Heat Developed in the Ammoniation of Superphosphates with Anhydrous Ammonia JOHN 0. HARDESTY AND WILLIAM H. ROSS Fertilizer Research Division, Bureau of Chemistry and Soils, Washington, D. C.
T
HE treatment of superphosphate with free ammonia serves a double purpose in fertilizer manufacture. The ammonia acts as a conditioner for the superphosphate; the latter in turn functions as a neutralizing agent for the free ammonia and thus eliminates the expense incident to the conversion of this source of nitrogen into a form suited for direct use as a fertilizer. Free ammonia differs from the other basic materials used in conditioning superphosphate in that it is used as a liquid or in the form of aqueous solutions containing dissolved salts in addition to free ammonia. It therefore reacts more rapidly with the acid components of the mixture than the solid basic materials that are used as conditioners, and the heat developed in the reactions raises the mixture to a much higher temperature. The complete ammoniation of ordinary superphosphate is accompanied by four principal reactions which may be represented as follows (8):
+
&Po4 NHa = NH4HzPOa Ca(HzPO~)~-HzONHs = CaHP04 NH4HzPO4 Ha0 NH4H2PO4 Cas04 NHs = CaHPO4 (NH~)zSO~ 2CaHP04 Cas04 2NHs = CaS(PO& (NH&SOI
+ +
+
+ +
+
+ +
+
(1) (2) (3) (4)
If the ammonia added to a 20 per cent superphosphate is in excess of about 2.3 per cent, the reactions t h a t occur involve the calcium sulfate as well as the monocalcium phosphate in the superphosphate, as represented in Equations 3 and 4, and the ultimate products of the reaction when an acid-free superphosphate has absorbed the maximum of 8 or 9 per cent of ammonia are tricalcium phosphate and ammonium sulfate as represented in the composite equation:
The reactions represented by Equations 3 and 4 proceed much more slowly than the first two reactions, and the rate at which superphosphate reacts with ammonia therefore decreases rapidly as the ammonia content approaches the maximum that the superphosphate is capable of absorbing. This decrease in the rate of absorption is also accompanied by a decrease in the availability of the phosphoric acid present (15) due to formation of tricalcium phosphate (8, 10, 16) or other basic phosphates (12). I n the ammoniation of monocalcium phosphate monohydrate or of calcium sulfate-free double superphosphate, reactions 3 and 4 are replaced by reactions 6 and 7 (8, 16) :
Reactions 1 and 2 are common to the ammoniation of both superphosphate and double superphosphate. Reaction 7 proceeds much more slowly than reactions 1 , 2 , or 6, and does not occur to any considerable extent a t temperatures below 40' C . (16). If a double superphosphate contains some calcium sulfate, this will react as indicated in Equations 3 and 4, and some increase in citrate-insoluble P 2 0 6 will occur when the material is ammoniated in excess of 6 per cent (16). I n the absence of any considerable quantity of calcium sulfate the citrate-insoluble P20~ content of the material will remain unchanged for the most part until the treatment with ammonia exceeds 9 or 10 per cent. A double superphosphate will thus absorb without serious reversion about three times as much ammonia as an ordinary superphosphate per unit of weight. The capacity for heat development in the ammoniation of double superphosphate is therefore much greater than in the case of ordinary superphosphate. An elevation in the temperature of a fertilizer mixture increases the rates of the reactions that occur between the various components of the mixture and initiates reactions that do not normally occur a t ordinary temperatures (3, 9). Lundstrom and Whittaker (11) have shown that a t temperatures above 60" C . urea reacts with the acid phosphates in a mixture to form pyrophosphates and set free carbon dioxide. Loss of ammonia with elevation of temperature also occurs from mixtures that have been ammoniated so as to form diammoniqn phosphate, or t o which diammonium pklosphate has been added (2). Dolomite reacts with the monoammonium phosphate formed in an ammoniated mixture to evolve carbon dioxide, but the reaction a t ordinary temperatures proceeds only to the formation of available dibasic compounds. At temperatures of 60" C. or above, the reactionmay proceed to the formation of more basic compounds and the heat developed in the reaction may be sufficient to maintain the mixture, when stored in large piles, a t an elevated temperature for a considerable length of time. These conditions give rise t o a loss of ammonia when the predominating phosphatic component of the mixture is monoammonium phosphate ( 3 ) . The heat developed in ammoniation may be used to advantage, however, if applied in the granulation of the mixture as described by Ross and Hardesty (14). I n the operation of this process the heat developed in ammoniation is quickly dissipated during granulation and subsequent drying of the product, and the loss of plant food values that accompanies any prolonged storage of the mixture a t an elevated temperature is thereby avoided. The present paper describes a quantitative study that was made of the heat developed in the ammoniation of superphosphate and superphosphate mixtures with liquid anhy1283
1284
INDUSTRIAL AND ENGINEERING CHEMISTRY
drous ammonia. The purpose of the investigation was (a) the theoretical heats of reaction corresponding to the equations given above with the experimental values, (b) to study the conditions under which fertilizer mixtures may be ammoniated without loss of available plant food, and ( c ) to determine the extentto which the heat developed in ammoniation may be utilized in the granulation Of f e r t i h e r mixtures.
