1,721,145 research outputs found
ACID-BASE AND CATALYTIC PROPERTIES OF METAL-COMPOUNDS IN THE PREPARATION OF POLY(ETHYLENE-TEREPHTHALATE)
No full textX1114sci
CORRELATION OF ACIDITY OF METAL-ION WITH CATALYTIC ACTIVITY FOR THE FORMATION OF POLY(ETHYLENE-TEREPHTHALATE)
No full textX111sciescopu
Selective hydrogenation of SO2 to elemental sulfur over transition metal sulfides supported on Al2O3
No full textTo develop an active and selective catalyst for the selective catalytic reduction of SO2 to elemental sulfur with hydrogen, various transition metal sulfides supported on gamma-Al2O3 were studied. All the catalysts yielded high selectivities of sulfur regardless of the SO2 conversion achieved. It was believed that the SO2 hydrogenation to H2S that occurs over the metal sulfide phase was much slower than the Claus reaction (2H(2)S + SO2 reversible arrow S + 2H(2)O) over alumina support. Simply increasing the loading of the metal sulfide did not enhance the (overall) conversion of SO2. Among the catalysts tested, Fe group metals (Fe, Co, Ni) showed the highest catalytic activity (conversion of SO2). These metal sulfides experienced a phase transformation from a sulfur-deficient form to a catalytically active disulfide form (FeS2, CoS2, and NiS2) during the reaction, The volcano curves obtained by plotting the SO2 hydrogenation activity with physicochemical properties (heat of formation and bond dissociation energy) suggested that the active sites for the SO2 hydrogenation were sulfur vacancies.X1137sciescopu
Removal of sulfur fume by reactive absorption using cobalt-containing absorbents
No full textCobalt sulfide supported on alumina was found to have a potential use as a device trapping elemental sulfur over the temperature range 300-400 (degrees)C. Elemental sulfur in the gas phase can be removed during the deep sulfidation reaction with an accompanying phase change from Co(9)S(8) to CoS(2). Constant removal efficiency above 90% was achieved regardless of concentration difference in the inlet sulfur within a tested range of 900-4500 ppm. The sorbent can be easily regenerated by using hydrogen gas at the temperature range of 350-400 degreesC in a very short time period of less than 1 h. A repeated multicyclic test of absorption and regeneration has shown that the process is reversible and there is no appreciable sintering of particle size.X112sciescopu
Biodegradation of thiocyanate in biofilm reactor using fluidized-carriers
No full textFor the biological treatment of the wastewater containing highly concentrated thiocyanate, microorganisms for thiocyanate biodegradation were isolated and the biofilm reactor charged with fluidized-carriers of tube chip type was employed. The isolated microorganisms were presumed autotrophs. In a small-scale biofilm reactor for the performance test, the observed maximum degradation rate with 80 vol% of fluidized-carriers was 8.1 kg m(-3) day(-1), which was much higher than those observed in any other reactor systems. The high performance of biofilm reactor was presumed to result from the high concentration of microorganisms attached on fluidized-carriers with high surface area. In a bench scale biofilm reactor for the commercial plant design, the biofilm reactor system showed that thiocyanate of 7000 mg l(-1) was successfully degraded to more than 99.9% of removal efficiency within 36 h of total hydraulic retention time. (c) 2005 Elsevier Ltd. All rights reserved.X1136sciescopu
ACTIVE AND SELECTIVE COPPER-CATALYSTS SUPPORTED ON ALKALI-DOPED SILICA FOR THE DEHYDROGENATION OF CYCLOHEXANOL TO CYCLOHEXANONE
No full textCopper supported on alkali-doped silica was found to be the most effective among various types of copper-containing catalysts tested for the dehydrogenation of cyclohexanol to cyclohexanone. This catalyst could be used with lower copper content than others, and showed the highest conversion and selectivity and good resistance against thermal sintering.X117sciescopu
Simultaneous removal of COD, thiocyanate, cyanide and nitrogen from coal process wastewater using fluidized biofilm process
