Two-Stage Hydrocracking for Heavy Naphtha Conversion and Ethylene Yield
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Solution Overview
Problem
Existing hydrocracking processes yield low ethylene content and low-quality chemical raw materials due to inefficient conversion of hydrocarbon feedstocks, particularly heavy naphtha, which contains high alkane content and is difficult to dehydrogenate.
Innovation Solution
A two-stage hydrocracking process with selective cracking of n-alkanes and polycyclic hydrocarbons, using molecular sieves and hydrogenation catalysts to enrich low-carbon olefins and monocyclic cyclic hydrocarbons, followed by fractionation to separate and optimize feedstocks for ethylene and catalytic reforming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If heavy naphtha is used as feedstock for catalytic reformer, then feedstock adaptability is improved, but the alkane content is high and difficult to dehydrogenate, resulting in low aromatic yield
Solution Approach 1:
The process segments the hydrocracking into two distinct stages: first hydrocracking for selective n-alkane cracking, and second hydrocracking for more severe cracking of remaining heavy components. This segmentation allows each stage to be optimized for specific feedstock components, resolving the contradiction between handling high-alkane feedstocks and achieving high aromatic yield.
Solution Approach 2:
The process changes operating parameters between the two hydrocracking stages, with the first stage using milder conditions (lower temperature, lower pressure) for selective n-alkane conversion, and the second stage using more severe conditions for complete heavy component cracking. This parameter optimization enables effective processing of high-alkane feedstocks while maximizing aromatic production.
2Device complexity
If conventional single-stage hydrocracking is used, then process complexity is reduced, but the yield of chemical raw materials and quality of products are insufficient
Solution Approach 1:
The invention divides the hydrocracking process into two separate reaction zones with different catalysts and operating conditions, enabling selective conversion of different feedstock components. This segmentation achieves high yield of chemical raw materials (C2-C4 olefins) and quality reforming feedstocks, overcoming the limitations of single-stage hydrocracking despite increased process complexity.
Solution Approach 2:
The process employs composite catalytic systems with different functions in each stage: the first hydrocracking catalyst optimized for n-alkane cracking, and the second hydrocracking catalyst for severe cracking of heavy components. This composite approach maximizes product yield and quality while managing process complexity through functional specialization.
3Productivity
If severe hydrocracking conditions are applied to convert heavy naphtha, then conversion efficiency is improved, but the selectivity for n-alkane cracking decreases and excessive gasification occurs
Solution Approach 1:
The first hydrocracking stage performs preliminary selective cracking of n-alkanes under milder conditions, converting the majority of n-alkane content before the second stage. This preliminary action prevents excessive gasification in the second stage and maintains high selectivity for desired products while achieving overall high conversion efficiency.
Solution Approach 2:
The process optimizes parameters for each stage: the first stage uses lower temperature and pressure for selective n-alkane cracking, while the second stage uses higher temperature and pressure for complete heavy component conversion. This staged parameter optimization achieves both high conversion efficiency and maintained selectivity.
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
Significantly improves the yield and quality of low-carbon olefins and reforming raw materials by enhancing the conversion of hydrocarbon feedstocks, allowing for efficient production of ethylene and high-quality jet fuel, diesel, and lubricating oil base materials.
Implementation Method 1
subjecting a hydrocarbon oil raw material to a first hydrocracking reaction in the presence of hydrogen, so as to obtain a first hydrocracking reaction product, wherein the first hydrocracking catalyst includes a molecular sieve capable of selectively cracking n-alkane
Implementation Method 2
subjecting a hydrocarbon oil raw material to a first hydrocracking reaction in the presence of hydrogen
Implementation Method 3
subjecting the second hydrocracking reaction product to fractionation, so as to obtain a gas fraction, light naphtha, heavy naphtha, and tail oil
Data Source
Figure 1~2
AI summary
The present invention belongs to the technical field of hydrocarbon oil hydrogenation. Disclosed are a hydrogenation method and a hydrogenation system for a hydrocarbon oil. The method comprises the following steps: (1) subjecting a hydrocarbon oil raw material to a first hydrocracking reaction in the presence of hydrogen, so as to obtain a first hydrocracking reaction product, wherein in the first hydrocracking reaction product, the mass content of a C7+ n-alkane is 5% or below; (2) subjecting the first hydrocracking reaction product to a second hydrocracking reaction in the presence of hydrogen, so as to obtain a second hydrocracking reaction product; and (3) separating and fractionating the second hydrocracking reaction product. By taking a hydrocarbon oil as a raw material, the method can greatly improve the yield and quality of chemical raw materials (including a low-carbon olefin raw material and a reforming raw material).