S
UPERPHOSPHATE and double (triple) superphosphate are examples of fertilizer materials which contain essentially the same components but in different proportions. The first, with a plant food content of 16 to 20 per cent, is classed as an ordinary or low-analysis material, while the second, with a plant food content of 40 to 48 per cent, is a concentrated or high-analysis product. The use of double superphosphate thus affords a means of preparing a series of high-analysis fertilizers that have the same plant food elements in the same proportion and combinations as in the ordinary mixtures made from superphosphate (4). One of the recent develonments in the preparation of superphosphate mixtures is that of ammoniation with aqua or anhydrous ammonia, or with ammonia liquor containing a material such as urea or sodium nitrate in solution. The use of free ammonia instead of animonium salts in the preparation of fertilizer mixtures may cause marked changes in the chemical, physical, and physiological properties of the mixture. These changes, on the whole, are recognized to be favorable. The use of free ammonia in the preparation of fertilizer mixtures has therefore become general and is likely to increase with increase in the consumption of fertilizers. If high-analysis mixtures are to be prepared of similar composition and properties to those now on the market, it will become necessary to extend the process of ammoniation to the treatment of double superphosphate and of mixtures in which it is contained. The present paper gives results obtained in a study of the reactions involved in the ammoniation of double superphosphate and of its principal component, monocalcium phosphate. A study was also made of the ammoniation of dicalcium phosphate since this compound is formed in the process of ammoniating both monocalcium phosphate and double superphosphate.
Ammoniation
of Double Superphosphate A study is made of the reactions involved in the ammoniation of double superphosphate and of its principal component. monocalcium phosphate. IIonocalcium phosphate monohydrate will absorb a masimum of 12.7 per cent ammonia at 25" C., and of 16.2 per cent when treated at 100' C. with ammonia under pressure in a closed chamber. The products of the reaction at 25" C. up to a maximum absorption of 6.8 per cent ammonia are dicalcium phosphate and monoammonium phosphate. Further treatment with ammonia will change the monoammonium phosphate into diammonium phosphate. Dicalcium phosphate dihydrate will not undergo ammoniation at temperatures much below 40" C. At higher temperatures it reacts slow-ly with ammonia to form tricalcium phosphate and diammonium phosphate. Ammoniation of double superphosphate
Materials and Equipment
In the study of the ammoniation of double superphosphate, use was made of the apparatus represented in perspective in Figure 1and diagrammatically in Figure 2 : It comprises a tank for ammonia, a cylindrical bomb containing the sample to be ammoniated, and a buret for measuring any desired volume of ammonia into the cylindrical vessel. The stirrer in the ammonia tank shown in Figure 1 was for use only in subsequent work and was therefore not represented in Figure 2.
A safety valve adjusted to 150 pounds per square inch (10.5 kg. per sq. cm.) pressure was joined in the delivery tube connecting the buret with the bomb to guard against excessive pressures in the apparatus while working at temperatures above normal. The bomb was provided with a removable gas-tight top and a stirrer for agitating the sample as it was being ammoniated. The temperature at which the sample was ammoniated was controlled by surrounding the bomb with a suitable cooling or heating bath. Temperatures above normal were maintained by means of an electrical heater supported in the bath.
The analyses of the materials used in this work are given in Table I. The monocalcium phosphate was prepared by recrystallization of the c. P. product, followed by extraction with ether to remove free phosphoric acid (5). The dicalcium phosphate was Kahlbaum's standard chemical for analysis. The double superphosphate was a commercial product two years old prepared from Florida pebble phosphate. The free acids other than phosphoric in the double superphosphate used in this work amounted to less than 0.02 per cent. It follows therefore that the monocalcium phosphate in this sample is in equilibrium with a solution phase having a concentration of 60.8 per cent of phosphoric acid. According to Bassett ( I ) , dicalcium phosphate cannot exist in a system of this kind, and this finding has been confirmed by experiments in this laboratory ( 5 ) . From the data given in
FIGURE 1. AMMOSIATION APPARATUS 5 62
the materials, it was found impractical to prevent some localized variations in temperature during the initial treatment with ammonia. The tests at 100' C. were made by treating each sample with an excess of ammonia in the usual way and cooling before releasing the pressure. In order to determine the distribution of the absorbed ammonia between its mono- and di-compounds, portions of each material that had been ammoniated at the different temperatures were also subsequently heated at 110" C. for 24 hours to change any diammonium phosphate present into monoammonium phosphate. The results are given in Table 11. The first series of tests is designated the ''A series," and that in which the samples were ammoniated and subsequently heated to 110' C. is designated the "B series."
