Aqueous Phase Conditions Research Articles

In-situ X-ray Absorption Spectroscopy of Supported Ru Catalysts in the Aqueous Phase

The size of supported Ru metal particles on various supports was monitored by in situ X-ray absorption spectroscopy under aqueous phase conditions typical of biomass conversion reactions. In particular, Ru/γ-Al2O3, Ru/C, Ru/TiO2, and Ru/SiO2 were evaluated at the Ru K edge at 473 K in neutral water and 0.4 M NaOH. The as-prepared samples exposed to air contained oxidized Ru that was subsequently reduced by H2-saturated water solution. Significant growth of the metal particles was observed on the Ru/γ-Al2O3 and Ru/SiO2 samples during the aqueous treatments, whereas the Ru/TiO2 and Ru/C samples were quite stable under the conditions used here. Results from post-treatment X-ray diffraction and surface area analysis revealed major structural changes of the alumina and silica supports. The structural stability of the carbon and titania account for the lack of metal particle growth on those supports. Because a reference Pt/C catalyst revealed metal particle growth under the same conditions, the results for the ...

Using strong injection solvents with 100% aqueous mobile phase in RP-LC

When samples are dissolved for HPLC analysis, organic solvents are often used to enhance the solubility of the sample components. However, when the diluent becomes significantly stronger than the mobile phase, peak shape distortions may develop during injection. This is a serious problem for weakly retained analytes under 100% aqueous mobile phase conditions. Under these extreme conditions, even small amounts of solvent in the diluent can cause serious broadening or distortion effects. However, if the organic solvent used in the diluent elutes significantly after the analyte, the peak shape of the analyte will be relatively unaffected, even when a relatively strong solvent such as THF is used. This phenomenon is counterintuitive considering the usual practice of keeping the sample diluent as weak as possible. This report describes the potential analytical utility and limitations of this approach for the analysis of weakly retained analytes.

Metal Particle Growth during Glucose Hydrogenation over Ru/SiO2 Evaluated by X-ray Absorption Spectroscopy and Electron Microscopy

Biorenewable resources such as carbohydrates are considered alternative feedstocks for oxygenated chemicals. This work investigates the stability of silica-supported Ru catalysts in the aqueous phase conversion of glucose to sorbitol. In situ X-ray absorption spectroscopy at the Ru K edge revealed that air-exposed silica-supported Ru was in an oxidized state but was subsequently reduced in aqueous solutions saturated with 40 bar H(2) at 373 K. Furthermore, exposure to aqueous phase conditions resulted in the sintering of Ru particles on the silica surface. However, the presence of glucose in the aqueous phase stabilized the growth of the Ru particles. Batchwise hydrogenation of glucose at 373 K and 80 bar H(2) over a Ru/SiO(2) (2.67 wt %) catalyst is nearly 100% selective to sugar alcohol with an average turnover frequency of 0.21 +/- 0.04 s(-1). The hydrogenation reaction was not mass transfer limited according to the Madon-Boudart criterion.

Comparison of ethylammonium formate to methanol as a mobile-phase modifier for reversed-phase liquid chromatography

Ethylammonium formate (EAF), (C2H5NH3+HCO2-), is a room-temperature ionic liquid that has a polarity similar to that of methanol (MeOH) or acetonitrile. The separation at 1 mL/min of a test mixture of vitamins or phenols on a polystyrene-divinylbenzene column using either an EAF- or MeOH-water mobile phase is similar in terms of both resolution and analysis time. Because the viscosity of EAF is higher than that of MeOH, the plate count for phenol at room temperature is lower by about a factor of 1.1-1.4 depending on the flow rate. However, van Deemter plots show that this loss in plate count at 1 mL/min can be recovered and improved from 1500 to 2400 plates by working at a slightly elevated temperature of 55 degrees C. A slower flow rate such as 0.8 mL/min can also substantially improve the plate count as compared to 1-1.5 mL/min. Log P (octanol partition coefficient) versus log k' data for a variety of neutral test solutes are again similar whether EAF or MeOH is used as the organic modifier. Resolution of certain peak pairs such as 2,4-dinitrophenol/2,4,6-trinitrophenol and p-aminobenzoate/benzoate is enhanced using EAF as compared to MeOH. One advantage of EAF is that control of retention of solutes such as water-soluble vitamins under totally aqueous mobile phase conditions is environmentally preferable for quality control applications. In addition, EAF seems to be a milder mobile-phase modifier than MeOH for certain proteins such as lysozyme.

