Process for recycling polyacetals
View Patent ↗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. A process for the conversion of oxymethylene homo- or copolymers to cyclic acetals comprising the steps:
a) at least partly dissolving an oxymethylene homo- or copolymer in a liquid medium comprising an aprotic compound, the aprotic compound having boiling point of 120° C. or higher, determined at 1 bar; and
b) converting the at least partly dissolved oxymethylene homo- or copolymer in the presence of a catalyst to cyclic acetals.
2. A process according to claim 1 , wherein at least 20 wt.-% of the oxymethylene homo- or copolymer is dissolved in the aprotic compound.
3. A process according to claim 1 wherein the oxymethylene polymer is at least partly dissolved at a temperature higher than 100° C.
4. A process for the conversion of oxymethylene homo- or copolymers to cyclic acetals comprising the steps:
a) at least partly dissolving an oxymethylene homo- or copolymer in a liquid medium comprising an aprotic compound; and
b) converting the at least partly dissolved oxymethylene homo- or copolymer in the presence of a catalyst to cyclic acetals; and
wherein the cyclic acetals obtained are purified or separated.
5. A process according to claim 1 wherein the aprotic compound is liquid under the dissolution condition.
6. A process for the conversion of oxymethylene homo- or copolymers to cyclic acetals comprising the steps:
a) at least partly dissolving an oxymethylene homo- or copolymer in a liquid medium comprising an aprotic compound, and wherein the polyoxymethylene homo- or copolymer has a number average molecular weight (Mn) of more than 2,000 Dalton; and
b) converting the at least partly dissolved oxymethylene homo- or copolymer in the presence of a catalyst to cyclic acetals.
7. A process according to claim 6 wherein the aprotic compound has a boiling point of 120° C. or higher, determined at 1 bar.
8. A process according to claim 1 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.
9. A process according to claim 1 wherein the aprotic compound comprises a sulfur containing organic compound.
10. A process according to claim 1 wherein the aprotic compound comprises a dipolar nitro-group free compound.
11. A process according to claim 1 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.
12. A process according to claim 1 wherein the aprotic compound is sulfolane.
13. A process according to claim 1 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.
14. A process according to claim 1 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.
15. A process according to claim 1 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.
16. A process according to claim 1 , wherein higher than 30 percent of the oxymethylene homo- or copolymer is converted into the cyclic acetal.
17. A process according to claim 1 , further comprising the step of converting the cyclic acetals formed during the process into an oxymethylene polymer.
18. A process according to claim 1 , 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.