Showing papers on "Acetic acid published in 2011"

Modulated Synthesis of Zr‐Based Metal–Organic Frameworks: From Nano to Single Crystals

Abstract: We present an investigation on the influence of benzoic acid, acetic acid, and water on the syntheses of the Zr-based metal-organic frameworks Zr-bdc (UiO-66), Zr-bdc-NH(2) (UiO-66-NH(2)), Zr-bpdc (UiO-67), and Zr-tpdc-NH(2) (UiO-68-NH(2)) (H(2) bdc: terephthalic acid, H(2) bpdc: biphenyl-4,4'-dicarboxylic acid, H(2) tpdc: terphenyl-4,4''-dicarboxylic acid). By varying the amount of benzoic or acetic acid, the synthesis of Zr-bdc can be modulated. With increasing concentration of the modulator, the products change from intergrown to individual crystals, the size of which can be tuned. Addition of benzoic acid also affects the size and morphology of Zr-bpdc and, additionally, makes the synthesis of Zr-bpdc highly reproducible. The control of crystal and particle size is proven by powder XRD, SEM and dynamic light scattering (DLS) measurements. Thermogravimetric analysis (TGA) and Ar sorption experiments show that the materials from modulated syntheses can be activated and that they exhibit high specific surface areas. Water proved to be essential for the formation of well-ordered Zr-bdc-NH(2) . Zr-tpdc-NH(2), a material with a structure analogous to that of Zr-bdc and Zr-bpdc, but with the longer, functionalized linker 2'-amino-1,1':4',1''-terphenyl-4,4''-dicarboxylic acid, was obtained as single crystals. This allowed the first single-crystal structural analysis of a Zr-based metal-organic framework.

Production of furfural and carboxylic acids from waste aqueous hemicellulose solutions from the pulp and paper and cellulosic ethanol industries

Abstract: In this paper we present a new process to produce furfural and co-products of formic and acetic acids from waste aqueous hemicellulose solutions using a continuous two zone biphasic reactor. We estimate this approach uses 67% to 80% less energy than the current industrial processes to produce furfural. An economic analysis indicates that furfural can be produced with this process at 366 US$ per metric ton which is 25% of the selling price of furfural in the U.S. market today. This analysis assumes a plant capacity of 78 kiloton per year of furfural, 12 kiloton per year of formic acid and 44 kiloton per year of acetic acid (processing 160 ton per hour of hemicellulose solutions with a xylose concentration of 10.7 wt%) and is based on the data collected in this paper. Formic acid and acetic acid are probably produced from the acid hydrolysis of formylated and acetylated xylose oligomers, respectively. Furfural is produced in a two-step process consisting of the hydrolysis of xylose oligomers followed by the dehydration of xylose monomers and then extraction of the furfural into an organic solvent. Two types of hemicellulose solutions were used as the feedstock including a hot water extract and a green liquor extract derived from Northeastern hardwood trees. The hemicellulose solution contains mainly xylose oligomers as well as glucose, arabinose, lactic acid, acetic acid, formic acid, and other minor products. We found that the reaction temperature, the space velocity, the volumetric organic to aqueous phase ratio, and the acid concentration have significant effects on the furfural production. Under the optimized condition, a furfural yield of 90% can be achieved in the reactor from the hot water extract containing 10.7 wt% xylose. A conceptual design is performed for the integration of the production of furfural, formic and acetic acids, the liquid–liquid split, and subsequent three-stage distillations. We demonstrate that high purity (>99%) of furfural, formic and acetic acids can be obtained, with a final recovery of more than 97%, 56%, and 88% of the furfural, formic acid and acetic acid, respectively.

Rapid and highly selective conversion of biomass into value-added products in hydrothermal conditions: chemistry of acid/base-catalysed and oxidation reactions

Abstract: An overview of recent advances in research on selective conversion of carbohydrates into products with hydrothermal chemistry is given. Conversion methods tend to use acid- or base-catalysed reactions and oxidation reactions. Conversion products that can be selectively produced include acetic acid, formic acid, lactic acid, levulinic acid, 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (2-FA). Future conversion paths and possible new products that can be formed with hydrothermal chemistry include aldol/reverse condensation, dehydration, benzilic acid rearrangement, keto-enol tautomerization, Lobry de Bruyn–Alberda van Ekenstein transformation and oxidation reactions.

