Showing papers on "Acetic acid published in 2004"

Transformation of Oxygenate Components of Biomass Pyrolysis Oil on a HZSM-5 Zeolite. II. Aldehydes, Ketones, and Acids

Abstract: The catalytic transformation over a HZSM-5 zeolite of key components of the liquid product obtained by the flash pyrolysis of biomass, namely, acetaldehyde, ketones (acetone and butanone), and acetic acid, has been studied, and great differences in reactivity and degradation to coke have been found. Acetaldehyde has a low reactivity to hydrocarbons, with a noticeable deactivation caused by coke deposition, which can be attributed to its capacity for oligomerization with the trimer trimethyltrioxane obtained as an intermediate product. The transformation of ketones [less reactive than the alcohols studied in part I of this work (see the preceding paper in this issue)] and of acetic acid (which gives rise to acetone as the primary product) mainly occurs through decarboxylation and, to a lesser degree, dehydration. Above 400 °C, this transformation gives olefins and aromatics according to a reaction scheme similar to that better known for the reaction of alcohols. The generation of coke (attenuated by the pr...

Abnormal solvent effects on hydrogen atom abstraction. 2. Resolution of the curcumin antioxidant controversy. The role of sequential proton loss electron transfer.

Abstract: The rates of reaction of 1,1-diphenyl-2-picrylhydrazyl (dpph•) radicals with curcumin (CU, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione), dehydrozingerone (DHZ, “half-curcumin”), and isoeugenol (IE) have been measured in methanol and ethanol and in two non-hydroxylic solvents, dioxane and ethyl acetate, which have about the same hydrogen-bond-accepting abilities as the alcohols. The reactions of all three substrates are orders of magnitude faster in the alcohols, but these high rates can be suppressed to values essentially equal to those in the two non-hydroxylic solvents by the addition of acetic acid. The fast reactions in alcohols are attributed to the reaction of dpph• with the CU, DHZ, and IE anions (see J. Org. Chem. 2003, 68, 3433), a process which we herein name sequential proton loss electron transfer (SPLET). The most acidic group in CU is the central keto−enol moiety. Following CU's ionization to a monoanion, ET from the [−(O)CCHC(O)−]- moiety to dpph• yields the neutral [−(O)CCH...

Ethanol Electrooxidation on a Carbon-Supported Pt Catalyst: Reaction Kinetics and Product Yields

Abstract: The ethanol oxidation reaction (EOR) on a carbon-supported Pt nanoparticle catalyst was studied by cyclic voltammetry and potential-step measurements as a function of ethanol concentration and reaction temperature (23−60 °C), combining on-line mass spectrometric analysis of the reaction products and electrochemical current measurements. The effect of catalyst loading/electrode roughness was elucidated by comparison with a polycrystalline Pt electrode. Individual, absolute rates for CO2 and acetaldehyde formation were determined via the doubly ionized carbon dioxide molecular ion at m/z = 22 and the CHO+ fragment at m/z = 29, whereas acetic acid yields were calculated as the difference between the Faradaic current (charge) and the sum of the partial currents for oxidation to CO2 and acetaldehyde, calculated from the calibrated mass spectrometric currents. Incomplete ethanol oxidation to acetaldehyde and acetic acid prevails over complete oxidation to CO2 under all conditions, the dominant products being ac...

Bismuth Oxide Nanoparticles by Flame Spray Pyrolysis

Abstract: Bismuth oxide nanostructured particles were made via the flame spray pyrolysis (FSP) of bismuth nitrate that had been dissolved in a solution of ethanol/nitric acid or in acetic acid. These self-sustaining spray flames produced tetragonal β-Bi 2 O 3 . The use of ethanol/nitric acid solutions resulted in a mixture of hollow, shell-like, and solid nanograined particles. The particle homogeneity was improved as the content of acetic acid in the precursor solution increased. Solid bismuth oxide nanoparticles were prepared consistent with percolation theory, accounting for the specific volume of the product and the precursor. Using pure acetic acid as the solvent, the effect of FSP variables on spray flame and product powder characteristics was investigated. The specific surface area of the Bi 2 O 3 particles could be controlled over a range of 20-80 m 2 /g by the liquid feed and oxygen gas flow rates for powder production rates of 6-46 g/h.

