Low Methanol Concentrations Research Articles

One-dimensional steady state algebraic model on the passive direct methanol fuel cell with consideration of the intermediate liquid electrolyte

One-dimensional steady state performance equations of passive direct methanol fuel cell are formulated at the presence of intermediate liquid electrolyte. This model evaluates the effect of liquid electrolyte on the cell polarization curve in detail. It is shown that liquid electrolyte employed reduce the methanol crossover rate, increase the fuel utilization, and decrease the cathode voltage loss.The prediction shows that ohmic potential drop is significant at high polarization if low methanol concentration is fed. Cell is better performed without liquid electrolyte. On the other hand, the cathode voltage loss by the mixed potential is more influential at high methanol concentration. Thus, liquid electrolyte reduces the cathode over-potential, and cell performs better with the liquid film.

ESTERIFICACIÓN Y TRANSESTERIFICACIÓN DE ACEITES RESIDUALES PARA OBTENER BIODIESEL

Biodiesel is a biofuel produced from fats and oils and because of the disadvantages of fossil oils use, its production and consumption has increased in recent years. In this work the esterification of waste oil by acid catalysis and alkaline transesterification to obtain biodiesel was studied. The oil-methanol (6:1 and 5:1) ratio conditions and catalyst concentration were varied to select the most favorable for the process. The oils used were collected in restaurants in the city of Cartagena. It was found that the variable to greater effect on the reaction yield was the oil-methanol ratio, favoring low concentrations of methanol (6:1), from which yields higher than 93% are obtained. The catalyst concentration did not affect significantly the efficiency of esterification. The biodiesel obtained had good acidity characteristics and low sulfur content. Additionally the need for a pretreatment to

Human Papillomavirus 16 L1 Protein Expression and Self-Assembly in Recombinant Pichia pastoris

Human papillomavirus virus-like particles (HPV VLPs) have been shown to be effective in preventing cervical cancer when used as a prophylactic vaccine. However, little attention has been paid to the process of L1 expression and self-assembly of VLPs in vivo. In this study, the methanol concentration is optimized during fermentation to optimize L1 expression and self-assembly into VLPs. HPV 16 L1 was expressed in Pichia pastoris GS115, and successfully self-assembled into HPV 16 VLPs. The results demonstrate that there is a strong correlation between methanol concentration and the expression of HPV L1 as well as VLP formation. During the methanol induction phase, low concentrations of residual methanol (0.1-0.3%) promoted the expression of free L1 and increased the total content of L1, whereas a higher residual methanol concentration (0.32-0.6%) was conducive for the self-assembly of LI into VLPs. To conclude, if the residual methanol concentration is too low or too high, the levels of L1 can easily decrease during the fermentation process.

The Structure of Water-Methanol Mixtures Under an Electric Field: Ab Initio Molecular Dynamics Simulations

