Method for removing monoisocyanates from organic solution
AssigneesDow Global Technologies LLC, Dow Portugal Produtos Quimicos, Sociedade Unipessoal, LDA
InventorsRobert E. Hefner, Jr., Helge Braun, Armenio Costa, Brian Cramm
Life of this patent
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Abstract
Monoisocyanate impurities are removed from a process stream obtained when solvent is separated from a polyisocyanate product. The monoisocyanates are reacted with amine compounds at specific molar ratios to produce ureas. The ureas can be discarded by burning, landfilling or otherwise. Alternatively the ureas can be recycled back into the polyisocyanate manufacturing process, where they are formed into biuret compounds that can remain with the polyisocyanate product.
Claims15
A method for removing organic monoisocyanates from an organic solvent, comprising the steps of:
- a) contacting i) a starting solution containing at least 85 weight percent, based on the weight of the starting solution, of one or more organic solvents inert to reaction with isocyanate and amine groups and up to 15 weight percent, based on the weight of the starting solution, of organic isocyanate compounds that include at least one monoisocyanate, with ii) at least one amine, soluble in the one or more organic solvents, the amine having at least one primary or secondary amino group, in proportions sufficient to provide 0.01 to 0.8 equivalents of primary and/or secondary amino groups per equivalent of isocyanate groups in the starting solution;
- and
- b) reacting at least a portion of the monoisocyanate with at least a portion of the amine mixture to form one or more urea compounds.
An MDI and/or polymeric MDI manufacturing process, comprising the steps of:
- a) reacting aniline with formaldehyde in a solvent to produce a mixture of MDA, PMDA and unreacted aniline in the solvent;
- b) distilling aniline from the mixture produced in step a) to produce a process stream containing the solvent, MDA, PMDA and residual aniline;
- c) phosgenating the process stream from step b) to form an isocyanate process stream containing the solvent, MDI, one or more polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups and phenyl isocyanate;
- d) separating MDI and polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups and phenyl isocyanate from the isocyanate process stream obtained in step c) by distillation to produce a solvent stream containing solvent, 0.2 to 10 weight percent phenyl isocyanate based on the weight of the solvent stream and 0.0001 to 5 weight percent, based on the weight of the solvent stream, of MDI and/or one or more polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups;
- e) combining the solvent stream obtained in step d) with aniline at a ratio of 0.01 to 0.8 moles of aniline per mole of phenyl isocyanate and reacting at least a portion of the aniline with phenyl isocyanate to form urea compounds;
- f) reacting at least a portion of the urea compounds with a polyisocyanate to form biuret compounds.
Dependencies are inferred from the claim text.