Showing papers on "Acetic acid published in 2018"

Catalytic oxidation of carbohydrates into organic acids and furan chemicals

Abstract: A wide variety of commodity chemicals can be produced from the catalytic oxidation of carbohydrates or carbohydrate derived molecules including formic acid, acetic acid, glycolic acid, gluconic acid, glucaric acid, malonic acid, oxalic acid, 2,5-diformylfuran (DFF), 5-hydroxymethyl-2-furancarboxylic acid (HFCA), 5-formyl-2-furancarboxylic acid (FFCA), and 2,5-furandicarboxylic acid (FDCA). This review will highlight the recent research progress in the development of new routes for the production of organic acids and furan compounds via catalytic oxidation reactions. Particular attention will be paid to these one-pot reactions with the requirements of an acidic site and a metal site. For the one-pot transformation of cellobiose or lignocellulose into gluconic acid, these reactions were performed via a one-step strategy using a single catalyst containing an acidic site and a metal site. However, a two-step strategy was adopted for the oxidative transformation of carbohydrates into DFF or FDCA in order to avoid the oxidation of the carbohydrates. The first step was performed for the dehydration of carbohydrates into 5-hydroxylmethylfuran (HMF) in the presence of an acid catalyst, and the second step was performed for the oxidation of HMF into DFF or FDCA with a metal catalyst.

Single rhodium atoms anchored in micropores for efficient transformation of methane under mild conditions.

Abstract: Catalytic transformation of CH4 under a mild condition is significant for efficient utilization of shale gas under the circumstance of switching raw materials of chemical industries to shale gas. Here, we report the transformation of CH4 to acetic acid and methanol through coupling of CH4, CO and O2 on single-site Rh1O5 anchored in microporous aluminosilicates in solution at ≤150 °C. The activity of these singly dispersed precious metal sites for production of organic oxygenates can reach about 0.10 acetic acid molecules on a Rh1O5 site per second at 150 °C with a selectivity of ~70% for production of acetic acid. It is higher than the activity of free Rh cations by >1000 times. Computational studies suggest that the first C–H bond of CH4 is activated by Rh1O5 anchored on the wall of micropores of ZSM-5; the formed CH3 then couples with CO and OH, to produce acetic acid over a low activation barrier. Catalytic transformation of CH4 under mild conditions has implications to shale gas utilization. Here, the authors report the transformation of CH4 to acetic acid through coupling of CH4, CO and O2 on single-site Rh1O5 anchored in microporous aluminosilicates in liquid phase.

Acetic Acid Bacteria in the Food Industry: Systematics, Characteristics and Applications.

Abstract: The group of Gram-negative bacteria capable of oxidising ethanol to acetic acid is called acetic acid bacteria (AAB). They are widespread in nature and play an important role in the production of food and beverages, such as vinegar and kombucha. The ability to oxidise ethanol to acetic acid also allows the unwanted growth of AAB in other fermented beverages, such as wine, cider, beer and functional and soft beverages, causing an undesirable sour taste. These bacteria are also used in the production of other metabolic products, for example, gluconic acid, l-sorbose and bacterial cellulose, with potential applications in the food and biomedical industries. The classification of AAB into distinct genera has undergone several modifications over the last years, based on morphological, physiological and genetic characteristics. Therefore, this review focuses on the history of taxonomy, biochemical aspects and methods of isolation, identification and quantification of AAB, mainly related to those with important biotechnological applications.

Microbial Electrosynthesis of Isobutyric, Butyric, Caproic Acids, and Corresponding Alcohols from Carbon Dioxide

Abstract: Microbial electrosynthesis is potentially a sustainable biotechnology for the conversion of the greenhouse gas CO2 into carboxylic acids, thus far mostly limited to acetic acid (C2). Despite the environmental benefits of recycling CO2 emissions to counter global warming, bioelectrochemical production of acetate is not very attractive from an economic point of view. Conversely, carboxylates and corresponding alcohols with longer C content not only have a higher economical value as compared to acetate, but they are also relevant platform chemicals and fuels used on a diverse array of industrial applications. Here, we report on a specific mixed reactor microbiome capable of producing a mixture of C4 and C6 carboxylic acids (isobutyric, n-butyric, and n-caproic acids) and their corresponding alcohols (isobutanol, n-butanol, and n-hexanol) using CO2 as the sole carbon source and reducing power provided by an electrode. Metagenomic analysis supports the hypothesis of a sequential carbon chain elongation process...

Direct Conversion of Syngas into Methyl Acetate, Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether.

