1NDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1929
Figure 4-Hydration
of Cured Hide during Soaking a n d Liming
sary before rapid multiplication of bacteria begins; in other words, there is a period of lag. A second period then ensues
379
in which there is a very rapid multiplication of bacteria and which is known as period of logarithmic increase. The first or lag period corresponds to the initial contraction in volume of our system hide-water, the second period, to the increase in volume of the system. With acid solutions stronger than pH 2, bacterial action and, consequently, degenerative changes were so decreased that no increase in volume of the system occurred and as a result curves of the same type as those obtained for fresh steer corium (Figure 2) resulted. Figure 4 shows the result of soaking cured steer hide in water for 24 hours and then placing the hide in saturated lime solution (containing excess solid Ca(OH)*). As has already been noted, in the soak there was an initial contraction with subsequent increase in volume of the system. I n the lime solution a regular contraction of the system resulted, as would be expected, since theoretically all bacterial action should be practically nil. Moreover, in the lime solution the system attained a practical equilibrium in 24 hours. It is very probable that if the soaking period had been made less than 24 hours, the total net contraction of the system or the hydration of the skin should be materially greater. These preliminary results indicate that valuable information can be obtained by this method with respect to the effect of various anions, post mortem changes, and cure upon the hydration of fresh and cured animal skin. The investigation of these factors upon hydration of animal skin is now under way.
Preparation of Potassium Nitrate’ Arnon L. Mehring, Wm. H. Ross, and Albert R. Merz BUREAUOF CHEMISTRY AND SOILS, WASHINGTON, D.
c.
H E u s e of potassium The advantages of potassium nitrate as a fertilizer c o u n t r i e s , c h i e f l y India, nitrate as a fertilizer over other nitrates are discussed and various commer- Ceylon, Mexico, and Egypt. was first suggested by cia1 processes for its manufacture are reviewed. A Its presence there is due to G l a u b e r * in 1656. A few preliminary report is given of a laboratory study Of the the decomposition of organic years later its value was dis- reactions involved in the conversion of potassium chloride matter by nitrifying organcussed by Digby3 in what is to potassium nitrate by treatment with nitric acid or isms in soil containing solusaid to be the earliest record nitrogen peroxide. ble potassium c o m p o u n d s . known of the actual use of Evaporation of soil moisture artificial fertilizers as distinct from decaying organic matter. brings this material to the surface, where it accumulates as Potassium nitrate was also used by Home* in the &st pot an efflorescence. When used as a source of potassium nitrate, experiments ever recorded and by Liebig and by Lawes and this coating is scraped a t frequent intervals from the surface Gilbert in their epoch-making experiments. of the soil and extracted with boiling water. The yield of Many workers have since demonstrated the superior crude potassium nitrate is 2 to 8 per cent of the weight of the properties of potassium nitrate as a fertilizer material. One soil scrapings. of these reports was recently made by Frowein,4 who superDuring the Crimean War the demand for potassium nitrate vised a series of experiments with six standard farm crops for the manufacture of gunpowder became so great that extending over a period of years a t several German agri- artscial saltpeter plantations were created. Garbage, cultural experiment stations, in which the same amounts of animal refuse, and other decaying organic matter were mixed the plant food elements were derived from various materials. with limestone or old plaster, wetted with urine, and allowed I n general, potassium nitrate gave better results than equiva- to ferment in piles protected from the rain. After complete lent amounts of potash and nitrogen derived from other decomposition, which required a year or two in .northern materials. Europe, the piles were mixed with hardwood ashes and lixThe world supply of potassium nitrate was formerly derived iviated. The yield was about 5 kg. of potassium nitrate per from incrustations on the soils around habitations in tropical cubic meter. For many years European Governments perPresented as a part of the Symposium on “Concentrated Fertilizers mitted their subjects to pay taxes with saltpeter and this and Fertilizer Materials” before the Division of Fertilizer Chemistry at the practice was quite general among the peasants. 76th Meeting of the American Chemical Society. Swampscott, Mass., SepMany of the Chilean nitrate deposits contain from 5 to 7 tember 10 to 14, 1928. per cent, with a maximum of 17 per cent, of potassium nitrate. a Russell, “Plant Nutrition and Crop Production,” Berkeley, 1926. Only a few of the officinas have employed methods for cona Digby, “A Discourse Concerning the Vegetation of Plants,” London, centrating the potash, but a considerable tonnage of material 1669 Frowein, Chem -Zlg , 61,341 (1927). containing 20 to 80 per cent potassium nitrate has been made.
