Formation of Carbonyl Sulfide during Molecular Sieve Dehydration Process from High Sour Natural Gas in China

Abstract Molecular sieves with high silica content are usually selected for dehydration of sour natural gas because of their tolerance to H2S. Some special acid-resistant molecular sieves can maintain their dehydration capabilities over long period.But carbonyl sulfide (COS) is formed by the reaction of H2S and CO2, which is catalyzed by molecular sieves during natural gas dehydration. The overall development program at Luojiazhai Gas Field(high sour gas contents) of petrochina southwest oil and gas field company chose the molecular sieve adsorption process to dehydrate sour natural gas, but the gas field has not been developed up to now.A set of of the molecular sieve adsorption equipments has been applied at Liangfeng gathering station of Wanzhou city. This is the first plant for high sour gas dehydration using molecular sieve in China. The wet natural gas contains 9% H2S, 11% CO2 and 200ppmv COS. The dry gas flows to a natural gas treating plant to remove H2S and CO2 to meet pipeline specifications. We found that the water dew points of the treated gas were always lowered to less than -10☐.But this molecular sieve displayed a certain extent of catalytic activity for the reaction converting H2S and CO2 to COS and H2O. The generated amount of changed greatly during operating cycle. The concentration of COS will rise while hot stripping gas moves through the bed. So for sour gas dehydration and desulfurization, these data may prevent serious design errors. Molecular sieve manufactures were able to gain valuable assistance.