Ady2p is essential for the acetate permease activity in the yeast Saccharomyces cerevisiae

Abstract: To identify new genes involved in acetate uptake in Saccharomyces cerevisiae, an analysis of the gene expression profiles of cells shifted from glucose to acetic acid was performed. The gene expression reprogramming of yeast adapting to a poor non-fermentable carbon source was observed, including dramatic metabolic changes, global activation of translation machinery, mitochondria biogenesis and the induction of known or putative transporters. Among them, the gene ADY2/YCR010c was identified as a new key element for acetate transport, being homologous to the Yarrowia lipolytica GPR1 gene, which has a role in acetic acid sensitivity. Disruption of ADY2 in S. cerevisiae abolished the active transport of acetate. Microarray analyses of ady2Delta strains showed that this gene is not a critical regulator of acetate response and that its role is directly connected to acetate transport. Ady2p is predicted to be a membrane protein and is a valuable acetate transporter candidate.

Brønsted acidic ionic liquids: the dependence on water of the Fischer esterification of acetic acid and ethanol

Abstract: Initial studies involving the Fischer esterification of acetic acid utilizing task specific ionic liquid (TSIL) 1 and ethanol revealed an interesting trend when comparing overall conversions with the level of reuse. A rise in product yield was observed up to the third recycling of the ionic liquid (IL) medium. Post-run analyses revealed that the TSIL remained unchanged and the by-products of the reaction, acetic acid and water, were being retained. Use of TSILs in the Fischer esterification reaction was both high yielding and programmable if the proper ratio of both water and reagents to immobilized medium was observed.

A comparative esterification of benzyl alcohol with acetic acid over zeolites Hβ, HY and HZSM5

Abstract: The esterification of benzyl alcohol with acetic acid has been studied over zeolites Hβ, HY, and HZSM5. In the case of zeolites Hβ and HY, apart from the expected product benzyl acetate, dibenzyl ether was also formed. In the absence of a catalyst and also over zeolite HZSM5 only the ester was formed. Acidic sites responsible for the reaction are predominantly inside the pores of the zeolites. The pore architecture seems to influence the product selectivity. Kinetic studies have shown that the esterification reaction follows the Eley–Rideal mechanism. The energy of activation for the reaction follows the order: Hβ

Synthesis and characterization of polyaniline doped with organic acids

Abstract: Spectroscopic [UV–visible and Fourier transform IR (FTIR)] and thermal properties of chemically synthesized polyanilines are found to be affected by varying the protonation media (acetic, citric, oxalic, and tartaric acid). The optical spectra show the presence of a greater fraction of fully oxidized insulating pernigraniline phase in polyaniline doped with acetic acid. In contrast, the selectivity in the formation of the conducting phase is higher in oxalic acid as a protonic acid media. The FTIR spectra of these polymers reveal a higher ratio of the relative intensities of the quinoid to benzenoid ring modes in acetic acid doped polyaniline. Scanning electron micrographs revealed a sponge-like structure derived from the aggregation of the small granules in acetic acid and oxalic acid doped polyaniline. A three-step decomposition pattern is observed in all the polymers, regardless of the protonic acid used for the doping. The second step loss related to the loss of dopant is found to be higher in the oxalic acid doped polymer. In accordance with these results the conductivity is also found to be higher in oxalic acid doped material. The temperature dependent conductivity measurements show the thermal activated behavior in all the polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2043–2049, 2004

Volatile fatty acid production during anaerobic mesophilic digestion of solid potato waste

