Fischer Tropsch Catalyst Regeneration via ROR Method
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Solution Overview
Problem
Fischer Tropsch catalysts used in converting light hydrocarbons to heavier hydrocarbons face activity loss over time, requiring regeneration to maintain productivity, with existing methods like hydrogen treatment and ROR being inefficient or costly, especially when trying to maintain activity at elevated pressures.
Innovation Solution
A ROR (reduction oxidation reduction) method is employed at elevated pressures near normal operating conditions, using diluent gases like argon, light hydrocarbons, or helium to adjust mole weight and hydrogen concentration within existing recycle compressor limits, avoiding nitrogen and carbon dioxide in reduction steps to prevent inhibition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a simple hydrogen treatment step is used to regenerate the catalyst, then the process is simple and low cost, but the effectiveness for recovery of lost activity is relatively low
Solution Approach 1:
The regeneration process is divided into three distinct steps (reduction, oxidation, reduction) rather than using a single hydrogen treatment step. This segmentation allows each step to perform a specific function: the first reduction removes heavy hydrocarbons, the oxidation restructures the metal surface, and the second reduction restores the active reduced form, achieving superior activity recovery compared to simple hydrogen treatment
Solution Approach 2:
The invention changes the parameters of the regeneration process by introducing oxygen during the oxidation step and controlling the reduction-oxidation-reduction sequence. This parameter change transforms the catalyst surface structure and composition, enabling recovery of dispersed metal atoms and restoration of active sites that cannot be achieved by hydrogen treatment alone
2Productivity
If temperature is increased to maintain stable catalyst activity, then catalyst activity is maintained, but the amount of undesirable light hydrocarbon products increases and desirable heavy hydrocarbon products decrease
Solution Approach 1:
The ROR regeneration process is performed preliminarily to restore catalyst activity before returning to normal Fischer-Tropsch operation. By restoring dispersed metal surface atoms and active sites through the reduction-oxidation-reduction sequence, the catalyst maintains high activity at lower temperatures, preventing the formation of excessive light hydrocarbon byproducts that would occur at elevated temperatures
3Productivity
If the ROR method is used to regenerate the catalyst at elevated pressure, then catalyst activity recovery is improved, but the mole weight and hydrogen concentration may exceed the design limits of the recycle compressor
Solution Approach 1:
A diluent gas is introduced as an intermediary substance during the ROR regeneration process. The diluent gas mixes with the hydrogen and oxygen streams, reducing the overall mole weight and hydrogen concentration of the gas mixture to within the recycle compressor's design limits. This allows the ROR process to proceed at elevated pressures for effective catalyst regeneration without exceeding compressor operational constraints
Solution Approach 2:
The invention changes the composition parameters of the regeneration gas by adding a diluent gas. This parameter change adjusts the mole weight and hydrogen concentration to satisfy compressor design limits while maintaining elevated pressure conditions that are beneficial for catalyst activity recovery during the ROR process
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 regenerates Fischer Tropsch catalysts with minimal additional equipment and cost, maintaining catalyst activity over extended periods, as demonstrated by experiments showing relative activity recovery within the ROR process.
Implementation Method 1
The logic of using hydrogen is based on the fact that it may be useful to remove heavy hydrocarbons and reduce any oxidized surface cobalt
Implementation Method 2
the oxidation step restructures the metal surface atoms improving dispersion
Implementation Method 3
The synthesis gas is then converted to heavy hydrocarbon products with a Fischer Tropsch catalyst
Data Source
AI summary
A method is disclosed for activating or regenerating a Fischer Tropsch catalyst used in a gas-to-liquids process operating in recycle mode. The method permits the use of specific inert gases to adjust the mole weight of the gas so that the recycle compressor designed for normal steady state operation can also be used in the ROR method. Nitrogen and carbon dioxide are specifically excluded for the reduction steps of the ROR method as they have been demonstrated to have a negative effect on the method. Nitrogen is used in the oxidation step with small amounts of oxygen containing gas, preferably air, and may be modified with the addition of argon, helium, or carbon dioxide if the mole weight of the oxidation gas needs to be modified to satisfy the requirements of the compressor.