Processes for the manufacture of acetals

1. A process for preparing acetals from aldehydes and alcohols by reactive distillation, which comprises

a) feeding aldehyde and alcohol to the reaction/distillation zone of a distillation column and at least partly converting them to the acetal,

b) heating the column bottom disposed below the reaction/distillation zone,

c) feeding an extractant into a rectifying section of the column, disposed above the reaction/distillation zone and

d) condensing a product having more than 90% by weight of acetal at the top of the column and wherein the reactive distillation and the extractive distillation are combined in one column and wherein the reaction/distillation zone is obtained by charging one or more sections of the column with an acidic fixed bed catalyst.

2. The process as claimed in claim 1 , wherein the reaction/distillation zone consists of one or more sections of the column which are charged with an acidic fixed bed catalyst.

3. The process as claimed in claim 1 , wherein a reflux ratio between R=0.5 and R=10 is set in the column.

4. The process as claimed in claim 1 , wherein the top product of the column is concentrated to a content of at least 99% by weight of acetal by not more than two subsequent separating operations.

5. The process as claimed in claim 1 , wherein aldehyde and alcohols having one or two carbon atoms are used as reactants.

6. The process as claimed in claim 5 for the preparation of methylal from formaldehyde and methanol.

7. The process as claimed in claim 1 , wherein the reactants are mixed and fed to a prereactor before they are introduced into the reaction/distillation zone of the column.

8. The process as claimed in claim 7 , wherein the conversion in the prereactor based on the reactant used in stoichiometric deficiency is 10-50%.

9. The process as claimed in claim 1 , wherein the conversion, based on the reactant used in stoichiometric deficiency, is more than 80%.

10. The process as claimed in claim 1 , wherein the extractant is a substance which is present in the process in any case.

11. The process as claimed in claim 1 , wherein the extractant is water.

12. The process as claimed in claim 3 , wherein the reflux ratio R is between 1 and 8.

13. The process as claimed in claim 1 , wherein the top concentration is more than 95% acetal.

14. The process as claimed in claim 1 , wherein the top concentration is more than 97% acetal.

15. The process as claimed in claim 1 , wherein the top concentration is more than 98% acetal.

16. The process as claimed in claim 4 , wherein the purity of the acetal after the subsequent not more than two separation steps is at least 99.9%.

17. The process as claimed in claim 7 , wherein the conversion in the prereactor based on the reactant used in stoichiometric deficiency is 15-40%.

18. The process as claimed in claim 1 , wherein the conversion, based on the reactant used in stoichiometric deficiency is more than 95% and the extractant is demineralized water and the reflux ratio R is between 2 and 6.

19. The process as claimed in claim 1 , wherein the extractant is demineralized water.

20. The process as claimed in claim 1 , wherein the reactive distillation zone consists essentially of 18 to 40% by weight of a formaldehyde solution, alcohol and an acidic fixed bed catalyst.

21. The process as claimed in claim 1 , wherein said process is carried out in the absence of a defoamer.