Corrosion in Piperazine at Pilot Plants

Abstract

Corrosion measurements are presented from two 2017 pilot plant campaigns. Corrosion was evaluated at the Separations Research Program (SRP) pilot plant in April 2017. The SRP pilot plant uses air/CO2 and 5 m piperazine (PZ) with an oxidation inhibitor. Stainless steel (316L) and carbon steel (C1010) were evaluated with electrical resistance corrosion probes and corrosion coupons at two locations in the process. A second pilot plant campaign was conducted in June 2017 at the National Carbon Capture Center (NCCC) with 7 m monoethanolamine (MEA). Stainless steel and carbon steel were evaluated with corrosion coupons at four locations in the process. These two pilot plant campaigns allow the direct comparison between corrosion in MEA and PZ systems. Protective product layers were not seen on carbon steel in 7 m MEA. This is likely because high ferrous solubility in MEA solutions prevents precipitation of ferrous products. This led to unacceptably high carbon steel corrosion at high temperature. Despite the lack of protective ferrous corrosion products, corrosion of carbon steel was slow at absorber conditions, suggesting carbon steel construction is appropriate for at least low temperature equipment in MEA operation. In 5 m PZ at hot lean conditions protective layers of Fe3O4 and FeCO3 were observed, suggesting that ferrous products are either less soluble in PZ than MEA, or that ferric production is slow or minor. These protective films sometimes led to very low corrosion rates at hot, lean conditions. Protective films formed preferentially at higher temperature in the stripping system, but were absent in the absorber. This counterintuitive result means that carbon steel corrosion can actually be slower at higher temperature. Carbon steel construction is most likely appropriate both for low temperature equipment in the absorber as well as at least some equipment at high temperature.