Monovalent Salt Preservation for Composite Membrane Permeability
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Solution Overview
Problem
Composite semipermeable membranes used in reverse osmosis, nanofiltration, and forward osmosis experience significant decreases in water permeability when stored or transported in high-temperature environments, particularly due to the use of preservation solutions that do not effectively maintain pore integrity.
Innovation Solution
A method using an aqueous solution containing inorganic or organic salts composed only of monovalent cations and anions as a preservation solution, which maintains the water permeability of composite semipermeable membranes by minimizing ion size mismatch and preventing moisture discharge, even at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the membrane element is transported and stored in a refrigerated container to maintain water permeability in high-temperature environments, then the water permeability is maintained, but the transportation and storage costs increase and environmental load increases
Solution Approach 1:
The invention changes the chemical composition parameters of the preservation solution by specifying precise concentrations of monovalent cations (0.01-5 wt%, preferably 0.1-2 wt%) and monovalent anions (0.01-5 wt%, preferably 0.1-2 wt%), replacing the need for refrigeration with optimized chemical preservation that maintains membrane performance at lower cost
Solution Approach 2:
The invention uses a simple, inexpensive aqueous solution containing common monovalent salts (such as NaCl, NH4Cl, KCl, NaNO3, HCOONa, CH3COONa) as preservation medium, replacing expensive refrigeration infrastructure and operations while achieving the same protective function during transportation and storage
2Reliability
If an aqueous solution containing inorganic salt is used as preservation solution for microfiltration or ultrafiltration membranes, then anti-freezing and anti-microbial performance is achieved, but it is unclear whether the water permeability is maintained for composite semipermeable membranes with significantly different pore sizes in high-temperature environments
Solution Approach 1:
The invention applies local quality by tailoring the preservation solution composition to match the specific requirements of composite semipermeable membranes with controlled pore sizes (0.01-10 μm), using monovalent ions that appropriately interact with the membrane structure without causing excessive osmotic pressure or ion accumulation that would occur with divalent ions, thereby achieving both anti-freezing properties and water permeability maintenance
Solution Approach 2:
The invention optimizes the concentration parameters of monovalent cations (0.01-5 wt%) and monovalent anions (0.01-5 wt%) in the preservation solution to achieve the right balance between anti-freezing capability, anti-microbial activity, and maintenance of water permeability for composite semipermeable membranes with varying pore sizes, while avoiding the harmful effects of divalent ion accumulation
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 proposed method effectively maintains the water permeability of composite semipermeable membranes during storage and transportation in high-temperature environments, reducing the need for refrigerated storage and lowering transportation and storage costs while minimizing environmental impact.
Implementation Method 1
A composite semipermeable membrane is called an RO (reverse osmosis) membrane... and is usable for production of ultrapure water, seawater desalination, desalinization of brackish water, and reuse of wastewater
Implementation Method 2
a composite semipermeable membrane that allows monovalent ions to selectively permeate therethrough is used as an NF membrane for separating and removing divalent ion salts such as magnesium sulfate
Implementation Method 3
a composite semipermeable membrane that allows monovalent ions to selectively permeate therethrough is used as an FO (forward osmosis) membrane
Implementation Method 4
it is considered that the composite semipermeable membrane that allows monovalent ions to selectively permeate therethrough is likely to diffuse the monovalent cations and the monovalent anions into a separation functional layer when the preservation solution is in contact with the composite semipermeable membrane
Implementation Method 5
The inorganic salt preferably exhibits anti-freezing, and anti-microbial and anti-fungal performance in addition to prevention of membrane drying
Data Source
Figure 1
AI summary
Provided are a method for preserving a composite semipermeable membrane which is less likely to cause a decrease in the water permeability of the composite semipermeable membrane even in a high-temperature environment, a preservation solution used for the method, and a spiral membrane element including the preservation solution. A method for preserving a composite semipermeable membrane that allows monovalent ions to selectively permeate therethrough, the method includes using an aqueous solution containing an inorganic salt and/or an organic salt composed only of monovalent cations and monovalent anions as a preservation solution to be brought into contact with the composite semipermeable membrane.