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Oct. 4, 1949. J. A. SHAW ETA 2,483,440 SILVER ACETYLIDE COMPOUND AND PROCESS OF MAKING SAME Filed Feb. 7, 1946

- TORS. 2:- 5. foSAAA/19.azzoWNESSE3, SAY a BA / vac/r ATTORNEY Patented Oct. 4, 1949 2,483,440

UNITED STATES PATENT OFFICE

SILVER, ACETYLDE COMPOUND AND PROCESS OF MAKING SAME Joseph A. Shaw and Elton Fisher, Pittsburgh, Pa., assignors to Koppers Company, Inc., Fittsburgh, Pa., a corporation of Delaware Application February 7, 1946, Serial No. 646,185 2 Claims. (C. 260-430) 2 This invention relates to a silver acetylide com tion is described in the co-pending application of pound. More particularly the invention relates Joseph A. Shaw, Ser. No. 637,740, filed December to a non-explosive silver acetylide compound and 28, i945, for “Treatment of coke oven gas,' now the process of making the compound. abandoned. It is well known that Silver nitrate is an effec To produce the new compound silver acetylide, tive absorbent for olefines. However, the use of Ag2C2.6AgNO3, acetylene C2H2 is bubbled through silver nitrate has been avoided commercially for 3, Solution of silver nitrate having a concentra absorption of olefines, Such as ethylene and pro tion of more than 20% anhydrous AgNO3 in the pylene from coke oven or coal gas because Such Solution. From many tests it has been found gases also contain acetylene. Acetylene custo that, a silver nitrate solution containing 31% marily reacts with the silver nitrate to form sil anhydrous silver nitrate (AgNO3) gives a very de wer acetylide Ag2C2. AgNO3, which is a dangerous Siirable product. This strong silver nitrate solu and powerful explosive. A rise in temperature to tion Will normally be reduced by hydrogen asso about 210 C. Or an electrostatic spark are suffi ciated with acetylene gas, particularly if coke cient to detonate the dry substance. OVera Or Coal gaS is being used as the source of Coke oven and coal gas contain hydrogen as acetylene. It has been found that if a small Well as olefines and acetylene. If silver nitrate airaouint of ferric nitrate Fe(NO3)3, is contained Solution of strong concentration is used for ab in the silver nitrate solution, metallic silver will Sorbing the olefines, the hydrogen reduces the not be precipitated. silver nitrate to deposit metallic silver from the absorbent Solution with the consequent loss of If acetylene is bubbled through a weak solu expensive silver nitrate and interference with tion of silver nitrate, that is 10% or less by weight, smooth mechanical operation of the process. For of anhydrous AgNO3 in the Solution, a white crys this reason dilute silver nitrate has been used taine compound Ag2C2. AgNO3 is formed. This as an absorbent solution, which was accompanied conpound is very explosive under moderate heat by the inevitable explosion risk. ing and therefore involves risk in its formation The present invention is based upon the dis and handling. The explosive silver acetylide is covery that a strong silver nitrate solution may not very soluble in the dilute silver nitrate solu be safely used for the absorption of olefines that tion, but as the concentration of the silver nitrate are associated with acetylene. Such strong silver Solution is increased, the solubility of the ex nitrate Solutions react with the acetylene to form plosive Silver acetylide increases. As the strength a new connpound of silver and acetylene, which of the silver acetylide solution used for absorption can be Saifely handled Without explosion risk. is increased up to 20% the explosive silver acet The primary object of the present invention is ylide compound dissolves in the Solution and to provide a new compound, silver acetylide : tends to change its form from the explosive silver Ag2C2,6AgNO3, and the method of making the acetylide over to the safe silver acetylide con compound. pond Ag2C2.6AgNO3. With this and other objects in view, the inven In Table 1 is shown the solubility of the silver tion consists in the new silver acetylide com acetylide compound in the silver nitrate absorp pound Ag2C2.6AgNO3, and the process of making tion solution and illustrates how the eXplosive the acetylide. silver acetylide is transformed into the safe silver The principal application of the present inven acetylide compound. TABLE 1. Solubility of silver acetylide in its mother liquor Solubility Graper Formula of Crystals Type of Mother Liquor (Agucous Solutions) Temp.

