A Crosslinked Copolymer with N‐Bromosulfonamide Pendant Groups as Oxidant for Residual Sulfides in Alkaline Media

Abstract

A redox copolymer, a macromolecular analogue of Bromamine T was prepared and developed as a solid phase oxidizing reagent for sulfides being in trace concentration in aqueous solutions. The resin was prepared starting from Amberlyst 15 by a four-step transformation of the sulfonic groups to N-bromosulfonamide. The product containing 3.30 meq active bromine/g showed strong oxidizing properties and was employed in batch as well as in flow processes for removal of sulfides from solutions by their transformation to sulfates. The starting solution contained 64.0 or 320.0 mg S 2- /dm 3 . The effects of various parameters on the reaction course have been studied (mole ratio of reagents, alkalinity of the reaction, media flow rate in the column processes). The solid phase oxidation carried out in a dynamic regime provided to drive the reaction to completion. Thus, sulfide free effluents (<10 μg S 2- /dm 3 ) were obtained in the column processes. The permissible flow rate, close to 10-12 bed volumes/h, was satisfactory. The sulfide oxidation proceeded quickly in aqueous media of various alkalinity, especially in those of strong alkalinity. As the transformation of sulfides to sulfates was accompanied by a drop of the pH value of the reaction medium, it was necessary to maintain it not lower than 6.0. Otherwise, the active bromine content in the resin decreased and the yield of the column process was unsatisfactory. Moreover, in acidic media a considerable part of sulfides transformed to elemental sulfur which contamined the resin phase and caused turbidity of the effluent. By reacting a stoichiometric amount of reagents in batch regime not only sulfate, but also various intermediate products were found in the solution. The exhausted copolymer contained unsubstitued sulfonamide groups; it could be regenerated and reused repeatedly for the next processes.