to
VOL. 29, NO. 11
The cylinder, in which was stored the anhydrous ammonia used in the tests, was connected with the illium bomb when in position in the calorimeter by spiral steel tube A (Figure 21, steel needle valve B , thick-walled Pyrex glass buret C, a second needle valve BI, the capillary steel tubing of 1-mm. bore D, and a third needle valve Bz which connected capillary tubing D with the illium bomb through capillary tubes DI and Dz and couplings E and El. Spiral tube A and Pyrex buret C were mounted in a constant-temperature water bath maintained at 300 C. Needle valve Bz was held in a rigid position by a slotted support (not
FIGURE1. APPARATUS FOR MEASURING HEATSOF AMMONIATION
The heat developed in the ammoniation of superphosphate and superphosphate mixtures with Urea-Ammonia Liquor or with Nitrogen Solution should be somewhat less than with liquid anhydrous ammonia. Direct measurements of the heat developed in ammoniation reactions with these materials are now in progress.
Apparatus The apparatus used in this work consisted of a BurgessParr adiabatic calorimeter with such modifications and accessory equipment as were necessary to adapt it to the measurement of the heat developed in ammoniation reactions. The apparatus is shown in perspective in Figure 1, and diagrammatically in Figure 2. The water equivalent of the calorimeter is usually determined by burning an organic material of known heat of combustion, such as chemically pure benzoic acid. The results obtained in four determinations of the water equivalent of the apparatus, using Bureau of Standards benzoic acid sample 39d, varied from 2419 to 2429 calories with a mean value of 2422 calories (20' C . ) . The illium bomb that accompanied the calorimeter was unsuited for ammoniation reactions and a second illium bomb (Figure 3), provided with an illium stirrer mounted on the cover of the bomb by means of a packing nut, was constructed for measuring heats of ammoniation. When the bomb was placed in the calorimeter, as shown in Figure 2, the stirrer could be rotated by a special pulley and shaft mounted on the cover of the calorimeter in the same way as the pulleys and shafts that were provided with the instrument for driving the water stirrers. The lugs on the bottom of the bomb fitted into slots in the bottom of the oval water container. This prevented movement of the bomb when the stirrer was rotated and maintained the bomb in its proper position in the water container.
shown) mounted on a side wall of the oval water container. The valve with its attached tubing and couplings could be readily removed when desired by disconnecting couplings E and El. Valve Bz could be opened or closed while in position by means of the elongated valve stem which extended through the cover of the calorimeter. The buret was filled from the ammonia cylinder (not shown) by gently opening valve B while valve Ba a t the top of the buret also remained open. When the buret was filled, both valves were closed and the ammonia was allowed to remain in the buret before using until it had reached the temperature of the bath. The water equivalent of the ap aratus when using the attachments required in measuring the feat developed in ammoniation reactions was found to be 2452 calories. This was determined by making a benzoic acid combustion in the first illium bomb while it was surrounded in the oval water container by valve BI with attachments and by a quantity of illium metal equivalent to the weight of the stirrer and the excess weight of the second bomb over the first.
