Acid-water Mixtures Research Articles

Solubility determination as an alternative to migration measurements

ABSTRACTSolubility values for six UV stabilisers (Cyasorb UV-1164, Tinuvin P, Tinuvin 234, Tinuvin 326, Tinuvin 327 and Tinuvin 1577) and five antioxidants (Irgafos 168, Irganox 1010, Irganox 3114, Irganox 3790 and Irganox 565) were determined in all the liquid food simulants (3% (m/V) acetic acid–water mixture, 10% (V/V), 20% (V/V), 50% (V/V) ethanol–water mixture and vegetable oil) proposed in European Union Regulation No. 10/2011/EC, as well as in fruit juice and cola drink. The applied method was obtained by modification of the method for the determination of water solubility as described in OECD guideline Test No. 105. By using ultrasonication and shorter equilibration time, the time demand of the solubility determinations were decreased notably. Solubility values proved to be lower than the specific migration limits (as specified in 10/2011/EC) at 25°C for almost all target compounds in food simulants A, B, C and D1 as well as in fruit juice and cola drink. The exceptions were Tinuvin P and Irganox 3790 in simulant D1. The solubility in food simulant D2 was higher than 1000 µg ml–1 for all target compounds. These results show that the solubility of some additives in food simulants can be so low that it makes migration studies for certain additive–food simulant pairs dispensable.

Iron-catalyzed hydrogenation and dehydrogenation reactions with relevance to reversible hydrogen storage applications

AbstractToday’s energy concerns require the development of suitable solutions for the storage of energy from renewable resources. Although the chemical storage of energy using molecular hydrogen as energy carrier is one of the best options, this type of energy storage requires the conversion of hydrogen to liquid organic hydrogen careers (LOHCs) for practical reasons. This goal is challenging and highly desirable at the same time. In comparison to dihydrogen, hydrogen storage in LOHCs offers easier handling and minimum dangers involved in their production, storage, and reconversion. To achieve efficient processes based on LOHCs highly active catalyst systems are required which ideally are based on cheap and abundant metals such as iron. This review summarizes recent advances in ironcatalyzed hydrogenation and dehydrogenation reactions, with relevance to reversible hydrogen storage in small molecules. It entails the dehydrogenation reactions of formic acid and methanol water mixtures, the reverse reaction, the hydrogenation of CO2, dehydrogenation of alcohols, and the hydrogenation of different carbonyl compounds as the formal reverse reaction, as well as hydrogenation and dehydrogenation reactions of N-heterocyclic compounds and hydrogen release reactions from amino boranes.

Kinetics and Mechanism of Oxidation of some α - Hydroxy Acids by Tripropylammonium Fluorochromate in Aqueous Acetic Acid Medium

The oxidation of some α-hydroxy acids like glycolic, lactic and mandelic acids by tripropylammonium fluorochromate (TriPAFC) have been studied in aqueous acetic acid medium. The oxidation leads to the formation of the corresponding oxo acids. The reaction is first order with respect to TriPAFC, hydroxy acids and (H + ) and the reaction is catalyzed by hydrogen ions. The reaction has been studied in different percentage of acetic acid-water mixture. A suitable mechanism has been proposed.

Recovering ultraclean lignins of controlled molecular weight from Kraft black-liquor lignins.

By operating in a region of liquid-liquid equilibrium, hot acetic acid-water mixtures can be used to simultaneously clean, fractionate, and solvate Kraft black-liquor lignins. Lignin-rich liquid phases of controlled molecular weight with key metals contents reduced to <50 ppm are obtained without a washing step.

Complexation of Eu(III) with cucurbit[n]uril, n = 5 and 7: a thermodynamic and structural study.