Liquid methanol and water are examples of hydrogen-bonded systems which exhibit abnormal high proton conductivity.[1][2] Their mixture is of fundamental interest due to the rich and complex structure and topology of the hydrogen-bonded network in the solution. Previous studies suggest that the water-methanol mixtures exist in form of ice-like water cages surrounding the hydrophobic groups of the methanol molecules.[3] Recent experimental and theoretical studies proposed a new picture that, at low methanol concentrations, the mixture is consist of two separate percolating hydrogen-bonded networks.[4][5] Ab-Initio Molecular Dynamics (AIMD) simulations were performed using the VASP code[6] to understand the local hydrophobic structures in water-methanol mixtures, especially under the influence of electric field. Simulations of the water-methanol mixtures were performed at five concentrations: pure water, XM = 0.25 (20 H2O and 7 CH3OH molecules), XM = 0.50 (13 H2O and 14 CH3OH), XM = 0.75 (7 H2O and 20 CH3OH), and pure methanol in a supercell of length 12.22 Å. The finite electric field applied is between 0.25 and 0.75 V/Å.The structure of pure methanol after applying electric field (E = 0.25 V/Å) along c-axis at 300 K is shown in Fig. 1 (a). It appears that most of the hydrogen-bonded network adopts motif structures, which is the predominant feature as predicted in the previous works. In the case of pure water (Fig. 1(b)), we see a different scenario. Under low electric field (E = 0.25 V/Å), the water molecules have evolved into separated cluster layers with hydrogen bond pointing outwards the empty space. With the electric field increased to E = 0.75 V/Å, a small amount of water molecules at the edges of two nearby cluster layers reach out to form a connecting cluster between the two layers. Also, there is no evidence of auto dissociation of the water molecules when subject to the electric fields being applied in this study.Among the mixture structures, the mixture systems with concentration between XM = 0.25 and XM = 0.50 are of particular interest. The methanol and water are reported to form separate percolating hydrogen-bonded networks in the XM range of [0.25, 0.50].5 Instead, our results of XM = 0.25 mixture system shows that, before applying electric field, the structure of water in the mixture are still close to that of pure liquid water. There is evidence of the formation of water clusters, and the methanol molecules are randomly distributed in the water clusters. However, when a weak electric field (E = 0.25 V/Å) is applied, the methyl groups are aligned and form hollow channels inside the water clusters. (Fig. 1(c)) This local hydrophobic structure provides driving force for fast proton transport via structural or Grotthuss-type diffusion in the water-methanol mixtures.In the XM = 0.50 mixture, the resulted structures before and after applying the electric field show similar features of random mixing between the methanol and water molecules. (Fig. 1(d)) There is no evidence of separate hydrogen-bonded water and methanol networks. In summary, from a molecular level, our AIMD simulations illustrate interesting features of a local hydrophobic structure in water-methanol mixtures when under an electric field. With the absence of ice-like water structure, the water molecules tend to present in the form of pure liquid water and form clusters. With a low electric field, the hydrophobic groups of the methanol molecules align themselves and form channels inside the water clusters. The abnormal high proton conductivity can be explained by this type of local structure based on a structural or Grotthuss-type diffusion mechanism. Acknowledgement The authors gratefully acknowledge the support by the U.S. Army Research Office under Contract No. W911NF-07-1-0085.

Endogenous Methanol Regulates Mammalian Gene Activity

We recently showed that methanol emitted by wounded plants might function as a signaling molecule for plant-to-plant and plant-to-animal communications. In mammals, methanol is considered a poison because the enzyme alcohol dehydrogenase (ADH) converts methanol into toxic formaldehyde. However, the detection of methanol in the blood and exhaled air of healthy volunteers suggests that methanol may be a chemical with specific functions rather than a metabolic waste product. Using a genome-wide analysis of the mouse brain, we demonstrated that an increase in blood methanol concentration led to a change in the accumulation of mRNAs from genes primarily involved in detoxification processes and regulation of the alcohol/aldehyde dehydrogenases gene cluster. To test the role of ADH in the maintenance of low methanol concentration in the plasma, we used the specific ADH inhibitor 4-methylpyrazole (4-MP) and showed that intraperitoneal administration of 4-MP resulted in a significant increase in the plasma methanol, ethanol and formaldehyde concentrations. Removal of the intestine significantly decreased the rate of methanol addition to the plasma and suggested that the gut flora may be involved in the endogenous production of methanol. ADH in the liver was identified as the main enzyme for metabolizing methanol because an increase in the methanol and ethanol contents in the liver homogenate was observed after 4-MP administration into the portal vein. Liver mRNA quantification showed changes in the accumulation of mRNAs from genes involved in cell signalling and detoxification processes. We hypothesized that endogenous methanol acts as a regulator of homeostasis by controlling the mRNA synthesis.

