Modified Y-Type Molecular Sieve for Catalytic Cracking Stability
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Solution Overview
Problem
Conventional Y-type molecular sieves used in catalytic cracking have poor thermal and hydrothermal stability, leading to low lattice collapse temperature, low crystallinity retention, and reduced selectivity, which limits the production of branched hydrocarbons in gasoline, especially for heavy oil processing.
Innovation Solution
A modified Y-type molecular sieve with a modifying metal content of 0.5-6.3 wt% (magnesium or calcium) and reduced sodium content, subjected to ion exchange, roasting, and reaction with silicon tetrachloride to achieve enhanced stability and increased secondary pore volume, resulting in improved acid distribution and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional hydrothermal method is used to prepare high-silica Y-type molecular sieve, then rare earth ion exchange and high-temperature roasting are performed, but the molecular sieve structure is damaged and thermal stability is poor
Solution Approach 1:
The patent changes the preparation parameters by using a lower silica-alumina ratio (4.5-5.2) in the initial NaY molecular sieve and controlling the roasting temperature (350-480°C) and time (4-7 hours) to prevent structure damage while achieving dealumination and stability improvement
Solution Approach 2:
The patent performs preliminary ion exchange with rare earth ions before roasting to stabilize the molecular sieve structure, and conducts dealumination at controlled conditions before final silicon supplementation, preventing structure damage that would occur if these steps were performed in conventional sequence or under severe conditions
2Reliability
If excessive dealumination is performed to improve stability, then non-framework aluminum increases, but selectivity decreases
Solution Approach 1:
The patent controls the dealumination process by limiting non-framework aluminum content to 5-15 wt% through controlled roasting conditions (350-480°C for 4-7 hours), and subsequently supplements silicon to achieve optimal SiO2/Al2O3 ratio (7.3-14.0), thereby maintaining both stability and selectivity
Solution Approach 2:
The patent uses rare earth ions as intermediaries during ion exchange to stabilize the molecular sieve structure during dealumination, preventing excessive structure damage and controlling non-framework aluminum formation while maintaining selectivity
3Adaptability or versatility
If conventional Y molecular sieve composition is used, then structure adjustment is limited, but product composition cannot be optimized for branched hydrocarbons
Solution Approach 1:
The patent creates a composite molecular sieve structure by incorporating multiple elements (rare earth ions, magnesium, calcium, silicon) into the Y-type molecular sieve framework, enabling both structure adjustment and optimized product composition with 10-30 wt% branched hydrocarbons in gasoline
Solution Approach 2:
The patent introduces specific modifying metals (magnesium 0.5-4.5 wt%, calcium 0.7-6.3 wt%) at controlled locations within the molecular sieve structure to create local active sites that enhance both structural stability and catalytic selectivity for branched hydrocarbon formation
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 modified Y-type molecular sieve exhibits high thermal and hydrothermal stability, reducing coke selectivity and increasing gasoline and liquefied gas yields, with higher content of branched hydrocarbons, particularly dimethyl-branched hydrocarbons, enhancing the quality of catalytically cracked gasoline.
Implementation Method 1
a NaY molecular sieve is subjected to multiple times of rare earth ion exchange
Implementation Method 2
then treated with steam, which makes the dealumination of the molecular sieve during the steam treatment difficult
Implementation Method 3
then to a hydrothermal treatment... high-temperature roasting
Data Source
AI summary
A modified Y-type molecular sieve has a modifying metal content of about 0.5-6.3 wt % calculated on the basis of an oxide of the modifying metal and a sodium content of no more than about 0.5 wt % calculated on the basis of sodium oxide. The modifying metal is magnesium and/or calcium. The modified Y-type molecular sieve has a proportion of non-framework aluminum content to the total aluminum content of no more than about 20%, a total pore volume of about 0.33-0.39 ml/g, a proportion of the pore volume of secondary pores having a pore size of 2-100 nm to the total pore volume of about 10-25%, a lattice constant of about 2.440-2.455 nm, a lattice collapse temperature of not lower than about 1040° C., and a ratio of B acid to L acid in the total acid content of no less than about 2.30.