Study of the Reaction Mechanism of Triazines and Associated Species for HS Scavenging

Natural gas produced worldwide contains, among other compounds, HS and CO. Both gases in the presence of free water can generate problems of corrosion in pipes and subtract calorific value to this gaseous hydrocarbon. Natural gas containing HS and CO above the permissible limits should be treated to remove these components. Particularly, HS is removed mainly using hexahydro-1,3,5-tris-(-2-hydroxyethyl)--triazine (TZ), which is the liquid scavenger of HS leading on the market. By means of computational methods, we have studied the reaction of HS with TZ, oxazolidine, and oxazinane to elucidate, explain, or confirm different aspects related to their proposed reaction mechanisms. Our results validate thermodynamically the production of TZ from MEA and formaldehyde, justify the presence of mixtures of TZ and oxazolidine in some commercial products, and explain why in the complexity of the HS scavenging mechanism with TZ, tritiane is not formed and dithiazine will prefer to react by polymerization to form amorphous dithiazine and that the scavenging capacity for HS should follow the TZ ≫ oxazinane > oxazolidine sequence.