DE903459C - Process for the production of condensed polycyclic aromatic hydrocarbons and their homologues and substitution derivatives from mixtures containing them - Google Patents

Description

Process for the recovery of condensed polycyclic aromatic Hydrocarbons and their homologues and substitution derivatives from such Mixtures containing the invention relates to a method for separation polycyclic aromatic hydrocarbons from mixtures with other organic ones Compounds, especially for separating naphthalene compounds from monocyclic ones aromatic and alkylated monocyclic aromatic compounds.

According to the process of the invention, polycyclic ones become aromatic Hydrocarbons with condensed (fused) benzene nuclei and their homologues and substitution derivatives thereby of aliphatic, monocyclic, aromatic, Heterocyclic and naphthene compounds are separated off by treating them with tetrahalophthalic acid canhydrides converts to solid complex compounds. These crystalline complexes from polycyclic aromatic hydrocarbons and a tetrahalophthalic anhydride in a molar ratio of i: i form when a tetrahalophthalic anhydride with a polycyclic aromatic compound is brought together. Because the complex at ordinary temperature Essentially insoluble in hydrocarbons, it is easy to remove from the mixture to separate the organic compounds. The separation of the complex from hydrocarbon solutions will be at a temperature below 65 "and usually at one temperature carried out between 10 and 503, in which the complex in .einer hydrocarbon solution is essentially insoluble. After the complex has been separated off, it becomes the polycyclic aromatic hydrocarbons either by heating the complex, whereby it is broken down into its component parts, or by treatment with a dilute one aqueous alkali solution obtained. The decomposition of the complex in the heat is carried out at Temperatures above 95 °, usually at a temperature between 12 and 26o °, with dilute alkali solution, on the other hand, at temperatures above 10 °, usually at one Temperature between 25 and 5o "carried out.

The method of the present invention is for the separation of Naphthalene of monocyclic and alkylated monocyclic aromatic compounds of particular advantage. So far, the main source of naphthalene has been coal tar. It is well known that certain oils with cyclic constituents that by Heat or catalyst cleavage of hydrocarbons are obtained, significant Contains quantities of naphthalene. However, it was difficult to separate the naphthalene from it, since the normal procedures for decomposing mixtures, such as extraction with solvents, azeotropic distillation and crystallization, no satisfactory separation of naphthalene of alkylated monocyclic aromatic compounds with boiling points, which are similar to that of naphthalene. According to the present invention the naphthalene can now be separated very easily and effectively from cyclic fission oils will. The naphthalene obtained and its homologues are of high purity and essentially free of alkylated monocyclic aromatic compounds, since the tetrahalophthalic anhydride a specific complexing agent for polycyclic is aromatic hydrocarbons.

Tetrachlorophthalic acid, tetrabromophthalic acid, tetraiodophthalic acid and tetrafluorophthalic anhydride or mixtures thereof can be used as complexing agents can be used, but preferably tetrachlorophthalic anhydride, as it is the easiest accessible and cheapest.

The process of the invention is also suitable for the separation of others polycyclic aromatic hydrocarbons as naphthalene from mixtures of organic Connections applicable; z. B. also form anthracene and phenanthrene complexes with Tetrahalophthalic anhydride. In addition, homologous polycyclic aromatic Hydrocarbons such as methylnaphthalene and ethylphenanthrene, as well as substituted ones polycyclic aromatic compounds such as a-chloronaphthalene, naphthols and anthraquinone, separated from mixtures with organic compounds according to the process of the present invention will. Tetrahalophthalic anhydride, on the other hand, does not form complexes with ordinary ones heterocyclic or heterocyclic compounds with condensed ring systems, like dithienyl, furthermore not with aliphatic and monocyclic aromatic compounds as well as their homologues. The polycyclic aromatic hydrocarbons made with Tetrachlorophthalic anhydride form complexes, such compounds are fused with Benzene nuclei. Polycyclic aromatic compounds with non-fused benzene nuclei, like diphenyl, do not form complexes with tetrachlorophthalic anhydride.

