Phosgene Generator Start-Up Chlorine Control
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Solution Overview
Problem
Existing phosgene production methods fail to maintain low chlorine content during start-up and shutdown periods, leading to increased chlorine levels in the product stream, which can result in quality losses and safety issues.
Innovation Solution
The method involves flushing the phosgene generator with carbon monoxide to displace chlorine from the activated carbon catalyst and reactor periphery before restarting production, ensuring that the chlorine concentration remains below 100 ppmv during start-up, by maintaining a controlled carbon monoxide supply and heating the catalyst to prevent chlorine accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the phosgene generator is shut down and restarted after a predetermined downtime, then production can be resumed, but chlorine accumulates on the activated carbon catalyst during shutdown, leading to high chlorine content in the product stream during start-up
Solution Approach 1:
The patent applies preliminary action by introducing carbon monoxide into the phosgene generator before the actual production start-up to displace chlorine from the activated carbon catalyst. This pre-treatment step reduces the chlorine content on the catalyst surface, ensuring that when production begins, the chlorine content in the product stream remains below 100 ppmv, thus preventing quality losses and safety issues associated with high chlorine levels.
2Manufacturing precision
If carbon monoxide is used in excess to maintain low chlorine content in phosgene, then product quality is improved, but material loss increases due to non-recyclable excess CO
Solution Approach 1:
The patent applies self-service by using the excess carbon monoxide that would otherwise be wasted and vented to the atmosphere as a useful reagent during the start-up phase. The CO serves dual purposes: it displaces chlorine from the catalyst during the preliminary treatment, and then continues to react with chlorine during production to maintain low chlorine levels in the phosgene product. This eliminates the need to vent excess CO, converting a material loss into a beneficial function.
3Manufacturing precision
If the chlorine content in phosgene is kept low to prevent quality losses in downstream processes, then product quality is maintained, but additional purification steps may be required increasing process complexity
Solution Approach 1:
The patent converts the harmful effect of excess carbon monoxide (which would normally be wasted and contribute to material loss) into a beneficial function. By utilizing the excess CO to displace chlorine from the catalyst during start-up and to react with chlorine during production, the system maintains low chlorine content in the phosgene product without requiring additional purification steps, thus eliminating both material loss and the need for complex purification equipment.
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 chlorine content in the phosgene produced during start-up and shutdown periods, maintaining product quality and safety by preventing excessive chlorine levels in the phosgene stream, allowing for its direct use in isocyanate production without additional purification steps.
Implementation Method 1
the activated carbon catalyst is freed from chlorine by adding carbon monoxide to such an extent that during the start-up time, a maximum concentration of chlorine in the gas stream immediately downstream of the reaction space of 1000 ppmv is not exceeded
Implementation Method 2
producing phosgene by reacting carbon monoxide with chlorine in the gas phase on an activated carbon catalyst
Implementation Method 3
The formation of phosgene is a highly exothermic reaction with an enthalpy of formation of -107.6 kJ/mol
Data Source
AI summary
The present invention relates to a method for operating a phosgene generator for producing phosgene by reacting carbon monoxide with chlorine in the gas phase on an activated carbon catalyst arranged in a reaction chamber, in which method, after a predefinable operating period, the phosgene production is at least temporarily interrupted by shutting down the phosgene generator over a shutdown period and, after a predefinable downtime, is resumed by starting up the phosgene generator over a start-up period, wherein the method is characterized in that the activated carbon catalyst, before the phosgene generator is started up, is freed of chlorine by adding carbon monoxide so that, during the start-up period, a maximum concentration of chlorine in the gas stream immediately downstream of the reaction chamber of 1000 ppmv is not exceeded. The invention also relates to the use of the phosgene thus obtained in the production of polycarbonate and isocyanates.