Osmotically driven membrane processes and systems and methods for draw solute recovery

Abstract

The invention relates to osmotically driven membrane processes and systems and methods for recovering draw solutes in the osmotically driven membrane processes. Osmotically driven membrane processes involve the extraction of a solvent from a first solution to concentrate solute by using a second concentrated solution to draw the solvent from the first solution across a semi-permeable membrane. Draw solute recovery may be carried out by various means including with the use of a membrane device. The draw solute recovery may also include the use of multi-stage solute recovery using distillation columns and/or membranes, where the recovery may be assisted by a heat pump.

What is claimed is: 
     
         1 . An apparatus for recovering draw solution solutes from a dilute draw solution, the apparatus comprising:
 an osmotically driven membrane system comprising a source of dilute draw solution comprising thermally removable solutes; and   a separation system in fluid communication with the osmotically driven membrane system and comprising at least one membrane contactor having a first side and a second side, wherein the first side is in fluid communication with the source of dilute draw solution.   
     
     
         2 . The apparatus of  claim 1 , wherein the separation system further comprises:
 a source of thermal energy in communication with the dilute draw solution for vaporizing at least a portion of draw solutes out of the dilute draw solution; and   a source of absorbing solution in fluid communication with the second side of the membrane contactor, wherein at least a portion of the vaporized draw solutes pass from the first side to the second side of the membrane contactor and are absorbed by the absorbing solution.   
     
     
         3 . The apparatus of  claim 2 , wherein the absorbing solution comprises the source of thermal energy. 
     
     
         4 . The apparatus of  claim 3 , wherein the separation system further comprises a condenser in communication with the absorbing solution as it exits the at least one membrane contactor. 
     
     
         5 . The apparatus of  claim 3 , wherein the separation system further comprises a heat pump in communication with the membrane contactor. 
     
     
         6 . The apparatus of  claim 5 , wherein the separation system further comprises a reboiler in communication with the heat pump and a source of water discharged by the membrane contactor. 
     
     
         7 . The apparatus of  claim 2 , wherein the membrane contactor is a selective membrane that substantially inhibits the transfer of water vapor, but facilitates the transfer of vaporized draw solutes. 
     
     
         8 . The apparatus of  claim 7 , wherein the selective membrane is a suspended liquid membrane. 
     
     
         9 . An apparatus for recovering draw solution solutes from an osmotically driven membrane system, the apparatus comprising:
 a membrane module configured for receiving a dilute draw solution from the osmotically driven membrane system, the membrane module comprising at least one membrane system; and   a heat pump module in fluid communication with the membrane module for providing a source of thermal energy to the membrane module.   
     
     
         10 . The apparatus of  claim 9 , wherein the at least one membrane system comprises at least one membrane system for stripping solutes out of the dilute draw and at least one membrane system for bringing draw solution solutes into contact with an absorbing solution. 
     
     
         11 . The apparatus of  claim 9 , wherein the heat pump module comprises a heat pump in fluid communication with a source of vaporized draw solutes discharged by the membrane module and with a reboiler in fluid communication with a source of water discharged by the membrane module. 
     
     
         12 . An apparatus for recovering draw solution solutes from an osmotically driven membrane system, the apparatus comprising:
 a first distillation column comprising:
 a first inlet coupled to a first source of dilute draw solution for introducing a portion of dilute draw solution into a first end of the first distillation column; 
 a first heat transfer means coupled to the first distillation column at a second end, the first heat transfer means having an inlet coupled to a first source of thermal energy and an outlet coupled to the first distillation column for directing thermal energy to the first distillation column to cause the dilute draw solution solutes in the first distillation column to vaporize; 
 a first outlet for removing the vaporized dilute draw solution solutes from the first distillation column; and 
 a second outlet for removing a bottoms product from the first distillation column; 
   a heat pump coupled to the first outlet of the first distillation column; and   a second distillation column comprising:
 a first inlet coupled to a second source of dilute draw solution for introducing a portion of dilute draw solution into a first end of the second distillation column; 
 a second heat transfer means coupled to the second distillation column at a second end, the second heat transfer means having an inlet coupled to the heat pump for receiving the vaporized dilute draw solution solutes for use as a second source of thermal energy, a first outlet coupled to the second distillation column for directing the second source of thermal energy to the second distillation column to cause the dilute draw solution solutes in the second distillation column to vaporize, and a second outlet configured to return the vaporized dilute draw solution solutes from the first distillation column condensed within the second heat transfer means to the osmotically driven membrane system; 
 a first outlet for removing the vaporized dilute draw solution solutes from the second distillation column; and 
 a second outlet for removing a bottoms product from the second distillation column. 
   
