Low Molecular Weight Polyether Production via Acidified Starter and High Temperature
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Solution Overview
Problem
Double metal cyanide catalysts used in polyoxyalkylene polyol production face issues such as deactivation in the presence of high hydroxyl groups, inability to polymerize with low molecular weight initiators like glycerin, and the production of high molecular weight polymers that cause foaming difficulties in polyurethane foam synthesis.
Innovation Solution
A continuous process maintaining high temperatures (at least 135°C) during oxyalkylation with a double metal cyanide catalyst, using low molecular weight starters with specific molecular weights and acidification to prevent catalyst deactivation, and controlling unreacted alkylene oxide concentrations to optimize polyether polyol production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If double metal cyanide catalysts are used to polymerize alkylene oxide, then low unsaturation and low polydispersity are achieved, but catalyst deactivation occurs in the presence of high concentrations of hydroxyl groups
Solution Approach 1:
The low molecular weight starter is acidified before introduction into the reactor, performing the protective action in advance. This preliminary acidification prevents catalyst deactivation when the hydroxyl-containing starter is introduced, allowing the catalyst to maintain activity throughout the polymerization process.
Solution Approach 2:
An acid substance acts as an intermediary between the hydroxyl groups and the catalyst. The acid protonates the hydroxyl groups, creating a protective effect that prevents direct interaction between the hydroxyl groups and the catalyst sites, thereby preventing deactivation.
2Manufacturing precision
If double metal cyanide catalysts are used for polymerization, then low molecular weight polyols are produced, but high molecular weight polymer tail is generated causing foaming difficulties
Solution Approach 1:
The reaction parameters are optimized by controlling the alkylene oxide to starter ratio, temperature, and residence time. These parameter adjustments ensure that polymerization occurs primarily at the desired low molecular weight range while minimizing the formation of high molecular weight tails that would cause foaming difficulties.
3Quantity of substance
If low molecular weight starters like glycerin are used, then low molecular weight polyols are produced, but catalyst deactivation is accelerated
Solution Approach 1:
The low molecular weight starter is acidified before introduction into the reactor, performing the protective action in advance. This preliminary acidification prevents catalyst deactivation when the hydroxyl-containing starter is introduced, allowing the catalyst to maintain activity throughout the polymerization process.
Solution Approach 2:
An acid substance acts as an intermediary between the hydroxyl groups and the catalyst. The acid protonates the hydroxyl groups, creating a protective effect that prevents direct interaction between the hydroxyl groups and the catalyst sites, thereby preventing deactivation.
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 efficiently produces low molecular weight polyoxyalkylene polyether polyols with controlled hydroxyl content, preventing catalyst deactivation and minimizing high molecular weight polymer formation, thus enabling sustainable and efficient production for polyurethane applications.
Implementation Method 1
The continuous process polymerizes an alkylene oxide with a starter compound in the presence of a double metal cyanide catalyst
Implementation Method 2
said oxyalkylation in the continuous oxyalkylation reactor occurs at a sufficiently high temperature (preferably at least at 135° C., and more preferably at least 140° C.) to prevent deactivation of the DMC catalyst
Data Source
AI summary
This invention relates to an improved continuous process for the production of low molecular weight polyoxyalkylene polyether polyols. These polyoxyalkylene polyether polyols have a hydroxyl content of from about 3.4 to about 12.1% by weight, and may also be characterized as having an OH number of from about 112 to about 400. The process comprises establishing oxyalkylation conditions in a continuous reactor in the presence of a DMC catalyst; continuously introducing alkylene oxide and a low molecular weight starter into the continuous reactor; recovering a partially oxyalkylated polyether polyol from the reactor; and allowing the recovered partially oxyalkylated polyether polyol to further reactor until the unreacted alkylene oxide content of the mixture is reduced to 0.001% or less by weight.