Hygroscopicity of Fertilizer Salts Reciprocal Salt Pairs ALBERT R. MERZ,WILLIAM H. FRY, JOHN 0. HARDESTY, AND J. RICHARD ADAMS Fertilizer and Fixed Nitrogen Investigations, Washington, D. C.
I
N A previous paper (1) a
of a given system can coexist as The vapor pressures of saturated solutions of solid phases in equilibrium with s t u d y w a s m a d e of t h e mixtures of fertilizer salts not having common solution and water vapor. hygroscopicities of various ions have been determined ai 30" C., and calculaAbove this particular temperafertilizer materials and of mixtions made of the relative humidities prevailing tures of these having common ture or transition point, one salt over the solutions. I t has been found that the pair is stable-i. e., capable of ions. The n i t r o g e n f i x a t i o n coexisting in contact with the soproducts-calcium nitrate and hygroscopicity of such mixtures is, in general, lution-and below it the reciproammonium n i t r a t e , as well as greater than that of the most hygroscopic salt cal pair is stable. At the higher urea-were found a m o n g t h e present in the solid phase, which was previously temperatures there are two solumost hygroscopic of fertilizer maobserved to be true in the case of mixiures of bility curves, the solid phases beterials. The fertilter salts with fertilizer salts having common ions. ing the stable salt pair and either two elements available for plant of the salts of the reciprocal pair; food-potassium nitrate, monoA system of expressing hygroscopicities by at the lower temperatures there potassium phosphate, and mononumbers directly proportional to this property is will likewise be two solubility ammonium phosphateproved proposed. c u r v e s , the solid phases here to be the least hygroscopic of being the salts of the reciprocal soluble materials. The hygroscopicity of a mixture was found, in general, to be greater than pair (now the stable pair) and either of the salts of tce salt pair stable a t the higher temperatures. When, therefore, that of its more hygroscopic ingredient. The present paper reports the results of a similar study of the stable salt pair at a given temperature is brought in conmixtures of two fertilizer salts not having a common ion. tact with relatively little water, the question is presented as to Such salts are capable, by double decomposition, of giving a which of the salts of the unstable salt pair forms the third second salt pair, and systems involving such salts and water solid phase as the result of partial double decomposition. This salt is always the one that is less soluble in the saturated are known as reciprocal salt pairs. solution of the stable salt pair, and it is impossible to obIDENTIFICATION OF SOLIDPHASES tain the more soluble salt as the third solid phase by the addiThe same apparatus and procedure for determining vapor tion of water to the stable salt pair alone. The more soluble pressures were employed in this investigation as described in salt must be initially in admixture with the stable salt pair the previous paper (1). The monocalcium phosphate used for it to form the third solid phase. The solution obtained in this work was purified by ether extraction of the chemically on the addition of the water to the stable salt pair is therefore pure salt. All the other salts were purified by recrystalliza- always the one with the highest vapor pressure. If, on the tion. To identify the solid phases present in each case, other hand, the unstable salt pair is brought in contact with a the usual microscopic petrographic methods were used (7). little water, double decomposition takes place and the salts The procedure was much simplified, however, by the fact that of the stable salt pair separate out. Which of the salts of the the number of possible salts in a given sample was limited. unstable salt pair remains as the third solid phase depends on It was consequently seldom necessary to determine all the the relative proportions of the original salts. The comparatively simple relationships stated above apply optical constants of any given salt, since the possible salts differed sufficiently in one or more constants to permit of to those reciprocal salt pairs where no double salts or solid differentiation. Measurements of the optical axial angles solutions are formed, or where solid solutions are formed, were in most cases sufficient, but recourse to the determina- the components of which do not form continuous series of tion of refractive indices was occasionally necessary. Pure solid solutions. Examples of such systems are that of salts were used as checks throughout the work, and with K + N a + C1- NOa- ( 4 ) , in which neither double saltsnor solid only one substance (calcium nitrate) were optical abnormali- solutions appear, and that of K + NH4+ C1- NO- ( 6 ) , in ties noticed, This abnormality consisted of