Abstract: The production of volatile fatty acids by anaerobic digestion of solid potato waste was investigated using a batch solid waste reactor with a working capacity of 2 dm(-3) at 37degreesC. Solid potato waste was packed into the digester and the organic content of the waste was released by microbial activity by circulating water over the bed, using batch loads of 500g or 1000 g potato waste. The sequence of appearance of the volatile fatty acids was (acetic, propionic); (n-butyric); (n-valeric, iso-valeric, caproic); (iso-butyric). After 300 h digestion of potato waste on a small scale, the fermentation products were chiefly (mg g(-1) total VFAs): acetic acid (420), butyric acid (310), propionic acid (140) and caproic acid (90), with insignificant amounts of iso-butyric acid, n-valeric and iso-valeric acids. When the load of potato solids was increased, the volatile fatty acid content was similar, but butyric acid constituted 110 mg g(-1) and lactic acid 400 mg g(-1) of the total volatile fatty acids. The maximum soluble chemical oxygen demand (COD) achieved under the experimental conditions used was 27 and 37 g COD dm(-3) at low and high loadings of potato solids, respectively. The total volatile fatty acids reached 19 g dm(-3) of leachate at both loads of potato solid waste. Gas production was negligible, indicating that methanogenic activity was effectively inhibited. (C) 2004 Society of Chemical Industry. (Less)

Fermentation Microorganisms and Flavor Changes in Fermented Foods

Abstract: Food fermentation processes often result in profound changes in flavor relative to the starting ingredients. However, fermenting foods are typically very complex ecosystems with active enzyme systems from the ingredient materials interacting with the metabolic activities of the fermentation organisms. Factors such as added salt, particle sizes, temperature, and oxygen levels will also have important effects on the chemistry that occurs during fermentation. This is a brief review of recent research on flavor changes in food fermentations. The emphasis will be on the role of lactic acid bacteria in changing the compounds that help determine the character of fermented foods from plant-based substrates. actic acid bacteria influence the flavor of fermented foods in a variety of ways. In many cases, the most obvious change in a lac- tic acid fermentation is the production of acid and lowering pH that results in an increase in sourness. Since most of the acid produced in fermentations will be produced by the metabolism of sugars, sweetness will likely decrease as sourness increases. The produc- tion of volatile flavor components tends to be the first mechanism considered for the development of flavor specific to a particular fermented food. In addition to this direct mechanism, however, there are less direct ways in which fermentation microorganisms affect flavor. Lowering the pH in lactic acid fermentations may re- duce the activity or completely inactivate enzymes in the plant that generate either flavor components or flavor precursor compounds. Finally, the fermentation microorganisms may directly metabolize precursor flavor compounds or flavor components themselves. Some examples of these different flavor modification mechanisms will be given. Prevention of flavor formation P urge-and-trap analysis of the volatile components found in cu- cumber slurries before and after cucumbers were fermented in a 2% reduced-salt brine. Comparison of volatile components be- fore and after fermentation led to the conclusion that the major effect of the fermentation on flavor volatiles was to prevent enzy- matic formation of E,Z-2,6-nonadienal and 2-nonenal by enzymes present in cucumbers (Zhou and McFeeters 1998). These alde- hydes are the major compounds responsible for fresh cucumber flavor (Schieberle and others 1990). However, a few days into cu- cumber fermentation, the pH drops low enough to inactivate the enzymes which form these compounds when cucumber tissue is disrupted. Among the volatile components identified in the fer- mented cucumbers, only benzaldehyde, ethyl benzene, and o-xy- lene were not observed in fresh cucumber slurries (Table 1). The lack of the flavor impact of volatile aldehydes is certainly the major effect of the fermentation on flavor. More recently, Marsili and Miller (2000) found a low volatility fla- vor impact compound in fermented pickled cucumber brines. Ad- dition of saturating salt to brine samples heated to 50 °C, sampling with an SPME (solid-phase microextraction) fiber and followed by GC-olfactometry led to recognition of a compound with an odor close to that of the fermentation brine. The compound with a fer- mentation brine odor was identified as trans-4-hexenoic acid. They also tentatively identified the presence of cis-4-hexenoic acid. In a reconstitution experiment, a solution that contained 25 ppm trans- 4-hexenoic acid, 10 ppm phenyl ethyl alcohol, 0.65% lactic acid, 0.05% acetic acid, and 8% NaCl had an odor very similar to that of brine from fermented cucumbers. The concentrations of the lactic acid, acetic acid, and NaCl are reasonable for commercial brines after the completion of fermentation. The addition of phenyl ethyl alcohol gave only a small improvement in the odor match. Thus, the trans-4-hexenoic acid was the key component in the simulated brine solution. Unfortunately, the origin of trans-4-hexenoic acid in fermentation brines is not known.