Performance evaluation of a direct methanol fuel cell (DMFC) with novel anode flow field operating with neat methanol

This paper reports the structural effect of a novel anode flow field on the performance of a direct methanol fuel cell (DMFC) operating with neat methanol. The anode flow fields with various vaporization channel configurations, open ratios, gap aspect ratios and vaporization channel lengths are designed, fabricated and tested on DMFCs. Results show that the DMFC with an anode flow field with central vapor inlet yields better performance than that with vapor inlet in the corner. Both the open ratio and aspect ratio of the anode flow field have significant influences on cell performance. Larger open ratio and larger aspect ratio lead to more uniform reactant distribution in the in-plane direction, but can result in a lower methanol concentration in the anode catalyst layer (ACL), which makes the DMFC suffers larger polarization loss at moderate and high current densities. In addition, it is found that a longer vaporization channel facilitates the cell to work at lower temperature, which is promising to operate a neat-methanol-fed DMFC by self-heating.

Effects of methanol on the hydrogen bonding structure and dynamics in aqueous N-methylacetamide solution

The effect of methanol on the hydrogen bonding structure and dynamics in aqueous solution of N-methylacetamide (NMA) is investigated by classical molecular dynamics simulations. The modifications of structure and interaction between water and NMA in presence of methanol are calculated by different site–site radial distribution functions and average interaction energies between these species in the solution. It is observed that the methyl–methyl interaction between NMA and methanol prefers even at lower methanol concentration. The slower translational and rotational dynamics of NMA is observed in water–methanol mixtures as it is found for both water and methanol in the mixtures. The lifetime and structural-relaxation time of NMA–water and NMA–methanol hydrogen bonds show a strong increase with addition of methanol in the solution, whereas the change is not linearly dependent on concentration. It is also found that the lifetime of water–water and water–methanol hydrogen bond increases with increasing methanol concentration in the solution.

Differences in the methanol-to-olefins reaction catalyzed by SAPO-34 with dimethyl ether as reactant

Abstract Dimethyl ether (DME) was compared to methanol as the reactant for making olefins with a SAPO-34 catalyst. Their similar selectivities showed that they have the same mechanism, but they also gave notable differences in catalyst stability and how product selectivities changed with time-on-stream. These differences were caused by DME hydrolysis equilibrium being pushed toward DME by a low water concentration, which resulted in a low methanol partial pressure and slower kinetics. The higher methanol partial pressure with the methanol feed caused the hydrocarbon pool to form faster. Conversely, the lower methanol partial pressure with the DME feed formed the hydrocarbon pool slower and showed that during the early induction period, propene selectivity was much higher than ethene selectivity. The use of DME and low water concentration were advantageous because the lower methanol concentration in the catalyst resulted in much slower deactivation, which in addition to better catalyst stability, also gave a higher selectivity to propene.

Discrepancies between diagnoses of methanol and ethylene glycol intoxication based on determinations performed in the regional clinical toxicology centre and in the department of forensic medicine.

The situations in which autopsy blood toxicology results do not confirm methanol and/or ethylene glycol intoxications diagnosed during patients` hospitalizations are frequently observed in the Department of Forensic Medicine in Lublin. In order to verify inconsistent findings, serum samples of 18 individuals, routinely stored in the regional clinical toxicology centre after testing, were re-examined using the specific method of gas chromatography (GC). None of the fatal methanol intoxications was confirmed; toxic concentration of glycol was detected only in one case whereas the remaining determinations were negative or revealed "congeneric" concentrations. In cases of negative results of chromatographic re-analyses, the difference between hospital analysis and GC results were on average 29.6 mg% (max. 127.7 mg%) for glycol and 31.8 mg% (max. 80.0 mg%) for methanol. Severe metabolic acidosis was found in all hospitalized patients. In the hospital setting, "intoxications" were diagnosed even when low concentrations of methanol or glycol (below the cut-off values) were detected with spectrophotometry, which is the method still used in the hospital laboratory. The diagnosis of methanol intoxication in a car accident victim was particularly bizarre; as were the methanol intoxication diagnoses established in cases of acute diabetes-associated complications (4), pancreatitis (1), pneumonia (2) and peritonitis (1), gastrointestinal haemorrhage (1), and decompensated hepatic cirrhosis (1). The therapeutic management based on those diagnoses was incorrectly targeted at the non-existing intoxication that was considered the cause of patient's deteriorating condition. Our findings indicate inadequate knowledge of physicians to interpret and critically verify toxicological results. Moreover, low cost and speed of spectrophotometric analysis should not veil its significant limitations: mainly low specificity and interference with exo- and endogenous blood constituents, especially in cases of concomitant metabolic disorders.

