Catalyst Slip-Stream Rejuvenation for Dehydrogenation
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Solution Overview
Problem
In paraffin dehydrogenation processes using fluidized catalysts, catalyst deactivation occurs due to coke deposition, requiring frequent regeneration, which necessitates large vessels and high air flow volumes, making it costly and inefficient.
Innovation Solution
Implementing a continuous cycling process where a small slip-stream of spent catalyst is rejuvenated for an extended period, reducing the need for large regeneration vessels and air flow, with rejuvenation occurring in the presence of oxygen-containing gases, even concurrently with coke and fuel burning, allowing for efficient heat transfer without direct fuel contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If catalyst is regenerated by burning supplemental fuel and subjugating carbon-burned catalyst to additional oxygen treatment for more than 2 minutes in each cycle, then catalyst activity is maintained over thousands of cycles, but large vessels and high volumes of air flow are required
Solution Approach 1:
The catalyst regeneration process is segmented into two distinct functions: (1) coke combustion in the regenerator, and (2) metal re-oxidation in a separate oxygen contact step. This segmentation allows the oxygen treatment to be applied selectively to restore metal activity without requiring extended residence times that would necessitate large vessels
Solution Approach 2:
The catalyst is pre-treated by combusting coke before oxygen exposure. This preliminary action removes carbon deposits that would otherwise consume oxygen and extend the required treatment time, enabling effective metal re-oxidation in a shorter contact time and smaller vessel
2Reliability
If catalyst is regenerated by burning supplemental fuel and subjugating carbon-burned catalyst to additional oxygen treatment for more than 2 minutes in each cycle, then catalyst activity is maintained over thousands of cycles, but high volumes of air flow are needed
Solution Approach 1:
The harmful effect of extended oxygen treatment is extracted by separating the coke combustion function from the metal re-oxidation function. By taking out the coke removal step as a preliminary action, the subsequent oxygen exposure time is reduced to only what is necessary for metal re-oxidation, significantly reducing air flow volume requirements
Solution Approach 2:
The process changes the sequence and duration of treatment parameters: coke is removed first (changing the catalyst state), then oxygen is introduced for a shorter duration (changing the exposure time parameter), achieving effective regeneration with reduced air flow volume
3Ease of manufacture
If smaller vessel sizes are used for regeneration, then cost is reduced, but residence time may be insufficient to maintain activity over thousands of cycles
Solution Approach 1:
The regeneration process is segmented into coke combustion and metal re-oxidation steps. This segmentation reveals that metal re-oxidation requires only brief oxygen exposure, allowing smaller vessels to be used while maintaining catalyst activity over thousands of cycles
Solution Approach 2:
Coke combustion is performed as a preliminary action before oxygen treatment. This removes carbon deposits that would otherwise require extended oxygen exposure times, enabling smaller vessels to provide sufficient residence time for metal re-oxidation while maintaining long-term catalyst activity
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 maintains catalyst activity for thousands of cycles with significantly reduced vessel size and air flow, achieving reversible deactivation and minimizing equipment size and catalyst inventory, while maintaining high olefin production efficiency.
Implementation Method 1
The catalyst may be regenerated in a catalyst regenerator by combusting coke from the catalyst in the presence of oxygen
Implementation Method 2
combusting coke from the catalyst in the presence of oxygen
Implementation Method 3
The hot regenerated catalyst may then be transferred back to the reactor to catalyze the reaction. If insufficient heat is provided to drive the endothermic reaction, olefin production can suffer
Implementation Method 4
Paraffin dehydrogenation (PDH) is a process in which light paraffins such as ethane and propane can be dehydrogenated to make ethylene and propylene, respectively
Data Source
AI summary
A fluidized catalytic reactor system cycles from 0.05-5% of catalyst at a time through a rejuvenation unit to be heated in the presence of oxygen to maintain catalyst activity. The use of the rejuvenation unit that may be 2% of the size of the main catalyst regeneration unit allows for reduction in equipment size and in catalyst inventory. The catalyst that is sent to the rejuvenation unit may be spent catalyst but may be partially or fully regenerated catalyst. The rejuvenation unit may be heated by combusting fuel or by hot flue gas.