Ethylene Oxide Catalyst Initiation via High CO2 Feed
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Solution Overview
Problem
The start-up process for highly selective silver-based catalysts, especially those containing rhenium, requires a special procedure to achieve optimal performance, and existing methods involve high-temperature activation for extended periods, which is inefficient and not fully productive during the activation phase.
Innovation Solution
The process involves operating the catalyst as a standard silver-based catalyst with a feed gas composition containing greater than 10 vol% carbon dioxide, ethylene, oxygen, and a moderator at temperatures between 180°C to 220°C, followed by adjusting the temperature and gas composition to achieve desired ethylene oxide production and selectivity, with the carbon dioxide concentration being reduced to maintain optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature activation is used for extended periods to initiate rhenium-containing Ag-based catalysts, then the catalyst achieves expected performance, but the activation time and energy consumption increase significantly
Solution Approach 1:
The patent applies preliminary action by pre-chlorinating the catalyst with ethyl chloride before introducing oxygen. This preliminary chlorination step prepares the catalyst surface in advance, creating the necessary chemical environment for high selectivity operation. The catalyst is pre-treated with a feed containing ethylene, methane and ethyl chloride to establish the proper surface chemistry before the main reaction begins, thereby reducing the extended high-temperature activation period required by conventional methods.
2Ease of operation
If pre-chloriding with ethyl chloride is performed before oxygen introduction, then catalyst activity is enhanced and startup temperature is reduced, but the process complexity increases
Solution Approach 1:
The patent merges the pre-chloriding step with the standard startup procedure by using ethyl chloride that is already present in the normal feed composition. Instead of requiring a separate pre-treatment step with pure ethyl chloride, the method combines the chlorination function with the regular reaction feed, thereby reducing process complexity while maintaining the benefit of enhanced catalyst activity and lower startup temperatures.
Solution Approach 2:
The feed gas mixture serves multiple functions simultaneously: it provides ethylene as substrate, oxygen as oxidant, ethyl chloride as chlorinating agent for catalyst activation, and acts as the reaction medium. This multi-functionality eliminates the need for separate pre-chloriding equipment and procedures, simplifying the overall process while achieving the desired catalyst activation.
3Productivity
If the catalyst is operated as a standard Ag-based catalyst during activation, then the activation efficiency increases, but the selectivity for ethylene oxide production decreases compared to high-selectivity catalysts
Solution Approach 1:
The patent applies parameter changes by adjusting the feed composition parameters during activation, specifically maintaining higher concentrations of ethyl chloride and operating at optimized temperature ranges. These parameter adjustments enable the catalyst to achieve both high activation efficiency and acceptable selectivity. The feed composition is carefully controlled to balance the competing requirements of catalyst activation and ethylene oxide production during the startup phase.
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 method allows the catalyst to operate at a higher work rate with selectivity ranging from 80% to 84%, producing 50 to 350 Kg of ethylene oxide per m³ of catalyst per hour, and stabilizes performance similar to a standard catalyst, improving efficiency and productivity during the activation phase.
Implementation Method 1
In the catalytic oxidation of ethylene to ethylene oxide, the start-up operation of a highly selective Ag-based catalyst requires a special procedure
Implementation Method 2
the concentration of carbon dioxide in the feed is greater than 10 vol.% during the activation period
Implementation Method 3
In the catalytic oxidation of ethylene to ethylene oxide
Data Source
AI summary
A process for initiating a highly selective ethylene oxide catalyst is provided in which the highly selective ethylene oxide catalyst is operated first as a 'standard' Ag-based catalyst (e.g., a catalyst that contains only silver and alkali metal, especially cesium). Moreover, the inventive initiation procedure is more efficient when the concentration of carbon dioxide in the feed is higher than 6 vol. %, and even more efficient when the concentration of carbon dioxide in the feed is higher than 10 vol. %, of the feed mixture during the initiation period.