Recovery of CO2 From Carbonate Solutions with Electrodialysis

A new type of CO2 separation process from flue gas stream was developed. The system is composed of the absorption step with an alkaline (e.g., sodium hydroxide) solution, and the recovery step with electrodialysis. The absorption step is a conventional gas absorption tower, where the flue gas containing CO2 is contacted with a stream of alkaline solution. The CO2 is captured in the form of carbonate ions and bicarbonate ions with alkaline metal ions as the counter cation. The solution is then moved to the electrodialysis unit, where a unit cell is composed of a sheet of cation exchange membrane sandwiched with two sheets of bipolar membrane. The carbonate solution is fed to the one room of the cell and then transported to the other room. In the electrodialysis cell, the pH of the carbonate solution was reduced by the protons supplied from one side of the bipolar membrane. At the same time, sodium ions were transported to the other room through the cation exchange membrane. And sodium hydroxide is recovered with hydroxyl ions supplied from the bipolar membrane. Optimization of the CO2 separation process with the presents system was conducted based on the experimental results on the electrodialysis and literature data on the CO2 absorption processes. An optimization was performed on the basis of minimization of power consumption or operation cost based on the degree of carbonation.