an occasionally which the solid solutions of potassium and ammonium chlooptically positive character instead of the normal negative rides and of potassium and ammonium nitrates that form do not vary continuously in composition from pure salt to pure character. I n Table I are given the results for the reciprocal salt salt. Such systems display two triple salt points. pairs examined. The determinations listed in the first part SYSTEMSOF A SINQLETRIPLESALTPOIXT of the table were made at 30" C. Since calcium chloride I n cases where two of the salts form a continuous series has a transition point a t 30' C. (61,the hexahydrate being in equilibrium with the tetrahydrate at this temperature, the of solid solutions, there will be a t a given temperature only measurements for those systems in which this salt appears one instance of three solid phases being in equilibrium with as one of the solid phases were made a t 25' C. and are given solution instead of two such triple salt points. This point will be one of maximum solubility; i. e., the solution will in the second part of the table. be one of maximum hygroscopicity. An example of such a SYSTEMS OF Two TRIPLESAET POINTS system is that of K+ NH4+ C1-H2PO4- (2). If, for example, Reciprocal salt pairs constitute four-component systems 100 moles of monoammonium phosphate and 100 moles of so that there is only one temperature a t which all four salts potassium chloride are brought in contact with 8.1 moles of 136
I N D U STR I A L A N D E N GI N EER I N G C H E M IST R Y
February, 1933
137
TABLEI. VARIOUSPRESSURES OF SATURATED SOLUTIONS OF RECIPROCAL SALTPAIRS
SYSTEM
SOLIDPHASES REPREBENTINQ:
STABLESALTPAIRS
Stable salt pairs A T 33'
KN03; Ca(HzPO4)z
KP*'Oa Ca(HzPO4)z Hz0
NaNOa: Ca(HzP0c)r
NaNOx; Ca(HzP01)a H a 0
NHdNOa; Ca(HzP04)z
NH4NOs; Ca(HzPO4)a HzO
KNOa; NHcCl
K ( X H t ) N 0 3 : 4 NH4(K) C1
Unstable salt pairs
C.
NaNOs; NHcCl
NaNOa; NH4CI
KNo3; NaCl
KNOa; NaCl
KHzPO4. NH4Cl KHzPO41 NaNOa
( K , Nll4)HzPOa;b NH4(K)C1 KHzPO4; XaNOa
27.95 14.04 21.69 11.60 16.81 8.35 21.60 17.42 16.53 13.45 21.30 19.51 23.18 20.03 19.99 19.03 20.30 15 44 25.16 22.70 22.02 19.61 27.83 23.33 21.10 29.37 27.92 24.38 29.87 Not detd. 29.72 29.18 24.24 9.68
("4, K)HzPO4: K(NH4)NOa NH4HrPO4; NaNOa
K +Ca ++Cl-NOa
-
KCI; Ca(NOs)a.4HzO
NHcCl; Ca(HzP0c)z
NHcCI; Ca(HzP04)rHzO
+
water (less than 0.75 per cent of the total weight) a t 0" C., there will be present a t equilibrium the solution of maximum solubility with composition 0.287 K, 0.713 KH4, 0.913 C1, 0.087 H2PO4, 8.1 H20, and three solid solutions: (1) 99.91 moles of composition 24 per cent KHzPOd, 76 per cent NH4H,P04; (2) 5.92 moles of composition 4.5 per cent KCl, 95.5 per cent KH4C1; and (3) 93.17 moles of composition 81 per cent KC1, 19 per cent NH4Cl. so4--, in which both amThe system K + "4' monium and potassium sulfates and monoammonium and monopotassium phosphates form continuous series of solid solutions, is an extreme case in which there is no triple salt point. There is, however, a point of maximum solubilityi. e., maximum hygroscopicity-at which the two solid solutions, each of definite composition for the given point, are in contact. SYSTEMS OF THREE OR MORETRIPLE SALTPOISTS In a number of systems double salts form. The number of triple salt points may then be three or even more. Such a system is that of I(+ Na' SOa- SOa-- ( 3 ) . The unstable sa16 pair in this system is potassium sulfate and sodium nitrate, fertilizer salts that are frequently mixed. whereas the fertilizer manufacturer never mixes the stable salt pair, sodium sulfate and potassium nitrate. Three saturated solutions may be formed from the unstable salt pair, each dependent upon the relative proportions of the two salts originally present. For example, if the mixture contains 3.84 per cent of water a t 30" C., different molecular proportions of potassium sulfate and sodium nitrate will react to give the solutions and salts on the right of the equations: glaserite 38.2Hz0 = 34.254(KNOa)r 5.122(3KzS04.Nazdarapskite 904) 14.694(2NazSO~*(NaNOa)z*2HzO) 4- 1.175(0.323Kz 0.677Naz 0.104SO4 0.896(NOa)z 4- 7.5OHzO) (1)
5o&so4 + 5O(NaNOa)p
+ +
87.8 44.1 68.1 36.4 52.8 26.2 67.9 54.7 51.9 42.2 66.9 61.3 72.8 62.9 62.8 59.8 63.8 48 5 79.0 71.3 69.2 61.6 87.4 73.3 66.3 92.3 87.7 76.6 93.8
12.2 55.9 31.9 63.6 47.2 73.8 32.1 45.3 48.1 57.8 33.1 38.7 27.2 37.1 37.2 40.2 36 2 51 5 21.0 28.7 30.8 38.4 12.6 26.7 33.7 7.7 12.3 23.4 6.2
9i:4 91.7 76.1 30.4
i:6 8.3 23.9 69.6
A T 25" C., WITH CALCIUM C H L O R I D E A 8 O N E S A L T
KC1; Ca(N03)z
KNOa CaClr1HzO NHiHzPOe CaClrlHzO KCl; Ca(HzP01)z K + C a +CI-HZPOIKC1; Ca(HzPO4)z.HzO KHzPO4 CaClz.?HzO 0 Formulas such as this represent solid solutions t h a t do not form a continuous series from pure salt t o ure salt. b Formulas such as this represent solid solutions t h a t form a continuous series from pure salt to pure a&.