LAWRER-CE M. WHITE, JOHN 0. HARDESTY, AND WILLIAhI H. ROSS Fertilizer Inrestigations, Bureau of Chemistry a n d Soils, Washington, D. C.
Table I1 shows that the rate of absorption of ammonia at 0" and 30' is less than a t 100" C. This is particularly true in the case of dicalcium phosphate which undergoes little or no ammoniation a t temperatures of 30" C. or lower. The data given in Table I1 show further that the monoand dicalcium phosphate samples that were ammoniated at 100" C. lost half their ammonia content when heated atf 110' C. for 24 hours. This indicates that the ammoniation of the samples had proceeded to the formation of diammonium phosphate. When the monocalcium phosphate and double superphosphate samples were treated with ammonia at 0" and 30" C., however, the loss of ammonia on heating to 110" C. was considerably less than half of the total absorbed during ammoniation. This may be explained on the assumption that the monocalcium phosphate in the sampLe was only partially ammoniated under the conditions of the test and that the ammonia set free from any diammoniurn phosphate present on heating the mixture to 110" C. reacted with the unchanged monocalcium phosphate to form dicalcium phosphate and monoammonium phosphate.
differs from that of monocalcium phosphate only in that the calcium sulfate present will react with a portion of the dicalcium phosphate present to form tricalcium phosphate and ammonium sulfate when the absorption of ammonia is in excess of 6.1 per cent. The heat developed on treating double superphosphate with sufficient ammonia to give an 8 per cent product is sufficient to raise the temperature of the mass to 100' C. and vaporize about 50 per cent of the free and combined moisture, or to raise to about 100' C. a fertilizer mixture of average composition in which double superphosphate is substituted for ordinary superphosphate. Rapid cooling of such a mixture if accomplished by agitation will give a more or less granular product and prevent loss of ammonia by decomposition of any urea or diammonium phosphate present.
Ammoniation of Dicalcium Phosphate The extent to which dicalcium phosphate undergoes ammoniation was determined by treating the anhydrous and hydrated forms of the compound a t different temperatures with an excess of ammonia in the closed vessel represented in Figure 2. The ammonia was added very slowly over a period of 3 h o u r s i n o r d e r t o avoid any marked change in the temperature of the mass as a result of the heat d e v e l o p e d in the reaction.
