PROCESS FOR THE EPOXIDATION OF PROPENE

Abstract

In a process for the epoxidation of propene, comprising the steps: reacting propene with hydrogen peroxide in the presence of a titanium silicalite catalyst and a methanol solvent; separating non-reacted propene and propene oxide from the resulting reaction mixture to provide a solvent mixture comprising methanol and water in a combined amount of at least 90% by weight; and feeding this solvent mixture as a feed stream to a continuously operated methanol distillation column at a feed point in the middle section of said column to provide an overhead product comprising at least 90% by weight methanol and a bottoms product comprising at least 90% by weight water; the addition of a liquid defoamer, having a solubility in the feed stream of less than 10 mg/kg at 25 C. and a surface tension at the liquid air interface of less than 22 mN/m at 20 C., at or above the feed point in an amount exceeding the solubility of the liquid defoamer in the feed stream suppresses foam formation in the methanol distillation column.

Claims

1-10. (canceled)

11. A process for the epoxidation of propene, comprising the steps: a) reacting propene with hydrogen peroxide in the presence of a titanium silicalite catalyst and a methanol solvent; b) separating non-reacted propene and propene oxide from the reaction mixture obtained in step a) to provide a solvent mixture comprising methanol and water with a combined amount of methanol and water of at least 90% by weight; and c) feeding the solvent mixture obtained in step b) as a feed stream to a continuously operated methanol distillation column at a feed point in the middle section of said column providing an overhead product comprising at least 90% by weight methanol and a bottoms product comprising at least 90% by weight water; wherein a liquid defoamer having a solubility in the feed stream of less than 10 mg/kg at 25 C. and a surface tension at the liquid air interface of less than 22 mN/m at 20 C. is added to the distillation column at or above the feed point in an amount exceeding the solubility of the liquid defoamer in the feed stream.

12. The process of claim 11, wherein the liquid defoamer comprises a polydimethylsiloxane.

13. The process of claim 12, wherein the liquid defoamer comprises more than 5% by weight polydimethylsiloxane.

14. The process of claim 11, wherein the liquid defoamer comprises hydrophobized silica particles.

15. The process of claim 11, wherein the liquid defoamer is added in an amount of from 2 to 50 wppm calculated on the feed stream.

16. The process of claim 11, wherein the overhead product obtained in step c) is recycled to step a).

17. The process of claim 11, wherein the liquid defoamer is added to the feed stream before feeding said feed stream to the methanol distillation column.

18. The process of claim 11, wherein ammonia is added in step a).

19. The process of claim 11, wherein an acid is added in step c) at or above the feed point in an amount sufficient to protonate all ammonia and amines contained in the feed stream.

20. The process of claim 19, wherein the acid is added admixed with the liquid defoamer.

21. The process of claim 13, wherein the liquid defoamer comprises hydrophobized silica particles.

22. The process of claim 13, wherein the liquid defoamer is added in an amount of from 2 to 50 wppm calculated on the feed stream.

23. The process of claim 13, wherein the overhead product obtained in step c) is recycled to step a).

24. The process of claim 13, wherein the liquid defoamer is added to the feed stream before feeding said feed stream to the methanol distillation column.

25. The process of claim 13, wherein ammonia is added in step a).

26. The process of claim 13, wherein an acid is added in step c) at or above the feed point in an amount sufficient to protonate all ammonia and amines contained in the feed stream.

27. The process of claim 23, wherein the liquid defoamer is added to the feed stream before feeding said feed stream to the methanol distillation column.

28. The process of claim 23, wherein the liquid defoamer is added to the feed stream before feeding said feed stream to the methanol distillation column.

29. The process of claim 23, wherein ammonia is added in step a).

30. The process of claim 23, wherein an acid is added in step c) at or above the feed point in an amount sufficient to protonate all ammonia and amines contained in the feed stream.

Description

EXAMPLES

Example 1

[0019] In a continuously operated pilot plant, a mixture comprising propene and hydrogen peroxide in a methanol solvent was passed through a fixed bed containing a titanium silicalite catalyst. Non-reacted propene and propene oxide were separated from the resulting reaction mixture by pressure reduction and distillation and a solvent mixture comprising 79% by weight of methanol, 18.6% by weight of water, 1% by weight of 1,2-propanediol, 0.5% by weight of 1-methoxy-2-propanol, 0.5% by weight of 2-methoxy-1-propanol and 0.3% by weight of other byproducts was recovered. 4.5 kg/h of this solvent mixture was fed as a feed stream to the middle section of a rectification column having 30 stages. 10-50 ml/h of a 10% by weight aqueous sulfuric acid solution was added to the feed stream immediately before feeding it to the column. The rectification column was operated continuously at a pressure of 0.6 MPa and a bottom temperature of 155 to 160 C., providing an overhead product containing more than 90% by weight methanol and a bottoms product containing more than 90% by weight water. During operation of the column foam formation was observed in the stripping section of the column.

Example 2

[0020] Example 1 was repeated with 20 mg/kg of the defoamer TEGO Antifoam WM 20 being added to the feed stream. The defoamer TEGO Antifoam WM20 has a surface tension at the liquid air interface of 20 mN/m at 20 C. and is insoluble in water and methanol. No foam formation was observed during operation of the column.

Example 3

[0021] Example 1 was repeated with 20 mg/kg of the defoamer TEGO Antifoam 2290 being added to the feed stream. The defoamer TEGO Antifoam 2290 has a surface tension at the liquid air interface of 30 mN/m at 20 C. and is insoluble in water and methanol. Foam formation was observed during operation of the column.

Example 4

[0022] Example 1 was repeated with 20 mg/kg of the defoamer TEGILOXAN 1000 being added to the feed stream. The defoamer TEGILOXAN 1000 has a solubility in the feed stream of more than 10 mg/kg at 25 C. and a surface tension at the liquid air interface of 20 mN/m at 20 C. Foam formation was observed during operation of the column.