Abstract: Selective conversion of syngas (CO/H2 ) into C2+ oxygenates is a highly attractive but challenging target. Herein, we report the direct conversion of syngas into methyl acetate (MA) by relay catalysis. MA can be formed at a lower temperature (ca. 473 K) using Cu-Zn-Al oxide/H-ZSM-5 and zeolite mordenite (H-MOR) catalysts separated by quartz wool (denoted as Cu-Zn-Al/H-ZSM-5|H-MOR) and also at higher temperatures (603-643 K) without significant deactivation using spinel-structured ZnAl2 O4 |H-MOR. The selectivity of MA and acetic acid (AA) reaches 87 % at a CO conversion of 11 % at 643 K. Dimethyl ether (DME) is the key intermediate and the carbonylation of DME results in MA with high selectivity. We found that the relay catalysis using ZnAl2 O4 |H-MOR|ZnAl2 O4 gives ethanol as the major product, while ethylene is formed with a layer-by-layer ZnAl2 O4 |H-MOR|ZnAl2 O4 |H-MOR combination. Close proximity between ZnAl2 O4 and H-MOR increases ethylene selectivity to 65 %.

The Genealogical Tree of Ethanol: Gas-phase Formation of Glycolaldehyde, Acetic Acid, and Formic Acid

Abstract: Despite the harsh conditions of the interstellar medium, chemistry thrives in it, especially in star forming regions where several interstellar complex organic molecules (iCOMs) have been detected. Yet, how these species are synthesised is a mystery. The majority of current models claim that this happens on interstellar grain surfaces. Nevertheless, evidence is mounting that neutral gas-phase chemistry plays an important role. In this article, we propose a new scheme for the gas-phase synthesis of glycolaldehyde, a species with a prebiotic potential and for which no gas-phase formation route was previously known. In the proposed scheme, the ancestor is ethanol and the glycolaldehyde sister species are acetic acid (another iCOM with unknown gas-phase formation routes) and formic acid. For the reactions of the new scheme with no available data, we have performed electronic structure and kinetics calculations deriving rate coefficients and branching ratios. Furthermore, after a careful review of the chemistry literature, we revised the available chemical networks, adding and correcting several reactions related to glycolaldehyde, acetic acid and formic acid. The new chemical network has been used in an astrochemical model to predict the abundance of glycolaldehyde, acetic acid and formic acid. The predicted abundance of glycolaldehyde depends on the ethanol abundance in the gas phase and is in excellent agreement with the measured one in hot corinos and shock sites. Our new model overpredicts the abundance of acetic acid and formic acid by about a factor of ten, which might imply a yet incomplete reaction network.

Core-Shell Nickel Catalysts for the Steam Reforming of Acetic Acid

Abstract: To obtain a novel catalyst with high resistances to metal sintering and coke formation in the steam reforming of acetic acid, a series of nickel core-shell catalysts were prepared The effects of the shell thickness, shell species and core particle size on the catalytic activity in the steam reforming of acetic acid were investigated The prepared Ni@SiO2, Ni@Al2O3, Ni@CeO2 and Ni@TiO2 catalysts were characterized by BET, XRD, H2-TPR, DTG and HRTEM The prepared core-shell catalysts showed high resistances to nickel sintering, owing to the protection of the shells, in comparison with bare nickel particles Ni@SiO2 with a thin shell showed a higher activity than the corresponding catalyst with a thick shell due to the thin silica shell allowing the facile diffusion of reactants and products Because of the important role of the support in steam reforming reactions, the shell species greatly affected the catalytic activity in the steam reforming of acetic acid It was demonstrated that an alumina shell was best suited for the steam reforming of acetic acid among the studied shells owing to its excellent water dissociation ability The Ni@Al2O3-i catalyst showed excellent activity with an almost complete conversion and a hydrogen yield up to 912% at 750 °C due to its much smaller nickel particle size The coke formed on the spent core-shell catalysts after the activity tests was mainly graphic carbon, and the Ni@Al2O3-i catalyst exhibited a superior coke resistance with the smallest amount of formed coke HRTEM results of Ni@Al2O3-i indicated the alumina shell had a high hydrothermal stability and further confirmed the high sintering resistance in the steam reforming of acetic acid

Antifungal effect of organic acids from lactic acid bacteria on Penicillium nordicum

