Process for preparing an epoxide from an oxygenate
The invention relates to an integrated process for preparing an epoxide from an oxygenate, wherein the oxygenate is converted into a lower olefin and the lower olefin is subsequently epoxidised, and wherein isobutane obtained after hydrogenation and subsequent normal/iso separation of C4 hydrocarbons obtained as by-product of the oxygenate conversion, is converted into a hydroperoxide that is used for the conversion of the lower olefin into the corresponding epoxide.
1. A process for preparing an epoxide from an oxygenate, the process comprising the following steps:
a) contacting the oxygenate with a molecular sieve-comprising catalyst, at a temperature in the range of from 350 to 1000° C. to obtain an olefinic product stream comprising ethylene, propylene and C4 hydrocarbons;
b) separating ethylene and/or propylene and a fraction comprising C4 hydrocarbons including normal butane, isobutane, normal butene and isobutene, from the olefinic product stream;
c) hydrogenating at least part of the fraction comprising C4 hydrocarbons in a hydrogenation unit to obtain a saturated C4 hydrocarbon stream;
d) separating the saturated C4 hydrocarbon stream into a stream enriched in normal butane and a stream enriched in isobutane;
e) oxidizing the isobutane in the stream enriched in isobutane into tertiary butyl hydroperoxide; and
f) reacting tertiary butyl hydroperoxide obtained in step d) with ethylene and/or propylene separated from the olefinic product stream obtained in step a) to obtain the epoxide and tertiary butanol.
2. A process according to claim 1 , wherein the molecular sieve-containing catalyst is a zeolite-comprising catalyst.
3. A process according to claim 2 , wherein the zeolite-comprising catalyst comprises at least one zeolite selected from MFI, MEL, TON and MTT zeolites.
4. A process according to claim 3 , wherein the zeolite-comprising catalyst comprises at least one of ZSM-5, ZSM-11, ZSM-22 and ZSM-23 zeolites.
5. A process according to claim 1 , wherein the oxygenate is selected from the group consisting of alkanols and di-alkylethers having up to five carbon atoms.
6. A process according to claim 5 , where the oxygenate is methanol, dimethylether, or a mixture thereof.
7. A process according to claim 1 , further comprising the following step:
g) recycling at least part of the tertiary butanol obtained in step f) to step a).
8. A process according to claim 7 , wherein tertiary butanol is co-produced in step e) and wherein tertiary butanol produced in step e) is recycled to step a).
9. A process according to claim 7 , wherein the tertiary butanol recycled to step a) is dehydrated prior to recycling to step a).
10. A process according to claim 8 , wherein the tertiary butanol recycled to step a) is dehydrated prior to recycling to step a).
11. A process according to claim 1 , wherein at least part of the tertiary butanol obtained in step f) is first dehydrated and then hydrogenated to obtain isobutane and wherein the isobutane thus-obtained is recycled to step e).
12. A process according to claim 11 , wherein the dehydrated tertiary butanol is hydrogenated by supplying the dehydrated tertiary butanol to hydrogenation step c).
13. A process according to claim 1 , wherein a part of the fraction comprising C4 hydrocarbons obtained in step b) is recycled directly to step a).