Two-Stage Naphtha Hydrodesulfurization with H2S Removal
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Solution Overview
Problem
Conventional hydrodesulfurization processes for naphtha streams struggle to reduce sulfur content while minimizing olefin hydrogenation, leading to a decrease in the octane rating of gasoline, and existing methods either leave residual sulfur or require high temperatures that hinder selectivity.
Innovation Solution
A two-stage catalytic hydrodesulfurization process where a naphtha charge contacts a flow of hydrogen and at least one added non-reactive compound, with H2S removal between stages, to selectively reduce sulfur content while preserving olefins, using catalysts with optimized metal compositions and conditions to control reaction temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional hydrodesulfurization processes are used to reduce sulfur content, then sulfur content is reduced, but olefin hydrogenation occurs resulting in decreased octane rating
Solution Approach 1:
The hydrodesulfurization process is divided into two distinct reaction stages. The first stage uses a catalyst with high hydrodesulfurization activity to remove the majority of sulfur compounds. The second stage uses a catalyst with high selectivity to remove residual sulfur while minimizing olefin hydrogenation. This segmentation allows each stage to be optimized for its specific function, achieving overall sulfur reduction while preserving olefins.
Solution Approach 2:
Different catalyst compositions are used in different reaction stages to create local optimization. The first stage catalyst (e.g., CoMo or NiMo on alumina) is optimized for high sulfur conversion activity. The second stage catalyst (e.g., NiMo on silica-alumina or zeolite) is optimized for high selectivity with lower hydrogenation activity. This local quality differentiation resolves the contradiction between sulfur removal efficiency and olefin preservation.
2Productivity
If high temperatures are used to enhance hydrodesulfurization, then sulfur conversion is improved, but olefin hydrogenation is increased reducing selectivity
Solution Approach 1:
The temperature profile is segmented across two stages. The first stage operates at higher temperatures (300-350°C) to maximize sulfur conversion kinetics. The second stage operates at lower temperatures (250-300°C) to enhance selectivity and minimize olefin hydrogenation. This temporal and spatial segmentation of temperature conditions allows high productivity in the first stage and high precision in the second stage.
Solution Approach 2:
The process utilizes parameter changes between stages, specifically temperature and catalyst composition. By changing the temperature parameter from high in stage one to lower in stage two, and changing the catalyst composition to match each temperature regime, the process achieves both high sulfur conversion and high olefin selectivity in the overall process.
3Device complexity
If single-stage hydrodesulfurization is used, then process complexity is reduced, but sufficient sulfur removal while preserving olefins cannot be achieved
Solution Approach 1:
The process is segmented into two reaction stages with different catalysts and operating conditions. While this increases process complexity compared to a single stage, it enables the achievement of superior sulfur removal (>90%) with minimal olefin hydrogenation (<5-10%), which cannot be achieved in a single stage. The segmentation is necessary to resolve the performance contradiction.
Solution Approach 2:
The process extracts and removes H2S between the two reaction stages. This intermediate removal prevents H2S from participating in unwanted side reactions in the second stage and allows the second catalyst to operate under optimized conditions for selective sulfur removal. This extraction step is crucial for achieving high selectivity in the overall 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 process achieves a sulfur reduction of over 90% with minimal olefin hydrogenation, maintaining the octane rating and achieving higher selectivity compared to single-stage processes by controlling H2S recombination and using non-reactive compounds to inhibit olefin hydrogenation.
Implementation Method 1
a) In a first reaction stage, under first hydrodesulfurization conditions and using a first catalyst, a charge of naphtha is contacted with a flow of hydrogen and at least one added non-reactive compound
Implementation Method 2
contacting a naphtha charge with a flow of hydrogen and at least one added non-reactive compound wherein the H2 molar fraction ranges from 0.2 to 1
Implementation Method 3
c) The H2S is removed from the effluent from the first reaction stage
Implementation Method 4
using a catalyst based on transition metal-oxides from Group VI B, preferably MoO3, and transition metal oxides from Group VIII, preferably CoO, in the form of sulfides, supported on an appropriate porous solid
Data Source
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AI summary
A process for the selective hydrodesulfurization of a naphtha containing olefins and organosulfur compounds is disclosed, which minimizes the hydrogenation of the olefins and results in a product with a low sulfur content. The process involves a two-stage hydrodesulfurization with H2S removed from the first stage effluent. A flow of hydrogen and at least one added non-reactive compound is fed into the first stage, wherein the H2 molar fraction ranges from 0.2 to 1.0, and with H2S at the reactor intake limited to a maximum of 0.1 % by volume. The second stage involves a feedstream of hydrogen and at least one added non-reactive compound, wherein the H2 molar fraction ranges from 0.2 to 0.7 and with H2S at the reactor intake limited to a maximum of 0.05 % by volume.