Choice of ion-selective electrodes in potentiometric determination of mercaptans and hydrogen sulfide in condensates

Abstract

Ion-selective electrodes for the potentiometric analysis of sulfur content of high-sulfur gas condensates from fields in the Caspian lowlands and West Siberia were evaluated. The membrane electrodes are based on silver sulfide in combination with tungsten, copper, cadmium, lead, zirconium, and platinum. Tests were also conducted for titrants that form stable compounds with mercaptans as well as for solvents that would be compatible with the condensates and not stratify when the titrants were added. Anion-selective electrodes included iodine-selective, sulfide-selective, and thiocyanate-selective; cation-selective electrodes were cadmium-selective, copper-selective, and lead-selective. The preferred titrant was found to be either a solution of ammoniacal silver nitrate in isopropanol or a solution of silver nitrate in DMFA. Reduction and poisoning behavior along with service life and sensitivity were assessed. The electrodes were field tested and the procedure has been implemented at the Karachaganak field.