Extent Of Sulfur Removal Research Articles

Thiophene hydrodesulfurization catalysis on supported Ru clusters: Mechanism and site requirements for hydrogenation and desulfurization pathways

Kinetic and isotopic methods were used to probe elementary steps and site requirements for thiophene hydrogenation and desulfurization on Ru metal clusters. Turnover rates for these reactions were unaffected by whether samples were treated in H 2 or H 2S to form metal and sulfide clusters, respectively, before reaction. These data, taken together with the rate and extent of sulfur removal from used samples during contact with H 2, indicate that active structures consist of Ru metal clusters saturated with chemisorbed sulfur at temperatures, pressures, and H 2S levels relevant to hydrodesulfurization catalysis. Turnover rates and isotopic data over a wide range of H 2, H 2S, and thiophene pressures are consistent with elementary steps that include quasi-equilibrated H 2 and H 2S heterolytic dissociation and thiophene binding with η 1(S) or η 4 coordination onto sulfur vacancies. We conclude that hydrogenation proceeds via addition of protons (H δ+, as –S–H δ+ from H 2 or H 2S dissociation) to η 4 thiophene species, while desulfurization involves C–S activation in η 1(S) species aided by H δ− species formed via H 2 dissociation. Reactant concentrations influence hydrogenation and desulfurization turnover rates to the same extent, suggesting that the involvement of similar active structures, consisting of vacancies on sulfur-covered Ru clusters. Smaller turnover rates and stronger H 2S inhibition on smaller Ru clusters for hydrogenation and desulfurization routes reflect the stronger sulfur binding and the smaller vacancy concentrations on small clusters, which contain exposed atoms with lower average coordination. A preference for η 1(S) over η 4 thiophene species at the higher sulfur coverages that prevail on smaller Ru clusters causes desulfurization and hydrogenation rate ratios to increase with decreasing cluster size. We conclude that hydrogenation and desulfurization routes require similar active sites and that weaker M–S bonds lead to higher concentrations of kinetically-relevant sulfur vacancies. These elementary steps and site requirements are likely to also prevail on metals and sulfides with M–S bond strengths similar or higher than Ru–S, for which vacancy sites are also present as minority species.

Effect of barite on mineralogical composition and structure of iron ore sinter

Barite containing iron ore samples were sintered in a down draft sinter pot aiming at producing sinters having 0·5–5·5 mass%BaO. The influence of barite on maximum sintering temperature, extent of sulphur removal and FeO content in sinter was studied. Qualitative and quantitative phase analyses were carried out using electroprobe microanalyser (EPMA) while the different developed phases were identified with X-ray diffraction (XRD) techniques. The structure of sintered samples was microscopically examined. In sinter, the extent of sulphur removed slightly increases with BaO content up to 1·5 mass%, followed by a considerable increase in 2·5 mass%BaO containing sinter. The sintering temperature decreases with the increase in BaO content giving a maximum decrease in 2·5 mass%BaO. The increase in BaO content up to 1·5 mass% slightly decreases the magnetite content followed by a sharp decrease of 2·5 mass%. Barium ferrite was not detected in sinters containing up to 1·5 mass%BaO and most of BaO was directed to the slag. In 2·5 mass%BaO containing sinter, eutectic and needle structures of barium ferrite solid solutions were developed. The eutectic structure decreased while the needle structure increased in number and size of samples containing >2·5 mass%BaO.

CFD modelling of the flow and reactions in the Olympic Dam flash furnace smelter reaction shaft

The performance of flash furnace burners can be evaluated quickly and efficiently using CFD modelling. Gas flows are modelled using the conventional Eulerian approach, while Lagrangian particle tracking is used to model the flow of solid feed through the burner and into the reaction shaft. A composite particle model has been developed that considers the solid feed to be made up of single particles containing appropriate quantities of concentrate, flux and dust. Solid fuels (such as coal) can also be included in the composite particle. Reactions between the solids and gas are then modelled using standard heat and mass transfer relationships. Results from the modelling process are shown for BHP-Billiton’s Olympic Dam copper flash smelter with the burner that was used from 1998–2003. Flow patterns, temperature and gas composition distributions, particle dispersion and residence time, and overall extent of sulphur removal are predicted and used to evaluate furnace performance. However, results are sensitive to the assumed size of the composite particles, and plant measurements are required to determine the appropriate composite particle size to predict quantitative data.

