A PROCESS FOR PREPARING PROPYLENE OXIDE

Abstract

The present invention is related to a process for preparing propylene oxide, comprising (i) providing a stream comprising propene, hydrogen peroxide or a source of hydrogen peroxide, water, and an organic solvent; (ii) passing the liquid feed stream provided in (i) into an epoxidation zone comprising an epoxidation catalyst comprising a titanium zeolite, and subjecting the liquid feed stream to epoxidation reaction conditions in the epoxidation zone, obtaining a reaction mixture comprising propene, propylene oxide, water, and the organic solvent; (iii) removing an effluent stream from the epoxidation zone, the effluent stream comprising propylene oxide, water, organic solvent, and propene; (iv) separating propene from the effluent stream by distillation, comprising (iv.1) subjecting the effluent stream to distillation conditions in a distillation unit, obtaining a gaseous top stream S0 enriched in propene compared to the effluent stream subjected to distillation conditions, and a liquid bottoms stream S01 enriched in propylene oxide, water and organic solvent compared to the effluent stream subjected to distillation conditions; (iv.2) returning a condensed portion of the stream S0 to an upper part of the distillation unit.

Claims

1. A process for preparing propylene oxide, the process comprising: (i) providing a liquid feed stream comprising propene, hydrogen peroxide or a source of hydrogen peroxide, water, and an organic solvent; (ii) passing the liquid feed stream into an epoxidation zone comprising an epoxidation catalyst comprising a titanium zeolite, and subjecting the liquid feed stream to epoxidation reaction conditions in the epoxidation zone, thereby obtaining a reaction mixture comprising propene, propylene oxide, water, and the organic solvent; (iii) removing an effluent stream from the epoxidation zone, the effluent stream comprising propylene oxide, water, organic solvent, and propene; and (iv) separating propene from the effluent stream by distillation, comprising (iv.1) subjecting the effluent stream to distillation conditions in a distillation unit, thereby obtaining a gaseous top stream S0 enriched in propene compared to the effluent stream subjected to distillation conditions, and a liquid bottoms stream S01 enriched in propylene oxide, water and organic solvent compared to the effluent stream subjected to distillation conditions; and (iv.2) returning a condensed portion of the gaseous top stream S0 to an upper part of the distillation unit.

2. The process of claim 1, wherein the liquid feed stream further comprises propane; the reaction mixture further comprises propane; the effluent stream further comprises propane; the separating is separating the propene and propane; and the gaseous top stream S0 is enriched in the propene and propane.

3. The process of claim 1, wherein the distillation unit employed is at least one distillation tower wherein the distillation tower has from 3 to 50 theoretical trays.

4. The process of claim 1, wherein a rectifying section of the distillation unit consists of from 50 to 75% of theoretical trays and a stripping section of the distillation unit consists of from 25 to 50% of theoretical trays.

5. The process of claim 1, wherein the distillation unit is operated at a top pressure of from 0.5 to 2.8 bar.

6. The process of claim 1, wherein the distillation unit is operated at a top temperature of from 70 to 30 C.

7. The process of claim 1, wherein the gaseous top stream S0 removed from the distillation unit has a pressure of from 0.5 to 2.8 bar and a temperature of from 70 to 30 C.

8. The process of claim 1, wherein the condensed portion of the gaseous top stream S0 is regulated so that an oxygen concentration in an uncondensed portion of the gaseous top stream S0 is less than 10 vol. %.

9. The process of claim 1, further comprising: condensing a portion of the gaseous top stream S0 by compression to a pressure of from 5 to 20 bar, and adjusting the temperature to be of from 20 to 50 C.

10. The process of claim 1, wherein of from 50 to 90 weight-% of the gaseous top stream S0, which form the condensed portion of the gaseous top stream S0, are returned to the upper part of the distillation unit.

11. The process of claim 1, wherein the condensed portion of the gaseous top stream S0 is returned to the upper part of the distillation unit at a top of the distillation unit or within a rectifying section of the distillation unit.

12. The process of claim 1, wherein the condensed portion of the gaseous top stream S0, which is returned to the upper part of the distillation unit in (iv.2), has a temperature of from 20 to 50 C.

13. The process of claim 1, wherein the condensed portion of the the gaseous top stream S0 is heat exchanged with the gaseous top stream S0 prior to the returning to the upper part of the distillation unit.

14. The process of claim 1, wherein a temperature of the condensed portion of the the gaseous top stream S0 is decreased after compression and prior to the returning to the upper part of the distillation unit by 35 to 80 K.

15. The process of claim 1, which is a continuous process.

Description

SHORT DESCRIPTION OF THE FIGURES

[0209] FIG. 1 shows a block diagram of the process according to Comparative Examples 1. In FIG. 1, the letters and numbers have the following meanings: [0210] F, T1, T2, B streams according to a specifically preferred process as described in the examples [0211] S0, S1a streams according to a preferred process as described in the general description and the examples

[0212] FIG. 2 shows a block diagram of the process according to Example 1. In FIG. 2, the letters and numbers have the following meanings: [0213] F, T1, T2, T3, T4, T5, R, B streams according to a specifically preferred process as described in the examples [0214] S0, S1a streams according to a preferred process as described in the general description and the examples

[0215] FIG. 3 shows a block diagram of the process for Example 2. In FIG. 3, the letters and numbers have the following meanings: [0216] F, T1, T2, T3, T4, T5, R1, R2, B streams according to a specifically preferred process as described in the examples [0217] S0, S1a streams according to a preferred process as described in the general description and the examples

CITED LITERATURE

[0218] WO 2008/118265 A [0219] WO 2004/037802 A [0220] Ullmann's Encyclopedia of Industrial Chemistry, 5.sup.th edition, volume A 13 (1989) pages 443-466 [0221] EP 1 122 249 A1