Abstract: The control of fungal contamination is particularly important to avoid both spoilage of food and feed products and the occurrence of toxic compounds, known as mycotoxins. Some lactic acid bacteria (LAB) strains have shown the capacity to inhibit fungal growth and the production of mycotoxins. In this work, cell-free supernatants (CFS) of Lactobacillus plantarum UM55 and Lactobacillus buchneri UTAD104 were tested against Penicillium nordicum radial growth and OTA production. When CFS of these strains were used, the radial growth of the fungus was inhibited by less than 20%, but the production of OTA was reduced by approx. 60%. These antifungal effects resulted from organic acids produced by LAB. The CFS of L. plantarum UM55 contained lactic acid, phenyllactic acid (PLA), hydroxyphenyllactic acid (OH-PLA) and indole lactic acid (ILA), while L. buchneri UTAD104 CFS contained acetic acid, lactic acid and PLA. These organic acids were further tested individually for their inhibitory capacity. Calculation of the inhibitory concentrations (ICs) showed that acetic acid, ILA and PLA were the most effective in inhibiting P. nordicum growth and OTA production. When the inhibitory activity of LAB cells incorporated into the culture medium was tested, L. buchneri UTAD104 inhibited the production of OTA entirely in all conditions tested, but fungal growth was only inhibited completely by the highest concentrations of cells. Acetic acid production was primarily responsible for this effect. In conclusion, the ability of LAB to inhibit mycotoxigenic fungi depends on strain capability to produce specific organic acids, and those acids may differ from strain to strain. Also, the use of LAB cells, especially from L. buchneri, in food products prone to contamination with P. nordicum (e.g. dry-cured meats and cheeses) may be an alternative solution to control fungal growth and OTA production.

GC-MS Analysis of Short-Chain Fatty Acids in Feces, Cecum Content, and Blood Samples.

Abstract: Short-chain fatty acids, the end products of fermentation of dietary fibers by the gut microbiota, have been shown to exert multiple effects on mammalian metabolism. For the analysis of short-chain fatty acids, gas chromatography-mass spectrometry is a very powerful and reliable method. Here, we describe a fast, reliable, and reproducible method for the separation and quantification of short-chain fatty acids in mouse feces, cecum content, and blood samples (i.e., plasma or serum) using gas chromatography-mass spectrometry. The short-chain fatty acids analyzed include acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, and heptanoic acid.

Carbon fibers derived from fractionated-solvated lignin precursors for enhanced mechanical performance.

Abstract: The sustainable solvent system acetic acid + water was used to simultaneously fractionate, solvate, and clean a softwood Kraft lignin for conversion to carbon fibers. By exploiting the novel liquid...

Lachancea thermotolerans, the Non-Saccharomyces Yeast that Reduces the Volatile Acidity of Wines

Abstract: To improve the quality of fermented drinks, or more specifically, wine, some strains of yeast have been isolated, tested and studied, such as Saccharomyces and non-Saccharomyces. Some non-conventional yeasts present good fermentative capacities and are able to ferment in quite undesirable conditions, such as the case of must, or wines that have a high concentration of acetic acid. One of those yeasts is Lachancea thermotolerants (L. thermotolerans), which has been studied for its use in wine due to its ability to decrease pH through L-lactic acid production, giving the wines a pleasant acidity. This review focuses on the recent discovery of an interesting feature of L. thermotolerans—namely, its ability to decrease wines’ volatile acidity.

Use of a Potential Probiotic, Lactobacillus plantarum L7, for the Preparation of a Rice-Based Fermented Beverage.

Abstract: This study aimed to isolate potential probiotic lactic acid bacteria from a traditional rice-based fermented beverage "bhaati jaanr" and to evaluate their role during preparation of the beverage. Among various isolates, Lactobacillus plantarum strain L7 exhibited satisfactory in vitro probiotic characteristics such as acid resistance and bile tolerance, cell surface hydrophobicity, auto-aggregation, antibiotic susceptibility, and antimicrobial activities. Therefore, performance of L7 as a starter culture in rice fermentation was determined during a 6-day rice fermentation study. L. plantarum L7 decreased the pH, associated with an increase in total titratable acidity and organic acid production up to the 4th day of fermentation. The highest concentrations of succinic acid (0.37 mg/g), lactic acid (4.95 mg/g), and acetic acid (0.36 mg/g) were recorded on the 3rd, 4th, and 5th days of fermentation, respectively. Saccharifying (148.13 μg/min g-1) and liquefying (89.47 μg/min g-1) activities were the highest on days 3 and 2, respectively, and thereafter, they decreased. Phytase activity and the cleavage of free minerals (sodium, calcium, magnesium, manganese, and ferrous) increased up to days 3-4. The concentration of various accumulated malto-oligosaccharides (glucose, fructose, maltotriose, and maltoterose) was noted to be the maximum on days 4 and 5. Furthermore, gas chromatography-mass spectrometry analysis indicated the presence of various volatile compounds. The fermented material also exhibited 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging activity. Therefore, the probiotic, L. plantarum L7, has a significant role in the fermentation of this beverage and enhances its functional properties.