T
INDUSTRIAL AND ENGINEERING CHEMISTRY
380
Three methods5 of treatipg the brine prepared from caliche have been used. They, involve fractional crystallization during cooling of the hot' brine to ordinary temperature, evaporation of the brine, and refrigeration, respectively. In the refrigeration method the brine is allowed to cool until it is saturated with potassium nitrate, when it is separated from the crystals of sodium nitrate and further cooled to - 10' C., when a product is obtained containing much less boric acid, magnesium salts, and other impurities than when the other methods are employed. By adding a small quantity of water Table I-Evaporation
Vol. 21, No. 4
limited, although its superior qualit.ies as a fertilizer have long been recognized. This situation is likely to change, however, with the a d o p tion of concentrated fertilizers or if the cost of the organic ammoniates is still further increased. Potassium nitrate has little or no conditioning effect in itself, but the quantity of conditioner required to maintain it in good mechanical condition is much less than for any other nitrate. Its use is therefore very desirable in concentrated mixtures which require nitrate nitrogen as an essential component.
of Solutions of Potassium Chloride with Nitric Acid (Method 1)
~
ORIGINALSOLUTIONS EQUIMOLAR IN KCl
TIYEOF TEMP. DIGESTIONOF SOLN. Min.
c.
Concn. of acid H
%
0.233 0.239 0.239 0.285 0.286
"01
AND
ORIGINALSOLUTIONS CONTAINING 32% EXCESSHNOt
LOSS OF CONSTITUENTS
Nos
I
%1.29 1.76 2.45 12.63 25.46 53.63 67.01 81.50
% None None None 1.24 1.68 5.53 12.15 18.87
To dryness.
LO48 OF CONSTITUENTS
c1
Hz0
%
1.96 7.04 8.78 40.52 48.25 77.52 89.27 100.00
I
i
%
0.311 0.318 0.336 0.365 0.361
I
NOS
%
%
1.09 2.83 5.65 29.23 51.81 71.96 97.89 99.56
None None 0.015 1.96 8.89 15.05 31.90 32.24
Ha0
% 5.52 10.19 20.66 55.91 67.72 83.00 99.80 LOO.00
just before refrigerating, a product containing 60 to 85 per cent potassium nitrate and 98 per cent of total nitrates can be readily made in one operation. The annual production of Chilean nitrate is estimated to contain 120,000 tons of potash.
A study was therefore undertaken in this bureau several years ago as to the possibility of reducing the cost of preparing potassium nitrate by treating potassium chloride with such fixed nitrogen products as nitric acid or nitrogen peroxide.
Commercial Methods of Preparation
Experimental Studies
Much of the potassium nitrate of commerce is now made by the "conversion process," in which sodium nitrate and potassium chloride undergo a double decomposition. This process depends on the wide variation in the solubility of potassium nitrate in hot and cold solutions. In the operation of this process about equal weights of potassium chloride, sodium nitrate, and the mother liquor from a preceding batch are heated to boiling in large vats. The sodium chloride is soluble in this boiling solution to about the same extent as in cold solution and less so than any of the other possible salts present. The boiling solution, containing practically all the potassium as nitrate, is filtered from the solid sodium chloride and allowed to cool, whereupon most of it crystallizes out. These crystals contain 2 or 3 per cent of sodium chloride and are puriiied by recrystallization. The calcium and magnesium salts accumulating in the mother liquor are removed by the addition of sodium carbonate and the mother liquor is used again. Potassium nitrate may also be prepared by treating a solution of calcium nitrate with potassium sulfate. The resulting solution is filtered from the insoluble calcium sulfate formed in the reaction and concentrated to yield a high-grade potassium nitrate. This process was the first to use a synthetic nitrogen product in the preparation of potassium nitrate and a considerable tonnage of potassium nitrate has been produced in Germany in this way. The production of potassium nitrate by any double decomposition method involves an additional treatment of materiah which can be used directly in fertilizers, and its cost is therefore greater than that of equivalent mixtures of the materials from which it is prepared. Potassium nitrate is much less hygroscopic than other fertilizer nitrates, but this property alone does not give it any material advantage for use in low-grade fertilizers owing to the conditioning effect of the high proportion of organic ammoniates and other insoluble materials used in mixtures of this kind. The use of potassium nitrate in fertilizers has, therefore, always been 6
Holstein, J. IND.E N D .
CHEM., 12,
290 (1920).
