Search results for "E Conversion"
showing 10 items of 63 documents
Catalytic conversion of glucose to 5-hydroxymethylfurfural over biomass-based activated carbon catalyst
2020
Selective and efficient dehydration of glucose to 5-hydroxymethylfurfural (HMF) has been widely explored research problem recently, especially from the perspective of more sustainable heterogeneous catalysts. In this study, activated carbon was first produced from a lignocellulosic waste material, birch sawdust. Novel heterogeneous catalysts were then prepared from activated carbon by adding Lewis or Brønsted acid sites on the carbon surface. Prepared catalysts were used to convert glucose to HMF in biphasic water:THF system at 160 °C. The highest HMF yield and selectivity, 51% and 78%, respectively, were obtained in 8 h with a catalytic mixture containing both Lewis and Brønsted acid sites…
Chromated metal products may be hazardous to patients with chromate allergy.
2009
Background: Hidden allergen exposure may contribute to persistence and relapse of chromate dermatitis. According to case reports, chromated metal products, such as screws, fittings, etc., may be relevant allergen sources for patients sensitized to chromate. Objectives: To examine concomitant patch test reactivity to potassium dichromate 0.5% petrolatum (pet.) and three different types of chromated metal rings. Patients/Methods: Patients with proven or suspected chromate allergy were patch tested with potassium dichromate 0.5% pet. and three different types of chromated metal rings (yellow, olive, and black). Hexavalent chromium Cr(VI) release from the patch tested rings was chemically an…
The generalized H-point standard-additions method to determine analytes present in two different chemical forms in unknown matrix samples. Part II. C…
2000
The generalized H-point standard-additions method (GHPSAM) is used in order to obtain the total Cr(VI) and chromate concentration in water samples whose matrices are completely unknown. Moreover, a new methodology, which is a modification of the GHPSAM, is proposed for the simultaneous determination of the two major chemical forms of Cr(VI) present in the sample. The method is based on the location of spectral intervals where the behaviour of the interferent absorbance can be considered as linear. From these intervals, the analyte concentration free from bias error can be estimated. Spiked samples of dig and harbour water measured in the UV–visible spectral region have been tested to check …
Study of the Chemical Conversion of Aluminum Alloys by Coupling CFDE and EQCM
2004
The ability of the channel flow double electrode (CFDE) technique and electrochemical quartz crystal microbalance (EQCM) for studying in situ chromate phosphate conversion coating on 5182 aluminum alloys was explored. It was first demonstrated that aqueous Cr(VI) can be analyzed quantitatively with the CFDE technique by reduction into Cr(III) on a graphite electrode. Samples used for EQCM were quartz plated by physical vapor deposition using a 5182 alloy target, allowing thin layers of aluminum alloys with a similar chemical composition to be obtained. EQCM was adapted in order to account for the hydrodynamic conditions in an industrial process, by placing the quartz in a flow cell. In orde…
Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating
2017
We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of 3He ions to high energies in dedicated hydrogen–deuterium mixtures.…
Ionic Liquid Binary Mixtures, Zeolites, and Ultrasound Irradiation: A Combination to Promote Carbohydrate Conversion into 5-Hydroxymethylfurfural
2019
The efficient conversion of biomass into value-added compounds under mild and safer conditions is a cornerstone of present research efforts to meet the needs of the chemical industry with sustainable development. In this work, we studied the dehydration of fructose, glucose, and sucrose into 5-hydroxymethylfurfural (5-HMF), catalyzed by HY zeolite, in three ionic liquid mixtures differing for the cation, aromatic, or aliphatic. We investigated the effect of several operational parameters such as temperature, catalyst loading, zeolite counterion, solvent mixture, and added chloride. In the optimal experimental conditions, we obtained good conversions to 5-HMF especially for fructose and sucr…
Speciation of Cr in Leachates of a MSWI Bottom Ash Landfill
1998
Cr concentrations and speciation were determined in leachate from a municipal solid waste incinerator bottom ash landfill both experimentally and by thermodynamic model calculations. Total dissolved Cr concentrations of 0.2 mmol L-1 were determined by GFAAS. Two orders of magnitude lower values were determined upon preconcentration by an in-situ solid-phase extraction technique based on the 8-HQ cation exchanger that is specific for Cr(III) but unspecific for Cr(VI). This suggests that chromate dominates the dissolved Cr concentrations in the leachates but was up to 5 orders of magnitude undersaturated with respect to the solubility of CaCrO4 or BaCrO4. Chromate adsorption by oxyhydroxides …
An ESCA and Mössbauer study of the oxide layer formed on steel in water containing chromate and chloride ions
1983
Abstract The formation of oxidic layers on steel in chromate solutions was studied by photo-electron and Mossbauer spectroscopy. To simulate more aggressive realistic systems, some chloride ions were added to the solution. The layers formed under these conditions were found to be thicker by an order of magnitude than those formed in the absence of chloride ions. They probably consist of ferric and chromic oxides of the corundum type (Fe 1−2 Cr x ) 2 O 3 , with the Cr : Fe ratio being depth dependent. The oxide layer is subdivided into small regions behaving superparamagnetically. This heterogeneity of the layer is ascribed to the attack by the chloride ions. The structure of the oxides foun…
Cr(VI) sorption by intact and dehydrated Candida utilis cells in the presence of other metals
2002
This study examined the Cr(VI), Cu(II), Zn(II), Cd(II), Pb(II) sorption by intact and dehydrated Candida utilis cells. The anion [Cr2O7]2− and cation Me2+ sorption kinetics was investigated in both single- and dual-metal situations. Uptake of chromate anions occurred much more slowly singularly than with metal cations. A combination of Pb or Cu and chromate anions gave a synergistic effect for Cr(VI) sorption, but not Cd and Zn, which inhibited Cr(VI) sorption by dehydrated cells. The use of alcian blue to occupy maximum vacant adsorption sites on the cell surface unexpectedly did not influence further adsorption of Me2+. Metal uptake by C. utilis was 7 mg (135 μM) Cr, 23 mg (362 μM) Cu, 39…
Theoretical Insights into the Ferromagnetic Coupling in Oxalato-Bridged Chromium(III)-Cobalt(II) and Chromium(III)-Manganese(II) Dinuclear Complexes …
2012
Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) din…