Desulphurisation of high sulphur coal to improve industrial utilisation

Coal from northeastern India is considered to be a very good quality coking coal owing to its low ash content (<8%). It has an excellent caking property, and after carbonisation it can provide a very good CSR (coke strength, after reaction with CO2). On the other hand, its metallurgical application is not so encouraging as a result of its high sulphur content (3-7%). Normally the acceptable sulphur content in metallurgical coke is 0·7% maximum. About 90% of the sulphur is present in organic form, and the remaining 10% as pyrites and sulphates. Removal of sulphur from the organic types is somewhat complicated as it cannot be done by any physical process such as benificiation or flotation, whereas sulphur in pyrites and sulphates can be removed by physical means. With a view to lowering the sulphur content of the coal, desulphurisation studies were carried out at elevated temperatures ranging from 400 to 950°C under the flow of various reducing gases such as coke oven gas, water gas, steam and pure hydrogen. The retention time at each temperature of experimentation was usually varied at 15, 30 and 45 min. It was observed that the sulphur content in the coal was decreased in every experiment with the various reducing gases. The extent of sulphur removal in treatment of the coal with coke oven gas was up to 78·1%, that with steam 83·1% and that with water gas 85·7%. The minimum sulphur content found in desulphurised coal was 0·86%, which could not be used for metallurgical purposes unblended. In the case of experiments with steam, a severe loss of carbon (15-20%) was observed because of reaction with the steam, whereas no such losses were observed in experiments with the other two reducing gases. Hydrogen lowered the sulphur content at a faster rate in comparison with the other gases, but could not increase the degree of reduction. The present study may help to establish the technoeconomic feasibility of the processes; however, large scale experimental studies are required for confirmation. I&S/1721

Dissolution of lignites in tetralin under hydrogen or nitrogen: effects of extraction conditions on sulfur distribution among the products

Removal and distribution of sulfur among the extraction products of two Turkish lignites (Beypazari and Tuncbilek) were investigated. Extraction was carried out in tetralin at 325–425 °C under nitrogen or hydrogen. Increasing extraction time and temperature increased the amount of sulfur in both soluble and gaseous products. Most of the sulfur in Beypazari lignite was found in the soluble products, whereas most of that in Tuncbilek lignite passed into the gaseous products. The extraction process did not affect the ash sulfur, but the combustible sulfur content of the char decreased with increasing extraction time and temperature. The results suggest that these two lignites have substantially different sulfur functionalities, and that besides the extraction conditions, the structure of the sulfur in the original lignite has an important effect on the extent of sulfur removal and on the distribution of sulfur among the products. Prolonged extraction at high temperatures results in desulfurization of the soluble products, and interaction between H 2S and char is likely under these conditions.

Desulphurization of Steel During Melting

This paper examines the extent of sulphur removal from scrap metal charges when gases, which are oxidizing or reducing with respect to iron oxide at unit activity, are blown on to the charge. Sulphur can be removed extensively as gaseous species in the exhaust gas before melting is complete. The presence of ferrous oxide, introduced in solid form, and use of the above gas mixtures facilitates sulfur removal to very low levels during the melting period and in the absence of flux additions. A stable and low level of sulphur could be maintained at about the clear melt stage in the absence of slag or without any further treatment. The optimum operating conditions have been ascertained for desulphurization of steel during melting.

Removal of Sulfur Compounds from Coal by the Thermophilic Organism Sulfolobus acidocaldarius

The thermophilic, reduced-sulfur, iron-oxidizing bacterium Sulfolobus acidocaldarius was used for the removal of sulfur compounds from coal. The inclusion of complex nutrients such as yeast extract and peptone, and chemical oxidizing agents, 0.01 M FeCl(3) into leaching medium, reduced the rate and the extent of sulfur removal from coal. The rate of sulfur removal by S. acidocaldarius was strongly dependent on the sulfur content of the coal and on the total external surface area of coal particles. Approximately 96% of inorganic sulfur was removed from a 5% slurry of coal which had an initial total sulfur content of 4% and an inorganic (pyritic S and sulfate) sulfur content of 2.1%. This resulted in removal of 50% of initial total sulfur present in coal.

Removal of sulphur from coal by air oxidation at 350–450 °C

Abstract The extent of sulphur removal from seven U.S. coals has been studied by low-temperature oxidation. The total sulphur in these coals varied between 3 and 7% by weight. The pyritic sulphur constituted approximately 50% of the total sulphur. A major part of the study has been carried out at oxidation temperatures of 350, 400 and 450 °C. Temperature, up to 450 °C, is a prime factor determining the extent of desulphurization. The efficiency of removal is controlled by the diffusion of oxygen into coal and its pyrite. More than 90% of the pyritic sulphur can be removed at 450 °C in 10 min in some cases. The rate of removal is unaffected by the build-up of sulphur dioxide concentration in the air stream to at least 10%. That is, the level of sulphur dioxide concentration in the effluent gases can be increased for sulphuric acid manufacture by successive recycling of the effluent gases over fresh charges of coal. The calorific value and the VM decrease during this desulphurization treatment. The importance of the loss can be minimized if the desulphurized coal is fed directly to the boiler while at about 450 °C. The process can be made self-sustaining by proper control of the coal/air ratio.