The separation of the polycyclic aromatic hydrocarbons from mixtures in which they are dissolved, takes place by adding to the mixture Tetrachlorophthalic anhydride gives, separates the complex that forms and him broken down into its component parts.

Bringing together can be achieved by vigorously mixing the complexing agent and the mixture containing the polycyclic aromatic hydrocarbons take place, preferably at a temperature above 150 °, expediently from 60 ° to 200 °; at these temperatures the complexing agent is in most hydrocarbon mixtures soluble. Thorough mixing of the complexing agent with the polycyclic aromatic Hydrocarbons are effectively released by dissolving the complexing agent reached in the hydrocarbon mixture. After the dissolved complexing agent has cooled down containing mixture to a temperature between i o and 6 5 - separates the complex compound of polycyclic aromatic hydrocarbons and tetrachlorophthalic anhydride as a golden yellow solid body.

The complex formation can also be effected in such a way that solid tetrachlorophthalic anhydride is used at ordinary temperature in a mixture of the polycyclic hydrocarbons slurries. In such cases it is necessary to stir vigorously for a long time to achieve this the same degree of separation as that obtained using a solution of the complexing agent is achieved at elevated temperature.

Another option is that you can get a saturated solution of the complexing agent in a solvent such as acetone, to which the polycyclic aromatic hydrocarbons containing mixture there. A disadvantageous side effect when using this a-liquid system is that the use of the solvent brings a third component into the system, the recovery of which is additional Requires treatment.

The complex can be easily removed from the mixture of organic compounds separate, e.g. B. by filtering, decanting or centrifuging; becomes appropriate however, filtered. Rotary filters are used for large-scale operations a very effective means of removing the complex from the treated Mixture. The removal of the complex from the treated mixture is at Temperatures carried out below about 65 °; Have temperatures between io and 5o proved to be particularly effective for this. After the separation is complete it is advisable to carry out the precipitation with a light hydrocarbon, e.g. B. pentane, too wash to remove retained organic compounds from the complex. Pentane is an excellent solvent for this purpose.

The decomposition of the complex is carried out either by heating to a Temperature of over 95 reached, whereby the complex is broken down into its components that can be easily separated from each other or by treating with a dilute aqueous alkali solution, where z. B. the sodium salt of tetrahalophthalic acid forms. The polycyclic aromatic hydrocarbons of high purity can be obtained.

The heat decomposition of the complex is preferably carried out by simple distillation, in which the complex is heated to a temperature between approximately 120 and 26o, the polycyclic aromatic hydrocarbons being obtained as a distillate. The remaining molten tetrahalophthalic anhydride is returned to the process. Temperatures between 175 and 26o ° are usually used for simple distillation.

The complex compounds can also at a temperature of about about i so 'to be distilled with steam, one being made of polycyclic aromatic Hydrocarbons and water existing distillate receives. Tetrahalophthalic anhydrides are not hydrolyzed at temperatures above about i 50 @, so that the anhydride can be returned to the cycle. This procedure offers a clean Method of complex decomposition, as both the polycyclic aromatic hydrocarbon as well as the tetrachlorophthalic anhydride in one suitable for further use Form can be recovered as polycyclic aromatic hydrocarbons in are insoluble in the aqueous distillate.

The complex preventions can also be carried out in the presence of a solvent for polycyclic aromatic hydrocarbons, e.g. B. of petroleum hydrocarbons, are heated, forming two layers, one of which is the complexing agent and the others the solution of the polycyclic aromatic hydrocarbons in the solvent. A temperature of about 95 to 2o5` must be used will. It follows that when using low-boiling petroleum hydrocarbons required as a solvent to maintain the necessary decomposition temperature can be to work at increased pressure. The polycyclic aromatic hydrocarbons can be separated from the solvent by distillation.