Ozone–water contacting by ceramic membranes

Abstract A common process in water treatment is the wet oxidation for the removal of certain organic and inorganic pollutants. The strongest oxidant technically applied in this process is ozone, which is an unstable gas under normal conditions, and therefore is produced from oxygen on site, usually by electrical discharge. After that the ozone has to be transferred from that gas into the water to be treated. Conventionally ozone transfer is achieved by bringing the gas and water in direct contact by means of bubble columns, injectors or other similar devices. Under unfavorable conditions, however, these methods suffer from excessive formation of foam requiring an extra treatment and a high-energy demand for pumping gas or water. This project's approach was to improve the transfer by better control of gaseous and aqueous phase's conditions at the contact surface. This was achieved by means of a membrane both separating the two phases and allowing for an ozone transfer between them. Due to ozone's high oxidation potential, chemically inert ceramic membranes were chosen for that purpose. In experiments, it was found that the transfer of the unstable ozone molecules is not obstructed by ceramic membrane material. Transfer rates between gaseous ozone and model water were measured for conventional ceramic membranes, as well as specially designed ones. They are comparable to conventional methods or better on the base of mass transfer per reactor volume. In conventional oxide membranes, water enters the pores because of capillary effects in the hydrophilic material [Burggraaf, A.J. and Cot, L., 1996, Fundamentals of inorganic Membrane Science and Technology Elsevier Science, The Netherlands]. The water in the pores raises the diffusion resistance for the ozone thus decreasing the transfer itself. Consequently, the modification of the hydrophilic material features into a hydrophobic behavior was one promising approach for the optimization of the process. It was achieved through the application of a hydrophobic coating to the membrane surface, which greatly improved the transfer efficiency.

Synthesis of 11C‐labelled acamprosate for PET studies

AbstractA method for labelling acamprosate (calcium N‐acetyl homotaurinate), an anti‐craving compound for ethanol, with 11C, has been developed for in vivo studies with positron emission tomography (PET). The synthesis was based on the acylation of homotaurinate using [11C]acetyl chloride as the labelling agent. Reversed‐phase HPLC in highly aqueous mobile phase conditions was used for product purification. The radiochemical yield achieved was about 1.14 GBq (31 mCi) with a specific radioactivity of 8.14 GBq/µmol (220 mCi/µmol). For the identification of 11C‐radioactivity and determination of specific radioactivities, HPLC and 1H‐NMR were used. Copyright © 2001 John Wiley & Sons, Ltd.

Distribution of polycyclic aromatic hydrocarbons among different compartments of a river ecosystem

Distribution of PAHs in a river ecosystem was studied by sampling of four abiotic compartments (surface water, suspended matter, pore water and sediments) under two different hydro‐logical conditions. PAHs were detected at significant concentrations in both the solid and aqueous phase of the river ecosystem. Water concentrations were relatively low despite greater contamination of sediments. Lower MW PAHs were prevailing in the dissolved phase, higher MW PAHs in particulate materials. Concentrations of PAHs in surface waters were greater in summer than in fall. PAHs composition in the sediments was found to be relatively uniform across sites reflecting combustion generated PAH profile. Correlation and multivariate statistical analysis have shown differences between PAH patterns in solid and water samples. In aquatic samples and suspended matter, principal component analysis distinguished two separated groups of PAHs with different distribution depending on their molecular weight. In‐situ partition coefficients between the solid and aqueous phase did not differ very much between seasons. The role of organic carbon for PAHs partitioning to sediments in situ was examined. PAHs concentrations correlated to OC content only in summer. In‐situ Kocs were up to two orders of magnitude greater than tabulated Kocs based on the equilibrium partitioning model. The main reasons are the lower availibility of PAHs bound to particles from combustion sources to partition into the aqueous phase and dynamic conditions in the river ecosystem which do not enable the full equilibrium to appear.