Evaluation of ultraviolet, visible, and near infrared spectroscopy for the analysis of wine compounds

Abstract: Martelo-Vidal M.J., Vazquez M. (2014): Evaluation of ultraviolet, visible, and near infrared spectroscopy for the analysis of wine compounds. Czech J. Food Sci., 32: 37–47. Spectroscopy of UV-VIS-NIR combined with chemometric analyses was used as a non-destructive technique to build models for the quantitative characterisation of the main compounds of wine. The work in mixtures can give insight into how interferences affect the performance of calibrations in wines. Ethanol, glycerol, glucose, tartaric acid, malic acid, lactic acid, and acetic acid were evaluated as pure compounds and in mixtures. Different pre-treatments for the spectra and modelling strategies such as partial least squares (PLS) regression or Principal Component Regression (PCR) were evaluated. All pure compounds studied showed a good relationship between spectra and concentrations. However, interferences were observed in the mixtures and only good models for ethanol, tartaric acid, and malic acid were obtained. The best model was obtained in the NIR region for ethanol and in the UV region for tartaric acid and malic acid. The results indicate that NIR spectroscopy could be used as an alternative to conventional chemical methods for ethanol determination and UV spectroscopy for the determination of tartaric acid and malic acid.

Light-Driven C-H Oxygenation of Methane into Methanol and Formic Acid by Molecular Oxygen Using a Perfluorinated Solvent.

Abstract: The chlorine dioxide radical (ClO2. ) was found to act as an efficient oxidizing agent in the aerobic oxygenation of methane to methanol and formic acid under photoirradiation. Photochemical oxygenation of methane occurred in a two-phase system comprising perfluorohexane and water under ambient conditions (298 K, 1 atm). The yields of methanol and formic acid were 14 and 85 %, respectively, with a methane conversion of 99 % without formation of the further oxygenated products such as CO2 and CO. Ethane was also photochemically converted into ethanol (19 %) and acetic acid (80 %). The methane oxygenation is initiated by the photochemical Cl-O bond cleavage of ClO2. to generate Cl. and O2 . The produced Cl. reacts with CH4 to form a methyl radical (CH3. ). Finally, the oxygenated products such as methanol and formic acid were given by the radical chain reaction. A fluorous solvent plays an important role of inhibiting the deactivation of reactive radical species such as Cl. and CH3. .

Electrochemical Control of Redox Potential Arrests Methanogenesis and Regulates Products in Mixed Culture Electro-Fermentation

Abstract: This study demonstrates the feasibility of using solid electrodes as an alternative source or sink of electrons to regulate the redox potential of mixed culture anaerobic reactors, so tunable fermentation products can be generated. The product spectrum was characterized under the working potentials of −1.0, −0.6, and −0.2 V (versus Ag/AgCl), which spans the electron flow direction from cathodic current to anodic current. Results show that in neutral pH a more negative working potential led to higher production of CH4, H2, and acetic acid, while increasing the potential from −1.0 to −0.2 V (versus Ag/AgCl) greatly reduced methanogenesis by 68% and acetic acid generation by 33%. Lowering initial pH to 6.2 reduced such effects by electrical potential. The decrease of working potential slightly decreased butyric acid production and showed little impact on propionic acid under both pH conditions. When the reactor switched from poised conditions to open circuit condition, more propionic acid and acetic acid whi...

Ammonia Inhibition of Anaerobic Volatile Fatty Acid Degrading Microbial Communities.

