Capacitive deionization performance of CNTs-Si-Ag based electrodes for the removal of heat stable salts from methyldiethanolamine (MDEA) solution in natural gas sweetening units

Abstract

The presence of heat stable salts (HSS) in the gas sweetening absorption columns reduces the absorption capacity of the amine solutions. For the first time, the capacitive deionization (CDI) technique is used to clean the MDEA solutions from HSS. For this purpose, the hybrid material (CNTs-Si-Ag) was synthesized by using the sol–gel process followed by chemical reduction. This hybrid material was then utilized as CDI electrode material in order to remove the HSS from the lean amine solutions. TEM and SEM confirmed the well-ordered interconnected porous network containing silanized CNTs (carbon nanotubes) along with silver (Ag) nanoparticles. Nitrogen adsorption–desorption analysis and electrochemical studies (EIS and CV) evidenced the substantial conductivity, porosity, surface area and specific capacitance of the prepared material. The specific capacitance of the hybrid material was found to be 149.1 F g−1 at 10 mV s−1 heralding substantial electrosorption capacity for the removal of HSS. The continuous CDI experiments showed that the highest SAC of the newly prepared electrode is 21.5 mg g−1 with maximum ASAR of 0.17 mg g−1 min−1 under 1.0 V and the lowest SAC is 17.3 mg g−1 with ASAR of 0.12 mg g−1 min−1 under 0.8 V. This work introduced the CDI as a potential technique that can be used to clean amine solutions advantaged with its low maintenance, easy operation and environment friendliness.