Isocyanate Solvent Recirculation Water Control
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Solution Overview
Problem
Existing processes for producing isocyanates, such as diisocyanates and polyisocyanates, face challenges with solvent recirculation due to potential water contamination, which can lead to corrosion issues in plant equipment and the formation of hydrochloric acid when water reacts with phosgene, causing further corrosion problems.
Innovation Solution
A continuous process involving the reaction of an amine with phosgene using a solvent, followed by separation of crude isocyanate and solvent streams at different pressures, with subsequent purification of the solvent streams to minimize water content, specifically aiming to reduce water impurities below 100 ppm to prevent corrosion, and recycling the purified solvent streams back into the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solvent recirculation is implemented in the isocyanate production process, then productivity and resource efficiency are improved, but water contamination causes corrosion and safety problems
Solution Approach 1:
The solvent recirculation system is segmented into multiple streams: a first solvent stream from the reaction zone and a second solvent stream from the distillation zone. Each stream is treated separately, allowing targeted purification where needed while maintaining recirculation benefits.
Solution Approach 2:
Water and other impurities are extracted from the solvent streams through distillation and purification processes. The second solvent stream undergoes specific purification to remove water content, separating the harmful impurity from the useful solvent for safe recirculation.
2Device complexity
If solvent recirculation is performed without purification, then device complexity is reduced, but water content causes corrosion and hydrochloric acid formation
Solution Approach 1:
Purification steps are performed in advance before solvent recirculation. The second solvent stream is purified to remove water content prior to being mixed with the first solvent stream and recycled, preventing corrosion and acid formation downstream.
Solution Approach 2:
A purification unit acts as an intermediary between the distillation zone and the reaction zone. This intermediate purification step removes harmful water content from the second solvent stream, mediating between the need for recirculation and the need to prevent corrosion.
3Reliability
If water content in solvent is reduced to ≤100 ppm, then corrosion is prevented, but additional purification steps increase process complexity
Solution Approach 1:
Purification is applied locally to the second solvent stream that is most at risk of water contamination from the distillation zone. The first solvent stream from the reaction zone is reused without additional purification, as it is already within acceptable water content limits.
Solution Approach 2:
The water content parameter is controlled and changed through distillation and purification processes. The second solvent stream is purified to achieve a water content of ≤100 ppm, transforming it from a potentially harmful state to a safe recirculation state.
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 minimizes water impurities in the solvent streams, preventing corrosion and ensuring the safe recirculation of solvents, thereby maintaining equipment integrity and preventing unwanted byproduct formation.
Implementation Method 1
separating the crude isocyanate stream to obtain a purified isocyanate stream and a second solvent stream at a pressure ≤ ambient pressure
Implementation Method 2
subsequent purification of the solvent streams to minimize water content
Implementation Method 3
excess phosgene, the hydrogen chloride and the solvent are separated off from the reaction product (MDI) by distillation
Data Source
Figure 1
AI summary
The present invention relates to a process for the production of isocyanates, preferably diisocyanates and polyisocyanates of the diphenylmethane series (MDI), by reacting an amine with phosgene in the liquid phase or in the gas phase to form the corresponding isocyanates, subsequent removal of the solvent in at least two steps to obtain at least two solvent streams, individual treatment of the at least two solvent streams, and recirculation of at least a portion of the solvent streams.