Toluene Diisocyanate Production Purification
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Solution Overview
Problem
The production of toluene diisocyanate (TDI) often results in a colored product due to the presence of cyclic ketones and their reactive derivatives, which form adducts and dimers during distillation, leading to undesirable coloring.
Innovation Solution
Purifying toluenediamine to reduce its cyclic ketone content to less than 0.1% by weight before phosgenation, thereby minimizing the formation of color-imparting adducts and dimers during the TDI production process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional phosgenation of crude toluenediamine is performed, then production efficiency is maintained, but the TDI product becomes colored due to cyclic ketone impurities
Solution Approach 1:
The patent applies preliminary action by purifying the toluenediamine feedstock before phosgenation to remove cyclic ketone impurities. This pre-treatment step ensures that the subsequent phosgenation reaction produces colorless TDI product, avoiding the need for complex post-reaction purification while maintaining production efficiency.
Solution Approach 2:
The patent extracts and removes cyclic ketone impurities from the toluenediamine stream through purification processes before the phosgenation step. This extraction of harmful substances prevents them from participating in color-forming reactions during TDI production, thereby solving the coloring problem while preserving the main production pathway.
2Manufacturing precision
If multi-stage distillations are performed to remove low boilers and high boilers, then product purity is improved, but energy consumption increases
Solution Approach 1:
The patent performs preliminary purification of the toluenediamine feedstock to remove cyclic ketone impurities before phosgenation. This pre-removal of problematic substances eliminates the need for extensive multi-stage distillations during the main production process, thereby reducing energy consumption while maintaining product purity.
Solution Approach 2:
The patent converts the harmful effect of cyclic ketone impurities into a beneficial approach by addressing them in the feedstock purification stage rather than during product distillation. This strategic timing transforms a potential energy-intensive multi-stage separation problem into a more efficient single-stage or reduced-stage purification process.
3Ease of manufacture
If cyclic ketones are present in the toluenediamine, then they form reactive derivatives during phosgenation, but these derivatives form color-imparting adducts and dimers during distillation
Solution Approach 1:
The patent extracts and removes cyclic ketone impurities from the toluenediamine stream before phosgenation. This extraction prevents the formation of reactive cyclic isocyanatocycloalkenones and chloroisocyanatocycloalkenes that would otherwise form color-imparting adducts and dimers during distillation, thereby eliminating the harmful coloring effect while maintaining ease of manufacture.
Solution Approach 2:
The patent applies preliminary anti-action by removing cyclic ketone impurities before they can participate in harmful reactions. This pre-preventive measure stops the formation of color-imparting adducts and dimers at the source, avoiding the need for complex corrective measures during the distillation process while maintaining manufacturing ease.
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
Significantly reduces the color value of the distilled TDI, resulting in a product that is markedly less colored by minimizing the concentration of reactive cyclic isocyanatocycloalkenones and chloroisocyanatocycloalkenes in the distillation streams.
Implementation Method 1
phosgenating the toluenediamine formed in b) which contains a total of less than 0.1% by weight of cyclic ketones, based on 100% by weight of the toluenediamine, thus yielding toluene diisocyanate
Implementation Method 2
The oxidative introduction of a keto function by oxidative attack during the nitration process is also possible
Implementation Method 3
Cyclic ketones in the TDA, or the precursors thereof, can form during the hydrogenation of dinitrotoluene (DNT), for example, by replacement of an amino function by water in an aqueous medium
Data Source
AI summary
The invention relates to a process for the production of toluene diisocyanate, in which the crude toluenediamine obtained from the hydrogenation is purified and then phosgenated. The purification step reduces the total amount of cyclic ketones to less than 0.1% by weight, based on 100% by weight of the toluenediamine.