Showing papers on "Acetic acid published in 2021"

Direct and continuous generation of pure acetic acid solutions via electrocatalytic carbon monoxide reduction.

Abstract: Electrochemical CO2 or CO reduction to high-value C2+ liquid fuels is desirable, but its practical application is challenged by impurities from cogenerated liquid products and solutes in liquid electrolytes, which necessitates cost- and energy-intensive downstream separation processes. By coupling rational designs in a Cu catalyst and porous solid electrolyte (PSE) reactor, here we demonstrate a direct and continuous generation of pure acetic acid solutions via electrochemical CO reduction. With optimized edge-to-surface ratio, the Cu nanocube catalyst presents an unprecedented acetate performance in neutral pH with other liquid products greatly suppressed, delivering a maximal acetate Faradaic efficiency of 43%, partial current of 200 mA⋅cm-2, ultrahigh relative purity of up to 98 wt%, and excellent stability of over 150 h continuous operation. Density functional theory simulations reveal the role of stepped sites along the cube edge in promoting the acetate pathway. Additionally, a PSE layer, other than a conventional liquid electrolyte, was designed to separate cathode and anode for efficient ion conductions, while not introducing any impurity ions into generated liquid fuels. Pure acetic acid solutions, with concentrations up to 2 wt% (0.33 M), can be continuously produced by employing the acetate-selective Cu catalyst in our PSE reactor.

Structure and properties of chitosan films: Effect of the type of solvent acid

Abstract: The properties of chitosan films can be modified by changing the solvent type, attributing to the different interaction patterns between chitosan and acids. However, little is known about how these interactions affect the structure and properties of chitosan films. In this work, the influence of acid type on the structure and properties of chitosan films was studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). FTIR spectra showed that the ionic interactions and hydrogen bonding could occur between chitosan and acid ions. Structural analysis revealed that chitosan was partially crystalline in hydrochloric and acetic acid films, whereas it was amorphous in lactic and citric acid films. DSC result indicated that the glass transition temperature of chitosan was much lower in citric acid film with low water content than in all the other films, suggesting that the citrate ions interacted more strongly with chitosan. A melting transition appeared in hydrochloric and acetic acid films. In addition, the tensile strength of these films decreased with an increase in the volume of acid. These observations indicate that the choice of a proper solvent for chitosan may be desirable for certain special applications.

Insight into Acetic Acid Synthesis from the Reaction of CH4 and CO2

Abstract: The reaction of CH4 and CO2 to produce acetic acid is an atom-efficient way for using carbon resources and for mitigating CO2 emissions. This article provides a critical assessment of the progress ...

Direct copolymerization of ethylene with protic comonomers enabled by multinuclear Ni catalysts.

Abstract: Ethylene/polar monomer coordination copolymerization offers an attractive way of making functionalized polyolefins. However, ethylene copolymerization with industrially relevant short chain length alkenoic acid remain a big challenge. Here we report the efficient direct copolymerization of ethylene with vinyl acetic acid by tetranuclear nickel complexes. The protic monomer can be extended to acrylic acid, allylacetic acid, ω-alkenoic acid, allyl alcohol, and homoallyl alcohol. Based on X-ray analysis of precatalysts, control experiments, solvent-assisted electrospray ionization-mass spectrometry detection of key catalytic intermediates, and density functional theory studies, we propose a possible mechanistic scenario that involves a distinctive vinyl acetic acid enchainment enabled by Ni···Ni synergistic effects. Inspired by the mechanistic insights, binuclear nickel catalysts are designed and proved much more efficient for the copolymerization of ethylene with vinyl acetic acid or acrylic acid, achieving the highest turnover frequencies so far for both ethylene and polar monomers simultaneously.

Pyrolysis of Oxalate, Acetate, and Perchlorate Mixtures and the Implications for Organic Salts on Mars

Abstract: Organic salts, such as Fe, Ca, and Mg oxalates and acetates, may be widespread radiolysis and oxidation products of organic matter in Martian surface sediments. Such organic salts are challenging to identify by evolved gas analysis but the ubiquitous CO2 and CO in pyrolysis data from the Sample Analysis at Mars (SAM) instrument suite on the Curiosity rover indirectly points to their presence. Here, we examined laboratory results from SAM‐like analyses of organic salts as pure phases, as trace phases mixed with silica, and in mixtures with Ca and Mg perchlorates. Pure oxalates evolved CO2 and CO, while pure acetates evolved CO2 and a diverse range of organic products dominated by acetone and acetic acid. Dispersal within silica caused minor peak shifting, decreased the amounts of CO2 evolved by the acetate standards, and altered the relative abundances of the organic products of acetate pyrolysis. The perchlorate salts scrubbed Fe oxalate CO releases and shifted the CO2 peaks to lower temperatures, whereas with Ca and Mg oxalate, a weaker CO release was observed but the initial CO2 evolutions were largely unchanged. The perchlorates induced a stronger CO2 release from acetates at the expense of other products. Oxalates evolved ∼47% more CO2 and acetates yielded ∼69% more CO2 when the perchlorates were abundant. The most compelling fits between our organic salt data and SAM CO2 and CO data included Martian samples acquired from modern eolian deposits and sedimentary rocks with evidence for low‐temperature alteration.

