Silver Epoxidation Catalyst Calcination for High Selectivity
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Solution Overview
Problem
Existing processes for producing silver-based epoxidation catalysts are costly and inefficient, often requiring large amounts of inert gas and compromising catalyst performance, particularly selectivity, due to the use of oxygen-containing atmospheres during calcination steps.
Innovation Solution
A process involving the impregnation of a refractory support with silver ions and aminic complexing agents, followed by conversion to metallic silver using controlled oxygen and inert gas streams, with specific temperature and composition conditions to enhance catalyst selectivity and reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inert gas atmosphere is used during calcination to prevent oxygen absorption, then catalyst selectivity is maintained, but process costs increase due to large quantities of inert gas required
Solution Approach 1:
The calcination process is divided into two distinct stages: a first calcination stage performed in an oxygen-containing atmosphere to convert silver compounds to metallic silver, and a second calcination stage performed in an inert gas atmosphere to prevent oxygen absorption and maintain selectivity. This segmentation allows each stage to be optimized for its specific purpose, reducing overall inert gas consumption while maintaining catalyst performance.
Solution Approach 2:
The first calcination stage in an oxygen-containing atmosphere is performed as a preliminary action to completely convert silver compounds to metallic silver before the second stage. This preliminary oxidation ensures that when the inert gas atmosphere is applied in the second stage, there is no oxygen absorption by metallic silver, thereby maintaining high selectivity without requiring inert gas throughout the entire process.
2Quantity of substance
If oxygen-containing atmosphere is used during calcination, then inert gas consumption is reduced, but catalyst selectivity deteriorates due to oxygen absorption by silver
Solution Approach 1:
The calcination process is divided into two distinct stages: a first calcination stage performed in an oxygen-containing atmosphere to convert silver compounds to metallic silver, and a second calcination stage performed in an inert gas atmosphere to prevent oxygen absorption and maintain selectivity. This segmentation allows each stage to be optimized for its specific purpose, reducing overall inert gas consumption while maintaining catalyst performance.
Solution Approach 2:
The first calcination stage in an oxygen-containing atmosphere is performed as a preliminary action to completely convert silver compounds to metallic silver before the second stage. This preliminary oxidation ensures that when the inert gas atmosphere is applied in the second stage, there is no oxygen absorption by metallic silver, thereby maintaining high selectivity without requiring inert gas throughout the entire process.
3Reliability
If two-stage calcination process is implemented, then catalyst selectivity is improved, but process complexity increases
Solution Approach 1:
The same calcination reactor and gas delivery system are used for both the first and second calcination stages. The system's versatility allows it to handle different gas atmospheres (oxygen-containing and inert gas) and temperature profiles, eliminating the need for separate equipment for each stage and reducing overall process complexity despite the multi-stage nature of the process.
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 process achieves high catalyst selectivity and efficiency with reduced overall costs by utilizing oxygen-containing gases during calcination, simplifying and optimizing the production process.
Implementation Method 1
impregnating a particulate porous refractory support with a first aqueous silver impregnation solution
Implementation Method 2
converting at least part of the silver ions impregnated on the refractory support to metallic silver by heating
Implementation Method 3
converting at least part of the silver ions impregnated on the refractory support to metallic silver
Implementation Method 4
aqueous silver impregnation solution comprising silver ions and an aminic complexing agent selected from amines, alkanolamines and amino acids
Data Source
AI summary
A process for producing a silver-based epoxidation catalyst, comprising i) impregnating a particulate porous refractory support with a first aqueous silver impregnation solution comprising silver ions and an aminic complexing agent selected from amines, alkanolamines and amino acids; ii) converting at least part of the silver ions impregnated on the refractory support to metallic silver by heating while directing a stream of a first gas over the impregnated refractory support to obtain an intermediate catalyst, wherein the first gas comprises at least 5 vol.-% oxygen; iii) impregnating the intermediate catalyst with a second aqueous silver impregnation solution comprising silver ions, an aminic complexing agent selected from amines, alkanolamines and amino acids, and one or more transition metal promoters, in particular rhenium; and iv) converting at least part of the silver ions impregnated on the intermediate catalyst to metallic silver by heating while directing a stream of a second gas over the impregnated intermediate catalyst to obtain the epoxidation catalyst, wherein the second gas comprises at most 2.0 vol.-% oxygen, wherein the impregnated refractory support and the impregnated intermediate catalyst are each heated to a temperature of 200 to 800° C. The process of the invention surprisingly allows for obtaining a catalyst with high selectivity in a cost-efficient manner. The invention also relates to a silver-based epoxidation catalyst obtainable by such a process, and to a process for producing an alkylene oxide by gas-phase oxidation of an alkylene, comprising reacting an alkylene and oxygen in the presence of a silver-based epoxidation catalyst obtainable by the above process.