Method for the production of isobutene from commericial methyl tert-butly ether

1. A process for preparing isobutene by acid-catalyzed dissociation of methyl tert-butyl ether (MTBE), said process comprising:

fractionating a feed mixture comprising MTBE, C 4 - and C 5 -hydrocarbons, methanol, methyl sec-butyl ether, TBA and C 4 oligomers to form a product consisting of

a) a fraction a), comprising MTBE, MSBE, TBA and C4 oligomers. and

b) a fraction b), comprising C4- and C5-hydrocarbons, MTBE and methanol, dissociating by an acid-catalyzed reaction the MTBE present in the fraction a) to form a dissociation product comprising methanol and isobutene, and separating the dissociation product to form a separation product c) which comprises unreacted MTBE, methanol, isobutene and low boilers and high boilers in a column into an isobutene-containing top product and a bottom product comprising the unreacted MTBE and the major part of the methanol from the dissociation, and recirculating the bottom product to the feed mixture.

2. The process as claimed in claim 1 , wherein

the C 4 oligomers, MSBE and TBA are separated off from the fraction a) by means of a distillation, in which they are taken off as bottom product.

3. The process as claimed in claim 1 , wherein

the C 4 oligomers, MSBE and TBA are separated off from the fraction a) by means of a bleed stream.

4. The process as claimed in claim 1 , wherein

the isobutene-containing stream, which has been separated off from the dissociation product is fractionated in a purification column to give a bottom product consisting of pure isobutene and a top product comprising isobutene and volatile by-products.

5. The process as claimed in claim 1 , wherein

the isobutene-containing stream, which has been separated off from the dissociation product is scrubbed with water, and subsequently fractionated in a purification column to give a bottom product consisting of pure isobutene and a top product comprising isobutene and volatile by-products.

6. The process as claimed in claim 4 , wherein

water present in the isobutene-containing stream is removed by means of a decanter.

7. The process as claimed in claim 4 , wherein

water present in the isobutene-containing stream is removed by means of a decanter located in the top section of the purification column.

8. The process as claimed in claim 4 , wherein

water present in the isobutene-containing stream is removed by means of a decanter which is located at a the side offtake of the purification column.

9. The process as claimed in claim 1 , wherein the dissociation and the separation of the isobutene from the MTBE present in the fraction a) are carried out in a reactive distillation column.

10. The process as claimed in claim 2 , wherein

the isobutene-containing stream, which has been separated off from the dissociation product is fractionated in a purification column to give a bottom product consisting of pure isobutene and a top product comprising isobutene and volatile by-products.

11. The process as claimed in claim 3 , wherein

the isobutene-containing stream, which has been separated off from the dissociation product is fractionated in a purification column to give a bottom product consisting of pure isobutene and a top product comprising isobutene and volatile by-products.

12. The process as claimed in claim 2 , wherein

the isobutene-containing stream, which has been separated off from the dissociation product is scrubbed with water, and subsequently fractionated in a purification column to give a bottom product consisting of pure isobutene and a top product comprising isobutene and volatile by-products.

13. The process as claimed in claim 3 , wherein

the isobutene-containing stream, which has been separated off from the dissociation product is scrubbed with water, and subsequently fractionated in a purification column to give a bottom product consisting of pure isobutene and a top product comprising isobutene and volatile by-products.

14. The process as claimed in claim 5 , wherein

water present in the isobutene-containing stream is removed by means of a decanter.

15. The process as claimed in claim 5 , wherein

water present in the isobutene-containing stream is removed by means of a decanter located in the top section of the purification column.

16. The process as claimed in claim 6 , wherein

the water present in the isobutene-containing stream is removed by means of a decanter located in the top section of the purification column.

17. The process as claimed in claim 5 , wherein

water present in the isobutene-containing stream is removed by means of a decanter which is located at a side offtake of the purification column.

18. The process as claimed in claim 6 , wherein

the water present in the isobutene-containing stream is removed by means of a decanter which is located at a side offtake of the purification column.

19. The process as claimed in claim 7 , wherein

the water present in the isobutene-containing stream is removed by means of a decanter which is located at a side offtake of the purification column.

20. The process as claimed in claim 2 , wherein

the dissociation and the separation of the isobutene from the MTBE present in fraction a) are carried out in a reactive distillation column.