Propylene Yield Optimization in Fluid Catalytic Cracking
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Solution Overview
Problem
Current Fluid Catalytic Cracking (FCC) processes face challenges in achieving high propylene yields due to the inability to separate 4- and 5-carbon paraffins from olefins, leading to increased material recycling and higher capital and utility costs.
Innovation Solution
A process configuration that includes a first catalytic reactor, a fractionation zone, a separation unit to selectively separate C4 and C5 olefins from paraffins, and a second catalytic reactor, allowing for the recycling of C4 and C5 olefins to enhance propylene production while maintaining a traditional FCC unit configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If 4- and 5-carbon olefins are recycled back to the FCC unit to increase propylene yield, then propylene production increases, but the amount of material to be recycled increases rapidly due to inability to separate paraffins from olefins
Solution Approach 1:
The patent applies extraction by introducing a polar solvent into the C4-C5 hydrocarbon stream to selectively extract olefins from the mixture. The solvent forms an extract phase enriched in olefins (C4 and C5 olefins) while leaving paraffins in the raffinate phase. This extracted olefin-rich stream is then recycled to the FCC unit, enabling high propylene yield without excessive recycling of inert paraffin material.
2Productivity
If a second reactor optimized to convert olefins to propylene is added, then propylene yield improves, but a separate recovery section is needed increasing device complexity
Solution Approach 1:
The patent merges the fractionation zone functions with the olefin extraction and recycling system. The fractionation zone produces the C4-C5 hydrocarbon stream that feeds directly into the extraction process. This integrated configuration eliminates the need for a completely separate recovery section while maintaining the ability to optimize olefin conversion to propylene through controlled recycling.
3Device complexity
If 4- and 5-carbon paraffins are not separated from olefins, then the process configuration remains simple, but inert paraffin material must be recycled along with olefins reducing efficiency
Solution Approach 1:
The patent introduces a polar solvent as an intermediary substance that facilitates the separation of olefins from paraffins. The solvent temporarily associates with olefins through dipole-induced dipole interactions, enabling selective extraction. After extraction, the solvent is separated from the olefin-rich extract phase, and the olefins are recycled to the FCC unit. This intermediary approach achieves efficient separation without requiring complex direct separation methods.
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 configuration increases propylene yield significantly with reduced capital and utility costs by simplifying the overall process recovery section and providing a feed richer in olefins to the second reactor, achieving propylene yields greater than 20%.
Implementation Method 1
passing an effluent of the first catalytic reactor to a fractionation zone to produce a first fractionation zone stream and a second fractionation zone stream
Implementation Method 2
passing the second fractionation zone stream to a separation unit to produce a first separation unit stream comprising Cx paraffins, and a second separation unit stream comprising Cx olefins
Implementation Method 3
Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material
Data Source
AI summary
The present invention discloses a process optimizing the yield of propylene from a fluid catalytic cracking unit. The method combines a first catalytic reactor, a fractionation zone, a separation unit and a second catalytic reactor. The separation unit produces a first separation unit stream and a second separation unit stream, the first separation unit stream comprising Cx paraffins, and the second separation unit stream comprising Cx olefins, wherein the second separation unit stream is passed to a second catalytic reactor and the first separation unit stream is removed from the process.