Propene Oxide Distillation pH Control
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Solution Overview
Problem
Propene oxide produced by epoxidation of propene with hydrogen peroxide in the presence of a titanium zeolite catalyst, when neutralized with ammonia, may contain nitrogen compounds that cause quality issues when further processed into polyether polyols or polyurethanes due to the formation of byproducts like 1,2-propanediol, 1-methoxy-2-propanol, and 2-methoxy-1-propanol.
Innovation Solution
A process involving the reaction of propene with hydrogen peroxide in the presence of a titanium zeolite catalyst and a nitrogen-containing compound, followed by separation of non-reacted propene, and subsequent continuous distillation with an acid added to adjust the pH of the bottoms product stream to 3-4.5, reducing nitrogen compound entrainment in the overhead product stream and minimizing propene oxide hydrolysis and solvolysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ammonia is added to neutralize the titanium zeolite catalyst, then selectivity for propene oxide is improved, but nitrogen compounds are introduced which cause quality problems in downstream products
Solution Approach 1:
The patent applies preliminary action by adding acid to the distillation system before the nitrogen-containing compounds can be entrained into the overhead product stream. The acid is introduced into the distillation column at a point below the feed point, creating a treatment zone that neutralizes or removes nitrogen compounds (such as ammonia or amines) before they can contaminate the propene oxide product. This preliminary treatment prevents the harmful effect while maintaining the beneficial neutralization of the catalyst.
Solution Approach 2:
The patent uses acid as an intermediary substance in the distillation process. The acid acts as a mediator that interacts with nitrogen-containing compounds in the bottoms product stream, converting them or preventing their vaporization. This intermediary approach allows the system to maintain catalyst neutralization benefits while eliminating nitrogen compound contamination in the final product through the distillation separation process.
2Quantity of substance
If distillation is performed to separate propene oxide from the reaction mixture, then propene oxide is recovered, but nitrogen containing compounds can be entrained in the overhead product stream
Solution Approach 1:
The patent introduces acid as an intermediary substance into the distillation column that selectively interacts with nitrogen-containing compounds. This intermediary creates a chemical environment in the lower section of the column that prevents nitrogen compounds from vaporizing and entering the overhead product stream, while allowing propene oxide to be effectively separated and recovered in the distillate.
Solution Approach 2:
The patent changes the chemical parameters of the distillation system by introducing acid, which alters the vapor-liquid equilibrium and chemical composition in different sections of the column. This parameter change creates a pH gradient or chemical environment that suppresses the volatility or stability of nitrogen-containing compounds in the bottoms section, preventing their entrainment in the overhead stream while maintaining efficient propene oxide separation.
3Object-generated harmful factors
If pH is lowered to reduce nitrogen compound entrainment, then nitrogen content in product is reduced, but propene oxide hydrolysis and solvolysis increase
Solution Approach 1:
The patent segments the distillation column into different functional zones with different pH conditions. The lower section contains acid to suppress nitrogen compound volatility and prevent entrainment, while the upper section maintains conditions favorable for propene oxide recovery. This spatial segmentation allows the system to simultaneously achieve low nitrogen content in the product while minimizing hydrolysis and solvolysis losses through proper zone design and operation.
Solution Approach 2:
The patent applies local quality by creating a localized acidic environment in the lower section of the distillation column where nitrogen compounds are present, while maintaining different conditions in the upper section where propene oxide is recovered. This localized acid treatment selectively addresses the nitrogen compound problem without subjecting the entire system to low pH conditions that would cause widespread hydrolysis and solvolysis of propene oxide.
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 the nitrogen content in propene oxide, preventing quality issues in downstream products and maintaining high purity and yield of propene oxide.
Implementation Method 1
reacting propene with hydrogen peroxide in the presence of a titanium zeolite epoxidation catalyst
Implementation Method 2
subjecting the propene depleted reaction mixture of step b) to a distillation in a distillation column providing an overhead product stream comprising propene oxide and methanol and a bottoms product stream comprising methanol and water
Implementation Method 3
maintaining a low propene oxide hydrolysis and solvolysis in the distillation column
Data Source
AI summary
In the process for making propene oxide, propene is reacted with hydrogen peroxide in the presence of methanol, of a titanium zeolite epoxidation catalyst and of nitrogen containing compounds present in an amount of from 100 to 3000 mg/kg of hydrogen peroxide; non-reacted propene is separated from the reaction mixture; the propene depleted reaction mixture is continuously distilled in a distillation column providing an overhead product stream comprising propene oxide and methanol and a bottoms product stream; and propene oxide is separated from the overhead product stream. An acid is added to the propene depleted reaction mixture and/or to the distillation column at the same level or above the feed point for the propene depleted reaction mixture and/or contacted to the feed to the distillation column to provide an apparent pH in the bottoms product stream of from 3 to 4.5, which reduces the nitrogen content of the separated propene oxide.