PROCESS FOR PREPARING ISOOLEFINS
A continuous process for preparing an isoolefin having 4 to 6 carbon atoms is performed by cleaving a compound of the formula I R 1 —O—R 2 (I) wherein R 1 =a tertiary alkyl radical having 4 to 6 carbon atoms, and R 2 =H or an alkyl radical, in a gas phase over a solid catalyst, in the temperature range of 200 to 400° C., at a pressure of 0.1 to 1.2 MPa, in a reactor which is equipped with a heating jacket and is heated with a liquid heat carrier, wherein the cleavage is carried out in such a way that a temperature drop in the catalyst zone at any point in relation to the entrance temperature is less than 50° C., wherein (i) a reaction mixture in the reactor and (ii) the heat carrier in the jacket flow through the reactor in cocurrent, and wherein a temperature difference of the heat carrier between a feed point to the reactor and an outlet from the reactor is adjusted to less than 40° C.
1 . A continuous process for preparing an isoolefin having 4 to 6 carbon atoms, comprising:
cleaving a compound of the formula I
R 1 —O—R 2 (I)
wherein R 1 =a tertiary alkyl radical having 4 to 6 carbon atoms, and
R 2 =H or an alkyl radical,
in a gas phase over a solid catalyst, in the temperature range of 200 to 400° C., at a pressure of 0.1 to 1.2 MPa, in a reactor which is equipped with a heating jacket and is heated with a liquid heat carrier,
wherein said cleavage is carried out in such a way that a temperature drop in the catalyst zone at any point in relation to the entrance temperature is less than 50° C.,
wherein (i) a reaction mixture in the reactor and (ii) the heat carrier in the jacket flow through the reactor in cocurrent, and
wherein a temperature difference of the heat carrier between a feed point to the reactor and an outlet from the reactor is adjusted to less than 40° C.
2 . The process according to claim 1 , wherein said compound of the formula I is selected from the group consisting of tert-butanol, methyl tert-butyl ether, ethyl tert-butyl ether, tert-amyl methyl ether and mixtures thereof.
3 . The process according to claim 1 , wherein a mixture of at least two compounds of the formula I is used.
4 . The process according to claim 3 , wherein the mixture of compounds of the formula I used is a mixture which comprises tert-butanol and methyl tert-butyl ether.
5 . The process according to claim 1 , wherein the temperature drop in the catalyst zone is less than 30° C.
6 . The process according to claim 1 , wherein the heat carrier is passed into the heating jacket of the reactor at a temperature which is 10 to 30° C. higher than the temperature of a reactant flowing into the reactor.
7 . The process according to claim 1 , wherein the solid catalyst is selected from the group consisting of metal oxides, mixed metal oxides, acids on metal oxide supports, metal salts and mixtures thereof.
8 . The process according to claim 7 , wherein solid catalyst has a mean particle size of 2 to 4 mm.
9 . The process according to claim 1 , wherein compound I is MTBE, and
wherein compound I is cleaved over a catalyst which comprises magnesium oxide, aluminium oxide and silicon oxide to give isobutene and methanol.
10 . The process according to claim 1 , which is performed in a tubular reactor, tube bundle reactor or plate reactor.
11 . The process according to claim 1 , wherein the process is performed in a tube bundle reactor.
12 . The process according to claims 10 or 11 , which is performed in a tube bundle reactor whose individual tubes have a length of 1 to 15 m.
13 . The process according to claims 10 or 11 , which is performed in a tube bundle reactor whose individual tubes have an internal diameter of 10 to 60 mm.
14 . The process according to claims 10 or 11 , which is performed in a tube bundle reactor whose individual tubes have a thickness of the tube wall of 1 to 4 mm.
15 . The process according to claims 10 or 11 , which is performed in a tube bundle reactor in which the tubes have a separation of 3 to 15 mm from one another.