US1870334A - Extraction of ethylene from gaseous mixtures - Google Patents

Description

Aug. 9, 1932. H z I EXTRACTION 0F ETI-IYLENE FROM GASEOUS MIXTURES Filed March 18, 1929 2 Sheets-Sheet l REGTI FIOATION 'COLUMN 9:16

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The present invention relates to the extraction of ethylene from gaseous mixtures containing ethylene, in particular from the gases from coke furnaces to which the following description will, for the sake of clearness, be directed, but only by way of example.

It is known that ethylene, or liqpids rich in eth lene, may be collected in t e course of coo ing the gases from coke furnaces, before the main liquefaction of its essential elements, methane, carbon monoxide and nitrogen. Such a process has been described in French Patent No. 585,996 granted November 20, 1923, in which the liquefaction of the ethylene is effected jointly with the rectification of the liquids formed, by the circulation of these liquids in reverse direction to the gases arising in the liquefaction zone. Carried out in this way, the liquid rich in ethylene entrains in solution a certain amount of hydrocarbons or of condensible impurities which are liable to block the colder parts of the apparatus, and it is this liquid which is extracted outside.

In carrying into practice the process just.

referred to, it has been found that the elfect of rectification and washin thus obtained may be insuflicient due to t e fact that the washing liquid is only formed outside or inside the liquefaction tubes. This difficulty may certainly be remedied by replacing the liquefaction tubes by a rectification column traversed from below upwards by the ases treated, but difiiculties may then be found in suitably assuring, on account of the large exchange surfaces necessary, the cooling of such rectification column by the separated. gases, hydrogen, nitrogen, carbon monoxide, and methane, in the case of gases from coke furnaces.

The present invention has for its ob'ect to remedy in particular this defect and thus efiect an improvement in the process according to the above mentioned specification.

The invention consists in collecting the liquid rich in ethylene produced by the cooling of the gases, with or without simultaneous rectification, and in placing the said liquid in intimate contact with the gas remaining after this partial liquefaction; this contact furnishing a gas which may be again cooled to liquefya further portion thereof. Furthermore, an improvement in the washing is obtamed by adding this latter liquid to the first washing liquid, rich in ethylene, mentioned above. In these operations the success1ve coolings of the gas are obtained by causing them to circulate in indirect contact with the cold gases leaving the separating apparatus proper. The washing liquids entrain practically the whole of the impurities, such as the acetylene and the oxides of nitrogen which it was sought to eliminate; the cold of these liquids may then be simply recuperated or said liquids ma be rectified to separate therefrom a gas re atively pure and rich in ethylene, such rectification taking place, for example, through heating by indirect contact with the gaseous mixture treated.

The accompanying drawings show in diagram, and as an example, an apparatus for carrying out the present invention. The two figures show respectively the two portions of the apparatus out along line E-E.

In these drawings A and B are heat exchangers traversed successively by the gaseous mixture to be treated, which arrives in a compressed state at X, at the bottom of the exchanger A, and which is cooled in these exchangers by the cold gases, leaving at low temperature the separation apparatus of the said gaseous mixture; this apparatus is not shown.

In the exchanger A are condensed principally water vapor and the parts easily liquefiable contained in the gaseous mixture treated, for example, benzene. These liquids are collected in one or more fractions and drawn off. In the exchanger B the circulation of the compressed gases takes place from the top to the bottom; the hydrocarbons of a hi her boiling point than methane, and a part 0% the methane itself, being there condensed and falling in a liquid state to the bottom part of B. The mixture of liquids thus produced passes through the pipe 4 to the upper part of the rectifying column C, while the compressed gaseous mixture leaving the bottom of the exchanger B passes by waof pipe 3 to and through the lower part 0 said column.

In columnC the ascent of this {gas and its descent in the reverse direction t from 4 cause the desired washing, and the uant-ity of the washing liquid is increased by t e passage of the ases escaping from the top of the colunm L into a nest of tubes D cooled as will be seen later. The purified gas-v eous mixture leaves from the top part at 5 to as into the separation apparatus proper, and the liquid rich in ethylene containing also acetylene, oxides of nitrogen, and. other imurities, is drawn off at t e lower part of C y means of a tube-1O provided with a cock 11.

The nest of tubes is cooled at its lower part by the whole or a part of the methane or of the carbon monoxide or of the mixture of these gases leaving the separation apparatus, which enters at 7 and leaves at 9, and at its upper part b the whole or a part of the hydrogen or o the mixture of hydrogen and nitrogen coming from the same apparatus, which circulates from 6 to 8; these two streams of gases then passing through the heat exchangers B and A.

