aniline) (PNMA), poly( N -ethyl aniline) (PNEA), poly(2,3 dimethyl aniline) (P2,3-DMA), poly(2,5 dimethyl aniline) (P2,5-DMA) and poly(diphenyl amine) (PDPA) were found to be sensitive to different alcohols such as methanol, ethanol, propanol, butanol and heptanol vapours A negative change in resistance was observed upon exposing the polymers to methanol, ethanol or propanol vapours, whereas, a reverse trend has been observed for butanol and heptanol vapours Although, the magnitude of change in resistance was found to be very high in many cases: poor response time was observed for most of the polymers Rapid responses were exhibited only by P2,3-DMA and PAni for methanol and ethanol, respectively High sensitivity value (>80%) have been obtained for saturated methanol vapours compared to other alcohols in all polymers Further, measurable response (sensitivity ∼60%) has been obtained at lowest alcohol concentration of ∼3000 ppm with extended switching time The results are explained on the basis of vapour induced change in the crystallinity of the polymer The extent of change was found to be governed by the chain length of the alcohol and its chemical nature

Remarkably Active Catalysts for the Electroreduction of O 2 to H 2 O for Use in an Acidic Electrolyte Containing Concentrated Methanol

Abstract: Focusing on methanol tolerance, a series of heat‐treated metalloporphyrins were investigated by steady‐state voltammetry with a rotating disk electrode. The heat‐treated CoTPP/FeTPP (tetraphenylporphyrin) shows the optimum catalytic activity for oxygen reduction with an onset catalytic potential [0.9 V vs. reversible hydrogen electrode (RHE)] close to that of platinum black catalyst (1.0 V vs. RHE). However, the catalytic activity for oxygen reduction on platinum black catalyst is severely affected by the presence of 1.0 M methanol, resulting in a negative shift of the catalytic potential and a significant decrease in catalytic current. The catalytic activity for oxygen reduction on the heat‐treated metalloporphyrin is not appreciably affected by the presence of the same amount of methanol in an acidic electrolytic solution. The catalytic activity of the heat‐treated binary metalloporphyrin catalyst is better than that of only a heat‐treated single metalloporphyrin. The best heat‐treatment (HT) temperature for HT‐CoTPP/FeTPP is 600°C. The catalytic kinetic process is analyzed using various polarization curves for oxygen reduction at different rotation rates. The slopes obtained from the Koutecký‐Levich plots have verified that the heat‐treated metalloporphyrins can catalyze a four‐electron reduction of oxygen to water over a wide potential range. © 2000 The Electrochemical Society. All rights reserved.

Emissions of volatile organic compounds from Quercus ilex L. measured by Proton Transfer Reaction Mass Spectrometry under different environmental conditions

Abstract: Volatile organic compound (VOC) emissions of the Mediterranean holm oak (Quercus ilex L.) were investigated using a fast Proton Transfer Reaction Mass Spectrometry (PTR-MS) instrument for analysis. This technique is able to measure compounds with a proton affinity higher than water with a high time resolution of 1 s per compound. Hence nearly all VOCs can be detected on-line. We could clearly identify the emission of methanol, acetaldehyde, ethanol, acetone, acetic acid, isoprene, monoterpenes, toluene, and C10-benzenes. Some other species could be tentatively denominated. Among these are the masses 67 (cyclo pentadiene), mass 71 (tentatively attributed to methyl vinyl ketone (MVK) and metacrolein (MACR)), 73 (attributed to methyl ethyl ketone (MEK)), 85 (C6H12 or hexanol), and 95 (vinylfuran or phenol). The emissions of all these compounds (identified as well as nonidentified) together represent 99% of all masses detected and account for a carbon loss of 0.7–2.9% of the net photosynthesis. Of special interest was a change in the emission behavior under changing environmental conditions such as flooding or fast light/dark changes. Flooding of the root system caused an increase of several VOCs between 60 and 2000%, dominated by the emission of ethanol and acetaldehyde, which can be explained by the well described production of ethanol under anoxic conditions of the root system and the recently described subsequent transport and partial oxidation to acetaldehyde within the green leaves. However, ethanol emissions were dominant. Additionally, bursts of acetaldehyde with lower ethanol emission were also found under fast light/dark changes. These bursts are not understood.