When the separated complex is broken down a dilute aqueous Alkali solution forms a salt of a tetrahalophthalic acid by hydrolysis. Aqueous alkali hydroxide solutions, such as sodium hydroxide, or alkali salt solutions, such as Potassium carbonate, can be used to break down the complex. Usually one uses 1 to 2,000 solutions, but preferably 2 to 10 weight percent.

It is advisable to treat the complex with the aqueous alkaline solution to decompose at a temperature of 10 ° or above, expediently at 25 to 5o °; However Temperatures up to about 95` can also be used.

Contacting the complex with dilute alkali has the formation a system of two liquid phases, the upper layer of which is made of polycyclic aromatic hydrocarbons and the lower one consists of an aqueous alkali solution, in which a salt of tetrahalophthalic acid is contained in dissolved form. The polycyclic aromatic hydrocarbons are in the dilute aqueous alkali solution essentially insoluble and easily separated therefrom. The obtained in this way Polycyclic hydrocarbons can be dried in the usual way.

The tetrahalophthalic anhydride can be obtained from the dilute alkali solution obtained by neutralizing, filtering and dehydrating the acid to the anhydride will. To neutralize the alkali solution, concentrated acid is best Hydrochloric acid. Dilute acid can also be used, however is not recommended because of the large quantities required. Also gaseous H Cl and concentrated sulfuric acid can be used. After the neutralization will be the aqueous slurry of tetrahalophthalic acid to a temperature between 7 and 21: 'cooled in which the acid is essentially insoluble in water. The slurry is then filtered and the tetrahalophthalic acid is poured over 95 ° heated or by azeotropic distillation with benzene or toluene into the anhydride transferred, which can be returned to the cycle.

A preferred method of the present invention is shown schematically in the drawing Invention shown; here the decomposition of the complex takes place both by simple Heat treatment as well as steam distillation. There is the separation of Naphthalene from an oil of the type of a cracked distillate.

Tetrachlorophthalic anhydride is fed through tube i into a mixing vessel 2, which is equipped with a stirring device represented by propeller 3 is. In the mixing tank 2, the complexing agent is mixed with the oil that is passed through pipe q. in the mixing container 2 is passed, brought together. The mixing container 2 is opened maintained a temperature of about 175 °, at which the tetrachlorophthalic anhydride dissolves in the oil from which the naphthalene is to be secreted.

After thorough mixing in the mixing container 2, this becomes apparent from the Complexing agent and the oil-composing mixture through pipe 5 into the cooling container 6, in which the processed mixture is cooled to a temperature below 653 and becomes a solid complex of tetrachlorophthalic anhydride and naphthalene separates. the Mixture is at a temperature of io to 65 brought through tube 7 into the rotary filter i o, where the complete from the treated Mixture is filtered off. In the rotary filter there are devices for running Removal of the complex from the drum. There are also devices there for the continuous washing of the complex mass with a hydrocarbon, e.g. B. pentane, which is passed through tube i i into the rotary filter. The complex is going out the rotary filter i o removed by pipeline 14 connected to a screw conveyor can be equipped.

The complex is now in the container 15 to a temperature between 175 and heated to 26o °. At this temperature the complex decomposes and the naphthalene distilled off through pipe 16 and flows through a heat exchanger 17 in which it is condensed and passed through pipe 18 into a reservoir.

Molten tetrachlorophthalic anhydride is poured through pipeline 20 withdrawn from the container 15 and returned to the mixing container 2 again. To avoid crystallization of the tetrachlorophthalic anhydride in tube 2o, the pipe 20 must be surrounded by a steam jacket. In addition, the mixing container is located 2 and the container 15 close to one another in practice, so that tube 2o is very short.

In the drawing there is also another method of disassembling the complex shown. This procedure consists in keeping the complex at a temperature is distilled from about 12 to 20 ° with steam. The complex is through the Pipes 14 and 23 passed into the still 125 in which superheated steam is blown through pipe 24.

