Two-Stage Hydrocracking with Aromatic Saturation to Prevent HPNA Fouling
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Solution Overview
Problem
Current two-stage hydrocracking processes fail to achieve full conversion to materials boiling below the diesel cut point due to the accumulation of heavy polynuclear aromatics (HPNA's), which cause fouling and coking issues, necessitating the removal of unconverted oil (UCO) and requiring inefficient management strategies.
Innovation Solution
The process involves saturating aromatics in the first stage hydrocracking unit using hydrotreating catalysts to prevent HPNA formation, allowing for their hydrocracking in the second stage, thereby eliminating the need for UCO purge and enhancing diesel yield selectivity by integrating catalytic aromatics saturation with hydrocracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two-stage hydrocracking is used to manage HPNA rejection, then HPNA accumulation is controlled, but full conversion to materials boiling below diesel cut point cannot be achieved
Solution Approach 1:
The patent applies preliminary action by saturating aromatics in the first stage hydrocracking unit before the second stage processing. This pre-saturation prevents HPNA formation that would otherwise require purge operations, enabling full conversion without unconverted oil removal.
Solution Approach 2:
The patent changes the chemical state of aromatic compounds by saturating them in the first stage. This parameter change (from unsaturated to saturated aromatics) prevents HPNA accumulation and enables complete conversion in the second stage, eliminating the need for purge operations.
2Device complexity
If HPNA accumulation is allowed in recycle oil, then process complexity is reduced, but equipment fouling and coking occur
Solution Approach 1:
The patent performs preliminary saturation of aromatics in the first stage unit, which prevents HPNA formation before the oil enters the recycle stream. This preliminary action eliminates the harmful effect of equipment fouling while maintaining a relatively simple two-stage process structure.
Solution Approach 2:
The patent converts the potentially harmful aromatic compounds into beneficial saturated compounds in the first stage. This transformation prevents HPNA formation and equipment fouling while the saturated products become suitable feed for the second stage hydrocracking, turning a harmful substance into a useful intermediate.
3Reliability
If aromatic saturation is implemented in the first stage, then HPNA formation is prevented, but process complexity increases
Solution Approach 1:
The patent merges the aromatic saturation function with the first stage hydrocracking unit. By combining these functions in a single integrated unit rather than adding a separate saturation unit, the process achieves improved operational stability without proportionally increasing overall process complexity.
Solution Approach 2:
The first stage hydrocracking unit is designed to perform multiple functions: both hydrocracking and aromatic saturation. This multi-functionality reduces the need for additional dedicated equipment, achieving reliable HPNA prevention while minimizing the increase in process complexity.
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 achieves full conversion of hydrocarbon feed to products boiling below the diesel cut point, reduces equipment fouling, and increases cycle length by minimizing HPNA presence, resulting in higher yield and improved product quality with lower sulfur and nitrogen content.
Implementation Method 1
hydrotreating catalysts to prevent HPNA formation
Implementation Method 2
hydrotreating catalysts to prevent HPNA formation
Implementation Method 3
hydrocracking of the second hydrocracking feed stream over a second hydrocracking catalyst
Implementation Method 4
hydrocracking of the second hydrocracking feed stream over a second hydrocracking catalyst
Data Source
AI summary
A process and apparatus for two stage hydrocracking saturates aromatics from the first stage hydrocracking unit to prevent production of HPNA's. The saturated HPNA's can be hydrocracked in the second stage to minimize or eliminate purged unconverted oil to approach or obtain maximum conversion. In an aspect, the second stage hydrocracking reactor and hydrotreating reactor may be located in the same vessel.