Heat of Ammoniation of Phosphoric Acid
As a check on the accuracy of the apparatus for measuring heats of reaction, determinations were made of the heat developed in the ammoniation of a solution of pure phosphoric acid to form mono- and diammonium phosphates as represented in the following equations :
+ +
NHa(lig,) HaPOa(noH*O) = N H ~ H ~ ' O H~~(O~) O 2NHs(aq.) HaPO4(2o H ~ O ) = (NH4)zHP04(2oH ~ O ) The solution of phosphoric acid (1 mole per 20 moles of water) was added to the illium bomb, and, while the stirrer was in motion, the approximate quantity of pure anhydrous ammonia was run from the buret into the acid in the bomb as quickly as possible. The exact quantity that had actually been
NOVEMBER, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
1285
ing periods of time. This was done by passing an electric current through a platinum wire suspended as a coil in the first illium bomb, as --Monoammonium Phosphate-Diammonium Heat Phosphsteshown in Figure 4. The platinum wire used in Heat the r e s i s t a n c e coil had a total length of 3.66 developed developed Run HaPo4 NHa incalo- reaction Heat of Hap04 NHs in calo- reaction Heat of meters and a diameter of 0.305 mm. The changes No. taken added rimeter taken added rimeter Cram Gram Gram Gram made in the wiring of the apparatus to adapt it Grams Grams cal. cal./mole Crams @Tams cal. cd./mOk to this determination are also shown in Figure 4. 1 48.95 8.4680 8961 18,010 24 48 8 1911 7961 33,084 The continuous lines represent the original circuit 2 8.1500 8537 17,828 8.2524 SO47 33,192 3 48.95 8.3984 8763 17,758 24.48 8 5240 8203 32.760 4 48.95 8.1880 8585 17,846 24.48 8 3592 8154 33,204 and the broken lines the modified circuit' When 5 48.95 8.1440 8665 18,108 24.48 8.3187 8047 32,924 the modified circuit was used, the stirring motor M~~~ 33,056 was operated on a separate circuit. The elecMean 17,910 trical energy transformed into heat energy within the calorimeter was calculated by means of the equation: added was determined subsequently by analysis of the conH = 0.239CEt tents of the bomb. When undertaking an ammoniation, the where H = heat developed, volume of water normally used in the oval container surroundC = mean amperage of circuit ing the bomb was decreased by a quantity equal to the water E = mean observed drop in potential between terminals equivalent of the material in the bomb. A small correction of resistance coil t = time of current flow, seconds was also made for the heat developed by the stirrer during the neutralization of the The intervals a t which the C acid. The results obtained and E readings were made are given in Table I. TABLE11. CALORIMETRIC MEASUREMENT OF HEATDEVELOPED varied from 15 s e c 0 n d s, The heats of formation IN AN ELECTRIC RESISTANCE COIL when the time of current Mean Mean Heat Developed a8 Measured by: flow was 2 minutes, to 60 of NH4HzP04(400H,O) a n d Time of Voltage Am erage Temp. (NHdJ€P04(500H ~ O ) a r e Current across in d r c u i t , rise in CE drop seconds when the time of Flow Coil, E C calorimeter in coil 338,900 and 368,500 calocurrent flow was 60 minutes. Mzn. Gram cal. Cram. cal. ries, respectively (4). AcThe results obtained are 2 91 00 4 30 11 270 11,220 cording to tests made in this 4.25 10:770 10,850 given in Table 11. 89 00 laboratory, the heats of solu4 64.21 3.44 3.49 12:060 12 400 12,850 12 235 The results given in Table 62.00 tion of solid NH4H2P04 in 58.70 3.26 10,820 10:975 I1 show that the heat de20 and 400 moles of water 30 16 15 1.65 1 74 13:525 11 840 11 13:340 466 veloped in the calorimeter 17 82 are, respectively, -3455 and 17 74 1 74 13,305 13 280 as determined by tempera17 40 1.72 13,135 12:876 -4025 calories; the correture rise was in good agree60 s 55 1 07 7,805 7,870 sponding values for solid ment with that calculated (NH4)2HP04 a r e - 1980 f r o m t h e p o w e r input, and -3320 calories. The heat of formation of NH4H2P04(20 H ~ O )is therefore 339,470 calories, and of (SH4)2HP04(20B,o), 369,840 calories. The heat of formation of NH3(1iq.)from its elements is 16,070 calories, and of H3P04(20H~o),305,690 calories (4). It follows therefore that the heat developed in the neutralization of H3P04(20H ~ O )to form N H ~ H ~ P OH~~(OZ) O is 339,470 - (16,070 305,690) or 17,710 calories, and to form (NH&HP04(20H,o), 32,010 calories. The values calculated in this way from thermochemical data given in the literature agree within 1.2 per cent of the value (17,910 calories) found by experiment for the first reaction, and within 3.2 per cent of the value (33,055 calories) found for the second reaction. These variations between the calculated heats of reaction and those found by experiment are within what is considered to be the limits of error of the values given in the literature for the heats of formation of the reacting materials. IN AMMONIATION OF PHOSPHORIC TABLE I. HEATDEVELOPED ACID TO FORM MONO-AND DIAMMONIUM PHOSPHATES
--
+
Calorimetric Measurement of Electrical Energy The heat developed in the combustion of benzoic acid in oxygen, or in the neutralization of phosphoric acid with ammonia, is liberated in a very short time. The greater part of the heat developed in the ammoniation of superphosphate is also liberated in a comparatively short time, but the reaction is slow in going to completion. I n order to determine the effect of change in the speed of reaction on the accuracy of the results, measurements were made of the heat developed in the calorimeter when known amounts of electrical energy were transformed into heat energy within the bomb over vary-
A-SPIRAL STEEL T U X B 9 Bp.ANDbSTEFL NEEDLE VALVES ;-;~;DTDn~CAP,LLARY TUBING
f:i2;
STEEL
~ ~ ~ , ' ~ ' N G s
FIQURE 2. CROSSSECTION OF CALORIMETER AND WATER BATH
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VOL. 29, NO. I.€
-
TABLE111. PERCENTAGE COMPOSITION OF PHOSPHATIC MATERIALS Sample No. 1 108
4 12 0 13c a
b 6
d
Material Monocslcium phosphate" Fla. pebble superphosphate Tenn. su erphosphate Fla. peb&e double superphos hate Tenn. Xouble superphosphate
Moisture None 1.29 4.50 3.00 0.65
Y P h o s horic Ac.id (PnOs) $ater- CitrateFree sol. insol. Total Noneb 56.34 1.10d l7:Ol 0105 20.22 0.92 15.08 0.32 20.09
CaO 22.23 28.10 27.85
SO: None 29.29 30.00
FezOa None 0.64 2.00
AlrOa None 0.54 0.84
CaSOr None 49.8
3.561 0.52
18.00 18.48
1.90 2.10
1.60 1.30
1.30 1.00
3.3 3.5
41.63 42.20
*
Prepared as directed by Clark (6). pH of 0.01 M solution = 4.5. Analysis according to Hi11 and Hendrioks (7). Equivalent to 0.0157 mole per 100 grams of dry sample.