Long-term investigation of the photocatalytic hydrogen production on platinized TiO2: an isotopic study

Long-term investigations of the photocatalytic hydrogen production on platinized TiO2 photocatalysts have been carried out employing different solutions of (deuterated) water and (deuterated) methanol. The results indicate that methanol acts as a sacrificial reagent, i.e., as an “electron donor” and that the amount of evolved molecular hydrogen is equivalent to the amount of H2 expected from the complete reforming of methanol or even less depending on the used photocatalyst. No evidence for photocatalytic water splitting is observed even in the presence of very low methanol concentrations, i.e., no molecular oxygen has been detected. Based upon the isotopic labelling studies it was confirmed that H2 is mainly produced by the reduction of protons originating from water.

Operando Infrared (IR) Coupled to Steady-State Isotopic Transient Kinetic Analysis (SSITKA) for Photocatalysis: Reactivity and Mechanistic Studies

This paper reports the coupling of operando infrared (IR) and steady-state isotopic transient kinetic analysis (SSITKA) for air purification studies from volatile organic campounds (VOCs) by photocatalysis. Methanol photo-oxidation has been used as a model reaction. A new photocatalyst (TiO2-L) has been studied and compared to the reference material TiO2-P25. We show that turnover frequency (TOF) values are not really available in heterogeneous photocatalysis where the number and/or efficiency of active sites can vary from one TiO2 material to another and from one experimental setup to another. The influence of methanol concentration and reaction temperature on photocatalytic activity and on selectivity was also investigated. TiO2-L is as active as TiO2-P25 at low methanol concentration and is more selective at high methanol concentrations. SSITKA clarified the role of the surface formate species in the reaction mechanism. Most of these formate species are spectators and are not the main intermediates in ...

Synthesis and catalytic properties of Pd nanoparticles loaded nanoporous TiO2 material

In the present work, Pd nanoparticles were loaded on the nanoporous TiO2 material by a simple chemical deposition. The amount of Pd nanoparticles was determined by the loading times. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA) methods were used to characterize the surface morphology, composition and electro-catalyst activity of the nanoporous Pd/TiO2 material. CV and CA results exhibited the excellent methanol electro-oxidation performance of 6 times loaded sample. The effects of methanol concentration, H2SO4 concentration and upper scan limits on the electro-oxidation performance of six times loaded sample were investigated. In the solution with low methanol concentration, electro-oxidation of methanol was influenced by the amount of methanol molecules on Pd active sites. In the solution with high methanol concentration, electro-oxidation of methanol was controlled by intermediates diffusion. With increasing H2SO4 concentration, driving force of methanol oxidation decreased. However, the increase of bisulfate adsorption, the reduction of thermodynamic tendency and solution conductivity would result in the suppression of peak current density. The upper scanning limit had obvious influence on the active sites for the methanol oxidation reaction in the backward scanning stage. The generation of PdO at high potential was undesired for methanol electro–oxidation.

