Guard Bed System for Ethylene Oxide Reactor Iodide Removal
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Solution Overview
Problem
The formation of gaseous iodide impurities in the recycle gas stream during the production of ethylene oxide, ethylene carbonate, and ethylene glycol poses a challenge as these impurities poison the silver-based epoxidation catalyst, reducing its selectivity and activity and shortening its lifespan, necessitating the development of a process that minimizes iodide compound formation.
Innovation Solution
A process that involves a guard bed system with silver on alumina to treat the recycle gas stream, controlling ethane levels and the I-factor of chloride moderator species to maintain low levels of alkyl iodides and vinyl iodides, ensuring the epoxidation catalyst's performance is maintained by minimizing iodide impurities, and using a vinyl chloride moderator to prevent the formation of methyl and ethyl iodides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a guard bed system is used to remove iodide impurities from the recycle gas stream, then the epoxidation catalyst performance is protected, but the device complexity and operating costs increase
Solution Approach 1:
The harmful iodide impurities are extracted and removed from the recycle gas stream by passing it through a guard bed system containing adsorbent material. This separates the poison substances from the valuable recycle gas, protecting the downstream epoxidation catalyst while allowing the cleaned gas to be reused in the ethylene oxide reactor.
Solution Approach 2:
The guard bed system acts as an intermediary component positioned between the recycle gas stream and the epoxidation catalyst. This intermediate stage captures and retains iodide impurities, preventing them from reaching and poisoning the catalyst, thus serving as a protective barrier that extends catalyst life.
2Duration of action of stationary object
If the recycle gas stream is treated to remove iodide impurities, then catalyst lifespan is extended, but the volume of guard bed adsorbent required increases process complexity
Solution Approach 1:
The effectiveness of the guard bed system is optimized by adjusting parameters such as adsorbent material type, bed temperature, and gas flow rate. These parameter changes enhance the adsorption capacity and kinetics, allowing for more efficient iodide removal with potentially smaller adsorbent volumes, thus extending catalyst life without proportionally increasing guard bed size.
3Object-generated harmful factors
If ethane levels are controlled in the epoxidation feed stream, then alkyl iodide formation is minimized, but the precision of ethane control requires sophisticated monitoring systems
Solution Approach 1:
A feedback control system is implemented to monitor and adjust ethane levels in the epoxidation feed stream. By continuously measuring the ethane concentration and comparing it to target values, the system automatically adjusts process parameters to maintain optimal ethane levels, thereby minimizing alkyl iodide formation while adapting to changing process conditions.
Solution Approach 2:
Traditional mechanical control methods for ethane level regulation are replaced with advanced analytical detection and automated control systems. This substitution enables more precise and responsive monitoring of ethane concentrations, allowing for better minimization of harmful alkyl iodide formation through real-time data-driven adjustments.
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 effectively reduces alkyl iodide and vinyl iodide levels in the recycle gas stream to very low concentrations, thereby extending the catalyst's life and maintaining high ethylene conversion yields, reducing the need for frequent catalyst replacement and minimizing the volume of guard bed adsorbent required.
Implementation Method 1
contacting at least a portion of a recycle gas stream comprising an alkyl iodide impurity with a guard bed system positioned upstream of an ethylene oxide reactor to produce a treated recycle gas stream, wherein said guard bed system comprises a guard bed material comprising silver on alumina
Implementation Method 2
using a vinyl chloride moderator to prevent the formation of methyl and ethyl iodides
Implementation Method 3
contacting an epoxidation feed stream comprising an ethylene feed stream, oxygen, chloride moderator, and at least a portion of the treated recycle gas stream with an epoxidation catalyst in the ethylene oxide reactor to produce an epoxidation reaction product comprising ethylene oxide
Data Source
Figure 1
AI summary
The present application relates to a process for producing ethylene glycol and/or ethylene carbonate, said process comprising contacting at least a portion of a recycle gas stream comprising an alkyl iodide impurity with a guard bed system positioned upstream of an ethylene oxide reactor to produce a treated recycle gas stream, wherein said guard bed system comprises a guard bed material comprising silver on alumina; contacting an epoxidation feed stream comprising an ethylene feed stream, oxygen, chloride moderator, and at least a portion of the treated recycle gas stream with an epoxidation catalyst in the ethylene oxide reactor to produce an epoxidation reaction product comprising ethylene oxide; and contacting at least a portion of the epoxidation reaction product comprising ethylene oxide with a liquid absorbent in the presence of an iodide-containing catalyst in an absorber to produce a product stream comprising ethylene carbonate and/or ethylene glycol and the recycle gas stream comprising the alkyl iodide impurity, wherein the epoxidation feed stream comprising ethylene feed stream, oxygen, moderator compound, and treated recycle gas stream contacted with the epoxidation catalyst in the ethylene oxide reactor comprises no more than 8000 ppmv of ethane, and wherein a vinyl chloride moderator is added to the epoxidation feed stream, wherein the concentration of vinyl chloride moderator added to the epoxidation feed stream is controlled such that the I-factor representing the relative quantity of chloride moderator species present in the epoxidation feed stream, defined as I factor = ([vinyl chloride] + [ethyl chloride ]+ [methyl chloride] / 3 ) / ( [ethylene] +70* [ethane] ) is in the range of 0.02-0.4.