TABLEIV.
0.07 0.48
49.27 48.37
..
Ca(H~P04)t.Hz0 100 29.766
...
71.870 78.92
Equivalent to 0.1195 mole per 100 grams of dry sample.
f Equivalent to 0.0517 mole per 100 grams of dry sample.
Equivalent to 0.294 mole per 100 grams of dry sample.
HEATOF AMMONIATION OF SUPERPHOSPHATE OF VARYING MOISTURE CONTENT
has little or no effect on the heat developed in its ammoniation. The moisture content of the phosphatic materials Heat Developed er 100 Grams Dry Superphosphate used in all subsequent work was adjusted to 5 per cent exMoisture in #hen Treated with: cept when otherwise noted. Superphosphate 2 g. NHs 4 g. NHE 6 g. NHs % Cram cal. Gram ca2. Gram cal. The results obtained for the heat liberated when superphos3 1741 3270 4742 phate samples 10 and 4 and double superphosphate samples 5 1806 3295 4737 12 and 13 were treated with varying quantities of liquid am10 1821 3266 4746 3270 4755 15 1830 monia are given in Table V. The heat developed when the Mean & 3275 4750 samples are treated with quantities of ammonia not specified in the tables may be readily determined from the curves in Figure 5. TABLE V. HEATDEVELOPED ON TREATING SUPERPHOSPHATES Table V shows: (a) There is little difference in the total WITH VARYING QUANTITIES OF AMMONIA quantity of heat developed when the two types of ordinary Heat Developed per Qram Heat Developed per 100 superphosphate used in the tests are ammoniated up t o of NHs Absorbed Grams, Dry Basis NHI Fla. pebble Tenn. the point where caIcium sulfate enters into the reaction, 2.3 Added Fla. pebble Tenn. Gram8 Gram calories per cent, ( b ) The heat developed with further additions of Ordinary Superphosphate ammonia increases more rapidly with the Florida pebble 975 860 860 975 1.00 superphosphate than with the Tennessee superphosphate. 927 853 1280 1390 1.50 7
2.00 3.00 4.00 5.00 6.00 7.00 8.00 1.00 1.50 2.00 3.00 4.00 5.00 6.00 7.00 8.00 10.00 12.00
1700 1800 2475 2560 3210 3276 3920 4000 4600 4760 5275 5490 5925 6200 Double Superphosphate o in --900 1375 1390 1820 1830 2750 2675 3475 3650 ~_._. KOO 4180 4925 5300 5660 6100 6400 6880 7875 8475 9350 10075
900 853 819 800 792 784 775
850 825 803 784 767 764 741
900 927 916 917 912 900 883 871 860 848 840
o_i -n_ 917 910 892 869 836 821 so9 800 788 779
.
and that the agreement was equally good whether the heat was developed within 2 minutes or over a longer period of 60 minutes.
Heat of Ammoniation of Superphosphate The same procedure was followed in determining the heat developed in the ammoniation of different types of superphosphate as in the ammoniation of phosphoric acid. The composition of each of the phosphate materials used in the tests is given in Table 111. The quantity of material taken in most of the determinations amounted to 100 grams. The addition of this quantity of material to the bomb of the calorimeter had the effect of increasing somewhat the water equivalent of the apparatus. The necessary correction for this increase could be readily calculated for each material from its specific heat and moisture content, and this correction was applied in each determination. Table IV shows the heat cteveloped per 100 grams of dry superphosphate sample 10 when ammoniated in the presence of varying percentages of moieture. The results given in Table I V show that a variation in the moisture content of a superphosphate from 3 to 15 per cent
USEDIN MEASURING FIGURE3. ILLIUMBOMBAND STIRRER HEATSOF AMMONIATION (c) The heat evolved per unit of ammonia absorbed decreases somewhat with the degree of ammoniation. ( d ) This decrease is more marked with the ordinary than with the double superphosphate. These results could be explained, in part a t least, on the assumption that the samples contain hydrated as well as anhydrous calcium sulfate and that there is a larger proportion of the former in the Tennessee than in the Florida pebble superphosphate.
