US2909410A - Recovery of argon from an oxygen containing crude argon mixture - Google Patents

Description

G. FEDORKO RECOVERY OF ARGON FROM AN OXYGEN Oct. 20, 1959 CONTAINING CRUDE ARGON MIXTURE 2 Sheets-Sheet 1 Filed May 19, 1955 INVENTOR GEORGE FEDORKO HY M On Oh.

vm Ohmm 200 0h N QN ATTORNEY RECOVERY OF ARGON FROM AN OXYGEN CON- TAINING CRUDE ARGON MIXTURE George Fedorko, Allentown, Pa., assignor to Air Products Incorporated, a corporation of Michigan Application May 19, 1955, Serial No. 509,449

Claims. (Cl. 23-209) The present invention relates to a new and improved method for obtaining a substantially pure argon fraction from an oxygen and nitrogen containing stream, such as air, in which a small percentage of argon is present.

The prior art methods of separating argon from air or other oxygen and nitrogen containing mixtures in which a small percent of argon is present fail to provide' an economic method for separating argon as a substantially pure product. The more efficient prior art processes provide an argon product of, for example, 92% argon and 8% oxygen. Although this so-called technical argon is suitable for filling incandescent lamps, other uses of argon require that it be in a substantially pure state and without sacrificing economy during its production.

In accordance with the present invention, substantially pure argon is obtained by recovering an argon fraction containing oxygen of from 12 to 22 mol. percent concentration, mixing ammonia with the oxygen containing argon in critical proportions and reacting this mixture under conditions which yield a nitrogen oxide-free reaction mixture of argon, nitrogen, hydrogen and water vapor. This reaction mixture, after drying, may be readily separated to obtain substantially pure argon because of the spread in the boiling points of hydrogen, nitrogen and argon.

In the drawings:

Fig. 1 diagrammatically illustrates a layout of apparatus for practicing the process of this invention; and

Fig. 2 diagrammatically illustrates a layout of apparatus representing a form of crude argon converter suitable for use in connection with Fig. 1.

Referring to Fig. 1 of the drawings, the fractionating column generally indicated at 10 may, for optimum operation, be any conventional or preferred two-stage colunm. It includes a high pressure section 12 and a low pressure section 14 separated by a partition plate and refiuxing nitrogen condenser 16. Each of the sections is provided with bubble plates 18.

A partially liquefied air feed stream is fed to column 10 via line 20. A minor portion of this total air feed stream is obtained via line 22, heat exchanger 24, line 26 and expansion valve 28. The operation of heat exchanger 24 will be explained hereinafter. Another minor portion of the total air feed stream of line 20 is obtained via line 30, heat exchanger 32 and expansion valve 34. The operation of heat exchanger 32 will also be explained hereinafter. The balance of the air feed stream is supplied via line 36 after it has been compressed, dried, and cooled by exchange against cold products of the system and/or expansion while doing work. Any of the conventional heat exchange systems normally used in an air fractionating cycle will suflice' to provide this major portion of the air stream supply. United States Patent 2,626,510 is an example of a suitable system for this purpose.

Liquid crude oxygen collecting in pool 40 in the base of the high pressure section 12 passes through a conduit 2,909,416 Patented Oct. 20, 1959 42 to point 44. A minor portion of this crude oxygen is diverted at point 44 to conduit 46, expanded in expansion valve 48, cools argon pump 50, subcools counter-flowing argon in exchanger 52 and is then joined with the balance of the crude oxygen at point 54 after the balance has passed through conduit 56 and has been expanded in expansion valve 58. The crude oxygen stream now at a pressure approximating that of the low pressure section 14 of the column 10 passes via conduit 60 through one of the two hydrocarbon adsorbers 62 which are arranged in parallel. The onstream adsorber 62 functions by the use of any well-known hydrocarbon adsorbent material to remove hydrocarbons from the expanded oxygen stream While the otfstream hydrocarbon adsorber is being regenerated. The resulting hydrocarbon-free expanded crude oxygen stream passes via conduit 64 to the condenser 66 of crude argon column 68 and supplies the refrigeration necessary to condense an argon containing stream collecting in pool 70. Efiiuent crude oxygen stream from condenser 66 passes via liquid level control 72 as gaseous crude oxygen in conduit 74 and as liquid crude oxygen in conduit 76 to intermediate gaseous and liquid feed points in the low pressure section 14 of column 10.

