High Temperature Gaseous Desulfurization Using Cerium Oxides and Bastnaesite Concentrates

Abstract

<p>The high temperature gaseous desulphurization characteristics of calcined bastnaesite concentrates and cerium oxides have been investigated. The former is a solid solution of rare earth oxyfluorides (RE = La, Nd, Pr) and CeO₂, and has a fluorite type structure. The presence of dissolved CeO₂ in these concentrates is believed to be responsible for the reduction, desulfurization and regeneration characteristics of this mineral.</p> <p>The chemistry of the desulfurization and regeneration process has been elucidated using a fixed bed of cerium oxide at high temperatures (800-1000°C). Coal gases, similar in composition to those generated by a Koppers-Totzek gasification unit, were desulfurized from 1.0% H₂S by volume to less than 4 ngS/mL (3 ppm) in a laboratory scale reactor. This represents a desulfurization efficiency of 99.98%. Desulfurization takes place through a non-catalytic gas-solid reaction where the reactant is in the form of a non-stoichiometric oxide, CeO₂_n.</p> <p>2CeO₂_n(s) + (1-2x)H₂(g) = Ce₂O₂S(s) + 2(1-x)H₂O(g)</p> <p>Adsorption of sulfur is facilitated by the presence of oxygen vacancies in the reduced sorbents. An interactive computing system was used in conjunction with the Ce-O-S phase stability diagram to predict the compositions of reactants and products in terms of the sulfur and oxygen potentials of the gas phase.</p> <p>Regeneration of spent sorbents occurs readily in air, with the evolution of sulfur dioxide:</p> <p>Ce₂O₂S(s) + O₂(g) = 2CeO₂(s) + SO₂(g)</p> <p>Desulfurization efficiencies of cerium oxide compared favourably with those of similar high temperature technologies using iron oxide, limestone or dolomite.</p>