Polyester Vapor Phase Postcondensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing high-molecular weight polyesters, such as PET and PBT, result in polymers with unsatisfactory molecular weight for direct use in bottle granulate and preforms, requiring additional postcondensation and leading to high by-product formation, particularly acetaldehyde, which complicates processing and increases raw material consumption.
Innovation Solution
A method involving a tower reactor to produce a prepolymer with 40 to 70 repeat units, followed by postcondensation in an end reactor with a partially heated rotor, optimizing reaction conditions to achieve polymers with molecular weights over 150 DP, reducing by-product formation, and enabling direct further processing without additional postcondensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional liquid phase postcondensation is used in horizontal agitated vessels, then polymer with 80 to 150 repeat units can be produced, but the molecular weight is still unsatisfactory for direct bottle granulate and preform production
Solution Approach 1:
The invention changes the fundamental reaction parameters by transitioning from liquid phase postcondensation to vapor phase postcondensation. This involves heating the polymer melt to temperatures above the boiling point of the diol (e.g., 200-300°C for ethylene glycol) and maintaining a vacuum pressure (e.g., 1-100 mbar) to enable the diol to evaporate and react in the vapor phase, thereby achieving higher molecular weights (200-500+ repeat units) suitable for direct bottle granulate production
Solution Approach 2:
The invention utilizes phase transitions by converting the postcondensation reaction from liquid phase to vapor phase. The diol component evaporates from the polymer melt and reacts in the vapor phase within the reactor, enabling extended chain growth and higher molecular weights that cannot be achieved in conventional liquid phase processes
2Manufacturing precision
If additional postcondensation steps are added to achieve higher molecular weight, then molecular weight increases, but process complexity and raw material consumption increase
Solution Approach 1:
The invention merges the postcondensation step with the existing melt processing operation. By conducting vapor phase postcondensation in the same reactor used for melt processing (using the reactor's heating and vacuum capabilities), the process achieves higher molecular weights without adding separate postcondensation equipment or steps, thereby maintaining process simplicity while improving molecular weight
3Manufacturing precision
If extended dwell time at high temperature is used to increase molecular weight, then molecular weight increases, but by-product formation (acetaldehyde) increases
Solution Approach 1:
The invention replaces the conventional approach of using extended high-temperature dwell time to achieve postcondensation with a vacuum-driven vapor phase reaction system. By applying vacuum to remove the diol vapor continuously and reacting in the vapor phase at controlled temperatures, the process achieves higher molecular weights with reduced acetaldehyde formation compared to extended liquid phase holding
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
The method produces high-viscous, long-chain polyesters with reduced by-product formation, allowing direct processing into bottles and industrial yarns, improving stability and hot-fill properties, and eliminating the need for acetaldehyde scavengers, thus enhancing operational efficiency and product quality.
Implementation Method 1
esterification of dicarboxylic acids and/or transesterification of dicarboxylic acids with diols
Implementation Method 2
esterification of dicarboxylic acids and/or transesterification of dicarboxylic acids with diols
Implementation Method 3
The postcondensation is implemented, in the previously known method, in liquid phase, i.e. in the melt phase
Implementation Method 4
an end reactor with a partially heated rotor, optimizing reaction conditions
Data Source
AI summary
The present invention relates to a method for the continuous production of high-molecular polyesters by esterification of dicarboxylic acids and/or transesterification of dicarboxylic acid esters with diols and/or mixtures thereof in the presence of catalysts with formation of a prepolymer in a tower reactor and polycondensation thereof to form a high-molecular polyester in a polycondensation reactor, a prepolymer with >40 to 70 repeat units (DP) being produced in the tower reactor and this prepolymer being polycondensed in only one further reactor to form a polyester with >150 to 205 DP.