Oxazolidine-Based H2S and Mercaptan Scavengers: Uncovering the Myths

J. J. Wylde, G. N. Taylor, K. S. Sorbie, W. N. Samaniego, B. N. Allan

Research output: Contribution to journalArticlepeer-review

Abstract

Oxazolidine-based products were originally used for their biocide properties, but they have become more widely applied recently for scavenging H2S. Oxazolidine H2S scavengers offer an oil-soluble alternative to hexahydrotriazine water-based scavengers and may mitigate some of their drawbacks. While the same reactants are used for oxazolidine (an aldehyde and primary amine) as are used for hexahydrotriazines, the synthesis conditions are strictly anhydrous and involve the elimination of water to yield the 5-membered ring heterocyclic species. However, we find that their structural identity is more complex than might originally be suspected. The synthesis can be extended beyond the 2-carbon N,O spacer yielding a 5-membered heterocycle to include the 3-carbon N,O spacer, which leads to a 6-membered 1,3-oxazinane species. Oxazolidine-based scavengers are readily converted into the corresponding hexahydrotriazine and very likely owe a large degree of their scavenger activity to this hydrolytic conversion. Due to this conversion, oxazolidines may not be true "nontriazine"alternatives, but they are still very useful H2S scavengers, and both their chemistry and H2S scavenging efficacy deserve further study. This paper contributes to three important aspects of the study of oxazolidine H2S scavengers. First, this work presents several new results on the chemistry of the two bisoxazolidine H2S scavengers, 3,3′-methylenebis[5-methyloxazolidine] (MBO) and 3,3′-methylene-bisoxazolidine (unsubstituted-MBO or US-MBO). Our study focuses on the structure of the scavengers themselves as well as on their reaction with H2S mechanistically, including the reaction product characterization. Second, a benchmarking reference for the scavenging performance of MBO and US-MBO is presented using a range of standard industry techniques for H2S scavenger assessment. Third, we go some way toward explaining why the most commercial of the bisoxazolidines is in fact the monoisopropanolamine (MIPA)-derived MBO. This latter result is surprising given the relative availability and cost of monoethanolamine (MEA).

Original languageEnglish
Pages (from-to)12993–13010
Number of pages18
JournalEnergy and Fuels
Volume35
Issue number16
Early online date2 Aug 2021
DOIs
Publication statusPublished - 19 Aug 2021

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology

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