Calculated Heats of Reaction The heats of formation of the principal components of ordinary and double superphosphate and of their ammoniated products are given in Table VI.
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1287
Maximum Ammoniation Temperatures TABLEVI. HEATSOF FORMATION OF AMMONIATED SUPERPHOSPHATE COMPONENTS Component
Heat Of Formation4 Kg. cal.
Component
Heat 01 Formation0 KO.cal.
The temperature T to which a superphosphate or superphosphate mixture becomes heated by ammoniation, assuming no loss of heat by radiation, may be calculated from the formula :
T = H/MC where H = heat developed, in calories, by maw M of the ammoniated product C = average heat capacity of product 0 Calculated from the observed heat of 8( 400 moles of water (4.02 kg. 1 Rossini for the heat of formation o d Calculated from the observed heat of soh
By means of these data it is possible to calculate the approximate quantity of heat developed when an acid phosphate is treated with a given quantity of ammonia. Table VI1 gives the calculated and experimental values for the heat developed when pure, acid-free monocalcium phosphate monohydrate (sample 1) is treated with varying quantities of ammonia. In Table VI11 the calculated values for the heat developed in the principal reactions involved in ammoniation are compared with those found by experiment.
Knowing the heat developed by ammoniation and the heat capacities of the resulting products, it is thus possible to calculate the maximum temperature rise of any ammoniated product. The specific heats of most of the salts used in fertilizer mixtures are availsble in the literature, but no data could be found on the heat capacities of superphosphate and its ammoniated products. The heat capacities of the superphos-
:TO STIRRING
MOTOR
OVAL WATER CONTAINER
ON TREATING MONOCALCIUM TABLEVII. HEATDEVBLOPED PHOSPHATE MONOHYDRATE WITH VARYING QUANTITIESOF AMMONIA
NHI Added Grams 1 2 4 6
8
10 12
Heat Developed per 100 Grams, Dry Basis Found Calcd. 925 1815 3480 5150 6825 8500 10150
Heat Developed per Gram of NH; Absorbed Found Calcd. &am calories 863 925 863 1726 912 863 3452 870 863 5178 858 863 6767 853 848 8274 850 827 9781 846 815
The results given in Tables VI1 and VI11 show a good agreement between the calculated and experimental values for the heat developed in the ammoniation of pure monocalcium phosphate. The agreement in the case of the ordinary and double superphosphate samples is also as good as can be expected in view of the limited accuracy of the values available for the heats of formation of some of the reacting materials and of the uncertainty of the degree to which di- and tricalcium phosphates undergo hydration in ammoniation reactions. Hill and Hendricks ( 7 ) showed that a maximum of 9.7 per cent of the calcium sulfate in superphosphate sample 10 is present as the dihydrate or 32.8 per cent as the hemihydrate. I n calculating the heat developed in reactions 1 and 5 (Table VIII), it was assumed that 9.7 per cent of the calcium sulfate in the sample was present as the dihydrate. TABLEVIII. CALCULATED AND EXPERIMENTAL VALUES FOR HEATDEVELOPED IN TYPICAL AMMONIATION REACTIONS Reaction Represented by Equation No.