High power direct methanol fuel cell with a porous carbon nanofiber anode layer

Three anode electrodes containing Pt–Ru Black as a catalyst were fabricated with a porous layer made with different carbon materials: carbon black (CB), carbon nanofiber (CNF) and a combination of both carbon materials (CB+CNF). The carbon-based porous layer was coated onto a carbon cloth with PTFE pre-treatment for delivering hydrophobic properties and applied in direct methanol fuel cells (DMFCs). Characterisation of electrochemical properties for three different anode electrodes was performed with cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) at room temperature in a half-cell configuration. The evolution of the surface morphology of diffusion layer and electrodes was characterised by using variable-pressure scanning electron microscopy (VP-SEM). The electrochemical results indicate that electrode with CNF layer showed the highest current densities compared to CB and CB+CNF with the same catalyst loading. VP-SEM measurements show the network formation within the structure, which could facilitate the methanol mass transfer and improve the catalyst efficiency. The electrodes were applied to a single-cell DMFC, and the cell performance was experimentally investigated under passive operating mode and room temperature. A maximum power density of 23.0mWcm−2 at a current density of 88.0mAcm−2 with a 3M dilute methanol solution was achieved. The results show that the electrodes with a CNF layer could improve the performance of DMFC as compared with commercially used CB and prove it’s potentially application in DMFC technology especially for portable power source applications due to several advantages as followings: operating at low concentration of methanol, operating at room temperature, low catalyst loading in anode and cathode, cheaper, less hazardous and no parasitic load.

A Model of a High-Temperature Direct Methanol Fuel Cell

A steady-state, isothermal, one-dimensional model of a direct methanol proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBI) membrane, was developed. The electrode kinetics were represented by the Butler–Volmer equation, mass transport was described by the multicomponent Stefan–Maxwell equations and Darcy's law, and the ionic and electronic resistances described by Ohm's law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density, and diffusion coefficients, together with the effect of water transport across the membrane on the conductivity of the PBI membrane. The influence of methanol crossover on the cathode polarization is included in the model. The polarization curves predicted by the model were validated against experimental data for a direct methanol fuel cell (DMFC) operating in the temperature range of 125–175 °C. There was good agreement between experimental and model data for the effect of temperature and oxygen/air pressure on cell performance. The fuel cell performance was relatively poor, at only 16 mW cm−2 peak power density using low concentrations of methanol in the vapor phase.

Combined effects of mobile phase composition and temperature on the retention of phenolic antioxidants on an octylsilica polydentate column

Combined effects of temperature and mobile-phase composition on retention and separation selectivity of phenolic acids and flavonoid compounds were studied in liquid chromatography on a polydentate Blaze C8 silica based column. The temperature effects on the retention can be described by van’t Hoff equation. Good linearity of lnk versus 1/T graphs indicates that the retention is controlled by a single mechanism in the mobile phase and temperature range studied. Enthalpic and entropic contributions to the retention were calculated from the regression lines. Generally, enthalpic contributions control the retention at lower temperatures and in mobile phases with lower concentrations of methanol in water. Semi-empirical retention models describe the simultaneous effects of temperature and the volume fraction of the organic solvent in the mobile phase. Using the linear free energy-retention model, selective dipolarity/polarizability, hydrogen-bond donor, hydrogen-bond acceptor and molecular size contributions to retention were estimated at various mobile phase compositions and temperatures. In addition to mobile phase gradients, temperature programming can be used to reduce separation times.

Colorimetric Sensor Based on Self‐Assembled Polydiacetylene/Graphene‐Stacked Composite Film for Vapor‐Phase Volatile Organic Compounds

AbstractA portable litmus‐type chemosensor is developed for the effective detection of environmentally hazardous volatile organic compounds (VOCs) using polydiacetylene (PDA) and graphene stacked within a composite film. The graphene is exploited as a transparent and efficient supporter for the highly ordered PDA monolayer. This colorimetric sensor exhibits a sensitive response to low concentrations of VOCs (∼0.01%), including tetrahydrofuran (THF), chloroform (CHCl3), methanol (CH3OH), and dimethylformamide (DMF). The color change that is caused by relatively high concentrations of VOCs can be perceived by the naked eye, and it is noteworthy that a logarithmic relationship is observed between the chromatic response and the VOC concentration in the range of ∼0.01%–10%. The structural conformation changes of the PDA molecules, caused by interactions with VOCs, are directly observed by scanning tunneling microscopy (STM), which reveals the intrinsic mechanism of the chromatic variety at the molecular level.