The high pressure liquid nitrogen collecting in pool 78 below nitrogen condenser 16 passes through conduit 80 to nitrogen subcooler 82 and thence to point 84. A major portion of this high pressure liquid nitrogen stream at point 84 is fed via expansion valve 86 to the upper end of low pressure section 14 of column 10. The balanceof the high pressure nitrogen stream passes via conduit 88 and expansion valve 90 to pure argon column 92 where, as explained hereinafter, it functions as a por tion of the coolant necessary for conderser 94.

Product oxygen, as a liquid, is Withdrawn via conduit 96. If desired, a gaseous oxygen product could be withdrawn in the well-known manner. Product nitrogen stream is withdrawn from column 10 via conduit 98 as a gas, A portion of the gaseous nitrogen in conduit 98 is diverted via conduit 100 and flows through nitrogen subcooler 82 in countercurrent relation with high pressure liquid nitrogen flowing therethrough. The refrigeration value of eiiluent nitrogen in conduit 102 may be recovered by countercurrent flow against incoming air in conduit 36 in the manner explained above. The balance of the nitrogen flowing in conduit 98 passes through crude argon heat exchanger 104 and the efliuent nitrogen in conduit 106 may also be used for cooling the incommg air stream.

An argon rich gas is removed from low pressure section 14 of column 10 via line 108 and is fed to crude argon column 68 in countercurrent contact with a downwardly flowing liquid stream high in oxygen content. The liquid oxygen reflux stream is returned to column 10 via line 110. By the action of the cooling occurring in condenser 66 as previously described, a crude argon stream collects as a pool at 70 and is removed from crude argon column 68 by conduit 112. This crude argon gas mixture must contain oxygen in the range of 12 to 22 mol. percent for reasons that will become more apparent hereinafter. Such an oxygen content is ob tained by control of the point of removal of the feed stream via conduit 108, the degree of cooling obtained in condenser 66 as well as by the design of column 68 and the amount of crude argon withdrawn through conduit 112. The crude argon stream flowing in conduit 112 is heat exchanged against incoming air stream in exchanger 24 and its refrigeration value thereby recovered. Etfiuent from the heat exchanger 24 flows via conduit 114 through compressor 116 and is there compressed to a pressure of, for example, 15 to 25 p.s.i.g. After cooling in water cooled after-cooler 118, the compressed crude argon stream flows to crude argon converter 120. Prior to its entry into crude argon converter 120, as explained more frilly hereinafter, the crude argon gas stream is mixed with a proper amount of ammonia supplied from supply unit 122 and the resulting mixture is then reacted preferably in the presence of a catalyst to obtain a mixture of argon, nitrogen, hydrogen and Water vapor. It is of importance in this conversion that the hydrogen content of the outgoing gas stream via conduit 124 be from about 1 to 4% hydrogen.

It has been stated above that it is of importance that the oxygen content of the feed gas to the crude argon converter be between 12 and 22 mol. percent. It has further been stated that the hydrogen content of the efiiuent from the crude argon converter must be from about 1 to 4%. This hydrogen content in the efiluent stream is obtained by controlling the amount of ammonia added. The ammonia added should be in excess of that stoichiometrically required for reacting with the total oxygen content of the crude argon stream so that the formation of oxides of nitrogen is prevented and the product gas will contain no oxygen. This is assured if the effluent product from the crude argon converter contains from about 1 to 4% hydrogen. Furthermore, by using a crude argon gas mixture containing 12 to 22 mol. percent oxygen, sutficient heat is generated by the oxidation occurring in the presence of the catalyst, preferably a platinum catalyst, that the product gas will contain no ammonia vapor. If these conditions are met, the eflluent in conduit 124 may subsequently be separated to obtain a substantially pure argon stream free of contamination by oxygen, nitrogen oxides and ammonia.

