US1822751A - Process of extracting benzene hydrocarbons from gases - Google Patents

Description

p 1931- 'r. SCHNEIDER 1,822,751

PROCESS OF EXTRACTING BENZENE HYDROQARBONS FROM GASES Filed July 6, 1928 iii) Patented Sept. 8 .1931

PATENT FFHCE THEOIJOR SCHNEIDER, 0F RECKLINGI-IAUSEN, GERMANY, ASSIGNOR TO THE FIRM CARL STILL, OF REGKLINGHAUSEN, GERMANY PROCESS OF EXTRACTING BENZENE HYDROCARBONS FROM GASES Application filed July 6, 1928, Serial No. 290,888, and in Germany July 8, 1927.

in the operation of extracting benzene hydrocarbons from gases produced in carbonizing installations, by washing such gases with what are commonly known as wash oils, it is desirable to use as the wash oil one, generally produced on the works, which contains a certain quantity of naphthalene. Hitherto it has mostly been the use to limit by commercial agreement this accidental content of naphthalene, so far as fresh wash oil is concerned, and later in the use of the oil to maintain the quantity within contracted limits.

By the process of this invention there is used for the extraction of benzene hydrocarbons a wash oil with a naphthalene content which is kept comparatively high. In the selection of the quantity of naphthalene use is made of the circumstance that the gases from which the benzene is to be extracted always contain naphthalene because naphthalene itself belongs to the higher benzene hydrocarbons. The invention consists in special means for maintaining the naphthalene content of the wash. oil so high that the wash oil has a naphthalene vapor tension which is essentially in agreement with the partial pressure of the naphthalene vapor in the gases, that is to say that practically no naphthalene is absorbed from the gases by the wash oil containing naphthalene.

The invention will be more fully described with reference to the drawing, which represents in a somewhat diagrammatic manner a plant, suitable for carrying out the process, as a side elevation.

The cooled distillation gases from which the benzene hydrocarbons are to be recovered are admitted through a pipe 1 in the usual manner into the bottom of a vertical scrubbing tower 2 and are led away at the upper end, freed from their content of benzene, through a pipe 3. Instead of a single scrubber 2, as shown, a number of scrubbing towers connected in series may be used, as is usual in such installations. The filling of hurdles, checkerwork or the like arranged in the scrubbing tower 2 is sprinkled with debenzolized cooled wash oil taken from a tank 6 and forced by a pump 4- through a vertical pipe line 5. The wash oil, charged with benzene hydrocarbons, is discharged at the bottom of the tower 2 through a pipe 7 into a tank 8, from which it is drawn by a pump 9 into the distilling plant for being deprived of its benzene content.

The wash oil is first, through the pipe 18, led for being preheated by the vapors distilled of? and leaving the distillation appa- 'ratus to a reflux condenser 19explained below, travels around the cooling tubes 20 and leaves it through the pipe 21. A by-pass 22 provided with a controlling valve enables the proper regulating of the cooling eliect of the wash oil in the reflux condenser 19. The wash oil so preheated flows through the said pipe 21 to a heater 10, in which it is raised to the requisite distillation temperature of about 130 C. by the indirect heat of a steam coil 11. In this heated condition it is led through a pipe 12 into the distilling column 13 and is there freed from the absorbed benzene hydrocarbons and also from a portion of its naphthalene content by the direct steam injected through the perforated pipe 28. The distilled vapors flow from the topmost tray of the column 13 into the rectifying column 14 built immediately above it and therefrom through the pipe 15 into the reflux condenser 19. When the vapors traverse the tubes 20 thereof which are cooled by im the benzolised wash oil surrounding them, a iractionation takes place. Higher boiling oils containing naphthalene and part of the steam in ected are condensed and collected in the bottom portion of the apparatus 19, whereas the lower boiling constituents comprising mainly the benzol hydrocarbons go away as vapors through the pipe 16 and enter the condenser 17, in the upper part of 7, which they are condensed by means of cooling water. The resulting liquid condensate runs downwards and is separated into water and light Oll in the lower part of the condenser 17. The water is discharged through a pipe 23 into the waste, whereas the light oil runs through another pipe 24 into a storing tank 25.

The mixed condensate mentioned which arises in the reflux condenser 19 is in its bottom portion separated into a lower layer of water and an upper oily layer. The water is taken away by the pipe 26 and goes to the waste. The oil containing the naphthalene is led by the goose-neck pipe 27 to the upper part of the rectifying column 14: in order to act therein as a reflux condensate and to perform the rectifying of the arising distillation vapors. In this way, the naphthalene fractionated off from the vapors entering the reflux condenser 19 is finally returned to the treated Wash oil and passes along with the debenzolized Wash oil away from the distilling column 13 through the pipe 29.- This Wash oil containing naphthalene enters thereafter through the pipe connection 81 a plant of indirectly acting coolers 30 wherein it is cooled, by means of cold water, to the normal temperature. In this cooled condition the Wash oil is passed to the tank 6 mentioned above and repeats its circuit as explained.

Therefore, at the end of a single passage of the wash oil through the washer and then through the distillation apparatus, the wash oil again contains under the conditions of the process practically its original naphthalene content.

In case the fresh wash oil introduced into the plant from another part of the works has too small a content of naphthalene it is used repeatedly in the circuit, so that gradually it takes up naphthalene from the gases until its content of naphthalene is such that no more can be taken up in this manner, that is to say when a certain feature named of the invention, namely that the naphthalene vapor tension of the wash oil shall be in agreement with the partial pressure of naphthalene in the gases, has been achieved.

\Vhat I claim is:

1. A process of extracting benzene hydrocarbons from the gases produced by carbonization of solid fuel comprising the following steps: Washing the gases by means of a wash oil containing such an amount of naphthalene that there is practically no absorption of naphthalene from the gases; distilling 01? the benzol hydrocarbons and a portion of the naphthalene content from the wash oil; fractionating off the naphthalene from the distillation Vapors as a liquid condensate and returning the latter into the Wash oil undergoing distillation.

2. A process of extracting benzene hydrocarbons from the gases produced by carbonization of solid fuel comprising the following steps; Washing the gases by means of a wash oil containing such an amount of naphthalene that there is practically no absorption of naphthalene from the gases; distilling ofl the benzol hydrocarbons and a portion of the naphthalene content from the Wash oil; fractionating oil" the naphthalene from the distillation Vapors as a liquid condensate and returning the latter to the debenzolized wash oil on its way to said washing step.

In testimony whereof I atfix my signature.

THEODOR SCHNEIDER.

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