Two-Stage Hydrocracking for C2 and C3 Yield
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Solution Overview
Problem
Existing processes for converting naphtha to LPG suffer from unbalanced C3/C4 ratios and excessive methane production, failing to effectively produce C2 and C3 hydrocarbons with high yield and control over C4 derivatives, which are crucial for petrochemical demand.
Innovation Solution
A two-stage hydrocracking process is employed, where a mixed hydrocarbon stream undergoes mild first hydrocracking followed by severe C4 hydrocracking of the light hydrocarbon stream to optimize C4 conversion to C3, while preventing catalyst deactivation and allowing flexible operation conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hydrocracking severity is increased to shift products to ethane and propane, then C2 and C3 production is improved, but methane production becomes excessive
Solution Approach 1:
The hydrocracking process is divided into two distinct stages: a first hydrocracking stage that processes the mixed hydrocarbon feedstream under moderate conditions to produce an initial product slate, and a second C4 hydrocracking stage that specifically targets C4 hydrocarbons under severe conditions to convert them to C3 products. This segmentation allows each stage to be optimized for its specific function, preventing excessive methane formation while maximizing C2 and C3 yields.
Solution Approach 2:
Different hydrocarbon components are subjected to different cracking severities appropriate to their molecular size and structure. C4 hydrocarbons undergo severe cracking to produce C3, while C2 and C3 hydrocarbons are protected from excessive cracking that would produce methane. This local quality approach ensures each component is processed under optimal conditions for the desired product distribution.
2Productivity
If single-stage hydrocracking is used to maximize ethane production, then C2 production is improved, but C3/C4 ratio becomes unbalanced and methane production increases
Solution Approach 1:
The process separates C4 hydrocarbon conversion from general hydrocracking by implementing a dedicated second stage that processes only C4 hydrocarbons. This segmentation allows the first stage to produce a balanced product slate including ethane, while the second stage specifically adjusts the C3/C4 ratio by converting excess C4 to C3, achieving both goals simultaneously.
Solution Approach 2:
The first hydrocracking stage performs preliminary conversion of the mixed hydrocarbon feedstream to establish a baseline product distribution. The second C4 hydrocracking stage then performs a preliminary adjustment by specifically converting C4 hydrocarbons to C3, ensuring the final product meets the desired C3/C4 ratio before downstream processing.
3Productivity
If severe hydrocracking is applied to maximize C2 production, then ethane yield is improved, but catalyst deactivation occurs faster
Solution Approach 1:
The process segments catalyst usage into two stages: the first hydrocracking catalyst operates under moderate conditions with lower deactivation rates, while a separate second C4 hydrocracking catalyst handles the severe cracking of C4 hydrocarbons. This segmentation prevents the main catalyst from rapid deactivation while still achieving high ethane yields through the coordinated action of both catalysts.
Solution Approach 2:
Different catalysts are selected and positioned to match the specific requirements of each hydrocarbon fraction. The first catalyst is optimized for general hydrocracking under moderate conditions, while the second catalyst is specifically designed for severe C4 hydrocracking. This local quality matching extends overall catalyst lifetime while maintaining high 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 approach results in high yields of C2 and C3 hydrocarbons with controlled C4 production, maintaining catalyst longevity and optimizing the C3/C4 ratio, thus addressing the imbalance and methane production issues in existing technologies.
Implementation Method 1
a first hydrocracking unit (101) arranged for performing first hydrocracking of a mixed hydrocarbon feed stream (105) in the presence of a first hydrocracking catalyst
Implementation Method 2
a C4 hydrocracking unit (115) arranged for performing C4 hydrocracking of the light hydrocarbon stream (107) optimized for converting C4 hydrocarbons into C3 hydrocarbons in the presence of a C4 hydrocracking catalyst
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a process for producing C2 and C3 hydrocarbons, comprising a) subjecting a mixed hydrocarbon feedstream to first hydrocracking in the presence of a first hydrocracking catalyst to produce a first hydrocracking product stream; b) separating the first hydrocracking product stream to provide a light hydrocarbon stream comprising C4- hydrocarbons and c) subjecting the light hydrocarbon stream to C4 hydrocracking in the presence of a C4 hydrocracking catalyst to obtain a C4 hydrocracking product stream comprising C2 and C3 hydrocarbons.