m 2
1+5 1+2
1+2+6
NHs
Phosphatic Material
&td5tEEHeat Developed
Phosphate Urams Monocalcium phosphate 6 75 13 50 Fla. pebble superphosphate 2.30 8.41 Fla. pebble double euperphosphate 5.89 10.89
Calod. Found Gram calories 5825 5780 10910 11425 2125 2040 6888 6425 5535 9307
5250 9200
FIGURE 4. WIRING DIAGRAM OF CALORIMETER
phates used in this investigation and of two mixed fertilizers prepared according to the formulas given in Table IX were determined by the method of cooling as described by Marley (IS). I n making these determinations, about 200 grams of each material were heated to 45" C. in a Dewar flask that was closed with a paraffined cork stopper through which was passed a long glass tube with a capillary opening a t the top. The purpose of the glass tube was to prevent any appreciable loss of moisture while the material was being raised to the desired temperature. The glass tube was then quickly replaced by a thermometer subdivided into 0.02" C. divisions, and the rate of cooling in a calorimeter as described by Marley was observed between 31" and 27" C. The calorimeter was kept in a constant-temperature bath a t 28" C. during the cooling period. The moisture in the superphosphate samples was determined by storing for 7 hours in a vacuum over sulfuric acid. Knowing the heat capacity and moisture content of a material, its heat capacity in the dry state could readily be calculated. The ammoniated products used in the heat capacity determinations were prepared in the closed illium bomb shown in Figtwe 3. The ammoniated product was transferred to the
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ON TREATING SUPERPHOSPHATES WITH VARYING QUANTITIESOF LIQUIDAMMONIA FIGURE5 . HEATDEVELOPED
Dewar flask in such a way as to avoid any appreciable loss of moisture, and its heat capacity was then determined in the same way as described for the nonammoniated products. The materials and mixtures were not moisture-free when used in the determination of their heat capacities, but all results were calculated on the basis that the materials before ammoniation were moisture-free and that any water of hydration set free in ammoniation was still retained in the sample. The results obtained are as follows: NHa Added per 100 Grama
pohf~~f%
Material
Grams
Fla. pebble superphosphate Ammoniated Fla. pebble superphosphate
z3
4
Fla. pebble double superphosphate Ammoniated Fla. pebble double superphosphate
4 6
8
Mixed fertiliaer (4-9-5) Mixed fertilizer (8-18-10)
Herqt Capaclty at 27.6' C. G?am
cal./ororn/o C. 0.207 0.234 0.236 0.248 0 246 0.281 0.270 0.303 0 229 0,269
the mass and vaporize moisture present. The results show, for example, that the heat developed, when anhydrous ammonia is added to a superphosphate containing 5 per cent of moisture a t the rate of 3 grams per 100 grams of dry phosphate, is sufficient (assuming no loss of heat by radiation) to raise the temperature of the mass to 100 O C. and vaporize about 9 per cent of the total moisture present. The moisture vaporized when double superphosphate is treated with the equivalent quantity of anhydrous ammonia per unit of P206 (8.0 grams per 100 grams of dry material) amounts t o about 75 per cent of the total present. 12000
/
I1,OOO
10,000
, MONOCALCIUM PHOSPHATE MONO HYDRATE
n
The mixtures represented in Table IX were formulated on the basis that the materials used in their preparation contained 5 per cent of moisture before ammoniation. The moisture in the completed mixtures therefore represented that originally present together with the water of hydration set free in the ammoniation of the mixtures. TABLEIX. FORMULAS OF FERTILIZER MIXTURES Material
Single-Strength Double-Strength Mixture (4-9-5) Mixture (8-18-10) Lb./ton Lb./ton 948 .. 732 27 54 144 288 122 61 38 76 346 173 382 191 418
..
-
__
2000
2000
Table X shows the extent to which the heat developed in the ammoniation of superphosphate and superphosphate mixtures with anhydrous ammonia will raise the temperature of
Table X shows further that the use of 27 pounds of anhydrous ammonia in the preparation of a ton of mixed fertilizer (4-9-5) of 5 per cent moisture content will raise the temperature of the mixture to a maximum of 68' C. when the normal temperature is 25" C. This is in good agreement with observations made under commerical conditions (6). The use of an equivalent quantity of ammonia per unit of P2OSin the Preparation of the 8-18-10 mixture will raise the temperature to 100" C. and vaporize a small portion of the moisture present.
NOVEMBER, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLEX. MAXIMUM TEMPERATURE OF AMMONIATED MIXTURES
1289
.
Residual Moisture Combined Min. in Mixture NHa Water Total Moisture When Added per Initial Ammoniated Max. Set Moisture Vaporized cooled 100 Grams of Product Temp. Free by in Initial by Heat in rotary Dry Super- Heat DeHeat Total Rise Ammo- Ammoniated of AmmoAt dryer0 Material or Mixture Dhosuhate veloDed caDacits weight 25' C. niation Product niation 100" c. t o 50° C~. . Grams Qram calories Grams ' C. % ofmizture % yo of totat % % M oietjure in Original Supei.phosphate or Mixture, 5 Per Cent 6.61 2.00 107.26 87 1.7 None 6.61 Fla. pebble superphosphate No. 10 5.63 6.84 108.26 100 2.0 8.8 3.00 6.28 5.02 6.78 4.00 109.26 100 2.0 23.8 5.26 4.21 7.83 6.15 22.9 109.26 100 3.0 Fla. pebble double superphosphate No. 12 4 . 0 0 4.92 9.49 48.3 111.26 100 4.8 6.00 5.14 4.11 9.32 8.00 2.41 75.9 113.26 100 4.7 1.93 222.22 68 1.0 5.88 3.00 5.88 None Mixed fertilizer (4-9-5) 5.46 6.71 1.2 7.77 6.63 Mixed fertilizer (8-18-10) 287.60 100 1.8 5.30 Moisture in Original SUDerDhOSDhate or Mixture. 10 Per Cent - 77 1.6 ii3.11 11.48 None Fla. pebble superphosphate No. 10 2 00 1800 0 309 11.48 10.24 2560 114.11 98 1.9 11.62 None 3 00 11.62 9.39 0.309 0.321 4 00 3275 116.11 100 1.9 11.52 7.0 10.81 8.65 Fla. pebble double superphosphate No. 12 4 00 3650 116.11 100 2.9 12.52 8.1 0.350 11.63 9.30 6 00 0.339 5300 117.11 100 4.5 14.01 26.2 10.73 8.58 119.11 100 4.4 13.78 40.5 0,368 8 00 6880 8.68 6.94 2560 234.40 61 0.9 10.79 Mixed fertilizer (4-9-5) 3 00 None 10.79 0.306 10.32 Mixed fertilizer (8-18-10) 7.77 6725 0 342 303.10 90 1.7 11.49 None 11.49 9.65 a Average efficiency of dryer under conditions of the tests, 45 per cent with material containing 5 per cent moisture and 74 per cent with material containing 10 per cent moisture.