Table I, the principal components on the dry basis of the double superphosphate used in this study may be represented as follows (in per cent) ~
Monocalcium phosphate monohydrate, C~(HZPO~)Z.HIO Free phosphoric acid, HaPo, Iron hosphate (total iron expressed as
76.8 5.4
Aluminum phosphate (total aluminum expressed as hlPO4) Calcium sulfate, CaSOh
2.9 3.2
F&Od
3.0
Effect of Temperature on Ammoniatioii In studying the reactions involved in the ammoniation of double superphosphate and of monoand dicalcium phosphates, tests were first made of the effect of temperature on ammonia absorption by treating samples of the materials listed in Table I at temperatures of O", 25', and 100" C. with an excess of anhydrous ammonia under its normal pressure at room temperature. Each of the samples used in the tests was adjusted to an initial moisture content of 5 per cent. Loss of moisture during ammoniation was prevented by the closed cylindrical vessel in which the sample was contained. The ammonia was added very slowly over a period of 2 hours in order to prevent any marked increase in the temperature of the reacting mass due to the heat developed in the reaction. Each of the materials was st'irred c o n t i n u o u s l y t h r o u g h o u t the test, but, owing to the low h e a t c o n d u c t i v i t y of
- - -
-
lgl
,SAFETY
VALVE
VERY T U B E
-
ONIA VALVES TEMPERATURE CONTROL B A T H
AMMONIA
TANK
ELECTRIC HEATE
FIGURE2. DIAGRAM OF AMMONIATION APPARATUS 563
INDUSTRIAL AND ENGINEERING CHEMISTRY
564
VOL. 27, KO. 5
a t 110" C., and the results were expressed in terms of the original sample. P203 It was found that no loss of ammonia took MoisFree Water?uI aterial ture Hap01 sol. Total CaO FezOa .boa SOa F place on heating these samples until all Bhe monoMonocalcium phoscalcium phosphate had been changed into di56.34 22.23 Kone None None None phate Kone Nonea 56.34 c a l c i u m p h o s p h a t e . T h a t t h e ammonia Dicalcium phosNone . . . 41.30 32.52 Kone None None None phate 0.03 evolved on heating highly ammoniated Double superphosphate 3.34 5.19 42.24 48.61 17.76 1.6 1.2 1.79 1.77 samples does not react with any dicalcium phos" p H of 0 . 0 1 Msolution = 4.5. Dhate present mas shown b y m a i n t a i n i n - g a n air-drv, eauimolecular m i x t u r e of d i c a l c i u m phospiateand diammonium phosphate a t 110" C. for 48 hours. The ammonia in the residue amounted to half The curves represented in Figure 3 show the ammonia of the total initially present, showing that no fixation of the absorbed in 3 hours at different temperatures by the hydrated evolved ammonia occurred by ammoniation of the dicalcium dicalcium phosphate (I) in the form of a slurry, and (2) with a phosphate. moisture content of 5 per cent. The curles show that diIf the percentage of calcium and phosphoric acid in the calcium phosphate with a moisture content of 5 per cent beoriginal sample, the calcium and ammonia in the air-dried gins to ahsorb ammonia at a minimum temperature of about sample after ammoniation, and the ammonia lost on heating 40" C. and that the absorption of ammonia begins a t about are known, it is possible to calculate on the dry basis the per20" C. when the phosphate is treated in the form of a slurry. centages of ammonia absorbed and of the mono- and diThe product obtained in either case loses one-half of its amammonium phosphates formed in each of the ammoniated monia when heated to 110" C. for 24 hours, and the amproducts. I n the same may the phosphoric oxide combined moniation is accompanied by a n increase in both water-soluble as mono- and diammonium phosphate subtracted from the total in the sample gives the quantity combined as calcium TABLE 11. AMMONIAABSORBED BY PRIMARY AND SECOSDARY phosphate. From the ratio of the calcium to the phosphoric CALCIUM PHOSPHATES AT DIFFERENT TEMPERATURES oxide with which it is combined, the forms of the calcium Per Cent Ammonia Absorbed on Dry Basia -0' C . 7 -30" C . 7 -100' C.phosphates in the ammoniated mixture may be readily calcuA B A B A B lated by simultaneous equations. Material series series series series series series TABLEI. PERCENTAGE AXALYSIS OF PHOSPHATE MATERIALS 7
Monocalcium phosphate Dicalcium phosphate Double superphosphate
7.76 6 . 7 0 None None 11.16 6 . 5 5
-
10.38 6.67 0 . 0 6 0.02 12.79 6 . 8 1
15.83 6.15 13.37
7.90 2.97 7.04
and citrate-insoluble phosphoric acid. This shows that the treatment with ammonia changes dicalcium phosphate into tricalcium phosphate and diammonium phosphate: 3CaHP04.2H20
+ 2NH8 = Ca8(P0& + (NH4)zHPOd + 6H20
The total ammonia absorbed if the reaction goes to completion should amount to 6.2 per cent on the basis of the original dicalcium phosphate. The maximum found within the period of the tests was 5.4 per cent. That the reaction does not go to completion under the conditions of the tests is to be expected from the well-known action of precipitated tricalcium phosphate in forming a protectiye coating around the dicalcium phosphate particles. Thus Ross, Jacob, and Beeson (3) have shown that the reaction between three moles of lime and two moles of phosphoric acid goes to completion only when the solution in which the reacting materials are suspended is evaporated to dryness and the residue is ignited to a red heat. Anhydrous dicalcium phosphate in the absence of moisture does not absorb ammonia under any of the conditions described in these tests.