Metabolic pathway engineering based on metabolomics confers acetic and formic acid tolerance to a recombinant xylose-fermenting strain of Saccharomyces cerevisiae

Abstract: The development of novel yeast strains with increased tolerance toward inhibitors in lignocellulosic hydrolysates is highly desirable for the production of bio-ethanol. Weak organic acids such as acetic and formic acids are necessarily released during the pretreatment (i.e. solubilization and hydrolysis) of lignocelluloses, which negatively affect microbial growth and ethanol production. However, since the mode of toxicity is complicated, genetic engineering strategies addressing yeast tolerance to weak organic acids have been rare. Thus, enhanced basic research is expected to identify target genes for improved weak acid tolerance. In this study, the effect of acetic acid on xylose fermentation was analyzed by examining metabolite profiles in a recombinant xylose-fermenting strain of Saccharomyces cerevisiae. Metabolome analysis revealed that metabolites involved in the non-oxidative pentose phosphate pathway (PPP) [e.g. sedoheptulose-7-phosphate, ribulose-5-phosphate, ribose-5-phosphate and erythrose-4-phosphate] were significantly accumulated by the addition of acetate, indicating the possibility that acetic acid slows down the flux of the pathway. Accordingly, a gene encoding a PPP-related enzyme, transaldolase or transketolase, was overexpressed in the xylose-fermenting yeast, which successfully conferred increased ethanol productivity in the presence of acetic and formic acid. Our metabolomic approach revealed one of the molecular events underlying the response to acetic acid and focuses attention on the non-oxidative PPP as a target for metabolic engineering. An important challenge for metabolic engineering is identification of gene targets that have material importance. This study has demonstrated that metabolomics is a powerful tool to develop rational strategies to confer tolerance to stress through genetic engineering.

Surface only modification of bacterial cellulose nanofibres with organic acids

Abstract: Bacterial cellulose (BC) nanofibres were modified only on their surface using an esterification reaction with acetic acid, hexanoic acid or dodecanoic acid. This reaction rendered the extremely hydrophilic surfaces of BC nanofibres hydrophobic. The hydrophobicity of BC increased with increasing carbon chain length of the organic acids used for the esterification reaction. Streaming (zeta-) potential measurements showed a slight shift in the isoelectric point and a decrease in ζplateau was also observed after the esterification reactions. This was attributed to the loss of acidic functional groups and increase in hydrophobicity due to esterification of BC with organic acids. A method based on hydrogen/deuterium exchange was developed to evaluate the availability of surface hydroxyl groups of neat and modified BC. The thermal degradation temperature of modified BC sheets decreased with increasing carbon chain length of the organic acids used. This is thought to be a direct result of the esterification reaction, which significantly reduces the packing efficiency of the nanofibres because of a reduction in the number of effective hydrogen bonds between them.

Metal–Organic Frameworks of Vanadium as Catalysts for Conversion of Methane to Acetic Acid

Abstract: A catalytic system combining the high activity of homogeneous catalysts and the ease of use of heterogeneous catalysts for methane activation is reported. The vanadium-containing metal-organic frameworks (MOFs) MIL-47 and MOF-48 are found to have high catalytic activity and chemical stability. They convert methane selectively to acetic acid with 70% yield (490 TON) based on K(2)S(2)O(8) as an oxidant. Isotopic labeling experiments showed that two methane molecules are converted to the produced acetic acid. The MOF catalysts are reusable and remain catalytically active for several recycling steps without losing their crystalline structures.

Detoxification of woody hydrolyzates with activated carbon for bioconversion to ethanol by the thermophilic anaerobic bacterium Thermoanaerobacterium saccharolyticum

