High-temperature gases sulfidation

Cal,. M.P., Strickler, B.W., and Lizzio, A.A. (2000). High temperature hydrogen sulfide adsorption on activated carbon. I. Effect of gas composition and metal addition. Carbon, 38, 1757-65. 

Molybdenum and tungsten are unique in that they are resistant to sulfur, and, in fact, are commonly sulfided before use. The Bureau of Mines tested a variety of molybdenum catalysts (32). They are moderately active but relatively high temperatures are required in order to achieve good conversion, even at low space velocities. Selectivity to methane was 79-94%. Activity is considerably less than that of nickel. Although they are active with sulfur-bearing synthesis gas, the molybdenum and tungsten catalysts are not sufficiently advanced to be considered candidates for commercial use. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

Carbon dioxide gas can be useful in a variety of chemical experiments, too. The procedure for making carbon dioxide gas is essentially the same as it is for making hydrogen and hydrogen sulfide gases, except marble chips are used. Marble is a metamorphic rock that is created when limestone is placed under great pressure at high temperatures. Both limestone and marble are made up of calcium carbonate ... 

The catalyst is necessary to ensure that the components react with reasonable speed, bnt unfortnnately, the reaction does not always proceed to completion. For this reason, two or three stages are nsed, with sulfur being removed between the stages. For analysts it is valuable to know that carbon disulfide (CS2) is a by-product from the reaction in the high-temperature furnace. The carbon disulfide can be destroyed catalytically before it enters the catalytic section proper. Generally, the Clans process may remove only about 90% of the hydrogen sulfide in the gas stream, and as already noted, other processes, such as the Beaven process, SCOT process, or Wellman-Lord process are often used to recover additional sulfur. 

Elemental sulfur also is recovered as a by-product in processing natural gas and petroleum. Refining operations of natural gas and petroleum crude produce hydrogen sulfide, which also may occur naturally. Hydrogen sulfide is separated from hydrocarbon gases by absorption in an aqueous solution of alkaline solvent such as monoethanol amine. Hydrogen sulfide is concentrated in this solvent and gas is stripped out and oxidized by air at high temperature in the presence of a catalyst (Claus process). 

Iron sulfide (FeS), on the other hand, is much more difficult to decompose. Even at 800° to 850°C, FeS is relatively stable in reducing atmospheres, depending upon the relative concentrations of H2S, H2O, and H2 in the reacting gas. When one assesses the thermodynamics of this system, together with the reaction conditions in most synfuel processes, it will be found that iron sulfide is relatively stable until high temperatures are reached. 

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