Synthesis and Reaction Byproduct Characterization and Mechanistic Understanding of Hemiformal Based Hydrogen Sulfide Scavengers

Abstract

When hydrogen sulfide (H2S) gas is produced from oil reservoirs, it leads to a number of well-known problems relating to both metal corrosion and health and safety. Up to a certain concentration (∼1000s of ppm in the gas phase) the H2S can be removed by adding a chemical “scavenger” to the system, which reacts with H2S to form less harmful byproducts. A range of different chemical species have been applied as H2S scavengers in petroleum production systems, operating through either oxidative or nonoxidative mechanisms; the former group includes such species as alkaline sodium nitrite and hydrogen peroxide, and in the latter group triazine type scavengers have been very prominent. Although triazine based H2S scavengers have been hugely successful in practical and commercial terms, there have been associated issues with the related byproducts from the scavenging reaction (discussed in this work). An alternative non-triazine chemical range of H2S scavengers that has emerged in recent years has been based on hemiacetal chemistries, where a hemiacetal is produced by the reaction of an alcohol with an aldehyde. Where the aldehyde is formaldehyde, the resulting species are known as hemiformals. In this work, the synthetic chemical reaction pathway for hemiformals based on ethylene glycol and glycerol were studied. This work is novel in four major respects: (i) first, we examine hemiformal production via acid, base, and neutral catalysis systems; (ii) we perform detailed structural determinations of the oligomeric series thus produced (which are different) by analyzing the products by derivatized gas chromatography mass spectrometry and making subsequent structural assignments; (iii) we then assess the effectiveness of these species as H2S scavenging using an industry standard multiphase test methodology and make some correlation between their structure and performance; and (iv) finally, we studied the structures of product and byproducts of the scavenging reaction both before and after the scavenging reaction with H2S. This latter part of the study examines issues of byproduct structure early in the development of these newer products in order to address any problems that may be encountered “up front”. This greatly facilitates our application of using hemiformals as fully optimized non-triazine based scavengers by addressing byproduct chemical analysis of these relatively new H2S scavenger systems.

Scavenging Alkyl Mercaptans: Elucidation of Reaction Mechanisms and Byproduct Characterization

“…Hemiformal or formaldehyde releaser scavengers show reasonably good performance against mercaptans but with some degree of scatter in the results. The products used have been described in previous work by the current authors . On average, one would expect a performance optimized (i.e., specifically formulated) or synergized hemiformal to perform the best and this is observed in the case of H 2 S and methyl mercaptan.…”

“…The products used have been described in previous work by the current authors. 27 On average, one would expect a performance optimized (i.e., specifically formulated) or synergized hemiformal to perform the best and this is observed in the case of H 2 S and methyl mercaptan. However, the synergized hemiformal has a lower activity of the available formaldehyde.…”

Oxazolidine-Based H2S and Mercaptan Scavengers: Uncovering the Myths

“…During the development of H 2 S scavengers, one important aspect of a product is its behavior after it has been completely spent (or consumed) with H 2 S using the so-called "total spent evaluation". 36 This gives a worst-case view of how the spent fluid behaves, what it constitutes, and most importantly, the quantity and nature of any solid byproducts. Spent scavengers typically contain organic sulfides and, by their very nature, are invariably capable of forming solids, either as monomeric species or more frequently as polymeric materials, which inevitably renders them totally insoluble in all common solvents.…”

“…During the development of H 2 S scavengers, one important aspect of a product is its behavior after it has been completely spent (or consumed) with H 2 S using the so-called “total spent evaluation” . This gives a worst-case view of how the spent fluid behaves, what it constitutes, and most importantly, the quantity and nature of any solid byproducts.…”

Synthesis, Reaction Byproduct Characterization, and Mechanistic Understanding of Hemiformal Hydrogen Sulfide Scavengers: Part 2─Identification of Byproducts, Reaction Mechanisms, and Suppression Thereof

“…12,13 From the new technical results presented in this paper, it may be possible to design better processes for removal of H 2 S; in particular, the identification of the scavenging byproducts may lead to better ways to mitigate the inevitable solids that build up in field operations. This is the central applied contribution of this paper; building on our previous work, 12,13 the new mechanistic understanding of the intermediates and pathway to the solid byproduct formation gives us strong clues how to mitigate the highly undesirable solids formation. Indeed, given our proposed mechanism of intermediate formation, two chemical solid suppression approaches are tested in this work, and both are shown to work to some degree.…”