Abstract: Autohydrolysis is a simple, green method of recovering sugars from biomass, using only hot water. One potential drawback is that byproducts are formed during the autohydrolysis process that could interfere with subsequent hydrolysis and fermentation to ethanol. In the present work, autohydrolysis prehydrolyzate from mixed hardwood chips was detoxified with activated carbon and the removal efficiency of byproducts as well as the loss of sugars determined. The resulting detoxified prehydrolyzate was evaluated for the fermentation to ethanol with a thermophilic anaerobic bacterium. Activated carbon at a 2.5 wt % level on the prehydrolyzate was able to remove 42% of formic acid, 14% of acetic acid, 96% of hydroxymethylfurfural (HMF) and 93% of the furfural. However, 8.9% of sugars were also removed. The removal of HMF and furfural follow expected adsorption isotherms but formic acid, acetic acid, and sugars did not. Autohydrolysis prehydrolyzates from mixed hardwood detoxified with activated carbon can be fermented with Thermoanaerobacterium saccharolyticum strain MO1442 with an essentially 100% yield. T. saccharolyticum strain MO1442 is able to metabolize the glucose, xylose, and arabinose in the hydrolyzate. The results showed the detoxification process with activated carbon improved the ethanol yields by the removal of toxic compounds, mainly HMF and furfural, with moderate loss of fermentable sugars.

Reduction of N2O and NO Generation in Anaerobic−Aerobic (Low Dissolved Oxygen) Biological Wastewater Treatment Process by Using Sludge Alkaline Fermentation Liquid

Abstract: This paper reported an efficient method to significantly reduce nitrous oxide (N(2)O) and nitric oxide (NO) generation in anaerobic-aerobic (low dissolved oxygen) processes. It was found that by the use of waste-activated sludge alkaline fermentation liquid as the synthetic wastewater-carbon source, compared with the commonly used carbon source in the literature (e.g., acetic acid), the generation of N(2)O and NO was reduced by 68.7% and 50.0%, respectively, but the removal efficiencies of total phosphorus (TP) and total nitrogen (TN) were improved. Both N(2)O and NO were produced in the low dissolved oxygen (DO) stage, and the use of sludge fermentation liquid greatly reduced their generation from the denitrification. The presences of Cu(2+) and propionic acid in fermentation liquid were observed to play an important role in the reduction of N(2)O and NO generation. The analysis of the activities of denitrifying enzymes suggested that sludge fermentation liquid caused the significant decrease of both nitrite reductase activity to NO reductase activity ratio and NO reductase activity to N(2)O reductase activity ratio, which resulted in the lower generation of NO and N(2)O. Fluorescence in situ hybridization analysis indicated that the number of glycogen accumulating bacteria, which was reported to be relevant to nitrous oxide generation, in sludge fermentation liquid reactor was much lower than that in acetic acid reactor. The quantitative detection of the nosZ gene, encoding nitrous oxide reductase, showed that the use of fermentation liquid increased the number of bacteria capable of reducing N(2)O to N(2). The feasibility of using sludge fermentation liquid to reduce NO and N(2)O generation in an anaerobic-low DO process was finally confirmed for a municipal wastewater.

Reaction engineering analysis of hydrogenotrophic production of acetic acid by Acetobacterium woodii

Abstract: Great interest has emerged in biological CO2-fixing processes in the context of current climate change discussions. One example for such a process is the hydrogenotrophic production of acetic acid by anaerobic microorganisms. Acetogenic microorganisms make use of carbon dioxide in the presence of hydrogen to produce acetic acid and biomass. In order to establish a process for the hydrogenotrophic production of acetic acid, the formation of acetate by Acetobacterium woodii was studied in a batch-operated stirred-tank bioreactor at different hydrogen partial pressures (pH2) in the gas phase. The volumetric productivity of the batch processes increased with increasing hydrogen partial pressure. A maximum of the volumetric productivity of 7.4 gacetate L−1 day−1 was measured at a pH2 of 1,700 mbar. At this pH2 a final acetate concentration of 44 g L−1 was measured after a process time of 11 days, if the pH was controlled at pH 7.0 (average cell density of 1.1 g L−1 cell dry weight). The maximum cell specific actetate productivity was 6.9 gacetate g day−1 under hydrogenotrophic conditions. Biotechnol. Bioeng. 2011;108: 470–474. © 2010 Wiley Periodicals, Inc.

