Propylene Oxide Refining via Dual Azeotropic Rectification
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Solution Overview
Problem
The existing processes for refining crude propylene oxide products suffer from low purity due to the formation of azeotropes between methanol and propylene oxide, leading to impaired separation and increased complexity in the separation process.
Innovation Solution
A process involving two azeotropic rectification columns is employed, where the first column separates a majority of methanol from the crude product, and the second column separates a high-purity propylene oxide by adjusting the azeotropic conditions to achieve different azeotropic compositions, allowing for the recycling of the azeotrope to improve the separation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If azeotropic rectification is used to separate methanol and propylene oxide, then separation is achieved, but the product purity is limited due to azeotrope formation
Solution Approach 1:
The separation process is divided into two distinct stages: first azeotropic rectification to remove most methanol, then extractive rectification with glycerol to achieve high purity propylene oxide. This segmentation allows each stage to target specific separation needs, overcoming the limitation of single-stage azeotropic distillation.
Solution Approach 2:
Glycerol is introduced as an intermediary substance in the extractive rectification column. It selectively interacts with methanol through hydrogen bonding, changing the relative volatility relationship and enabling separation of the azeotropic mixture to achieve propylene oxide purity above 99.8%.
2Manufacturing precision
If extractive rectification with glycerol is employed, then propylene oxide purity exceeds 99.8%, but the process complexity increases
Solution Approach 1:
The glycerol used in extractive rectification is recovered from the bottom product through a dedicated recovery column and recycled back to the extractive rectification column. This self-service mechanism eliminates the need for continuous glycerol addition, reduces operational complexity, and improves process sustainability.
Solution Approach 2:
Instead of discarding the glycerol-containing bottom product from the extractive rectification column, the process recovers and purifies the glycerol through a separate recovery column. The recovered glycerol is then reused, transforming a waste stream into a valuable recycled material and simplifying overall material balance.
3Productivity
If multiple rectification columns are used in series, then separation efficiency improves, but the reaction time and device cost increase
Solution Approach 1:
The process changes the separation mechanism from pure azeotropic distillation to extractive distillation using glycerol as a selective solvent. This parameter change in the separation method allows for faster and more efficient separation in a single column, reducing the need for multiple sequential columns and decreasing overall processing time.
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 increases the purity of propylene oxide to over 95% by utilizing the differences in azeotropic compositions, simplifying the separation process and improving the overall efficiency of the propylene oxide production.
Implementation Method 1
in a first azeotropic rectification condition, a crude propylene oxide product is fed to a first azeotropic rectification column to conduct an azeotropic rectification, wherein a majority of propylene oxide and a part of methanol in a stream fed to the first azeotropic rectification column are discharged from the column top in an azeotrope form
Implementation Method 2
in a second azeotropic rectification condition, an azeotrope discharged from the column top of the first azeotropic rectification column is fed to a second azeotropic rectification column to conduct an azeotropic rectification, wherein a majority of methanol and a part of propylene oxide in a mixture fed to the second azeotropic rectification column are discharged from the column top of the second azeotropic rectification column in an azeotrope form
Implementation Method 3
the azeotrope discharged from the column top of the second azeotropic rectification column is partly or totally returned to the first azeotropic rectification column used in the step (1) to conduct an azeotropic rectification together with the crude propylene oxide product
Data Source
Figure 1
AI summary
A refining method for crude propylene oxide product and a preparation method for propylene oxide comprising the refining method. According to the refining method: a crude propylene oxide product is introduced into a first azeotropic distillation column and undergoes azeotropic distillation, the conditions of the first azeotropic distillation allowing most of the propylene oxide and part of the methanol from the material introduced into the first azeotropic distillation column to be collected in the form of an azeotrope from the top of the column, and allowing the remaining methanol and a small amount of the propylene oxide to be collected from the bottom of the column, the propylene oxide in the effluent from the bottom of the first azeotropic distillation column not exceeding 5% by weight; the azeotrope collected from the top of the first azeotropic distillation column is introduced into a second azeotropic distillation column and undergoes azeotropic distillation, the conditions of the second azeotropic distillation allowing most of the methanol and part of the propylene oxide from the compositions introduced into the second azeotropic distillation column to be collected in the form of an azeotrope from the top of the column, and allowing the remaining propylene oxide and a small amount of methanol to be collected from the bottom of the column, the methanol in the effluent from the bottom of the second azeotropic distillation column not exceeding 5% by weight; the azeotrope collected from the top of the second azeotropic distillation column is returned to the first azeotropic distillation column and undergoes azeotropic distillation with the crude propylene oxide product.