DD240739A1 - PROCESS FOR PREPARING ISOBUTENE - Google Patents

Abstract

Process for the preparation of isobutene by catalytic cleavage of methyl tert-butyl ether. According to the invention, methyl tert-butyl ether is cleaved in a temperature range of 440 K to 570 K and pressures of 0.1 to 1.0 MPa using a modified with calcium oxide gamma-alumina catalyst with high selectivity and in good yields to isobutene.

Description

Field of application of the invention

The invention relates to a process for the preparation of isobutene, starting from methyl tert-butyl ether.

Characteristic of the known technical solutions

Processes for the recovery of isobutene from C ₄ -hydrocarbon mixtures are known, for. B. extraction of isobutene with concentrated sulfuric acid and decomposition of the tert-butyl sulfate, separation with molecular sieves and dehydration of tert-butanol or isobutanol (Ullmann's Encyclopedia of Industrial Chemistry, 4th Edition, Verlag Chemie, Weinheim, 1975, Volume 9,

P. 38/39). There are also known processes, according to which isobutene obtained by catalytic cleavage of methyl tert-butyl ether

In general, acidic catalysts, eg. B. based on alumina. These strong acid catalysts have the disadvantage that side reactions of isobutene (oligomerization) and methanol (dehydration to dimethyl ether) occur to a significant extent.

In order to reduce or suppress the formation of the dimethyl ether, the catalytic cleavage of methyl tert-butyl ether is carried out in the presence of water or water vapor according to FR-PS 2 492 809. However, this process requires a complicated drying of the resulting isobutene and methanol, the presence of water leads to an increased tert-butanol formation and means additional energy consumption for steam generation or to achieve the necessary gap temperatures on the catalyst.

The well-known according to DD-PS 119 031 modified Al ₂ 0 ₃ -Si0 ₂ catalyst allows a process in which the dehydration of methanol plays only a minor role. In this catalyst surface hydroxyl groups are replaced by ether groups. This catalyst requires the preparation of expensive Tetraalkylorthosilicaten or other expensive organosilicon compounds in its preparation.

Object of the invention >

The object of the invention is the production of isobutene by an improved catalytic cleavage of the methyl tert-butyl ether.

Explanation of the essence of the invention

The object of the invention is to carry out the methyl tert-butyl ether for the production of isobutene with high selectivity and low formation of by-products. This object is achieved by a process for the preparation of isobutene by catalytic cleavage of methyl tert-butyl ether over solid inorganic catalysts at temperatures up to 570 K and pressures up to 1 MPa, according to the invention, the cleavage at temperatures of 440 K to 540 K and at pressures of 0.1 to 1.0 MPa, at a space velocity (LSHV-Liquid Howly Space Velocity), expressed in volume of liquid per volume of catalyst and hour from 0.5 to 20.0 on a catalyst made of alumina which optionally contains up to 5% by weight of SiO ₂ for stabilization and which has been modified with calcium salts of a thermally decomposable acid anion to 870 K, having a calcium content of from 0.5 to 5% by mass of CaO, based on the anhydrous material results and has a pH of 7.5 to 11 in a 10% suspension in salt-free water. The process for the catalytic cleavage of the methyl tert-butyl ether is advantageously carried out at a reaction temperature of 460 K to 520 K and at pressures of 0.1 to 0.6 MPa. The reaction is advantageously operated at a space velocity expressed in volume of liquid per volume of catalyst and hour (LSHV Liquid Howly Space Velocity) of 0.5 to 10.

Advantageously, the catalyst used contains alumina as a gamma-alumina. The pH of the 10% strength catalyst suspension in salt-free water is advantageously 8 to 10.

Surprisingly, it has been found that methyl tert-butyl ether can be converted to isobutene with high selectivity and a particularly long catalyst lifetime if a calcium oxide-modified aluminum oxide catalyst is used. The modification can be done in different ways. In the simplest case, the deformed clay, preferably gamma-alumina, which may also contain up to about 5% by weight of SiO ₂ for stabilization, can be mixed with the water-soluble Ca salt of an acid

- 3 - Z4U / da

example 1 catalyst MTBE Product composition [%] dimethyl H ₂ O C ₈ yield yield 65.2 2 isobutene methanol ether isobutene methanol 66.2 3 [%] N 98.9 4 18.3 7.3 99.4 91.8 CJL 21.7 7.6 2.7 0.1 99.6 82.9 6. A 22.8 48.8 26.4 0.4 3.1 0.2 99.3 78.3 7 A 9.6 57.3 30.1 1.9 0.2 <0.1 99.8 _ 95.2 8th B 26.6 46.4 29.4 3.6 0.8 0.1 99.8 88.4 9 B 9.8 57.3 28.4 6.3 1.4 0.2 98.6 86.5 10 B 2.5 61.9 29.5 1.2 2.2 0.3 99.6 93.7 11 B 0.2 62.6 30.4 2.9 0.5 <0.1 99.8 91.9 12 B 14.8 54.0 31.0 4.4 1.1 0.1 98.0 81.0 13 B 5.4 60.1 32.8 3.2 1.5 0.2 96.0 93.7 B 1.5 61.4 31.5 2.5 1.3 0.4 99.6 B 3.9 58.8 29.0 4.5 1.0 0.1 99.7 B 5.2 95.7 32.4 1.5 1.8 0.5 99.6 B 1.5 62.5 0.8 <0.1 B 4.9 60.3

which is thermally decomposable and whose anion can be removed in the temperature range up to about 870 K from the molds. But it is also possible to add the calcium salt already during the plasticization to the clay and only then to deform, dry and anneal.