The effiuent of the crude argon converter passes via conduit 124 through compressor 126 wherein it is recompressed to a pressure of from to p.s.i.g. Bypass conduit 128 around compressor 126 maintains a constant suction pressure and by-pass conduit 130 around compressor 116 maintains a constant discharge pressure, each of compressors 116 and 126 having a design capacity in excess of the desired total throughput of the process. As a result, the amount of feed through the converter is properly regulated.

After recompression in compressor 126, the argon containing stream passes via conduit 132 through water cooled after-cooler 134 and then via conduit 136 through one of the desiccant type driers 138 which are arranged in parallel. The resulting dry stream containing argon, nitrogen and hydrogen passes via conduit 140 to exchanger 142. In exchanger 142, this stream is cooled to a low temperature by heat exchange against liquid product passing through passage 144. The effluent cooled argon containing stream in conduit 146 then passes through heat exchanger 104 Where it is cooled to a saturated vapor. This saturated vapor is passed via conduit 148 to pure argon column 92 for separation into a nitrogen over-head product and a liquid pure argon product.

The reboiler coil 150 of pure argon column 92 is supplied with gaseous high pressure nitrogen via conduit 152. The effluent high pressure nitrogen from reboiler coil 150 is expanded in expansion valve 154 and passes via conduit 156 to condenser 94 as coolant therefore along with expanded nitrogen from expansion valve 90 as previously described. Effiuent impure nitrogen from condenser 94 via conduit 158 may be merged with the overhead nitrogen product in conduit 160 and the refrigeration value of the resultant merged streams may be recovered by heat exchange against the incoming air feed stream of conduit 36.

Liquid pure argon product collects in pool 162 and is withdrawn via conduit 164. After subcooling in subcooler 52, the pure argon product may be pumped via pump 51 through conduit 168 to exchanger 142 where it is heat exchanged against compressed incoming air and the dry argon containing stream of conduit 140. The

resultant pure gaseous argon product is then fed via conduit 170 to suitable gas collecting equipment or directly to a point of utilization of this product.

Figure 2 of the drawings illustrates a suitable form of crude argon converter and associated equipment for use in connection With Fig. 1. Crude argon stream, after cooling in after-cooler 118 of Fig. 1, flows via line 114 through constant pressure gas regulator 172 and flow control valve 188 to point 174. A supply of anhydrous ammonia 122 which may be in the form of cylinders of liquid ammonia passes via line 176 and shut off valve 178 to heat exchanger 180 Where it is vaporized by heat exchange against counter-fiowing water as described hereinafter From heat exchanger 180, the anhydrous ammonia vapor flows to a point of division 182. A major portion of this anhydrous ammonia flows via line 184 through constant pressure regulator valve 186 and flow control valve 190 to point 174. Adjustment of flow control valves 188 and 190 roughly determines the required ratio of ammonia to crude argon stream as hereinbefore described. Final adjustment of this ratio is obtained by means described hereinafter. The mixture of crude argon and ammonia vapor flows via line 192 to the crude argon converter 120. A catalyst bed is provided in converter 12%), the preferred form of catalyst being a platinum metal type catalyst supported on a carrier in pelleted form of for example one-eighth inch thick by one-eighth inch diameter. In view of the reaction temperatures occurring in unit 120, e.g., 1600 to 1800 F., this unit is designed accordingly.

