Hedewandr:
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.