DE2048309A1 - Isoprene prodn - by catalytic dehydration of 3-methyl-3-buten -1-ol - Google Patents

Abstract

Isoprene, is prepd. in high yield and purity by catalytic dehydration of 3-methyl-3-buten-3-ol-ol in the presence of Ce tert. phosphate, opt. supported on a carrier, at 180-300 degrees C, and pref. in the presence of steam and/or an inert gas.

Description

Process for Making Isoprene The present invention relates to a process for the production of isoprene by catalytic dehydration of 3-llethyl-3-buten-1-ol.

There are already a number of processes for the production of isoprene described. For example, it is known to produce isoprene by dehydrogenating C5 hydrocarbon mixtures to produce 5. It is also known by reacting isobutylene with formaldehyde first to produce 4,4-dimethyl-1,3-dioxane and from this by catalytic Isoprene cleavage.

Next is a method for producing isoprene by dehydration of 2-rlethyl-3-buten-2-ol, which is obtained by reacting acetone with acetylene can be obtained.

However, the mentioned processes have the disadvantage that the production the starting materials used in these processes are not sufficiently economical is and / or that the conversion to isoprene is not sufficiently selective and not in satisfactory yield runs. It is also from Petroleum Chemistry U.S.S.R. Bad 4, (1965), pages 211 to 220 known that in the dehydration of 3-methyl-3-buten-1-ol, at temperatures between 200 and 3000 C on tertiary calcium phosphate only moderate isoprene yields, e.g. of less than 20 7o of theory, achieved at 2500C will.

It has now been found that isoprene can be converted by catalytic dehydration of 3-methyl-3-buten-1-ol in the presence of a tertiary phosphate as a catalyst Can be advantageously produced at elevated temperature if the catalyst used is tertiary Cerium phosphate is used and the dehydration is carried out at 180 to 3000C ..

According to the process, a starting material becomes through implementation of isobutylene with formaldehyde in easier and more economical way can be obtained (see. The German Auslegeschrift 1 275 449), isoprene in excellent Yield and high purity obtained.

For the dehydration, the starting material is expediently in a Purity of at least 85% by weight, preferably at least 90 Ce., Used. In As a rule, technically pure 3-: ethyl-3-buten1-ol is used, which is generally Has a purity of 85 to 99% by weight. Surprisingly, be special obtain high yields if the starting material is reacted in a mixture with steam. In general, the amount of water vapor is 10 to 50% by volume, preferably 10 up to 30% by volume, based on the gaseous reaction gas. Because of the beneficial use from water vapor it is possible to directly dehydrate the water-containing one To use 3-rsetheyl-3-buten-1-ol, which is used in the industrial production of the rTethylbutenols obtained from isobutylene and formaldehyde before the purification by distillation will. When using water-containing starting material, this generally contains at most the same amount of water as is found in the starting material at saturation at around room temperature is resolved. The dehydration of the starting material will also produce beneficial results achieved in the presence of inert gases, e.g. nitrogen or argon. The inert gases are generally used in amounts of 10 to 40 vol. $, preferably 10 to 30 vol. 70, based on the gaseous mixture of starting material and inert gas. the Inert gases can be used both in addition to water vapor and instead of water vapor used in dehydration.

Tertiary cerium phosphate is used as the catalyst. The tertiary Cerium phosphate can be used as such or on an inert carrier material. Suitable carrier materials are, for example, pottery shards, titanium dioxide, natural or synthetic zeolites and especially pumice stone. The weight ratio of The carrier material for tertiary cerophate is generally 20: 1 to 1: 5. However, the tertiary cerium phosphate is preferably used as such. The cerium phosphate can be used as a powder or in a coarser form, e.g. in the form of balls, Tablets or StrEngen, for example with a diameter between 1 and 10 mm, used Powdered catalysts are used, for example, preferably in dehydration in the fluidized bed, while in the dehydration over fixed catalysts the catalyst is preferably used in a coarser form.

The dehydration is carried out at temperatures between 180 and 300 ° C, preferably 180 to 2800C, in particular carried out between 220 and 2500C. Of the applied pressure can vary within wide limits. Generally works one at atmospheric pressure or slightly reduced pressure. However, it is also possible to carry out the reaction at elevated pressure, for example at 10 atmospheres or more reduced pressure, for example of 100 torr.

The dehydration can be carried out batchwise.

However, the process is advantageously carried out continuously. The dehydration can be carried out, for example, in such a way that the gaseous 3-methyl-3-buten-1-ol, if necessary, in a mixture with steam and / or inert gas The reaction temperature passes through a tubular reactor filled with cerium phosphate granules or strands is filled. The duration of the dwell time can be within wide limits vary, as a rule, retention times between 0.01 and 15 seconds are maintained.

The work-up can e.g. be done in such a way that one does The gas mixture leaving the reactor is condensed and the condensate obtained, e.g. by Distillation separates0 Any unreacted methylbutenol is expedient returned to the reaction. In general, however, with one-time throughput Conversions of more than 98% can be achieved, so that the separation of unreacted Methylbutenol can be dispensed with at the high conversions mentioned above.

The catalyst to be used for the process is characterized by a lance life span. If activity falls, it can the catalyst by treatment with air and / or water vapor at temperatures between 200 and 6000C can be regenerated, whereby it regains the original activity, Isoprene is an important monomer for the production of valuable polymers, like synthetic rubber as well as a valuable intermediate product, e.g. for the Production of terpenes.

The parts by weight mentioned in the example relate to parts by volume like kilograms to liters.

Example Through a vertical pipe with a volume of 1 volume and a diameter to length ratio of the tube of 1 to 5, dis with particles is filled from tertiary cerium phosphate with an average grain size of 4 mm at 2300C and 700 Torr 2.5 parts by weight of 3-methyl-3-buten-1-ol, which is 2% by weight Contains water, passed through in gaseous form. The residence time is 5 seconds. The reaction mixture leaving the reaction tube is condensed and then rectified. With a single throughput, isoprene is obtained in a yield of 98% of theory.

Claims (3)

Claims 9 process for the production of isoprene by catalytic dehydration of 3-methyl-3-buten-1-ol in the presence of a tertiary phosphate as a catalyst at elevated temperature, characterized in that the catalyst used is tertiary Cerium phosphate is used and the dehydration is carried out at 180 to 300 ° C. 2. The method according to claim 1, characterized in that the Performs dehydration in the presence of steam and / or an inert gas. 3. The method according to claim 1 and 2, characterized in that a supported catalyst containing tertiary cerium phosphate is used.