Ethylene Oxide Quench Bleed Stripping for Formaldehyde Reduction
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Solution Overview
Problem
The recovery of ethylene oxide from ethylene oxide reactor effluents often results in a dilute solution with significant impurities like formaldehyde, which complicates the production of high-purity ethylene glycol and increases operating costs due to the need for additional treatment steps and costly chemical usage.
Innovation Solution
Introducing carbon dioxide vapor into the stripping steam of the quench bleed stripper to maintain a minimum 0.07 bar CO2 partial pressure, lowering the pH below 8.0 and reducing methylene glycol decomposition, thereby minimizing formaldehyde production and simplifying the process while reducing chemical costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional absorption/stripping systems are used to recover ethylene oxide from reactor effluent, then ethylene oxide can be recovered, but the resulting stream contains significant formaldehyde impurities that complicate further processing
Solution Approach 1:
The patent applies preliminary action by introducing carbon dioxide into the quench section before ethylene oxide absorption occurs. This pre-treatment step converts formaldehyde to methylene glycol and lowers the pH to suppress formaldehyde formation during subsequent absorption and stripping operations, preventing impurity accumulation before it becomes a problem
Solution Approach 2:
The patent changes the pH parameter of the quench liquid from conventional neutral to acidic range (pH 4-6) by adding carbon dioxide. This parameter change suppresses the decomposition of methylene glycol to formaldehyde and reduces formaldehyde formation during the absorption process, thereby improving the purity of recovered ethylene oxide
2Manufacturing precision
If additional treatment steps are added to improve ethylene oxide purity, then formaldehyde impurities can be reduced, but operating costs and process complexity increase
Solution Approach 1:
The patent extracts the pH control function from separate treatment steps and integrates it into the quench section by introducing carbon dioxide. This eliminates the need for additional neutralization columns or chemical treatment units, reducing process complexity while maintaining high ethylene oxide purity
Solution Approach 2:
The patent makes the quench liquid multi-functional by having it simultaneously absorb ethylene oxide, control pH through carbon dioxide introduction, and suppress formaldehyde formation. This consolidation of functions into a single step reduces the number of required treatment units and simplifies the overall process
3Reliability
If alkaline quench streams are used to neutralize acidic compounds, then acid neutralization is achieved, but chemical costs increase due to continuous caustic addition
Solution Approach 1:
The patent applies self-service by using carbon dioxide, a byproduct of the ethylene oxide reaction itself, to control pH in the quench section. This eliminates or reduces the need for external caustic chemicals, as the system uses its own reaction byproducts for pH control, thereby reducing chemical costs while maintaining effective acid neutralization
Solution Approach 2:
The patent converts carbon dioxide, which can be considered a waste gas byproduct, into a beneficial substance for pH control and formaldehyde suppression. By introducing this byproduct into the quench section, the system achieves acid neutralization and impurity suppression without requiring additional chemical inputs
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 effectively reduces formaldehyde impurities in the ethylene oxide stream, enhancing its purity and reducing operational complexity and chemical expenses, allowing for more efficient recovery and use in ethylene glycol production.
Implementation Method 1
Introducing carbon dioxide vapor into the stripping steam of the quench bleed stripper to maintain a minimum 0.07 bar CO2 partial pressure, lowering the pH below 8.0 and reducing methylene glycol decomposition
Implementation Method 2
introducing carbon dioxide vapor into the stripping steam
Implementation Method 3
the alkaline aqueous quench stream consists of mainly sodium bicarbonate buffered with dissolved CO2 (as carbonic acid) and has a pH in the range of 7.1-8.0
Implementation Method 4
absorption in process water, producing a very dilute EO solution
Implementation Method 5
ethylene oxide is then stripped from this dilute solution in a stripping column
Data Source
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AI summary
Ethylene oxide purification by quenching and washing ethylene oxide reactor effluent prior to passing the gaseous ethylene oxide-containing stream to an ethylene oxide absorber to form a dilute aqueous ethylene oxide and carbon dioxide solution and thereafter stripping that solution in an EO stripper to produce a gaseous ethylene oxide and carbon dioxide-containing overhead vapor which is then passed to a reabsorber wherein the ethylene oxide and part of the carbon dioxide vapors are absorbed to form an aqueous reabsorbate solution from which carbon dioxide is removed to produce an ethylene oxide-containing solution is improved by passing an impurities-containing liquid bleed stream obtained from the quench wash to a second, small quench bleed stripper where steam and carbon dioxide are added and gaseous overhead from that quench bleed stripper is passed to the reabsorber for recovery of the EO and removal of formaldehyde and other impurities.