The resultant reaction mixture containing argon, nitrogen, 1 to 4 percent hydrogen and saturated with water vapor passes from argon converter unit 120 via line 194 and flows to a point of division 196. Hydrogen analyzer and controller unit 198 samples the argon con taining stream flowing in 194 via valve 200 and line 282. A minor portion of the ammonia feed at division point 182 flows via line 234 through constant pressure regulator valve 2 1-6 to flow control valve 268, line 219 and its associated valve 212 permitting by-pass of valve 208 if desired. Valve 203 is opened and closed in response to the hydrogen content of the product emerging from unit 120 as determined by hydrogen analyzer and controller 193. Broken line 214 indicates this control diagrammatically. If the hydrogen content of the emerging gas from unit 120 is less than 1%, valve 208 is opened more so as to permit additional ammonia to be blended with the incoming gaseous mixture flowing to unit 124 This is accomplished by flow through line 216. If on the other hand the hydrogen content of the gases emerging from unit 12% is greater than the upper limit. 4%, valve 263 in response to unit 128 is regulated so as to reduce the flow of ammonia through litre 216 to the mixture of argon and ammonia flowing in line The product of the argon converter unit 120 flows from the point of division 196 via line 218 through heat exchangers 221} and 222 to line 124. Cooling water flowing in a countercurrent direction through heat exchangers 222 and 22$ via lines 224 and 226 is employed for cooling the argon product mixture of unit 121} to a temperature suitable for feed to compressor 126. Line 226 passes through exchanger and the heat recovered in exchanger 22?; is employed for vaporizing the ammonia flowing in countercurrcnt relation through cxchanger 180.

The above described arrangement (Figure 2) for controlling the admixture of anhydrous ammonia with the crude argon stream in proper proportions is for the purpose of illustration, it being apparent that other systems which will function to obtain the proper ratio of Ellimonia to argon will serve the purposes of the present inventron.

The following data is typical of the conditions existing in the argon containing stream as it is processed in accordance with the present invention. The crude argon mixture flowing in line 114 contains 12 to 22 mol. percent oxygen, nitrogen, and the remainder argon. This gas is dry and available at 2 for the compressor 116 which compresses it to a pressure of from 15 to 25 p.s.i.g. The product of reaction emerging from reactor 120 is saturated with Water and contains to nitrogen depending upon the oxygen and nitrogen in the feed stream to the converter 120, 1 to 4% hydrogen, and the remainder argon. After drying in one of the units 138, this reaction mixture is cooled to a temperature of for example -295 F. in exchanger 104. Colmm 92 operates at a pressure of 10 to 15 p.s.i.g. The bottom product from the column, substantially pure argon, is Withdrawn at this pressure as a saturated liquid and flows to pump 56} via exchanger 52. At this point, its temperature is approximately -293 F. The overhead from the column will vary in composition depend ing upon the feed to the column, its composition being 50% to 80% nitrogen, 8 to 12% hydrogen and the remainder argon. This gas leaves at a temperature of approximately -300 F.

The foregoing description of the present invention is for the purpose of illustration only and is not limited to the scope thereof which is set forth in the claims.

What is claimed is:

1. In the fractionation of air into oxygen and nitro gen rich fractions, the method of obtaining a substantially pure argon fraction which comprises the steps of withdrawing an oxygen containing argon stream from a fractionating operation, the oxygen constituting from 12 to 22 mol. percent of the Withdrawn composition, mixing ammonia with the oxygen containing argon stream, the amount of ammonia being in excess of that .stoichiometrically required to react with the oxygen present in the stream, reacting the resultant mixture at a sufficiently elevated temperature to produce a substantially nitrogen oxide-free reaction mixture of argon, nitrogen, hydrogen and Water vapor, and subsequently separating the reaction mixture to obtain substantially pure argon.

2. In the fractionation of air into oxygen and nitrogen rich fractions, the method of obtaining a substantially pure argon fraction which comprises the steps of withdrawing an oxygen containing argon stream from the fractionating operation, fractionating the withdrawn stream to obtain a crude argon mixture containing from 12 to 22 mol. percent oxygen, mixing ammonia with the crude argon mixture, the amount of ammonia being in excess of that stoichiometrically required to react with the oxygen of the crude argon mixture, reacting the re sulting mixture at a sufficiently elevated temperature to produce a substantially nitrogen oxide-free reaction mixture of argon, nitrogen and water vapor, and subsequently separating the reaction mixture to obtain substantially pure argon.