Non-isothermal modeling of a small passive direct methanol fuel cell in vertical operation with anode natural convection effect

A two-dimensional, non-isothermal model is presented for a small passive direct methanol fuel cell (DMFC) in vertical operation. The effect of natural convection at the anode in the fuel reservoir is considered. The coupled heat and mass transport of the whole cell, along with the electrochemical reactions occurring in the passive DMFC are modeled. The comprehensive model is solved numerically by the finite element method and validated against the experiment results reported in this paper. The numerical results show that when in vertical operation, the cell temperature increases gradually from the bottom of the cell to the top of the cell, resulting from natural convection at the anode. A higher cell temperature will lead to stronger natural convection in the fuel reservoir, which will in turn lead to a larger temperature difference across the cell. The results also indicate that the rate of methanol crossover increases with increasing methanol concentration from 1 M to 4 M. When incrementally increasing the current densities, the rate of methanol crossover decreased at low methanol concentration of 1 M–2 M but increased at high methanol concentration of 3 M–4 M.

Investigation of the effects of methanol presence on characteristics of sulfonated aromatic electrolyte membranes: Molecular dynamics simulations

Effects of methanol solvent on characteristics of water–methanol solvated sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) membranes were investigated at different methanol concentrations and temperatures using molecular dynamics simulations. Simulation results showed phase segregation of membrane on the uptake of methanol. Analysis of S–S RDFs revealed that the distance between sulfonic acid groups increased by increasing methanol concentration. Using RDFs of SPPO chains to solvent molecules, it was found that sulfonic acid groups were more solvated with water while aromatic backbone of SPPO exhibited stronger affinity toward methanol. From cluster size distribution examination, it was understood that larger solvent clusters formed at lower methanol concentrations. Diffusivity of water molecules decreased and that of methanol enhanced with an increase in methanol uptake. Calculated methanol diffusion coefficients were smaller in SPPO compared with Nafion, in agreement with experimental observations. Furthermore, increasing the temperature improved diffusivities for all permeants.

Novel Ion-Exchange Catalysts for Reactions Involving Lipophilic Reagents: Perspectives in the Reaction of Esterifications of Fatty Acids with Methanol

New catalysts for the esterification of fatty acids with methanol have been obtained from a gel type polystyrene-divinylbenzene resin (2 % cross-linked). To this purpose the starting resin was first acylated with either acetyl, butyrroyl or capryloyl groups and then sulfonated with concentrated sulfuric acid. The acylation degree ranged from 51 to 82 % and the ion exchange capacity ranged from 2.87 to 4.16 mmol/g. These catalysts were tested in the esterification of stearic acid with methanol (solution in edible oil: 5 % for the acid, 5 or 20 % for the alcohol) in a continuous glass reactor at 85 °C. At high relatively methanol concentration the catalytic activity is mainly correlated to the degree of swelling of the catalysts and the best one was the non-acylated benchmark (hence the most hydrophilic) material. At low methanol concentration the swelling is smaller and practically the same for all the catalysts. In spite of this their activity does not level down to the same value. Under these conditions the capryloyl functionalized catalysts, the most lipophilic ones, by far outperform the benchmark catalyst and in general the activity increases with the increasing lipophilic character of the catalyst. This is likely caused by the enhanced adsorption of the fatty acid close to the acidic active site, assisted by the lipophilic acyl groups.

The Technical Study on Photo-Catalytic Oxidation Treatment of Low Concentration Methanol Wastewater in Gas Field

Though analysis and determination on wastewater quality of Gas Field, it can be seen that the main organic matter in wastewater is low concentration methanol. Aiming at the characteristics of higher degree of mineralization, methanol and lower pH ,the experiment is focusing on the effect of manganese dioxide & hydrogen peroxide catalytic oxidation process on methanol wastewater treatment properties and functions.The results show, for low concentration methanol wastewater,the manganese dioxide used has a diameter of 5nm with a dosage of 300mg/L, also a illumination intensity of 120Q, when the dosing ratio with hydrogen peroxide is 1:10, after 8h reaction period, the degradation rate of methanol were all above 70.0%.The methanol content after treated can meet the reference standard for Gas Field reinjection water