The modification can also be such that the moldings are treated with the solution of a Ca salt, preferably at elevated temperatures between 320 and 370 K and particularly favorable in the temperature range between 340 and 350 K, their pH by addition or effect of Ca (OH) _{2 was} adjusted to between 8 and 12, and then dried and annealed. The catalysts used contain calcium in an amount of about 0.5 to 5 wt .-% CaO, based on the anhydrous material and have in a suspension of the milled catalyst in salt-free water (10 wt .-% solids) pH in Range of 7.5 to 11, preferably 8 to 10, on.

The alcohol is recovered from the process and can be used to synthesize new ethers.

The recovered isobutene can be used without special purification for the alkylation of phenols and alkylphenols.

If the isobutene is used for the polymerization, it can usually be purified by a subsequent pressure distillation of residues of methyl tert-butyl ether and dimethyl ether.

embodiments

Catalyst A

A catalyst of gamma-alumina, prepared in a known manner by deformation of a precipitation boehmits by screw extruder into strand moldings with a diameter of about 3 mm, drying the same at about 370 to 390 K and annealing in air for the purpose of production at about 770 K, pH of 10% catalyst suspension: 6.8; is treated with an about 1n Ca (NO ₃ ) ₂ solution for about 2 h at 340 to 350 K, the pH of which is adjusted to about 9 by the addition of Ca (OH) ₂ and maintained at this pH during the treatment by correspondingly giving way to Ca (OH) ₂ . The liquid: solids ratio is about 3: 1 and by pumping or stirring is provided for a circulation of the solution during the treatment time. After completion of the treatment, the solution is separated and the adhering solvent residues are removed by washing once with the same amount of salt-free water. The moldings are dried again and annealed. pH of the 10% catalyst suspension: / 0.9 Ca content of the catalyst, calculated as CaO and based on the anhydrous material: 3.8 mass%

 Catalyst B

A gamma-alumina containing about 3 wt .-% SiO ₂ for stabilization and in the form of a strand pellets with molding diameter of about 3 mm, is soaked using a Ca (NO ₃ ) ₂ solution in a known manner so that about 2 5% by weight of CaO, based on the anhydrous material. The impregnated moldings are dried in catalyst A and calcined to give catalyst B. pH of the 10% catalyst suspension: 8.5; Ca content, calculated as CaO and based on the anhydrous material 2.6% by mass.

Example 1 to 13

The catalytic cleavage of the methyl tert-butyl ether is carried out in a heated tubular reactor (diameter 35 mm, length 600 mm). 400 cm ^{3 of} catalyst are used. The dosage of the product is carried out by means of a piston metering pump. Before the reactor zone is a preheating zone of 1000 mm and a diameter of 5 mm, which is heated to 450 ° C. For temperature control, a temperature sensor was mounted in the center of the reactor. With a pressure regulator at the reaction outlet the working pressure is adjusted. Downstream is a cooling system in which the resulting from the reactor reaction mixture is liquefied. The analysis of the product composition was carried out by gas chromatography. The table below summarizes reaction conditions and results.

Examples 1 to 13 LHSV print temperature sales example catalyst Γ ml MTBEl [MPa] [K] MTBE L ml cont. J [%] 0.5 0.1 503 77.2 1 A 0.5 0.5 503 90.4 2 A 0.5 0.1 473 73.4 3 B 0.5 0.1 483 90.2 4 B 0.5 0.1 493 97.5 CJL B 0.5 0.1 503 99.8 6 B 1.0 0.1 483 85.2 7 B 1.0 0.1 493 94.6 8th B 1.0 0.1 503 98.6 9 B 2.5 0.1 523 96.3 10 B 0.5 0.5 493 94.2 11 B 1.0 0.5 513 98.5 12 B 2.5 0.5 523 95.1 13 B

Claims (6)

Invention claim: 1. A process for the preparation of isobutene by catalyzed cleavage of methyl tert-butyl ether on solid inorganic catalysts at temperatures up to 570 K and pressures up to 1 MPa, characterized in that the cleavage at temperatures of 440 K and at pressures of 0.1 MPa to 1.0 MPa, at a space velocity, expressed in volume of methyl tert-butyl ether per volume of catalyst and hour, from 0.5 to 20 on a catalyst consisting of alumina, optionally for stabilization up to 5 Wt .-% SiO ₂ and which has been modified with calcium salts of a thermally decomposable to 870 K acid anions that a calcium content of 0.5 to 5 Ma .-% CaO, based on the anhydrous material results, and in a 10 ° / oigen suspension in salt-free water has a pH of 7.5 to 11. 2. The method according to item 1, characterized in that the cleavage of methyl tert-butyl ether takes place in the temperature range from 460 K to 520 K. 3. The method according to item 1, characterized in that it is worked with a space velocity of 0.5 to 10. 4. The method according to item 1, characterized in that it is carried out at pressures of 0.1 to 0.6 MPa. 5. The method according to item 1, characterized in that the catalyst contains as alumina gamma-alumina. 6. The method according to item 1, characterized in that the pH of the 10% strength catalyst suspension in salt-free water is 8 to 10.