ZSM-5 Catalyst Synthesis via Mixed Template Agents
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Solution Overview
Problem
The existing methods for synthesizing ZSM-5 molecular sieves using organic amine template agents result in environmental pollution, high waste water generation, and poor catalytic performance due to non-homogeneous particles and low toluene conversion rates, while inorganic amine template agents lead to an 'inverse effect' with decreased para-selectivity.
Innovation Solution
A process using a combination of silica sol, water glass, or sodium silicate as silica sources, aluminium sulphate or sodium meta-aluminate as alumina sources, and a mixture of organic amine and alcohol or ether as template agents, with specific molar ratios and hydrothermal crystallization, followed by ion exchange and surface modification with organosilicon compounds to produce ZSM-5 molecular sieves with improved catalytic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If organic amine template agents are used to synthesize ZSM-5 molecular sieves, then crystallization rate and structural flexibility are improved, but environmental pollution and waste water generation increase
Solution Approach 1:
The patent introduces an inorganic amine template agent (ammonium fluoride, ammonium bifluoride, or ammonium fluosulfonate) as an intermediary substance that mediates the crystallization process. These inorganic templates serve the same structural directing function as organic templates but without the environmental pollution and waste water issues, effectively replacing the harmful organic intermediaries with benign inorganic ones.
Solution Approach 2:
The patent changes the chemical nature of the template agent from organic to inorganic, specifically using ammonium salts with different anions (fluoride, bifluoride, fluosulfonate). This parameter change maintains the template's ability to direct ZSM-5 crystallization while eliminating the environmental harm associated with organic templates.
2Object-generated harmful factors
If inorganic amine template agents are used to synthesize ZSM-5 molecular sieves, then environmental pollution is reduced, but catalytic performance deteriorates due to non-homogeneous particles
Solution Approach 1:
The patent creates a composite gel system combining inorganic amine template agents with silica sol and water glass. This composite approach allows the inorganic template to direct crystallization while the gel matrix ensures homogeneous particle formation, overcoming the particle uniformity issues that plague simple inorganic template systems.
Solution Approach 2:
The patent utilizes the sol-gel transition and hydrothermal processing to control particle formation. The gel structure provides a homogeneous distribution of template agents throughout the reaction medium, ensuring uniform nucleation and particle growth, which resolves the non-homogeneous particle problem.
3Loss of substance
If inorganic amine template agents are used, then waste water generation is minimized, but toluene conversion rate decreases
Solution Approach 1:
The patent modifies the external surface properties of ZSM-5 particles through selective coating with organosilicon compounds. This creates a local quality difference between the internal pore structure (which maintains shape selectivity) and the external surface (which reduces non-selective isomerization), thereby improving toluene conversion to para-xylene while using inorganic templates that minimize waste water.
Solution Approach 2:
The patent optimizes the silica/alumina ratio and crystal size parameters of the ZSM-5 molecular sieves synthesized with inorganic templates. By carefully controlling these parameters and performing external surface modification, the catalyst achieves high toluene conversion rates despite using environmentally friendly inorganic template agents.
4Manufacturing precision
If ZSM-5 molecular sieves are modified to improve para-selectivity, then shape selective alkylation performance is enhanced, but external surface isomerization activity increases
Solution Approach 1:
The patent applies organosilicon compound coatings specifically to the external surface of ZSM-5 particles. This selective modification creates different functional zones: the internal pore structure maintains its shape-selective alkylation activity for para-xylene production, while the external surface coating suppresses non-selective isomerization reactions, thereby resolving the contradiction between selectivity and unwanted side reactions.
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
This process reduces environmental pollution, minimizes waste production, and achieves high toluene conversion rates and selectivity for para-xylene production, overcoming the limitations of previous methods by producing catalysts with enhanced catalytic activity and selectivity.
Implementation Method 1
hydrothermally-crystallizing the synthesis mixture at 120-200°C for 10-200 hours to obtain the liquid product containing ZSM-5 molecular sieves
Implementation Method 2
converting the molecular sieves to NH4-type ZSM-5 molecular sieves by ion exchange
Implementation Method 3
modifying the catalyst matrix with at least one organosilicon selected from the group consisting of phenylmethylpolysiloxane, hydroxyl silicone oil, amino silicon oil and dimethyl silicon oil so as to support organosilicon on the surface of the molecular sieves
Data Source
AI summary
The present invention relates to a process for the manufacture of catalysts used for producing para-xylene by toluene shape selective alkylation. The invention is primarily used for solving the problems in the old technology, e.g., high requirements on the environment and great treatment of waste water containing organic amines when synthesizing ZSM-5 molecular sieves by using an organic amine as the template agent; small and non-homogeneous particles of the molecular sieves when synthesizing ZSM-5 molecular sieves by using an alcohol or ether as the template agent, such that the catalyst prepared thereby has low catalytic selectivity and low toluene conversion rate, etc. Said problems are better solved in the present invention by synthesizing ZSM-5 molecular sieves using the combination of organic amines and alcohols or ethers as the template agents (having a weight ratio of organic amines/alcohols=0.05-150, and organic amines/ethers=0.05-150), and modifying with organosilicon so as to obtain the catalysts. Said catalysts can be used in the industrial production of para-xylene manufactured by toluene shape selective alkylation.