Solvent-based recovery and recycle of polyamide material

Abstract

A process is disclosed for recovering polyamide material from post-industrial and post-consumer products containing the polyamide material and insoluble materials. The process includes the steps of: (a) contacting the post-industrial and post-consumer products with a suitable solvent in a reactor; (b) dissolving and partially depolymerizing the polyamide material in the solvent to form a solution by operating the reactor at a predetermined temperature and pressure and for a time sufficient to decrease the average molecular weight of the depolymerized polyamide to less than 90% of the initial molecular weight; (c) separating the insoluble material from the solution; and (d) recovering the depolymerized polyamide from the separated solution. The process may also include the step of repolymerizing the depolymerized polyamide.

What is claimed is:  
     
         1 . A process for recovering polyamide material having an initial average molecular weight from post-industrial and post-consumer products containing the polyamide material and insoluble materials, the process comprising the steps of: 
 (a) contacting the post-industrial and post-consumer products with a suitable solvent in a reactor;    (b) dissolving and partially depolymerizing the polyamide material in the solvent to form a solution by operating the reactor at a predetermined temperature and pressure and for a time sufficient to decrease the average molecular weight of the depolymerized polyamide to less than 90% of the initial average molecular weight;    (c) separating the insoluble material from the solution; and    (d) recovering the depolymerized polyamide from the separated solution.    
     
     
         2 . The process of  claim 1 , further comprising the step of repolymerizing the depolymerized polyamide.  
     
     
         3 . The process of  claim 2 , wherein the repolymerized polyamide has an average molecular weight substantially the same as the initial average molecular weight.  
     
     
         4 . The process of  claim 1 , wherein the solvent is an aliphatic alcohol.  
     
     
         5 . The process of  claim 4 , wherein the solvent is anhydrous methanol.  
     
     
         6 . The process of  claim 4 , wherein the solvent is a solution containing at least 90% methanol.  
     
     
         7 . The process of  claim 4 , wherein the solvent is anhydrous ethanol.  
     
     
         8 . The process of  claim 4 , wherein the solvent is a solution containing at least 90% ethanol.  
     
     
         9 . The process of  claim 1 , wherein the reactor is operated at a temperature between 160° C. and 210° C. and a pressure sufficient to keep the solvent in liquid phase for 30 to 400 minutes.  
     
     
         10 . The process of  claim 9 , wherein the pressure is at least 350 psig.  
     
     
         11 . The process of  claim 2 , wherein the repolymerization occurs through a solid-phase repolymerization process at a temperature between 160° C. and the temperature at which the polyamide melts.  
     
     
         12 . The process of  claim 2 , wherein the repolymerization occurs through a melt-phase repolymerization process at a temperature above the melting temperature of the polyamide.  
     
     
         13 . The process of  claim 1 , wherein the insoluble material is separated by passing the solution through suitable filtration means.  
     
     
         14 . The process of  claim 13 , wherein the filtration means is selected from the group consisting of glass fibers, insoluble material residue and a combination of these.  
     
     
         15 . The process of  claim 14 , wherein the filtration means comprises insoluble material residue that has accumulated on the filtration means.  
     
     
         16 . The process of  claim 14 , wherein the filtration media is glass fibers.  
     
     
         17 . The process of  claim 1 , wherein the depolymerized polyamide is recovered by a method selected from the group consisting of precipation of the depolymerized polyamides, spray drying, and flash evaporation.  
     
     
         18 . The process of  claim 17 , wherein the depolymerized polyamide is recovered by cooling the separated solution to a temperature sufficient to cause precipitation of the depolymerized polyamides.  
     
     
         19 . The process of  claim 17 , wherein the depolymerized polyamide is recovered by adding to the separated solution an anti-solvent agent to cause precipitation of the depolymerized polyamides.  
     
     
         20 . The process of  claim 18  or  claim 19 , further comprising the step of purifying the separated solution after the depolymerized polyamide is recovered, and using the purified solution as the solvent in step (a).  
     
     
         21 . The process of  claim 1 , wherein the post-industrial and post-consumer products include one or more of carpet waste, glass-reinforced nylon, air-intake manifolds, radiator end-caps, coated fabrics, air bag fabrics and mineral-filled nylon.  
     
     
         22 . The process of  claim 1 , wherein the insoluble material includes TiO 2 .