     
     
         13 . The apparatus of  claim 12 , further comprising:
 a second heat pump coupled to the first outlet of the second distillation column; and   at least a third distillation column comprising:
 a first inlet coupled to a third source of dilute draw solution for introducing a portion of dilute draw solution into a first end of the third distillation column; 
 a third heat transfer means coupled to the third distillation column at a second end, said third heat transfer means having an inlet coupled to the second heat pump for receiving the vaporized dilute draw solution solutes for use as a third source of thermal energy for use with the third distillation column, a first outlet coupled to the third distillation column for directing the third source of thermal energy to the third distillation column to cause the dilute draw solution solutes in the third distillation chamber to vaporize, and a second outlet configured to return the vaporized dilute draw solution solutes from the second distillation column condensed within the third heat transfer means to the osmotically driven membrane system; 
 a first outlet for removing the vaporized draw solution solutes from the third distillation column; and 
 a second outlet for removing a bottoms product from the third distillation column. 
   
     
     
         14 . The apparatus of  claim 12 , wherein the first and second distillation columns are configured for parallel operation and the first and second sources of dilute draw solution are the osmotically driven membrane system. 
     
     
         15 . The apparatus of  claim 12 , wherein the first and second distillation columns are configured for series operation and the second source of dilute draw solution is the bottoms product of the first distillation column. 
     
     
         16 . An apparatus for recovering draw solutes from an osmotically driven membrane process, the apparatus comprising:
 an osmotically driven membrane system comprising a source of dilute draw solution comprising thermally removable solutes; and   a separation module in fluid communication with the osmotically driven membrane system, the separation module comprising:
 at least one of a membrane device or a distillation apparatus in fluid communication with the source of dilute draw solution; and 
 at least one heat pump coupled to the at least one of a membrane device or a distillation apparatus and configured to provide a source of thermal energy to the at least one of a membrane device and a distillation apparatus to vaporize the thermally removable solutes. 
   
     
     
         17 . The apparatus of  claim 16 , wherein the at least one of a membrane device or a distillation apparatus comprises at least one membrane contactor configured to at least one of bring vaporized draw solutes in contact with an absorbing solution or strip draw solutes from the dilute draw solution. 
     
     
         18 . The apparatus of  claim 17 , wherein the membrane contactor is a suspended liquid membrane. 
     
     
         19 . The apparatus of  claim 16 , wherein the at least one of a membrane device or a distillation apparatus comprises a multi-stage solute recovery apparatus. 
     
     
         20 . The apparatus of  claim 19 , wherein the multi-stage solute recovery apparatus comprises a multi-stage column distillation apparatus. 
     
     
         21 . A method of recovering draw solutes from an osmotically driven membrane system, the method comprising the steps of:
 providing a source of dilute draw solution from the osmotically driven membrane system, wherein the dilute draw solution comprises thermally removable solutes;   introducing at least a portion of the dilute draw solution to a separation system;   introducing a source of thermal energy to the separation system;   vaporizing the dilute draw solution solutes out of the dilute draw solution;   recovering the vaporized dilute draw solution solutes; and   recycling the draw solution solutes from the separation system to the osmotically driven membrane system.   
     
     
         22 . The method of  claim 21 , wherein the step of vaporizing the dilute draw solution solutes comprises exposing the dilute draw solution solutes to the source of thermal energy via a membrane contactor to strip the solutes from the dilute draw solution. 
     
     
         23 . The method of  claim 21 , wherein the step of recovering the vaporized draw solution solutes comprises exposing the vaporized draw solution solutes to an absorbing solution via a membrane contactor. 
     
     
         24 . The method of  claim 21 , wherein the step of vaporizing the dilute draw solution solutes comprises exposing the dilute draw solution to a multi-stage solute recovery process. 
     
     
         25 . The method of  claim 24 , wherein the dilute draw solution and source of thermal energy flow in series through at least a first distillation column and a second distillation column. 
     
     
         26 . The method of  claim 21 , wherein the step of vaporizing the dilute draw solution solutes comprises assisting the source of thermal energy with a heat pump.