The liquid drawn off through the tube 10 generally contains a marked proportion of methane which has been condensed by the nest of tubes D. If the gaseous mixture obtained from the evaporation of the said liquid be used, it is sent back to the proper compartment of the exchanger A to recover its frigidity.

But starting from the liquid in question a gas rich in ethylene may also be obtained by sending this liquid to the upper part of the rectifying column G after having expanded it b the cock 11 to the desired pressure. In its escent in G, the liquid meets the vapours comin from the liquid evaporated in the vaporizer E situated at the lower part of G. These vapours rise from E into G through a tube 13, while the liquid produced by the rectification descends from G into E through a tube 14. The rectification thus roduced furnishes on the one hand a gas ric in methane,

which passes out at the upper part through valve 1 and may, for example, be joined to the methane leaving the separation apparatus proper, and on the other hand a gas rich in ethylene, which leaves through a tube 15 and passes, after having traversed a valve 16, to a compartment of the heat exchanger A. The column may be provided with other exits permitting the separate collection of other elements constituting the ethylene liquid treat ed; for example, a gas rich in ethane could be drawn off from an outlet tube 19. The vaporizer E is heated by the whole or a part of the compressed gaseous mixture treated on its passage between the heat exchangers A and B. The gaseous mixture leaving A arrives at 1, rises in the nest of tubes E, and leaves by the tube 2 to pass to the exchanger B. The liquids only s ightly volatile which accumuhe liquid late in E are withdrawn through a purging cock 18.

What I claim is:

1. A method of extracting, by liquefaction, the ethylene in ethylene-containing gaseous mixtures, which comprises the steps of coolin the gaseous mixture to liquefy substantia ly the whole of the ethylene, thereby dissolving in said li uid a part of the acetylene and mtro en oxi es contained in said mixture, furt ier dissolving the remaining part of the acetylene and nitrogen oxides by circulatin the liquid obtained in said partial lique action in intimate contact with, and in the opposite direction to, the gaseous fraction remaining after the said liquefaction, separating the cold gases of said gaseous mixture, iquefying a art of the aseous mixture remaining after t e further issolving operation in indirect heat-exchange with said. separated cold gases, and adding said liquefied part to the liquid rich in ethylene obtained in the first liquefaction.

2. A method of extracting, by liquefaction, the ethylene in ethylene-containing gaseous mixtures, which comprises the steps of coolin the gaseous mixture to liquefy substantia ly the whole of the ethylene, thereby dissolving in said liquid a part of the acetylene and nitrogen oxides contained in the gaseous mixture, further dissolving the remaining part of the acetylene and nitrogen oxides by circulating the liquid obtained in said partial liquefaction in intimate contact with, and in the opposite direction to, the gaseous fraction remaining after the said liquefaction, se arating the cold gases of said gaseous mixture, liquefying a part of the gaseous mixture remaining after the further dissolving operation In indirect heat-exchange with said separated cold gases, adding t e liquefied part to the liquid rich in ethylene obtained in the first liquefaction, and submitting the liquid resulting from the further dissolving operation to a rectification by heating it in indirect heat exchange with the gaseous mixture to be treated.

3. A method of extracting, by liquefaction, the ethylene in ethylene-containing gaseous mixtures, which comprises the steps of cooling the gaseous mixture by heat exchan with the se arated gases, so as to liquefy su stantially t e whole of the ethylene thereby dissolving in said liquid a part of the acet lene and nitrogen oxides contained in said mixture, further dissolving the remaining part of the acetylene and nitrogen oxides by circulating the liquid obtained in said partial liquefaction in intimate contact with and in the opposite direction to the gaseous fraction remaining after the said liquefaction, separating the gaseous mixture into its constituents by liquefaction, liquefying a art of the aseous mixture remainin after t e further issolving operation in indirect heat exchange with said separated constituents, adding said liquefied part to the liquid rich in eth lene obtained in the first liquefaction, recti ying the liquid resulting from the further dissolving operation while utilizing the gaseous mixture as a heating agent in said rectification, and circulating in indirect contact with the gaseous mixture the ethylene resulting from said rectification and the separated gases which have been used to cool the gaseous mixture and thereby liquefy substantially the whole of its ethylene.

In testimony whereof I afiix my signature.

HENRI LANTZ.

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