Forward Osmosis Draw Solution Design for Leakage Control
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Solution Overview
Problem
Existing forward osmosis processes face challenges in maintaining high water permeation rates through semi-permeable membranes while preventing draw solution solute leakage to the feed side and achieving effective stripping performance, as previous solutions either compromised on volatility, solubility, or membrane permeability.
Innovation Solution
Employing a draw solution with a cation source and an anion source having a molecular weight of 31 or greater and a Henry's law constant of 1.0×104 (Pa/mol·fraction) or higher, along with specific acid dissociation and base dissolution constants, to inhibit solute leakage and enhance volatilization, thereby maintaining high permeation rates and stripping efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a draw solution with high volatility is used to enhance stripping performance, then the solute can be easily volatilized and recovered, but the solute leakage through the semi-permeable membrane increases
Solution Approach 1:
The invention changes the physical-chemical parameters of the draw solution by selecting solutes with specific molecular weights (31 or greater) and specific Henry's law constants (1.0×10^4 Pa/mol·fraction or higher). This parameter optimization allows the solution to maintain both high volatility for effective stripping and low membrane permeability to prevent solute leakage, resolving the contradiction between stripping performance and solute retention.
Solution Approach 2:
The invention uses a composite draw solution containing both a cation source and an anion source with specifically controlled properties. The combination of these two components creates a synergistic effect where the cation source provides structural stability (molecular weight ≥31) to reduce leakage, while the anion source with high Henry's law constant ensures volatility for effective stripping, thus resolving the contradiction.
2Productivity
If a draw solution with high solubility is used to maintain high water permeation rates, then water permeation is enhanced, but the solute leakage through the membrane increases
Solution Approach 1:
The invention optimizes the molecular weight parameter of the cation source to be 31 or greater, which creates an optimal balance: the solution maintains high solubility and water permeation rate for high productivity, while the larger molecular size prevents excessive solute leakage through the membrane pores.
3Extent of automation
If a solute with low molecular weight is used to enhance volatility, then stripping performance improves, but solute leakage through the membrane increases
Solution Approach 1:
The invention precisely controls the molecular weight parameter at 31 or greater, which is the critical threshold that simultaneously satisfies both requirements: molecules of this size have sufficient volatility for effective stripping while being large enough to minimize leakage through the semi-permeable membrane, thus resolving the contradiction between volatility and leakage prevention.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively maintains high water permeation rates, reduces solute leakage, and enhances stripping performance, allowing for efficient water separation without the need for frequent replenishment of draw solution components.
Implementation Method 1
When two solutions of differing solute concentrations are brought into contact through a semi-permeable membrane, osmotic pressure is generated between the two solutions. The solvent of the solution on the side of low solute concentration, that is, the side of low osmotic pressure, passes to the side of high solute concentration, that is, the side of high osmotic pressure.
Implementation Method 2
in stripping column 14, the solute component of the draw solution is volatilized from the draw solution that has been diluted by the water of the seawater, thereby separating out the water 16 and solute component 15 of the draw solution
Data Source
AI summary
A forward osmosis apparatus includes a diluting component for bringing a feed solution and a draw solution containing 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 separator for separating the draw solution that has been diluted by the diluting component into the cation source and anion source and into water; and a dissolving apparatus, returning the cation source and the anion source that have been separated by the separator 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 1.0×104 (Pa/mol·fraction) or greater in a standard state.