DE1130422B - Process for the production of p-xylene from isobutylene polymers by catalytic aromatization with simultaneous degradation - Google Patents

Description

Process for the production of p-xylene from isobutylene polymers by catalytic aromatization with simultaneous degradation addition to patent 1 103 906 It is known that aliphatic hydrocarbons with at least Convert 6 carbon atoms into aromatics with the same number of carbon atoms. Further it is known to use mixtures of higher aliphatic hydrocarbons at the same time To catalytically aromatize degradation to aromatics with a lower carbon number. In the main patent 1103 906 is also described that a dodecylene fraction obtained by polymerization of isobutylene had been obtained as triisobutylene by depolymerization and simultaneous aromatization predominantly under suitable test conditions p-xylene yields existing C8 aromatics.

It has now been found that p-xylene according to the main patent by catalytic aromatization and simultaneous selective degradation of one by polymerizing dodecylene-containing polymer mixture obtained from isobutylene while observing short residence times at 400 to 650 ° C can be produced in such a way that the starting material those predominantly containing isobutylene in the catalytic polymerization Raw polymerization mixtures obtained from starting products, including polymers low molecular weight aliphatic hydrocarbons with at least 8 and at most Contains 16 carbon atoms without further purification or distillation.

The higher polymers contained in the crude product split in this Fall to lower polymers and give an additional yield of aromatics.

This method can be used because of the saving in distillation costs and the avoidance of undesirable, poorly usable by-products even then still be economical if the yield of the resulting aromatics is lower and the composition is less valuable than using equal amounts by weight of the pure fractions.

In the catalytic dimerization of isobutylene, in which usually certain amounts of n-butylene are still present, fall according to the various processes Crude products in addition to diisobutylene (2,4,4-trimethylpentene-1 and -2) still varying amounts (10 to 500/0) of triisobutylene, traces of tetraisobutylene and more more or less large proportions of copolymers mainly of isobutylene and n-butylene contain. The proportions of the copolymers can be up to 50% in individual processes and be more. Since there is no suitable use for them, are they can only be used as motor fuel. When choosing suitable dimerization conditions, which largely depends on the isobutylene content of the available starting material depend, crude polymerization products can be obtained, which are used in the aromatization according to the aromatization conditions described in the main patent p-xylene in the same or provide almost the same purity and yield as pure, through fractionated Diisobutylene (2,4,4-trimethylpentene-1 and -2) and triisobutylene obtained by distillation. In particular, if you want to produce p-xylene, you use it as the starting product for the execution of the present process advantageous such polymer mixtures, into which as little n-butylene as possible is polymerized.

The reaction according to the invention thus not only saves the high costs of distillation and the accumulation of inferior by-products, but still contributes to an increased level p-xylene yield, based on the starting mixture, at. With the use of dimerization raw products for flavoring under the flavoring conditions specified in the main patent This results in a decisive simplification and cheaper production of p-xylene.

Example 1 A crude polymer which consists of a mixture of 91.4% isobutylene and 8.6% n-butylene by dimerization over solid contact by known methods and that was about 7 to 8% gas (mostly isobutylene), about 68010 Diisobutylene (fraction from bp 99 to 104 ° C) and about 19% residue (essentially Triisobutylene) is flavored under the conditions of the main patent. A p-xylene content in the xylene isomer mixture of 94.80 / 0 and a p-xylene content are obtained in the liquid catalyst of 180/0.

One was then flavored under the same test conditions Test substance of pure diisobutylene gave a p-xylene yield in the xylene isomer mixture of 94.60 / o and in the liquid catalyst of 19%.

Example 2 An analogous to example 1 from a starting product of 85.0% Isobutylene, 14.30 / 0 n-butylene and 0.70 / 0 saturated C4 hydrocarbons crude polymerization product was degassed (content of dissolved C4 hydrocarbons about 60/0). A subsequent fractional distillation gave 75.00 / o diisobutylene and 22% residue (essentially triisobutylene). The flavoring of the raw Dimerisate after degassing, the one obtained therefrom by fractional distillation Brought fraction from bp 99 to 104 ° C and the test substance from pure diisobutylene The following results: The p-xylene content in the xylene isomer mixture was: when degassed crude dimerizate ...... 93.50 / 0 for the fraction from bp 99 to 104 ° C 93.60 / 0 pure test substance 93.7% / 0.

The p-xylene content in the flavored liquid polymer was in all three cases at 23%; the crude dimer was found to be within the accuracy of the measurement even a slightly higher value.

Example 3 A polymer blend comprising 11% gas, 620% diisobutylene and 220/0 residue (essentially tri- isobutylene) and through polymerization using a starting product of 33.8% isobutylene and 66.2% n-butylene was produced by sulfuric acid, was flavored according to the method of the main patent and brought the following results: The p-xylene content in the xylene isomer mixture was: for the crude polymerization product ... 93.30 / o for the pure test substance ... 94.10 / 0 The p-xylene content in the liquid polymer was: in the case of the crude polymerization product ... 18.00 / 0 for pure test substance ... .......... 19.00 / 0.

The results are therefore the same within the measurement accuracy.

Claims (1)

PATENT CLAIM: Process for the production of p-xylene by catalytic Flavoring and simultaneous selective degradation of a by polymerizing Isobutylene obtained, dodecylene-containing polymer mixture while observing short residence times at 400 to 6500 C according to Patent 1 103 906, characterized in that that as the starting material in the catalytic polymerization of predominantly Isobutylene-containing starting materials resulting crude polymerization mixtures, which, among other things, contain polymers of low molecular weight aliphatic hydrocarbons Contain at least 8 and at most 16 carbon atoms, without further purification or distillation can be used. References considered: U.S. Patents No. 2,212 026, 2,337,190; Fuel Chemistry, 20 (1939), pp. 1 to 9; Proceeding of the Royal Society, A, 184 (1945), pp. 447-463. Older patents considered: German Patent No. 1 103 906.