Aromatic Isocyanate Mixing Chamber Segmentation
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Solution Overview
Problem
Existing processes for preparing isocyanates by reacting amines with phosgene in the liquid phase often result in high levels of secondary component formation, such as urea and high-viscosity by-products, due to inadequate mixing and residence time in the reaction chamber.
Innovation Solution
A process where the amine and phosgene are first mixed in a mixing chamber with the amine added coaxially and phosgene added through multiple planes at right angles to the axis, ensuring a mean residence time of no more than 18.5 ms in the mixing chamber to minimize secondary component formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the amine and phosgene are mixed with insufficient residence time in the mixing chamber, then secondary component formation is reduced, but mixing homogeneity deteriorates
Solution Approach 1:
The mixing chamber is segmented into multiple zones with different flow patterns. The first mixing zone provides intense turbulent mixing for rapid homogenization, while the second mixing zone provides gentler mixing to maintain homogeneity without excessive residence time. This segmentation allows the reaction mixture to achieve uniform composition quickly while minimizing the total time in the chamber, thereby reducing secondary component formation.
Solution Approach 2:
The mixing chamber employs dynamic flow conditions with varying velocity profiles across different zones. The first mixing zone creates high-velocity turbulent flow for rapid initial mixing, while the second zone transitions to lower velocity laminar or transitional flow that maintains homogeneity. This dynamic approach optimizes the balance between mixing efficiency and residence time, preventing secondary reactions while ensuring complete mixing.
2Stability of the object's composition
If the residence time in the mixing chamber is extended, then mixing homogeneity is improved, but productivity decreases
Solution Approach 1:
The mixing chamber is divided into two functional segments: a first mixing zone for rapid initial homogenization and a second mixing zone for final composition stabilization. This segmentation enables the process to achieve adequate mixing homogeneity in a shorter total residence time compared to a single long mixing chamber, thereby maintaining higher productivity while ensuring product quality.
Solution Approach 2:
The first mixing zone is designed to rapidly rush the reactants through an intense mixing phase, achieving most of the homogenization quickly. This allows the mixture to pass through the mixing chamber faster than traditional single-zone designs, reducing overall residence time and increasing productivity while still achieving the required mixing homogeneity before the mixture enters the reactor.
3Object-generated harmful factors
If rapid mixing is achieved through intense turbulence, then secondary component formation is reduced, but energy consumption increases
Solution Approach 1:
The mixing energy is segmented and applied selectively: the first mixing zone receives high energy input to create intense turbulence for rapid initial mixing and prevent secondary component formation. The second mixing zone receives minimal energy input, just enough to maintain homogeneity. This segmented energy application reduces total energy consumption compared to continuous high-energy mixing, while still achieving the goal of minimizing secondary components.
Solution Approach 2:
The mixing process employs periodic variation in intensity: high-energy turbulent mixing in the first zone for a short duration to rapidly homogenize the reactants, followed by lower-energy maintenance mixing in the second zone. This periodic action pattern optimizes energy efficiency by applying high energy only when necessary for rapid mixing, rather than maintaining high energy input throughout the entire residence time.
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 reduces the formation of secondary components, achieving a lower level of unwanted by-products and optimizing the production of isocyanates by ensuring rapid and homogeneous mixing.
Implementation Method 1
Rapid mixing of the amine with the phosgene is necessary... rapid mixing and a short residence time in the reaction chamber are required
Data Source
AI summary
The invention relates to a process for preparing isocyanates by reacting the corresponding amines with phosgene in the liquid phase, if appropriate in the presence of at least one inert medium, in which the amine and the phosgene are first mixed in a mixing chamber (1) to give a reaction mixture and the reaction mixture is fed to a reactor, the amine being added through an orifice (3) arranged coaxially to the mixing chamber (1) and the phosgene being added through feed orifices (5) in at least two planes (7, 9) arranged at right angles to the axis (11) of the mixing chamber (1), or the phosgene being added through the orifice (3) arranged coaxially to the mixing chamber and the amine through the feed orifices (5) in at least two planes (7, 9) arranged at right angles to the axis (11) of the mixing chamber (1). At least one plane (9) is arranged upstream and at least one plane (7) downstream of the orifice (3) arranged coaxially to the mixing chamber (1) in main flow direction of the reaction mixture. The mean residence time of the reaction mixture in the mixing chamber (1) is not more than 20 ms.