US2605170A - Nitrogen production - Google Patents

Description

Patented July 29, ,1952

NITROGEN PRODUCTION James P. Fugassi, Pittsburgh, Pa., assigner to the United States of America as 'Secretary of the Navy Application May 6, 1946, serial No. 667,555

1 Claim.

This invention pertains to a compact apparatus for producing nitrogen from air at high rates of ilcw and particularly to a device which will furnish a continuous supply of nitrogen containing two per cent or lessv of oxygen at high rates of flow.

Nitrogen is obtained by extracting oxygen from air. This is done by passing air over a heated metal such as copper. Oxygen in the air is removed by reaction with the metal. For copper, the equation for the reaction is 2Cu-|-O2 2Cu0. After a certain time interval when the rate of the reaction between the metal and oxygen becomes too slow, the resulting metal oxide is reduced by passing a hydrocarbon over the metal oxide. In the case of copper oxide, the equation for the reaction is tion apparatus as connected to the timer unit.

Experiments were conducted to develop the present apparatus in its iinal form. To perform the desired operations in the simplest form, two heated metal tubes, preferably copper, were selected and packed with small pieces of metal such as copper gauze, sponge copper, vpieces of-copper wire or clippings. A two-step cycle was utilized. In the first step, air was passed through the rst tube while hydrocarbon was passing through the second tube. In the second step, the cycle was reversed after about one minute. The cycle was thus completed and then repeated.

The present apparatus is designed to perform the two steps of the cycle in a continuous automatic opera-tion.

The apparatus as shown in Figure l uses a tube of the order of 0.5 inch in diameter and. twenty feet long. Copper is preferred, although other metal tubes could be used if so desired. The tube I is coiled in a flat coil or helix. as shown, to conserve space and to obtain greatest efficiency. AThe tube is packed with a suitable represented by the Y 2 ller such as copper gauze `which has been found to oder the greatest surface area.

An air inlet 2 and gasoline pipette 3 communicate with the intake of tube I. The length of cycle and of each step is controlled automatically by an external clock device fitted with conventional electrical contacts which energize or de-energize solenoid valves 4 to perform the de sired operations. Gasoline exhaust 5 and nitrogen outlet 6 are provided at the exhaust end of coil I.

Nitrogen outlet B leads to a storage tank to be collected, or to its place of use. parent that proper control of the solenoid valves 4 at the inlet and outlet ends of tube I will result in automatic performance of the alternate oxistep is of approximately one minute duration.

,not necessary.

The apparatus produces approximately one cubic foot of nitrogen during the cycle containing less than two per cent oxygen. Figs. 2 and 3 illustrate the timing mechanism. The timer I0 is provided with a contact arm II adapted in rotation to make and break contact in sequence with electrical contacts I2 separatedrby spaces I3. A battery I4 is circulated through the timer motor, the relay I 5 and in parallel to the various contacts I2. Since the arm II is electrically conductive and the battery has connection to `the timer arm shaft end at I6, current flows through the relay I5 whenever the switch I'I is closed and arm II engages a contact I2, thereby energizing the relay and lifting armature I8 and valve arm 20 against the tension of spring I9 vto its up position. On disengagement of arm II with contact I2 the relay is deenergized and the spring returns the armature to its normal down position.

As appears from Fig. 2, alternate movement of the armature successively opens and closes one of each pair of valves 4, 4a and 4b being open while 4c and 4d are closed, and this position changing at the next cycle alternation to 4a and 4b being closed and 4c and 4d being open. Fig. 3 is illustrative also of this valve relationship, including the valve unit 4. and respective pair valves 4a, 4c and 4b, 4d. The respective closed and open positions of timer arm II are designatedas M and O, the cycle alternations being designated as M-OMO etc.

Preferably tube I is heated in any desired manner to a temperature of 500 C'. provided that complete oxidation of the hydrocarbon is If complete oxidation of the hydrocarbon is required to lower hydrocarbon It will be ap- 3 consumption,v the temperature should be raised to '700 C. Higher temperatures could not be used in the present apparatus because the reduction cycle is strongly exothermic as no thermostatic control is used. Because of the strong evolution of heat during the reduction cycle, localized superheating results so that in certain cases there is melting ofthe filling material and destruction of the catalytically active surface. Consequently, it is desirable to pass a stream of cold air over the outside of the tube when reduction is taking place. This can be thermostatically controlled.

When using a copper filling, it is desirable to treat the copper so that iron oxide is added.

This can be done by soaking the copper lling in a concentrated aqueous solution of ferrie nitrate for several hours. The copper lling is then removed, drained, and then heated to about 500 C. until nitrogen oxide fumes cease to be evolved. The iilling after cooling is then ready for use. The addition of iron oxide is especially effective in increasing the efficiency of oxidation of the Y hydrocarbon.r It has little or no effect on the rate of oxidation of copper 4by air.

For Ithe reduction operation, any hydrocarbon that can be volatilized at temperatures up to 200 C. can be used. These include hydrocarbons such as cyclohexane, hexane, gasoline, and

kerosene. It Was found that one gallon of gasot line would furnish 300D-5000 cubic feet of nitrogen.

Although the present apparatus yields nitrogen up to one cubic foot a minute, it is obvious that the use of more tubes or larger tubes would permit any rate of flow desired.

Various experiments Were conducted to Vdetermine the most efficient tube length and diameter, as Well as tube lling. Tubes ranging indiameter from 0.5-4 inches in diameter were used and various lling materials were used. All Aunits were heated With gas ames. The temperature was measured by attaching a thermocouple to the outer surface of the unit. Manual control was usedto keep the temperature constant. After a period'of operation, it was found thaty certain of these units contained solid globules of copper, which seems to indicate that during one of the cycles, overheating resulted in fusionof parts of the charge. Several charges 4 were made to minimizelocalized overheating. Tubes of smaller diameter offered the highest ratio of external surface area to Volume. The tube of smaller diameter proved to be the most efiicient with the least quantity of lling. Coarse ,copper gauze (14 mesh) proved to be the most Vand results in clogging. The best results were obtained in using a bent copper tube twenty feet long and 0.5 inch in diameter. The tube contained tightly rolled copper gauze Weighing tvvo` pounds and proved to be the most efiicient one 'considering the Weight of gauze used.

What is claimed is:

A method of producing nitrogen at reduced temperatures comprising heating to about 500 C. a single spirally coiled tubular chamber having closely adjacent coil sections and containing copper, passing air for approximately one minute through said chamber to oXidiZe the copper and obtain nitrogen, passing a hydrocarbon volatilizable at temperatures up to 200 C. through said chamber for approximately one minute to reduce the copper oxide, and continuously repeating said Valternate air and hydrocarbon passages at a rate such that the exothermic heat due to the oxide reduction when combined With the applied heat and the heat due to radiation between said adjacent sections or. said coil is sufficient to obtain nitrogen with an applied heat of about 500 C.

JAMES P. FUGASSI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,396,320 Cole Nov.8, 1921 2,022,813 Ruys Dec. 3, 1935 2,035,106 Vesterdal Y Mar. 24, 1936 2,464,265 Searle Mar, 15, 1949 OTHER REFERENCES Ind. & Eng. Chem., September 1946, vol. 38, No. 9, pages 916-922.

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