N H +Ca++Cl-HzPO4-
RELATIY E HUMIDITIES OF AIR I N HYQROVAPOR EQUILIBRIUM SCOPICITY PRES SUR^ WITH SOLN. No. Mm. Hg %
+
+
+
++ + + + +
++
Below 7 Below 7 17.6 Below 7 18.6 Below 7
-
'
..
..
7i:9
26: 1
78:3
2i17
..
..
++
80KzS04 ZO(NaN0s)l 38.4Hz0 18.244(KNOa)z 19.500(3K1SO4.NazSO4) 1.629KzSO4 2.126(0.765Kn 0.235Naz 0.174S01 0.826(NOa)a 18.06Hz0) .(2) 20KzS04 80(NaNOa)r 37.9Hz0 = 19.622(KNOa)z 9.976(2NaaS04.(NaNOs)z.2HzO) 49.173(NaNOa)z 1.276(0.296Kz 0.704Naa 0.037SO4 0.963(NOs)r 6.23HzO) (3)
+ +
+
+
++
+
+
In consequence of the formation of darapskite, containing water of crystallization, the free water in the resultant mixtures of Equations 1 and 3 will be but 0.9 and 0.8 per cent, respectively.
IKTERPRETATION OF RESULTS The first column of Table I lists the various systems studied. The second column gives the stable salt pair for each system. The third column gives the solid phases representing these stable salt pairs. I n those systems where more than one pair of salts appear in this column, the first pair for a given system is the one that is actually present when a relatively small quantity of water is added to the stable salt pair. The f i s t salt in column 4 for each system is the salt of the unstable salt pair that is actually present under the same conditions. The subsequent pairs of salts in column 3 and salts in column 4 are formed only when the water is added to a mixture of the salts of the unstable salt pair. The relative proportions of the salts of the unstable salt pair determine whether these subsequently listed salts or the same salts as in the case of the addition of the water to the stable salt pair are those actually in equilibrium with the solution formed. Column 5 gives the vapor pressures of the respective saturated solutions, and column 6 the corresponding relative humidities of the air in equilibrium therewith. Where one of the salts of the unstable salt pair of a given system is a nonfertilizer salt-for example, calcium chloride in all the systems of the second part of Table I-the fer-
138
INDUSTRIAL AND ENGINEERING CHEMISTRY
tilizer manufacturer need be interested only in the highest vapor pressure of the system. Where, however, one of the salts of the stable salt pair is a nonfertiliaer salt-for example, sodium chloride in the system K + N a + C1- NOS--the lowest vapor pressure may determine the hygroscopicity of the mixture, particularly if the salt of the unstable salt pair listed opposite this vapor pressure is used in relatively large quantity in the mixture of the two salts of the unstable salt pair. Comparisons of the values obtained in this study with those reported in the previous paper for single salts (1) will aid in forming an idea of the hygroscopicities of the mixtures. As was observed in the case of mixtures of fertilizer salts containing common ions, it is here also seen that the hygroscopicity of mixtures is, in general, greater than that of the most hygroscopic salt present in the solid phase. Exceptions to this occur in those systems in which calcium sulfate or its double salts are present.
