Gasoline Hydrodesulfurization Sequence for Low Mercaptan and Octane Retention
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Solution Overview
Problem
Existing methods for producing low-sulfur gasoline face challenges in reducing mercaptan content while maintaining octane rating and minimizing hydrogen consumption, particularly in catalytic cracking processes where recombination mercaptans are difficult to remove without causing gasoline cracking or catalyst coking.
Innovation Solution
A process involving a sequence of two hydrodesulfurization reactors with specific catalysts and conditions, followed by H₂S separation, allows for the selective conversion and removal of recombination mercaptans under mild conditions, using catalysts with Group VIB and Group VIII metals supported on alumina, with controlled temperature and hydrogen flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional catalytic hydrodesulfurization processes are used to desulfurize high-sulfur base gasolines, then sulfur content is reduced, but monoolefins are hydrogenated resulting in significant loss of octane rating and high hydrogen consumption
Solution Approach 1:
The invention changes the operating parameters by conducting hydrodesulfurization at lower temperatures (200-350°C) and using specific catalyst formulations (CoMo or NiMo on alumina) to achieve selective desulfurization. This parameter optimization allows reducing sulfur content while minimizing unwanted olefin hydrogenation and reducing hydrogen consumption compared to traditional high-temperature processes
Solution Approach 2:
The invention applies local quality by using specific catalyst formulations with particular metal compositions (CoMo or NiMo) supported on alumina with controlled surface area and pore volume. These locally optimized catalyst properties enable selective hydrodesulfurization activity while maintaining olefin stability, addressing the contradiction between sulfur removal and octane preservation
2Quantity of substance
If traditional catalytic hydrodesulfurization processes are used to desulfurize high-sulfur base gasolines, then sulfur content is reduced, but octane rating is significantly lost due to monoolefin hydrogenation
Solution Approach 1:
The invention optimizes process parameters including temperature (200-350°C), pressure (3-10 bar), and space velocity (0.5-5 h⁻¹) to achieve selective hydrodesulfurization. These parameter changes ensure that sulfur compounds are converted to H2S and removed while monoolefins remain largely unaffected, preserving octane rating
Solution Approach 2:
The invention uses locally optimized catalyst formulations (CoMo or NiMo on alumina with specific surface area 100-300 m²/g and pore volume 0.3-0.6 cm³/g) that provide high desulfurization activity with low olefin hydrogenation activity, thus maintaining octane stability while reducing sulfur content
3Quantity of substance
If severe conditions are used to remove recombination mercaptans, then mercaptan content is reduced, but gasoline cracking and catalyst coking occur
Solution Approach 1:
The invention changes the operating conditions by conducting the process at moderate temperatures (200-350°C) and pressures (3-10 bar) with controlled space velocity (0.5-5 h⁻¹). These parameter changes create a thermodynamic environment favorable for mercaptan decomposition and H2S removal while avoiding severe conditions that would cause gasoline cracking and catalyst coking
Solution Approach 2:
The invention uses an intermediary approach by introducing a two-stage process with an intermediate storage step. The first stage converts sulfur compounds to H2S, which is then removed in the intermediate step. The second stage completes desulfurization under milder conditions, preventing catalyst deactivation while achieving low mercaptan content
4Quantity of substance
If severe conditions are used to remove recombination mercaptans, then mercaptan content is reduced, but energy costs increase
Solution Approach 1:
The invention optimizes energy parameters by operating at moderate temperatures (200-350°C) and pressures (3-10 bar) with controlled space velocity (0.5-5 h⁻¹). These parameter changes reduce the energy input required compared to severe conditions, while still achieving mercaptan removal through favorable thermodynamic equilibrium and efficient H2S removal in the intermediate storage step
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
The process effectively reduces mercaptan content to below 10 ppm while limiting octane loss and hydrogen consumption, suitable for existing refinery units with improved catalyst life and reduced energy costs.
Implementation Method 1
a) In at least one reactor, 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 contacted at a temperature between 210 and 320°C
Implementation Method 2
The first stage, also called the selective HDS stage, generally aims to achieve deep desulfurization of the gasoline with minimal olefin saturation
Implementation Method 3
c) a separation step of the H2S formed and present in the effluent from step b is carried out
Data Source
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AI summary
The present application relates to a method for treating a gasoline containing sulfur-containing compounds and olefins, comprising the following steps: a) a step of hydrodesulfurization in the presence of a catalyst comprising an oxide support and an active phase comprising a group VIB metal and a group VIII metal, b) a step of hydrodesulfurization at a higher temperature than that of step a) and in the presence of a catalyst comprising an oxide support and an active phase constituted of at least one group VIII metal, c) a step of separating the H2S formed, d) a step of hydrodesulfurization with a low hydrogen/feedstock ratio and in the presence of a hydrodesulfurization catalyst comprising an oxide support and an active phase comprising a group VIB metal and a group VIII metal or an active phase constituted of at least one group VIII metal, e) a step of separating the H2S formed.