+
I
The mixtures containing 10 per cent of moisture were prepared by adding the required quantity of water to the 5 per cent mixture. This extra addition of moisture reduced the maximum temperature of the single-strength mixture from 68" to 61" C. and of the double-strength mixture from 100" to 90" c. In most fertilizer mixtures an elevation of temperature accelerates reactions that cause reversion of phosphoric acid (3, Q), decomposition of urea (12) and other easily decomposable materials, and even loss of ammonia ( 2 ) . The reactions are likely to be more serious in high- than in lowanalysis mixtures owing to the higher temperatures reached by the former mixtures when treated with an equivalent quantity of ammonia per unit of P z O ~ . The heat developed by ammoniation, however, may be economically advantageous if utilized to facilitate the granulation of the mass. Undesirable reactions are thereby prevented by the rapid cooling incident to the granulating process. The presence of any considerable quantity of an organic conditioner in a fertilizer mixture increases the moisture required to granulate the mass. Mixtures of this kind are usually of satisfactory drillability without granulation. The method of improving the drillability of fertilizer mixtures by granulation is therefore of special application when applied in the treatment of inorganic mixtures. The moisture required in the granulation of inorganic mixtures varies from about 6 to 15 per cent. A mixture with an initial moisture content of 10 per cent, together with that set free in ammoniation, should be sufficient to granulate most but not all fertilizer mixtures. Granulation occurs automatically when an ammoniated superphosphate or fertilizer mixture of the proper moisture content is rolled in a drum or rotary dryer (18). The passage of the granulated product through the dryer countercurrently to a stream of air not only cools the mixture but also eliminates moisture in addition to that vaporized a t 100" C. The moisture vaporized when each of the ammoniated products listed in Table X was passed in granular form through a small rotary dryer at such a rate as to cool it from 100" to 50" C. amounted, on an average, to 45 per cent of the quantity corresponding to the heat loss when the initial moisture content was 5 per cent, and to 74 per cent when the initial moisture content was 10 per cent. Ammoniated mixtures ordinarily contain dicalcium phosphate. According to Bassett (1) this material does not undergo hydration a t the temperature of ammoniation, but results obtained in this laboratory indicate that an ammoniated
superphosphate may contain a limited quantity of hydrated dicalcium phosphate. Some of the drying effect observed in the passage of the granular products through the dryer may therefore have been due to hydration rather than to loss of water by vaporization, but the drying effect due to hydration is apparently relatively small. The results given in the last column of Table X indicate that the heat developed in ammoniation is sufficient to granulate and dry double superphosphate and also certain mixtures that can be granulated with a low moisture content but that additional heat is required to granulate and dry ordinary superphosphate and mixed fertilizers that require a relatively high moisture content for satisfactory granulation.
Summary Use was made of a modified Burgess-Parr adiabatic calorimeter to measure the heat developed in the ammoniation of superphosphate and superphosphate mixtures. The heat liberated per gram of liquid anhydrous ammonia absorbed by 100 grams of Florida pebble superphosphate decreased from 975 to 775 calories when the ammonia absorbed was increased from 1 to 8 grams. The corresponding values for double superphosphate were 900 and 840 calories as the ammonia absorbed was increased from 1 to 12 grams. The calculated values for the heat of reaction in the ammoniation of monocalcium phosphate, ordinary superphosphate, and double superphosphate were found to be in good agreement with the experimental values. The heat developed on treating 105 parts of superphosphate containing 5 per cent of moisture with 3 parts of anhydrous ammonia is sufficient to raise the mixture from a normal temperature of 25" to 100" C. and vaporize 9 per cent of the moisture present. The corresponding maximum temperature when the superphosphate contains 10 per cent of moisture is only 98" C. The treatment of a double superphosphate with 6 parts of ammonia will raise the temperature of the product to 100" C., with both 5 and 10 per cent of moisture present, and vaporize, respectively, a minimum of 48 and 26 per cent of the total moisture present. The treatment of a mixed fertilizer of average composition with 27 pounds of ammonia per ton will raise the temperature of the mixture from 26" to 68" C. when the moisture content is 5 per cent, and to 61" C. when the moisture content is 10 per cent. The corresponding maximum temperatures for a double-strength mixture are, respectively, 100" and 90" C.
