US2040108A - Recovery of krypton and xenon - Google Patents

Description

May 12, 1936 J. SCHLITT 2,040,108,

RECOVERY OF KRYPTON AND XENON Filed April 11, 1935 70 3 EXCHA N667? 2 AIR INVENTCR Jere 44 L. sew/1% I ATTORNEYS Patented May 12, 1936 PATENT OFFICE 2,040,108 RECOVERY or KRYPTON AND XENON Joseph L. Schlitt, Darien, Conn., assignor to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York Application April 11, 1935, Serial No. 15,799

, 4 Claims.

This invention relates to the separation of the rare gases krypton and xenon from the atmosphere and the recovery of these gases in quan-' ton and xenon, and the ordinary methods of separating air for the recovery of nitrogen, oxygen and argon take no account of the rarer gases.

No practicable method of recovering these gases has been available heretofore, and consequently the gases have been used only for experimental or scientific purposes.

It is the object of the present invention to provide a simple, practical and efiective method of separating and recovering krypton and xenon from the atmosphere.

A further object of the invention is the provision of a method of treating relatively tremendons volumes of air at a cost which permits the recovery and use of krypton and xenon for various commercial and industrial purposes.

In carrying out the present invention, no attempt is made to recover all of the nitrogemoxy- 5 gen and argon as separate gases of substantialpurity, since the primary function of the method is the recovery of the rarer gases krypton and xenon. Advantage is taken of the known methods of separating the nitrogen and oxygen constituents of the atmosphere, but following the primary separation of these constituents they are utilized for the purpose of concentrating krypton and xenon from additional quantities of air. The

subsequent rectification of the liquids which ordinarily are rectified directlyafter initial separation produces a liquid containing considerably greater proportions of krypton and xenon than are usually present in the liquid product of the rectification. This liquid is subjected then to 40 a further rectification to effect separation of oxygen, leaving a liquid concentrate rich in krypton and xenon which can be withdrawn and utilized. A portion 'of the oxygen'and also of the nitrogen is also recoverable, but the major portion of all of the air treated is returned to the atmosphere as a gaseous mixture from which the krypton and xenon has been removed.

The method as thus generally outlined will be better understood byreference to the follow- 50 mg specification and the accompanying diagram matic drawing, illustrating an apparatus which is adapted for use in the practice of the method. It will be understood that details of the apparatus well known in the art are not illustrated 55 or described, the purpose being to present simtreated. The liquid flows backwardly and acply and clearly the essentials of the invention as hereinafter claimed.

Referring to the drawing, a portion of the air to be treated, after initial compression to a suitable pressure and cooling in the usual exchang- 5 ers, is introduced through a pipe 5- to the bottom compartment 6 of a column 1. The air passes upwardly through tubes 8 immersed in a liquid product accumulated as hereinafter described, and thence downwardly through tubes 9 into a collector Hi. In passing through the tubes 8, the air is subjected to selective liquefaction with the resulting formation of a liquid in phase equilibrium with the composition of the air, that is to say, a liquid containing approximately from to of oxygen, the balance being nitrogen withsome of the argon and a considerable proportion of the krypton and xenon of the air cumulates in the compartment 6.

The unliquefied residue, consisting largely of nitrogen, in passing downwardly through the tubes this also liquefied and accumulates in the collector in. This liquid also may contain some 25 krypton and xenon as well as a portion of the argon.

The two liquids which, in an ordinary air liquefaction system, are introduced at separate levels in a rectification column to immediately effect 30 a further separation of the constituents, are conducted instead through pipes I and I2 to a column I3 having separate compartments l4 and I5,

. each provided with the usual trays it, over which the liquids flow in direct contact with relatively 5 large volumes of air introduced through a pipe I! under pressure suificient only to ensure movement of the air through the apparatus. For

the purpose of moving the air, an ordinary blow- .er may be employed. 0

The air is introduced through the pipe I! to 4 the lower compartment l4 and thence through a pipe l8 and valves l9 and 20 to the upper compartment IS. The effect will be to wash from the large volume of entering air, by means of the liquids introduced through the pipes II and l2, substantially all of the krypton and xenon, together with some of the oxygen, while the effiuent from the upper compartment [5, escaping through the pipe 23, will consist of a gaseous 0 mixture, principally nitrogen, but containing oxygen and argon. The effluent may be sent to an exchanger through a valve 24 and pipe 25, or delivered through a pipe 26 for use as hereinafter described. The two liquids, enriched in krypton and nitrogen with some or .liquid and passes finally through xenon, which'accumulate in the bottom of of the compartments l4 and I5, are withdrawn through pipes 2! and 28, controlledby valves 30 and 3|, and are delivered to separate levels of the column 1 in which the usual rectification trays 29 are disposed.

In flowing downwardly over the trays 29, the two liquids introduced to the column 1 are subjected to rectification with vapors arising from the body of liquid surrounding the tubes 8 and 9. This liquid is vaporized in the initial condensation of the entering air and the resulting vapors, together with those formed during the rectification,-pass upwardly through the column 1 and escape as an efliuent, consisting principally of all of the argon present in the liquid, through a pipe 33. The liquid flowing downwardly through the column finally accumulates about the tubes 8 and 9 and consists principally of oxygen with substantially all of the krypton and xenon which has been separated from the air entering through the pipes 5 and I 1.

