Successive Hydrocracking Process for C2-C3 Yield Optimization
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Solution Overview
Problem
Existing processes for converting middle distillates to LPG suffer from imbalanced C3/C4 ratios and excessive methane production, which are not optimal for petrochemical demand or fuel applications, and lack control over C4 production and composition.
Innovation Solution
A successive hydrocracking process is employed, where the product streams from each hydrocracking step are separated and recycled back to subsequent steps with increasing severity, optimizing conditions to maximize C2-C3 hydrocarbon yield while minimizing C1 production, and including specific separations to control C4 hydrocracking and produce BTX products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hydrocracking severity is increased to shift products to ethane and propane, then C2-C3 hydrocarbon yield is improved, but methane production becomes excessive
Solution Approach 1:
The hydrocracking process is divided into multiple stages with increasing severity. The first stage operates at moderate conditions to convert heavy hydrocarbons to C5-C12 fractions, while subsequent stages progressively increase severity to convert lighter fractions to C2-C3 products. This segmentation allows optimization of each stage to minimize methane formation while maximizing desired product yield.
Solution Approach 2:
Before the severe hydrocracking stage that produces C2-C3 hydrocarbons, a preliminary hydrocracking stage is performed to convert heavy hydrocarbons to intermediate C5-C12 fractions. This preliminary action prepares the feedstock for the subsequent severe cracking stage, reducing the formation of excessive methane by pre-processing the heavy fractions.
2Productivity
If single stage hydrocracking is used to maximize ethane production, then C2 production is improved, but C3/C4 ratio becomes unbalanced and recycle stream size increases
Solution Approach 1:
The hydrocracking process is segmented into multiple stages, each optimized for different product distributions. The first stage produces a balanced mix including C3-C4 fractions, while subsequent stages progressively increase ethane production. This segmentation allows control over the C3/C4 ratio while maximizing overall C2 production.
Solution Approach 2:
Different stages of the hydrocracking process have different local qualities optimized for specific objectives. The first stage has conditions optimized for converting heavy hydrocarbons with moderate severity, while subsequent stages have increasingly severe conditions optimized for maximizing lighter hydrocarbon production. This local optimization at each stage achieves both balanced C3/C4 ratios and high C2 production.
3Productivity
If high severity hydrocracking is applied to limit recycle stream size, then processing efficiency is improved, but methane production becomes excessive
Solution Approach 1:
The hydrocracking process is divided into stages with progressively increasing severity. The first stage operates at moderate conditions to convert heavy hydrocarbons to C5-C12 fractions, reducing the amount of heavy material requiring severe cracking. Subsequent stages then apply higher severity to the reduced feedstock, improving processing efficiency while minimizing methane formation that would result from applying high severity to the full feedstream.
4Productivity
If existing processes focus on maximizing C2 production, then ethane yield is improved, but C4 production control and composition control are lacking
Solution Approach 1:
The multi-stage hydrocracking process provides control over C4 production at each stage. The first stage operates at conditions that limit excessive C4 formation, while subsequent stages are optimized for C2 production. This segmentation allows independent control of C4 production levels and composition (normal versus iso-butanes) while maintaining high ethane yield.
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 a high yield of C2-C3 hydrocarbons with controlled C4 production and composition, reducing methane production and improving the balance of C3/C4 ratios, thereby enhancing the production of desired petrochemicals and fuels.
Implementation Method 1
converting middle distillates to LPG by successive hydrocracking
Implementation Method 2
converting naphtha or middle distillates or like material to LPG by cracking, such as hydrocracking
Data Source
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AI summary
The invention relates to a process for producing C2 and C3 hydrocarbons, comprising a) subjecting a mixed hydrocarbon stream comprising a middle distillate to first hydrocracking in the presence of a first hydrocracking catalyst to produce a first hydrocracking product stream, b) subjecting a second hydrocracking feed stream to second hydrocracking in the presence of a second hydrocracking catalyst to produce a second hydrocracking product stream, wherein the second hydrocracking is more severe than the first hydrocracking and c) subjecting a C4 hydrocracking feed stream to C4 hydrocracking optimized for converting C4 hydrocarbons into C3 hydrocarbons in the presence of a C4 hydrocracking catalyst to obtain a C4 hydrocracking product stream, wherein the C4 hydrocracking is more severe than the second hydrocracking, wherein the first hydrocracking product stream, the second hydrocracking product stream and the C4 hydrocracking product stream are fed to a separation system which provides - the second hydrocracking feed stream separated from the first hydrocracking product stream, - the C4 hydrocracking feed stream separated from the second hydrocracking product stream, - a first recycle stream to be recycled back to the first hydrocracking, - a second recycle stream to be recycled back to the second hydrocracking, - a third recycle stream to be recycled back to the C4 hydrocracking, - a hydrogen recycle stream of H2 or H2 and C1 to be recycled back to the first hydrocracking, the second hydrocracking and/or the C4 hydrocracking and - a C2 and C3 product stream of C3- hydrocarbons, wherein the second hydrocracking feed stream is a stream of C12- hydrocarbons excluding C10-C12 hydrocarbons having di-ring structures, wherein the first recycle stream is a stream of C13+ and C10-C12 hydrocarbons having di-ring structures, wherein the C4 hydrocracking feed stream is a stream of C5-, C4- or iC4-, wherein the second recycle stream is a stream of C6+, C5+ or nC4+ 30 wherein the third recycle stream is a stream of nC4+ or C4+.