Composite Zeolite Catalyst for Heavy Aromatic Transalkylation
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Solution Overview
Problem
Catalyst systems for transalkylation of heavy aromatics face challenges in maintaining activity and selectivity, particularly in converting C9+ aromatics to xylenes, with existing catalysts showing reduced performance and increased aging rates as the feed composition shifts towards higher C9+ content.
Innovation Solution
A catalyst composition comprising a mixture of MEL framework zeolite (such as ZSM-11) and MOR framework zeolite (such as mordenite) with specific weight ratios and metal combinations, including Pt and Sn, which enhances aromatic selectivity and reduces catalyst aging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing catalyst systems are used for transalkylation of heavy aromatics, then transalkylation activity is achieved, but catalyst aging rate increases and aromatic selectivity decreases as feed composition shifts towards higher C9+ content
Solution Approach 1:
The patent employs a composite catalyst system comprising two distinct molecular sieves (first molecular sieve with Constraint Index 3-12 and second molecular sieve with Constraint Index less than 3) combined with metal components. This composite structure allows the first molecular sieve to provide transalkylation activity while the second molecular sieve maintains catalyst stability and reduces aging, thereby resolving the contradiction between maintaining high activity and extending catalyst lifetime under high C9+ feed conditions.
2Productivity
If transalkylation activity is increased to convert more C9+ aromatics, then xylene production increases, but aromatic selectivity decreases due to increased dealkylation and loss of valuable aromatics
Solution Approach 1:
The patent segments the catalytic function into two distinct molecular sieves with different Constraint Indices. The first molecular sieve (CI 3-12) selectively promotes transalkylation reactions to produce xylenes, while the second molecular sieve (CI less than 3) provides shape selectivity to prevent excessive dealkylation and preserve aromatic selectivity. This functional segmentation allows high xylene yield to be achieved without sacrificing aromatic selectivity.
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 composition demonstrates improved aromatic selectivity, increased xylene yield, and extended catalyst lifetime, effectively addressing the challenges of converting heavy aromatics while minimizing ethyl-substituted aromatic conversion losses.
Implementation Method 1
Catalysts and corresponding catalytic methods are provided for conversion of aromatic hydrocarbons to more valuable products, such as transalkylation of heavy aromatics to make xylenes
Implementation Method 2
Metal function is required to saturate olefins formed during dealkylation while maintaining the integrity of the aromatic saturations
Data Source
AI summary
Methods and corresponding catalysts are provided for conversion of an aromatics feed containing C8+ aromatics, particularly C9+ aromatics, to form a converted product mixture comprising, e.g., benzene and/or xylenes. The aromatic feed can be converted in the presence of a catalyst that includes a mixture of a first zeolite having an MEL framework, such as ZSM-11, and a second zeolite having a MOR framework, such as mordenite, particularly a mordenite synthesized using TEA or MTEA as a structure directing agent. The weight ratio of the first zeolite to the second zeolite in the catalyst can be from 0.3 to 1.2, or from 0.3 to 1.1, or from 0.3 to 1.0. The catalyst can further include one or more metals supported on the catalyst, such as a combination of metals.