Process for producing a cyclic acetal

Abstract

The present invention relates to a process for producing cyclic acetal comprising i) preparing a reaction mixture comprising a) a formaldehyde source in a liquid medium and b) a catalyst; ii) converting the formaldehyde source into cyclic acetals, wherein the final conversion of said formaldehyde source to said cyclic acetal is greater than 10% on basis of the initial formaldehyde source.

Claims

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): ##STR00010## 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.sub.1-C.sub.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): ##STR00011## wherein R.sup.1 and R.sup.2 are independently selected from C.sub.1-C.sub.8-alkyl which can be branched or unbranched.

12. The process according to claim 1 wherein the aprotic compound is represented by formula (III): ##STR00012## 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.sub.1-C.sub.8-alkyl which can be branched or unbranched; or the aprotic compound is represented by formula (IV): ##STR00013## wherein R.sup.3 and R.sup.4 are independently selected from C.sub.1-C.sub.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.

Description

EXAMPLES

Example 1

(1) Anhydrous formaldehyde was prepared by the thermal decomposition of paraformaldehyde (essay: 96 wt %, from Acros Organics) at a rate of ca. 1 g/min at appr. 120 C. and a pressure of 80 mbar. The formaldehyde gas was absorbed in a absorption column containing 500 g sulfolane (<0.1 wt % water) with 0.1 wt % triflic acid at around 40 C. After 1 hr, the sulfolane in the adsorption column was neutralized with triethylamine and analyzed by GC and sulfite titration. The following composition was found:
Trioxane: 8.3 wt %
Tetroxane: 1.1 wt %
Formaldehyde: 0.6 wt %
Methyl formate: 0.5 wt %

(2) Final conversion of formaldehyde to trioxane in the reaction mixture: 77.5%

(3) Final conversion of formaldehyde to trioxane and tetroxane in the reaction mixture: 88%

Example 2

(4) 500 g of an aqueous 80 wt. % solution of formaldehyde were mixed with 500 g of sulfolane at 80 C. 40 g of concentrated sulfuric acid were added and the clear mixture was heated to 100 C. and kept there for 15 min. Then 50 ml were distilled off at atmospheric pressure and analyzed:
The distillate contained:
32 wt % trioxane
0.05 wt % methyl formate

Comparative Example 3

(5) To 100 g of a 60 wt.-% solution of formaldehyde in water at 100 C. 5 g of sulfuric acid is added. After 15 min ca. 5 g were distillated off at atmospheric pressure. The trioxane concentration in the distillate was 22 wt.-%.
This shows that the process of the invention is more effective and requires less energy to separate the cyclic acetal due to the higher trioxane concentration in the distillate.

Example 4

(6) 9 g of commercial paraformaldehyde with a water content of ca. 4 wt % (essay: 96 wt % from Acros Organics) were added to 91 g of sulfolane at 145 C. with stirring. As the paraformaldehyde dissolves, the temperature decreases to 122 C. The clear solution was allowed to cool to 100 C. At that temperature 0.3 ml of a 10 wt % solution of triflic acid in sulfolane was added. After 1 min, the homogeneous solution was allowed to cool to 60 C., was neutralized with triethylamine and then analyzed. The following composition was found:
Trioxane: 7.0 wt %
Tetroxane: 0.6 wt %
Formaldehyde: 1 wt %

Example 5

(7) 10 g of dried Polyoxymethylene Copolymer (with a low Dioxolane content) (TICONA trade name: Hostaform HS 15) with melt index of 1.5 g/10 min were dissolved in 90 g of sulfolane at 145 C. with stirring. The clear solution was added to 20 g sulfolane (at 120 C.) containing 0.4 ml of a 10 wt % solution of triflic acid in sulfolane. After the addition was completed, the homogeneous solution was cooled to 60 C., neutralized with triethylamine and then analyzed. The following composition was found:
Trioxane: 7.1 wt %
Tetroxane: 0.75 wt %
Formaldehyde: 0.4 wt %
Methylformate: <20 ppm

Example 6

(8) Example 5 was repeated, except that perchloric acid (70 wt % in water) was used for triflic acid: 10 g of dried Polyoxymethylene Copolymer (with a low Dioxolane content) (TICONA trade name: Hostaform HS 15) with melt index of 1.5 g/10 min were dissolved in 90 g of sulfolane at 145 C. with stirring. The clear solution was added to 20 g sulfolane (at 120 C.) containing 1.2 ml of a 2 wt % solution of perchloric acid (70 wt % in water) in sulfolane. After the addition was completed, the homogeneous solution was cooled to 60 C., neutralized with triethylamine and then analyzed. The following composition was found:
Trioxane: 7.2 wt %
Tetroxane: 0.8 wt %
Formaldehyde: 0.3 wt %
Methylformate: <20 ppm

