Polyamide-epichlorohydrin wet-strength resins with reduced content of epichlorohydrin-derived by-products in-situ solvent extraction

Abstract

A process for reducing the concentration of epichlorohydrin by-products in the manufacture of polyamide-epichlorohydrin resins, comprising reacting polyaminopolyamide prepolymer in aqueous solution with epichlorohydrin and an immiscible solvent for the epichlorohydrin, continuing the reaction of the prepolymer with the epichlorohydrin to produce the desired viscosity of the aqueous phase, stabilizing the resin product by diluting or acidifying the aqueous phase, separating the solvent from the aqueous resin, and treating the solvent phase with caustic to convert epichlorohydrin by-products to epichlorohydrin for recycling.

I claim: 
     
       1. A process for reducing the concentration of epichlorohydrin by-products in the manufacture of polyamide-epichlorohydrin resins, comprising reacting polyaminopolyamide prepolymer in aqueous solution with epichlorohydrin, in the presence of a water-immiscible solvent for the epichlorohydrin, continuing the reaction of the prepolymer with the epichlorohydrin to produce the desired viscosity of the aqueous phase, stabilizing the resin product by diluting or acidifying the aqueous phase, separating the solvent from the aqueous resin, and treating the solvent phase with caustic to convert epichlorohydrin by-products to epichlorohydrin, wherein the weight ratio of organic solvent to aqueous reaction mixture is between about 0.1 and about 10, and wherein the lower limit of the temperature range over which the process is carried out is about 20° C. and the upper limit is the lower of the reflux temperature of the water-immiscible solvent and 85° C. 
     
     
       2. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, in which the epichlorohydrin content of the solvent containing converted epichlorohydrin is determined and the solvent is recycled in a repetition of the reaction step. 
     
     
       3. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, which includes the steps of removing the solvent by heating the combined and reacting prepolymer and epichlorohydrin solutions to distill off the solvent before the desired viscosity of the aqueous phase is reached, and adding it back to the aqueous phase after the resin is stabilized to extract the epichlorohydrin reaction by-products at that stage. 
     
     
       4. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, which includes the steps of adding water to the solvent layer after it is separated from the aqueous resin solution, heating the solvent layer with caustic either before or after the addition of water, and cooling the solvent phase to its freezing point to extrude the epichlorohydrin reaction by-product or converted by-product, respectively, from the frozen solvent, and to dissolve the epichlorohydrin product in water. 
     
     
       5. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 4, in which the step of cooling the solvent phase to its freezing point is carried out before treating it with caustic. 
     
     
       6. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 5, in which the frozen solvent is separated from water and remelted for re-use. 
     
     
       7. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 4, which includes the step of determining the epichlorohydrin content of the water in which it is dissolved, for recycling to the reaction. 
     
     
       8. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, in which the weight ratio of organic solvent to aqueous reaction mixture is between about 0.1 and about 10. 
     
     
       9. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 8, in which the weight ratio of organic solvent to aqueous reaction mixture is between about 0.2 and about 2.0. 
     
     
       10. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 9, in which the weight ratio of organic solvent to aqueous reaction mixture is between about 0.5 and about 1.5. 
     
     
       11. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, in which the boiling point of the solvent at atmospheric pressure is not below about 60° C. 
     
     
       12. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, in which the boiling point of the solvent is above about 75° C. 
     
     
       13. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, in which the solvent is a monoester having 4 to 7 carbon atoms. 
     
     
       14. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 3, in which the boiling point of the solvent at atmospheric pressure is below about 80° C. 
     
     
       15. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 14, in which the boiling point of the solvent at atmospheric pressure is below about 60° C. 
     
     
       16. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 15, in which the boiling point of the solvent at atmospheric pressure is below about 50° C. 
     
     
       17. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 13, in which the solvent is ethyl acetate. 
     
     
       18. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 13, in which the solvent is ethylbutyrate. 
     
     
       19. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, in which the solvent is an ether having 5 to about 12 carbon atoms. 
     
     
       20. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 19, in which the solvent is t-butyl methyl ether. 
     
     
       21. A process for reducing the concentration of epichlorohydrin by-products as claimed in claim 1, in which the polyaminopolyamide prepolymer is diethylenetriamine-adipic acid polyamide.