DE2311914A1 - PROCESS FOR PRE-TREATMENT OF HYDROCARBONS BEFORE FLAVOR EXTRACTION - Google Patents

Description

PATENTATIVE OFFICE TlEDTKE - Bühling - KlNNE

TEU (0611) 53M53-56 TELEXi 524845 tipat CABLE ADDRESS: Germaniapatent Munich

8000 Munich 2

Bavariaring4 _March 9th! 973 P.O. Box 202403

Imperial Chemical Industries, Limited London, Great Britain

Process for the pretreatment of hydrocarbons prior to aromatics extraction

The invention relates to the treatment of a hydrocarbon feedstock for an aromatics extraction, in particular the treatment of an aromatics-containing mineral oil for improvement its usefulness for such aromatics extraction.

Aromatic hydrocarbons such as benzene, toluene and the three isomeric xylenes are important chemicals and are largely petrochemical Origin. They are usually obtained from the crude oil distillation by known reforming processes Naphtha fraction (boiling range. 52 to 2O5 ° C) generated and can usually from the reformed fraction after hydrogenation of the sulfur and nitrogen compounds present by various Extraction process can be obtained. The naphtha fraction can alternatively also initially be a thermal or Be subjected to steam cracking, ethylene, propylene and a number of higher olefinically unsaturated hydrocarbons, how butadiene and isoprene are formed. Cracking is followed by a series of distillations to produce the cracked product separate into a number of fractions of hydrocarbons of similar boiling points, the aromatic C ^ to Cq hydrocarbons together with Cr and higher alkanes, Alkenes, cycloalkanes, and cycloalkenes are generally contained in a fraction commonly referred to as "split benzene" zin ".

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The mineral spirits can also be subjected to an aromatic extraction after the lower boiling C, - hydrocarbons usually removed by distillation, a process often referred to as "depentanization". In turn it is necessary to remove the sulfur and nitrogen compounds present in the depentanized mineral spirits before the extraction to hydrogenate, which is usually done at elevated temperature with molecular hydrogen on a catalyst such as Foh ^ lt and Molybdenum on an aluminum oxide carrier. However, it has been found that other components of the depentanized White spirit can have a detrimental effect on the activity and life of the catalyst.

It is therefore an object of the present invention to reduce the depentanized To treat mineral spirits in such a way that the activity and service life of the catalyst are improved.

According to the invention, the method for treating a mineral spirit is before the aromatics recovery from him characterized in that one

a) the gap gasoline to obtain a first distillate fraction distilled boiling under atmospheric pressure to 90 ⁰ C, especially up to 80 ⁰ C,

b) the residue of this distillation is heated in the liquid phase to a temperature in the range from 200 to 350 ° C,

c) the heated product for the separation of a second distillate fraction boiling under atmospheric pressure up to 250 ° C distilled and

d) this second distillate fraction is hydrogenated.

The second distillate fraction from stage d). is for extraction aromatic hydrocarbons from it.

The gap gasoline is obtained from a cracked thermally or with steam crude oil fraction, the naphtha (boiling range 32 ⁰ C to 205 ⁰ C) or gas oil (boiling range 205 ⁰ C to 430 ° C) can be.

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The gasoline is separated from the cracked product by distillation and boils under atmospheric pressure usually in the range of O ⁰ C to 25O ⁰ C. It can contain the following hydrocarbons: isoprene, cis- and trans-piperylene, n-pentane, iso-pentane, Pentene-1, cyclopentadiene, dicyclopentadiene trans-pentene-2, 2-methylbutene-2, cyclopentene, cyclopentane, benzene, toluene, ethylbenzene, o-, m- and p-xylene, n-propylbenzene, 2-, 3- and 4 —Ethyltoluene, mesitylene, pseudocumene and styrene.

The gap gasoline is usually distilled under atmospheric pressure, so that an up to 90 ⁰ C, advantageously to 80 ° C boiling, the above-mentioned hydrocarbons of isoprene to cyclopentane as well as some benzene containing distillate and a larger portion of the benzene and the remaining part of the mentioned hydrocarbons apply containing and, for example in the range of 80 ° C or 90 ⁰ C to 25O ⁰ C boiling residue. In practice, the distillation is usually carried out continuously in a distillation column or in columns, the cracked gasoline being introduced continuously approximately in the middle of the column and the two fractions being continuously withdrawn from the top and bottom of the column. For the sake of simplicity, the residue from the bottom of the column is referred to in this description as "depentanized cracked gasoline".

