Ammonia-CO2 Draw Solution Osmotic Separation
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Solution Overview
Problem
Current forward osmosis desalination processes face challenges in efficiently separating solutes from aqueous solutions and maintaining osmotic concentration gradients, leading to suboptimal water recovery and increased energy requirements due to biological fouling and concentration polarization.
Innovation Solution
A system utilizing a semi-permeable membrane with a concentrated draw solution of ammonia and carbon dioxide at a molar ratio of at least 1:1, coupled with a distillation column and recycle system to recover solutes and maintain osmotic gradient, along with control measures for biological fouling, such as degassing and osmotic shock, to enhance water extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a concentrated draw solution is used to maintain osmotic gradient, then water recovery rate is improved, but biological fouling and concentration polarization increase leading to higher energy consumption
Solution Approach 1:
The patent changes the chemical composition parameters of the draw solution by using ammonia and carbon dioxide in a controlled molar ratio (at least 1:1). This parameter change allows the system to maintain high osmotic pressure for improved water recovery while the specific chemistry of ammonium carbonate/bicarbonate reduces biological fouling compared to traditional draw solutions, thereby lowering energy consumption for fouling control
Solution Approach 2:
The patent employs a composite approach by combining ammonia and carbon dioxide to form a mixed chemistry draw solution containing ammonium carbonate, ammonium bicarbonate, and dissolved gases. This composite chemical system provides both high osmotic pressure for water recovery and inherent resistance to biological fouling, resolving the contradiction between productivity and energy consumption
2Stability of the object's composition
If ammonia and carbon dioxide are used in a molar ratio of at least 1:1, then osmotic concentration gradient is maintained, but system complexity increases due to recycle system and distillation column
Solution Approach 1:
The patent utilizes phase transitions of ammonia and carbon dioxide (gas to dissolved state in water) to create the draw solution. By controlling the molar ratio of at least 1:1, the system maintains stable osmotic concentration gradient through equilibrium chemistry of ammonium carbonate and bicarbonate formation, while the phase transition nature allows for relatively simple regeneration compared to non-volatile solutes
Solution Approach 2:
The patent uses water as an intermediary medium that dissolves both ammonia and carbon dioxide, facilitating their interaction to form the active draw solutes (ammonium carbonate and bicarbonate). This intermediary approach simplifies the system by using a common solvent rather than requiring separate handling systems for each component, thereby reducing overall system complexity while maintaining gradient stability
3Manufacturing precision
If semi-permeable membrane is used for separation, then solute separation efficiency is improved, but membrane fouling from biological activity increases reducing flux
Solution Approach 1:
The patent changes the chemical environment parameter by using an alkaline draw solution (ammonia-carbon dioxide system) that creates unfavorable conditions for biological growth. This parameter change maintains high solute separation efficiency through the semi-permeable membrane while reducing biological fouling that would otherwise decrease membrane flux and reliability
Solution Approach 2:
The patent converts the potential harm of concentrated draw solutions (which typically promote biological fouling) into a benefit by selecting ammonia and carbon dioxide as the draw solutes. These substances create an alkaline environment that inhibits biological activity, thereby maintaining membrane flux and reliability while preserving the high separation efficiency enabled by the concentration gradient
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 system effectively recovers water by maintaining osmotic gradients and controlling fouling, improving water recovery rates and reducing energy consumption through efficient solute recycling and gradient management.
Implementation Method 1
a forward osmosis desalination process involves a container having two chambers separated by a semi-permeable membrane. One chamber contains seawater. The other chamber contains a concentrated solution that generates a concentration gradient between the seawater and the concentrated solution. This gradient draws water from the seawater across the membrane
Implementation Method 2
a separation system fluidly connected downstream of the second chamber comprising a distillation column, the separation system configured to receive a dilute draw solution from the second chamber and to recover draw solutes and a solvent stream
Implementation Method 3
a recycle system comprising an absorber configured to facilitate reintroduction of the draw solutes to the second chamber to maintain the desired molar ratio
Data Source
AI summary
Separation processes using engineered osmosis are disclosed generally involving the extraction of solvent from a first solution to concentrate solute by using a second concentrated solution to draw the solvent from the first solution across a semi-permeable membrane. Enhanced efficiency may result from using low grade waste heat from industrial or commercial sources.