P-Modified MWW Molecular Sieve for Selective p-Xylene Catalysis
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Solution Overview
Problem
Existing molecular sieves used in the bio-based synthesis of p-xylene from biomass-derived 2,5-dimethylfuran and ethylene suffer from high acid strength leading to low product selectivity and poor catalyst stability due to carbon deposition, with traditional silicon-aluminum molecular sieves and modified SCM-1 materials still exhibiting strong acid sites.
Innovation Solution
A P-modified MWW molecular sieve with an A Pδ-7 /A P ratio of ≥40% and a two-dimensional layered structure, prepared by P-modification of a H-type MWW molecular sieve, which reduces strong acid sites and enhances carbon deposition resistance, stability, and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional silicon-aluminum molecular sieves or modified SCM-1 materials are used, then the catalyst provides necessary acid catalysis for the reaction, but strong acid sites cause low product selectivity due to side reactions
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition of the molecular sieve through phosphorus incorporation. The P-modified MWW molecular sieve changes the acid site distribution by introducing phosphorus atoms that interact with aluminum sites, transforming strong acid sites into weaker acid sites with appropriate catalytic activity. The 31P NMR analysis shows phosphorus occupies aluminum sites, creating P-Al species that provide moderate acidity suitable for the Diels-Alder reaction while suppressing unwanted side reactions.
Solution Approach 2:
The patent creates a composite material system by combining phosphorus-modified MWW molecular sieve with specific pore structure characteristics. The composite nature involves the integration of phosphorus species within the MWW framework, creating a new catalytic material with optimized properties. The material exhibits both the structural benefits of MWW molecular sieve and the acid site modulation effects of phosphorus modification, achieving high selectivity for p-xylene production.
2Reliability
If traditional silicon-aluminum molecular sieves are used, then the catalyst provides strong acid sites for catalysis, but the small external specific surface area causes rapid carbon deposition and catalyst deactivation
Solution Approach 1:
The patent modifies the surface area parameter by changing the molecular sieve structure from traditional three-dimensional frameworks to two-dimensional layered MWW structure. This structural transformation dramatically increases the external specific surface area, providing more exposed active sites that are accessible to reactants. The increased surface area reduces carbon deposition rate per active site and improves mass transfer, thereby enhancing catalyst stability and reducing deactivation.
3Productivity
If strong acid catalysts are used to promote the reaction, then the reaction rate increases, but DMF undergoes self-polymerization and hydrolysis side reactions
Solution Approach 1:
The patent precisely controls the acid strength parameter by incorporating phosphorus into the molecular sieve framework. The phosphorus modification creates acid sites with optimized strength that is sufficient to catalyze the Diels-Alder reaction between DMF and ethylene but not strong enough to trigger DMF self-polymerization or hydrolysis. The 31P NMR data confirms phosphorus occupies aluminum sites, creating P-Al species with moderate acidity that achieves the desired selectivity.
4Object-generated harmful factors
If phosphorus modification is applied to eliminate strong acid sites, then product selectivity improves, but catalyst acidity may be reduced below optimal levels
Solution Approach 1:
The patent optimizes the phosphorus content parameter to achieve the right balance between eliminating strong acid sites and maintaining sufficient catalytic activity. By controlling the amount of phosphorus incorporated into the MWW framework, the catalyst achieves moderate acid strength that is optimal for the Diels-Alder reaction. The phosphorus modification creates a distribution of acid sites with varying strengths, where the majority are moderate-strength sites suitable for the target reaction.
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 P-modified MWW molecular sieve exhibits high selectivity and stability in converting 2,5-dimethylfuran and/or 2,5-hexadione to p-xylene, minimizing side reactions and maintaining catalyst activity through reduced strong acid sites and improved carbon deposition resistance.
Implementation Method 1
DMF and ethylene first undergo a Diels-Alder cycloaddition reaction to generate a cycloaddition intermediate, oxa-norbornene
Implementation Method 2
which then undergoes a dehydration reaction under acid catalysis to generate PX and water
Implementation Method 3
A P-modified MWW molecular sieve with an A Pδ-7 /A P ratio of ≥40%, prepared by P-modification of a H-type MWW molecular sieve, which reduces strong acid sites
Data Source
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AI summary
The present invention relates to the field of molecular sieves, and particularly relates to a P-modified MWW molecular sieve, and a preparation method therefor and the use thereof. The molecular sieve shows APδ-7/AP ≥ 40%, and preferably ≥ 50%, wherein APδ-7 represents a peak area of a P-species signal peak, which has a chemical shift within the range of -22 ppm to 8 ppm in a 31P MAS NMR spectrogram, and AP represents the total peak area of all signal peaks in the 31P MAS NMR spectrogram. A catalyst which contains the molecular sieve of the present invention has high levels of activity, selectivity and stability, and has an excellent carbon deposition resistance capability.