Formation, Chemical Characterization, and Oxidative Dissolution of Amorphous Polymeric Dithiazine (apDTZ) during the Use of the H₂S Scavenger Monoethanolamine-Triazine

Hexa-1,3,5-hydrotriazines form the main product class used for chemical hydrogen sulfide (H₂S) scavenging. The reaction mechanism between these triazine species and H₂S is discussed in detail with the emphasis laid upon the reaction products and their fate. The paper goes on to then describe a novel method of oxidative dissolution of these reaction products, including a full analysis of the resultant species and a mechanistic postulation. The single reaction product of monoethanolamine (MEA)-triazine (1,3,5-tris(2-hydroxyethyl)hexahydro-s-triazine) has been repeatedly found by the authors to be initially monomeric 5-(2-hydroxethyl)-hexahydro-1,3,5-dithiazine which, when separated out of aqueous solution, invariably polymerizes to an insoluble, solid polymeric species. This solid product is referred to as amorphous polymeric 5-(2-hydroxyethyl)-hexahydro-1,3,5-dithiazine, abbreviated as apDTZ. The occurrence of this material in oil production systems causes heavy deposits or fouling in pipelines, valves, chokes, and turbine blades. Its removal by any means other than physical intervention is extremely challenging. The current work shows how the presence of a terminal hydroxyl functionality is critical in enabling the dithiazine to polymerize to form the apDTZ. This work goes onto dispel previous misconceptions in the industry and the literature regarding this process which is finally systematically addressed. Specifically, two very important issues are dealt with in this work which were previously unresolved in the literature. An explanation why the thiadiazine reaction product (first sulfur molecule substitution) from tris(2-hydroxyethyl) triazine (MEA-triazine) is never observed. Following upon the above explanation, why the dithiazine (second sulfur molecule substitution) in all cases never progress to the trithiane (third sulfur molecule substitution). This is probably the greater misconception in the industry and literature regarding triazine and H₂S reactions. Despite the widespread occurrence of apDTZ in the oil and gas industry, there are very few studies of effective methods for its removal. This study presents such a process.