Catalysts based in cerium oxide for wet oxidation of acrylic acid in the prevention of environmental risks

Abstract: Acrylic acid is a refractory compound for the non-catalytic wet oxidation (WO) process and can seriously damage the environment when released in industrial effluents. Oxidation of acrylic acid by catalytic wet oxidation (CWO) was studied in slurry conditions in a high-pressure batch reactor at 200 °C and 15 bar of oxygen partial pressure. Several solid cerium-based catalysts prepared in our laboratory were used (Ag/Ce, Co/Ce, Mn/Ce, CeO, MnO) and evaluated in terms of activity, selectivity and stability. Mn/Ce shows the higher activity in 2 h with 97.7% reduction of total organic carbon (TOC) followed by: MnO(95.5%)>Ag/Ce(85.0%)>Co/Ce(65.1%)>CeO(61.2%). Attempts were also carried out to analyze the influence of different Mn/Ce molar ratios. High percentages of Mn lead to practically total organic carbon concentration (TOC) abatements while low ratios lead to the formation of non-oxidizable compounds. Acrylic acid was readily degraded by all the catalysts pointing out the high importance of using a catalytic process. pH was an indicator of the reaction pathway and acetic acid was found as the major reaction intermediate compound; however it is completely oxidized after 2 h with exception for Co/Ce, CeO and MnO. Carbon adsorption and leaching of metals were poorly found for Mn/Ce indicating high stability. The catalyst microstructure after the reaction was analyzed and formation of whiskers of β-MnO2 (or less probably MnOOH) were observed at the catalyst surface. Therefore, Mn/Ce revealed to be a promising catalyst for the treatment of effluents containing acrylic acid; nevertheless, its commercialization depends on further research.

Dynamic Viscosities, Densities, and Speed of Sound and Derived Properties of the Binary Systems Acetic Acid with Water, Methanol, Ethanol, Ethyl Acetate and Methyl Acetate at T = (293.15, 298.15, and 303.15) K at Atmospheric Pressure

Abstract: Dynamic viscosities, densities, and speeds of sound of acetic acid with water, methanol, ethanol, methyl acetate, and ethyl acetate at T = (293.15, 298.15, and 303.15) K have been measured over the whole composition range and at atmospheric pressure along with the properties of the pure components. Excess molar volumes and deviations in isentropic compressibility and viscosity for the binary systems at the above-mentioned temperatures were calculated. These results were fit to the Redlich−Kister equation to determine the fitting parameters and the root-mean-square deviations. The UNIQUAC equation was used to correlate the viscosity experimental data.

Determination of adsorption and kinetic parameters for methyl acetate esterification and hydrolysis reaction catalyzed by Amberlyst 15

Abstract: In this paper, the adsorption equilibrium constants, dispersion coefficients, and kinetic parameters were obtained for the liquid phase reversible reaction of methanol with acetic acid catalyzed by Amberlyst 15. The adsorption and kinetic parameters are determined corresponding to two different mobile phases, methanol and water. Such parameters are required for three different applications of the model reaction: namely, synthesis of methyl acetate, removal of dilute acetic acid from wastewater, and hydrolysis of methyl acetate. Experiments were conducted in a packed bed reactor in the temperature range 313–323 K using a rectangular pulse input. A mathematical model for a quasi-homogeneous kinetics was developed. The adsorption and kinetic parameters together with their dependence on temperature were determined by tuning the simulation results to fit the experimentally measured breakthrough curves of acetic acid, water (or methanol) and methyl acetate using a state-of-the-art optimization technique, the genetic algorithm. The mathematical model was further validated using the tuned parameters to predict experimental results at different feed concentrations and flow rates. The kinetics reported in this study was obtained under conditions free of both external and internal mass transfer resistance. The computed parameters were found to predict experimental elution profiles for both batch and plug flow reactors reasonably well. © 2003 Elsevier B.V. All rights reserved.

