Oligomerization Catalyst for Dilute Ethylene Conversion
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Solution Overview
Problem
The challenge is to effectively utilize dilute ethylene from FCC dry gas streams in refinery processes, as existing methods are hindered by impurities that poison catalysts and render ethylene recovery economically unjustified due to its low reactivity and the incompatibility of catalysts with trace impurities.
Innovation Solution
Feeding the FCC dry gas stream to an impurity-resistant oligomerization catalyst, specifically a catalyst with metals from Group 6, 8, 9, and 10 on an amorphous silica-alumina support, to convert ethylene to butenes and higher olefins, which can then be recycled to an FCC unit for enhanced propylene production, while the unconverted gases are burned as fuel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional oligomerization catalysts are used to convert ethylene in dry gas, then ethylene conversion is achieved, but the catalyst quickly deactivates due to impurities such as carbon oxides, ammonia and hydrogen sulfide
Solution Approach 1:
The patent changes the chemical parameters of the catalyst by selecting metals from Groups 6, 8, 9, and 10 (such as chromium, nickel, cobalt, iron, manganese, zinc, or calcium) that are inherently more resistant to impurity poisoning. This parameter change in catalyst composition allows the catalyst to maintain activity and stability in the presence of carbon oxides, ammonia, and hydrogen sulfide impurities in the dry gas stream.
Solution Approach 2:
The patent employs a composite catalyst system combining metal components from Groups 6, 8, 9, and 10 with a silica-alumina support. This composite structure provides both the active sites for oligomerization and resistance to impurity deactivation, creating a more robust catalyst that can process impure dry gas feeds effectively.
2Quantity of substance
If gas recovery systems are used to recover ethylene from dry gas, then ethylene recovery is achieved, but the process is not economically justified due to the dilute concentration of ethylene
Solution Approach 1:
The patent changes the concentration parameter by converting dilute ethylene (5-50 wt-%) directly to higher concentration olefin products through oligomerization. This parameter transformation eliminates the need for expensive separation and concentration equipment, making the process economically viable by directly producing valuable C4+ olefins from the dilute feed.
Solution Approach 2:
The patent converts the harmful effect of dilute concentration (which makes recovery economically unjustified) into a benefit by using the dilute stream as direct feed for oligomerization. The low concentration is no longer a disadvantage but becomes acceptable feedstock for producing high-value olefin products, turning an economic liability into an asset.
3Productivity
If conventional oligomerization processes use propylene or butylene from LPG or dehydrogenated feedstocks, then liquid fuel production is achieved, but dilute ethylene is little used as feedstock due to its much lower reactivity
Solution Approach 1:
The patent changes the reactivity parameter by selecting metal catalysts from Groups 6, 8, 9, and 10 that have appropriate activity for oligomerizing ethylene at its naturally occurring low concentrations. These catalysts provide the necessary reactivity enhancement to process dilute ethylene streams effectively, expanding feedstock flexibility to include refinery dry gas that was previously unusable.
Solution Approach 2:
The patent creates a universal catalyst system that can process multiple feedstock types including dilute ethylene from FCC dry gas, making the oligomerization unit versatile. The catalyst is designed to handle impure, dilute streams that conventional processes cannot, allowing the same process to produce liquid fuels from various refinery gas streams.
4Productivity
If FCC operation shifts toward high propylene production, then propylene output increases, but the amount of dry gas produced increases significantly with high ethylene content
Solution Approach 1:
The patent implements a feedback loop where the dry gas stream containing ethylene, which is a byproduct of propylene production, is fed back to an oligomerization unit. The ethylene is converted to C4+ olefins that are then recycled to the FCC unit, creating a closed-loop system that eliminates ethylene loss and enhances overall propylene production by converting the byproduct back into valuable feedstock.
Solution Approach 2:
The patent merges two processes: the FCC propylene production process and the oligomerization of dry gas ethylene. By combining these processes and recycling the oligomerized products back to the FCC unit, the system creates a synergistic effect where ethylene that would otherwise be lost is converted into additional propylene production, amplifying the overall productivity.
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 allows for the stable conversion of dilute ethylene to higher-value propylene, overcoming catalyst deactivation issues and increasing propylene production while allowing the remaining gases to be used as fuel, thus enhancing the economic viability of ethylene recovery.
Implementation Method 1
contacting a dilute ethylene stream with an olefin oligomerization catalyst to convert the ethylene to butenes and higher olefins
Implementation Method 2
Catalytic cracking can create a variety of products from larger hydrocarbons
Implementation Method 3
regenerating the stream of spent catalyst by combustion of coke from the spent catalyst to provide regenerated catalyst
Data Source
AI summary
The process converts ethylene in a dilute ethylene (dry gas) stream that may be derived from an FCC product to propylene. The process includes an oligomerization step to convert ethylene in the dilute ethylene stream to heavier olefins, and a second reaction step to convert the heavier olefins to propylene. The oligomerization catalyst may be an amorphous silica-alumina base with a Group VIII and/or VIB metal. The catalyst is resistant to feed impurities such as hydrogen sulfide, carbon oxides, hydrogen and ammonia. At least 50 wt-% of the ethylene in the dilute ethylene stream can be converted to C4+ olefins and recycled to the FCC for cracking to propylene.