Selective H₂ Evolution and CO₂ Absorption in Electrolysis of Ethanolamine Aqueous Solutions

Abstract

Selective H2 evolution and CO2 absorption in several ethanolamine aqueous solutions are comparatively investigated using a new electrolysis reactor. H2 bubbles are generated from a cathode in any ethanolamine electrolyte, and its experimental gas evolution rates are correlated by Faraday’s first rule. No or smaller amounts of CO2 and N2 bubbles than stoichiometric ones are generated on an anode through the reaction between hydroxide ions and ethanolamine ones. No CO or O2 is observed in the system exhaust, and most of the CO2, along with N2, is still absorbed in ethanolamine aqueous solutions with the addition of KOH and/or HCOOH under high pH conditions. Variations of the concentrations of coexisting ions dissolved in the electrolytes of mono- or tri-ethanolamine (MEA or TEA) and ethylenediamine (EDA) solutions with CO2 absorption are calculated using the equilibrium constants to relate the concentrations of solute ions. Electric resistivities of the ethanolamine aqueous solutions are correlated by the pH value and are analyzed in terms of equilibrium constants among the concentrations of coexisting ions. Conditions of the MEA electrolyte to achieve high-performance electrolysis is discussed for selective H2 generation.

Keywords

• electrolysis
• hydrogen
• ethanolamine
• carbon dioxide absorption