Formic Acid Triggers the “Acid Crash” of Acetone-Butanol-Ethanol Fermentation by Clostridium acetobutylicum

Abstract: Solvent production by Clostridium acetobutylicum collapses when cells are grown in pH-uncontrolled glucose medium, the so-called "acid crash" phenomenon. It is generally accepted that the fast accumulation of acetic acid and butyric acid triggers the acid crash. We found that addition of 1 mM formic acid into corn mash medium could trigger acid crash, suggesting that formic acid might be related to acid crash. When it was grown in pH-uncontrolled glucose medium or glucose-rich medium, C. acetobutylicum DSM 1731 containing the empty plasmid pIMP1 failed to produce solvents and was found to accumulate 0.5 to 1.24 mM formic acid intracellularly. In contrast, recombinant strain DSM 1731 with formate dehydrogenase activity did not accumulate formic acid intracellularly and could produce solvent as usual. We therefore conclude that the accumulation of formic acid, rather than acetic acid and butyric acid, is responsible for the acid crash of acetone-butanol-ethanol fermentation.

Structure and Catalysis of Cellulose‐Derived Amorphous Carbon Bearing SO3H Groups

Abstract: The correlation between catalytic performance and structure of a cellulose-derived and carbon-based solid acid (CCSA), an amorphous carbon bearing SO(3)H, COOH, and phenolic OH groups, was investigated. Sulfonation of partially carbonized cellulose under a N(2) atmosphere resulted in the formation of a CCSA, which was amorphous carbon consisting of small polycyclic aromatic carbon sheets with a high density of SO(3)H groups (ca. 2 mmol g(-1)). CCSAs were prepared from carbon precursors, which were obtained at temperatures ≤723 K, and exhibited a high catalytic performance for the esterification of acetic acid with ethanol and for the hydrolysis of cellobiose, although the surface areas were small (<5 m(2) g(-1)). In contrast, CCSAs, which were prepared from carbon precursors obtained at ≥823 K, exhibited much lower catalytic activities for both reactions, although the CCSAs had sufficient amounts of SO(3)H groups. Structural analyses, including spectroscopic analysis of CCSAs with adsorbed probe molecules, revealed that cross-linking between the polycyclic aromatic carbon sheets caused the sharp decrease in activity.

pH-Dependent and Carrier-mediated Transport of Salicylic Acid Across Caco-2 Cells

Abstract: The transport of monocarboxylic acid drugs such as salicylic acid was examined in the human colon adenocarcinoma cell line, Caco-2 cells that possess intestinal epithelia-like properties. [14C]Salicylic acid transport was pH-dependent and appeared to follow the pH-partition hypothesis. However, 10 mM unlabelled salicylic acid significantly reduced the permeability coefficient of [14C]salicylic acid. Kinetic analysis of the concentration dependence of the permeation rate of salicylic acid across Caco-2 cells showed both saturable (Kt = 5.28 +/- 0.72 mM Jmax = 36.6 +/- 3.54 nmol min-1 (mg protein)-1) and nonsaturable (kd = 0.37 +/- 0.08 microL min-1 (mg protein)-1) processes. The permeation rate of [14C]salicylic acid was competitively inhibited by both acetic acid and benzoic acid, which were demonstrated in our previous studies to be transported in the carrier-mediated-transport mechanism which is responsible for monocarboxylic acids. Furthermore, certain monocarboxylic acids significantly inhibited [14C]salicylic acid transport, whereas salicylamide and dicarboxylic acids such as succinic acid did not. From these results, it was concluded that the transcellular transport of [14C]salicylic acid across Caco-2 cells is by the pH-dependent and carrier-mediated transport mechanism specific for monocarboxylic acids.

Effect of changing solvents on poly(ε-caprolactone) nanofibrous webs morphology

Abstract: Polycaprolactone nanofibers were prepared using five different solvents (glacial acetic acid, 90% acetic acid, methylene chloride/DMF 4/1, glacial formic acid, and formic acid/acetone 4/1) by electrospinning process. The effect of solution concentrations (5%, 10%, 15% and 20%) and applied voltages during spinning (10KV to 20KV) on the nanofibers formation, morphology, and structure were investigated. SEM micrographs showed successful production of PCL nanofibers with different solvents. With increasing the polymer concentration, the average diameter of nanofibers increases. In glacial acetic acid solvent, above 15% concentration bimodal web without beads was obtained. In MC/DMF beads was observed only at 5% solution concentration. However, in glacial formic acid a uniform web without beads were obtained above 10% and the nanofibers were brittle. In formic acid/acetone solution the PCL web formed showed lots of beads along with fine fibers. Increasing applied voltage resulted in fibers with larger diameter.