Fischer-Tropsch Kerosene Hydroprocessing With Heavy Fraction Recycle
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Solution Overview
Problem
Existing processes for producing kerosene from Fischer-Tropsch derived products face limitations in yield and quality, particularly in achieving high yields of premium kerosene meeting Jet A-1 specifications without additional catalytic dewaxing or oligomerization steps, and often result in suboptimal freezing points and aromatics content.
Innovation Solution
A process involving a hydroprocessing step using a catalyst with a molecular sieve of 5-7 angstrom pore size and SiO2/Al2O3 ratio of at least 25, combined with Group VIII metals, to convert a C5+ fraction from a Fischer-Tropsch product, followed by separation to obtain a kerosene fraction with a Final Boiling Point of at most 302°C and a flashpoint of at least 38°C, with recycling of a heavier fraction for further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional hydroprocessing catalysts are used to produce kerosene from Fischer-Tropsch products, then the process requires additional catalytic dewaxing or oligomerization steps, but this increases device complexity and reduces productivity
Solution Approach 1:
The patent combines multiple catalytic functions (hydrocracking, hydroisomerization, and dewaxing) into a single hydroprocessing catalyst system. This merging of functions eliminates the need for separate catalytic dewaxing or oligomerization steps, thereby reducing device complexity while maintaining high kerosene yield above 70%.
Solution Approach 2:
The hydroprocessing catalyst is designed with multi-functionality, performing hydrocracking, hydroisomerization, and dewaxing activities simultaneously. This universal catalyst approach allows a single process unit to achieve what previously required multiple specialized units, improving productivity without increasing device complexity.
2Manufacturing precision
If the effective cut point is lowered to increase kerosene yield, then the freezing point specification for Jet A-1 fuel is not met, but if the cut point is raised to improve freezing point, then kerosene yield decreases
Solution Approach 1:
The patent optimizes the effective cut point parameter at 315-330°C in the separation step, combined with optimized hydroprocessing conditions (temperature, pressure, catalyst composition). This parameter optimization allows the kerosene fraction to meet the freezing point specification of below -47°C while achieving high yield above 70%, resolving the trade-off between precision and productivity.
Solution Approach 2:
The patent applies local quality improvement by enhancing the molecular structure of specific components within the kerosene fraction through targeted hydroisomerization and hydrocracking. This creates local molecular modifications that improve cold flow properties (freezing point) without requiring a broader change in the separation cut point, thereby maintaining high yield.
3Manufacturing precision
If conventional catalysts with lower SiO2/Al2O3 ratio are used, then the hydroprocessing activity is higher, but the selectivity for premium kerosene with low aromatics content is reduced
Solution Approach 1:
The patent changes the catalyst composition parameter by using molecular sieves with SiO2/Al2O3 ratios of at least 25 (preferably 30-50). This compositional parameter change provides optimal balance between hydroprocessing activity and selectivity, achieving both high conversion and premium kerosene quality with low aromatics content meeting Jet A-1 specifications.
Solution Approach 2:
The patent employs composite catalyst materials combining molecular sieves (with specific SiO2/Al2O3 ratios) and Group VIII metals. This composite structure integrates the shape-selective properties of molecular sieves for aromatics reduction with the hydrogenation activity of Group VIII metals, achieving both high activity and premium product quality simultaneously.
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
Achieves a kerosene yield of over 70% with premium quality, meeting Jet A-1 specifications for freezing point and aromatics content, without additional catalytic dewaxing or oligomerization, and optimizing the effective cut point for improved yield and quality.
Implementation Method 1
step d) is carried out by contacting the C5+ fraction with a first catalyst, wherein the first catalyst comprises a molecular sieve with a pore size between 5 and 7 angstrom and a SiO2/AlO3 ratio of at least 25 and a group VIII metal
Implementation Method 2
both catalysts have hydrocracking and hydroisomerising activity
Implementation Method 3
the second catalyst is more active in hydroisomerisation and less active in hydrocracking compared to the first catalyst
Implementation Method 4
separating the mixture as obtained in step (d) thereby at least obtaining the kerosene fraction and the heavier fraction
Data Source
AI summary
The present invention provides a process to prepare kerosene, the process at least comprising the steps of: (a) providing a syngas stream comprising hydrogen (H2) and carbon monoxide (CO); (b) subjecting the syngas stream provided in step (a) to a Fischer-Tropsch reaction thereby obtaining a Fischer-Tropsch product comprising at least 50 wt. % of compounds boiling above 370° C.; (c) separating the Fischer-Tropsch product into at least a C1-C4 fraction, H2O and a C5+ fraction; (d) subjecting the C5+ fraction as separated in step (c) to hydroprocessing thereby obtaining a mixture comprising at least a kerosene fraction and a heavier fraction; (e) separating the mixture as obtained in step (d) thereby at least obtaining the kerosene fraction and the heavier fraction; (f) recycling at least a part of the heavier fraction as obtained in step (e) to the hydroprocessing of step (d).