Multi-stage Glycolic Acid Crystallization for Low Diglycolic Impurities
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Solution Overview
Problem
Current industrial processes for producing glycolic acid result in high impurity levels, particularly diglycolic acid, which adversely affect the gas barrier properties of polyglycolic acid resins, and existing purification methods struggle to achieve both high yield and high purity glycolic acid effectively.
Innovation Solution
A multi-stage crystallization process with cascaded loops and high recycle rates, where liquid or solid portions are recycled within and between loops, minimizing purge loss and achieving high purity glycolic acid with low diglycolic acid impurities, utilizing multiple crystallization loops with evaporators, solid/liquid separators, and wash solutions to isolate high purity crystalline glycolic acid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If distillation is used for purification, then glycolic acid can be separated from impurities, but significant heating results in formation of polycondensation products
Solution Approach 1:
The patent employs crystallization, a phase transition process, to purify glycolic acid. The crude glycolic acid is cooled to crystallize pure glycolic acid while leaving impurities in the mother liquor. This avoids thermal decomposition and polycondensation that would occur with distillation, achieving purification without generating harmful byproducts.
2Device complexity
If single stage crystallization is used, then process is simple, but purity improvement for diglycolic acid is only moderate (88%)
Solution Approach 1:
The patent divides the purification process into multiple sequential crystallization stages. Each stage further purifies the glycolic acid by removing additional impurities including diglycolic acid. This segmented approach achieves high purity (greater than 99.9%) that cannot be obtained in a single stage, while maintaining reasonable process complexity through systematic repetition of crystallization steps.
3Manufacturing precision
If high purity is achieved through multiple purification steps, then glycolic acid quality improves, but recovery yield decreases
Solution Approach 1:
The patent optimizes the crystallization process to maximize both purity and recovery. Mother liquors from each crystallization stage are analyzed and selectively discarded only when impurity concentrations exceed acceptable thresholds. This selective discarding approach maintains high purity while maximizing glycolic acid recovery, achieving both high purity and high yield simultaneously.
4Productivity
If industrial processes are used to produce glycolic acid, then production volume is high, but impurity levels including diglycolic acid are high
Solution Approach 1:
The patent extracts and removes impurities from industrially produced glycolic acid through multiple crystallization stages. Each stage selectively separates pure glycolic acid crystals from the mother liquor containing impurities such as diglycolic acid. This extraction process maintains high production volume while achieving the high purity levels needed for polyglycolic acid resin manufacturing.
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 process achieves high yield and high purity glycolic acid with less than 20% purge loss, significantly reducing diglycolic acid impurities, thereby enhancing the gas barrier properties of polyglycolic acid resins.
Implementation Method 1
a) providing a first aqueous feed stream comprising at least 60 weight % glycolic acid and at least 0.2 weight % of an undesirable impurity; b) isolating high purity crystalline glycolic acid using a crystallization process
Implementation Method 2
said process comprising a first crystallization loop and a second crystallization loop; said first crystallization loop comprising: (i) a first crystallizer; (ii) a first evaporator;
Data Source
AI summary
The present invention relates to a high yield process to prepare high purity crystalline glycolic acid using a multi-loop crystallization process characterized by high liquid and/or solid recycle, said process suitable for large scale purification and producing high purity glycolic acid with low diglycolic acid content.