Membrane Dialysis for Isocyanate Monomer Separation
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Solution Overview
Problem
Existing methods for reducing monomeric isocyanate content in isocyanate-containing prepolymers, used in aerosol-based foams and adhesives, are complex and costly, and distillation processes lead to thermal stress that alters crosslinking properties and viscosity, necessitating a new approach that avoids these limitations.
Innovation Solution
The process involves dissolving prepolymers in a solvent and using a permeable membrane with pore sizes between 5 to 400 nm to separate low molecular weight monomers, such as MDI, TDI, and HDI, through dialysis, which can be carried out under normal or elevated pressure, using solvents like ethers and ketones, and membranes made from plastics like polysulfones and polyether sulfones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If distillation is used to remove monomeric isocyanates, then monomer content is reduced, but thermal stress alters crosslinking properties and viscosity
Solution Approach 1:
The patent extracts monomeric isocyanates from prepolymer mixtures using a semi-permeable membrane that selectively allows monomers to pass through while retaining larger prepolymer molecules. This physical separation method removes harmful monomers without applying thermal stress that would alter the prepolymer's crosslinking properties and viscosity.
Solution Approach 2:
The semi-permeable membrane acts as an intermediary between the monomer-containing prepolymer mixture and the separation medium. The membrane's pore structure (5-400 nm) enables selective transport of monomeric isocyanates while blocking larger prepolymer molecules, achieving separation without direct thermal or chemical intervention on the prepolymer.
2Manufacturing precision
If reaction control measures are implemented to limit monomeric isocyanate content, then monomer content is reduced, but process complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by performing membrane separation after prepolymer formation but before final product use. This post-synthesis treatment removes monomers that formed during production without requiring complex real-time control of the crosslinking reaction, simplifying the overall manufacturing process while achieving the desired monomer content.
3Manufacturing precision
If thin-film distillation with entrainer is used, then monomer removal is achieved, but flame retardant residues remain in prepolymer
Solution Approach 1:
The patent extracts monomeric isocyanates using a semi-permeable membrane without requiring high-boiling entrainers like phosphoric acid esters. The membrane's selective permeability based on molecular size allows monomer removal while leaving the prepolymer free of flame retardant residues, eliminating the need for subsequent removal steps.
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 method effectively reduces monomeric isocyanate content to detection limits with minimal thermal stress, maintaining the crosslinking properties and viscosity of the prepolymers, allowing for more flexible formulation of aerosol can propellants and adhesives.
Implementation Method 1
dialyzed against the solvent using a permeable membrane with a pore size in the range of 5 to 400 nm
Implementation Method 2
separation of low-molecular-weight components from isocyanate-containing prepolymers using permeable membranes
Data Source
Figure 1
AI summary
The invention relates to a method for separating isocyanate monomers from isocyanate-containing mixtures by supplying the mixture in a solvent and dialyzing the dissolved mixture against the solvent by means of a permeable membrane having a pore size of 5 to 400 nm. Said method can be used especially for separating isocyanate monomers from prepolymers containing isocyanate groups for the production of adhesives, insulation foams and assembly foams.