Application of (phosphine)gold(I) carboxylates, sulfonates and related compounds as highly efficient catalysts for the hydration of alkynes

Abstract: The catalytic activity of a series of six gold(I) complexes LAuX (L=Ph3P, X=CO2C2F5, SO3-p-tol, SO3Et, SSO2-p-tol; L=Me3P, (p-tol)3P, X=CO2C2F5), as well as the silver(I) complexes Ph3PAgOC(O)C2F5 and Ph3PAgOS(O)2-p-tol·EtOH, regarding the hydration of 3-hexyne forming 3-hexanone in the presence of BF3·Et2O as a co-catalyst has been investigated. It could be shown that all the gold compounds are catalytically active with (Ph3P)AuOC(O)C2F5 (1) being the most active. Using 1, hydration of 3-hexyne takes place at room temperature and turnover frequencies (TOFs) as high as 3900 h−1 can be reached without any notable catalyst deterioration (MeOH as solvent, 70 °C). The silver complexes on the other hand did not furnish 3-hexanone under reaction conditions. This observation is explained with silver being the stronger acceptor compared to gold which can be derived from the crystal structures of representative examples. An optimization of the co-catalyst concentration showed that with increasing concentration the reaction rate increases significantly reaching saturation at approximately 5 mol%. This indicates that the Lewis acid BF3·Et2O plays a role in several steps of the catalytic cycle. 1 was also successfully employed as a catalyst to react acetic acid with 3-hexyne forming 3-hexene-3-acetate but due to water being present in the glacial acetic acid 3-hexanone was also formed.

The effect of raw glycerol concentration on the production of 1,3‐propanediol by Clostridium butyricum

Abstract: Raw glycerol, the main by-product of the bio-diesel production process, was converted to 1,3-propanediol by Clostridium butyricum F2b. In batch cultures, 47.1 g dm−3 of 1,3-propanediol were produced. Continuous cultures were conducted at a constant dilution rate (= 0.04 h−1) and various inlet glycerol concentrations with 1,3-propanediol produced at levels up to 44.0 g dm−3. At increasing glycerol concentrations in the inlet medium, biomass yield decreased. This decrease was attributed to the microbial metabolism being directed towards the biosynthesis of organic acids (and hence carbon losses as CO2) instead of biochemical anabolic reactions. An autonomous analytical model was developed, and quantified the effect of inlet glycerol concentration on the production of biomass and metabolites. Indeed, high inlet substrate concentrations positively affected the biosynthesis, principally of butyric acid and to a lesser extent that of acetic acid. In contrast, at increased glycerol concentrations, the relative increase of 1,3-propanediol production per unit of substrate consumed was lower as compared with that of acetic and, mainly, butyric acid. This could be explained by the fact that the butyric acid pathway represents an alternative and competitive one to that of 1,3-propanediol for re-generation of NADH2 equivalents in the microbial cell. Copyright © 2004 Society of Chemical Industry

Saccharibacter floricola gen. nov., sp. nov., a novel osmophilic acetic acid bacterium isolated from pollen.

