Olefin Cracking Integration with Metathesis for Propylene Yield
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Solution Overview
Problem
The existing methods for increasing propylene yields in hydrocarbon cracking units, such as using metathesis reactors, consume ethylene and do not effectively convert 1-butene to propylene, leading to inefficient production and catalyst deactivation, while rebuilding and re-cracking C4 streams presents a complex and costly approach.
Innovation Solution
The process involves adding an alkylation reactor and an olefin cracking unit to convert unprocessed effluent products from hydrocarbon cracking units, separating C4 streams into normal butane and isobutane streams, and dimerizing isobutane to form larger hydrocarbons, which are then cracked to produce additional ethylene and propylene, with recycling of non-ethylene and non-propylene streams to enhance propylene yields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a metathesis reactor is added to convert butene to propylene, then propylene yield increases, but ethylene is consumed and catalyst deactivation occurs due to isobutene and 1-butene presence
Solution Approach 1:
The C4 stream is separated into two distinct streams: a normal butane stream (n-butane and 2-butene) for metathesis reactor feed, and an isobutane stream (isobutane, isobutene, and 1-butene) for alkylation reactor feed. This segmentation prevents harmful substances from reaching the metathesis catalyst while directing them to an appropriate processing unit.
Solution Approach 2:
The harmful substances (isobutene and 1-butene) are extracted from the C4 stream by separating it into normal butane and isobutane streams. This removal prevents catalyst deactivation in the metathesis reactor while the extracted components are processed through alkylation to produce valuable products.
2Productivity
If isobutane stream is dimerized in an alkylation reactor to form larger hydrocarbons, then propylene yield increases through subsequent cracking, but additional processing equipment is required
Solution Approach 1:
The alkylation reactor and olefin cracking unit are integrated into a combined processing train that handles the isobutane stream. This merging of functions allows the system to convert low-value C4 components into valuable light olefins (ethylene and propylene) while sharing infrastructure and optimizing overall plant efficiency.
Solution Approach 2:
The olefin cracking unit serves multiple functions: it cracks the dimerized C8+ hydrocarbons from the alkylation reactor, produces additional light olefins (ethylene and propylene), and generates a butane/butene recycle stream for the metathesis reactor. This multi-functionality maximizes the value of the added equipment.
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 significantly increases propylene yields without consuming ethylene, achieving a 60% conversion of larger olefins to ethylene and propylene, and allows for efficient recycling of butenes, thereby improving overall light olefin production with minimal capital investment.
Implementation Method 1
The isobutane stream is passed to an alkylation reactor to dimerize some of the isobutane stream to form larger hydrocarbons having 8 or more carbon atoms
Implementation Method 2
The olefin cracking unit produces ethylene and propylene, and produces a stream rich in butanes and butenes for recycle to the metathesis reactor
Implementation Method 3
The pygas is selectively hydrogenated to remove diolefins
Data Source
AI summary
A process for increasing the propylene yields for hydrocarbon cracking processes. The process includes adding using alkylation of the C4s coming from the hydrocarbon cracker, and passing larger olefins to an olefin cracking unit.