Ammoniation of Monocalcium Phosphate I n making a quantitative determination of the products formed in the ammoniation of monocalcium phosphate, varying percentages of ammonia were added to weighed portions of the material in a closed chamber a t 25' and a t 100" C. The samples ammoniated a t 100" C. were cooled in an atmosphere of ammonia. The moisture in each sample was adjusted before treatment to a uniform content of 5 per cent. The ammoniated products were then placed in storage for one month, allowed to air-dry, and passed through a 40-mesh screen. Weighed samples prepared in this way were then analyzed for calcium, total ammonia, and ammonia lost on heating
TEMPEMURE
OF AMUONIATION,~~
FIGURE3. AMMONIATION OF DICALCIUM PHOSPHATE DIHYDRATE The results obtained in this way on treating monocalcium phosphate monohydrate with varying quantities of ammonia at 25" and at 100" C. are given in Table 111. The data show that the ammoniation of monocalcium phosphate at 25" C. proceeds in two steps only. I n the first step the monocalcium phosphate is changed by reaction with the ammonia into dicalcium phosphate and monoammonium phosphate. I n the second step the monoammonium phosphate is changed into diammonium phosphate. Little or no reaction takes place under these conditions between the ammonia and the di-
COMPOSITIOS o s DRYBASISOF PRODUCTS TABLE111. PERCENTAGE OBTAINED O S L4MMONIATINGMONOCALCIUM PHOsPHaTE IN A CLOSEDVESSEL Loss of NHs on Sample NHa No. Absorbed H%%:t 85
86 87 88 90
1.89 3.83 6.55 8.38 11.08
Kone None 0.07 1.85 4.62
93 94 95 96 97 91 92
2.05 4.38 6.54 8.73 11.21 13.78 15.84
None Sone None 2.29 4.86 6.79 7.92
-Composition of Ammoniate:d Product Ca(H~P04)z.CaHPOr C a a ( P 0 h NHiHzPOi (NHd2HPOa Hz0 , Ammoniating Temperature 250 c. 72.18 None 15.08 Xone 12.75 None 30.64 43.47 None 25.90 None 51.83 4.33 0.54 43.30 52.24 1.80 None 14.30 31.66 0.05 51.63 None 35.82 12.50 hnimoniating Temperature, 1000 C . 16.38 None 69.77 None 13.85 35.06 None 35.32 Sone 29.62 52.33 None 3.45 None 44.22 51.51 None 2 . 6 7 17.77 28.05 50.80 None 1.43 37.65 10.13 32.23 13.60 None 52.64 1.54 32.80 5.69 61.45 &-one None
MAY, 1935
INDUSTRIAL AND ENGIKEERING CHEMISTRY
calcium phosphate formed in the first step, and no appreciable increase in citrate-insoluble Pz06 takes place. Although ammonia has little effect on dicalcium phosphate a t 25" C., i t reacts with it at 100" in an atmosphere of ammonia, as already explained, to form tricalcium phosphate and diammonium phosphate, The ammoniation of monocalcium phosphate is therefore accompanied by two types of reactions a t 25" C. and by the same two reactions and a third reaction when the temperature of the material is above the minimum required to ammoniate dicalcium phosphate, and the ammonia is supplied at a pressure in excess of the decomposition pressure of diammonium phosphate a t the prevailing temperature. These three types of reactions may be represented as follows: Ca(HzP04)2.Hz0 NH3 = CaHP04 NH4HgPO4 H t 0 NH4HzPO4 NH3 = (NH4)2HPOd 3CaHP04 f 2NH3 = Cal(PO4)t (NH4)zHPOd
+ +
+
100
\I
90 80
1
j
'
\~ 1
I
, \ ,
+
+
The curves in Figure 4 represent graphically, on the basis of these equations, the theoretical variation in composition of the products obtained when monocalcium phosphate is treated with varying percentages of ammonia at 25" C., and in Figure 5 the corresponding variation in the composition of the products when the same material is ammoniated a t 100" C. in a closed chamber. These curves indicate that the reactions taking place in the ammoniation of pure monocalciuni phosphate are the same at 25" and 100" C. u p to a maxinium absorption of 12.7 per cent of ammonia; that monocalcium phosphate is completely changed into dicalcium phosphate when the ammonia absorbed amounts to 6.8 per cent; that dicalcium phosphate changes into tricalcium phosphate
