Selective Hydrodesulfurization with Interstage Stripping
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Solution Overview
Problem
Current hydrodesulfurization processes for olefinic naphtha streams face challenges in reducing sulfur content while minimizing olefin saturation and mercaptan formation, leading to increased operational complexity and costs, as they often result in the undesirable hydrogenation of olefins and formation of mercaptan sulfur compounds.
Innovation Solution
A multi-stage process involving hydrodesulfurization followed by interstage stripping and mercaptan decomposition, using specific catalysts and conditions to convert sulfur to hydrogen sulfide and decompose mercaptans, thereby reducing sulfur content and mercaptan formation while retaining olefins, includes hydrodesulfurization at 450°F to 800°F with hydrogen-containing treat gas, interstage stripping, and mercaptan decomposition at 500°F to 900°F with a mercaptan decomposition catalyst.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional hydrodesulfurization is applied to olefinic naphtha, then sulfur content is reduced, but olefin saturation increases and octane value decreases
Solution Approach 1:
The process is divided into multiple stages: first stage hydrodesulfurization, interstage stripping to remove H2S, and second stage hydrodesulfurization. This segmentation allows sulfur removal while preventing olefin saturation by eliminating H2S between stages, thereby maintaining octane value.
Solution Approach 2:
Interstage stripping is performed between the two hydrodesulfurization stages to remove H2S before it can react with olefins. This preliminary action prevents mercaptan formation and olefin saturation that would otherwise occur in a single-stage process.
2Productivity
If hydrodesulfurization is operated at greater severities to meet lower sulfur specifications, then sulfur removal efficiency increases, but mercaptan formation increases
Solution Approach 1:
The process converts the harmful effect of H2S (which causes mercaptan formation) into a benefit by using interstage stripping to remove H2S. The stripped H2S is then used as fuel gas, transforming a harmful byproduct into an energy source while preventing mercaptan contamination.
Solution Approach 2:
Interstage stripping removes H2S before the second hydrodesulfurization stage, preventing H2S from reacting with olefins to form mercaptans. This preliminary removal of H2S allows the process to operate at high severity without increasing mercaptan content.
3Stability of the object's composition
If selective hydrodesulfurization is used to retain olefins, then octane value is maintained, but H2S reacts with olefins to form mercaptans
Solution Approach 1:
The process segments the hydrodesulfurization into two stages with interstage stripping in between. This segmentation prevents H2S from being present during the entire process, eliminating the opportunity for H2S to react with retained olefins and form mercaptans.
Solution Approach 2:
Interstage stripping performs preliminary removal of H2S after the first hydrodesulfurization stage, preventing H2S from reacting with olefins before the second desulfurization stage. This timing prevents mercaptan formation while maintaining selective olefin retention.
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 effectively reduces sulfur and mercaptan content in olefinic naphtha, retains higher olefin concentrations, and lowers operational complexity and capital expenditures by minimizing olefin saturation and mercaptan formation, achieving lower mercaptan sulfur content and higher octane values compared to conventional methods.
Implementation Method 1
hydrodesulfurizing said olefinic naphtha feedstream in the presence of a hydrogen-containing treat gas and a hydrodesulfurization catalyst, at hydrodesulfurization reaction stage conditions... to convert a portion of the elemental and organically-bound sulfur in said olefinic naphtha feedstream to hydrogen sulfide
Implementation Method 2
conducting said hydrodesulfurization reaction effluent stream to an interstage stripping zone... wherein the hydrodesulfurization reaction effluent stream is contacted with a hydrogen-containing stripping gas and is separated into... an interstage stripper lower boiling stream which contains substantially all of the H2S
Implementation Method 3
heating said mercaptan decomposition feedstream prior to conducting it to a mercaptan decomposition reaction stage that contains a mercaptan decomposition catalyst... thereby decomposing at least a portion of the mercaptan sulfur to produce a mercaptan decomposition reactor product stream
Data Source
AI summary
A process for the selective hydrodesulfurization of olefinic naphtha streams containing a substantial amount of organically-bound sulfur and olefins. The olefinic naphtha stream is selectively desulfurized in a hydrodesulfurization reaction stage. The hydrodesulfurized effluent stream is separated into a light and heavy liquid fraction and the heavier fraction is further processed in a mercaptan destruction reaction stage to reduce the content of mercaptan sulfur in the final product.