DE950632C - Process for the enrichment or separation of one or more m-dialkylbenzenes from mixtures containing one or more of these aromatics - Google Patents

Description

Process for enrichment or separation of one or more m-Dialkylbenzenes from mixtures which contain one or more of these aromatics the The invention relates to a process for the separation of one or more m-Diajkylbenzenes, in particular m-xylene, from mixtures which contain one or more of these aromatics.

Such mixtures are usually mixtures of m-dialkylbenzenes with other dialkylbenzenes, monoallcylbenzenes or others, usually saturated Hydrocarbons. The method is particularly useful for the treatment of fractions applicable that boil in a narrow range, e.g. B. of mixtures of isomeric aromatics.

The process is particularly important for the separation of m-xylene, starting from a mixture of xylenes (including ethylbenzene), and in particular for the removal of m-xylene from a mixture, which mainly consists of m-xylene and p-xylene consists of too much p-xylene.

Attempts have already been made to achieve the above separation by fractional Achieve distillation. However, this is only possible if the boiling points of the The constituents to be separated are sufficiently distinguished from the others by their boiling point Differentiate mixture components. In this way you can get o-xylene from a mixture separate the xylenes, but it is not possible in this way to separate between to achieve m- and p-xylene.

It has also been suggested to do this separation by stripping out the m-dialkylbenzenes with help a liquid mixture of boron fluoride and hydrogen fluoride to effect.

According to the invention, the separation in question is effected, by placing the mixture at a relatively low temperature (not higher than about room temperature.) extracted with an extractant, the whole or to a essential part of a compound of aluminum chloride, an m-dialkylbenzene or a higher alkyl-substituted benzene and optionally hydrogen chloride and / or the corresponding bromine compound.

As a rule, this compound contains 2 molecules of Al, C13 or Al brd on I molecule of alkylbenzene.

Small amounts of aluminum chloride can be found in this compound dissolve or more amounts of alkylbenzene, as will be explained below, therein be dissolved (bound in the form of a complex) or remain dissolved. The relationship from Al Gl3 or Al Bf3 to alkylbenzene can therefore something, e.g. B. IoO / o, both in the deviate from value 2 in one direction as well as in the other.

These complexes can also contain hydrogen chloride or hydrogen bromide complex-bound included.

This is the case when the extraction is in the presence of liquid Hydrogen chloride or hydrogen bromide is carried out.

Under certain conditions, small amounts can also be used other polar substances may be present in the complexes. The amount of hydrogen chloride or hydrogen bromide can e.g. B. to 1 molecule per molecule of alkylbenzene.

Such complexes are e.g. B. obtained by at low temperature, z. B. oO, aluminum chloride with one of the said alkylbenzenes, z. B. m-xylene, brings together, passing through hydrogen chloride.

The corresponding bromine complex compound can be prepared in a similar manner will.

The amount of alkylbenzene present in the complex compounds is fixed bound. - It is not possible to make them free from it and at the same time that Recover aluminum chloride unchanged.

However, if a further amount of m-dialkylbenzene, in this case m-xylene, is added, this compound selectively forms complexes with m-xylene of the species A12 C16 m-xylene (m-xylene) ,, in which hydrogen chloride can also be present. In of the formula n can have the value from 1 to 5 inclusive. These n-molecules of m-xylene are only loosely bound and can easily be split off from the complex compound will.

The method according to the invention has the properties mentioned above Made use of. If z. B. treated a mixture of m- and p-xylene according to the invention is, preferably attaches to the compound A12 C16 m-xylene that is present in the mixture m-xylene. The loosely bound quantities of m-xylene can, however, easily be extracted from the complex compounds can be made free and thus free m-xylene can be recovered.

The extraction can be carried out continuously in one or more stages or discontinuously, batchwise or gradually, in direct current, in cross-flow or be carried out in countercurrent. The extractant can be in a still recovered in the manner to be specified and circulated in the process.

The extraction should take place at relatively low temperatures, in are usually carried out below room temperature and often at oO or below, in order to exclude the occurrence of undesired side reactions.

It is advisable to carry out the extraction according to the invention in the presence of non-aromatic hydrocarbons such as hexane, heptane, cyclohexane, aromatic-free Gasoline, aromatic-free luminous oil or paraffinum liquidum, carry out their boiling points or boiling point ranges differ from that of the starting mixture. By the addition of such hydrocarbons dilutes the starting mixture, and the This improves the selectivity of the separation.

Very good results can be obtained when making the extraction is carried out as a process with two washing liquids, i.e. in which the starting material extraction is carried out with two extraction agents, which run in countercurrent to one another, the compound in question, e.g. B.

Addition compound of aluminum chloride and m-xylene, as the one Extractant and a non-aromatic hydrocarbon of the above Kind, e.g. B. hexane, can be used as the other extractant. To this Way it is possible to achieve a complete rectification of the starting mixture, z. B. from a mixture of p-xylene and m-xylene, both compounds in high purity to win.

As the compound of aluminum chloride or aluminum bromide and alkylbenzene is quite viscous, it is desirable to use a diluent for this compound to use. This diluent should not react with the compound at least not in a way that the good properties of the extractant get lost.

Liquid anhydrous hydrogen chloride or hydrogen bromide can used as a diluent for the complex extractant who-4 1. Um to keep all or at least some of the hydrogen chloride in a liquid state, need higher pressures, e.g. About 20 atmospheres or higher. As a result of The presence of hydrogen chloride makes the extractant much less viscous, and the extraction is made considerably easier. Most likely the extractant and the hydrogen chloride form a complex compound, in which the hydrogen chloride is relatively loosely bound.