565
1
PER CENT AMMONIA
FIGURE 4. COMPOSITION OF PRODUCTS OBTAINED ON AMMONIATINGMONOCALCI~M PHOSPHATE AT 25" C. IN A CLOSEDVESSEL
Ammoniation of Double Superphosphate
Double superphosphate differs from pure monocalcium phosphate in that it contains small amounts of free phosphoric acid, calcium sulfate, iron and aluminum phosphates, and other impurities. When ammonia is added to a material of this kind, it first reacts to neutralize the free acid with formation of monoammonium phosphate and to convert the monocalcium phosphate into dicalcium phosphate. Keenen ( 2 ) has shown that calcium sulfate also enters into the reaction with further addition of ammonia to giye di- or tricalcium phosphate and ammonium sulfate. The different . . steps in the absorption of ammonia by double TABLE 11'. PERCENTAGE COMPOSITION ON DRY BASIS OF PRODUCTS OBsuperphosphate a t a temperature above that a t TAISED O S .4YI\IOSIATING DOUBLE SUPERPHOSPHATE .4T 100" c. which dicalcium phosphate will undergo aniIS A CLOSEDVESSEL moniation may then be represented as follo~v~: Losu o f NHa on Sample NH3 Heat@%, No. Absorbed a t 110 25 1.44 None 22 4.82 None 26 6.02 None 5 6.44 0.09 124 8.66 2.01 31 11.31 4.88 99 12.99 6.14 100 13.25 6.27 102 13.65 6.49 101 13.78 6.59
--Composition NE& -,: ("4):HPOI None 9 75 32 54 Sone Xone 40.68 39.64 0.70 26.12 15.61 5.38 37.89 None 47.62 None 48.63 None 50.38 None 51.10
of Ammoniated ProductC a ( H ~ P 0 4 )-z CaHP04 Ca3(P04)2 3.99 Sone 6'9.06 30.99 Sone 13.79 40.61 None 1.14 Sone 40.69 1.47 34.97 6.18 None 34.49 5,57 None 20.67 15.60 None 17.01 18.22 None 10.62 22.88 Sone 8.15 24.72 None
________
f KHS = Tu"1H,PO4 Ca(HZPOa)2,H2O S H 3 = CaHP04 NHiHzPOi HZO 2CaHPOi CaSOI f 2XH3 = Cas(P04h (XH4),S04 NH,H,POI XH3 = (NHI)?HPOd 3CaHPOa 2NH3 = Ca,(PO& (?;HI)zHP04
&POI
+
+ + +
+
+-
+
+
The curves in Figure 7 show on the basis of these equations the theoretical variation in the composition of the products o b t a i n e d w h e n double superphosphate is treated with varying percentages of ammonia a t 100" C. in a closed vessel. I n determining the composition of the products from the analytical data, the same procedure was used as that de-
and diammonium phosphate when treated a t 100" C. with more than 12.7 per cent of ammonia in a closed chamber; and that the percentages of ammonia in the products obtained when monocalciuni Dhowhate is ammoniated to the maximum a t 2 5 " a n d 100" C. a;e 12:7and 16.2 per cent, respectively. The points shown in Figures 4 and 5 indicate the 100 composition of the products a t different steps of the am90 moniation as actually found by analysis. The close proximity of the points to the curves shows that the 80 analytical results are in good agreement with the theo70 retical values. Figure 6 shows the theoretical variations in coinposi3Ition of the products obtained when monocalcium phos=2 50 phate is treated with varying percentages of ammonia $ 40 at 100" C. in a closed chamber and then cooled out of r 3 30 contact with ammonia a t a sufficiently slow rate to bring u about the decomposition of the diarnmonium phosphate g 20 present. The maximuin quantity of ammonia in the IO products obtained under these conditions is 8.8 per cent. The extent to which monocalcium phosphate will retain I 2 3 4 5 6 7 8 9 IO II 12 13 14 15 16 ammonia a t 100" C. under these conditions is thus only PER CENT AMMONIA about two-thirds as great as a t ordinary temperatures, FIGURE 5. COMPOSITIOS OF PRODUCTS OBTAINEDON AMMOXIATand the formation of tricalcium phosphate ismuch greater. ING MONOCALCICM PHOSPHATE AT 100" C. IN A CLOSEDVESSEL,