Cucurbit[n]urils (CBn) are a new class of macrocyclic cage compounds capable of binding organic and inorganic species, owing to their unique pumpkin like structure comprising of both a hydrophobic cavity and a hydrophilic portal. The thermodynamics of the complexation of Eu(III) with CBn of a different cavity size viz. cucurbit[5]uril (CB5) and cucurbit[7]uril (CB7) has been studied by UV-Vis spectroscopy and calorimetry at 25 °C whereas the structure of the complexes was investigated using time resolved fluorescence spectroscopy (TRFS) and extended X-ray absorption fine structure spectroscopy (EXAFS) in a formic acid-water mixture (50 wt%). This is the first report on the structural investigation of Eu-CBn complexes in solution. The thermodynamic data (ΔG, ΔH and ΔS) for Eu(III) complexation with CBn reveal the formation of a 1 : 1 complex with CB5, while both 1 : 1 and 1 : 2 complexes are observed with CB7. The signatures of these species are observed in ESI-MS measurements, which corroborates with the species postulated in thermodynamic studies. The complexation reactions are found to be driven by ΔS as ΔH is either small negative or positive indicating the formation of inner sphere complexes, which is in line with TRFS and EXAFS results. These studies show that Eu(III) caps one of the CB5 portals by binding with all the carbonyl groups in the 1 : 1 Eu-CB5 complex, whereas in the 1 : 1 Eu-CB7 complex, Eu(III) interacts with only a few of the carbonyl groups of CB7. The computational studies (DFT calculations) on Eu-CB5 and Eu-CB7 complexes further support the experimental data.

Direct quantitative analysis of amino acids in fermented beverage of plant extract using high performance liquid chromatography-tandem mass spectrometry

A method was established for underivatized amino acid determination in fermented beverage of plant extract. Samples were diluted with methanol for five times, extracted by ultrasonic vibration for 30 min, and high-speed centrifuged for 15 min at 10,000 r/min. The supernatant was separated and detected by, high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The chromatographic column was Venusil ASB C18 (250 mm x 4.6 mm, 5 µm). The elution was performed at a flow rate of 0.5 mL/min using the mobile phases of methanol-acetic acid-water mixture. The MS detector was set as follows: ion source voltage 3 kV, ion source temperature 150 t, solvent temperature 350 t, gas flow rate 800 L/h. The collision gas was argon with a pressure of 0.17 Pa. The quantitation analysis was carried out with peak area in extracted ion chromatograms. Good linearities were acquired in the range of 0.5-200 µmol/L (r2 > 0.99) for the amino acids. The recoveries were between 86% and 110%. There were 16 amino acids in the fermented beverage of plant extract quantitatively analyzed. The method is simple, rapid, accurate and reliable in quantitative analysis of amino acid samples in the fields of pharmaceutical, food and natural products.

Improving enzymatic hydrolysis of corn stover pretreated by ethylene glycol-perchloric acid-water mixture.

To improve the enzymatic saccharification of lignocellulosic biomass, a mixture of ethylene glycol-HClO4-water (88.8:1.2:10, w/w/w) was used for pretreating corn stover in this study. After the optimization in oil-bath system, the optimum pretreatment temperature and time were 130 °C and 30 min, respectively. After the saccharification of 10 g/L pretreated corn stover for 48 h, the saccharification rate was obtained in the yield of 77.4 %. To decrease pretreatment temperature and shorten pretreatment time, ethylene glycol-HClO4-water (88.8:1.2:10, w/w/w) media under microwave irradiation was employed to pretreat corn stover effectively at 100 °C and 200 W for 5 min. Finally, the recovered hydrolyzates containing glucose obtained from the enzymatic hydrolysis of pretreated corn stovers could be fermented into ethanol efficiently. These results would be helpful for developing a cost-effective pretreatment combined with enzymatic saccharification of cellulosic materials for the production of lignocellulosic ethanol.

The influence of physical state on shikimic acid ozonolysis: a case for in situ microspectroscopy

Abstract. Atmospheric soluble organic aerosol material can become solid or semi-solid. Due to increasing viscosity and decreasing diffusivity, this can impact important processes such as gas uptake and reactivity within aerosols containing such substances. This work explores the dependence of shikimic acid ozonolysis on humidity and thereby viscosity. Shikimic acid, a proxy for oxygenated reactive organic material, reacts with O3 in a Criegee-type reaction. We used an environmental microreactor embedded in a scanning transmission X-ray microscope (STXM) to probe this oxidation process. This technique facilitates in situ measurements with single micron-sized particles and allows to obtain near-edge X-ray absorption fine structure (NEXAFS) spectra with high spatial resolution. Thus, the chemical evolution of the interior of the particles can be followed under reaction conditions. The experiments show that the overall degradation rate of shikimic acid is depending on the relative humidity in a way that is controlled by the decreasing diffusivity of ozone with decreasing humidity. This decreasing diffusivity is most likely linked to the increasing viscosity of the shikimic acid–water mixture. The degradation rate was also depending on particle size, most congruent with a reacto-diffusion limited kinetic case where the reaction progresses only in a shallow layer within the bulk. No gradient in the shikimic acid concentration was observed within the bulk material at any humidity indicating that the diffusivity of shikimic acid is still high enough to allow its equilibration throughout the particles on the timescale of hours at higher humidity and that the thickness of the oxidized layer under dry conditions, where the particles are solid, is beyond the resolution of STXM.

