Alkanediol and Dialkyl Carbonate Process with Recycle Split
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Solution Overview
Problem
The existing process for preparing alkanediol and dialkyl carbonate from alkylene carbonate and alkanol results in the formation of high-boiling by-products like polyglycols, which are difficult to separate due to their similar boiling points with alkylene carbonate, and does not effectively address the presence of polyglycols in the feed material or unconverted alkylene carbonate in the reactor effluent.
Innovation Solution
A process involving transesterification of alkylene carbonate with alkanol, followed by separation of dialkyl carbonate and alkanol, with the recycle stream of unconverted alkylene carbonate being split into portions for recycling and hydrolysis to prevent polyglycol buildup and convert alkylene carbonate into alkanediol and carbon dioxide, facilitating easier separation of polyglycols from the hydrolysis stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transesterification process is carried out to convert alkylene carbonate and alkanol into dialkyl carbonate and alkanediol, then the production of target products is achieved, but high-boiling by-products such as polyglycols are formed and accumulate in the system
Solution Approach 1:
The patent extracts and removes polyglycols from the reaction system through a specific separation step. The bottom product stream containing polyglycols and unconverted alkylene carbonate is separated from the top product stream containing dialkyl carbonate and alkanol. This extraction of harmful by-products prevents their accumulation and allows the main transesterification process to continue efficiently.
Solution Approach 2:
The patent utilizes differences in boiling points and physical properties to separate polyglycols from other components. By controlling temperature and pressure parameters during distillation and extraction steps, the system selectively removes polyglycols while maintaining the desired target products. The parameter changes enable selective separation based on volatility and solubility differences.
2Productivity
If the bottom product stream containing polyglycols and unconverted alkylene carbonate is recycled to the reaction zone, then unconverted alkylene carbonate can be converted to dialkyl carbonate, but polyglycols accumulate and complicate separation
Solution Approach 1:
The patent segments the recycle stream into two separate streams: one containing polyglycols and unconverted alkylene carbonate, and another containing dialkyl carbonate and alkanol. This segmentation allows different fates for each component - the first stream is processed to remove polyglycols while the second stream is recovered as product. The segmentation simplifies the overall separation process by handling components separately rather than attempting to separate all components simultaneously.
3Productivity
If polyglycols are present in the alkylene carbonate feed material or in the reaction system, then the transesterification can proceed, but the similar boiling points of polyglycols and alkylene carbonate make separation very difficult
Solution Approach 1:
The patent introduces water as an intermediary substance to facilitate the separation of polyglycols from alkylene carbonate. Water forms a separate phase with polyglycols through hydrolysis, creating a liquid-liquid separation system. This intermediary enables separation based on immiscibility rather than relying solely on boiling point differences, making the separation process more feasible and practical.
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 prevents the accumulation of polyglycols, allows for the conversion of unconverted alkylene carbonate into valuable alkanediol, and simplifies the separation of polyglycols from alkylene carbonate, improving the efficiency and yield of target products.
Implementation Method 1
reacting an alkylene carbonate and an alkanol feedstock into a reaction zone under transesterification conditions to obtain a product mixture of dialkyl carbonate, unconverted alkanol, the alkanediol, and unconverted alkylene carbonate
Implementation Method 2
another portion is subjected to hydrolysis to yield alkanediol and carbon dioxide
Implementation Method 3
separating dialkyl carbonate and alkanol from the product mixture to obtain a bottom product stream containing alkanediol and unconverted alkylene carbonate
Data Source
AI summary
An alkanediol and a dialkyl carbonate are prepared in a process comprising: (a) reacting an alkylene carbonate and an alkanol feedstock into a reaction zone under transesterification conditions to obtain a product mixture of dialkyl carbonate, unconverted alkanol, the alkanediol, and unconverted alkylene carbonate; (b) separating dialkyl carbonate and unconverted alkanol from the product mixture to obtain a bottom product stream containing alkanediol and unconverted alkylene carbonate; (c) recovering the dialkyl carbonate; and (d) separating alkanediol from the bottom product stream to leave a recycle stream comprising unconverted alkylene carbonate, wherein the recycle stream comprising unconverted alkylene carbonate is split in at least two portions, and at least one portion is recycled to the reaction zone and another portion is subjected to hydrolysis to yield alkanediol and carbon dioxide.