Abstract: Three Gram-negative, aerobic, rod-shaped bacterial strains were isolated, from the pollen of Japanese flowers, as producers of xylitol; these strains were subjected to a polyphasic taxonomic study. Phylogenetic analyses of the 16S rRNA gene sequences demonstrated that these three isolates formed a new cluster within a group of acetic acid bacteria in the alpha-Proteobacteria. The characteristics of the three isolates were as follows: (i) their predominant quinone was Q-10; (ii) their cellular fatty acid profile contained major amounts of 2-hydroxy acids and an unsaturated straight-chain acid (C(18 : 1)omega7c); and (iii) their DNA G+C contents were in the range 51.9-52.3 mol%, which is around the lower limit of the reported range for the genera of acetic acid bacteria. The negligible or very weak productivity of acetic acid from ethanol and the osmophilic growth properties distinguished these strains from other acetic acid bacteria. The unique phylogenetic and phenotypic characteristics suggest that the three isolates should be classified within a novel genus and species with the proposed name Saccharibacter floricola gen. nov., sp. nov. The type strain is strain S-877(T) (=AJ 13480(T)=JCM 12116(T)=DSM 15669(T)).

Catalytic and FT-IR study on the reaction pathway for oxidation of propane and propylene on V- or Mo–V-based catalysts

Abstract: A series of V- and Mo–V-based catalysts, i.e. undoped and K-doped VO x /Al 2 O 3 , MoVNbO, MoVSbO and MoVTeNbO mixed metal oxides, have been tested in the oxidation of propane and propylene. All the catalysts are active and relatively selective in the partial oxidation of propane and propylene, although the nature of reaction products changes depending on the characteristics of the catalysts. Thus, acrylic acid (MoVTeNbO), acetic and acrylic acid (MoVSbO), acetic acid (MoVNbO) and propylene and CO x (supported catalysts) were the most important products obtained from both propane and propylene. FT-IR spectroscopy of NH 3 indicates the presence of Bronsted and Lewis acid sites, although the acidity decreases in the order: MoVNbO > VO x /Al 2 O 3 > MoVSbO > MoVTeNbO > K-doped VO x /Al 2 O 3. FT-IR studies of propylene adsorbed and desorbed at different temperatures allowed us to propose three different intermediates: (i) a π-allylic compound, intermediate in the selective oxidation of propylene to acrylic acid; (ii) an enolic-type compound, intermediate in the hydration/oxidation of the olefin to form acetone and acetic acid; (iii) a π-bonded propylene species interacting with Lewis acid sites, precursor in the deep oxidation of propylene. Accordingly, the key factors in the achievement of an active and selective catalyst for the oxidation of propane to acrylic acid as MoVTeNbO mixed oxides is tentatively proposed. The role of acid sites in selective and non-selective pathways are also discussed.

Production of fermentable media from vine-trimming wastes and bioconversion into lactic acid by Lactobacillus pentosus

Abstract: Trimmings of vineshoots, an agricultural waste with little use, were hydrolysed with dilute sulphuric acid (1–5%) in order to obtain sugar solutions suitable as fermentation media. The operational conditions for hydrolysis were selected on the basis of both the generation of hemicellulosic sugars (mainly xylose) and glucose and the concentrations of reaction byproducts affecting fermentation (furfural, hydroxymethylfurfural and acetic acid). Hemicellulosic hydrolysates were supplemented with nutrients and fermented with Lactobacillus pentosus, without any previous detoxification stage, to produce lactic acid. Under the best operational conditions assayed (3% H2SO4 and 15 min), 21.8 g lactic acid l−1 was produced (QP = 0.844 g l−1 h−1, YP/S = 0.77 g g−1), which represents a theoretical yield of 99.6%. Acetic acid was the primary byproduct formed from xylose, at about 25% of the lactic acid level. Copyright © 2004 Society of Chemical Industry

2-Dimethylarsinothioyl acetic acid identified in a biological sample: the first occurrence of a mammalian arsinothioyl metabolite.

Abstract: Arsenic in sheep's clothing: the first characterization of a thio-organoarsenate compound (2-dimethylarsinothioyl acetic acid) isolated from a biological source (a rare breed of seaweed-eating sheep; see picture) is reported. The result indicates that mammalian arsenic metabolism is much more complex than has been claimed before, which opens up new questions about the toxicity of such organoarsenothio(y)l compounds.