Isothermal and Adiabatic Absorption for Phosgene Recovery
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Solution Overview
Problem
Current processes for producing isocyanates result in high concentrations of phosgene in the hydrogen chloride stream, leading to material losses and safety concerns, with existing separation methods being energetically unfavorable and inefficient.
Innovation Solution
A two-stage absorption process involving isothermal and adiabatic absorption steps, where phosgene is partially condensed and then absorbed in a solvent, followed by further adiabatic absorption to achieve low phosgene concentrations in the hydrogen chloride stream, minimizing material losses and enhancing safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional separation methods are used to remove phosgene from the hydrogen chloride stream, then phosgene recovery is achieved, but energy consumption increases and process complexity increases
Solution Approach 1:
The invention changes the temperature parameter of the absorption process by implementing a two-stage system with isothermal absorption at lower temperatures followed by adiabatic absorption at higher temperatures. This parameter variation optimizes phosgene absorption efficiency while reducing energy consumption compared to conventional single-stage methods
Solution Approach 2:
The separation process is divided into two distinct stages: isothermal absorption and adiabatic absorption. Each stage operates under different thermal conditions to maximize phosgene recovery efficiency while minimizing overall energy requirements and process complexity
2Loss of substance
If conventional separation methods are used to remove phosgene from the hydrogen chloride stream, then phosgene recovery is achieved, but device complexity increases
Solution Approach 1:
The separation process is divided into two distinct stages: isothermal absorption and adiabatic absorption. Each stage operates under different thermal conditions to maximize phosgene recovery efficiency while minimizing overall energy requirements and process complexity
Solution Approach 2:
The absorption system serves multiple functions: it removes phosgene from the hydrogen chloride stream, recovers phosgene for reuse, and does so through a integrated two-stage process that combines isothermal and adiabatic operations in a unified configuration
3Loss of substance
If high concentrations of phosgene are present in the hydrogen chloride stream, then material loss is reduced, but safety hazards increase
Solution Approach 1:
The invention changes the temperature parameter of the absorption process by implementing a two-stage system with isothermal absorption at lower temperatures followed by adiabatic absorption at higher temperatures. This parameter variation optimizes phosgene absorption efficiency while reducing energy consumption compared to conventional single-stage methods
Solution Approach 2:
The process converts the potentially harmful presence of phosgene in the hydrogen chloride stream into a beneficial recovery opportunity. By using the two-stage absorption system, phosgene that would otherwise be wasted or pose safety risks is efficiently captured and reused in the phosgene synthesis process
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 effectively reduces phosgene content in the hydrogen chloride stream to less than 0.5 wt%, minimizing raw material loss and improving process safety, while also optimizing energy usage and reducing the number of equipment components, thereby enhancing the economic viability of the process.
Implementation Method 1
the vapor mixture formed when phosgene and amine are reacted is subjected to at least one isothermal absorption treatment and at least one adiabatic absorption treatment
Implementation Method 2
the vapor mixture formed when phosgene and amine are reacted is subjected to at least one isothermal absorption treatment
Implementation Method 3
the vapor mixture formed when phosgene and amine are reacted is subjected to at least one isothermal absorption treatment and at least one adiabatic absorption treatment
Data Source
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AI summary
Isocyanates are produced by a) reacting at least one amine with phosgene, optionally in the presence of a solvent to produce the corresponding isocyanate and a stream containing hydrogen chloride, phosgene and optionally solvent, low-boiling compounds and inert substances is obtained, b) separating the stream containing hydrogen chloride, phosgene and optionally solvent, low-boiling compounds and inert substances in an at least two-stage sequence of absorption steps that includes (1) at least one isothermal absorption step and (2) at least one adiabatic absorption step, to obtain (i) a hydrogen chloride stream containing phosgene in concentrations of at most 0.5 wt.% (based on the weight of the hydrogen chloride stream) and (ii) a liquid phosgene stream, and c) recycling the liquid phosgene stream (ii) to the reaction of amine with phosgene.