Layered Catalyst System for Ethylene Yield via Butene Cracking
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Solution Overview
Problem
Conventional methods for converting saturated paraffins to olefins, such as thermal cracking and catalytic cracking, struggle to control product selectivity and often produce excessive higher olefins like butenes, while lower olefins like ethylene, which are more commercially attractive, are produced in lower amounts.
Innovation Solution
A catalyst system comprising a first layer of dehydrogenation active metal on a solid support and a second layer of cracking catalyst, specifically a ZSM-5 zeolite or silicalite with a transition metal like molybdenum, tungsten, or rhenium, is used to shift the product distribution by cracking higher olefins into lower olefins, particularly increasing ethylene production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If catalytic cracking is used to convert saturated paraffins to olefins, then the operating conditions become less severe, but the product selectivity cannot be controlled and higher olefins are produced in high amounts
Solution Approach 1:
The catalyst system is divided into two distinct layers: a first layer containing dehydrogenation active metal on solid support for dehydrogenation, and a second layer containing cracking catalyst for cracking. This segmentation allows each layer to perform its specific function optimally, with the cracking layer selectively converting higher olefins to lower olefins while maintaining mild operating conditions throughout the process.
Solution Approach 2:
The invention uses a composite catalyst system combining two different catalyst types in a layered structure. The first layer uses dehydrogenation catalyst (e.g., Pt, Pd, Ir on alumina or silica) while the second layer uses cracking catalyst (e.g., ZSM-5 zeolite with Si/Al ratio 20-1500). This composite approach enables both dehydrogenation and selective cracking functions to be integrated, achieving controlled product distribution with high ethylene selectivity under mild conditions.
2Adaptability or versatility
If dehydrogenation followed by metathesis is used to convert saturated paraffins to olefins, then olefin distribution can be adjusted, but high amounts of higher olefins such as butenes are produced
Solution Approach 1:
The invention extracts and removes the undesired higher olefins from the product distribution by introducing a second layer of cracking catalyst. This cracking layer specifically targets and converts higher olefins (like butenes) into lower olefins (ethylene, propylene), effectively taking out the harmful higher olefin products from the final mixture while maintaining the ability to adjust overall olefin distribution through catalyst composition control.
Solution Approach 2:
The invention changes the key parameter of product distribution by adding the cracking catalyst layer. By controlling the weight ratio of the first layer to the second layer (from 50:1 to 1:20, preferably 40:1 to 1:1) and adjusting the ZSM-5 silica to alumina ratio (20-1500), the system can optimize the balance between dehydrogenation and cracking activities, thereby controlling the final olefin distribution with reduced higher olefin content.
3Quantity of substance
If a larger portion of the cracking catalyst layer is used, then higher olefin reduction increases, but equilibrium limitation prevents further reduction
Solution Approach 1:
The invention applies partial action by using a moderate amount of cracking catalyst (weight ratio of first layer to second layer from 50:1 to 1:20) rather than excessive cracking catalyst. This partial application is sufficient to achieve the desired higher olefin reduction to below 50 mol% while avoiding the equilibrium limitation that would occur with excessive cracking. The optimal ratio balances higher olefin conversion with maintaining overall process productivity and avoiding side reactions.
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
The catalyst system significantly reduces higher olefin production, especially butenes, while increasing the yield of ethylene, even with a small portion of the cracking catalyst layer, achieving a favorable product distribution.
Implementation Method 1
a first composition comprising a dehydrogenation active metal on a solid support
Implementation Method 2
the cracking catalyst consists of a molecular sieve, the said molecular sieve being a ZSM-5 zeolite having a silica to alumina ratio in the range of 20 to 1500 and/or silicalite
Implementation Method 3
the cracking catalyst is for cracking olefins, preferably for cracking butene into ethylene
Data Source
AI summary
The present invention relates to a catalyst system comprising: i. a first layer of a hydrocarbon conversion catalyst, the hydrocarbon conversion catalyst comprising: a first composition comprising a platinum group metal on a solid support; and a second composition comprising a transition metal on an inorganic support; ii. a second layer comprising a cracking catalyst; and to a process for conversion of a hydrocarbon feed utilizing this catalyst system.