Fischer-Tropsch Off-Gas Segmentation for Paraffin Production
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Solution Overview
Problem
The existing processes for preparing paraffin products from carbonaceous feedstocks face inefficiencies due to CO2, CH4, and inert buildup in Fischer-Tropsch reactors, and imbalances in the H2/CO ratio, which affect hydrocarbon production and catalyst stability.
Innovation Solution
A process involving partial oxidation of carbonaceous feedstocks, followed by a Fischer-Tropsch reaction, hydrogenation of off-gas using a copper-zinc catalyst with a specific steam/off-gas ratio, and subsequent conversion using a nickel-based catalyst to optimize the H2/CO ratio and reduce oxygenate formation, which enhances catalyst stability and product quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If off-gas is recirculated to the Fischer-Tropsch reactor, then hydrocarbon production is maintained, but CO2, CH4 and inerts build up reducing productivity
Solution Approach 1:
The off-gas stream is divided into two separate streams: a first off-gas stream containing CO and H2 is recirculated to the Fischer-Tropsch reactor, while a second off-gas stream containing CO2, CH4 and inerts is directed to a gasifier. This segmentation prevents harmful substance buildup in the reactor while maintaining hydrocarbon production.
Solution Approach 2:
The harmful components (CO2, CH4, inerts) are extracted from the off-gas stream and separated into a dedicated gasifier stream, removing them from the Fischer-Tropsch reactor cycle to prevent buildup and maintain productivity.
2Quantity of substance
If off-gas is fed back to gasifiers, then H2 and CO are produced, but H2/CO ratio becomes imbalanced
Solution Approach 1:
The off-gas is segmented into two streams with different compositions: the first stream (CO and H2) is sent to the Fischer-Tropsch reactor, while the second stream (CO2, CH4, inerts) goes to the gasifier. This segmentation allows independent control of H2/CO ratio in the reactor feed.
Solution Approach 2:
Different parts of the off-gas stream are given different destinations based on their composition: CO and H2-rich portions go to the reactor where they are needed, while CO2, CH4 and inerts are directed to the gasifier where they can be converted to H2 and CO with appropriate H2/CO ratio.
3Device complexity
If all off-gas is recirculated to Fischer-Tropsch reactor, then process simplicity is maintained, but catalyst stability deteriorates due to harmful substance buildup
Solution Approach 1:
The off-gas stream is divided into two separate streams with different compositions: a first off-gas stream containing CO and H2 is recirculated to the Fischer-Tropsch reactor, while a second off-gas stream containing CO2, CH4 and inerts is directed to a gasifier. This segmentation prevents harmful substance buildup in the reactor while maintaining hydrocarbon production.
Solution Approach 2:
The harmful components (CO2, CH4, inerts) are extracted from the off-gas stream and separated into a dedicated gasifier stream, removing them from the Fischer-Tropsch reactor cycle to prevent buildup and maintain productivity.
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 process stabilizes catalyst performance, maintains optimal process conditions throughout the catalyst's lifetime, increases catalyst lifespan, and produces a gas suitable for further reforming without oxygenate interference, ensuring efficient hydrocarbon production and hydrogen generation.
Implementation Method 1
subjecting at least a part of the off-gas from the Fischer-Tropsch reaction to hydrogenation using a steam/off-gas mol ratio in the range of between 0.5 and 1.5, preferably between 0.7 and 1.5, and a catalyst comprising copper and zinc or a catalyst comprising copper, zinc and manganese
Implementation Method 2
In the second reactor carbon monoxide is removed via a shift reaction with water. This reaction results in carbon dioxide and hydrogen
Implementation Method 3
In another method described in US2008023497A1 and in EP1860063, Fischer-Tropsch off-gas is subjected to hydrogenation using a pre-reforming catalyst which also promotes methanation of carbon monoxide
Implementation Method 4
performing a Fischer-Tropsch reaction using the mixture as obtained in step (a) and recovering an off-gas from the Fischer-Tropsch reaction
Implementation Method 5
partial oxidation of the carbonaceous feedstock to obtain a mixture comprising hydrogen and carbon monoxide
Data Source
AI summary
The invention relates to a process for preparing a paraffin product from a carbonaceous feedstock comprising (a) partial oxidation of the carbonaceous feedstock to obtain a mixture comprising hydrogen and carbon monoxide, (b) performing a Fischer-Tropsch reaction using the mixture as obtained in step (a) and recovering an off-gas from the Fischer-Tropsch reaction and a paraffin product, (c) hydrogenating at least a part of the off-gas from the Fischer-Tropsch reaction using a steam/off-gas mol ratio in the range of between 0.5 and 1.5 and a catalyst comprising copper and zinc, followed by a conversion step (d) using a nickel based catalyst, and (e) preparing a hydrogen comprising gas from at least a part of the off-gas from the Fischer-Tropsch reaction.