Investigation of Hydrate-induced Ice Desalination (HIID) and its application to a pretreatment of reverse osmosis (RO) process

Abstract

In this study, freeze desalination which utilizes CO2 gas hydrate itself as a refrigerant (referred to as Hydrate-induced Ice Desalination, HIID) was systematically investigated and evaluated as a pretreatment method for seawater reverse osmosis (RO) process. To the best of the authors' knowledge, the HIID is the first approach to use the hydrate dissociation energy to freeze seawater in an instant for desalination. The endothermic energy related to hydrate dissociation was the most dominant factor in the freezing of seawater. Using the HIID technique, the rejection of ions with 3.5wt% NaCl was about 67%. Increasing the concentration of salts enhanced rejection of component ions. However, humic acid organic rejection decreased due to agglomeration of organics in presence of salts. The HIID process showed similar levels of cation rejections-approximately 65% of seawater, except boron and potassium. The rejection of cations might be determined by the solubility of salts at various brine concentration. Using HIID as a pretreatment of seawater at 225psi, the RO process showed ~14 LMH and about 99% cation rejections except boron. This study shows that HIID can be utilized as a pretreatment of seawater desalination and further development might make HBID technology run on its own.