The influence of system parameters on the stability of colloidal liquid aphrons

An investigation was carried out on the effect of process parameters involved in Pre-Dispersed Solvent Extraction (PDSE) on the stability and interactions in dilute dispersions of Colloidal Liquid Aphrons (CLAs). The aim of this work was to derive empirically-based engineering relationships that could be used in the design of PDSE processes. For this investigation, CLAs were formulated with an Aliquat 336/n-octanol/Softanol 120 solvent phase, and a Synperonic A20 aqueous phase. These CLAs were intended for use in the reactive pre-dispersed solvent extraction of polar solutes such as phenylalanine. Light scattering measurements over a range of continuous aqueous and CLA phase conditions were used as a method of obtaining a measure of the rate of disappearance of CLAs from dispersion (a measure of stability), and a comparison of stability under different conditions. Two forms of CLA interaction occurring by independent mechanisms were identified – CLA break-up, and CLA flocculation. Break-up was found to be a first order process, allowing CLA stability to be characterised by a first order half-life (typical half-life 15–40 min). This was proposed to occur on collision of CLAs with sufficient energy to overcome the stabilising forces provided by the surfactants at the interfaces of the CLAs. It was shown that flocculation occurred at high ionic strengths (>0.1 M NaCl), and that it was not part of the break-up mechanism. An apparent size dependent CLA half-life was proposed to be due to smaller particles having a lower collision energy on average. The data suggested that the resistance to CLA break-up was not charge repulsion, but derived from an interaction between molecules of one of the surfactants making up the aqueous ‘shell’ of the CLAs (Synperonic A20). Finally, the basis for a semi-empirical design equation for prediction of CLA half-life developed from the Arrhenius equation was proposed. © 1999 Society of Chemical Industry

The influence of system parameters on the stability of colloidal liquid aphrons

An investigation was carried out on the effect of process parameters involved in Pre-Dispersed Solvent Extraction (PDSE) on the stability and interactions in dilute dispersions of Colloidal Liquid Aphrons (CLAs). The aim of this work was to derive empirically-based engineering relationships that could be used in the design of PDSE processes. For this investigation, CLAs were formulated with an Aliquat 336/n-octanol/Softanol 120 solvent phase, and a Synperonic A20 aqueous phase. These CLAs were intended for use in the reactive pre-dispersed solvent extraction of polar solutes such as phenylalanine. Light scattering measurements over a range of continuous aqueous and CLA phase conditions were used as a method of obtaining a measure of the rate of disappearance of CLAs from dispersion (a measure of stability), and a comparison of stability under different conditions. Two forms of CLA interaction occurring by independent mechanisms were identified – CLA break-up, and CLA flocculation. Break-up was found to be a first order process, allowing CLA stability to be characterised by a first order half-life (typical half-life 15–40 min). This was proposed to occur on collision of CLAs with sufficient energy to overcome the stabilising forces provided by the surfactants at the interfaces of the CLAs. It was shown that flocculation occurred at high ionic strengths (>0.1 M NaCl), and that it was not part of the break-up mechanism. An apparent size dependent CLA half-life was proposed to be due to smaller particles having a lower collision energy on average. The data suggested that the resistance to CLA break-up was not charge repulsion, but derived from an interaction between molecules of one of the surfactants making up the aqueous ‘shell’ of the CLAs (Synperonic A20). Finally, the basis for a semi-empirical design equation for prediction of CLA half-life developed from the Arrhenius equation was proposed. © 1999 Society of Chemical Industry

Degradation, Cleanup, and Reusability of Octylphenyl- N, N′-diisobutylcarbamoylmethyl Phosphine Oxide (CMPO) during Partitioning of Minor Actinides from High Level Waste (HLW) Solutions

ABSTRACT The radiolytic degradation of the extractant mixture 0.2 M octylphenyl-N,N′-diiso-butylcaibamoylmethyl phosphine oxide (CMPO) + 1.2 M tributyl phosphate in n- dodecane [to be utilized for the partitioning of minor actinides from high level waste (HLW) solutions of PUREX origin] has been investigated in contact with 3 M HNO3 or synthetic pressurized heavy water reactors (PHWR)-HLW solution under dynamic conditions. The distribution ratios of Am, Zr, Fe, and Ru with the irradiated extractant mixture at varying doses have been determined under various aqueous phase conditions and correlated with the formation of degradation products. Various cycles ofloading the extractant mixture with Am from PHWR-HLW, irradiating at a fixed gamma dose, and then primary and secondary clean-up of the solvent has been carried out to illustrate its reusability during partitioning of minor actinides from actual HLW solutions. The degradation products of CMPO have been identified by employing GC and GC-MS techniques.

