Diphenylmethane Di- and Polyamine Purification via Two-Stage Distillation
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Solution Overview
Problem
The production of di- and polyamines of the diphenylmethane series with low water and aniline content is challenging, as higher levels lead to side reactions and impurities in isocyanate production, and existing methods do not efficiently optimize distillation for energy use or recycle aniline effectively.
Innovation Solution
A process involving a two-stage distillation with flash evaporation and subsequent cooling to achieve di- and polyamines with less than 1000 ppm water and 200 ppm aniline, using the heat of the product for energy optimization and minimizing aniline recycling, ensuring low energy consumption and reduced by-product formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional distillation is used to remove water and aniline, then water and aniline are removed from di- and polyamines, but energy consumption is high and distillation is not optimized
Solution Approach 1:
The distillation process is divided into multiple stages: a first distillation stage operating at higher temperature to remove bulk water and aniline, followed by a second distillation stage at lower temperature to achieve the required purity levels. This segmentation allows optimization of energy use at each stage while achieving the target specifications of less than 1000 ppm water and less than 200 ppm aniline.
2Ease of repair
If aniline is recycled into the reaction, then aniline is reused, but MDA is also recycled which reduces process efficiency
Solution Approach 1:
The process extracts and separates aniline from the reaction mixture through distillation, allowing aniline to be recycled into the reaction while preventing MDA from being recycled. This selective extraction ensures that only the desired reactant (aniline) is reused, maintaining process efficiency and productivity.
3Ease of operation
If di- and polyamines are stored at high temperatures, then storage is simplified, but aniline is released again reducing product quality
Solution Approach 1:
The process performs preliminary cooling of the di- and polyamines immediately after the second distillation stage, before storage or further processing. This preliminary cooling action prevents subsequent aniline release during storage, maintaining the low aniline content achieved during distillation and ensuring product quality.
4Ease of manufacture
If water and aniline content in di- and polyamines is high, then production is easier, but side reactions occur leading to increased by-products
Solution Approach 1:
The process changes the parameters of water and aniline content in the di- and polyamines by implementing a two-stage distillation process. The first stage removes bulk contaminants, while the second stage achieves the precise parameter targets of less than 1000 ppm water and less than 200 ppm aniline, thereby preventing side reactions and by-product formation during isocyanate production.
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 production of di- and polyisocyanates with reduced by-products and impurities, maintaining product quality by cooling the di- and polyamines post-distillation, and achieving stable process control with low primary energy use.
Implementation Method 1
in the pre-evaporation stage, aniline and water are partially separated from the organic phase containing di- and polyamines by flash evaporation
Implementation Method 2
aniline and water still present are separated in the subsequent distillation stage
Implementation Method 3
the di- and polyamines containing less than 1000 ppm of water and less than 200 ppm of aniline are subsequently cooled
Data Source
Figure 1~2b
Figure 3~6
AI summary
Preparation of di- and polyamine of the diphenylmethane series comprises transferring aniline and formaldehyde to a reaction mixture containing di- and polyamine, in the presence of an acid catalyst, neutralizing the reaction mixture containing di- and polyamine, introducing the neutralized reaction mixture containing di- and polyamine into an organic phase containing di- and polyamine and an aqueous phase, distillatively separating water and aniline form the organic phase, and cooling the obtained di- and polyamine. Preparation of di- and polyamine of the diphenylmethane series comprises: (a) transferring aniline and formaldehyde to a reaction mixture containing di- and polyamine, in the presence of an acid catalyst, (b) neutralizing the reaction mixture containing di- and polyamine, (c) introducing the neutralized reaction mixture containing di- and polyamine into an organic phase containing di- and polyamine and an aqueous phase, (d) distillatively separating water and aniline form the organic phase, where the distillation in step (d) comprises at least a pre-evaporation step and at least a distillation step; in the pre-evaporation step aniline and water are partially separated from the organic phase containing di- and polyamine by open evaporation; the further aniline and water are removed in the subsequent distillation step and the obtained di- and polyamine contains less than 1000 ppm of water and less than 200 ppm of aniline, based on the weight of di- and polyamine, and (e) cooling the obtained di- and polyamine. An independent claim is included for the preparation of di- and polyisocyanate of the diphenylmethane series comprising preparing di- and polyamine and subsequently reacting the amine with a phosgene.