Two-Compartment Electrodialysis Stack for Ammonium Sulfate Recovery
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Solution Overview
Problem
Current electrodialytic processes are inefficient for recovering ammonia and sulfuric acid from ammonium sulfate-rich wastewaters due to high energy requirements and membrane limitations, particularly when dealing with high concentrations of ammonium sulfate, which leads to diffusion issues and water transport challenges.
Innovation Solution
A two-compartment electrodialysis process with a specific stack structure using anion-conducting and bipolar membranes, combined with water electrolysis, allows for the efficient separation of ammonium sulfate into ammonia and sulfuric acid, minimizing residence time and energy consumption by using a simpler cell structure that can be scaled up effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional electrodialytic processes are used to recover ammonia and sulfuric acid from ammonium sulfate-rich wastewaters, then separation of ammonium sulfate is achieved, but energy requirements become excessively high and membrane limitations occur due to high concentrations
Solution Approach 1:
The electrodialysis stack is divided into repeating units, each containing a specific sequence of membranes (anion-conducting membrane, bipolar membrane, cation-conducting membrane) that create distinct compartments. This segmentation allows optimized local conditions in each compartment type, reducing overall energy requirements while maintaining reliable membrane operation even at high ammonium sulfate concentrations.
Solution Approach 2:
Different membrane types are strategically positioned to create locally optimized environments: anion-conducting membranes in compartments where anion transport is prioritized, bipolar membranes where pH control is critical, and cation-conducting membranes where cation transport is needed. This local optimization reduces energy consumption and prevents membrane failure at high concentrations.
2Productivity
If high concentrations of ammonium sulfate are treated, then recovery efficiency improves, but diffusion issues and water transport challenges increase
Solution Approach 1:
The system is pre-configured with alternating compartments designed for specific functions: some compartments are optimized for concentrating ammonium sulfate while others are designed for producing ammonia or sulfuric acid. This preliminary arrangement of functional zones allows high concentrations to be handled efficiently without causing diffusion issues, as each compartment's composition is controlled for its specific purpose.
Solution Approach 2:
Bipolar membranes act as intermediaries between compartments with different pH conditions. These membranes facilitate controlled water transport and pH gradient management, allowing high concentrations of ammonium sulfate to be processed while maintaining stability in each compartment. The bipolar membranes mediate the interaction between high-concentration feed and product compartments.
3Manufacturing precision
If complex multi-chamber cell structures are used, then separation performance improves, but device complexity and scaling difficulty increase
Solution Approach 1:
The complex separation function is achieved through segmentation into repeating units rather than a single complex multi-chamber structure. Each repeating unit contains a standardized sequence of membranes and compartments that can be replicated and stacked. This modular segmentation maintains high separation performance while simplifying the overall design and enabling easy scaling by adding more repeating units.
Solution Approach 2:
The repeating unit design creates universal building blocks that perform multiple functions: separation, concentration, and pH control all occur within the standardized sequence of anion-conducting membrane, bipolar membrane, and cation-conducting membrane. This multi-functionality in a universal module reduces device complexity compared to specialized multi-chamber structures while maintaining high separation performance.
4Manufacturing precision
If longer residence time is used for complete separation, then recovery completeness improves, but energy consumption and processing time increase
Solution Approach 1:
The electrodialysis stack is pre-configured with compartments specifically designed to drive the separation reaction to completion. The alternating sequence of anion-conducting, bipolar, and cation-conducting membranes creates cumulative pH gradients and concentration differences that force complete separation in a single pass. This preliminary design of the separation path eliminates the need for extended residence times while achieving complete recovery.
Solution Approach 2:
The repeating unit structure ensures continuous useful action throughout the stack: as ammonium sulfate moves through successive compartments, separation is continuously driven forward by cumulative pH gradients and ion transport. This continuous action across multiple compartments achieves complete recovery faster than single-chamber systems would require, reducing processing time while maintaining completeness.
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 process enables the recovery of ammonia and sulfuric acid from high-concentration ammonium sulfate wastewaters with improved energy efficiency and cost-effectiveness, allowing for swift ammonia removal and handling of high ammonium sulfate content, making it suitable for industrial-scale applications.
Implementation Method 1
Its purpose is to split water molecules diffusing into the BPM into base anions and acid cations at the contact surface of the ionically positively charged portion and of the ionically negatively charged portion when an electric field is applied.
Implementation Method 2
Electrodialysis is a membrane separation method in which the ionic constituents of an electrolyte are separated on at least one selectively ion-conducting membrane within an electric field.
Implementation Method 3
An AEM has better ion conductivity for anions than for cations. It is ionically positively charged.
Implementation Method 4
A CEM has better ion conductivity for cations than for anions. It is ionically negatively charged.
Data Source
AI summary
The invention relates to the electrodialytic production of ammonia and sulfuric acid from ammonium-sulfate-rich (waste) waters. An object of said invention was to provide a process for recovering ammonia and sulfuric acid from waters containing ammonium sulfate in high concentrations. The process should be practicable on an industrial scale and have good energy efficiency. This problem is solved by a combination of electrodialysis and water electrolysis. It results in ammonium sulfate being split back into ammonia and sulfuric acid. Unlike conventional three-chamber processes, the process of the invention employs a cell having only two compartments, which can however be multiply parallelized within the stack. This type of scale-up is much more cost-effective than connecting multiple cells in parallel.