A novel cyclic process using CaSO 4 /CaS pellets for converting sulfur dioxide to elemental sulfur without generating se
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I. INTRODUCTION
II. EXPERIMENTAL
NOVEL process for converting sulfur dioxide to elemental sulfur by a cyclic-reaction scheme involving calcium sulfide and calcium sulfate was developed, as described in Part I.[1] This process reduces sulfur-dioxide gas with calcium sulfide yielding elemental sulfur and calcium sulfate that is, in turn, reduced by hydrogen (or other suitable reducing agents) to regenerate calcium sulfide. The overall process begins with calcium sulfate as the starting material and consists of the following two reactions in which the solids are repeatedly regenerated and used without net generation or consumption:
Experiments were carried out in a thermogravimetic analysis (TGA) unit, described in detail elsewhere,[2–4] and followed the procedure outlined in Part I.[1] Anhydrous calciumsulfate powder (99.5 pct purity) used for pellet production was obtained from Aldrich Chemical Co. (Milwaukee, WI) and was sized at ⬍44-m size. In preliminary experiments carried out in this work with loose powder, it was determined that the rate of reduction of plain calcium sulfate was quite slow and nickel catalyst increased the rate considerably. Thus, all the subsequent study was done with pellets that contain the nickel catalyst. The calcium-sulfate powder was impregnated with nickel by mixing 5 g of calcium sulfate in 100 mL of 5 wt pct nickel-nitrate solution for 24 hours. Reagent-grade nickel nitrate [Ni(NO3)2 ⭈ 6H2O] supplied by Alfa AESAR Co. (Ward Hill, MA) was used to prepare the solution. The use of nickel-nitrate solutions of higher concentrations did not increase the kinetics of reduction of calcium sulfate. The nickel-impregnated calcium-sulfate powder was then dried at 443 K for 3 hours in an oven before being palletized by the procedure described in Part I.[1] Two or three pellets of about 0.5-cm diameter each weighing about 100 mg were placed on a shallow sample holder in the TGA apparatus. The reactor was an INCONEL*
A
CaSO4 (s) ⫹ 4H2 (g) ⫽ CaS (s) ⫹ 4H2O (g)
[1]
CaS (s) ⫹ 2SO2 (g) ⫽ CaSO4 (s) ⫹ S2 (g)
[2]
A detailed kinetic analysis for Reaction [1] was presented in Part I.[1] Part II of this study investigated the kinetics of the hydrogen reduction of calcium-sulfate pellets under the conditions of negligible mass-transfer effects. During preliminary tests in this work, a small addition of a nickel catalyst was found to greatly increase the reduction rate, and thus, all the calcium-sulfate pellets used in this work were impregnated with nickel.
*INCONEL is a trademark of Special Metals Corp., Huntington, WV. BYUNG-SU KIM, formerly Graduate Student, Department of Metallurgical Engineering, University of Utah, is Senior Researcher, Recycling Research Center, Korea Institute of Geoscience & Mineral Resources, Daejeon, Korea 305-350. HONG YONG SOHN, Professor of Metallurgical Engineering and Adjunct Professor of Chemical and Fuels Engineering, is with the University of Utah, Salt Lake City, UT 84112-0114. Contact email: [email protected] Manuscript submitted December 4, 2001. METALLURGIC
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