Method for producing isophorone

1. A process for preparing isophorone, the process comprising:

(i) reacting acetone via a catalysed aldol condensation in a reactor, thereby obtaining a reaction product,

(ii) working-up the reaction product, thereby obtaining a stream of value,

(iii) hydrolyzing the stream of value in a hydrolysis apparatus,

(iv) separating the stream of value into an organic fraction and an aqueous fraction,

(v) recovering isophorone from the organic fraction,

(vi) distilling the aqueous fraction in a distillative workup apparatus comprising a top and a bottom,

(vii) passing vapours from the top of the distillative workup apparatus onward into the hydrolysis apparatus, and

(viii) subjecting water from the bottom of the distillative workup apparatus to a flash evaporation, thereby obtaining purified water which is recycled into the reactor for preparing isophorone.

2. The process according to claim 1 , wherein the catalysed aldol condensation is performed in a liquid phase at a temperature of from 100 to 250° C., and a pressure of from 5 to 50 bar.

3. The process according to claim 1 , wherein the catalysed aldol condensation is performed in a gas phase at a temperature of from 100 to 400° C.

4. The process according to claim 1 , wherein the catalysed aldol condensation is performed in a supercritical range at a temperature of from 250 to 350° C. and a pressure of from 50 to 200 bar.

5. The process according to claim 1 , wherein a homogeneous or a heterogeneous catalyst is used in the catalysed aldol condensation.

6. The process according to claim 1 , wherein the catalysed aldol condensation occurs in a liquid phase with a homogeneous catalyst.

7. The process according to claim 6 , wherein the homogeneous catalyst is alkali of <1% by weight.

8. The process according to claim 1 , wherein the catalysed aldol condensation is performed in at least one reactor selected from the group consisting of a tubular reactor, a stirred tank, a stirred tank cascade, a fixed bed reactor, a reactive distillation column, a microstructured reactor, and a loop reactor.

9. The process according to claim 1 , wherein the catalysed aldol condensation is performed in a reactive distillation column, a tubular reactor or a fixed bed reactor.

10. The process according to claim 1 , wherein said working-up (ii) comprises (ix) separating the reaction product into individual components and removing the individual components in full or in part.

11. The process according to claim 10 , wherein the individual components are removed by at least one separation method selected from the group consisting of distillation, flash evaporation, crystallization, extraction, sorption, permeation, and phase separation, continuously or batchwise, in one or more stages.

12. The process according to claim 1 , wherein said distilling (vi) is performed spatially separately from the catalysed aldol condensation or takes place in a reaction apparatus.

13. The process according to claim 10 , wherein the individual components are removed via a reactive distillation spatially separately from the catalysed aldol condensation.

14. The process according to claim 10 , wherein the individual components are removed in three fractions:

a) a fraction comprising unconverted acetone, water and low boilers, wherein the fraction a) is condensed and then recycled into the reactor;

b) a fraction comprising enriched coloured substances, wherein the fraction b) is purified further and materials of value are recycled into the reactor; and

c) a fraction comprising isophorone, more highly condensed products, water, and catalyst, wherein the fraction c) is subsequently subjected to a hydrolysis.

15. The process according to claim 14 , wherein the fraction a) is withdrawn as a vapour stream comprising acetone, water, and low boilers comprising diacetone alcohol and mesityl oxide, condensed and added again to the reactor with a feedstock comprising acetone, water, and catalyst.

16. The process according to claim 14 , wherein the fraction b) is withdrawn as a sidestream of a distillation column.

17. The process according to claim 14 , wherein the fraction b) is purified by a combination of neutralization or extraction and subsequent distillation in a reactive distillation column, thereby obtaining a worked-up phase.

18. The process according to claim 17 , wherein the worked-up phase of the fraction b) is conducted into the hydrolysis apparatus with products of value comprising isophorone and high boilers, with or without catalyst.

19. The process according to claim 17 , wherein any further phase of the fraction b) comprises acetone, diacetone alcohol and mesityl oxide, and is recycled into the reactor.

20. The process according to claim 14 , wherein the fraction c) is subjected to the hydrolysis in which by-products are converted partly or fully to isophorone, acetone and other products of value.

21. The process according to claim 1 , wherein said hydrolyzing (iii) is performed in a reactive distillation column in which low boilers comprising acetone, diacetone alcohol and mesityl oxide are obtained and recycled into the reactor.

22. The process according to claim 14 , wherein the hydrolysis of the fraction c) is performed in an apparatus via a reactive distillation with a simultaneous separation of the reaction product into the fractions a), b), and c).

23. The process according to claim 14 , wherein the hydrolysis of the fraction c) is effected at a water concentration of 0.1-99.9% by weight.

24. The process according to claim 14 , wherein the hydrolysis of the fraction c) is effected at a catalyst concentration of 0.001-10% by weight.

25. The process according to claim 14 , wherein the hydrolysis of the fraction c) is performed at a pressure of 1-200 bar.

26. The process according to claim 14 , wherein the hydrolysis of the fraction c) is effected at a temperature of 100-300° C.

27. The process according to claim 14 , wherein the hydrolysis of the fraction c) is performed in a reactive distillation column at a temperature or a temperature profile established according to boiling temperatures in bottoms and at individual separation or reaction stages.

28. The process according to claim 14 , wherein the fraction c) is separated into an organic fraction d) and an aqueous fraction e).

29. The process according to claim 28 , wherein the organic fraction d) is purified by distillation.

30. The process according to claim 28 , wherein the aqueous fraction e) is supplied to a wastewater cleaning operation, which optionally is performed in one or more distillation columns.

31. The process according to claim 30 , wherein the wastewater cleaning operation is performed at a pressure of 1-200 bar.

32. The process according to claim 30 , wherein the wastewater cleaning operation is effected at a system pressure established in an overall hydrolysis/wastewater column system.

33. The process according to claim 30 , wherein a pressure in the flash evaporation is below a pressure in the wastewater column.

34. The process according to claim 33 , wherein vapours g) obtained from the flash evaporation consist essentially of pure water and are condensed and recycled as water into the reactor.