REACTION OF POTASSIUM CHLORIDE WITH NITRIC ACIDNitric acid is a liquid at ordinary temperatures, having a boiling point of 86' C. under normal pressure. Hydrochloric acid, on the other hand, boils at -83.5' C., and is therefore a gas a t ordinary temperatures. If nitric acid is added to a concentrated solution of potassium chloride, the partial pressure of the hydrochloric acid in solution would therefore be expected to be much greater than that of the nitric acid, and some replacement of the acid radical should take place. This has been found to be the case, but the reaction is complicated by the fact that hydrochloric and nitric acids, in excess of certain limiting concentrations, react on each other to form chlorine and nitrosyl chloride. 3HC1
+
"03
= 2H20
+ NOCl + Cln
A mixture of the ordinary concentrated hydrochloric and nitric acids of the laboratory in the proportion of 3 mols to 1 has an acid hydrogen concentration of about 1 per cent. A mixture of this concentration reacts to evolve chlorine and nitrosyl chloride a t ordinary temperatures. No appreciable reaction takes place, however, if the concentration of the mixture is reduced to one having an acid hydrogen concentration of 0.58 per cent a t ordinary temperatures or to 0.36 per cent a t 100" C. It has been found that the presence of the alkali chlorides or nitrates in an acid mixture of this kind has no appreciable effect on nitrosyl chloride formation. These results show that, in the preparation of potassium nitrate by treatment of potassium chloride with nitric acid, loss of nitrogen as nitrosyl chloride will occur if the concentration of the acid hydrogen exceeds 0.58 per cent on the basis of the acid solution a t 25' C. or 0.36 per cent a t 100" C. A study was accordingly undertaken of the loss of nitrogen when potassium chloride was (1) treated with an equivalent quantity of nitric acid and the solution evaporated to dryness; (2) digested with an equivalent quantity of the acid while the volume of solution was maintained constant; and (3) boiled with an equivalent quantity of the acid under a reflux condenser.
April, 1929
I X D U S T R I A L A N D ENGINEERIXG CHEMISTRY
Method 1. When potassium chloride was treated according to the first of these three procedures with an equivalent amount of 20 per cent nitric acid and the solution evaporated to dryness, no appreciable loss of nitrogen occurred, as shown in Table I, until the concentration approached that at which nitrosyl chloride is formed. The analysis of the residue showed a loss of 19 per cent of nitrogen and 81 per cent of chlorine, and that the recovered product consisted of a mixture containing 85 per cent of potassium nitrate and 15 per cent potassium chloride. I n order to bring about complete volatilization of the chlorine, i t was found necessary to treat the potassium chloride with a 32 per cent excess of nitric acid. The evaporated residue then consisted of pure potassium nitrate with a loss of nitrogen equal to the excess of nitric acid added. The gases evolved in these experiments consist of a mixture of hydrochloric acid, nitric acid, chlorine, nitroeyl chloride, and a relatively large proportion of water vapor. The recovery and separation of a mixture of this kind offers little promise of commercial application. Method 2. I n the second set of experiments potassium chloride was digested with an equivalent quantity of a 15 to 25 per cent nitric acid solution in an open vessel or a t reduced pressure under such conditions that little or no loss of nitrogen occurred as nitrosyl chloride. This was accomplished by continuously replacing the water lost by evaporation or by adding the nitric acid solution a t such a rate that the acid concentration of the solution did not exceed that a t which nitrosyl chloride was formed. The solution was cooled a t the end of the digestion to crystallize out potassium nitrate and the mother liquor used again in the next batch. The volatilized gases consist of a mixture of hydrochloric acid with a smaller proportion of nitric acid and a relatively large proportion of water vapor. The recovery of this nitric acid would seem to offer the same difficulty as in the first of the procedures outlined. A number of German patents6 describe methods for preparing potassium nitrate according to this procedure, but no means are outlined for recovering the volatilized nitric acid. Method 3. I n the third set of experiments solid potassium chloride was digested under a reflux condenser with 40 to 50 per cent nitric acid. The gas evolved under these conditions consists almost entirely of a mixture of chlorine and nitrosyl chloride, provided the reagents used in the digestion are not taken in such a proportion as will give a final concentration of either hydrochloric or nitric acid in excess of its boiling point mixture. REACTIONOF POTASSIUM CHLORIDEWITH NITROGEN PEROXIDE-The process differs from the other two procedures in that the evolved gas, containing very little water vapor, may be easily treated for the recovery of the nitrogen of the nitrosyl chloride by absorbing the gas in concentrated sulfuric acid and subsequently treating with steam to drive off nitrogen peroxide. The process would therefore be particularly applicable in connection with a plant for the absorption of nitrogen peroxide as produced in the oxidation of ammonia. Nitrogen peroxide also reacts with potassium chloride solution with evolution of hydrogen chloride to form a solution of potassium nitrate in strong nitric acid. It was found in a study of this reaction that when a 12 per cent nitrogen peroxide-air mixture is passed over a potassium chloride solution a t room temperature a t such a rate that all the chlorine is evolved as hydrochloric acid, a solution is recovered which contains about 20 per cent of potassium nitrate in 45 per cent nitric acid. The results obtained when this solution is digested under a 6 German Patents 391,011; 392,094; and 393,535; cf. also U.S. Patents 1,036,611and 1,036,833.