566
INDUSTRIAL AND ENGINEERING CHEMISTRY
scribed in connection with the ammoniation of monocalcium phosphate. All samples were adjusted to a free moisture content of 5 per cent before animoniating- and then allowed to stand for one month b e f o r e being analyzed. T h e comp o s i t i o n of t h e ammoniated s a m ples with respect to the components which undergo change on ammoniation was determined by analysis and calculation and expressed on a dry basis in a s i m i l a r w a y t o t h a t de1 2 3 4 5 6 7 8 9 scribedin connection PER CENT AMMONIA with the ammoniaFIGURE6. COMPOSITIONOF PROD- tion of monocalcium UCTS OBTAINED ON AMMONIATING p h o s p h a t e . In MONOCALCIUM PHOSPHATE AT 100" C. making the calcuIN A CLOSED VESSEL WITH SUBSElations, it was asQUENT HEATING AT 100' C. I N AN OPEN VESSEL sumed, on the basis of Keenen's investigations ( 2 ) >that the calcium sulfate in double superphosphate remains unchanged until all the nionocalcium phosphate is converted into dicalcium phosphate, and that any further addition of ammonia reacts to change the calcium sulfate into tricalcium phosphate and ammonium sulfate. The results obtained in this way for the composition of the ammoniated double superphosphate samples are given in Table IV and are represented by the points shown in Figure 7. The close proximity of the points to the theoretical curves throughout their entire range supports the conclusions that the different steps involved in the ammoniation of double superphosphate are as indicated by the equations given for this series of reactions. The curves in Figure 7 show that the monocalcium phosphate in the type of double superphosphate used in this work is completely changed into dicalcium phosphate when the ammonia absorbed amounts to 6.1 per cent; that a further addition of ammonia leads to the formation of a small quantity of tricalcium phosphate by reaction with the calcium sulfate and a portion of the dicalcium phosphate present; that no further increase in tricalcium phosphate takes place until the ammonia absorbed is in excess of 12 per cent; and that the maximum quantity of ammonia that the material is theoretically capable of absorbing when ammoniated a t 100' C. in a closed chamber is 14.4 per cent. The maximum actually found by repeated treatments with ammonia is 13.8 per cent. However, if the material is maintained during the treatment with ammonia a t a temperature below that a t which dicalcium phosphate undergoes ammoniation, no tricalcium phosphate will be formed other than that due to the calcium sulfate present, and the ammonia in the product representing maximum ammoniation under these conditions will be in the neighborhood of 12 per cent. It was also found that little or no tricalcium phosphate is formed, in addition to that resulting from the calcium sulfate present, when double superphosphate is treated with ammonia in an open or partially closed vessel. The temperature to which the mass is raised by the heat developed in the reaction quickly reduces the partial pressure of unabsorbed ammonia below the minimum required to ammoniate the dicalcium phosphate present, and conversion of the latter to tricalcium phosphate is thereby prevented. Table V shows the available and citrate-insoluble phos-
VOL. 27, NO. 5
phoric acid (P20s) actually found in samples of double superphosphate when treated in a rotating drum with the quantit,ies of ammonia indicated. The values found for citrate-insoluble phosphoric acid are in every case considerably below that which would correspond to the tricalcium phosphate present. This is to be expected from the work of Ross, Jacob, and Beeson (3)who showed that a considerable portion of the phosphoric acid in precipitated tricalcium phosphate is soluble in neutral ammonium citrate solution. TABLE \'. PERCEKTAGE AVAILliBLE AND CITRATE-ISSOLUBLE PHOSPHORIC ACID IN AIR-DRIED PRODUCTS OBTAISED O S AMMONIATING DOUBLE SUPERPHOSPHATE IS A ROTATIKG DRVM No. 12 216 217 218 219 220 221