The depentanized cracked gasoline is heated in step b) to a temperature in the range from 200 to 350 ° C. under a pressure which is sufficient to keep it in the liquid phase. This pressure is expediently the self-adjusting pressure at the heating temperature, which is usually 20 to 41 ata. The temperature is preferably ^250-5 OO ⁰ C and the heating time is preferably between 0.5 and 4 hours. If desired, the heating can take place in batches in a stirred tank. However, it is preferably

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nuierlich, for example carried out during passage through a tubular reactor.

The product of the heating stage is distilled, usually working under atmospheric pressure. "The distillation gives the second ^{distillate fraction boiling at 1 ata to 250 °} C., preferably up to 180 ° C., as well as a high-boiling polymeric residue one or more distillation columns carried out continuously, for example in a first column for the flash distillation, which is followed by a second column for the fractional distillation.

The second distillate fraction can be hydrogenated in the liquid phase or vapor phase with molecular hydrogen over a suitable catalyst. The catalyst can consist of at least one metal, such as iron, cobalt, nickel, tungsten, molybdenum, platinum or palladium, for example as the metal itself or as an oxide or sulfide on an inert support such as aluminum oxide or silica, for example cobalt and molybdenum on aluminum oxide or Platinum on alumina .. If desired, a two-stage catalysis can be used, for example a first stage in which cobalt or nickel and molybdenum on alumina or palladium on alumina is used, and a second stage in which the catalyst is platinum on alumina or cobalt and Is molybdenum on alumina. The hydrogenation is preferably effected at 100 to 600 ⁰ C under 20 to 34 ata pressure of hydrogen. In a preferred two-stage hydrogenation reaction is carried out in the first stage at 100 to 300 ⁰ C, preferably 120 to 25O ° C in the liquid phase and in the second stage between 300 and 600 ⁰ C, preferably 350 to 55O ⁰ C in the vapor phase.

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The hydrogenated distillate fraction from step d) is well suited for the extraction of its aromatic content, it being possible for any of the numerous known extraction processes to be used. These processes work with one or more solvents which selectively extract the aromatics, in particular benzene, toluene and xylenes, from the distillate fraction. The aromatics are then separated from the solvent by normal or extractive distillation. Preferred extractants are diethylene glycol and / or dipropylene glycol with a small amount of water, tetramethylene sulfone, N-methylpyrrolidone, dimethyl sulfoxide or propylene carbonate. Less favorable extraction agents are silver fluorate, N-methylformamide, polyalkylene glycol, morpholine or alkyl carbamates. The extraction can take place at temperatures between ambient temperature and 10O ⁰ C under atmospheric pressure or overpressure, for example up to 14 ata.

In a preferred embodiment of the method a, obtained by Dampfkrackung of naphtha gap petrol (boiling range 10-220 ⁰ C at 1 ata) in a continuously operated distillation column having 10 to 15 theoretical plates at a Köpftemperatur of 65 ° C and a bottom temperature of 150 ⁰ C distilled. The distillate obtained in this column with a boiling range of 10 to 8O ⁰ C at 1 ata contains acyclic and cyclic alkanes and alkenes containing 5 or 6 carbon atoms. The column residue with a boiling range from 80 to 220 ^° C. at 1 ata contains the desired benzene, toluene and the xylenes together with other aromatic hydrocarbons and styrene. This residue is then passed continuously through a tubular reactor in which the residue temperature is kept ^{at 270 to 290 ° C.} The pressure of 27 ata in the tubular reactor is sufficient to keep the depentanized cracked gasoline in the liquid phase. The Ver-

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dwell time in the reactor "is one hour. When leaving the reactor, the hot product is fed directly to a flash evaporation vessel and the flash distillate formed is fed to a second continuous distillation column, which has a reflux ratio of 2: 1 and a top and bottom temperature of 175 works to 185 ° C or 200 ° to 210 ⁰ C. the distillate from this second column, boiling at one atmosphere at temperatures up to 180 ⁰ C. the residue from the flash distillation vessel is a polymeric oil containing higher aromatic hydrocarbons.

The distillate from the second continuous column is heated to 120 ⁰ C, with hydrogen in a molar ratio of 1: 1 and then passed through a two-stage Hydrierkatälysator, namely only in the liquid phase at 120 to 150 ⁰ C on sulfided nickel and molybdenum on aluminum oxide and in the second stage in the vapor phase at 480 to 510 ⁰ C over platinum on aluminum oxide. The pressure in the hydrogenation plant is 24 to 27 ata.

After the hydrogenation, the hydrocarbon product can be condensed and fed to an extraction column maintained at 40 ° C in which it is countercurrent to a stream of tetramethylene sulfone to be led. The tetramethylene sulfone extract is separated off and purified, and the aromatic hydrocarbons are of the extract by vacuum distillation in a column separated, their top and bottom temperatures at 70 and 170 ° C lie. The aromatic hydrocarbons are taken off at the top, while the tetramethylene sulfone is drawn off from the bottom of the column and returned to the extraction process will.

