PERFORMANCE OF SILICA-SUPPORTED COPPER-OXIDE SORBENTS FOR SOX/NOX-REMOVAL FROM FLUE-GAS .1. SULFUR-DIOXIDE ABSORPTION AND REGENERATION KINETICS

Sulphur dioxide absorption and regeneration kinetics of several silica-supported copper oxide (CuO) sorbents were studied in a microbalance over a temperature range of 300 to 450-degrees-C. The porous silica support was prepared according to a sol-gel technique, and CuO was deposited on this support through an ion-exchange technique to achieve a uniform, highly dispersed CuO deposition. During up to 75 cycles of oxidation, sulphation, and reduction, the ion-exchanged sorbents did not show a significant loss in chemical activity except for some deactivation in the first 1-3 cycles. The sulphation kinetics of the preoxidised ion-exchanged sorbents were found to be in agreement with literature data for impregnated alumina-supported CuO sorbents. In case of direct contact of reduced ion-exchanged sorbents with simulated flue gas, the simultaneous and fast oxidation was determined to have a large positive effect on the sulphation rate up to approximately 60% conversion to copper sulphate. This was mainly attributed to structural effects inside the CuO deposits. For the sulphated ion-exchanged sorbents, the reduction by hydrogen was identified as an autocatalytic reaction. The autocatalytic effect was also observed during the (much slower) reduction by methane, but there it was preceded by a period in which a second autocatalytic effect appeared. The reaction kinetics of the ion-exchanged sorbents developed were furthermore compared with experimental results of other silica-supported CuO sorbents prepared by vacuum impregnation and homogeneous deposition-precipitation.