The m-dialkylbenzene loosely bound in the extractant in the course of the extraction can be made free from it by treating with a non-aromatic hydrocarbon, like hexane, Heptane, cyclohexane, an aromatic-free gasoline, a Aromatic-free luminous oil or Paraffinum liquidlium, arus washes, their. boiling point or boiling range differ from that of the starting material. The washing out can be in one or more stages or continuously, gradually or intermittently, take place in cocurrent or in crossflow, but preferably in countercurrent.

Usually the type of hydrocarbon used to wash off is the same as that used as the second solvent in the extraction. At the However, an excess of this hydrocarbon should be used for washing, in order to wash out the m-dialkylbenzene as completely as possible. The m-dialkylbenzene can can be obtained from the hydrocarbon phase by distillation.

The extractant and the hydrocarbon used for washing can be recycled for further use in the process.

At the beginning of the extraction it is also possible to use aluminum chloride only and hydrogen chloride to begin with. The extractant then forms automatically with the help of hydrogen chloride from aluminum chloride and that present in the starting mixture m-dialkylbenzene. The complex compound thus obtained can then be used as an extractant be used.

The present method is opposite to the known extraction with hydrogen fluoride and boron trifluoride advantageous. This extraction takes place namely the processing of the separate phases, d. H. the extraction of m-dialkylbenzene, by distillation. Effect hydrogen fluoride and boron fluoride at the high temperatures prevailing in the distillation column easily a Isomerization of the separated xylenes.

This applies in particular to the isomerization of p-xylene to m-xylene. In the present process, however, such isomerization hardly occurs.

In addition, when working with hydrogen fluoride, the application is special precautionary measures necessary.

Example I A mixture of 15.5 parts by weight of p-xylene and 12 parts by weight m-xylene, dissolved in 15 parts by weight of n-heptane, was in one stage with 15 parts by weight Al2 Cl6 m-xylene (Io parts by weight Al Cl3), which contained some H Cl, extracted. The extraction temperature was oO.

Two phases were formed, which were then separated from each other became. The upper, heptane-rich raffinate phase was washed with water to remove any traces to remove aluminum chloride and hydrogen chloride. This phase contained I2 Parts by weight of p-xylene and 7 parts by weight of m-xylene.

The lower extract phase was in one stage with four times the amount by weight n-heptane extracted. There were 4 parts by weight of m-xylene and 3 3 parts by weight of p-xylene obtained from the heptane phase.

To ensure complete separation of the components of the starting mixture to achieve, of course, the extraction according to the invention must be carried out on a larger scale Number of stages to be performed.

Example 2 A mixture of 8.1 parts by weight of p-xylene and 2.8 parts by weight m-xylene was dissolved in 38, I parts by weight of n-heptane and in a stage with 30, I Parts by weight Al2 Cl6 m-xylene (22.1 parts by weight Al Cl3) extracted. Additionally was 37 parts by weight of anhydrous hydrogen chloride under a pressure of about 20 at added. The extraction temperature was oO.

After separation of the phases formed was by reducing the The greater part of the hydrogen chloride is removed under pressure. Then the top Phase washed with water to remove all traces of hydrogen chloride remaining and remove aluminum chloride. This phase then yielded 5.7 parts by weight of p-xylene and 5.4 parts by weight of m-xylene.

The lower phase was four times in cross flow with four times the amount by weight n-Heptane extracted A total of 2.2 parts by weight of p-xylene and 5.9 parts by weight Obtained m-xylene from the lower phase.

An almost complete separation of the two components, m-xylene and p-xylene can be achieved by adding the starting table (I part by weight) introduces into the fifth stage of a twelve stage extraction system. 1.5 parts by weight the complex compound and 1.5 parts by weight of hydrogen chloride are in the twelfth Stage and I, 8 parts by weight of heptane and 0.7 parts by weight of hydrogen chloride abandoned in the first stage.

The extraction phase withdrawn from the first stage contains m-Xylcl, and the raffinate phase leaving the twelfth stage contains p-xylene, both with a purity of about 95%.

Claims (6)

PATENT CLAIMS 1. Process for the enrichment or separation of one or more m-dialkylbenzenes, in particular m-xylene, from mixtures which contain one or more of these aromatics, in particular from mixtures of isomers Aromatics, characterized in that the mixture is at a relatively low temperature (no higher than about room temperature) is extracted with an extractant, all or a considerable part of a complex compound of aluminum chloride or aluminum bromide, an m-dialkylbenzene or a higher dialkyl-substituted one Benzene and optionally hydrogen chloride and / or from the corresponding bromine compound consists. 2. The method according to claim I, characterized in that as the extractant a compound is used that is 2 or about 2 molecules of aluminum chloride or aluminum bromide for every 1 molecule of m-dialkylbenzene. 3. The method according to claim I and 2, characterized in that the Extraction additionally in the presence of a non-aromatic hydrocarbon, such as hexane, heptane, cyclohexane, aromatic-free gasoline, aromatic-free luminous oil or Paraffinum liquidum, its boiling point or boiling points; area yourself differs from that of the starting material. 4. The method according to claim I to 3, characterized in that the The starting mixture is extracted in one operation with two washing liquids, wherein a non-aromatic hydrocarbon of the type listed in claim 3 acts as a second extractant. 5. The method according to claim I to 4, characterized in that the m-Dialkylbenzene from the extract phase by washing out with an excess of non-aromatic Hydrocarbons such as hexane, heptane, cyclohexane, aromatic-free gasoline, aromatic-free Luminous oil or Paraffinum liquidum whose boiling point or boiling range differs from that distinguish the starting material, is separated. 6. The method according to claim I to 5, characterized in that liquid, anhydrous hydrogen chloride or hydrogen bromide is used as a diluent will.