Modified Y-type Molecular Sieve for Heavy Oil Cracking
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Solution Overview
Problem
Current Y-type molecular sieves face challenges in cracking heavy oils due to limited pore size and poor thermal stability, leading to reduced accessibility and activity for polycyclic compounds, and existing methods for improving stability often compromise crystallinity and specific surface area.
Innovation Solution
A modified Y-type molecular sieve with a rare earth oxide content of 4-12% and phosphorus content of 0-10% is developed, featuring a lattice constant of 2.440-2.455 nm, high thermal stability, and a significant percentage of secondary pores, achieved through ion-exchange with a rare earth salt, roasting in a steam atmosphere, and Si-Cl4 isomorphous substitution, followed by acid treatment and optional phosphorus modification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrothermal dealuminization method is used to prepare ultra-stable molecular sieves, then thermal stability is improved, but crystallinity and specific surface area are compromised
Solution Approach 1:
The patent applies parameter changes by optimizing the hydrothermal dealuminization process with specific control of temperature (600-825°C), time, and steam atmosphere composition. By precisely adjusting these parameters, the method achieves ultra-stability while minimizing crystallinity loss and surface area reduction, resolving the contradiction between thermal stability improvement and crystallinity maintenance.
Solution Approach 2:
The patent creates a composite modified Y-type molecular sieve by combining dealuminization treatment with subsequent modification steps (such as phosphorus or rare earth addition). This composite approach allows the molecular sieve to gain ultra-stability from dealuminization while the additional modifications can restore or enhance crystallinity and surface area properties that were compromised during the dealuminization process.
2Productivity
If pore size of molecular sieve is reduced to 0.74 nm, then cracking activity is improved, but accessibility to polycyclic compounds is reduced
Solution Approach 1:
The patent applies segmentation by creating a hierarchical pore structure with both primary pores (0.74 nm) for high cracking activity and secondary pores (larger size) for accessibility to polycyclic compounds. This segmented pore system allows different functional zones within the molecular sieve to serve different purposes: the fine primary pores provide high cracking activity while the larger secondary pores facilitate access to bulky polycyclic molecules, resolving the contradiction between cracking activity and accessibility.
Solution Approach 2:
The patent applies local quality by creating different pore size distributions in different regions or aspects of the molecular sieve structure. The molecular sieve is designed to have fine pores in certain locations for high cracking activity and coarser pores in other locations for better accessibility to polycyclic compounds, allowing local optimization of properties that would be contradictory in a uniform structure.
3Productivity
If secondary pores are increased to improve accessibility, then cracking capability for residual oils is improved, but crystallinity and specific surface area are reduced
Solution Approach 1:
The patent applies parameter changes by carefully controlling the dealuminization conditions (temperature, time, steam atmosphere) to create secondary pores while minimizing crystallinity loss. By optimizing these parameters, the method achieves improved cracking capability for residual oils through secondary pore formation while maintaining high crystallinity and specific surface area, resolving the contradiction between productivity improvement and manufacturing precision maintenance.
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 sieve exhibits enhanced thermal and hydrothermal stability, increased cracking activity for heavy oils, improved gasoline and liquefied gas yields, and reduced coke selectivity, while maintaining high crystallinity and specific surface area.
Implementation Method 1
subjecting a NaY molecular sieve to ion-exchange with an aqueous solution containing ammonium ions to reduce the content of sodium ion in the molecular sieve
Implementation Method 2
Hydrothermal dealuminization method is one of the most widely used methods for preparing ultra-stable molecular sieves in the industry
Implementation Method 3
gas phase Si—Al isomorphous substitution reaction, where the aluminum in the framework of the molecular sieve is directly substituted by the silicon in the gaseous silicon tetrachloride
Implementation Method 4
subjecting the ammonium ion-exchanged molecular sieve to roasting at 600-825° C. in steam atmosphere to allow it to be ultra-stabilized
Data Source
AI summary
A modified Y-type molecular sieve has a rare earth oxide content of about 4% to about 12% by weight, a phosphorus content of about 0% to about 10% by weight, a sodium oxide content of no more than about 1.0% by weight, a total pore volume of about 0.36 to 0.48 mL/g, a percentage of the pore volume of secondary pores to the total pore volume of about 20% to about 40%, a lattice constant of about 2.440 nm to about 2.455 nm, a percentage of the non-framework aluminum content to the total aluminum content of no more than about 10%, a lattice collapse temperature of not lower than about 1060° C., and a ratio of Brønsted acid to Lewis acid of no less than about 3.50. The preparation of the molecular sieve includes ion-exchange with rare earth, hydrothermal roasting, gas phase ultra-stabilization, acid treatment, and an optional phosphorus modification.