DE1185599B - Process for the production of pure p-xylene and m-xylene from mixtures of aromatic hydrocarbons containing them - Google Patents

Description

Process for the recovery of pure p-xylene and m-xylene from them containing Mixtures of aromatic hydrocarbons From aromatic hydrocarbon mixtures, which contain m- and / or p-xylene in addition to other aromatic hydrocarbons, especially from crude xylenes, it is known that m- and p-xylene are obtained in such a way that m-xylene is sulfonated with 80% to concentrated (98%) sulfuric acid, the m-xylenesulfonic acid separates off the non-sulfonated hydrocarbons Distillation separates and hydrolyzes the m-xylene sulfonic acid. With all known Processes in which sulfonated with concentrated sulfuric acid or with oleum is, at best, a 91% p-xylene and only about 950% p-xylene is obtained m-xylene. Correspondingly, it is not possible to use the total amount of what is present in a mixture To win p- or m-xylene, but not more than 900 / o.

It has been found that p-xylene and m-xylene from mixtures of aromatic Hydrocarbons containing p- and m-xylene by selective sulfonation, Separation and distillation of the unsulfonated components, hydrolysis of the sulfonated ones Proportions and distillation of the hydrolyzed mixture in greater purity and higher Yield than previously obtained when using chlorosulfonic acid for sulfonation with a Brings iron content below 1 1% in the hydrocarbon mixture to be separated or if you have chlorosulfonic acid of this purity and the hydrocarbon mixture to be separated introduces into a reaction mixture, which consists of chlorosulfonic acid of this purity and Hydrocarbon mixtures containing p- and m-xylene in a previous batch was obtained, and the sulfonation at a temperature below 600 C, preferably between 0 and 200 C.

To carry out the process, the hydrocarbon mixture is the p- and m-xylene contains, especially one of the o-xylene by distillation to a large extent freed crude xylene, submitted. It is then left with thorough mixing, for. B. by Stir, slowly add chlorosulfonic acid. One uses a chlorosulfonic acid, the iron content of which is below 11%, especially below 0.1%. You can use commercial Use chlorosulphonic acid if it does not have a higher iron content. One can but also use purified chlorosulphonic acid, which is often present Impurities, e.g. B. sulfur trioxide, sulfur dioxide, hydrogen chloride, thionyl chloride, Sulfuryl chloride and metal salts. Depending on the type of contamination you can use different cleaning methods, e.g. B. distillation or Blow out with an inert gas, e.g. B. nitrogen, air or carbon dioxide, at room temperature or at elevated temperature. If you use any existing sulfur trioxide it can be converted to chlorosulfonic acid with the aid of hydrogen chloride.

The molar ratio of the hydrocarbon to chlorosulfonic acid is preferably chosen so that the sum of the number of moles of all aromatic hydrocarbons except for p-xylene and the number of moles of chlorosulphonic acid correspond approximately to the ratio 1: 1. However, the use of a molar ratio greater than 1: 1 is possible if you only attaches importance to the production of pure m-xylene.

Since the sulfonation takes place very quickly, the process is very good easily perform continuously. The residence times are intended to avoid side reactions to avoid being less than 10 hours, preferably less than 30 minutes. One can go to completion of the reaction after mixing the reactants work briefly at about 60 to 700 C. As in the implementation of hydrogen chloride is split off, it is advantageous to use this hydrogen chloride with the help of an inert To displace the gas stream, e.g. with air or nitrogen, from the reaction mixture. You can also use an inert solvent to remove the aromatic hydrocarbon dilute, e.g. with aliphatic or cycloaliphatic hydrocarbons or halogenated aliphatic hydrocarbons. for example octane or cyclohexane, Ethylene chloride or carbon tetrachloride.

One can, especially in the case of continuous execution, also proceed in this way, that one submits the finished reaction mixture and in this at the same time under Stir the hydrocarbons to be separated and the chlorosulfonic acid introduces.

The reaction mixture is then worked up in an known way. The sulfonated and the non-sulfonated portions are separated by the unchanged hydrocarbons, advantageously under reduced Pressure, distilled off or by dissolving the sulfonic acids by adding water and then separating the aqueous and organic layers. From the non-sulfonated The p-xylene is obtained by fractional distillation. The sulfonated Fractions are hydrolyzed, expediently in several stages with increasing temperature from about 100 to 2000 C. The hydrolyzed mixture is also fractionally distilled, whereby the m-xylene is obtained.

