We have seen recently a sharp increase of COS (carbonyl sulfide) content on the propylene stream produced in one of our FCC’s.We could list a couple of recent changes that could be possibly related to the increase such as a change in the catalyst system and a change of the regenerator CO2/CO ratio. What is it the experience with COS formation and which operational changes could have influence on COS formation ?
COS can be formed in the FCC riser by the reaction of H2S with CO2 to form COS and H2O. Thus, increasing the amount of CO2 in the riser (by increasing inerts carryover from the regenerator or by increasing CO2/CO ratio), or increasing the amount of H2S (higher sulfur feed or higher riser outlet temperature) could increase the formation of COS. Decreasing the amount of H2O in the riser (reduced steam rates) might also enhance COS formation. Generally, controlling operating conditions to inhibit COS formation is not cost effective. COS can be removed from the propylene stream via amine treating or with a bed of absorbent.