38 1 >f
reflux condenser with different proportions of solid potassium chloride are given in Table 11. Table 11-Fractional Distillation of 20 Per Cent Potassium Nitrate and 45 Per Cent Nitric Acid Solution with Varying Proportions of Solid Potassium Chloride ~ _ _ _ _
LOSS OF
MOLECULAR RATIO KCI TO FREEHNOJ
ci
Acid
I 49.02 %
0.50 0.75 1.00 1.25 1.50 2.00
CONSTITUENTS
% 8.01 12.75 15.50 16 49 15 68 15 70
65.39 75.80 79 21 81 66 80.06
Ratio N0::Cl (by wt.)
% 72.34 65.06 56.23 47.03 39 44 31.07
0.49 0.58 0.61 0.62 0.58 0.56
If the loss of nitrogen and of chlorine occurs only as NOCl and C1, the ratio of NO3 to C1 by weight will have a value of 0.583. This value is in close agreement with the experimental values given in the last column of Table 11. A large excess of either nitric acid or potassium chloride leads to a somewhat lower ratio showing a loss of chlorine in excess of that called for by the equation: "0s 3HC1 = NOCl 4-CL 4-2H20 Table I11 gives the results obtained when solid pota.ssium chloride was fractionally distilled with equimolar solutions of nitric acid of varying concentrations. In these experiments the solutions also contained the same relative proportion of potassium nitrate as shown in Table 11.
+
Table 111-Fractional Distillation of Equimolar Solutions of Potass i u m Chloride and Nitric Acid of Varying Concentrations CONCENTRATION O F HNOJTAKEN
LOSS O F
AcidH
% 55 50 45 40 30
% 0.64 0 48
CONSTITUENTS
~
I
I
Ratio NOa:C! (by wt.)
NO3
%
% 16.81 17.03 15.50 14.13 5.26
81.31 78.35 75.80 68.48 22.42
% 58.47 57.84 56.24 50.51 15.90
0.63 0.65 0.61
0.62 0.87
The ratios given in the last column of Table I11 show that the loss of nitrogen in these experiments is somewhat in excess of the theoretical value, but this additional loss of nitrogen decreases as the nitric acid approaches a concentration of 45 per cent. The percentage recovery of potassium nitrate on cooling the residue from a fractionally distilled equimolar solution of 45 per cent HNOs plus 20 per cent KNOS with solid potassium chloride is given in Table IV. The results show that upwards of 90 per cent of the potash in the digested solution may be recovered by crystallization on cooling the solution to 10' C. Table IV-Recovery of Potassium Nitrate o n Cooling the Residue from a Fractionally Distilled Equimolar Solution of 45 Per Cent HNOJ 20 Per Cent KNOs with Solid Potassium Chloride
+
TEMPERATURE O F SO1,UTION
c. 30 25 20 15 10 0
RECOVERY OF KNOI
KCl IN RECOVERED Kh.0~
93
%
84.0 89.3 90.1 91.1 94.0 94.4
None None None 0.07 Trace 0.07
A study of the best means of utilizing the mother liquor recovered in the crystallization of the potassium nitrate is still in progress. The results so far obtained seem to indicate that its acid hydrogen concentration a t ordinary temperatures is sufficiently below that a t which nitrosyl chloride is formed to permit its return to the absorbing system without appre-
INDUSTRIAL AND ENGINEERING CHEMISTRY
382
ciable loss of nitrogen in the evolved gas. The process of preparing potassium nitrate from potassium chloride and nitrogen peroxide thus becomes a cyclic one when operated in connection with a plant for the absorption of nitrogen peroxide. As thus operated the process consists in passing a nitrogen peroxide-air mixture countercurrently over a potassium chloride solution in absorbing towers to form a solution of potassium nitrate in strong nitric acid, digesting the recovered solution under a reflux condenser with solid potassium chloride equivalent to the free nitric acid present,
Vol. 21, No. 4
cooling to crystallize out high-grade potassium nitrate, and returning the mother liquor to the absorbing system for use again in the process. The chlorine and nitrosyl chloride evolved in the digestion with potassium chloride may be separated by passing over concentrated sulfuric acid. The nitrogen of the nitrosyl chloride is thereby absorbed as nitrosyl sulfuric acid and may be recovered as nitrogen peroxide in the usual way for return to the absorbing system. The products of the process are thus potassium nitrate, chlorine, and hydrochloric acid.
