Draw solution for forward osmosis process
A forward osmosis apparatus is improved. A forward osmosis apparatus, comprising a diluting means for bringing a feed solution and a draw solution comprising a cation source and an anion source in an ionized state into contact through a semi-permeable membrane and diluting the draw solution with water separated from the feed solution by means of the semi-permeable membrane; a separating means for separating the draw solution that has been diluted by the diluting means into the cation source and anion source and into water; and a dissolving means, returning the cation source and the anion source that have been separated by the separating means to, and dissolving the cation source and anion source in, the draw solution that has been diluted; wherein the molecular weight of the cation source in an uncharged state is 31 or greater and the Henry's law constant of each of the anion source and cation source is 1.0×10 4 (Pa/mol·fraction) or greater in a standard state.
1. A draw solution for a forward osmosis process, comprising an anion source and a cation source and water,
wherein the cation source has a molecular weight of 31 or greater in an uncharged state;
each of the anion source and cation source in water has a Henry's law constant of 1.0×10 4 (Pa/mol·fraction) or greater in a standard state;
each of the anion source and cation source in the draw solution has a concentration immediately prior to being contacted with the semi-permeable membrane of 2.4 mol or more per kilogram of water;
the anion source has an acid dissociation constant (pKa) of 6.0 to 7.0 as an uncharged material in a standard state; and
the cation source has a base dissolution constant (pKb) of 2.0 to 4.5 as an uncharged material in a standard state.
2. The draw solution for a forward osmosis process according to claim 1 , wherein each of the anion source and the cation source has a concentration of 2.4 mol or more per kilogram of the water.
3. The draw solution for a forward osmosis process according to claim 1 , wherein the anions are carbonate ions and/or hydrogen carbonate ions, and the cation source is one or more members selected from the group consisting of trimethyl amine, dimethyl ethyl amine, isopropyl amine, dimethyl amine, and diethyl amine.
4. The draw solution for a forward osmosis apparatus according to claim 1 , wherein the cation source contains a compound represented by formula (I):
R n —NH( 3−n )
wherein R denotes a linear or branched aliphatic group with 1 to 4 carbon atoms and n denotes 1, 2, or 3.
5. A forward osmosis apparatus, comprising a draw solution comprising an anion source, a cation source and water, wherein the cation source has a molecular weight of 31 or greater in an uncharged state, and each of the anion source and cation source in water has a Henry's law constant of 1.0×10 4 (Pa/mol·fraction) or greater in a standard state.
6. The forward osmosis apparatus according to claim 5 , wherein the anion source has an acid dissolution constant (pKa) of 6.0 to 7.0 as an uncharged material in a standard state.
7. The forward osmosis apparatus according to claim 5 , wherein the cation source has a base dissolution constant (pKb) of 2.0 to 4.5 as an uncharged material in a standard state.
8. The forward osmosis apparatus according to claim 5 , wherein the cation source in water has a Henry's law constant of 3.0×10 4 (Pa/mol·fraction) or greater in a standard state.
9. The forward osmosis apparatus according to claim 5 , wherein each of the anion source and the cation source has a concentration of 2.4 mol or more per kilogram of the water.
10. The forward osmosis apparatus according to claim 5 , wherein the anions are carbonate ions and/or hydrogen carbonate ions, and the cation source is one or more members selected from the group consisting of trimethyl amine, dimethyl ethyl amine, isopropyl amine, dimethyl amine, and diethyl amine.