Polycarbonate Polyol Purification via Evaporation and Stripping
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Solution Overview
Problem
Current processes for producing polycarbonate polyols result in unwanted side reactions that produce cyclic alkylene carbonates, which are difficult to completely remove, leading to residual impurities in the final product.
Innovation Solution
A two-stage purification process involving an evaporation unit and a stripping column, operated at reduced pressure and temperature, effectively removes cyclic alkylene carbonates with a combination of evaporation and stripping, utilizing an inert gas to further purify the polycarbonate polyols, and includes features like recycling and heating to maintain product integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional separation processes are used to remove cyclic alkylene carbonates, then the purification process is simple, but the residual impurity content remains above 1% and cannot be reduced below 1%
Solution Approach 1:
The purification process is divided into two distinct stages: a first purification stage using vacuum stripping to remove the majority of cyclic alkylene carbonate impurities, followed by a second purification stage using azeotropic distillation to remove residual impurities. This segmentation allows each stage to be optimized for its specific function, achieving overall high purification performance that reduces impurity content below 1%.
2Manufacturing precision
If high temperature and long duration vacuum stripping is used to remove cyclic alkylene carbonates, then the purification performance improves, but the thermal stress on polycarbonate polyols increases and apparatus construction becomes more complex
Solution Approach 1:
The purification process is divided into two distinct stages: a first purification stage using vacuum stripping to remove the majority of cyclic alkylene carbonate impurities, followed by a second purification stage using azeotropic distillation to remove residual impurities. This segmentation allows each stage to be optimized for its specific function, achieving overall high purification performance that reduces impurity content below 1%.
Solution Approach 2:
The process employs different temperature and pressure parameters for each purification stage. The first stage uses vacuum stripping at reduced pressure and moderate temperature, while the second stage uses azeotropic distillation with specific temperature control. This parameter optimization removes impurities effectively while minimizing thermal stress on the polycarbonate polyols.
3Manufacturing precision
If a single-stage purification process is used, then the apparatus construction is simple, but the purification performance is insufficient to reduce cyclic alkylene carbonate content below 1%
Solution Approach 1:
The purification process is divided into two distinct stages: a first purification stage using vacuum stripping to remove the majority of cyclic alkylene carbonate impurities, followed by a second purification stage using azeotropic distillation to remove residual impurities. This segmentation allows each stage to be optimized for its specific function, achieving overall high purification performance that reduces impurity content below 1%.
Solution Approach 2:
The apparatus is designed with multi-functional components that can serve both purification stages. The system includes a vacuum source that can operate at different pressure levels, heating systems that can maintain different temperature profiles, and collection systems that handle both stages. This multi-functionality reduces overall apparatus complexity despite the two-stage process.
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 significantly reduces the concentration of cyclic alkylene carbonates to below 100 ppm, achieving high purification performance with a simplified apparatus design and minimal thermal stress on the polycarbonate polyols.
Implementation Method 1
in the evaporation unit (1) converting a portion of the impurities to the gas phase and removing the gaseous impurities via a gas outlet line (12)
Implementation Method 2
removing a further portion of the impurities from the partly purified polycarbonate polyol by means of stripping in countercurrent by an inert gas stream
Implementation Method 3
comprising an evaporation unit provided with a heater
Data Source
AI summary
The present invention relates to a purifying apparatus for polycarbonate polyols, especially for removal of cyclic alkylene carbonates, comprising an evaporation unit (1) provided with a heater (10) and having an inlet (6) disposed at the top end thereof and a bottoms vessel (11), and a stripping column (2) connected downstream of the evaporation unit (1) and having a top (21) and a bottom (23), wherein a feed (5) for the polycarbonate polyol to be purified opens into the inlet (6) to the evaporation unit (1) and a gas outlet line (12) and a connecting line which opens into the top (21) of the stripping column (2) and is equipped with a pump (18) depart from the evaporation unit (1), and wherein a gas inlet line (24) for an inert gas opens into the bottom (23) of the stripping column (2) and a product line (27) for the purified polycarbonate polyol departs from the bottom (23) of the stripping column (2) and a gas outlet line (25) departs from the top (21) of the stripping column (2). The invention additionally relates to a process for purifying polycarbonate polyols with such a purifying apparatus.