Phosgene HCl Separation Distillation Reflux Solvent Scrubbing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for separating hydrogen chloride and phosgene in isocyanate production face challenges during start-up, requiring additional safety measures and costly equipment due to the need for initial reflux generation, which is not feasible without pre-existing hydrogen chloride, and often necessitate discarding hydrogen chloride during the start-up period.
Innovation Solution
A process involving a distillation column where a mixed stream of hydrogen chloride and phosgene is separated, with compressed hydrogen chloride partially condensed and recycled as reflux, and an absorbing solvent introduced to scrub phosgene, allowing for efficient separation and reducing start-up costs and safety risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If distillative separation is carried out at increased pressure to avoid low overhead temperatures and cryogenic cooling, then the temperature control is improved, but the energy consumption increases
Solution Approach 1:
The patent utilizes the phase transition of hydrogen chloride from gas to liquid through compression and condensation. By compressing the overhead stream and condensing it in a condenser, liquid HCl is formed which then evaporates in the distillation column to provide reflux, enabling temperature control without cryogenic cooling
Solution Approach 2:
The patent implements a feedback mechanism where condensed liquid HCl from the overhead stream is recycled back to the top of the distillation column as reflux. This self-regulating system maintains proper column temperature and separation efficiency without requiring external cryogenic cooling
2Temperature
If compression and condensation of hydrogen chloride is used to generate reflux, then the temperature control is improved, but the device complexity increases
Solution Approach 1:
The overhead stream serves multiple functions: it is compressed to generate pressure, condensed to form liquid reflux, and the uncondensed portion is discharged. The condenser both cools the stream and generates the reflux necessary for column operation, combining multiple functions in a single system
3Reliability
If additional safety measures and equipment are installed to handle phosgene during start-up, then the safety is improved, but the cost increases
Solution Approach 1:
The patent introduces absorbing solvent before the start-up phase to pre-absorb any phosgene that might be present in the overhead stream. This preliminary protective measure prevents phosgene from reaching the compressor during start-up, eliminating the need for additional safety equipment
Solution Approach 2:
The absorbing solvent acts as an intermediary substance between the distillation column and the compressor. It selectively absorbs phosgene from the overhead stream, protecting the compressor and downstream equipment from phosgene exposure without requiring complex safety systems
4Manufacturing precision
If absorbing solvent is introduced to scrub phosgene from the overhead stream, then the purity of hydrogen chloride is improved, but the loss of substance increases
Solution Approach 1:
The patent recycles the absorbing solvent from the bottom stream back to the top of the distillation column for continued use. This recovery and reuse mechanism minimizes solvent loss while maintaining its effectiveness in absorbing phosgene from the overhead stream
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 enables cost-effective and safe start-up of hydrogen chloride/phosgene separation without additional safety risks, allowing for efficient recycling of phosgene and hydrogen chloride, meeting purity requirements for downstream processes.
Implementation Method 1
The large boiling-point difference between hydrogen chloride and phosgene permits distillative separation
Implementation Method 2
compressing at least a portion of the top stream
Implementation Method 3
at least partially condensing the compressed top stream to form a liquid stream
Implementation Method 4
decompressing at least a portion of the liquid stream to form a cooled liquid stream
Implementation Method 5
Absorption utilizes an absorbing solvent to scrub out phosgene from a gaseous mixed stream containing hydrogen chloride and phosgene
Data Source
AI summary
A process of separating phosgene and hydrogen chloride, comprises: conveying a mixed stream containing hydrogen chloride and phosgene into a distillation column; withdrawing from the distillation column a bottom stream containing phosgene; withdrawing a top stream containing hydrogen chloride; compressing at least a portion of the top stream and at least partially condensing the compressed top stream to form a liquid stream, decompressing at least a portion of the liquid stream to form a cooled liquid stream and a cooled gas stream; and recycling the cooled liquid stream to the top of the distillation column as a reflux; the process additionally comprising temporarily introducing an absorbing solvent into the distillation column, in particular during starting-up and/or shutting-down of the process. The process allows for safe operation even when hydrogen chloride production only gradually begins or decreases, without the necessity of storing hydrogen chloride.