Continuous Polyether Polyol Production with DMC Catalysts
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Solution Overview
Problem
Double metal cyanide (DMC) catalysts used for polymerizing alkylene oxides face challenges such as deactivation in high hydroxyl group concentrations, leading to inefficient production of low equivalent weight polyols and the formation of ultra high molecular weight 'tails' that complicate foaming processes.
Innovation Solution
A continuous process involving a double metal cyanide catalyst, where an initiator and alkylene oxide are fed to a reactor maintained at temperatures above 150°C with controlled unreacted alkylene oxide and hydroxyl content, followed by non-isothermal reaction to reduce residual alkylene oxide to 0.5% or less, producing polyether polyols with hydroxyl content between 3.4% to 20% and minimizing ultra high molecular weight material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If DMC catalysts are used to polymerize alkylene oxide in high hydroxyl group concentrations, then polydispersity is reduced, but the catalyst deactivates and productivity decreases
Solution Approach 1:
The patent changes the temperature parameter to above 150°C, which fundamentally alters the reaction kinetics and catalyst behavior. This temperature change prevents catalyst deactivation in high hydroxyl environments while maintaining low polydispersity, resolving the contradiction between composition stability and productivity.
Solution Approach 2:
The patent performs preliminary alkoxylation of the initiator before the main polymerization reaction. This preliminary action reduces the initial hydroxyl group concentration that would otherwise cause catalyst deactivation, enabling efficient continuous production while maintaining the polydispersity benefits of DMC catalysts.
2Stability of the object's composition
If DMC catalysts are used in continuous polymerization, then polydispersity is reduced, but ultra high molecular weight tails form that complicate foaming processes
Solution Approach 1:
The patent employs temperature above 150°C and controlled residence time in a continuous reactor to prevent the formation of ultra high molecular weight tails. These parameter changes maintain the polydispersity advantage while eliminating the harmful high molecular weight byproducts that complicate foaming processes.
Solution Approach 2:
The patent uses continuous polymerization with controlled residence time distribution, which prevents the prolonged exposure to reaction conditions that lead to ultra high molecular weight tail formation. The continuous process maintains narrow polydispersity while avoiding the harmful side products.
3Quantity of substance
If alkali metal hydroxide catalysts are used instead of DMC catalysts, then low equivalent weight polyols can be produced, but monofunctional initiators form as impurities and production costs increase
Solution Approach 1:
The patent uses temperature above 150°C with DMC catalysts to achieve reaction rates and conversions comparable to alkali metal hydroxide catalysts. This enables production of low equivalent weight polyols (85-500) without forming monofunctional initiator impurities, as DMC catalysts do not promote the rearrangement reactions that produce harmful byproducts.
4Productivity
If a single-stage continuous process is used with DMC catalysts, then production efficiency is improved, but catalyst deactivation occurs in high hydroxyl environments
Solution Approach 1:
The patent uses temperature above 150°C in a single-stage continuous process, which fundamentally changes the catalyst stability profile. At this elevated temperature, the DMC catalyst remains stable and active even in high hydroxyl group concentrations, enabling efficient one-stage production without catalyst deactivation.
Solution Approach 2:
The patent performs preliminary alkoxylation of the initiator to reduce initial hydroxyl concentration, which prevents catalyst deactivation during the main polymerization reaction. This preliminary action enables reliable continuous production with DMC catalysts in a single stage.
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 efficiently produces polyether polyols with a wide range of hydroxyl equivalent weights, overcoming catalyst deactivation and reducing ultra high molecular weight 'tails', allowing for cost-effective production and suitable polyurethane foam formulations.
Implementation Method 1
double metal cyanide catalysts are increasingly being used to polymerize propylene oxide to produce polyether polyols
Implementation Method 2
the continuous reactor is maintained at a polymerization temperature in excess of 150° C.
Implementation Method 3
the partially polymerized mixture withdrawn from the reactor in step a) is permitted to further react non-isothermally until the unreacted alkylene oxide content of the mixture is reduced to 0.5% or less by weight
Data Source
AI summary
Polyether polyols having equivalent weights of up to 500 are continuously prepared in the presence of a double metal cyanide catalyst. A first step of the reaction is performed at a temperature of at least 150° C., while controlling the hydroxyl content and unreacted alkylene oxide content of the reaction mixture to within certain ranges. A portion of that reaction mixture is withdrawn and permitted to react non-isothermally to consume the unreacted alkylene oxide. This process is highly efficient, does not result in catalyst deactivation, as is commonly seen in previous processes, and does not produce a significant ultra high molecular weight tail.