Influence of indigenous lactic acid bacteria on the volatile flavor profile of light-flavor Baijiu

Abstract: Baijiu (Chinese liquor) is a type of traditional distilled spirit drink produced by spontaneous fermentation. Lactic acid bacteria as the predominant bacteria during the fermentation of Baijiu may influence the flavor through the production of enzymes and metabolites. Results showed that there was significant difference in lactic acid bacteria counts between different fermentation periods. Indigenous lactic acid bacteria with high alcohol tolerance and esterase activity were selected for fortified fermentation. Inoculation with indigenous lactic acid bacteria significantly changed the flavor profile of Baijiu. All the selected strains promoted the formation of ethyl acetate which is an important flavor in Baijiu. Lactobacillus acetotolerans significantly promoted the formation of ethyl acetate, ethyl lactate, ethanol, acetic acid, and 2,4-di-tert-butylphenol. Sensory analysis revealed higher harmony in the samples fermented with L. hilgardii and L. acetotolerans, and higher intensive ester aroma in the samples fermented with L. planturum. The generation of flavors such as esters, alcohols and acids were species or even strain dependent. The results of this work will broaden our knowledge regarding the role of indigenous lactic acid bacteria during Baijiu manufacturing, and provide a potential approach for improving the flavor of Baijiu.

Y-doped ZnO films for acetic acid sensing down to ppb at high humidity

Abstract: Acetic acid is a potential breath marker for cystic fibrosis and gastroesophageal reflux. Also, it is a key tracer for aroma development in the food industry for chocolate and coffee processing. However, its selective detection down to relevant parts per billion (ppb) concentrations under realistic relative humidity (RH) is most challenging, especially with low-cost sensors. Here, highly porous Y-doped ZnO films for sensing acetic acid down to 10 ppb within 2 min at 90% RH are prepared by single-step flame-aerosol deposition with close control over their composition. X-ray diffraction and energy-dispersive X-ray spectroscopy reveal Y traces inside the ZnO wurtzite nanoparticles assuring small (below 25 nm) and thermally stable crystal sizes even upon annealing at 500 °C for 5 h in air. Separate Y2O3 nanoparticles are formed at elevated Y-contents. At an optimal Y-content of 2.5 mol% and sensing at 350 °C, remarkable selectivities of acetic acid over H2 (200), acetone (15), ethanol (5) and isoprene (3) are obtained. This is attributed to the high surface basicity of Y-doped ZnO featuring up to three orders of magnitude higher acetic acid selectivity than less basic SnO2 and WO3 sensors. Additionally, the influence of RH (10 – 90%) on acetic acid sensing is examined. This sensor is compact and inexpensive, thus promising for integration into hand-held and low-cost food processing or breath monitors.

Classification of acetic acid bacteria and their acid resistant mechanism.

Abstract: Acetic acid bacteria (AAB) are obligate aerobic Gram-negative bacteria that are commonly used in vinegar fermentation because of their strong capacity for ethanol oxidation and acetic acid synthesis as well as their acid resistance. However, low biomass and low production rate due to acid stress are still major challenges that must be overcome in industrial processes. Although acid resistance in AAB is important to the production of high acidity vinegar, the acid resistance mechanisms of AAB have yet to be fully elucidated. In this study, we discuss the classification of AAB species and their metabolic processes and review potential acid resistance factors and acid resistance mechanisms in various strains. In addition, we analyze the quorum sensing systems of Komagataeibacter and Gluconacetobacter to provide new ideas for investigation of acid resistance mechanisms in AAB in the form of signaling pathways. The results presented herein will serve as an important reference for selective breeding of high acid resistance AAB and optimization of acetic acid fermentation processes.

Acetic acid stress in budding yeast: From molecular mechanisms to applications.

Abstract: Acetic acid stress represents a frequent challenge to counteract for yeast cells under several environmental conditions and industrial bioprocesses. The molecular mechanisms underlying its response have been mostly elucidated in the budding yeast Saccharomyces cerevisiae, where acetic acid can be either a physiological substrate or a stressor. This review will focus on acetic acid stress and its response in the context of cellular transport, pH homeostasis, metabolism and stress-signalling pathways. This information has been integrated with the results obtained by multi-omics, synthetic biology and metabolic engineering approaches aimed to identify major cellular players involved in acetic acid tolerance. In the production of biofuels and renewable chemicals from lignocellulosic biomass, the improvement of acetic acid tolerance is a key factor. In this view, how this knowledge could be used to contribute to the development and competitiveness of yeast cell factories for sustainable applications will be also discussed.

Volatile Organic Compounds in Breads Prepared with Different Sourdoughs

Abstract: Sourdough is an old example of a natural starter composed of a mixture of flour, water, and metabolites and is produced by naturally occurring lactic acid bacteria and yeasts that influence bread aroma In this work, four types of sourdough were used to prepare bread: one sourdough with yeast beer and three with bacteria and yeasts The physicochemical parameters (pH, moisture, water activity, and organic acids) of the bread and sourdoughs were assessed Lactic, acetic, and succinic acids were found in considerable amounts in sourdoughs and the corresponding breads The fermentation quotient (molar ratio between lactic and acetic acid) ranged from 039 to 34 in sourdoughs Lactic acid was prevalent in all types of bread and showed the highest value in bread made from sourdough with a 15 bacteria/yeast ratio (872224 mg/kg) Moreover, volatile organic compounds were identified in bread samples Alcohols, aldehydes, and acetic acid were mainly found The alcohol concentration ranged from 14088 to 40120 ng/g Aldehydes ranged from 18501 to 45495 ng/g, and acetic acid ranged from 9140 to 17381 ng/g Bread prepared from sourdough with a 15 bacteria/yeast ratio showed a considerable amount of alcohols and acetic acid