Process For Recycling Polyacetals

Abstract

A process for recycling polyoxymethylene polymers is disclosed. A polyoxymethylene polymer is at least partially dissolved in an aprotic compound. The resulting solution or suspension (liquid mixture) is then contacted with a catalyst which causes the polyoxymethylene polymer to be converted into a cyclic acetal. The cyclic acetal can be separated, collected and used in other processes. In one embodiment, the cyclic acetal may be used to produce a polyoxymethylene polymer.

1 .- 20 . (canceled) 
     
     
         21 . A process for the recycling of oxymethylene homo- or copolymers comprising the steps:
 a) at least partly dissolving an oxymethylene homo- or copolymer in an aprotic compound;   b) converting the at least partly dissolved oxymethylene homo- or copolymer in the presence of a catalyst to cyclic acetals; and   c) converting the cyclic acetals obtained in step b) optionally together with comonomer(s) to oxymethylene polymers.   
     
     
         22 . A process according to  claim 21 , wherein at least 20 wt.-% of the oxymethylene homo- or copolymer is dissolved in the aprotic compound. 
     
     
         23 . A process according to  claim 21 , wherein the oxymethylene polymer is at least partly dissolved at a temperature higher than 100° C. 
     
     
         24 . A process according to  claim 21 , wherein the aprotic compound has a boiling point of 120° C. or higher, determined at 1 bar. 
     
     
         25 . A process according to  claim 21 , wherein the oxymethylene polymer, the aprotic compound and the catalyst form a reaction mixture and wherein the reaction mixture comprises at least 60 wt.-% of the aprotic compound, wherein the weight is based on the total weight of the reaction mixture. 
     
     
         26 . A process according to  claim 21 , wherein the aprotic compound comprises a sulfur containing organic compound. 
     
     
         27 . A process according to  claim 21 , wherein the aprotic compound comprises a dipolar nitro-group free compound. 
     
     
         28 . A process according to  claim 21 , wherein the aprotic compound is represented by formula (I): 
       
         
           
           
               
               
           
         
         wherein 
         n is an integer ranging from 1 to 6, and 
         wherein the ring carbon atoms may optionally be substituted by one or more substituents, selected from C 1 -C 8 -alkyl which may be branched or unbranched. 
       
     
     
         29 . A process according to  claim 21 , wherein the aprotic compound is sulfolane. 
     
     
         30 . A process according to  claim 21 , wherein the aprotic compound is represented by formula (II): 
       
         
           
           
               
               
           
         
         wherein R 1  and R 2  are independently selected from C 1 -C 8 -alkyl which may be branched or unbranched. 
       
     
     
         31 . A process according to  claim 21 , wherein the aprotic compound is represented by formula (III): 
       
         
           
           
               
               
           
         
         wherein 
         n is an integer ranging from 1 to 6, and 
         wherein the ring carbon atoms may optionally be substituted by one or more substituents, selected from C 1 -C 8 -alkyl which may be branched or unbranched; or 
         the aprotic compound is represented by formula (IV): 
       
       
         
           
           
               
               
           
         
         wherein R 3  and R 4  are independently selected from C 1 -C 8 -alkyl which may be branched or unbranched. 
       
     
     
         32 . A process according to  claim 21 , wherein the conversion to the cyclic acetal is carried out at a temperature ranging from 40° C. to 130° C. and is carried out at a pressure of from 10 millibars to 10 bars. 
     
     
         33 . A process according to  claim 21 , wherein higher than 30 percent of the oxymethylene homo- or copolymer is converted into the cyclic acetal. 
     
     
         34 . A process according to  claim 21 , further comprising the step of converting the cyclic acetals formed during the process into an oxymethylene polymer. 
     
     
         35 . A process according to  claim 21 , wherein the oxymethylene homo- or copolymer is at least partly dissolved in the aprotic compound while being heated and wherein the resulting liquid medium is cooled prior to being contacted with the catalyst.