MDI Purification via Distillation with Scrubbing Liquid
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Solution Overview
Problem
Existing processes for purifying 4,4'-methylenediphenyl diisocyanate (MDI) are inefficient in removing aromatic halogen compounds, leading to contamination and quality issues in subsequent processing, and are costly or require significant equipment and thermal stress, which affects the purity and stability of MDI.
Innovation Solution
A distillation process using a column to contact a gaseous stream of MDI with a liquid compound having a higher boiling point and low hydrolyzable chlorine content, reducing the chlorine content in the MDI to below 100 ppm, and incorporating a quenching step to minimize dimer formation and enhance purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing distillation processes are used to purify MDI, then some chlorine removal is achieved, but the hydrolyzable chlorine content remains above 100 ppm and aromatic halogen compounds are not effectively removed
Solution Approach 1:
The patent changes the operating parameters of the distillation process, specifically controlling the reflux ratio between 0.5 and 2.0 and the top column temperature between 160-200°C, to achieve effective removal of aromatic halogen compounds and reduce hydrolyzable chlorine content below 100 ppm
Solution Approach 2:
The patent introduces a scrubbing liquid that acts as an intermediary substance to selectively remove aromatic halogen compounds from the MDI vapor phase during distillation, achieving purification that conventional direct distillation cannot accomplish
2Productivity
If high temperature distillation is used to separate MDI components, then separation efficiency is improved, but thermal stress degrades MDI purity and promotes dimer formation
Solution Approach 1:
The patent optimizes the distillation temperature parameters, maintaining the top column temperature between 160-200°C and controlling the reflux ratio between 0.5 and 2.0, achieving effective separation without excessive thermal stress that would degrade MDI quality
Solution Approach 2:
The patent implements continuous reflux during distillation, where the condensed vapor continuously returns to the column to maintain separation efficiency while controlling thermal exposure, preventing dimer formation while achieving high purity
3Manufacturing precision
If multiple distillation columns and complex equipment are used to achieve high purity MDI, then purification effectiveness is improved, but equipment costs and process complexity increase significantly
Solution Approach 1:
The patent makes a single distillation column perform multiple functions by optimizing operating conditions (reflux ratio 0.5-2.0, temperature 160-200°C) to simultaneously achieve separation of MDI isomers, removal of aromatic halogen compounds, and reduction of hydrolyzable chlorine content below 100 ppm, eliminating the need for multiple specialized columns
Solution Approach 2:
The patent changes the operational parameters of the distillation process to achieve enhanced purification performance in a single column, using controlled reflux ratios and temperature profiles that enable one piece of equipment to replace what would traditionally require multiple units
4Ease of operation
If MDI is stored in liquid form for extended periods, then handling and transport are facilitated, but dimerization occurs leading to turbidity, sedimentation, and quality degradation
Solution Approach 1:
The patent performs preliminary purification during the distillation process itself, removing impurities and controlling dimer formation before storage by maintaining specific temperature and reflux conditions, so that the MDI is already optimized for stability before it enters the storage phase
Solution Approach 2:
The patent controls the temperature and reflux parameters during distillation to minimize dimerization reactions, and the purified product can then be stored at controlled temperatures to maintain chemical stability while in liquid form
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 effectively reduces hydrolyzable chlorine and dimer content in MDI, improving its quality, stability, and integration into existing production processes with reduced equipment costs and thermal stress, resulting in a high-purity MDI suitable for polyurethane production.
Implementation Method 1
purification by distillation of a mixture I containing 4,4'-methylenediphenyl diisocyanate
Implementation Method 2
gaseous stream consisting of the mixture I is brought into contact in the column K1 with at least one liquid compound A
Data Source
Figure 1
AI summary
The invention relates to a process for purifying mixtures comprising 4,4'-methylene diphenyl diisocyanate, comprising the distillative purification of a mixture I comprising 4,4'-methylene diphenyl diisocyanate having a content of hydrolysable chlorine to ASTM D4663-10 of more than 100 ppm by means of a column K1, wherein the gaseous stream consisting of mixture I is contacted in column K1 with at least one liquid compound A which has a boiling point which is the same as or higher than 4,4'-methylene diphenyl diisocyanate and which has a content of hydrolysable chlorine to ASTM D4663-10 of at most 100 ppm, and wherein the gaseous stream O which is obtained at the top of the column and comprises 4,4'-methylene diphenyl diisocyanate has a content of hydrolysable chlorine to ASTM D4663-10 of at most 100 ppm.