--
NHa
Sample
Absorbed None 2.23 4.06 6.27 7.48 9.93 12.38
-
Total 48.61 48.61 47.81 47.51 47.46 45.98 44.26
Phosphoric Acid (PpOr) WaterCitrateCitratesol. sol. insol. 42.24 6.30 0.07 15.05 0.22 33.34 33.27 14.31 0.28 28.94 17.93 0 64 28.36 18.23 0.87 27.51 17.27 1.20 27.63 14.98 1.65
While it is assumed for the purpose of this paper t'hat tricalcium phosphate can be formed and exists under the given experimental conditions, there is no direct experimental proof that a more basic phosphate may not also be formed. The rate of absorption of ammonia by double superphosphate is similar to that by straight superphosphate. When ammoniated as in ordinary commercial practice, both will absorb upwards of 70 per cent of the maximum that they are capable of absorbing within a period of about 2 minutes. Maximum absorption was obtained only by prolonged or 00
5 + Z 2
8
70 60 50 40
0
5 a
30 20 10 I
2
3
4
5
6
7
8
9 1 0 1 1 PER CENT AMMONIA
1
2
1
3
1
4
FIGURE 7. Cowosrno~OF PRODUCTS OBTAINEDON AMMONIATING DOUBLESUPERPHOSPHATE AT 100" C. IN A CLOSEDVESSEL repeated treatment with ammonia a t a temperature and pressure above that a t which dicalcium phosphate undergoes ammoniation,
Heat of Reaction The heat developed in the ammoniation of double superphosphate decreases somewhat with the degree of ammoniation but approximates 840 calories per gram of ammonia in 100 grams of the ammoniated product. The specific heat of a material of this kind in a dry state was found to be 0.228. It follows therefore that the heat evolved in preparing an 8 per cent product from a sample containing, e. g., 10 per cent of moisture will raise the temperature of the mass from 20" to 100' C., and vaporize about 50 per cent of the free moisture and that originally combined in the monocalcium phosphate in the sample. This evolution of heat is sufficient to granulate the material, and a granular product was always obtained when provision was made to agitate the mass in the
MAY, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
process of cooling. Rapid cooling, as by passing the material countercurrent to a stream of air in a rotary drier, will also be advisable in order to prevent loss of ammonia by decomposition of the diammonium phosphate present or of the urea when use is made of urea-ammonia liquor. The substitution of double superphosphate for ordinary superphosphate in a fertilizer mixture of average rornposition mill increase its plant food content about 50 per cent. Thus a 8-10-4 mixture containing 1100 pounds (500 kg.) of 18 per r m t superphosphate per ton (0.907 metric ton) d l become a 4..5-15-G mixture by replacing the superphosphate with an equivalent quantity (440 pounds, or 200 kg.) of a 45 per cent double superphosphate. If a mixture of this kind is assumed to contain G per cent of moisture, then the heat developed on adding 35.2 pounds (16 kg.) of ammonia (S per cent of the double superphosphate) will raise the temperature of the mixture from 20" to about 100" C. Thiq temperature i, likewise
567
sufficient to cause decomposition of urea or dianimonium phosphate unless provision is made to dissipate the heat within a reasonable time after ammoniation. 9rapid dissipation of the heat if accoinpaiiied by agitation of the inass, as in a rotary drier, offers the further advantage that it will bring about a partial granulation of the entire mass, thereby reducing the tendency of the mixture to segregate and greatly improving it,udrillability.