It is known to react xylene with chlorosulfonic acid by the optionally frozen hydrocarbons in optionally cooled Brings chlorosulfonic acid. However, this gives xylenesulfonic acid chlorides or Sulfones and not sulfonic acids. In addition, this mode of operation is selective Sulphonation of m-xylene is much worse than in the process of the invention.

In the following examples, parts mean unless otherwise indicated, parts by weight. Parts by weight and parts by volume are in relation to how Kilograms to liters.

Example 1 In an enamelled container with a stirrer, 1060 Parts of xylene isomer mixture composed of 65 percent by weight of m-xylene and 33 percent by weight of p-xylene and submitted 2 weight percent ethylbenzene. Leave for about 30 minutes at a temperature of 10 to 150 C 780 parts of chlorosulfonic acid, the 0.050 / a iron contains, run in and stir the mixture for a short time, at the same time passing a stream of air through the device to remove the hydrogen chloride. During the reaction 245 parts of hydrogen chloride are evolved, 700 parts of which Water can be absorbed. After the reaction, 1000 parts of water are allowed into the reaction mixture run in and separates the organic from the aqueous layer. 349 parts are obtained Xylene, from which 345 parts of p-xylene, mp = 11.30 C, are obtained by distillation, those according to the Raman and ultrared spectrum to from from p-, to 2 0 / G from m-xylene and consist of 1% ethylbenzene. The p-xylene yield is 950/0 that of the original existing amount.

The aqueous xylenesulfonic acid solution is at 140 to 1450 C in one Still with descending condenser treated with steam.

In this way, a distillate is obtained in the boiling range from 140 to 1450 C, which contains 690 parts of xylene with 970 / o m-xylene.

Continuing the distillation gives a temperature of 180 to 2000.degree 20 parts of ethylbenzene.

If 1060 parts 960% are used instead of chlorosulphonic acid Sulfuric acid is obtained, even if one after completing the reaction the addition of the reactants heated to 800 C, from the non-sulfonated Portions 401 parts of a mixture of 630/0 p- and 37 0 / o m-xylene.

The hydrocarbon mixture is left in chlorosulfonic acid run in at 10 to 150 C, the unreacted is obtained in the distillation Hydrocarbon mixture 512 parts of a mixture of isomers, m.p. - 130 C, from 530/0 p- and 470/0 m-xylene.

Example 2 In a vertical enamelled tube, whose Diameter is related to height as 1:10 and that has a volume of 100 parts by volume in which a stirrer with several arms distributed over the entire height is attached continuous sulfonation is carried out.

The tube is first coated with a mixture of 36 percent by weight p-xylene and 64 percent by weight m-xylene sulfonic acid filled. At the head of the pipe one leaves every hour 106 parts by weight of a mixture of 500/0 m- and 500/0 p-xylene and 58.3 parts Chlorosulphonic acid, which contains only 0.0080 / 0 iron, enter. The hydrogen chloride gas is discharged at the top of the reaction tube; at the bottom of the pipe will be hourly 146 parts of reaction mixture consisting of 52 parts by weight of 970% p-xylene and 94 parts by weight of m-xylenesulfonic acid, removed. There is a temperature gradient in the pipe maintained in such a way that 20 ° C measured at the top of the tube, 600 C at the bottom will.

The reaction mixture is worked up as in Example 1. You get 52 parts by weight of 970% p-xylene and 52 parts by weight of 970% m-xylene.

Claims (2)

Claims: 1. Process for the production of pure p-xylene and m-xylene from these containing mixtures of aromatic hydrocarbons by selective Sulphonation, separation and distillation of the unsulphonated components, hydrolysis the sulfonated portions and distillation of the hydrolyzed mixture, d a d u r c h g e - indicates that chlorosulfonic acid with an iron content is used for sulfonation introducing less than 10 / o into the hydrocarbon mixture to be separated or that chlorosulfonic acid this purity and the hydrocarbon mixture to be separated into one at the same time Introduces reaction mixture, which consists of chlorosulfonic acid of this purity and p- and obtained m-xylene-containing hydrocarbon mixtures in a previous batch was, and the sulfonation at a temperature below 600 C, preferably between 0 and 200 C. 2. The method according to claim 1, characterized in that the Sulfonation of the reactants is carried out with such a quantitative ratio, that the sum of the number of moles of all aromatic hydrocarbons except p-xylene and the number of moles of chlorosulfonic acid correspond approximately to the ratio 1: 1. Considered publications: German Patent Specifications No. 840 238, 854 345; German patent application p6273IVd / 12OD (published on 12. 10. 1950); German interpretative document No. 1 070623.