Solar-Thermal Desalination Using Thermo-Responsive Ionic Liquids
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Solution Overview
Problem
Current desalination technologies face challenges in treating produced waters and complex brines due to high osmotic pressure and energy consumption, with existing methods like reverse osmosis and thermal techniques being inefficient and costly, particularly for non-traditional saline sources.
Innovation Solution
A forward osmosis system using a mixture of water and ionic liquids as a draw solution, coupled with a photonic heater that converts solar energy into infrared radiation for phase separation above the ionic liquid's lower critical solution temperature, allowing for efficient water extraction and regeneration of the draw solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If reverse osmosis is used for desalination, then water can be extracted from saline sources, but the process requires high-grade electrical energy and cannot handle high osmotic pressure feeds
Solution Approach 1:
The patent changes the phase separation mechanism from vapor-liquid (requiring high temperature and high energy) to liquid-liquid phase separation triggered by temperature change above LCST. This parameter change in the separation mechanism enables low-energy regeneration of the draw solution while maintaining water extraction capability
Solution Approach 2:
The patent utilizes liquid-liquid phase transition of ionic liquids above their lower critical solution temperature (LCST) to separate water from the draw solution. This phase transition occurs at low temperatures without requiring vaporization, dramatically reducing the energy input needed for water recovery compared to conventional thermal distillation
2Productivity
If thermal techniques like MSF or MED are used, then desalination can be achieved, but the large enthalpy of vaporization requires high-temperature heat and consumes excessive energy
Solution Approach 1:
The patent replaces the liquid-vapor phase transition (requiring ~2400 J/g) with a liquid-liquid phase transition occurring above the LCST of ionic liquids. This phase transition occurs at much lower temperatures and with minimal energy input, as it only requires overcoming the relatively small enthalpy of mixing rather than the large enthalpy of vaporization
Solution Approach 2:
The patent changes the fundamental separation parameter from temperature-driven vaporization to temperature-triggered liquid-liquid phase separation. By adjusting the temperature above the LCST, the system achieves efficient water separation without the high energy costs associated with conventional thermal desalination processes
3Productivity
If conventional draw solutions are used in forward osmosis, then water can be concentrated, but the draw solution requires high energy input for regeneration
Solution Approach 1:
The patent employs ionic liquids that undergo liquid-liquid phase separation above their LCST, enabling the draw solution to be regenerated through simple heating rather than energy-intensive evaporation or reverse osmosis. This phase transition property allows for easy separation of water from the ionic liquid draw solution with minimal energy input
Solution Approach 2:
The ionic liquid draw solution exhibits self-phase-separation behavior when heated above LCST, automatically separating into water-rich and ionic liquid-rich phases without requiring additional separation equipment or high energy input. This self-service property simplifies the regeneration process and reduces operational complexity
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 enables continuous, energy-efficient desalination of produced waters with a solar-thermal conversion efficiency of 50%, reducing energy costs and environmental impact, and demonstrates compatibility with commercial membranes and real produced water samples.
Implementation Method 1
Water in the wastewater diffuses across the osmotic membrane to the draw solution to form a diluted draw solution
Implementation Method 2
The thermal separator includes a photonic heater. The thermal separator is operable to heat the diluted draw solution with the photonic heater above a lower critical solution temperature (LCST) of the ionic liquid
Implementation Method 3
heat the diluted draw solution with the photonic heater above a lower critical solution temperature (LCST) of the ionic liquid to phase separate the diluted draw solution into the ionic liquid and treated water
Data Source
AI summary
This disclosure provides systems, methods, and apparatus related to water desalination. In one aspect, a method includes generating a diluted draw solution using forward osmosis. Wastewater is on a first side of an osmotic membrane and a draw solution is on a second side of the osmotic membrane. The draw solution comprises a mixture of water and an ionic liquid. Water in the wastewater diffuses across the osmotic membrane to the draw solution to form the diluted draw solution. The diluted draw solution is heated using a photonic heater to a temperature above a lower critical solution temperature (LCST) of the ionic liquid to phase separate the diluted draw solution into the ionic liquid and treated water.