A portion of the liquid, together with vapors from the lower part of the column I, is delivered through pipes 34 and 35 controlled by valves 36 and 31 to intermediate levels of an auxiliary column 38 containing the usual trays 39 and having at the bottom a coil 40 which is supplied with air previously compressed and cooled through a pipe 4|. In traveling through the coil, the air causes vaporization of the liquid surrounding the coil and is itself liquefied and, it may be, somewhat subcooled; The liquid travels through the pipe 42 and valve 32 to the chamber 6, thus joining the liquid accumulating in that chamber. The vapor passes upwardly through the trays in contact with the downwardly flowing tubes 43 of a condenser which is cooled by the efiluent escaping from'the column 1, through the pipe ,33. A valve 44 controls'the flow of the eflluent which escapes finally through a pipe 45 to an exchanger. By utilizing the pipe 26 a portion of the eflluent from the rectifier l3 The condenser 43 separates from the vapors a liquid which becomes much concentrated in krypton and xenon when it reaches the bottom of rectifier 38. The eflluent from this rectifier escapes through a pipe 46 and consists of substantially pure oxygen which may be delivered through an exchanger to a suitable collector in which the oxygen maybe accumulated for use. The liquid at the bottom of the rectifier may be withdrawn through a pipe 47. It consists of a concentrate of krypton and xenon and is the principal product of the method as described. It may be utilized after further purification for any desired purpose.

From the foregoing description it is very evident that the process forming the subject matter of this application is an efiicient and practicable method of extracting the krypton and xenon from large bodies of atmospheric air while at the same time an air separation apparatus each for the production of high purity oxygen is operated in connection therewith. The relation between the air separation apparatus, which is of the well known Claude type, and the apparatus by means of which krypton and xenon are extracted from a large body of air not treated in the air separation apparatus proper, is such thatan important advantage and economy in the air separation process itself is secured. This arises from the fact that the two liquids intowhich the air entering the Claude column is may be similarly utilized.

liquid fractions in order converted are enriched in oiwgen by reason of their passage through the krypton-xenon extractors 9 and I5. That is to say, the two liquids entering the krypton-xenon extractors through pipes 1 and I3 respectively and re-entering the Claude rectifier through pipes 21 and 23 respectively both carry a higher percentage of oxygen after leaving the krypton-xenon extractors than when they enter. Of course, a consequence of this fact is that the effluent vapor leaving the 4 top of the krypton-xenon extractors contains a higher percentage air.

The method, as will be evident, afiords the possibility of treating large quantities of air and the recovery therefrom in a simple and satisfactory manner of the krypton and xenon content of the air, together with a separate portion consisting of oxygen in substantial purity. Thus, krypton and xenon in quantities enabling the use of these products for various commercial purposes are made available.

Various changes may be made in the details of the procedure and apparatus employed without departing from the invention or sacrificing any of the advantages thereof.

I claim:

of nitrogen than atmospheric 1. The method of separating and recovering fractions each enriched in one of the major constituents of air, washing volumes of air relatively said liquid fractions to produce liquids enriched in krypton and xenon, rectifying the liquids with vapors produced therefrom and thereby accumu-' lating a liquid containing substantially all of the krypton and xenon from the air treated.

' 2. The method of separating and recovering krypton and xenon from the atmosphere which comprises, separating the air initially into liquid fractions each enriched in one of the major con stituents of air, washing volumes of air relatively large with respect to said liquid fractions with said liquid fractions to produce liquids enriched in krypton and xenon, rectifying the liquids with vapors produced therefrom and thereby accumulating a liquid containing substantially all of'the krypton and xenon from the air treated, and subjecting the last mentioned liquid to further rectification with vapors produced therefrom to further concentrate the krypton and xenon by separating oxygen therefrom.

3. The method of separating and recovering oxygen, krypton and xenon from the atmosphere which comprises compressing a portion of the air to be treated and separating this portion into two liquid fractions, one of which is enriched in oxygen, krypton and xenon, and the other of which is enriched in nitrogen, washing volumes of uncondensed, substantially uncompressed cold air which are relatively large with respect to said to enrich both liquids in krypton, xenon and oxygen, and thereafter rectifying the liquid resulting from the washing of said air to produce a liquid containing substantially all the krypton and xenon contained in both the compressed and uncompressed air and substantially more oxygen than was contained in the primary compressed portion of the air.

4. The method of separating and recovering oxygen, krypton and xenon from the atmosphere large with respect to said liquid fractions with v which comprises compressing a portionof the air gen, krypton and xenon, and the other of which compressed anduncompressed air and substanis enriched in nitrogen, washing volumes of untially more oxygen than was contained in the pricondensed, substantially uncompressed cold air mary compressed portion of the air, and. subject- I which are relatively large with respect to said liqing the last-mentioned liquid to further rectificauid fractions in order to enrich both liquids in tion with vapors produced therefrom to further krypton, xenon and oxygen, thereafter rectifyconcentrate the krypton and xenon and separate ing the liquid resulting from the washing of said oxygen therefrom. air to produce a liquid containing substantially JOSEPH L. SCHLI'I'I. all the krypton and xenon contained in both the i

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