In steam distillation, the complex is at a temperature between i 50 and 20 ° decomposed, and a distillate of steam and naphthalene is obtained, the is withdrawn through tube 26 upwards. After cooling in the heat exchanger 27 the distillate is passed into the separator 29, in which the naphthalene from water is separated. The water is out through pipe 31 and the naphthalene through pipe 3o the separator 29 removed.

Tetrachlorophthalic anhydride is passed through from the still 25 Pipe 35 diverted and fed back to the mixing container 2 through pipes 35 and 2o. Feed oil can be introduced through pipe 36 to serve as a carrier in pipes 35 and 2o to serve for the complexing agent returning to the mixing vessel 2 when the decomposition of the complex is done by steam distillation.

The filtrate obtained in filter io consists of polycyclic aromatic hydrocarbons, essentially free cyclic compounds; they are withdrawn from the rotary filter io through pipe 37 and into the washing tower38 directed. The washing liquid obtained by washing the complex with pentane is combined with the filtrate and also flows through pipe 37 into the washing tower 38. The filtrate combined with the pentane washing liquid - is treated with dilute alkali, z. B. 30'oigem sodium hydroxide, brought together in the washing tower. The alkali gets through Pipe 39 passed into tower 38. The alkali wash removes any remaining oil from the oil Tetrachlorophthalic anhydride. The alkali solution is drawn out of the tower through pipe 38 " 38 removed.

The washed oil is brought into the separator 41 through pipe 40, where it is freed from pentane, which pulls up from the separator 41 upwards and is fed back through pipe 42 to the rotary filter io. That from his salary Oil freed of polycyclic aromatic hydrocarbons is removed from the separator 41 removed through tube 43.

The following examples illustrate the process of the present invention. EXAMPLE 1 A cracked distillate with a specific gravity of 0.8540 and a total content of aromatic compounds of 50 percent by weight, of which ii percent by weight is naphthalene and 20o methylnaphthalene, was mixed with tetrachlorophthalic anhydride in a ratio of 12 kg of tetrachlorophthalic anhydride to 160 l of cracked distillate. This mixture was heated to a temperature of 175 - and stirred thoroughly. Thereafter, the mixture was cooled to a temperature below 65-, whereby the complex salt precipitated, which was filtered off at about 32- and the precipitate was washed with pentane. 29 kg of precipitate is obtained on 160 l of cleavage distillate which, according to the analysis, contained 11.50% naphthalenes. This precipitate was distilled with steam at a temperature of 177 °, with 10.5 kg of naphthalenes being separated from each 16o l of cleavage distillate, which consist of 950, 'o naphthalene, 40; o a-methylnaphthalene and 10o / 3-methylnaphthalene . The filtrate and the combined pentane washing solution were washed with an alkali solution and separated. 1431 oil per 16o l of cracked distillate were obtained; they did not contain any significant amounts of naphthalene. The oil treated in this way contained approximately 1.500.10 tetrachlorophthalic anhydride; the oil could be further freed from tetrachlorophthalic anhydride by an additional alkali wash. Example 2 A cracked distillate with a total content of aromatic compounds of 48 percent by weight, of which naphthalene accounts for about 1o.6% and methylnaphthalenes for about 0.70 / 0, and tetrachlorophthalic anhydride in a ratio of 63.5 kg of tetrachlorophthalic anhydride to 1 6o 1 of cracked distillate given a mixing container heated to 177 '. After thorough mixing, the mixture was cooled to below about 65 ", filtered and the precipitate washed with pentane to remove adsorbed oil. The solid product was distilled in a still with superheated steam at a temperature of about 150 °. From steam distillation 16.41, - of material per 16o l of cracked oil were obtained this material contained 930110 naphthalene, 20/0 α-methylnaphthalite and 2% β-methylnaphthalene. The oil filtrate obtained was 1251 per 16o l of cracked distillate Compounds of which about 1% was naphthalene and less than 0.50; ö a- and β-methylnaphthalene The pentane solution was distilled and washed with alkali to give 14.71 oil per 160 liters of cracked distillate, with an approximate naphthalene content of 4 percent by weight and a content of α- and β-methylnaphthalene of less than 0.5% Example 3 A cracked distillate with a specific gravity of 0.8540 un d a total content of aromatic substances of 50 percent by weight, of which ii percent by weight is naphthalene and about 2 percent by weight is methylnaphthalene, was mixed with tetrachlorophthalic anhydride in the ratio of 12 kg tetrachlorophthalic anhydride to 16o 1 fission distillate. The mixture was heated to a temperature of 175 ° and stirred thoroughly. The mixture was then cooled to a temperature below 65-, filtered at approximately 32 'and the precipitate washed with pentane. Filtration gave i 29.4 kg of solid product per 160 l of cleavage distillate, the analysis of which gave i 1.5% of naphthalenes. This precipitate was treated with an aqueous sodium hydroxide solution in the ratio of 93.5 kg of sodium hydroxide to 16o 1 of cleavage distillate, whereby two layers were formed, the upper naphthalenes and the lower the sodium salt of tetrachlorophthalic acid. The layers were separated and 10.5 kg of naphthalenes per 160 l of cracked distillate were obtained. The naphthalene content contained 95% naphthalene, 4% α-methylnaphthalene and 10% β-methylnaphthalene. The filtrate and the pentane solution were combined, washed with alkali, separated, 1431 oil per 16o l of cracked distillate being obtained which no longer contained any appreciable amounts of naphthalene. The treated oil contained approximately 1.50% tetrachlorophthalic anhydride; this oil can still be freed from tetrachlorophthalic anhydride by fractional distillation.

