Potential of osmotic membrane crystallization using dense membranes for Na2CO3 production in a CO2 capture scenario

The potential of a membrane crystallizer equipped with a BW-30 reverse osmosis membrane has been investigated for recovering Na2CO3 from aqueous streams, targeting its application in CO2 mitigation. The effect of various crystallization conditions, such as the concentration of the osmotic solution, the concentration of the Na2CO3 solution, as well as membrane orientations on the process performance has been systematically determined. This dense membrane crystallizer was thought to be better than the membrane contactor applied in previous work due to its higher water flux, marked as 0.210 L·m-2·h-1 in forward osmosis (FO) mode and 0.164 L·m-2·h-1 in pressure retard osmosis (PRO) mode compared with 0.08 L·m-2·h-1 for the membrane contactor. Compared with the PRO mode, the FO mode was found to be a better alternative with higher water permeability and draw solute rejection. The concentration of the osmotic solution was the key parameter to condition the applicability of this system. The long-term operation of the system can be realized without any membrane damage and fouling. In addition, Na2CO3·10H2O crystals were obtained with a superhigh purity of 99.98%. Therefore, this osmotic crystallizer equipped with a dense membrane was proven to be an effective alternative for Na2CO3 crystallization for the application in CO2 capture process