MCM-22 Molecular Sieve Crystallinity and Stability Optimization
Solution Overview
Problem
MCM-22 family molecular sieves used in hydrocarbon conversions face challenges related to crystallinity, stability, and adsorption capacity, particularly in achieving higher crystallinity and thicker platelet morphology while maintaining low external surface area and controlled mesitylene uptake.
Innovation Solution
The development of an MCM-22 family molecular sieve with specific X-ray diffraction patterns, platelet morphology, and surface area characteristics, achieved through a method involving silicon sources, alkali metal hydroxides, directing agents, and controlled crystallization conditions, to enhance its catalytic performance in hydrocarbon conversions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MCM-22 family molecular sieves are used for hydrocarbon conversion, then catalytic activity is achieved, but crystallinity and stability are insufficient
Solution Approach 1:
The patent applies parameter changes by modifying the synthesis conditions including temperature (100-250°C), time (1-72 hours), and composition ratios (SiO2/Al2O3 from 10 to infinity, H2O/SiO2 from 1 to 20, OH−/SiO2 from 0.001 to 2, M+/SiO2 from 0.001 to 2, R/SiO2 from 0.001 to 0.34) to optimize the molecular sieve structure. These parameter adjustments achieve higher crystallinity and stability while maintaining catalytic activity through controlled crystallization processes.
2Reliability
If platelet thickness is increased to improve stability, then catalytic stability improves, but external surface area increases which reduces selectivity
Solution Approach 1:
The patent resolves this contradiction by changing the synthesis parameters including using specific directing agents (R) with controlled ratios (R/SiO2 from 0.001 to 0.34), adjusting alkalinity (OH−/SiO2 from 0.001 to 2), and controlling crystallization temperature and time. These parameter changes enable the formation of thicker platelets with controlled external surface area, achieving both stability and selectivity through optimized crystal growth conditions.
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 resulting MCM-22 family molecular sieve exhibits improved crystallinity, stability, and controlled adsorption properties, leading to enhanced catalytic activity and selectivity in hydrocarbon conversion processes, with specific characteristics such as increased platelet thickness and reduced external surface area.
Implementation Method 1
Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions
Implementation Method 2
Molecular sieve materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion
Data Source
AI summary
An MCM-22 family molecular sieve having an X-ray diffraction pattern of the as-synthesized MCM-22 family molecular sieve including d-spacing maxima at 12.4±0.25, 3.57±0.07 and 3.42±0.07 Angstroms and at least one peak between 26.6° and 29° (2θ). The peak between 26.6° to 29° (2θ) has a two theta (2θ) of about 26.9°. A method of manufacturing an MCM-22 family molecular sieve, said method comprising the steps of (a) combining at least one silicon source, at least one source of alkali metal hydroxide, at least one directing-agent (R), water, and optionally one aluminum source, to form a mixture having the following mole composition:Si:Al2=10 to infinityH2O:Si=1 to 20OH−:Si=0.001 to 2M+:Si=0.001 to 2R:Si=0.001 to 0.34wherein M is an alkali metal; (b) treating said mixture at crystallization conditions for less than 72 hr to form a treated mixture having said MCM-22 family molecular sieve, wherein said crystallization conditions comprises a temperature range from about 160° C. to about 250° C.; and (c) recovering said MCM-22 family molecular sieve.