The high degree of purity of the in the preceding examples from the Fission distillates of separated naphthalene is particularly noteworthy. For example The naphthalene content contains almost 100,000 naphthalene, including methylnaphthalenes; in example 2, the naphthalene content in the analysis showed almost 97% of naphthalene Methylnaphthalenes; in Example 3, 100% naphthalene with methylnaphthalenes.

The refining oil from which the complex is separated can be obtained by ' simple fractionation of tetrachlorophthalic anhydride still present therein to be freed. The tetrahalophthalic anhydrides have very high boiling points and are stable so that one obtained by fractionation from the refining oil Distillate is free from tetrahalophthalic anhydride. When carried out on a large scale This method is preferable to washing with alkali solutions.

Claims (1)

PATENT CLAIMS: 1. Process for the recovery of condensed polycyclic aromatic hydrocarbons and their homologues and substitution derivatives from mixtures containing those alongside other hydrocarbons of similar boiling point contain, by reacting these mixtures with tetrahalophthalic anhydrides with the formation of complex compounds, characterized in that the mainly from the tetrahalophthalic anhydrides and the condensed polycyclic aromatic Complex compounds consisting of hydrocarbons from the mixtures mentioned at temperatures below 65 ° separated in solid form and then by heating to temperatures between 95 and 26o °, advantageously 175 to 26o °, or by reaction be decomposed with dilute alkaline solutions. z. Method according to claim i, characterized in that the solid complex compounds by dissolving the tetrahalophthalic anhydride in the starting mixture at temperatures above 150 ° and subsequent cooling of the mixture can be obtained at temperatures below 65 °. 3. The method according to claim i or 2, characterized in that tetrachlorophthalic anhydride as a complexing agent is used. 4. The method according to claim i or 2, characterized in that the Complex compounds by heating with steam to temperatures between i 5o and 26o °. 5. The method according to claim i or 2, characterized in that that the complex compounds by heating to temperatures between 95 and 2o5 ° decomposed in the presence of a solvent for polycyclic aromatics. 6th Process according to Claim i or 2, characterized in that the complex compounds by reaction with i- to 20% alkali solutions at temperatures between io and 95 ° can be dismantled. Referred publications: Ber. German chem. Ges., Vol. 55, 1922, P. 413 ff., Especially p. 418 and q.19.