Literature Cited i l l Bassett, 2. anory. Cliem., 5 9 , l (1908). ( 2 ) Keenen, IND. ENG.CHEJI.,22, 1378 (1930). (3) Ross, Jacob, and Beeson, J . Assoc. Oficial d g r . Cherfc., 15, 2 2 i (1932). (4)Ross and hlehring, IXD. EKG.GHEJI.,Sews Ed., 1 2 , 4 3 0 (1934). ( 5 ) Ross, Mere, and Beeson, J . Assoc. Oficinl.4gr. C'he?n., 18 (May 15, 1935).
RECEIVED February 5 , 1935.
Paraffin Wax Tensile Strength and Density at Various Temperatures W.F. SETER AND KURA\IITSU IUOUYE, Cni+ersity of British Columbia, Vancoutrr, Canada Data on the clen5itj 01 d d A R A FF I S The tensile or breaking strength of comparaffin wax are rathei meager. wax is cornrllercial p a r a ~ l n , ~ was a ~ investigated at monly reThe density appears to depend temperatures betiteen -10' and 30" C. It 170tll upon the meltingpointalld garded a$ a solid. It possesses \arks considerabl? with the temperature$ the m y in nhich the wax has h t h a cryitalline c t r u c t u r e reaching a inaxinium \ alue of 32 kg. per been prepared. Thus according and the property of resisting to Carpenter (3),who measured deformation when wbjected to sq. cnl. at :&o11t 3" C. The density \+-as the densities of paraffin a t varihhearing stresaec. There are, also nleasured o,er the silme temperature our temperatures, some paraffin howerer, two classes of solids. the interval. There appeared to be no direct may contain as much a' 20 per ordinary crystalline type and linear relationshiPr between the two Wancent b y volume of entraimed air. plastic solids which are really Ilorri. and Adkinq (i). deterviscous liquids. According to tities %neasured. niined the density over a range of Bingham ( I ) , "if a body is contemperature froin 15.5O to 54.4' C., but in view of the specific tinuously deformed by a very small shearing stress, it is a nature of this property their results mere not directly appliliquid; whereas if the deformation stops increasing after a time, cable to the present nriters' tensile measurements; it was the substance is a solid." Thus, as Clerk Maxwell has therefore deemed expedient to ineasiire the densities of the pointed out, sealing wax, although much harder than paraffin particular samples used throughout the investigation. wax, must be classed as a liquidwhile thelatter. because of the fact that increase of deformation stops after a time vhen it iq subjected to a shearing stress, can be classed as a true solid. Tensile Strength It will be shown later that paraffin wax can fulfill both condiFor the determination of tensile strength of paraffin wax tions, depending upon the temperature. The critical temperathe apparatus shonn in Figure 1 was constructed ture for ordinary commercial wax, with a melting point of 33 ', was found to be about 30" C.; above this temperature it beIt consisted of a quadripod, a stirrer, a balance, a holdei for the haved like a liquid and below like a solid. Thus when the specimen, a Denar flask, and a thermometer. The quadripod, temperature lies above this critical point, paraffin wax cannot made of t n o brass plates and foul glass rods, nas rigidlj attached he said to possess a breaking or tensile strength. to a framenork. The balance was placed on heavy, wellbraced table of auch a height that a cord through the tip of the Carpenter ( 3 ) seems t o have been the first to invent a balance arm could pass vertically to the center of the bottom method of testing the breaking strength of paraffin wax. As plate of the quadripod. One end of the cord was fastened to the his method was intended for only a comparative study of a screw cap ( a ) which was designed t o fit one end of the holder of qeries of waxes under the same general conditions, it could the specimen whose shape and dimensions are given in Figure 1. After the specimen had been put into place and the balance adnot be used for obtaining the tensile strength in absolute justed, the former was immersed in the water by raising the Deunits. Hence a special method based on those procedures nar flask. The stirrer was then ut in motion and the temperawhich are used for measuring the tensile strength of other ture regulated by the addition opeither hot or cold water a$ the materials, had to be devised. experiment demanded. The temperature was measured by an
