Regenerating Scrapped MF Membranes into PA Nanofiltration
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Solution Overview
Problem
Scrapped microfiltration (MF) membranes in water treatment systems face contamination issues leading to decreased water flux and eventual replacement, resulting in environmental burdens and lack of feasible methods for upgrading to high-pressure membranes, while existing methods only focus on downgrading high-pressure membranes.
Innovation Solution
A cleaning-repairing-interfacial polymerization method is introduced to regenerate polyamide nanofiltration (NF) membranes from scrapped MF membranes using sodium hypochlorite, oxalic acid, polydopamine, and a reaction system of piperazine and trimesoyl chloride to form a continuous and dense active layer, enhancing membrane performance and extending service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If cleaning is conducted to wash away contaminants on the surface of a scrapped MF membrane, then the construction of a reaction platform is facilitated, but the mechanical properties of the membrane are compromised and aging rate is accelerated
Solution Approach 1:
The patent uses sodium hypochlorite and oxalic acid with optimized concentrations and treatment times to clean the membrane surface. By carefully controlling the cleaning parameters (concentration, time, temperature), the method removes contaminants while minimizing damage to the membrane's mechanical properties, thus resolving the contradiction between effective cleaning and maintaining membrane strength.
Solution Approach 2:
The patent introduces polydopamine as an intermediary substance that forms a repair layer on the cleaned membrane surface. This intermediary layer protects the membrane from further damage during subsequent interfacial polymerization steps while providing a suitable platform for NF membrane formation, thus mediating between the need for surface cleaning and preservation of mechanical integrity.
2Reliability
If interfacial polymerization is conducted to form a PA layer on the surface of a scrapped MF membrane, then a highly-selective NF membrane is obtained, but the complexity of the process increases
Solution Approach 1:
The patent divides the complex transformation process into distinct sequential stages: (1) cleaning with sodium hypochlorite and oxalic acid, (2) repair with polydopamine coating, and (3) interfacial polymerization to form PA layer. This segmentation of the process into manageable steps makes the overall complex transformation from MF to NF membrane more controllable and reproducible, while ensuring high selectivity.
Solution Approach 2:
The patent ensures continuous transformation of the membrane through each stage without interruption. The cleaning stage prepares the surface, the polydopamine repair stage immediately follows to protect and enhance the surface, and the interfacial polymerization continuously forms the NF active layer. This continuous useful action maintains high selectivity while managing process complexity through systematic progression.
3Ease of manufacture
If scrapped MF membranes are directly buried as solid wastes, then disposal is simple, but environmental burden increases
Solution Approach 1:
Instead of directly discarding scrapped MF membranes through burial, the patent recovers and regenerates them by transforming them into functional NF membranes through cleaning, repair, and interfacial polymerization. This recovery process eliminates the need for landfill disposal while reducing environmental burden, thus resolving the contradiction between disposal simplicity and environmental protection.
Solution Approach 2:
The patent converts the harm of scrapped membranes (environmental pollution from burial) into a benefit by regenerating them into valuable NF membranes with high selectivity. The scrapped MF membranes, which would otherwise be waste, are transformed into functional separation membranes, thus converting the harmful disposal issue into a beneficial resource recovery process.
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 method effectively recycles membrane materials, reduces environmental impact, prolongs membrane service life, and lowers disposal costs by transforming scrapped MF membranes into high-performance NF membranes with improved filtration capabilities.
Implementation Method 1
Sodium hypochlorite and oxalic acid are used for deeply cleaning the scrapped MF membrane
Implementation Method 2
the MF membrane is placed in a cup-shaped reaction vessel and reacted with a solution A for 1 h to 3 h; after the reaction is completed, the solution is poured out; and then the MF membrane is reacted with a solution B for 1 h to 3 h
Implementation Method 3
Polydopamine (PDA) is used as a repairing agent to construct a reaction platform on the membrane surface
Implementation Method 4
a reaction system of piperazine and trimesoyl chloride (TMC) are used to form a PA active layer
Implementation Method 5
The interfacial polymerization in the last step is conducted to form a continuous and dense PA layer on the surface of a scrapped MF membrane
Implementation Method 6
which plays a role of selectively trapping solutes to obtain a highly-selective NF membrane
Data Source
AI summary
A polyamide (PA) nanofiltration (NF) membrane and a preparation method thereof by regeneration from a scrapped microfiltration (MF) membrane are provided. The method adopts a cleaning-repairing-interfacial polymerization upgrading strategy, where, sodium hypochlorite and oxalic acid are used for deeply cleaning a scrapped MF membrane. PDA is used as a repairing agent to construct a reaction platform on the membrane surface, and finally a reaction system of piperazine and trimesoyl chloride (TMC) are used to form a PA NF membrane with a PA active layer. The repairing can construct a coating with a given thickness and prominent hydrophilicity on the membrane surface, which provides favorable base membrane conditions for upgrading and preparing an NF membrane.