HYGROSCOPICITY NUMBERS It has been the custom to determine the relative hygroscopicities of salts by giving the vapor pressures of their saturated solutions and the relative humidities of the air in equilibrium with the solutions. Since, however. these values vary inversely with the hygroscopicities, a system of ex-
Vol. 25, No. 2
pressing hygroscopicities by numerical values having a direct linear relationship to this property of salts is desirable Such a system is satisfactorily supplied by subtracting the relative humidity corresponding to the vapor pressure from 100. The resulting figure is directly proportional to the hygroscopicity of the salt or salt mixture and may be called the hygroscopicity number. Since hygroscopicities vary with temperature, the temperature for which the hygroscopicity number is given must be stated.
LITERATURE CITED (1) Adams, J. R., and Merz, A. R., ISD. EKG.CHEX., 21, 303-7 (1929). ( 2 ) Askenasy, P., and Nessler, F., Z. anorg. allgem. Chem., 189, 305 (1930). (3) Cornec, E., Krombach, H., and Spack, A., Ann. chim., 13, 525 (1930). (4) Froweid, F.,’ and Muhlendahl, E. Ton, 2. angew. Chem., 39, 1488 (1926). (5) International Critical Tables, Vol. IV, pp. 229, 247, MrGrawHill, 1926. (6) Janecke, E., Z.angem. Chem.,41,916 (1928). (7) Johannsen, A., Manual of Petrographic Methods, 2nd ed., McGraw-Hill, 1918. RECEIVEDSeptember 3, 1932. Presented before the Division of Fertiliser Chemistry a t the 78th Meeting of the American Chemical Society, Minneapolis, hlinn., September 9 to 13, 1929.
Sulfonated Higher Alcohols New D et er gent s D. H. KILLEFFER,50 E. Forty-first St., New York, N. Y.
S
OAP has for so many centuries been the world’s detergent that the threat to its supremacy by the introduction of a new series of compounds possessing much better cleansing power without soap’s inadequacies becomes a matter of moment. From Germany come details of a new method of hydrogenating fatty oils and fatty acids to yield the corresponding alcohols and the preparation from these of sulfuric acid derivatives whose properties closely approach those of the ideal detergent. Already plans are completed and active steps are being taken to begin production of these materials in this country, so that the gap between discovery and utilization on a large scale here has almost been crossed. This development is one of those founded on a need already in existence which had not been satisfied before because an essential step in the operation had not been commercially feasible. As a consequence of this existing demand, commercial growth abroad has been strikingly rapid and may be expected to be even more so in this country once production is started. In essence, the basis for the development is the commercial solution of the problem of reducing fatty acids and esters to corresponding alcohols and the elaboration of these to form sulfuric acid derivatives, marketed as sodium salts. So stated it appears extremely simple, but, m-hen it is realized that the only satisfactory method heretofore known for reducing fats and fatty acids to alcohols has been their reduction with metallic sodium in absolute alcohol solution, the commercial feasibility of that step of the process has appeared decidedly remote. The problem of commercial reduction has now been solved and production has been carried out on a large scale by a fundamental modification of the direct hydrogenation process.
COMPARISOX OF OLD AND KEW METHODS OF HYDROGENATION To understand the new method it will be well to contrast i t with the ordinary hydrogenation procedure conducted to saturate unsaturated compounds and to harden liquid fats. Essentially this process consists in suspending a finely divided nickel catalyst in hot oil and passing hydrogen into it a t a relatively low pressure. In practice the temperature may be as high as 200’ C. and the hydrogen pressure as high as 15 atmospheres, although it is usual to operate as low as 180’ C. and 3 atmospheres. Under such conditions the liquid fatty oil (glyceride) is changed only with respect to its double bonds, which are broken and saturated by the direct addition of hydrogen to the molecule. KO change in any other part of the molecule occurs under such conditions, and the resulting saturated (or partly saturated) fat possesses a higher melting point than the original oil. This procedure has been practiced on a large commercial scale in this country for many years and is well known. On the other hand, higher pressures and temperatures permit the hydrogen to react with the -COOH group in the fatty acid molecule and to reduce it to an alcohol group (-CH20H) or to a hydrocarbon group (--CHs), depending on the points a t which these variables are controlled. The method was developed and applied by Schrauth of the Deutsche Hydrierwerke A.-G., who applied for patents covering his invention in 1928. Kormann, of The H. Th. Bohme A.-G. of Chemnitz, Germany, developed a similar process a t about the same time. Two Americans have carried out similar experiments (presumably a t a later date) and reached similar results but without the plant-scale reduction t o practice which followed Schrauth’s discovery almost a t once.
