DD240739C2 - 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 calcium oxide-modified 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 ₁ hydrocarbon-containing mixtures are known ζ 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 (Ulimanns Encyclopadie der technischen Chemie, 4 Edition Verlag Chemie, Weinheim, 1975, Volume 9, S 38/39) There are also known processes according to which isobutene obtained by catalytic cleavage of methyl tert-butyl ether

In general, acid catalysts, ζ B based on alumina are used These strong acid catalysts have the disadvantage that side reactions of the isobutene (oligomerization) and the 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 the 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 extensive drying of the resulting isobutene and methanol, the presence of water leads to an increased tert-butanol formation and means an additional energy consumption for steam generation or to achieve the necessary gap temperatures at the catalyst

The modified Al ₂ O ₃ SiO ₂ catalyst known from DD PS 119 031 permits a process in which the dehydration of the methanol plays only a minor role. In this catalyst, surface hydroxyl groups are replaced by ether groups. This catalyst requires the use of expensive tetraalkylorthosilicates or others in its preparation expensive organo silicon compounds

Object of the invention

The aim 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 tert-butyl ether of methyl 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 printing 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 which consists of alumina which optionally contains up to 5 % by mass of SiO _{2 for} stabilization and which has been modified with calcium salts of a thermally decomposed 870 K saureamone to give a calcium content from 0 5 to 5 mass% CaO, based on the anhydrous material and resulting in a 10% Suspe 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 carried out 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 as alumina contains 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 into isobutene with high selectivity and particularly long catalyst stoichiometry when a calcium oxide-modified alumina catalyst is used. The modification can be carried out in different ways. In the simplest case, the deformed alumina, preferably gamma alumina, can be used for stabilization may also contain up to about 5% by mass SiO ₃ with the water-soluble Ca salt of an acid

It is also possible, however, to add the calcium salt to the clay during plastification and only then to dry and to heat it

The modification can also be done so 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 The catalysts used contain calcium in an amount of about 0 5 to 5% by mass of CaO, based on the anhydrous material, and have been suspended in a suspension of the ground catalyst in salt-free water (10% by mass). Solid content) pH values in the range of 7 to 11, preferably 8 to 10

The alcohol is recovered from the process and can be used for the synthesis of new ethers The recovered isobutene can be used without special purification for the alkylation of phenols and alkylphenols Isobutene used for polymerization so it can in the usual way by a downstream pressure distillation of residues Methyl tert-butyl ether and dimethyl ether are purified

Exemplary embodiments

Catalyst A

A gamma alumina catalyst prepared in a known manner by deformation of a precipitation boehmite by means of screw extruder to strand moldings having a diameter of about 3 mm drying it at about 370 to 390 K and annealing in air for preparation at about 770 K pH of the 10% catalyst suspension 6 8 is treated with an approximately 1n Ca (NO ₃ J 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 treatment by adding ca (OH) ₂ gives according to the liquid solids ratio is about 3 1 and by pumping or stirring is provided for a circulation of the solution during the treatment tent After completion of the treatment, the solution is separated and the adhering remnants by washing once with the same amount of liquid of salt-free water The moldings are dried again and annealed pH value of the 10% catalyst orsuspension / 0.9 Ca content of the catalyst, calculated as CaO and based on the anhydrous material 3.8 Ma%

Catalyst B

A gamma alumina which contains about 3% by weight of SiO 2 for stabilization and is in the form of extruded granules having a molding diameter of about 3 mm is impregnated in a known manner using a Ca (NO ₃ J ₂ solution such that about 2 5% by mass CaO, based on the anhydrous material are applied to the impregnated moldings are dried and annealed in Catalyst A and give catalyst B pH value of the 10% catalyst suspension 8.5 Ca content, calculated as CaO and based on the anhydrous material 2 6 Ma%

Example 1 to 13

For the catalytic cleavage of the methyl tert-butyl ether, working in a heated tube reactor (diameter 35 mm, length 600 mm) 400 cm ^{3 of} catalyst are used The product is metered by means of a piston metering pump In front of the reactor zone there is a preheating zone of 1 000 mm and a Diameter of 5 mm heated to 450 ^° C. A temperature sensor was mounted in the center of the reactor for temperature control. A pressure regulator at the reaction outlet adjusts the working pressure. Downstream is a cooling system in which the reaction mixture from the reactor is liquefied. The product composition was analyzed Gas Chromatographic The following table summarizes reaction conditions and results

Examples 1 to 13 LHSV print temperature sales example catalyst Γ ml MTBEl [MPa] [K] MTBE [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 5 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 3 10 ΰ 0.5 0.5 493 94 2 11 B 1 0 0.5 513 98 5 12 B 25 05 523 95 1 13 B

Example Catalyst Production Composition [%]

MTBE isobutene Methanoi dimethyl H ₂ OC ₈ Yield yield

ether isobutene methanol

1 A 22.8 48.8 18.3 7.3 2.7 0.1 99.4 65 2 2 A 9.6 57.3 21.7 7.6 3.1 0.2 99.6 66.2 3 B 26.6 46.4 26.4 0.4 0.2 <0.1 99.3 98.9 4 B 9.8 57.3 30.1 1.9 0.8 0.1 99.8 91.8 5 B 2.5 61.9 29.4 3.6 1.4 0.2 99 8 82.9 6 B 0.2 62.6 28.4 6.3 2.2 0.3 98.6 78.3 7 8th 14.8 54.0 29.5 1.2 0.5 <0.1 99.6 95.2 8th B 5.4 60.1 30.4 2.9 1.1 0.1 99.8 88.4 9 B 1.5 61.4 31.0 4.4 1.5 0.2 98.0 86.5 10 B 3.9 58.8 32.8 3.2 1.3 0.4 96.0 93.7 11 B 5.2 95.7 31.5 2.5 1.0 0.1 99.6 91.9 12 B 1.5 62.5 29.0 4.5 1.8 0.5 99.7 81 0 13 B 4.9 60.3 32.4 1.5 0.8 <0.1 99.6 93.7

Claims (1)

Invention claim: A process for the preparation of isobutene by catalyzed cleavage of methyl tert-butyl ether over 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 in volume of methyl tert-butyl ether per volume of catalyst and hour, is carried out from 0.5 to 20 on a catalyst consisting of alumina which optionally contains up to 5% by mass of SiO _{2 for} stabilization and that with calcium Salts of a thermally decomposed 870 K Saureamons was that a calcium content of 0.5 to 5 Ma% CaO based on the anhydrous material, resulting, and in a 10% suspension in salt-free water has a pH of 7 5 to 11 2 Process according to item 1, characterized in that the cleavage of the methyl tert-butyl ether takes place in the temperature range from 460 K to 520 K. 3 Method according to item 1, characterized in that a space velocity of 0 5 to 10 is used 4 Method according to item 1, characterized in that at pressures of 0.1 to 0 6 MPa is used 5 Method according to item 1, characterized in that the catalyst contains as alumina gamma alumina 6 Process according to item 1, characterized in that the pH of the 10% strength catalyst suspension in salt-free water is 8 to 10.