Reactions of silica-supported copper oxide as a regenerable sorbent for flue gas desulphurisation

Abstract

Silica-supported copper oxide can be used as a regenerable sorbent for flue gas desulphurisation. At 700 K, interaction of sulphur dioxide and molecular oxygen with copper (oxide) leads to the formation of copper sulphate, while upon regeneration of the sorbent metallic copper is formed with simultaneous release of water and sulphur dioxide. The sulphur dioxide present in the flue gas at low concentrations can be trapped and made available at high concentrations by alternating the reaction with copper oxide in the presence of oxygen with the subsequent reduction of the copper sulphate thus formed. Temperature-programmed sulphation, regeneration and oxidation experiments have been used to study the reactivity of two copper-on-silica sorbents exhibiting different copper particle size distributions. A high dispersion of the copper particles is a prerequisite for a high absorption rate. After a small initial decrease of the SO 2-absorption rate, the CuU20 sorbent containing small silica-supported copper particles shows a stable activity, whereas the CuI20 sorbent containing large copper particles shows hardly any activity for SO 2-absorption. As demonstrated by XRD, sulphation results in the formation of anhydrous bulk copper sulphate. Upon regeneration, the bulk of the sulphate particles reacts to metallic copper. Measurements of the total hydrogen consumption during regeneration and subsequent temperature-programmed oxidation suggest the retention of sulphur, probably as a surface cuprous sulphide. The retention of sulphur in the regenerated sorbent decreases the absorption rate and the absorption capacity, whereas the consumption of reducing agent is increased. Some reactions are proposed to explain the formation of a surface copper sulphide.