Riser Reactor Feed Injection for Propene Selectivity
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Solution Overview
Problem
In fluid catalytic cracking (FCC) units, recycling C4+ alkenes back to risers for further processing does not optimize propene yield due to high residence times, which crack oligomerized products predominantly back to butenes, reducing selectivity and impacting high octane gasoline production.
Innovation Solution
Feeding oligomerized products separately at a higher location in the riser reduces residence time, enhancing selectivity to propene and high octane gasoline by cracking linear species more efficiently while preserving branched species, thereby reducing recycling of butenes and increasing production of high octane gasoline and propene.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If C4+ alkenes are recycled back to the riser for further processing, then the FCC unit can maintain continuous operation, but the high residence time causes oligomerized products to crack predominantly back to butenes, reducing propene selectivity
Solution Approach 1:
The riser is divided into two separate feed injection points: a lower location for virgin feed and an upper location for recycled C4+ oligomerized products. This segmentation allows different residence times for different feed streams, enabling continuous operation while improving propene selectivity for the recycled portion.
Solution Approach 2:
Different parts of the riser are assigned different functions based on local conditions. The lower riser section handles virgin feed with longer residence time for complete conversion, while the upper riser section handles recycled oligomers with shorter residence time to maximize propene selectivity and prevent back-cracking to butenes.
2Productivity
If residence time is increased to ensure complete cracking of feed, then conversion is improved, but oligomerized products crack back to butenes instead of producing propene, reducing selectivity
Solution Approach 1:
The system dynamically adjusts residence time based on the feed stream being processed. By injecting recycled oligomers at a higher location, the effective residence time for this stream is reduced compared to virgin feed, allowing optimization of both conversion and selectivity for different feed compositions.
3Productivity
If linear oligomerized species are cracked, then propene production is enhanced, but highly branched species are also cracked, reducing high octane gasoline content
Solution Approach 1:
The upper riser section applies partial cracking action to recycled oligomers, sufficient to convert linear species to propene but limited enough to preserve highly branched species that contribute to high octane gasoline content. This controlled partial action optimizes both propene yield and gasoline quality.
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 increases propene selectivity and preserves high octane branched species, optimizing product mix and reducing butene recycling, thus improving overall FCC unit performance.
Implementation Method 1
Fluid catalytic cracking process
Data Source
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AI summary
One exemplary embodiment can be a process for fluid catalytic cracking. The process can include providing a first feed including one or more heavy hydrocarbons to a riser of a riser-reactor, and obtaining a second feed from an oligomerization zone. Usually, the second feed includes one or more light alkene oligomeric hydrocarbons and is provided downstream from the first feed for producing propene.