o C. Trace. AgaC2AgNO3------9N, AgNO3-s-s-s-s------25 0.532 -----do------10% AgNO3 in NHNQ3- 23 2.9 AggC36AgNO3 - 20%, AgNO3 in NHNO3- 28 3.4 ----- do------25% AgNO3 in NHNOg- 28 9. s -----do------35% AgNO3 in NHNO3------3: 4. do------|31% AgNO3; 3.2% Fe (NO3)3; 11%HNO3-...------. 2,483,440 3. 4 With reference to Table 1 it may be stated that silver nitrate, even though no precipitate is as the acetylene reacts with the silver nitrate So formed. lution, nitric acid is formed. Also nitric acid acts Based on this characteristic of strong silver ni to minimize the precipitation of metallic silver trate Solutions, we were able to design a rather by hydrogen. Commercially we are accordingly 5 excellent analytical method for the direct deter principally interested in acidified silver nitrate mination of even traces of acetykene in gas by di solutions. For this reason nitric acid was added rect Scrubbing of a gas stream with strong silver to the solution in providing the data of Table 1. nitrate Solution, followed by high dilution with The presence of nitric acid in the solution tends water, filtering and weighing of the Ag2C2AgNO3. to decrease the solubility of the silver acetylide Previously no such method was available. compounds in the silver nitrate solution. How When acetylene addition to the previously men ever, the strength of the silver nitrate Solution as tioned strong solution is carried sufficiently far, a it increases tends to compensate the reduction in Silver carbide does precipitate out in accordance solubility caused by the nitric acid. The mother With fixed solubility laws. This precipitate is liquor at the bottom of the table which consists wholly the rhombohedral crystal of Ag2C26AgNO3 of 31% silver nitrate solution, 3.2% of ferric ni shown in Figure 3 of the drawing. The trate solution, and 11% of nitric acid is the pre ferred adsorption solution which is used for ab sorbing acetylene and olefines from a gas contain has a pronounced tendency to form Supersatu ing hydrogen such as coke oven gas or coal gas. : rated solutions in strong silver nitrate solution. It Will be seen that the solubility of the silver acet A clear SuperSaturated Solution may be main ylide in this absorption solution is less than in tained for Several weeks, but upon vigorous shak the 20% or stronger silver nitrate solutions. With ing a copious precipitation of Ag2C26AgNO3 will such an absorption solution, however, the silver precipitate. nitrate will not be reduced to deposit metallic Silver. In Table 2 is shown the form of crystalline silver When the explosive silver acetylide compound acetylides formed with different strengths of sil is formed in very dilute silver nitrate Solution, wer nitrate solutions. As might be expected in the substance, AG2C2AgNO3, appears as minute borderline concentrations two of these crystal needle-like crystals as illustrated in Figure 1. If : forms can exist simultaneously but these areas the silver nitrate concentration of the acetylene are rather narrow. treated solution be about 3–5%, much larger and TABLE 2 longer needies and crosses appear and if the Form of precipitate eacpectancy strength of the solution be still further increased, the small needles disappear leaving only the large , 10 ml. AgNO3 used at 25° C. in all instances needles and crosses as illustrated in Figure 2. Careful chemical analysis has shown, however, CE Type of Solution Results (DeterminedScopically) Micro that both of these classes of crystals have the chemical formula Ag2C2-AgNO3 and both are dan 1.8 15% AgNO3 iN HNO3-... No precipitate. 3.0 -----do------Needles with crosses. gerous devastating explosives. If the concentra 5.0 20% AgNO3 1 NHNO3--- No precipitate. tion of the silver solution be sufficiently increased 7.47 ----- do------A few rhombs. 10.0 ----- do------Rhombs and a few crosses. to 25% or above, these crystals will go into Solu 15 -----do------Mostly crosses but a few tion. If the volume be sufficient, the solution will rhombs. be permanent. Apparently the only Way to obtain 24.9 25% AgNO3 1N HNO3. Rhombs only. the Ag2C2AgNO3 complex from this solution is to redilute the solution or otherwise diminish the In the accompanying drawing are illustrated concentration of silver nitrate as by chemical in Figures 1 and 2 photomicrographs of the silver means. If the volume is insufficient to maintain acetylide compound Ag2C2. AgNO3. The photo a clear solution, a silver acetylide complex Will micrographs of Figures 1 and 2 are 120 diameters be precipitated, but the precipitate will be the while the photomicrograph in Figure 3 is 70 rhombohedral crystals of