Low By-Product Polyphenylene Polymethylene Polyisocyanates
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Solution Overview
Problem
Current methods for producing polyphenyl polymethylene polyisocyanates (pMDI) face challenges in achieving low by-product content, particularly high levels of chlorinated compounds, ureas, carbodiimides, and uretonimine conversion products, which affect the NCO content and quality of the final product.
Innovation Solution
The process involves reacting polyphenyl polymethylene polyamines with organic carbonates to form polyphenyl polymethylene polycarbamates, which are then thermally cleaved to produce pMDI, with prior treatment to convert free amino and urea groups into amide or higher-substituted ureas using derivatizing reagents to minimize carbodiimides and uretonimines, and subsequent filtration over a solid acidic adsorbent to remove residual amines and ureas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosgenation of polyphenyl polymethylene polyamines is used to produce pMDI, then the production process is efficient and widely used, but high levels of chlorinated compounds and by-products are formed
Solution Approach 1:
The patent extracts and removes harmful chlorinated compounds and by-products from the pMDI product through specific purification steps, including treatment with bases to remove carbamoyl chlorides and distillation to separate low-boiling chlorinated impurities, thereby resolving the contradiction between efficient production and harmful by-product formation
Solution Approach 2:
The patent changes process parameters such as reaction temperature, base concentration, and distillation conditions to optimize the balance between production efficiency and by-product reduction, achieving lower chlorinated compound content while maintaining productive output
2Productivity
If complex polyamine-containing mixtures are reacted with phosgene, then pMDI is produced efficiently, but N,N-disubstituted carbamoyl chlorides and chlorinated phenyl isocyanates are formed as by-products
Solution Approach 1:
The patent applies preliminary action by adding bases such as alkali metal hydroxides or carbonates before or during the phosgenation reaction to preemptively neutralize carbamoyl chlorides and prevent the formation of chlorinated phenyl isocyanates, thereby improving product purity without significantly affecting production rate
Solution Approach 2:
The patent introduces base compounds as intermediary substances that mediate between the phosgene reaction and the final product, capturing harmful intermediates like carbamoyl chlorides and converting them into removable salts, thus enhancing manufacturing precision
3Reliability
If hydrolyzable halogen compounds are present in isocyanates, then the reaction with polyols is influenced, but rapid yellowing of the isocyanates occurs
Solution Approach 1:
The patent removes hydrolyzable halogen compounds through base treatment and distillation processes, eliminating the root cause of both reaction instability and yellowing, thereby simultaneously improving reliability and ease of manufacture
4Manufacturing precision
If filtration over solid acidic adsorbent is performed to remove residual amines and ureas, then carbodiimides and uretonimines are minimized, but additional process steps are required
Solution Approach 1:
The patent applies local quality by using solid acidic adsorbents with specific properties (acidity, surface area, pore structure) targeted at capturing residual amines and ureas in specific zones of the reaction mixture, efficiently minimizing carbodiimides and uretonimines while managing process complexity
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 results in pMDI with an NCO content of at least 29%, containing less than 2% by weight of ureas, less than 8% by weight of carbodiimides and/or uretonimines, and low organic chlorine compounds, improving the product's quality and reducing by-product formation.
Implementation Method 1
reacting polyphenyl polymethylene polyamines with organic carbonates to form polyphenyl polymethylene polycarbamates
Implementation Method 2
the polyphenyl polymethylene polycarbamates are thermally cleaved to give the polyphenyl polymethylene polyisocyanates
Implementation Method 3
filtration over a solid acidic adsorbent to remove residual amines and ureas
Data Source
AI summary
The invention relates to polyphenyl polymethylene polyisocyanates having an NCO number of at least 29% comprising less than 2% by weight ureas, less than 8% by weight carbodiimides or uretonimines and less than 1000 ppm organic chlorine compounds.The polyphenyl polymethylene polyisocyanates can be prepared according to the invention by reacting(i) polyphenyl polymethylene polyamines with organic carbonates to give the corresponding polyphenyl polymethylene polycarbamates,(ii) by thermally cleaving the polyphenyl polymethylene polycarbamates to give the polyphenyl polymethylene polyisocyanates,wherein, prior to the thermal cleavage, the free amino groups or urea groups present in the carhamate crude mixture comprising the polyphenyl polymethylene polycarbamates are reacted with a derivatizing reagent to give amide groups or urethane groups.The polyphenyl polymethylene polyisocyanates can further be prepared according to the invention, prior to the thermal cleavage, by removing compounds having free amino groups or urea groups present in the carbamate crude mixture from the carbamate crude mixture by filtration of the carbamate crude mixture comprising the polyphenyl polymethylene polycarbamates over a solid acidic adsorbent in the presence of an acid dissolved in the carbamate crude mixture.