Hydrogen Production from Sodium Borohydride in Boric Acid-water Mixtures

Borohydride, which reacts slowly with water, is developed as hydrogen production and storage options. The reaction is significantly accelerated by the rise of temperature or by the addition of acidic substances. Boric acid (H3BO3) can be used as an alternative to water for the hydrogen production in the hydrolysis of sodium borohydride (NaBH4). The effect of H3BO3 and NaBH4–H3BO3 molar ratios was studied at 30, 40, 50, 60, and 80°C on the hydrogen production of NaBH4. All of these results show that H3BO3 is a relatively green acid compound for hydrogen generation from NaBH4 and the H3BO3-water-NaBH4 system being quite simple for single-use applications. It was found that the reaction between H3BO3 and NaBH4 complied with a second order kinetics rate with 0.5 reaction orders versus NaBH4 concentration and 1.5 orders versus H3BO3 concentration, and the activation energy for conversion was calculated as 18.01 kJ mol−1.

Measurement on the solubility of adipic acid in various solvents at high temperature and its thermodynamics parameters

This work presents measurements of the solubility of adipic acid in water, acetic acid, acetic acid-water mixture (ratio of 1:1, v/v), cyclohexanol and cyclohexanone at the temperature ranging from 303.0 to 403.0K. The reliability experimental method used in this work for studying the solubility of adipic acid was verified using the published solubility data at low temperatures. The modified Apelblat equation was applied in order to correlate the solubility of adipic acid in the above-mentioned solvents. The results showed that data obtained from our method were acceptable for measuring the solubility of adipic acid at high temperatures. The solubilities of adipic acid obtained from the modified Apelblat equation fitted well with the experimental data. The total average relative deviation was 2.55%. Moreover, the molar enthalpy and the molar entropy of dissolution of adipic acid in water, acetic acid, acetic acid–water mixtures, cyclohexanol and cyclohexanone at temperatures ranging from 303.0 to 403.0K were calculated.

Analysis of sorption and permeation of acetic acid–water mixtures through unfilled and filled blend membranes

A systematic method was employed for making blend membranes from two different hydrophilic polymers. Accordingly, blend membranes of polyvinyl alcohol (PVA) and sodium carboxy methyl cellulose (CMC) at three different wt ratio i.e. PVA:CMC wt ratio of 1:0.25, 1:0.5 and 1:0.75 were prepared. These blend membranes were designated as PC1, PC2 and PC3, respectively. Each of these membranes was crosslinked with 2wt% (of total polymer) maleic acid. These membranes were used for pervaporative (PV) separation of acetic acid–water mixtures at different feed compositions and temperatures. PC2 membrane showing optimum flux and water selectivity was further filled with 1, 2 and 3wt% (of total polymer) hydrophilic bentonite filler to produce three different filled membranes i.e. B1PC2, B2PC2 and B3PC2, respectively. These filled membranes were also used for separation of acetic acid–water mixtures. Both unfilled and filled membranes were characterized by FT-IR and UV spectroscopy, SEM, XRD, DSC and mechanical properties. Sorption of the membranes was analyzed by Flory–Huggins thermodynamics. Partial permeability of water and acid through the membranes were determined. Diffusion coefficient of permeants was also determined using a model based on free volume theory. Among these six membranes B2 PC2 membrane showed optimum performance in terms of flux and selectivity.

Separation of Acetic Acid from Acetic Acid-Water Mixture by Crystallization

Separation of acetic acid from acetic acid and water mixture was carried out by melt crystallization. The effect of the cooling rate, the amount of seeds, the seeding temperature, the sweating rate, and the sweating fraction on the distribution coefficient was investigated. The acetic acid was successfully separated by single-stage melt crystallization. As the sweating fraction is increased, the crystalline layers grown at lower cooling rates are purified more highly. Eventually, the crystallization rate is much more important than the sweating rate. The effective distribution coefficient ranges from 0.01 to 0.25 for the crystal growth rates of 1.2 × 10−6 m/s to 4 × 10−6 m/s.