Ag2C26AgNO3, a Sub diameters. The crystals of Figure 1 are pre stantially non-explosive material as illustrated in cipitated from a one hundredth normal silver Figure 3. nitrate Solution while the crystals of Figure 2 are Likewise, if acetylene or an inert gas contain precipitated from an 8% silver nitrate solution. ing acetylene be passed through a silver nitrate 5 5 It Will be seen that the crystal structure of the solution, a silver carbide precipitate Will be Ag2C2.AgNO3 is very fine needle-like crystals while formed. If the scrubbing solution has a low con the crystal structure of the acetylide centration of silver nitrate, only a Small portion of the acetylene will be removed in any one scrub Ag2C2.6AgNO3 bing stage, as evidenced by the fact that many 60 is large rhombohedral crystals. scrubbing stages may be placed in series and The silver acetylide Ag2C2.6AgNO3 has been Ag2C2AgNO3 will appear in the last stage long be referred to as a safe acetylide compound. This fore the silver nitrate in the first stage has been Compound Will decompose when heated to a seriously depleted. But where solutions of about moderate temperature but the decomposition is 25% silver nitrate or higher concentration are not a violent explosive decomposition such as the employed, no initial precipitation of silver carbide explosion or decomposition of the compound takes place at all. However, our tests show that Ag2C2. AgNO3 when heated to its detonative tem even with coke oven gas carrying only 0.05% perature. The compound Ag2C2.6AgNO3 is in the acetylene and passing at the rate 0.5 cubic feet per form of Comparatively large white rhombohedral hour through a half inch diameter test tube con 70 crystals which, in polarized light, exhibit a high taining about a one inch Seal of 30% silver ni degree of Coloration, but are Water-White in trate, ninety-eight per cent of the acetylene is re transmitted light. If the rhombohedral crystals moved in the first paSS. This is quite an unusual or a strong silver nitrate solution containing the scrubbing efficiency and certainly is evidence of a rhombohedral crystals is diluted with water, the chemical combination of the acetylene with the rhombohedral crystals will be decomposed and 2,483,440 5 6 form the explosive type of silver acetylide We claim: Crystals. 1. A silver acetylide Ag2C2.6AgNO3 crystalliz The rhombohedral crystals may be separated able as white rhombohedral crystals, which are from the solution in which they are precipitated readily soluble in strong silver nitrate Solutions. by decantation or filtration. However, the silver 2. A process of making silver acetylide nitrate solution always contains some Silver Ag2C2.6AgNO3 comprising: absorbing acetylene in acetylide in solution. In order to separate all of an aqueous Solution of silver nitrate containing the silver acetylide from the silver nitrate Solu nitric acid in which the concentration of silver tion, the acetylide compound may be precipitated nitrate during absorption is maintained at by mercuric nitrate to form a mercury acetylide 10 greater than 20% by weight of the solution. silver nitrate compound HgC2.3AgNO3, which may then be separated from the silver nitrate JOSEPH. A. SHAW. solution by decantation or filtration or the ELTON FISHER acetylene may be destroyed by boiling the above mercury precipitate with an excess of mercuric 5 REFERENCES CITED nitrate and nitric acid. The following references are of record in the X-ray diffraction analyses were made of the file of this patent: Ag2C2, AgNO3 and Ag2C2.6AgNO3. The lines on the stable Salt Ag2C2.6AgNO3 diffraction analyses UNITED STATES PATENTS were quite clear and distinct and could be taken 20 Number Name Date with a comparatively short exposure. On the 1875,924 Horsley ------Sept. 6, 1932 other hand, the lines on the X-ray diffraction 2,150,349 Wan Peski et al. ---- Mar. 14, 1939 analyses of the explosive compound Ag2C2. AgNO3 were very faint and, in fact, a very long ex OTHER REFERENCES pOSure of the camera was required to get any 25 Stettbacher I, Zentralblatt Chem. II, 1919, picture. The heat energy of the X-ray camera, pages 126 and 127. apparently acted to decompose the salt while Stettbacher II, Chem. Abstracts, vol. 35 (1941), the exposure was being taken. Many attempts page 3091. were made to get a good exposure but it would Chavastelon, Compte rendu, vol. 124, pages 1364 appear that the Salt would decompose before an 30 and 1365 (1897). analysis showing the lines could be made. (Copies in Patent Office Library.) The preferred form of the invention having been thus described, what is claimed as new is: