Oxalic acid

About: Oxalic acid is a research topic. Over the lifetime, 11584 publications have been published within this topic receiving 173263 citations. The topic is also known as: ethanedioic acid & H2ox.

Catalytic degradation of Orange II in a ferrioxalate-assisted photo-Fenton process using a combined UV-A/C–solar pilot-plant system

Abstract: The catalytic degradation of Orange II in a ferrioxalate-assisted photo-Fenton process with combined solar and artificial ultraviolet light sources and continuous addition of H 2 O 2 was investigated. The reaction was carried out in a pilot plant consisting of a compound parabolic collector (CPC) solar reactor in series with a UV-A/C reactor. An optimization study was done using a multivariate experimental design including the following variables: pH, H 2 O 2 flow rate, UV-lamp exposure time, average temperature, average solar power and initial concentrations of Fe(II) and oxalic acid. The photocatalytic degradation efficiency was determined by the analysis of color and total organic carbon (TOC) removal. Under the optimum conditions, TOC removal increased to 99% in only 45 min, and this system permitted the use of a low ferrous concentration of only 2 mg L −1 . In addition, oxalic acid was used for pH adjustment. Thus, the operating costs of Fe removal, chemicals and electric power were reduced. Artificial UV-A/C light can be used either to increase the efficiency of the single-solar process or as an alternative to solar CPC on cloudy days. The overall rate constant was split into three components: direct oxidation by hydrogen peroxide, photolytic breakdown of dye–oxalate complexes chromophore group and oxidation by hydroxyl radicals. The influence of the Fe catalyst on the molecular and/or radical reactions was studied by conducting the reaction in the presence and absence of tert-butyl alcohol; the radical mechanism's contribution to the overall degradation increased with increasing iron levels.

Preparation of supported metal catalysts starting from hydrotalcites as the precursors and their improvements by adopting “memory effect”

Abstract: Hydrotalcite-like compounds (HTlcs) can be used as the catalysts as it is since they contain various transition metal cations as the catalytically active species well dispersed on the basic support materials. Moreover, increasing numbers of the applications of HTlcs after the heat treatment have been found since the oxides with very small crystal size, stable to thermal treatments, are obtained after the calcination. The oxides possess interesting properties such as high surface area, basic properties and further form small and thermally stable metal crystallites by reduction. Moreover, the calcined oxides show a unique property, i.e., “memory effect,” which allows the reconstitution of the original hydrotalcite structure. We have developed the catalytic applications of hydrotalcites as it is and moreover the mixed oxides derived from hydrotalcites for various catalytic reactions, i.e., oxidation, dehydrogenation and reforming of hydrocarbons, and even for the reforming of methanol and the CO shift reaction. Aerobic oxidation of alcohols, Baeyer−Villiger oxidation of ketones and O3 oxidation of oxalic acid have been successfully carried out with the Mg−Al hydrotalcites containing Ni, Fe and Cu, respectively, as the catalysts in liquid phase. In the O3 oxidation of oxalic acid, the catalytic activity was enhanced by the “memory effect,” i.e., Mg(Cu)–Al hydrotaclite was reconstituted on the surface of Mg(Cu,Al)O periclase particles and oxalic acid was incorporated as anions in the hydrotalcite layer, resulting in an enhanced oxidation of oxalic acid. As the catalysts in the vapor phase reactions, Mg/Fe/Al mixed oxides prepared from Mg–Al(Fe) hydrotalcites and effectively catalyzed the dehydrogenation of ethylbenzene. Supported Ni metal catalysts have been prepared from Mg(Ni)–Al hydrotalcites and successfully used in the steam reforming and the oxidative reforming of methane and propane. Moreover, the Ni catalysts have been improved by combining a trace amount of noble metals by adopting the “memory effect” and used in the production of hydrogen for the PEFC under the daily startup and shutdown operation. Also starting from aurichalcite or hydrotalcite precursor as the precursor, Cu/Zn/Al catalysts with high Cu metal surface area have been prepared and successfully applied in the steam reforming of methanol and dimethyl ether, and moreover in the CO shift reaction.

Morphology and citric acid production of Aspergillus niger PM 1

Abstract: Aspergillus niger PM 1 was grown in a tubular loop and a stirred tank bioreactor. Batch fermentations were performed under various agitation conditions and pH. Citric acid, oxalic acid, extracellular polysaccharides and proteins were assayed. The following morphological parameters were measured: mean perimeter of clumps, mean perimeter of the central core of clumps, mean length of filaments and mean diameter of filaments. Citric acid production and morphology in both reactors were dependent on agitation intensity and pH. The length of the filaments was shown to be the only parameter that could be related to citric acid production in both reactors: the shorter the filaments the more citric acid was produced. However, for the same amount of citric acid produced the morphology of the organism grown in the stirred tank differed considerably from that grown in the loop reactor.