Synthesis and characterization of Na 5[Co(CO) 3(P{(CH 2) nC 6H 4-P-SO 3} 3) 2], n = 1, 2, 3, and 6. Novel zwitterion

The electron donating water soluble phosphines, P{(CH 2) nC 6H 4- p-SO 3Na} 3, n = 1, 2, 3 and 6, react rapidly with Co 2(CO) 8 under two phase reaction conditions to yield the disproportionation products, [Co(CO) 3(P{(CH 2) nC 6H 4- p-SO 3Na 3} 2] [Co(CO) 4]. Selective precipitation yields the formally zwitterionic complex anions as the sodium salt, [Co(CO) 3(P{(CH 2) nC 6H 4- p-SO 3} 3) 2] 5−. The anions can be used as precursors to water soluble cobalt hydroformylation catalysts under two phase and supported aqueous phase conditions. The tendency to form alcohol products is low with these complexes. The behavior of the catalysts is consistent with an active species that remains water soluble during the reaction and is not leached into the nonaqueous phase.

Dendrimer electrokinetic capillary chromatography: unimolecular micellar behaviour of carboxylic acid terminated cascade macromolecules

Dendritic (cascade) macromolecules with carboxylic acid terminal moieties are examined as micellar substitutes for the separation of a homologous series of alkyl parabens via electrokinetic capillary chromatography employing aqueous mobile phase conditions; separations using the dendrimers yield excellent efficiency and resolution, while higher generation dendrimers demonstrate enhanced affinity for the parabens relative to lower generation dendrimers and so provide superior separations under identical conditions; the cascades are also shown to be sensitive to solution pH and the technique is extended to the separation of components found in a common cough medicine.

Reordering / resonation studies of alkylamide phases

A series of chemically bonded liquid chromatographic packings containing a specific interaction site localized in the interior region of the attached ligands has been prepared by a two-step synthetic route. In the first-step an amino phase is formed and then it is converted to an alkylamide group via reaction with an acid chloride. Using this procedure materials have been prepared with immobilized terminal alkyl groups with chain lengths ranging from C 5 to C 8. Subsequently, the conformation of these modified surfaces have been investigated as a function of temperature under totally aqueous mobile phase conditions. Plots of ln k′ vs. 1 / T curves have been found to be similar to those reported for alkyl phases. However, the onset of reordering/ resolvation of the attached ligands is shifted to lower temperatures and the incremental change per methylene group is smaller.

Release and recovery of porcine pepsin and bovine chymosin from reverse micelles: a new technique based on isopropyl alcohol addition.

After complete solubilization by the direct method, porcine pepsin was not released from AOT in isooctane reverse micelles even under aqueous-phase conditions which would not ordinarily allow uptake. Similarly, bovine chymosin, once forward-transferred at a pH below its isoelectric point, was not back-transferred into an aqueous contact phase buffered at a pH value above its isoelectric point. These results show that there is significant hysteresis in the forward- and backward-transfer processes and further imply that kinetics, and not equilibrium, control uptake or release processes for these enzymes. The addition of 10-15% isopropyl alcohol to the aqueous phase increases the rate of protein release dramatically and allows for nearly complete back-transfer of porcine pepsin and 70% back-transfer of bovine chymosin. IPA addition does not destroy the functional integrity of the system since forward transfer of bovine chymosin still occurs at pH values below (but not above) the pI of the protein.

Liquid chromatography studies of solute-chain interaction under reordering/resolvation conditions—I Correlations between solute structure and changes in retention for hydroxylated aliphatic and aromatic compounds

The current investigation is an extension of previous liquid chromatography studies involving conformational changes of n-alkyl-bonded phases under totally aqueous mobile phase conditions. Relative changes in retention, Δ k′ r , before and after reordering/resolvation of an octyl phase have been studied with various linear, branched, cyclic and aromatic compounds. The magnitude of Δ k′ r can be correlated to structural features in the solute, such as size, shape, rigidity and substitution. The largest values of Δ k′ r were obtained for rigid solutes with multiple hydroxy groups.

X‐Ray photoelectron spectroscopic study of the aqueous oxidation of stellite‐6 alloy

AbstractThe aqueous oxidation of the cobalt allow Stellite‐6 has been studied in pH 10 water 285°C, as a function of dissolved oxygen concentration and length of exposure time. The result surface films were analysed by X‐ray photoelectron spectroscopy (XPS) and other techniques. Using XPS, a quantitative measurement of the oxide and metallic surface components was obtained and depth‐concentration profiles were determined. The effect of gaseous oxidation on the surface composition was also studied, and from a comparison of the oxidation behaviour under aqueous and gas phase conditions, solid state and solution‐transport processes could be distinguished. The gas phase studies showed that cobalt ions diffuse preferentially to the outer surface. During aqueous oxidation, however, the surface composition is found to be depleted in cobalt; preferential dissolution of the cobalt component of the alloy is therefore occurring under these aqueous conditions.