Comparative Example 7

(9) Example 5 was repeated, except that nitrobenzene was used for sulfolane as a solvent: 10 g of dried Polyoxymethylene Copolymer (with a low Dioxolane content) (TICONA trade name: Hostaform HS 15) with melt index of 1.5 g/10 min were dissolved in 90 g of nitrobenzene at 145 C. with stirring. The clear solution was added to 20 g nitrobenzene (at 120 C.) containing 0.4 ml of a 10 wt % solution of triflic acid in sulfolane. After the addition was completed, the homogeneous solution was cooled to 60 C., neutralized with triethylamine and then analyzed. The following composition was found:
Trioxane: 6.2 wt %
Tetroxane: 0.7 wt %
Formaldehyde: 0.7 wt %
Methylformate: 0.5 wt % The GC spectrum also showed a new peak with a retention time beyond that of nitrobenzene, which was not further analyzed but is believed to be a reaction product of nitrobenzene with formaldehyde. Thus, nitrobenzene is not stable under reaction conditions, produces side products (methylformate) and consequently has a lower yield in trioxane.

Example 8

(10) Example 5 was repeated, except that a mixture of Dimethylsulfone (30 g) and Sulfolane (60 g) was used for sulfolane as a solvent: 10 g of dried Polyoxymethylene Copolymer (with a low Dioxolane content) (TICONA trade name: Hostaform HS 15) with melt index of 1.5 g/10 min were dissolved in a mixture of Dimethylsulfone (30 g) and Sulfolane (60 g) at 145 C. with stirring. The clear solution was added to 20 g sulfolane (at 120 C.) containing 0.4 ml of a 10 wt % solution of triflic acid in sulfolane. After the addition was completed, the homogeneous solution was cooled to 60 C., neutralized with triethylamine and then analyzed. The following composition was found: Trioxane: 7.1 wt % Tetroxane: 0.6 wt % Formaldehyde: 0.8 wt % Methylformate: 9.4 ppm

Example 9

(11) Example 4 was repeated except that strongly acidic ion exchange resin (Amberlyst 15, wet form, from DOW CHEMICAL) was used instead of triflic acid as catalyst. Before use the resin was conditioned to sulfolane (exchange of water in the pores of the resin by sulfolane)
9 g of commercial paraformaldehyde with a water content of ca. 4 wt % (essay: 96 wt % from Acros Organics) were added to 91 g of sulfolane at 145 C. with stirring. As the paraformaldehyde dissolves the temperature decreases to 122 C. The clear solution was allowed to cool to 100 C. At that temperature 10 g of Amberlyst 15 was added. After 10 min at 100 C. the reaction mixture was allowed to cool to 50 C., and no precipitate formed, indicating the conversion of the paraformaldehyde to trioxane. The concentration of the trioxane in the reaction mixture is estimated to be above 6 wt %.

Example 10

(12) Anhydrous formaldehyde was prepared by the thermal decomposition of paraformaldehyde (essay: 96 wt %, from Acros Organics) at a rate of ca. 1 g/min at appr. 120 C. and a pressure of 80 mbar. The formaldehyde gas was absorbed in a absorption column containing 500 g sulfolane (<0.1 wt % water) with 0.1 wt % triflic acid. After 50 min, the sulfolane in the adsorption column was neutralized with triethylamine and analyzed by GC and sulfite titration. The following composition was found:
Trioxane: 8.3 wt %
Tetroxane: 1.1 wt %
Formaldehyde: 0.6 wt %

Example 11

(13) Anhydrous formaldehyde was prepared by the thermal decomposition of paraformaldehyde (essay: 96 wt %, from Acros Organics) at a rate of ca. 1 g/min at appr. 120 C. and a pressure of 80 mbar. The formaldehyde gas was absorbed in a absorption column containing 500 g sulfolane (<0.1 wt % water) at a temperature of 100 C. After 50 min, a solution of paraformaldehyde in sulfolane was obtained. To this solution 0.4 ml of a 10 wt % solution of triflic acid in sulfolane was added. After a reaction time of 1 min at 105 C. the homogeneous solution was neutralized with triethylamine and analyzed by GC and sulfite titration. The following composition was found:
Trioxane: 8.1 wt %
Tetroxane: 0.9 wt %
Formaldehyde: 0.9 wt %