Abstract: Ammonia inhibition is an important reason for reactor failures and economic losses in anaerobic digestion. Its impact on acetic acid degradation is well-studied, while its effect on propionic and butyric acid degradation has received little attention and is consequently not considered in the Anaerobic Digestion Model No. 1 (ADM1). To compare ammonia inhibition of the degradation of these three volatile fatty acids (VFAs), we fed a mixture of them as sole carbon source to three continuous stirred tank reactors (CSTRs) and increased ammonium bicarbonate concentrations in the influent from 52 to 277 mM. The use of this synthetic substrate allowed for the determination of degradation efficiencies for the individual acids. While butyric acid degradation was hardly affected by the increase of ammonia concentration, propionic acid degradation turned out to be even more inhibited than acetic acid degradation with degradation efficiencies dropping to 31 and 65% for propionic and acetic acid, respectively. The inhibited reactors acclimatized and approximated pre-disturbance degradation efficiencies toward the end of the experiment, which was accompanied by strong microbial community shifts, as observed by amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism (T-RFLP) of mcrA genes. The acetoclastic methanogen Methanosaeta was completely replaced by Methanosarcina. The propionic acid degrading genus Syntrophobacter was replaced by yet unknown propionic acid degraders. The butyric acid degrading genus Syntrophomonas and hydrogenotrophic Methanomicrobiaceae were hardly affected. We hypothesized that the ammonia sensitivity of the initially dominating taxa Methanosaeta and Syntrophobacter led to a stronger inhibition of the acetic and propionic acid degradation compared to butyric acid degradation and hydrogenotrophic methanogenesis, which were facilitated by the ammonia tolerant taxa Syntrophomonas and Methanomicrobiaceae. We implemented this hypothesis into a multi-taxa extension of ADM1, which was able to simulate the dynamics of both microbial community composition and VFA concentration in the experiment. It is thus plausible that the effect of ammonia on VFA degradation strongly depends on the ammonia sensitivity of the dominating taxa, for syntrophic propionate degraders as much as for acetoclastic methanogens.

Enhanced Xylooligosaccharides Yields and Enzymatic Hydrolyzability of Cellulose using Acetic Acid Catalysis of Poplar Sawdust

Abstract: To increase the value and promote the utilization of woody processing residues, poplar sawdust was used to produce xylooligosaccharides (XOS) with polymerization degrees of 2–6 by acetic acid catal...

HAA1 and PRS3 overexpression boosts yeast tolerance towards acetic acid improving xylose or glucose consumption: unravelling the underlying mechanisms

Abstract: Acetic acid tolerance and xylose consumption are desirable traits for yeast strains used in industrial biotechnological processes. In this work, overexpression of a weak acid stress transcriptional activator encoded by the gene HAA1 and a phosphoribosyl pyrophosphate synthetase encoded by PRS3 in a recombinant industrial Saccharomyces cerevisiae strain containing a xylose metabolic pathway was evaluated in the presence of acetic acid in xylose- or glucose-containing media. HAA1 or PRS3 overexpression resulted in superior yeast growth and higher sugar consumption capacities in the presence of 4 g/L acetic acid, and a positive synergistic effect resulted from the simultaneous overexpression of both genes. Overexpressing these genes also improved yeast adaptation to a non-detoxified hardwood hydrolysate with a high acetic acid content. Furthermore, the overexpression of HAA1 and/or PRS3 was found to increase the robustness of yeast cell wall when challenged with acetic acid stress, suggesting the involvement of the modulation of the cell wall integrity pathway. This study clearly shows HAA1 and/or, for the first time, PRS3 overexpression to play an important role in the improvement of industrial yeast tolerance towards acetic acid. The results expand the molecular toolbox and add to the current understanding of the mechanisms involved in higher acetic acid tolerance, paving the way for the further development of more efficient industrial processes.

Mechanistic insight into the quantitative synthesis of acetic acid by direct conversion of CH4 and CO2: An experimental and theoretical approach

Abstract: Conversion of CH4 and CO2 into value-added products has vital environmental and economic importance. Their direct conversion to acetic acid is challenging due to their high activation energy. Hence, kinetic and mechanistic information are crucial for the carbonylation of CH4 with CO2. Regarding this, single and dual component catalysts with different combinations of ZnO-, CeO2-, and MnO2- supported montmorillonite (MMT) were prepared and characterized by XPS, Raman, and XRD. Quick solid-state NMR, TGA, and FT-IR techniques were used and Langmuir-Hinshelwood model was considered to investigate mechanistic steps involved in the conversion of CH4 and CO2 to acetic acid. The obtained mechanistic and kinetic results were also theoretically proved by density functional theory (DFT) calculations. We found that ZnO and CeO2 dual active sites preferentially adsorb the CH4 and CO2, respectively that avoid surface adsorption competition. The rate of acetic acid formation was maximum when these sites exist at appropriate concentration (Ce: 0.44 wt%, Zn: 2.20 wt%). DFT calculations elucidated that the formation of acetic acid is strongly favored on ZnO catalyst with easier migration of the adsorbed CO2 from CeO2 to the ZnO side.