Diaryl Carbonate Process Stream Segmentation
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Solution Overview
Problem
The integration of diaryl carbonate and dialkyl carbonate production processes is hindered by contamination of alkylene glycol with aromatic alcohol, leading to cumbersome purification and the need for additional distillation columns.
Innovation Solution
A process where an aromatic alcohol and dialkyl carbonate are passed into a first transesterification zone to produce a diaryl carbonate-rich stream, with subsequent separation and recycling of streams to avoid contamination, allowing for distillation of an alkanol stream and a contaminated dialkyl carbonate stream, which is then recycled, eliminating the need for an additional distillation column.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If phenol-contaminated dimethyl carbonate stream is recycled to extractive distillation, then material utilization is improved, but alkylene glycol product becomes contaminated with phenol
Solution Approach 1:
The process divides the recycling path into two separate streams: one for dimethyl carbonate and one for phenol. The extractive distillation column separates these components, allowing dimethyl carbonate to be recycled to the alkanediol production while phenol is diverted to the diaryl carbonate production. This segmentation prevents phenol contamination of the alkylene glycol product while maintaining material utilization.
2Manufacturing precision
If additional distillation column is added to purify phenol-contaminated stream, then product purity is improved, but device complexity increases
Solution Approach 1:
The extractive distillation column serves multiple functions: it purifies dimethyl carbonate for recycling to alkanediol production, separates phenol for recycling to diaryl carbonate production, and prevents phenol contamination of the alkylene glycol product. By making this single column multi-functional, the process achieves the purification needed without adding extra distillation columns, thus avoiding increased device complexity.
3Manufacturing precision
If phenol is removed from dimethyl carbonate stream before recycling, then product purity is improved, but loss of substance increases
Solution Approach 1:
Instead of treating phenol contamination as a problem to be eliminated through disposal or destruction, the process converts it into a beneficial resource. The phenol separated in the extractive distillation column is not discarded but is instead recycled to the diaryl carbonate production where it serves as a valuable reactant. This transforms the harmful contamination into a useful material flow, achieving both product purity and substance recovery.
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 ensures the purity of alkanediol products by preventing aromatic alcohol contamination in the second transesterification zone and allows for complete recycling of aromatic alcohol without additional distillation, reducing costs and operational complexity.
Implementation Method 1
a transesterification of dialkyl carbonate takes place whereby overall the diaryl carbonate is produced and as by-product alkanol is obtained
Implementation Method 2
Both the diphenyl carbonate stream and the stream comprising dimethyl carbonate and methanol contain phenol. The diphenyl carbonate stream is therefore subjected to distillation to yield purified diphenyl carbonate and phenol
Implementation Method 3
In the extractive distillation an extractant is being used. Examples of extractants are alkylene carbonates
Data Source
AI summary
Diaryl carbonate is prepared by reaction of an aromatic alcohol with a dialkyl carbonate, which dialkyl carbonate has been prepared by the reaction of an alkanol and an alkylene carbonate, which process comprises the following steps : (a) passing an aromatic alcohol and a dialkyl carbonate into a first transesterification zone to obtain a first product stream containing diaryl carbonate, alkanol, unconverted dialkyl carbonate and unconverted aromatic alcohol; (b) separating the first product stream into a diaryl carbonate-rich product stream, an aromatic alcohol-rich recycle stream and a second recycle stream comprising alkanol, dialkyl carbonate and aromatic alcohol; (c) feeding alkanol and alkylene carbonate into a second transesterification zone to obtain a second product stream comprising alkanediol and unconverted alkanol and dialkyl carbonate; (d) separating alkanediol from the second product stream to yield an alkanediol product stream and a mixture of dialkyl carbonate and unconverted alkanol; (e) subjecting the mixture of dialkyl carbonate and unconverted alkanol and the second recycle stream comprising alkanol, dialkyl carbonate and aromatic alcohol to the same distillation to obtain an alkanol stream as the lower-boiling fraction and a contaminated stream comprising dialkyl carbonate and aromatic alcohol as the higher-boiling fraction; (f ) recycling the alkanol stream of step e) to the second transesterification zone; and (g) passing the contaminated stream comprising dialkyl carbonate and aromatic alcohol, and the aromatic alcoholrich recycle stream to the first transesterification zone.