Hydrodesulfurization Reactor for FCC Gasoline
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Solution Overview
Problem
Current hydrodesulfurization processes for petroleum distillate streams face challenges in minimizing the formation of recombinant mercaptans, which leads to reduced octane ratings and increased sulfur content in gasoline products, necessitating the development of more effective methods to control mercaptan formation during the desulfurization of FCC gasoline.
Innovation Solution
A process involving a catalytic distillation reactor system followed by a high temperature, low pressure hydrodesulfurization reactor, where the overheads from the catalytic distillation reactor are heated and further treated to reduce mercaptan content, thereby minimizing recombinant mercaptan formation and achieving a hydrocarbon stream with reduced sulfur content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If standard hydrodesulfurization conditions (600-780°F, 600-3000 psig) are used to remove sulfur from FCC gasoline, then sulfur content is reduced, but recombinant mercaptans form and octane rating decreases
Solution Approach 1:
The patent changes the operating parameters from standard HDS conditions (600-780°F, 600-3000 psig) to elevated temperature (800-950°F) and reduced pressure (100-500 psig). This parameter shift suppresses the equilibrium of recombinant mercaptan formation while maintaining effective sulfur removal through the modified catalyst system.
Solution Approach 2:
The patent employs a composite catalyst system comprising a sulfided cobalt-molybdenum catalyst combined with a zeolite component (such as USY, beta, or ZSM-5). This composite structure provides both hydrodesulfurization activity and shape-selective properties that reduce mercaptan formation, resolving the contradiction between sulfur removal and mercaptan suppression.
2Productivity
If high pressure and temperature are applied to remove sulfur compounds, then desulfurization efficiency increases, but olefin saturation occurs and octane rating is reduced
Solution Approach 1:
The patent inverts the conventional pressure-temperature relationship by operating at elevated temperatures (800-950°F) but reduced pressures (100-500 psig). This parameter change favors desulfurization while minimizing olefin saturation, as the lower pressure reduces hydrogen solubility and subsequent hydrogenation of olefins.
Solution Approach 2:
The composite catalyst provides different functional zones: the sulfided Co-Mo component performs hydrodesulfurization while the zeolite component provides shape-selective catalysis that promotes sulfur removal pathways sparing olefins. This local functional differentiation enables selective desulfurization without extensive olefin saturation.
3Quantity of substance
If conventional HDS reactors are used, then sulfur removal is achieved, but the process complexity increases due to multiple stages needed to control mercaptans
Solution Approach 1:
The patent merges hydrodesulfurization and mercaptan control functions into a single reactor by using a composite catalyst system. The sulfided Co-Mo catalyst handles sulfur removal while the zeolite component simultaneously suppresses mercaptan formation, eliminating the need for separate treatment stages and reducing process complexity.
Solution Approach 2:
The composite catalyst performs multiple functions within a single reactor: hydrodesulfurization of various sulfur compounds, suppression of recombinant mercaptan formation, and preservation of olefin content. This multi-functionality simplifies the overall process design compared to conventional multi-stage approaches.
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 the sulfur content in hydrocarbon streams, preserves olefin content, and minimizes the formation of recombinant mercaptans, resulting in a higher value end product with lower sulfur levels, thus addressing the limitations of existing hydrodesulfurization methods.
Implementation Method 1
contacting the hydrocarbons and mercaptans in the presence of the hydrodesulfurization catalyst at a temperature in the range of 500 to 700° F. and a pressure of less than 320 psi
Implementation Method 2
the overheads from the catalytic distillation reactor are heated and further treated
Data Source
AI summary
A process for reducing the sulfur content of a hydrocarbon stream, including: feeding hydrogen and a hydrocarbon stream including sulfur compounds to a catalytic distillation reactor having one or more hydrodesulfurization reaction zones; concurrently in the catalytic distillation reactor: fractionating the hydrocarbon stream into a heavy fraction and a light fraction; contacting hydrogen and the light fraction to form H2S and a light fraction of reduced sulfur content; recovering the light fraction, H2S, and hydrogen as an overheads; recovering the heavy fraction; heating the overheads to a temperature from 500 to 700° F.; feeding the heated overheads and hydrogen to a high temperature low pressure reactor to form H2S and a reactor effluent of reduced mercaptan content; separating the reactor effluent, H2S, and unreacted hydrogen to form a light hydrocarbon fraction and a fraction including H2S and hydrogen; recycling a portion of the light hydrocarbon fraction to the catalytic distillation reactor.