A study of the regeneration of fresh and aged SOx adsorbers under reducing conditions

Sorption of SO2 over a commercial SOx adsorber was studied at a laboratory scale using a fixed bed reactor. The adsorbent material contains mainly alumina, barium oxide and precious metals. Sulphates formed by SO2 sorption are reduced by carbon monoxide or hydrogen in the presence of water. The main species emitted during the reduction was H2S. The species COS was emitted at a very low level when carbon monoxide was used as a reducing agent. The total removal of sulphur was not possible in the absence of water, the sulphur remaining bonded to platinum (or palladium) sites. The role of water is to hydrolyse these sulphides, leading to H2S or COS. The species SO2 was also emitted when an aged catalyst was used, without a loss of the catalytic reduction efficiency. After a first sequence adsorption–regeneration, the adsorption capacity was not affected and the second regeneration was more efficient. Such a SOx adsorber can be placed upstream a NOx adsorber to avoid poisoning of this latter by SO2.