United States Patent [191 [111 3,768,865 [45] Oct

United States Patent [191 [111 3,768,865 [45] Oct. 30, 1973 Dehn [54] PROCESS FOR THE DISPOSAL OF SALT SOLUTIONS CONTAMINATED WITH [56] References Cited AZIDE ‘ UNITED STATES PATENTS [75] Inventor: Frederick C. Dehn, New 2,348,16l 5/1944 Van DUZCC ................... .. 166/305 D Martinsville, W. Va. 3,l96,6l9 7/l965 Shock . .. 6l/.5 X 3,135,50l 6/1964 Dahms et al .......................... .._299/4 [731 Assignee: PPG Industries, Inc., Pittsburgh, Pa. [221 Filed: July 13, 1972 Primary Examiner--Ernest R. Purser Attorney-Russell A. Eberly [211 Appl. No.: 271,436 Related 0.8. Application Data [57] ABSTRACT [63] Continuation-impart of Ser. No. 92,37], Nov. 24, 1970, abandoned. The disposal of salt solutions contaminated with azide is accomplished by depositing the solution in a subter U-S- Cl ------------------------- -- 299/4, 23/157, 61/0-5, ranean cavity, maintaining the solution in the subter [52] 166/305 D ranean cavity until it is essentially free of azide, and [51] Int. Cl ........................................... .. E2lb pumping the essentially azidefree solution to the gun [53] Field of Search ..................................... .. 61/05; face - 23/157-163, 190, 191, 356, 360;166/305 299/4, 5;D 18 v Claims,_ 2 Drawing_ Figures_ 39 38 ‘a 341 1\ 4 45 Na. N3 Aun No.0“ Lew-mun] HCl 16- |'——W 4~ 4.0 _ b ,42 : " l2‘ ~ ' <—-sTeAm l4 _' _ KNS. DRIPS Patented‘ Oct. 30, 1973 3,768,865 2 Sheets-Sheet 1 V =03:nzaz8: $502563 p.01. INVENTOR FPEDfk/CK c. UEHN ATTORNEYj Patented Oct. 30, 1973 3,768,865.‘ 2 Sheets-Sheet >3 mom/m c. aemv BY awkqghm ATTORNEY-s 3,768,865 1 2 PROCESS FOR THE DISPOSAL OF SALT drochloric acid as the feed acid and to deposit solutions SOLUTIONS CONTAMINATED WITII AZIDE of the by-product sodium chloride in a sodium chloride well. The azide contaminant often decomposes with the CROSS-REFERENCE TO RELATED APPLICATION passage of a short time, usually a matter of a few weeks This application is a continuation-in-part of the appli or months. Rarely does azide persist longer than about cation Ser. No. 92,371, filed Nov. 24, 1970 and now four weeks. Upon reduction of the azide concentration abandoned. to an insigni?cant value, e.g., 30 parts per billion parts Those engaged in axide chemistry are often faced of by-product salt, the well may be placed into produc with the disposal of a salt solution contaminated with tion retrieving most of the salt deposited. If the solution azide. Usually the salt is a by-product of a process pumped into the well was not saturated, additional salt wherein a metal azide, an organic azide, or hydrazoic values would also be recovered. Of course, the accept acid is produced. Potassium azide, for example, may be able value for an insigni?cant concentration will vary produced from sodium azide and potassium carbonate depending upon the use to which the brine is put. In a by metathesis. The resulting by-product sodium car producing ?eld where a large cavity is connected to the bonate often contains small amounts of azide as a con surface by at least two wells, azide contaminated salt taminant which greatly enhances the problem of dis solution may be pumped into the cavity through one posal. well while the other well is producing. If the average Hydrazoic acid is becoming of increasing importance residence time is on the order of the time it takes the primarily as an intermediate in the preparation of vari azide to decompose, the azide concentration can be ous azide compounds such as its salts. Hydrazoic acid 20 brought to a very low value. The large amount of dilu is bioactive and may be produced for those purposes. tion taking place also aids in reducing the azide con One particularly favorable use for hydrazoic acid is the centration. preparation of alkali metal azide or alkaline earth metal Often two relatively large chambers are connected by azide by contacting the hydrazoic acid with the appro a narrow passageway. One or more wells connect each priate basic compound such as the hydroxide. 