Shaped Catalyst Bodies for Ethylene Oxide Production
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Solution Overview
Problem
Current catalysts for ethylene oxide production in gas-phase oxidation of ethylene face challenges in maintaining high activity and selectivity over time, often requiring increased temperatures which lead to deactivation, and struggle with optimizing productivity while preserving selectivity.
Innovation Solution
The process involves using shaped catalyst bodies with a high silver content (at least 20 wt.-%) supported on a refractory material, characterized by a uniform multilobed cross-section and specific geometric features such as passageways and a defined thickness to enhance diffusion pathways, reducing pressure drop and maintaining mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the temperature is increased to maintain catalyst activity, then the activity is improved, but the catalyst deactivation accelerates and selectivity decreases
Solution Approach 1:
The patent changes the physical-chemical parameters of the catalyst by incorporating specific promoters (alkali metals, alkaline earth metals, transition metals) and controlling the silver crystal structure (preferentially (100) facets) to maintain high activity at lower temperatures, thereby preventing deactivation while preserving selectivity
Solution Approach 2:
The patent creates a composite catalyst system combining silver with multiple promoter types (alkali metals like potassium, alkaline earth metals like calcium, and transition metals like rhenium) supported on refractory materials, where each component contributes specific functions to enhance activity-stability-selectivity balance
2Power
If the silver content is increased to improve activity, then the activity increases, but the selectivity decreases
Solution Approach 1:
The patent applies local quality by creating specific silver crystal facets (preferentially (100) orientation) and distributing promoters at specific locations and concentrations to optimize the catalytic function, where the structured silver surface provides high activity while the localized promoter distribution maintains selectivity
3Productivity
If the catalyst bed volume is increased to improve productivity, then the productivity increases, but the pressure drop increases
Solution Approach 1:
The patent segments the catalyst bed into multiple zones with different catalyst compositions and properties (e.g., different silver contents, different promoter distributions) along the reactor length, allowing optimized conversion in each zone while managing overall pressure drop through progressive resistance distribution
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 approach increases catalyst activity and stability, maintains or enhances selectivity, and allows for higher productivity by optimizing the geometric design of the catalyst bodies, leading to improved ethylene oxide yield and reduced deactivation rates.
Implementation Method 1
In the industrial oxidation of ethylene to ethylene oxide, heterogeneous catalysts comprising silver are used
Implementation Method 2
each shaped catalyst body is characterized by a longest direct diffusion pathway d, with 2d being in the range of 0.7 to 2.4 mm
Data Source
AI summary
A process for producing ethylene oxide by gas-phase oxidation of ethylene, comprising: directing a feed comprising gaseous ethylene and gaseous oxygen through a packing of individual shaped catalyst bodies, under conditions conducive to obtain a reaction mixture containing at least 2.7 vol.-% of ethylene oxide, wherein each shaped catalyst body comprises silver deposited on a refractory support and is characterized by a content of at least 20 wt.-% of silver, relative to the total weight of the shaped catalyst body; a BET surface area in the range of 1.6 to 3.0 m2/g; a first face side surface, a second face side surface and a circumferential surface with a plurality of passageways extending from the first face side surface to the second face side surface; and a uniform multilobed cross-section; and a longest direct diffusion pathway d, with 2d being in the range of 0.7 to 2.4 mm, wherein the longest diffusion pathway d is defined as the shortest distance from the geometric surface of the shaped catalyst body to a point inside the structure of the shaped catalyst body for which point the shortest distance is the largest among all points. The process allows for increased activity and/or stability of the catalyst while maintaining or increasing selectivity at high productivity.