Separation and Purification Technology, Vol.207, 58-67, 2018
Adsorption/desorption behavior of carbonyl sulfide gas on Scheelite type MWO4 adsorbent
This study focused the metal oxide adsorbents to remove small amounts of carbonyl sulfide (OCS) during coal gasification, which was a preliminary step for Integrated Gasification Fuel Cell operation. This study attempted to improve the function of the adsorbent by introducing two kinds of metal species, alkaline earth metals (M = Ca, Mg, Sr, and Ba) and W, fabricated as a Scheelite-typed MWO4 crystal. COS gases were broken down into CO and S segments on the surface of the adsorbents, and were then adsorbed onto the alkaline and W sides. The COS removals decreased in the order of CaWO4 > SrWO4 > BaWO4 > MgWO4 > WO3. When the adsorbent had an ideal basicity, the CO and S adsorbed well on the surface of the adsorbent, resulting in easy breakage of the CO and S bonds. But, this study indicated that it was more influential to optimally align the adsorbate and adsorbent surface. For the Scheelite-type CaWO4 adsorbent, the distance of the adsorbing active site, Ca-O-W, was similar in size to the COS adsorbate molecule, suggested a good alignment approaching the C-axis of the adsorbent. Moreover, an important result in this study determined by mass spectroscopy was that when COS adsorption was saturated on the MWO4 surface, the adsorbed COS gases could desorb from the MWO4 surface with CO2, SO2, CS, and CS2 gases, which are more toxic than COS. This can be considered to other secondary environmental pollutants.