Treatment of Herráez equation correlating viscosity in binary liquid mixtures exhibiting strictly monotonous distribution

Recently, Herráez et al. proposed a new correlation equation, which introduces a correcting polynomial as an exponential-acting upon the molar fraction of one of mixture components. This equation is found to be widely applicable with more reasonable accuracy in systems exhibiting monotonous distribution than those presenting an extremum. In previous works, we have found that the first adjustable parameter of this equation is a universal exponent (0.5 or 1) for dioxane–water and isobutyric acid–water mixtures characterising the presence of solute–solute or solute–solvent interaction at very high dilution. In this work, we have tested this equation in 48 systems, and we have noted that several data on binary mixtures exhibiting monotonous variation are well represented by the two sides of this equation. We have mathematically justified the four distinct values of the universal exponent classifying the nature of each solute–solvent couple in dilute region.

Molecular dynamics simulations of the water adsorption around malonic acid aerosol models

Water nucleation around a malonic acid aggregate has been studied by means of molecular dynamics simulations in the temperature and pressure range relevant for atmospheric conditions. Systems of different water contents have been considered and a large number of simulations have allowed us to determine the phase diagram of the corresponding binary malonic acid-water systems. Two phases have been evidenced in the phase diagrams corresponding either to water adsorption on a large malonic acid grain at low temperatures, or to the formation of a liquid-like mixed aggregate of the two types of molecules, at higher temperatures. Finally, the comparison between the phase diagrams simulated for malonic acid-water and oxalic acid-water mixtures emphasizes the influence of the O : C ratio on the hydrophilic behavior of the aerosol, and thus on its ability to act as a cloud condensation nucleus, in accordance with recent experimental conclusions.

Sorption and permeation of acetic acid–water mixtures by pervaporation using copolymer membrane

AbstractPoly (acrylonitrile‐co‐methyl acrylate) copolymer designated as PANMA was used for making pervaporation membrane. This membrane was used for separation of acetic acid–water mixtures over the concentration range of 80–99.5 wt% acetic acid in water. Interaction parameters based on Flory–Huggins lattice model and engaged species induced clustering (ENSIC) model was used to explain swelling of the membranes. Coupling in sorption was explained in terms of activity coefficient of water and acid in feed and membrane using Flory–Huggins model and also by interpolating ENSIC parameters. Flow coupling in pervaporation was also determined from phenomenological deviation coefficients. Intrinsic membrane properties like partial permeability and membrane selectivity of the solvents were also determined. Diffusion coefficient and plasticization coefficient of the solvents were obtained using a modified solution–diffusion model. The copolymer membrane showed high flux and water selectivity for highly concentrated acid. Thus, at 30°C temperature 1–20 wt% water in feed was concentrated to 82–84 wt% water in permeate and for 0.95 wt% water in feed, the membrane showed thickness normalized flux and water selectivity of 1.71 kg m−2 h−1 mμ and 409, respectively. OLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Determination of antioxidant property and their lipophilic and hydrophilic phenolic contents in cereal grains

In order to supply new information on the antioxidant function of cereal foods, the antioxidant activity and total phenolic contents of both lipophilic and hydrophilic components of 24 cereal grains from China were systematically evaluated using spectrophotometric methods. The lipophilic components of cereals were extracted with tetrahydrofuran, and the hydrophilic ones were extracted with a methanol-acetic acid-water (50:3.7:46.3, v/v/v) mixture. Main phenolic compounds and their contents were also quantified using high-performance liquid chromatography equipped with a photodiode array detector. The results showed that different cereals had diverse antioxidant capacities and the variation was very large. Phenolic compounds gallic acid, kaempferol, quercetin, galangin and cyanidin 3-glucoside were widely found in those cereals. The pigmented cereals, such as black rice, red rice and purple rice, possessed the highest antioxidant capacities and total phenolic contents among tested cereals, and could be important sources of natural antioxidants for health promotion and disease risk reduction.