3. In the fractionation of air into oxygen and nitrogen fractions in which compressed air is refrigerated and supplied to a fractionating operation having a high pressure stage and a low pressure stage, the method of obtaining a substantially pure argon fraction which comprises the steps of withdrawing an oxygen containing argon stream from the low pressure stage, fractionating the Withdrawn argon stream to obtain a crude argon mixture containing from 12 to 22 mol. percent oxygen, mixing ammonia with the crude argon mixture, the amount of ammonia being in excess of that stoichiometrically required to react with the oxygen of the crude argon mixture, reacting the resulting mixture at a sufficiently elevated temperature to produce a substantially nitrogen oxide-free reaction mixture of argon, nitrogen, 1 to 4% hydrogen and water vapor, and subsequently separating the reaction mixture to obtain substantially pure argon.

4. In the continuous fractionation of air into oxygen and nitrogen fractions in which compressed air is refrigerated and supplied to a fractionating operation having a high pressure stage and a low pressure stage, the meth- 0d of obtaining a substantially pure argon fraction which comprises the steps of withdrawing an oxygen containing argon stream from the low pressure stage, fractionating the argon stream to obtain a crude argon mixture containing from 12 to 22 mol. percent oxygen, mixing ammonia with crude argon mixture, the amount of ammonia being in excess of that stoichiometrically re quired to react with the oxygen of the crude argon mixture, reacting the resulting mixture at a sufficiently elevated temperature to produce a substantially nitrogen oxide-free reaction mixture of argon, nitrogen, l to 4% hydrogen and water, subsequently removing water from the reaction mixture, and fractionating the resulting mixture to obtain substantially pure argon.

5. In the continuous fractionation of air into oxygen and nitrogen fractions in which compressed air is refrigerated and supplied to a fractionating operation having a high pressure stage and a low pressure stage, the method of obtaining a substantially pure argon fraction which comprises the steps of withdrawing an oxygen containing argon stream from the low pressure stage, fractionating the argon stream to obtain a crude argon mixture containing from 12 to 22 mol. percent oxygen, mixing ammonia with the crude argon mixture, the amount af ammonia being in excess of that stoichiometrically required to react with the oxygen of the crude argon mixture, reacting the resulting miXtm'e in the presence of a. catalyst at a sufficiently elevated temperature to produce a substantially nitrogen oxide-free reaction mixture of argon, nitrogen, 1 to 4% hydrogen and water, subsequently removing Water from the reaction mixture, and fractionating the resulting mixture to obtain substantially pure argon.

istry, 4th ed., 1937, vol. 1, pages 462-463.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nom 2,909,410 October 2Q, 1959 George Fedorko It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 34, for "conderser" condenser 5 column 6, line 11, after "hydrogen" insert a cemman Signed and sealed this 19th day of April 1960 (SEAL) Attest:

KARL Ha AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No& 2,909,410 October 20, 1959 George Fedorko It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 34, for conderser" reed m condenser column 6, line 11, after hydrogen" insert a commao Signed and sealed this 19th day of April 196% (SEAL) Attest:

KARL Hu 7 AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents

Claims (1)

1. IN THE FRACTIONATION OF AIR INTO OXYGEN AND NITROGEN RICH FRACTIONS, THE METHOD OF OBTAINING A SUBSTANTIALLY PURE ARGON FRACTION WHICH COMPRISES THE STEPS OF WITHDRAWING AN OXYGEN CONTAINING ARGON STREAM FROM A FRACTIONATING OPERATION, THE OXYGEN CONSTITUTING FROM 12 TO 22 MOL. PERCENT OF THE WITHDRAWN COMPOSITION, MIXING AMMONIA WITH THE OXYGEN CONTAINING ARGON STREAM, THE AMOUNT OF AMMONIA BEING IN EXCESS OF THAT

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