Fresh Insight into the H2S Scavenging Mechanism of MEA-Triazine vs. MMA-Triazine

Abstract

Abstract Hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine (I) (more commonly referred to as MEA-triazine) and Hexahydro-1,3,5-trimethyl-s-triazine (II) (more commonly referred to as MMA-triazine) are the most ubiquitous triazine based scavengers in today’s oil and gas processing industry. (I) is very substantially more prevalent than (II) despite having several very well characterized drawbacks. Perhaps the most problematic and well recognized of these is the propensity for the single byproduct, 5-hydroxyethyldithiazine (V), to undergo further reaction with H2S and ultimately ring open the dithiazine molecule to form the polymeric solid known as amorphous dithiazine. Current understanding is that (II) is more favorable as it forms no such solids due to a crucial difference in molecular structure. An understanding of what drives this reaction and what structural features are essential for this to happen are key to mitigating the operational challenges posed by the use of triazine chemistry. The understanding that MMA triazine is only, in some cases, the next "go to" product; where the draw backs of MEA-triazine prevent its use, is challenged in this paper in light of fresh insight. A comparative model for the reaction of these two molecules is presented and an explanation offered, hitherto not reported, which accounts for many of the anomalies when a comparison of these two very similar scavenger molecules is made. The intermediate on the pathway to the dithiazine, namely thiadiazine, is usually not given much consideration and yet compelling evidence is presented that it holds the key to understanding the important differences shown by these two members of the triazine scavenger class, together with structure activity considerations. The conclusion endorses the validity and efficacy of MMA-triazine and suggests it should occupy an almost equivalent performance role to MEA-triazine in the H2S scavenger product portfolio.