High Purity 2,4'-MDI Production via Distillation and Crystallization
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Solution Overview
Problem
The production of polyurethanes is hindered by the presence of 2,2′-MDI, which is unreactive and can migrate, leading to impaired polymer properties and contamination issues, while current methods struggle to achieve high purity 2,4′-MDI due to the accumulation of 2,2′-MDI and other impurities in the MDI isomer mixtures.
Innovation Solution
A process involving the reaction of aniline and formaldehyde with an acid catalyst to form diamines and polyamines, followed by phosgenation, and subsequent separation techniques such as distillation and crystallization to achieve an MDI fraction with at least 99% 2,4′-MDI, while minimizing 2,2′-MDI, solvent residues, and phenyl isocyanates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional distillation or crystallization is used to separate MDI isomers, then 4,4'-MDI and mixed products can be obtained, but high purity 2,4'-MDI cannot be achieved due to accumulation of 2,2'-MDI and other impurities
Solution Approach 1:
The patent employs multiple distillation steps with varying parameters (temperature, pressure, reflux ratios) to selectively separate MDI isomers. The process uses a first distillation at specific conditions to obtain a crude 2,4'-MDI fraction, then a second distillation with different parameters to purify it further, achieving high purity while preventing impurity accumulation
Solution Approach 2:
The separation process is divided into multiple sequential stages: initial distillation to obtain crude 2,4'-MDI, followed by further distillation or crystallization steps. This segmentation allows each stage to target specific impurities, progressively purifying the product without allowing 2,2'-MDI and other impurities to accumulate
2Reliability
If 2,2'-MDI is present in MDI mixtures, then polyurethane production is hindered due to unreactive nature and migration, but complete removal is difficult with current methods
Solution Approach 1:
The patent specifically targets and extracts 2,2'-MDI from the MDI mixture through controlled distillation and crystallization processes. By designing separation conditions that exploit the different physical properties of 2,2'-MDI compared to 2,4'-MDI and 4,4'-MDI, the process effectively removes this harmful component while maintaining ease of manufacture
Solution Approach 2:
The patent uses intermediate fractions and controlled crystallization as intermediary steps to selectively remove 2,2'-MDI. These intermediary processes act as mediators between the crude mixture and the final pure product, enabling effective removal of the unreactive isomer without compromising the overall manufacturing process
3Manufacturing precision
If multiple separation steps are implemented to achieve high purity 2,4'-MDI, then purity is improved, but process complexity increases
Solution Approach 1:
The patent combines distillation and crystallization operations in an integrated process flow, where each method complements the other. By merging these separation techniques rather than using them independently, the process achieves high purity 2,4'-MDI while managing overall process complexity through synergistic operation
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 effectively produces MDI mixtures with high 2,4′-MDI content, reducing interference in polyurethane production and achieving low levels of 2,2′-MDI and other impurities, resulting in improved polymer properties and compliance with foodstuff safety standards.
Implementation Method 1
condensation of aniline and formaldehyde
Implementation Method 2
phosgenation of the corresponding diamines and polyamines
Implementation Method 3
separated in the polymer/monomer separation by means of simple evaporation or distillation
Implementation Method 4
separated by distillation or by crystallisation
Implementation Method 5
separated by distillation or by crystallisation into the 4,4'-MDI isomers
Implementation Method 6
separated by distillation or by crystallisation
Data Source
AI summary
The present invention relates to a process for the production of MDI fractions containing 2,4′-MDI, and in which the 2,2′-MDI component from the MDA production is largely removed from the isomer mixture. Highly reactive monomeric MDI products can be produced in this way. These MDI products are characterised in their processing by significantly reduced emissions of MDI monomers.