Selective Removal of Ammonium Thiocyanate from Wet Oxidative Desulfurization Processes as an Added Value Product

High Resolution Image Download MS PowerPoint Slide Nanofiltration (NF) for selective separation of NH 4 SCN from scrubbing solutions of desulfurization processes for coke oven gas offers high potential for gaining high-value products while reducing energy and space demand in subsequent downstream processes. Such a new NF process is developed following a systematic approach. Initially, feasible membranes were identified based on their material characteristics and applicability using a dead-end cell and a model process solution. Five polymer membranes were screened for their separation performance: DK and NFS made of polyamide (PA), TS40 and XN45 made of polypiperazine-amide (PPA), and NP030 made of poly(ether sulfone) (PES). Two membranes (DK and TS40) showed suitable flux and selectivity for NH 4 SCN. The separation performance of these two membranes was then systematically assessed in detail with a crossflow setup using a flat sheet module, varying transmembrane pressure (TMP) (10–20 bar), pH value (8–10) of the feed, and the composition of the alkaline feed containing NH 4 SCN, (NH 4 ) 2 S 2 O 3 and (NH 4 ) 2 SO 4 in a range of 10–25 g L –1, 0–50 g L –1, and 0–25 g L –1, respectively. Here, retention of bivalent ions up to 99.8% and selectivities between mono- and bivalent ions up to 1677 are found. Further proof of concept is then provided by applying a real scrubbing solution from an existing desulfurization pilot plant in short and long-term experiments. Here, no decrease in the flux was observed after 12 h of operation, and the retention of bivalent ions (S 2 O 3 2– and SO 4 2– ) remained high >96% with a permeation of SCN – > 110%. This also results in high selectivities up to 537. To our knowledge, these experimental results are the first successful demonstration of the potential of NF for recovering valuable materials from coking plants with this complex solution matrix.