Crystallisation-Assisted Membrane Distillation for Desalination
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Solution Overview
Problem
Current membrane distillation processes for desalination face issues such as crystallization on membrane surfaces leading to clogging, high energy consumption, and contamination risks due to the use of foreign substances, particularly when dealing with high salt concentrations like seawater or brine.
Innovation Solution
A process that prevents or reduces crystallization on membrane surfaces by using a crystallization agent with higher water solubility than the target compound, typically an inorganic salt, to induce crystallization of the first compound, followed by membrane separation to produce pure water, where the crystallization agent is recycled and minimizes contamination risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If membrane distillation is used for desalination of high salt concentration streams, then separation of pure water is achieved, but crystallization occurs on membrane surfaces causing clogging and flux decrease
Solution Approach 1:
The patent applies preliminary action by adding a crystallization agent to the feed stream before membrane distillation to induce crystallization of salts in the bulk solution. This prevents supersaturation at the membrane surface, thereby avoiding crystallization on the membrane and subsequent clogging, while maintaining stable membrane performance throughout the process
Solution Approach 2:
The patent introduces a crystallization agent as an intermediary substance that mediates between the high salt concentration feed stream and the membrane distillation process. This agent induces crystallization in the bulk solution, acting as a buffer to prevent direct crystallization on the membrane surface, thus protecting the membrane from clogging
2Reliability
If thermal evaporation methods are used for desalination, then pure water and concentrated brine are produced, but high energy consumption and scaling problems occur
Solution Approach 1:
The patent applies parameter changes by modifying the thermal process parameters - using lower temperatures combined with crystallization agent addition. This shifts the separation mechanism from pure thermal evaporation to a combined crystallization-membrane separation process, reducing energy consumption while maintaining desalination effectiveness and avoiding scaling
3Reliability
If antisolvent induced crystallisation is used to prevent membrane clogging, then crystallization is induced, but foreign substances are introduced causing product contamination
Solution Approach 1:
The patent applies parameter changes by selecting a crystallization agent with specific properties - high water solubility and common ion effect - rather than using traditional antisolvents. This changes the crystallization mechanism from antisolvent-induced to supersaturation-controlled, preventing foreign substance contamination while maintaining membrane performance stability
Solution Approach 2:
The patent applies homogeneity by using a crystallization agent that is chemically compatible with the feed stream (same ion type, high water solubility). This ensures the agent mixes uniformly with the feed without introducing foreign substances, maintaining product purity while preventing membrane clogging through controlled crystallization
4Reliability
If reverse osmosis is used for desalination, then separation is achieved, but high pressures are required especially at high osmotic pressure
Solution Approach 1:
The patent applies parameter changes by shifting from pressure-driven reverse osmosis to temperature-driven membrane distillation combined with crystallization. This changes the driving force parameter from high pressure to moderate temperature difference, reducing mechanical stress while maintaining separation quality through the combined crystallization-membrane separation mechanism
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
This approach effectively separates the target compound from the feed stream, reducing energy costs and contamination risks, while maintaining membrane integrity and efficiency by recycling the crystallization agent and producing a high-purity water product.
Implementation Method 1
adding a crystallisation agent to the feed stream, thereby causing crystallisation of at least part of the first compound from the feed stream
Implementation Method 2
the crystallisation agent has a higher water solubility than the first compound
Implementation Method 3
the liquid stream is subjected to a membrane separation process, comprising membrane distillation or osmotic distillation
Implementation Method 4
membrane distillation (MD), osmotic distillation (OD)
Data Source
Figure 1~2
AI summary
The invention is directed to a process for separating a compound from an aqueous feed stream wherein said compound is dissolved. The process of the invention comprises - adding a crystallisation agent to said feed stream, thereby causing at least part of said first compound to crystallise, resulting in a mixture of crystals and a liquid, - separating at least part of the crystals from the liquid, leaving a supernatant, - subjecting at least part of the supernatant to a membrane separation process, producing a concentrate; wherein the crystallisation agent comprises a second compound with a higher solubility in water than the first compound; wherein said membrane separation process comprises membrane distillation, osmotic distillation or a combination of both.