Dehydrogenation Reactor Shutdown via Reducing Gas Treatment
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Solution Overview
Problem
Dehydrogenation catalysts with chromium become spent after prolonged use, requiring shutdown procedures that fail to maintain chromium in a reduced oxidation state, affecting catalyst replacement and efficiency.
Innovation Solution
A method involving controlled cooling and treatment with a reducing gas to bring chromium in the catalyst to a reduced oxidation state, comprising multiple temperature stages and gas purging steps to ensure chromium is predominantly in a reduced state upon shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequent high temperature regeneration cycles are used to maintain catalyst activity, then catalyst performance is improved, but chromium oxidation state is worsened (chromium becomes over-oxidized)
Solution Approach 1:
The invention applies preliminary action by performing a controlled reduction treatment with a reducing gas (such as hydrogen or carbon monoxide) during the shutdown cooling process, before the catalyst is removed from the reactor. This preliminary reduction step ensures chromium is in the desired reduced oxidation state (Cr2+ or Cr3+) before catalyst removal, preventing over-oxidation that would occur with frequent high temperature regeneration cycles.
2Loss of time
If the catalyst bed is cooled directly to ambient temperature without reducing gas treatment, then shutdown time is reduced, but chromium oxidation state is worsened
Solution Approach 1:
The invention merges two processes - the cooling process and the reducing gas treatment process - into a single integrated operation. The reducing gas is introduced during the cooling phase from elevated temperature to intermediate temperature, combining the thermal management function with the chemical reduction function. This eliminates the need for separate cooling and reduction steps, maintaining chromium in the reduced oxidation state without extending shutdown time.
3Productivity
If multiple alternating dehydrogenation and regeneration cycles are performed, then catalyst productivity is improved, but catalyst lifetime is worsened (catalyst becomes spent faster)
Solution Approach 1:
The invention applies parameter changes by modifying the oxidation state parameter of chromium during the shutdown procedure. By controlling the reducing gas treatment and temperature parameters during cooling, the chromium is maintained in a reduced oxidation state (changing the chemical parameter), which extends catalyst lifetime and delays the point at which the catalyst becomes spent and requires replacement.
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
The method effectively ensures that at least some, and preferably a majority, of the chromium in the catalyst is in a reduced oxidation state upon shutdown, facilitating efficient catalyst replacement and maintaining reactor performance.
Implementation Method 1
treating the catalyst bed with a reducing gas to bring the chromium in the catalyst to a reduced oxidation state
Implementation Method 2
cooling the catalyst bed with a first cooling gas to a second elevated temperature T2 lower than T1
Data Source
AI summary
A procedure for shutting down a dehydrogenation reactor having a catalyst bed with a chromium-containing catalyst operating at a first elevated temperature comprises cooling the catalyst bed with a first cooling gas to a second elevated temperature lower than the first elevated temperature, removing the first cooling gas, introducing a reducing gas to the catalyst bed, cooling the catalyst bed with a second cooling gas from the second elevated temperature to a third elevated temperature, removing the reducing gas, cooling the catalyst bed to a fourth elevated temperature, and introducing air to cool the catalyst to ambient temperature, whereby the dehydrogenation reactor is shut down. The second cooling gas may be the same as, or different from, the reducing gas. Moreover, the reducing gas may be purged from the reactor by a third cooling gas.