Purification of Phosphoric Acid via Suspension Melt Crystallization
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Solution Overview
Problem
Current purification methods for orthophosphoric acid, such as solvent extraction, chemical precipitation, and suspension-based crystallization, are complex, costly, and often require multiple steps to achieve ultra-purity, generating waste streams and being unsuitable for electronic-grade applications due to impurity incorporation and high viscosity issues.
Innovation Solution
A suspension-based melt crystallization process combined with a wash column for continuous operation, which produces a slurry of orthophosphoric hemi-hydrate crystals with low crystal growth rates, effectively excluding impurities and achieving high purity in a single step, reducing energy consumption and waste generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If solvent extraction or chemical precipitation methods are used to purify phosphoric acid, then the purification process can remove impurities, but the process becomes complex requiring multiple steps and generates waste streams that must be treated separately
Solution Approach 1:
The purification process is segmented into distinct functional zones within the crystallizer: a cooling section for crystal formation, a separation section for crystal-mother liquor separation, and a heating section for melting crystals. This segmentation allows each zone to perform its specific function efficiently, achieving high purity without requiring multiple separate process steps.
Solution Approach 2:
The invention merges cooling, crystallization, separation, and melting operations into a single integrated crystallizer unit that operates continuously. This consolidation eliminates the need for multiple separate purification steps and waste stream treatment systems, reducing overall process complexity while maintaining high purity output.
2Manufacturing precision
If multiple purification processes are executed in series to remove all impurities, then the purity level increases, but the process complexity and cost increase prohibitively
Solution Approach 1:
The crystallizer operates continuously with feed stream entering at the bottom, crystals forming throughout the cooling zone, and purified product continuously removed. This continuous operation eliminates idle time between purification steps and maintains optimal operating conditions constantly, achieving high purity efficiently without the intermittent nature of batch processes requiring multiple sequential steps.
Solution Approach 2:
The process utilizes controlled changes in temperature parameters to drive the purification: cooling the feed stream to initiate crystallization, maintaining temperature gradients through the crystallizer zones, and heating the separated crystals to melt and purify them. These parameter changes enable a single-step process to achieve the same purity as multiple steps would require.
3Speed
If layer crystallization processes are used, then crystal growth rates are relatively high, but the process requires frequent repetition of batch steps increasing operational complexity
Solution Approach 1:
The system dynamically adjusts operating parameters including temperature gradients, feed flow rates, and crystal removal rates to optimize both crystal growth speed and operational simplicity. The continuous operation with controlled temperature dynamics allows high crystal growth rates while maintaining a simple, automated process that requires frequent repetition of batch steps.
Solution Approach 2:
By implementing continuous crystallization and product removal rather than batch processing, the system maintains optimal crystal growth conditions continuously. This eliminates the need to repeatedly start and stop the crystallization process, reducing operational complexity while sustaining high crystal growth rates through continuous feed and product removal.
4Productivity
If suspension-based crystallization is used to achieve continuous operation, then the process can operate continuously, but high viscosity of the acid stream complicates the separation process
Solution Approach 1:
The crystallizer is divided into distinct temperature zones: a cooling zone where crystals form from the supersaturated solution, a separation zone where crystals are removed from the mother liquor, and a heating zone where crystals are melted. This segmentation allows the system to overcome high viscosity by using temperature-driven phase changes rather than relying solely on mechanical separation, reducing energy consumption while maintaining continuous operation.
Solution Approach 2:
The process utilizes phase transitions of phosphoric acid between liquid and solid states to achieve separation. By cooling the acid stream, phosphoric acid crystallizes from the liquid phase; the crystals are then separated from the liquid mother liquor; finally, the crystals are melted back to liquid phase for purification. These phase transitions enable effective separation despite high viscosity, reducing the energy required for mechanical separation processes.
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 method achieves high-purity orthophosphoric acid with metal ion content below 1000 ppb, meeting electronic-grade standards, while being economically attractive and operationally simple, with efficient separation performance suitable for large-scale industrial use.
Implementation Method 1
a suspension-based melt crystallization process combined with a wash column for continuous operation, which produces a slurry of orthophosphoric hemi-hydrate crystals with low crystal growth rates
Implementation Method 2
sweating the obtained hemihydrate crystals by melting a controlled amount of 10 to 40 wt. % of the hemihydrate crystals
Data Source
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AI summary
The invention relates to a method for the purification or recovery of orthophosphoric acid rich streams by suspension-based melt crystallization. The orthophosphoric acid is crystallized as the hemi-hydrate form and subsequent separation of such crystals in a wash-column produce a high purity acid/water solution that has been depleted of most of the metals and impurities other than water, thereby separating an orthophosphoric acid rich feed liquor into an ultra-pure orthophosphoric acid hemi-hydrate and a mother liquor containing almost all impurities originally present in the feed. The orthophosphoric acid rich feed liquor typically contains no more than 15wt% water and 1wt% other impurities. Individual metal ion composition in the purified orthophosphoric acid product is in the range of 100 to1000 ppb (parts per billion = 1/1000 ppm) of each metal ion. The metal ion composition of the resulting purified product is thus typically below the detection limit of typical analysis equipment.