Development of Thermodynamic Parameters for Amine-Containing H2S Scavengers

Removal of H₂S from oil and gas streams has been a priority, oftentimes a necessity, for upstream crude oil/gas facilities for decades. However, the advances in production, namely horizontal drilling and hydraulic fracking, have produced oils and natural gases that contain higher concentrations of H₂S than previously seen. These sour crudes must undergo separation and/or conversion processes to lower the H₂S content prior to entering the midstream pipelines and railcars to prevent equipment corrosion/fouling and to reduce human exposure. H₂S scavengers can be categorized into regenerative and non-regenerative types. Regenerative, including alkanolamines, are used in typical absorption and stripping recovery processes and are betters suited for larger wellhead facilities. Small well head facilities, on the other hand, benefit from non-regenerative scavengers, including acrolein, formaldehyde, glyoxal, and triazines, that react with H2S and incorporate the sulfur into a hydrocarbon molecule. Triazine-based scavengers have become the most widely used of the reactive-type scavengers. 1,3,5-hexahydrotriazine is the most frequently used non-regenerative scavenger; however, its byproducts are deleterious to downstream equipment (i.e. overhead condensers) due to basic conditions (pH 8).

These harmful effects have led to molecular adaptations to the basic triazine molecule whose byproducts would be benign to equipment fouling and corrosion. Varying side chains have the impact of making the triazine scavenger more (or less) soluble in aqueous (or non-polar crudes). In addition, these side chains could be tailored to be more active for sour gas, rather than sour liquid crude, streams. Side chain modifications lead to uncertainty of solubility, liquid/gas interactions, and possible byproduct complications. Since scavengers such as melamine and cyanuric acid have been studied extensively, this study focuses on developing thermodynamic parameters (i.e. solubility, scavenger/ion interations, etc.) to for implementation into activity coefficient models for triazines containing ethanolic, amino, bromine, and acrolein substituents, including tris (2,3-dibromopropyl) isocyanurate, 1,3,5-Triacryloylhexahydro-1,3,5-triazine, and 1,3,5-Tris (2-hydroxyethyl) cyanuric acid . Using potentiometric titration and GC-MS analyzes, the solubility of these compounds in water and in saltwater solutions (using different NaCl concentrations) has been evaluated. The solubility results have yielded insightful information towards the ionic mediums in which these materials could be used. Moreover, the octanol/water partition coefficients have been determined to examine the potential fate these scavengers considering environmental factors. The experimental results and model development will be presented.