Adipic Acid Purification via Three-Stage Crystallization
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Solution Overview
Problem
Traditional adipic acid production methods fail to achieve high enough purity and quality to meet the requirements of high-end applications, particularly due to the presence of trace impurities and nitrate contamination, which limits the product's application range and market competitiveness.
Innovation Solution
A three-stage purification and separation process incorporating primary and secondary activated carbon decolorization and filtration, followed by tertiary ultrafine filtration, to effectively remove impurities and optimize water reuse, resulting in high-quality adipic acid suitable for civilian and industrial uses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional secondary recrystallization method is used, then production cost is reduced and process is simplified, but product purity and quality are insufficient for high-end applications
Solution Approach 1:
The purification process is divided into three distinct crystallization stages, each operating at different temperatures and removing different types of impurities. The first stage removes coarse impurities, the second stage removes fine impurities, and the third stage removes trace impurities, achieving progressive purification without requiring overly complex single-stage processes
Solution Approach 2:
Each crystallization stage is optimized with specific local conditions: first stage uses higher temperature (90-100°C) for coarse crystal formation, second stage uses intermediate temperature (80-90°C) for refined crystals, and third stage uses lower temperature (70-80°C) for ultra-pure crystals. This localized optimization of conditions at each stage achieves high purity without uniform complexity throughout the entire process
2Manufacturing precision
If multiple crystallization stages are added to improve purity, then product quality increases, but production time and process complexity increase
Solution Approach 1:
The three crystallization stages are designed to operate in continuous sequence without interruption. The mother liquor from each stage is directly fed into the next stage, and crystals are continuously harvested. This continuous operation eliminates idle time between stages and maintains productive action throughout the entire purification process
Solution Approach 2:
Each crystallization stage operates at different temperature parameters to optimize purification efficiency while controlling time. The temperature gradient (90-100°C → 80-90°C → 70-80°C) allows each stage to work at its optimal rate, preventing any single stage from becoming a time bottleneck while maintaining effective purification
3Manufacturing precision
If activated carbon adsorption is applied, then trace impurities and color are removed, but water-soluble impurities are still crystallized with adipic acid
Solution Approach 1:
Activated carbon adsorption is performed before each crystallization stage to pre-remove trace impurities and color substances from the solution. This preliminary treatment ensures that when crystallization occurs, fewer trace impurities are available to co-crystallize with the adipic acid, reducing the burden on the crystallization process itself
Solution Approach 2:
Activated carbon serves as an intermediary substance that selectively adsorbs trace organic impurities and color substances from the aqueous solution. This intermediary treatment step separates different types of impurities through different mechanisms: activated carbon handles trace organics while crystallization handles water-soluble inorganics, preventing either mechanism from being overwhelmed
4Manufacturing precision
If conventional purification methods are used, then production cost is controlled, but product color and UV value do not meet high-end user requirements
Solution Approach 1:
The patent specifically addresses color improvement through activated carbon adsorption at each stage and optimized crystallization conditions. The progressive removal of color substances through multiple stages of activated carbon treatment and temperature-controlled crystallization transforms the product from yellowish (conventional) to colorless or white (high-end), meeting stringent color requirements while maintaining manufacturing feasibility
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 method significantly improves the quality of adipic acid by reducing impurities and nitrate content, expanding its application field and enhancing market competitiveness, as demonstrated by improved color, UV transmittance, and purity indices.
Implementation Method 1
two-stage activated carbon to adsorb soluble impurities
Implementation Method 2
crystallizing adipic acid at a crystallization point of 65-75°C
Implementation Method 3
uses an excess of nitric acid to oxidize cyclohexanol
Data Source
Figure 1
AI summary
The present invention produces high-quality adipic acid by using a mixed liquid, containing materials such as nitric acid, adipic acid, glutaric acid and succinic acid, obtained by a nitric acid oxidation method through triple purification and separation, two-stage activated carbon absorption, and third-stage impurity filtering process. The present invention is characterized in: performing first purification and separation on the mixed liquid containing the adipic acid, dissolving, adding efficient activated carbon for first-stage activated carbon absorption and first-stage activated carbon filtering, performing second purification and separation, dissolving, performing second-stage activated carbon absorption and second-stage activated carbon filtering, setting a three-stage superfine filter to remove impurities before the third purification and separation, performing the third purification and separation to obtain adipic acid filter cakes, and drying the adipic acid filter cakes to obtain the high-quality adipic acid. The high-quality adipic acid produced by the production method is high in purity, few in impurities and widely applicable to high-end products.