25 chamber with the surface. Such a system is customarily , Hydrazoic acid may be prepared by several processes operated by pumping water into one chamber and for which the basic chemistry is known. However, re pumping brine from the other chamber to the surface. finements must be made to the laboratory processes If at least some of the water pumped into the first employing the basic chemistry in order to achieve a chamber is substituted by the azide contaminated by commercially successful plant capable of producing product salt solution from the production of hydrazoic sizable amounts of hydrazoic acid. One of the known acid, the principles of dilution and residence time may laboratory methods for producing hydrazoic acid is the be utilized to achieve a satisfactorily low azide level by acidi?cation of at least one alkali metal azide or alka the time the solution is withdrawn from the other line earth metal azide with an acid such as one or more chamber. of the strong mineral acids Such a process without fur 35 The basic principles of the present invention are illus ther re?nement presents a problem with respect to safe trated by reference to the drawings wherein like num disposal of the by-product salt of the acid which is al bers refer to like parts and wherein most always more or less contaminated with azide. FIG. 1 represents a process within the contemplation It is the purpose of this invention to provide a safe of the present invention and and efficient method of disposal of azide-contaminated FIG. 2 represents a modification to the process of salt. It has now been found that the azide-contaminated FIG. 1. salt may be disposed of by depositing a solution of the The process illustrated in FIG. 1 shows the formation same in a subterranean cavity. Wells are admirably of hydrazoic acid by acidifying sodium azide with hy suited for the purpose. The subterranean cavity should drochloric acid, The hydrazoic acid so produced is con be deep within the earth so that the solution will not be 45 tacted with potassium hydroxide to produce potassium mixed to any substantial degree with surface ground azide, although the hydrazoic acid can be put to a num waters. Most subterranean cavities used for the prac ber of other uses. Because sodium azide produced by tice of this invention are at least 300 feet from the sur the Wislicenus method produces one mole of sodium face of the earth. More often, they are at least 500 feet azide produced, it is often convenient to acidify the deep. It is preferred that they be at least 1,000 or even mixture rather than separate the sodium hydroxide l,500 feet below the surface. from the sodium azide before acidifying the sodium Many wells especially suitable for the practice of this azide. If the sodium hydroxide is not removed, addi invention have been or are presently used for the solu tional acid will be required to neutralize it when the so tion mining of salts. Examples of such salts are sodium dium azide is acidi?ed. 55 chloride, potassium chloride, and sodium carbonate. Referring now in more detail to FIG. 1, equimolar Wells used for the recovery of sulfur by the F rasch pro portions of sodium azide and sodium hydroxide are fed cess are also satisfactory. These wells may be aban through line 1 to mix tank 2 where they are contacted doned for production purposes. Alternatively, the well with hydrochloric acid introduced through line 4. A gas may be located in an active ?eld where one or more stream containing mostly nitrogen, a small percentage other wells are currently producing. In either case, the (usually about 3 per cent) of hydrazoic acid, some by-product salt from the production of hydrazoic acid water vapor, and some hydrogen chloride is introduced may be the same or different from the salt produced through line 6 and sparger 7 and bubbled through the from the field. - mixture in mix tank 2 to dilute any hydrazoic acid formed and sweep it from the mix tank through line 8. In a preferred embodiment of this invention, the salt 65 is the same as the principal salt comprising the subter Because hydrazoic acid is explosive in concentrated ranean deposit. Because hydrazoic acid is most often amounts, dilution by an inert gas such as nitrogen, he prepared from sodium azide, it is convenient to use hy lium, argon, neon, xenon, krypton, air, methane, eth 3,768,865 3 . 4 ane, water vapor, CF4,CF 3C1, or mixtures thereof is de values, its use is not mandatory and it may be omitted. sirable to reduce the possibility of an explosion. The Under such circumstances, line 42 would be connected gas in line 8 advantageously contains about 5 to 8 per directly to shaft 60. ' cent hydrazoic acid. Greater or lesser proportions may FIG. 2 shows a modi?cation of the process described be used if desired. Liquid from mix tank 2 having a pH with reference to FIG. 1. In FIG. 2 shaft 60 of a first of about 5 to 6 is forwarded to mix tank 10 through line well is shown connecting line 58 with chamber 64 of 12 by pump 14. Hydrochloric acid is introduced subterranean cavity 62. Subterranean cavity 62 com through line 16 to lower the pH of the reaction mixture prises chambers 64 and 66 connected by passageway to about 2 to 3.

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