Two-Stage Hydrodesulfurization for Low Sulfur Gasoline
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Solution Overview
Problem
Current processes for producing gasoline with low sulfur content, particularly from catalytic cracking, face challenges in reducing mercaptans while maintaining octane number, as they often result in high hydrogen consumption and olefin hydrogenation, leading to inefficiencies and difficulties in achieving stringent mercaptan specifications.
Innovation Solution
A process involving a sequence of two reactors with a higher hydrogen-to-hydrocarbon (H2/HC) ratio in the finishing stage, where fresh or recycled hydrogen is injected, optimizing the conversion of recombinant mercaptans by reducing partial pressures of H2S and olefins, while maintaining high temperatures to promote thermodynamic removal of mercaptans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional catalytic hydrodesulfurization processes are used to reduce sulfur content, then sulfur content is decreased, but hydrogen consumption increases and octane number is lost due to olefin hydrogenation
Solution Approach 1:
The invention changes the operating parameters by using a two-stage process with different H2/HC ratios in each stage. The first stage uses a lower H2/HC ratio (100-300 Sm3/m3) to remove most sulfur compounds, while the second stage uses a higher H2/HC ratio (300-600 Sm3/m3) to specifically address recombinant mercaptans. This parameter optimization reduces overall hydrogen consumption while achieving the required sulfur reduction to below 10 ppm.
Solution Approach 2:
The invention segments the hydrodesulfurization process into two distinct stages with different operating conditions and catalysts. The first stage uses a CoMo or NiMo catalyst at lower H2/HC ratio for bulk sulfur removal, while the second stage uses a NiMo catalyst at higher H2/HC ratio for mercaptan removal. This segmentation allows each stage to be optimized for its specific function, reducing total hydrogen consumption compared to a single-stage process.
2Manufacturing precision
If conventional hydrodesulfurization processes are used to reduce sulfur content, then sulfur content is decreased, but octane number is lost due to olefin hydrogenation
Solution Approach 1:
The invention optimizes the H2/HC ratio parameter in each stage to minimize olefin hydrogenation. The first stage operates at H2/HC ratio of 100-300 Sm3/m3 which is sufficient for sulfur removal but limits excessive olefin saturation. The second stage operates at higher H2/HC ratio of 300-600 Sm3/m3 but for a shorter contact time, specifically targeting recombinant mercaptans without causing significant octane loss. This results in total octane loss of less than 5 points.
Solution Approach 2:
The two-stage process segments the sulfur removal function from the mercaptan removal function. The first stage removes the majority of sulfur compounds including most mercaptans through hydrodesulfurization. The second stage specifically addresses the recombinant mercaptans formed in the first stage. This segmentation prevents the need for excessive olefin hydrogenation that would occur in a single-stage process aiming for both sulfur and mercaptan removal simultaneously.
3Manufacturing precision
If H2S removal is implemented between two reactor stages, then mercaptan conversion is improved, but process complexity and equipment requirements increase
Solution Approach 1:
The invention maintains continuous flow of the hydrocarbon stream through both reactor stages without interrupting for H2S removal. The H2S generated in the first stage remains in the stream and actually contributes to the chemistry in the second stage by serving as a reactant for mercaptan formation and subsequent removal. This continuous operation eliminates the need for intermediate separation equipment and maintains process simplicity while achieving superior mercaptan removal.
4Manufacturing precision
If high H2/HC ratio is used throughout the process, then mercaptan conversion is improved, but hydrogen consumption increases significantly
Solution Approach 1:
The invention applies different H2/HC ratio parameters in each stage based on the specific requirements. The first stage uses a moderate H2/HC ratio of 100-300 Sm3/m3 which is sufficient for bulk sulfur removal without requiring excessive hydrogen. The second stage uses a higher H2/HC ratio of 300-600 Sm3/m3 specifically where it is most effective for mercaptan removal. This staged parameter application achieves superior mercaptan conversion while minimizing total hydrogen consumption compared to using high H2/HC ratio throughout the entire process.
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 effectively reduces mercaptan content in gasoline to below 10 ppm while minimizing hydrogen consumption and olefin hydrogenation, thus preserving the octane number and simplifying integration with existing refinery units.
Implementation Method 1
the gasoline, hydrogen and a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a metal from group VIb and a metal from group VIII are brought into contact in at least one reactor at a temperature of between 210 and 320°C.
Implementation Method 2
a hydrodesulfurization catalyst comprising an oxide support and an active phase consisting of at least one metal from group VIII are brought into contact in at least one reactor
Implementation Method 3
Their formation or their decomposition obeys the thermodynamic equilibrium of the reaction between monoolefins and hydrogen sulfide to form recombinant mercaptans.
Data Source
AI summary
The present application relates to a method for treating a petrol containing sulphur compounds, olefins and diolefins, the method comprising the following steps: a) a step of hydrodesulphurisation in the presence of a catalyst comprising an oxide support and an active phase comprising a group VIB metal and a group VIII metal from, b) a step of hydrodesulphurising at least one portion of the effluent from step a) at a higher hydrogen flow rate/feed ratio and a temperature higher than those of step a) without removing the H2S formed in the presence of a catalyst comprising an oxide support and an active phase consisting of at least one group VIII metal, c) a step of separating the H2S formed in the effluent from step b).