Fischer-Tropsch Reactor Start-Up Catalyst Deactivation
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Solution Overview
Problem
The activity of Fischer-Tropsch catalysts decreases over time, especially during the start-up phase of a reactor, due to high relative humidity caused by initial high catalyst activity, leading to rapid and irreversible deactivation.
Innovation Solution
Supplying a feed gas stream containing a nitrogen-containing compound, such as ammonia, to the catalyst during the initial stages of reactor operation to decrease catalyst activity and maintain lower relative humidity, thereby slowing down deactivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fresh catalyst with high initial activity is used, then productivity is improved, but the catalyst deactivates rapidly due to high relative humidity during start-up
Solution Approach 1:
The patent applies preliminary action by introducing a nitrogen-containing compound into the synthesis gas feed stream before the Fischer-Tropsch reaction begins. This pre-treatment step modifies the catalyst surface in advance to reduce its initial activity, preventing the formation of excessive water vapor during start-up. The nitrogen compound adsorbs on active sites, creating a protective effect that stabilizes the catalyst during the critical initial operation phase when high relative humidity would otherwise cause rapid deactivation.
2Reliability
If the reaction temperature is kept low during start-up to avoid high product yield, then catalyst deactivation is reduced, but productivity decreases
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition of the feed stream rather than adjusting temperature parameters. By adding a nitrogen-containing compound to the synthesis gas, the catalyst's effective activity is reduced through chemical modification of the reaction environment. This allows the reaction temperature to be increased during start-up to maintain productivity, while the nitrogen compound continues to suppress water vapor formation and protect the catalyst from deactivation, thus decoupling the temperature-yield-stability relationship.
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 method allows for a higher reaction temperature during start-up, maintaining catalyst stability and productivity over a longer period, with the added benefit of improved heat recovery and reduced need for frequent catalyst regeneration.
Implementation Method 1
the activity of the catalyst is decreased by supplying a feed gas stream comprising a nitrogen-containing compound other than molecular nitrogen
Implementation Method 2
converting carbon monoxide and hydrogen supplied with the gaseous feed stream to the reactor into hydrocarbons
Implementation Method 3
a lot of water is produced in the Fischer-Tropsch hydrocarbon synthesis, resulting in a high relative humidity at the start of the Fischer-Tropsch process
Data Source
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AI summary
The invention relates to a method for start-up and operation of a Fischer-Tropsch reactor comprising the steps of: (a) providing a reactor with a fixed bed of reduced Fischer-Tropsch catalyst that comprises cobalt as catalytically active metal; (b) supplying a gaseous feed stream comprising carbon monoxide and hydrogen to the reactor, wherein the gaseous feed stream initially comprises a nitrogen-containing compound other than molecular nitrogen in an initial concentration in the range of from 0.1 to 50 ppmv based on the volume of the gaseous feed stream; (c) converting carbon monoxide and hydrogen supplied with the gaseous feed stream to the reactor into hydrocarbons at an initial reaction temperature, wherein the initial reaction temperature is set at a value of at least 200 °C and hydrocarbons are produced at a first yield; (d) maintaining the initial reaction temperature at the set value and maintaining the first yield by decreasing the concentration of the nitrogen-containing compound in the gaseous feed stream supplied to the reactor; (e) optionally increasing the reaction temperature after the concentration of the nitrogen-containing compound in the gaseous feed stream has decreased to a value below 100 ppbv.