MDI Preparation Single-Stage HCl Treatment
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Solution Overview
Problem
Existing methods for producing di- and polyisocyanates of the diphenylmethane series face challenges in achieving a bright color and reducing hydrolyzable chlorine content, often requiring complex processes, additional equipment, and non-system catalysts like metal oxides.
Innovation Solution
A single-stage hydrogen chloride treatment process in a bubble column or tray column with a contact time of 1 minute to less than 30 minutes is applied to the liquid product streams or reaction mixtures, eliminating the need for additional catalysts and reducing equipment complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multi-stage hydrogen chloride treatment is used after dephosgenation, then color values and chlorine content are reduced, but device complexity and process complexity increase
Solution Approach 1:
The patent combines the hydrogen chloride treatment step with the dephosgenation step into a single integrated process. The gaseous hydrogen chloride is introduced directly into the dephosgenation reactor where it simultaneously removes excess phosgene and treats the liquid product stream to reduce color values and chlorine content, eliminating the need for separate treatment stages and associated equipment
Solution Approach 2:
The dephosgenation reactor is designed to perform multiple functions: it removes excess phosgene from the reaction mixture, treats the liquid product stream with hydrogen chloride to reduce color and chlorine content, and prepares the product for subsequent processing. This multi-functional approach reduces the number of dedicated units required
2Object-affected harmful factors
If treatment with hydrogen chloride gas is performed after removal of substantial part of solvent, then color values are reduced, but mixture becomes more difficult to handle due to high viscosity
Solution Approach 1:
The patent performs the hydrogen chloride treatment action on the liquid product stream before substantial solvent removal occurs. By treating the less viscous mixture earlier in the process, the treatment is more effective and the mixture remains easier to handle during and after treatment, avoiding the difficulties associated with treating highly viscous materials
3Device complexity
If single-stage hydrogen chloride treatment is used, then device complexity is reduced, but effectiveness of treatment and deposit formation increase
Solution Approach 1:
The patent optimizes key parameters of the single-stage treatment including maintaining temperatures between 60-130°C, controlling the molar ratio of hydrogen chloride to isocyanate groups, and adjusting contact time to ensure effective treatment in one stage without excessive deposit formation, achieving both simplicity and reliability
4Object-affected harmful factors
If inert gas treatment is applied after hydrogen chloride treatment, then hydrolyzable chlorine content is reduced, but exhaust gas load and process complexity increase
Solution Approach 1:
The patent utilizes hydrogen chloride gas, which would normally be considered a harmful byproduct requiring removal, as a beneficial reagent to treat the liquid product stream. The hydrogen chloride reduces color values and chlorine content while the resulting gases can be more easily managed compared to traditional inert gas treatment approaches
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 approach significantly reduces color values and chlorine content in the MDI product, simplifying the process and minimizing exhaust gas production without requiring pure hydrogen chloride or complex cleaning steps.
Implementation Method 1
treatment with a gaseous hydrogen chloride stream in a single stage in a bubble column or in a tray column
Implementation Method 2
reaction of di- and polyamines of the diphenylmethane series with phosgene in the presence of a solvent in a phosgenation reactor to obtain a di- and polyisocyanate of the diphenylmethane series
Implementation Method 3
treatment with a gaseous hydrogen chloride stream in a single stage in a bubble column or in a tray column within a contact time of 1 minute to less than 30 minutes
Data Source
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AI summary
The invention relates to a method for producing di- and polyisocyanates of the diphenylmethane series, in which (i) the liquid product flow created in the phosgenation, (ii) the reaction mixture present in an optionally provided reactor for carbamic acid chloride cleaving, (iii) the liquid product flow leaving such an optionally provided reactor for carbamic acid chloride cleaving, (iv) the reaction mixture present in the dephosgenation, or (v) the liquid product flow created in the dephosgenation, is treated with a gaseous hydrogen chloride flow in one stage in a bubble column or in a plate column within a contact time of 1 min to less than 30 min. The product flow treated in this way or the reaction mixture treated in this way is fed directly (i.e. in particular without further treatment with an inert gas) to the next step of the reaction or workup.