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example 1

A signal obtained by Dampfkrackung gasoline with a boiling range of 10 to 22O ⁰ G has been shown in a column having 15 trays theoretj distilled to obtain a residue as depentanisierte
held.

rich from 10 to 220 ⁰ G was in a column with 15 theoretical

Jn1-based cracking gasoline with a boiling range from 80 to 220 ⁰ C

This depentanized cracked gasoline was passed through a thermal treatment plant, which consisted of a steel tube reactor divided into separately stirred chambers. The flow properties of the gasoline in the system corresponded to about 5 stirred tanks connected in series. The maximum temperature in the plant was 275 to 280 ^° C., the pressure 27 ata and the mean residence time 2 hours.

The thermally treated gasoline was then fed to a flash still, in which the pressure was released to 1.4 ata. A distillate with a boiling range of up to 220 ° C. was distilled over, and an oily residue remained (15% by weight of the amount used). The flash distillate was then distilled in a glass-lined vial at a reflux ratio of 2: 1, resulting in a distillate with a final boiling point of 180 ° C., which was condensed and fed to a hydrogenation plant with a catalyst made from freshly sulfided nickel / molybdenum on aluminum oxide. The inlet temperature to the catalyst bed was 200 ^° C., the pressure was 20 atm and the molar ratio of hydrogen to hydrocarbon was 1: 1.

In a comparative experiment without the heat treatment stage it was found that after 5 days of continuous operation the resin content of the hydrocarbon stream at the outlet of the catalyst bed was more than 10 times that of one

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Hydrocarbon stream with heat treatment. That in the stream contained resin causes a rapid decrease in activity in the second hydrogenation stage and also contaminates parts of the Plant, such as B. Heat exchanger. '

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Claims (12)

Claims 1. A method for treating a mineral oil before the extraction of aromatic hydrocarbons, characterized in that man a) the gap gasoline under a first decrease, boiling at atmospheric pressure to 90 ⁰ C distillate fraction distilled b) the residue from this distillation is heated in the liquid phase to temperatures of 200 to 35O ° C, c) the heated product to separate a second distillate fraction boiling at atmospheric pressure up to 250 ° C distilled and d) the second distillate fraction is hydrogenated. 2. The method according to claim 1, characterized in that the heating in stage b) is carried out continuously in a tubular reactor performs. 3. The method according to claim 1 or 2, characterized in that the distillation in stage c) is carried out in a flash distillation column and then carried out in a fractionation column. 4. The method according to any one of claims 1 to 3, characterized in that that the hydrogenation in stage d) in the presence of a catalyst made of iron, cobalt, nickel, tungsten, molybdenum, Platinum or palladium or their oxides or sulfides on an aluminum oxide or silicon dioxide carrier. 309839/1110 5. Procedure, according to. Claim A, characterized in that one a two-stage catalyst is used, for example, in the first stage with nickel or cobalt and molybdenum or Palladium on aluminum oxide and in the second stage with platinum or cobalt and molybdenum on aluminum oxide. 6. The method according to any one of claims 1 to 5? characterized in that the hydrogenation of stage d) is carried out at 100 to 600 ⁰ C under 20 to 34 ata hydrogen pressure. 7. The method according to claim 6, characterized in that the hydrogenation of stage d) is carried out in two stages, being in the first stage at 100 to 300 ⁰ C in the liquid phase and in the second stage at 300 to 600 ⁰ C in hydrogenated in the vapor phase. 8 * Method according to one of claims 1 to 7, characterized in that that the product hydrogenated in stage d) of an aromatic extraction is preferably carried out with a selective solvent, such as diethylene glycol and / or dipropylene glycol with a small amount of water, tetramethylene sulfone, H-methylpyrrolidön, Dimethyl sulfoxide, propylene carbonate, silver fluoborate, N-methylformamide, polyalkylene glycols, morpholine or alkyl carbamates. 9. A method according to any one of claims 1 to 8, characterized in that the gap is distilled gasoline under a decrease to 80 ⁰ C boiling distillate fraction in step a). 10.Verfahren according to any one of claims 1 to 9i, characterized in that the residue is heated ^{to temperatures of 200 to 300 0 C in step b).} 309839/1110 11. The method according to any one of claims 1 to 10, characterized in, that the heating in stage b) is carried out for a period of 0.5 "to 4 hours. 12. "The method according to any one of claims 1 to 11, characterized in that in step c) the product is distilled with separation of a fraction boiling ^{up to 180 ° C."} 309839/1110