Modeling Triple Conformational Disorder in a New Crystal Polymorph of cis-Aquabis(l-isoleucinato)copper(II)

The X-ray crystal and molecular structure of a new polymorph of cis-aquabis(l-isoleucinato)copper(II), obtained by recrystallization from an acetic acid–water mixture and determined at 120 and 295 K, revealed triple dynamic disorder over one isoleucinato ligand at both temperatures. The complicated multipart disorder was resolved with the help of extensive computational crystal structure simulations, which were undertaken for the first time to interpret disorder in a crystal of bioinorganic compound. The new polymorph (space group C2) is conformationally polymorphic with the already known P212121 crystal form. To discover the conformers that can participate in self-associations in solution, and to rationalize an interplay of intramolecular and intermolecular interactions in the crystallization of different conformers, conformational analyses of cis and trans isomers were performed using the same force field in vacuo, in aqueous solution, and for selected conformers in P212121 and C2 crystals. Three confor...

Separation of acid–water mixtures by pervaporation using nanoparticle filled mixed matrix copolymer membranes

AbstractBACKGROUND: Low energy and less expensive membrane based separation of acetic acid‐water mixtures would be a better alternative to conventional separation processes. However, suitable acid resistant membranes are still lacking. Thus, the objective of the present study was to develop mixed matrix membrane (MMM) which would allow high flux and water selectivity over a wide range of feed concentrations of acid in water.RESULTS: Three MMMs, namely PANBA0.5, PANBA1.5 and PANBA3 were made by emulsion copolymerization of acrylonitrile (AN) and butyl acrylate (BA) with 5.5:1 comonomer ratio and in situ incorporation of 0.5, 1.5 and 3 wt%, sodium montmorilonite (Na‐MMT) nanofillers, respectively. For a feed concentration of 99.5 wt% of acid in water the membranes show good permeation flux (2.61, 3.19, 3.97 kg m−2 h−1 µm−1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and very high separation factors for water (1473, 1370, 1292 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at 30 °C. Similarly for a dilute acid–water solution, i.e. for 71.6 wt% acid the membrane showed a very high thickness normalize flux (8.67, 9.44, 11.56 kg m−2 h−1 µm−1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and good water selectivity (101.7, 95.3, 79 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at the same feed temperature. The permeation ratio, permeability, diffusion coefficient and activation energy for permeation of the membranes were also estimated.CONCLUSION: Unlike most of the reported membranes, the present MMMs allowed high flux and selectivity over a wide range of feed concentrations. These membranes may also be effective for separating other similar organic‐water mixtures. Copyright © 2012 Society of Chemical Industry

Kinetics of reaction of sodium arsenite with chloroacetic acid in mixed solvents and effect of the nature of the cation of alkali metal hydroxide on the rate of Meyer reaction

The rate constants of the reaction of sodium arsenite with chloroacetic acid in mixtures of water with alcohols, acetone, tetrahydrofuran, dimethyl sulfoxide, dimethoxymethane, and 1,4-dioxane at 25°C were determined. By the examples of the reaction of chloroacetic acid with the lithium, sodium and potassium arsenites the effect of the nature of alkali metal hydroxide cation on the reaction rate of Meyer reaction is considered.

Assessment of Titratable Acidity in Fruit Using Short Wave near Infrared Spectroscopy. Part A: Establishing a Detection Limit Based on Model Solutions

Spectra (700–2500 nm) of citric acid dissolved in water possess features interpreted as being due to the dilution and perturbation of water OH stretching and combination bands (with the second and first overtones of OH stretching at 960 nm and 1420 nm, respectively, and a combination band of OH vibration at 2132 nm) and also to citric acid OH stretching and combination bands and citric acid CH2 bands (first overtone of CH2 stretching at 1680 nm and a combination band of CH2 at 2284 nm). A searching window method was used to optimise the wavelength region for a partial least squares (PLS) regression model development (around 743–904 nm for the region below 1100 nm). Despite the apparent lack of information below 1100 nm, a PLS regression model based on transmission spectra (743–904 nm) of pure citric acid—water mixtures (standard deviation = 6.65g citric acid 100 mL−1) yielded a root mean square error of cross-validation ( RMSECV) of 0.34% and correlation coefficient of determination ( Rcv2) = 0.998. However, if the matrix was varied with 0, 10 and 13% sucrose or fruit juice, RMSECV increased to 0.79%. This RMSECV value is proposed as a benchmark for attempts to assess titratable acidity of juice based on shortwave (700–1100 nm) near infrared spectra of intact fruit collected using silicon diode array instrumentation.