No full textSimultaneous removal of chemical oxygen demand (COD), thiocyanate (SCN), cyanide (CN), ammonia (NH4+-N) and total nitrogen (TN) from coal process wastewater was investigated using fluidized biofilm process at a laboratory scale and commercial scale. In the laboratory scale tests, the removal efficiencies of COD, SCN, CN, ammonia and TN were 97, 99, 99, 99 and 93%, respectively, at 1.0 day of hydraulic retention time (HRT) and 3.4 kg m(-3) day(-1) of COD loading. A commercial wastewater treatment plant with 3.4 day of HRT was revised to the fluidized biofilm process with anoxic-oxic-anoxic-oxic (AOAO) reactors arrangement. The results in the revised commercial plant were similar to those in the laboratory test. (c) 2005 Elsevier Ltd. All rights reserved.X1128sciescopu
Biokinetics on simultaneous biotiltration of H2S, NH3 and toluene in waste
No full textIn order to investigate inhibitory effects in the biofiltration system during simultaneous removal of ternary mixtures of NH3-H2S-toluene contaminants in air, a system modeling has been performed encompassing an inhibition biokinetic expression. Experimental data for removing the three contaminant gases were collected during a long term operation of two biofiltration systems that utilized mixtures of microorganisms fixed on zeocarbon and cork as microbial fixing carriers. Results of regression analyses of experimental data using suggested kinetic models reveal that there are no particular evidences or clues of interactions or inhibitions among microorganisms, and the three reactions are taken place independently within a finite area of biofilm that have been developed on the surface of packing materials.X111sciescopuskc
THE MORPHOLOGICAL AND SURFACE-PROPERTIES AND THEIR RELATIONSHIP WITH OXYGEN REDUCTION ACTIVITY FOR PLATINUM-IRON ELECTROCATALYSTS
No full textA series of iron-platinum bimetallic and pure platinum catalysts supported on carbon were prepared and characterized by means of H-2-O-2 titration, X-ray diffraction, TEM, XPS and cyclic voltammetry. Their catalytic activities for the electrochemical reduction of oxygen in 100% phosphoric acid were related to their physical properties. When the bimetallic catalysts were heated at 750 degrees C, a disordered alloy phase was formed. An almost completely ordered superlattice structure, Pt,Fe, was achieved when heated at 900 degrees C. The mass activity showed a maximum value as a function of Pt particle size for both pure platinum and platinum-iron catalysts, and no noticeable enhancement in the activity was found by alloying platinum with iron. The specific activity increased as the particle size was increased for pure platinum catalysts, whereas it was nearly independent of the particle size for Pt-Fe alloy catalysts. The specific activities of Pt alloys were much higher than those of pure platinum over the tested range of particle size. Therefore, it is expected that a Pt alloy catalyst having a superior mass activity can be made only if metal particles are kept extremely small; ie appreciately smaller than 3 nm. The increase in the specific activity is caused by increased chemisorption strength of hydrogen and simultaneous decrease in the oxygen chemisorption strength in the cathode.X1124sciescopu
SELECTIVE CATALYTIC REDUCTION OF SULFUR-DIOXIDE WITH HYDROGEN TO ELEMENTAL SULFUR OVER CO-MO/AL2O3
No full textThe selective reduction of sulfur dioxide with hydrogen to elemental sulfur was studied over Co-Mo/Al2O3. When the feed conditions were properly optimized (SO2/H-2 mole ratio = 1:3), a sulfur yield of about 80% was achieved at temperatures around 300 degrees C. The temperature is the lowest that has been reported so far for any catalyst for this reaction. The catalytic activity remained high and stable after presulfiding with 10% H2S in hydrogen. Little influence on the catalytic activity was observed if the water content in the feed was kept below 11 vol.-%. The overall reaction consisted of two individual steps occurring on two different sites; sulfur dioxide was first hydrogenated to hydrogen sulfide on the metal sulfide phase, then followed by the Claus reaction of hydrogen sulfide with sulfur dioxide to produce elemental sulfur on the acidic sites of the alumina support.X1144sciescopu
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