Proof of concept of hydrothermal oxidation for treatment of triazine-based spent and unspent H2S scavengers from offshore oil and gas production

The feasibility of the hydrothermal oxidation of a wastewater derived from H2S scavenging operations, carried
out in a topside offshore oil and gas installation, was demonstrated. The feed characterization showed the
presence of mainly unreacted triazine (unspent scavenger), monoethanolamine and dithiazine (spent scavengers). The spent and unspent scavengers (SUS) were subjected to hydrothermal oxidation in a batch reactor at
approximately 200 ◦C (low temperature, LT) and 350 ◦C (high temperature, HT), using oxygen in excess. The
experiments were performed for six reaction times at each temperature, in the range 3 to 360 min at LT and 1 to
120 min at HT. Diluted SUS (COD around 30 g/kg) was used as reactor feed. The three main compounds of the
SUS were not found in any of the oxidation products, which means they are fast converted. COD reductions up to
84% and 98% were obtained at LT and HT, respectively. A rate equation of second order with respect to the COD
was found suitable to represent the rate of disappearance of COD, with the rate constant at HT approximately 70
times higher than at LT. The extensive analysis carried out on the reaction products showed the presence of C1-
C4 carboxylic acids, pyridines and pyrazines as intermediate oxidation products. A clear trend towards complete
mineralization of organic nitrogen to ammonium, except for small amounts of nitrate at LT, and of organic sulfur
towards sulfate, was observed.