Electrochemical Separation and Concentration of <1% Carbon Dioxide from Nitrogen

Low energy separations for <1% gases would benefit gas treatment and sequestration. Theoretically, electrochemical pumping can separate and concentrate from the atmosphere or other gases with <1% at significantly lower energy cost than current systems. Principles of electrochemical pumping for separations are discussed and results for both organic solvent and ionic liquid working fluid systems are presented. Due to the large quantities of gases requiring processing during the separation/concentration of <1% gases, this work looked at solvents with negligible vapor pressures, specifically propylene carbonate and the room-temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. Other important parameters, as illustrated by the data and models presented, are low solubility in the solvent, high carrier solubility, binding constants, and the carrier's electrochemistry. Reported is the electrochemical pumping of from 0.5% (in nitrogen) to 100%, a 200-fold increase in partial pressure, using the carrier 2,6-di-tert-butyl-1,4-benzoquinone in a propylene carbonate solution. The ratio of moles pumped per electron mole was 0.43. The models determined the optimal solubility in the solvent and the required redox swing in the binding constants of the carrier. © 2003 The Electrochemical Society. All rights reserved.