Systems and methods for forward osmosis fluid purification

Abstract

A process for purification of fluids, for example, desalination of seawater or brackish water, using organic solutes in a concentrated water solution for use in a forward osmosis process, to extract fresh water out of salt water through the forward osmosis membrane, and subsequently separating the organic solutes out of the diluted forward osmosis permeate by cloud point extraction, thereby regenerating a concentrated organic solution for recycling to the forward osmosis process, and fresh water for potable water use.

1 . A forward osmosis fluid purification system comprising:
 a semi-permeable membrane having a feed solution-facing surface opposite a draw solution-facing surface;   a feed solution in communication with the feed solution-facing surface of the semi-permeable membrane, wherein the feed solution comprises a fluid to be purified and impurities dissolved in the fluid to be purified;   a draw solution in communication with the draw solution-facing surface of the semi-permeable membrane,
 wherein the draw solution comprises at least one cloud point solute, and 
 wherein the concentration of the at least one cloud point solute in the draw solution is greater than the concentration of the impurities in the feed solution; and 
   a precipitation system configured precipitate the at least one cloud point solute from the draw solution.   
     
     
         2 . The system of  claim 1 , wherein the feed solution comprises seawater or brackish water, and wherein the fluid to be purified is water. 
     
     
         3 . The system of  claim 1 , wherein the solubility of the at least one cloud point solute in the fluid to be purified is a molar ratio of at least 3:1. 
     
     
         4 . The system of  claim 1 , wherein at least one cloud point solute has a molecular weight between about 300 Da and 800 Da. 
     
     
         5 . The system of  claim 1 , wherein at least one cloud point solute comprises a hydrophobic component and a hydrophilic component. 
     
     
         6 . The system of  claim 4 , wherein at least one cloud point solute comprises a polyoxyorganic chain. 
     
     
         7 . The system of  claim 4 , wherein at least one cloud point solute comprises a polyethylene glycol or a polypropylene glycol. 
     
     
         8 . The system of  claim 7 , wherein at least one cloud point solute comprises a polyethylene glycol selected from the group consisting of FA PEG-300, FA PEG-400, PEG-400 ML, and FA PEG-600. 
     
     
         9 . The system of  claim 5 , wherein at least one cloud point solute comprises an ethoxylate. 
     
     
         10 . The system of  claim 9 , wherein at least one cloud point solute comprises a fatty acid ethoxylate or a fatty alcohol ethoxylate. 
     
     
         11 . The system of  claim 1 , wherein the concentration of the at least one cloud point solute in the draw solution is between about 30% and 75%. 
     
     
         12 . The system of  claim 11 , wherein the concentration of the at least one cloud point solute in the draw solution is between about 50% and 70%. 
     
     
         13 . The system of  claim 1 , wherein the precipitation system comprises a heater configured to heat the draw solution to at least the cloud point temperature of the draw solution. 
     
     
         14 . The system of  claim 1 , wherein the precipitation system comprises a gas treatment system configured to add at least one water-insoluble gas to the draw solution to lower the cloud point of the draw solution. 
     
     
         15 . The system of  claim 1 , further comprising a filtration system configured to remove the precipitated at least one cloud point solute from the fluid to be purified in the draw solution. 
     
     
         16 . The system of  claim 15 , wherein the filtration system comprises a nanofiltration membrane. 
     
     
         17 . The system of  claim 15 , wherein the filtration system comprises an ultrafiltration membrane. 
     
     
         18 . The system of  claim 15 , further comprising a redissolution system configured to redissolve the precipitated cloud point solutes to form a recycled draw solution.