Process for producing a cyclic acetal

1. A process for producing a cyclic acetal comprising:

contacting gaseous formaldehyde with a liquid medium comprising a liquid aprotic compound, wherein the liquid aprotic compound is selected from the group consisting of organic sulfoxides, organic sulfones, organic sulfonate esters, and mixtures thereof, in the presence of a catalyst; and

at least partially converting the gaseous formaldehyde into a cyclic acetal comprising trioxane.

2. The process according to claim 1 , wherein the aprotic compound is a polar aprotic compound.

3. The process according to claim 1 , wherein the catalyst is heterogeneous with the liquid medium.

4. The process according to claim 1 , wherein the weight ratio of gaseous formaldehyde to the aprotic compound is from about 1:50 to about 1:3.

5. The process according to claim 1 , wherein the aprotic compound has a boiling point of 140° C. or higher, determined at 1 bar.

6. The process according to claim 1 wherein higher than 30%, of the gaseous formaldehyde is converted into one or more cyclic acetals during the reaction.

7. The process according to claim 1 wherein the liquid medium comprises at least 60 wt.-%, of the aprotic compound.

8. The process according to claim 1 wherein the aprotic compound is selected from the group consisting of cyclic or alicyclic organic sulfoxides, alicyclic or cyclic sulfones, and mixtures thereof.

9. The 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 can be branched or unbranched.

10. The process according to claim 1 wherein the aprotic compound is sulfolane.

11. The 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 can be branched or unbranched.

12. The 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 can 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 can be branched or unbranched.

13. The process according to claim 1 wherein the reaction is carried out at a temperature ranging from 10° C. to 120° C.

14. The process according to claim 1 , wherein the catalyst comprises trifluoromethanesulfonic acid, perchloric acid, methanesulfonic acid, toluenesulfonic acid, sulfuric acid, or mixtures thereof.

15. The process according to claim 1 , wherein the catalyst is present in the liquid medium in an amount from about 0.001 wt % to about 15 wt %.

16. The process according to claim 1 , wherein the gaseous formaldehyde has a water content of less than about 5 wt.

17. The process according to claim 1 , further comprising the step of separating the cyclic acetal from the liquid medium by distillation.

18. The process according to claim 1 , further comprising the step of manufacturing polyoxymethylene from the cyclic acetal.

19. The process according to claim 1 , wherein the gaseous formaldehyde is absorbed in an absorption column containing the aprotic compound and the catalyst.

20. A process for producing cyclic acetal comprising

i) preparing a reaction mixture comprising

a) formaldehyde in a liquid medium and

b) a catalyst; that is heterogeneous with the liquid medium

ii) converting the formaldehyde into trioxane wherein the final conversion of the formaldehyde to the trioxane is greater than 10% on the basis of the formaldehyde.

21. The process according to claim 20 , wherein the catalyst comprises an acid ion-exchange material.

22. The process according to claim 1 , wherein the catalyst comprises an acid ion-exchange material.