The Fertilizer Triangle’ Firman E. Bear THEOHIOSTATEUNIVERSITY, COLUMBUS. OHIO
On January 5 and 6, 1928, the Middle West reprelist. I n 1927, of 185,388tons sentatives of the fertilizer industry and of agronomists ing the list of fertilizer of mixed fertilizer sold, 111,adopted the triangle principle as a means of choosing a analyses that are being 329 tons, or 60 per cent, belist of fertilizer ratios in a program of standardization. offered for sale has engaged longed to the standard list of This principle involves the use of an equilateral trithe attention of the fertilizer analyses. angle, the points of which represent 100 per cent nitroindustry and of agronomists M e a n w h i 1e developments gen, phosphoric acid, and potash, respectively. All for a number of years. The of considerable significance possible ratios of any two or all three of these lie within first general conference called had taken place in the fertithe boundaries of this triangle. to consider this matter took lizer industry. Double superThe problem involved is that of spacing the ratios in place in Chicago, October 19 p h o s p h a t e s containing 45 the triangle in such a manner as to cover the field and 20, 1922. At this conto 50 per cent of available equally well at all points. By drawing a series of nine ference there were present repphosphoric acid were being equally spaced lines parallel to each side of the triangle, offered for sale in quantity: resentatives of the fertilizer the intersecting points of these three series of lines industry and a g r o n o m i s t s Ammonium phosphate conmay be so located that they accomplish the purpose from Ohio, Indiana, Illinois, taining nearly 15 per cent of desired. Such a system of selecting ratios is parammonia and 60 per cent of M i c h i g a n , Wisconsin, and ticularly important in connection with the movement phosphoric acid was available Missouri. A list of fourteen from low to high and to concentrated analyses. Its use for purchase. Synthetic nianalyses was finally adopted. is urged for consideration by those concerned with the trogen materials were being The agronomists agreed to development of the fertilizer industry as a means of produced in large amounts, of c on f i n e their recommendasimplifying the program of standardization and elimiwhich the most concentrated, tions of mixed fertilizers to nating confusion on the part of the consumer. urea, contained 55 per cent of this list. The fertilizer proammonia. Large amounts of ducers agreed to feature these analyses-and to withdraw all others from their offerings as high-percentage potassium salts were available, ;ne of which had a potash content of 60 per cent. soon as it could be accomplished. It was evident that fertilizers which had been classed as The list chosen represented a compromise between the industry and the agronomists. The former, by reason of “high-analysis” were relatively low in analysis as compared established trade in certain analyses, wished to continue to with those which might be produced if the demand for them take advantage of the demand that had been created for them. should develop. Farmers were becoming interested in posThe latter, taking into consideration the matter of economy sible saengs of freight and handling charges that might be to the fertilizer user, desired higher analyses than were being effected in the use of these concentrated analyses. I n 1927, produced in quantity a t that time. However, no particular 1210 tons of 3-18-3 and 1674 tons of 4-244-one and onedifficulty was experienced in reaching an agreement, since half and two times the concentration, respectively, of the both groups recognized that there was no longer any valid standard 2-12-2 analysis-were sold in Ohio. Meanwhile excuse for the production of 1-8-2 and similar low analyses one of the producers of synthetic nitrogen was advertising a series of complete fertilizers called Nitrophoskas, one of that normally contain considerable amounts of filler. Following the Chicago meeting, other regional conferences which analyzed 18-30-15. With the production of concentrated materials came, not were held for the New England, the Atlantic Coast, and the Southeastern states. The lists of analyses chosen a t these only the possibility of producing much higher analyses, but a greater variety of them than before. Anticipating this four conferences are given in Table I. The success of these efforts a t standardization can be seen development, conferences of representatives of the fertilizer from data of fertilizer sales in one of the cooperating states, industry and agronomists were again called for the purpose of which Ohio is chosen as an example. Of 110,585 tons of of considering what modifications of the standard lists of mixed fertilizer sold during the year preceding the conference, analyses were desirable. Early in the discussion of this problem it became evident 1922, 16,630 tons, or 15 per cent, were analyses of the adopted that the best procedure was to reconsider the whole matter 1 Presented before the Division of Fertilizer Chemistry at the 76th on the basis of nutrient ratios. Assuming that B ratio of Meeting of the American Chemical Society, Swampscott, Mass., September ammonia t o phosphoric acid and potash of 1-3-1 was needed 10 to 14, 1928.
HE problem of simplify-
T
