Diaryl Carbonate Production via Distillation-Coupled Fixed Bed Reactors
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Solution Overview
Problem
Current processes for producing diphenyl carbonate involve energy-consuming and expensive methods to break azeotropic mixtures of dimethyl carbonate and methanol, limiting conversion efficiency due to the formation of azeotropes during separation.
Innovation Solution
A process utilizing a series of fixed bed reactors connected to a distillation column via side-draw and return streams, operating at different conditions than the column, to decouple reaction and separation requirements, allowing for 100% conversion of dialkyl carbonate to diaryl carbonate with minimal alcohol production as overheads and excess phenol as bottoms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dimethyl carbonate and methanol are separated by breaking the azeotropic mixture, then dimethyl carbonate can be recovered and recycled, but the process becomes energy consuming and expensive
Solution Approach 1:
The invention extracts and removes methanol from the reaction system through side-draw streams connected to distillation columns, preventing it from forming an azeotropic mixture with dimethyl carbonate. By continuously extracting the lighter component (methanol) at specific stages of the distillation column, the system avoids the need to break azeotropes, thereby reducing energy consumption while maintaining effective dimethyl carbonate recovery and recycling
Solution Approach 2:
The invention introduces an intermediary separation system (distillation column with side-draw) between the reaction and recycling processes. This intermediary system selectively separates methanol from the reaction mixture before it can form an azeotrope with dimethyl carbonate, allowing dimethyl carbonate to be recovered and recycled without the energy-intensive azeotrope breaking process
2Productivity
If continuous removal of lighter components is performed in two steps, then higher conversions to alkyl phenyl carbonate and diphenyl carbonate are achieved, but the process complexity increases
Solution Approach 1:
The invention merges multiple separation functions into a single integrated distillation column system with multiple side-draw streams. Instead of requiring separate distillation columns for each separation step, the system combines the removal of different lighter components (alkyl alcohol in the first step, dialkyl carbonate in the second step) within one column, achieving high conversion efficiency while reducing overall process complexity
Solution Approach 2:
The invention segments the distillation column into multiple functional zones with side-draw streams at different stages. The upper portion of the column handles the first separation step (removing alkyl alcohol), while the lower portion handles the second separation step (removing dialkyl carbonate). This segmentation allows each reaction step to proceed with continuous removal of its specific lighter component, maintaining high conversion efficiency
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 avoids the formation of azeotropes, achieving high conversion efficiency and cost-effectiveness by optimizing reaction conditions in each reactor stage, maximizing diaryl carbonate production while minimizing energy consumption.
Implementation Method 1
separating components by distillation
Implementation Method 2
the reaction rates are adequate in the temperature range set by the vapor-liquid equilibria of the distilling system
Implementation Method 3
contact the liquid with a transesterification catalyst under conditions conducive to transesterification
Implementation Method 4
contact the liquid with a disproportation catalyst under conditions conducive to disproportation
Data Source
AI summary
Diphenyl carbonate is produced by reacting phenol with diethyl carbonate in a series of fixed bed reactors each of which is connected at different position on a distillation column via side draw and return streams. The composition of material in a distillation column varies along the length of the column, which is predictable under a given set of conditions of temperature and pressure, thus withdrawing streams at different stages in the column, allows the reactor receiving the feed from a particular stage to be operated under conditions to maximize the desired reaction, while allowing the unreacted or byproduct to go back into the distillation and be sent to a stage (by the equilibrium of the distillation) where they are favorably treated in a reactor.