,
1290
INDUSTRIAL AND ENGINEERING CHEMISTRY
The danger of loss of available plant food in the ammoniation of high-analysis mixtures containing double superphosphate is therefore greater than for low-analysis mixtures unless means are taken to cool the mixture rapidly as in the process of granulation. The heat developed in ammoniation is sufficient to granulate and dry double superphosphate and also certain mixtures that can be granulated with a low moisture content, but some additional heat is necessary to granulate and dry ordinary superphosphate and mixed fertilizers that require a relatively high moisture content for satisfactory granulation.
Literature Cited (1) Bassett, 2.anorg. Chem., 53, 34 (1907); 59, 1 (1908). (2) Beeson, IND.ENG. CHBM.,29, 705 (1937). (3) Beeson and Ross, Ibid., 26, 992 (1934).
VOL. 29, NO. 11
(4) Biohowsky and Rossini, “Thermochemistry of Chemical Substances,” New York, Reinhold Publishing Corp., 1936. (5) Clark, J. them,, 35, 1232 (1931). (6) D,, pont de N ~E, I., and ~ co.,‘~ d ~ ~ ~~~ i ~ ~~ ~ ~ -, May, 1933. (7) Hill and Hendricks, IND. ENG.CBEM.,28,440 (1936).
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197 (1937). (10) Luckmann, Kunstd-iLnger u. Leim, 33, 131, 163,200 (1936). (11) Lundstrom and Whittaker, IND. ENG.CHEM.,29, 61 (1937). (12) MacIntire, Hardin, Oldham, and Hammond, Ibid., 29, 758 (1937). (13) Marley, proc. sot. (London), 45, 591 (1933). (14) R~~~ and Hardesty, Commercial Fertilizer Yearbook. D. 28 (1937). (15) Ross, Jacob, and Beeson, S. Assoc. Oficial Agr. Chem., 15, 227 (1932). ENG.CHEM.,27, 562 (1935). (16) White, Hardesty, and Ross, IND. RBCEIVEXI July 30, 1937.
Oat Hull Utilization by Fermentation L. A. UNDERKOFLER, ELLIS I. FULMER, AND MORTON M. RAYMAN Iowa State College, Ames, Iowa
ELLULOSIC materials constitute a large proportion of the agricultural and trade wastes, including wood waste, oat hulls, cottonseed hulls, corncobs, peanut husks, and others. The profitable disposal of such materials constitutes an industrial problem of considerable economic importance. Recent developments along this line have been the hydrolytic conversion of the pentosans of oat hulls into furfural (8) and the production of crystalline xylose by the hydrolysis of cotton seed hulls (6,I2). One of the most promising possibilities for the industrial utilization of wood waste is the Bergius process, (a) for the conversion of wood to carbohydrates, using concentrated hydrochloric acid. Probably the largest outlet for the crude sugar produced in this way will be in the fermentation industry for the production of industrial alcohol. Bergius mentions the well-known fact, however, that the xylose present in the mixed sugar solutions obtained in the process is not fermented by yeast. It might be desirable, therefore, to subject the wood to a prelirriinarymild acid hydrolysis, thus removing the xylose for use in a n appropriate fermentation process, and then to treat the residual cellulosic material by the Bergius process. The fermentative utilization of cellulosic materials, especially the pentosans, was recently reviewed by Fulmer (6). The purpose of the present paper is to present the results of an investigation to determine the best conditions and methods for the preparation and subsequent fermentation, by the butyl-acetone organism (Clostridiumacetobutylicum, r), of acid hydrolyzates from oat hulls. Oat hulls were selected as a representative cellulosic waste because of their uniformity in composition and ready availability in Iowa. The oat hulls were kindly furnished by The Quaker Oats Company. The butylacetonic fermentation is, next to the alcoholic fermentation, the most important industrial fermentative process. In this fermentation are produced solvents, in the approximate ratio
C
Butyl-Acetonic Fermentation of the Acid Hydrolyzate of 60 parts butyl alcohol, 30 parts acetone, and 10 parts ethyl alcohol, along with large quantities of carbon dioxide and hydrogen. Starch from corn has been used most extensively in this fermentation on the industrial scale, although various investigators have shown that, in the presence of suitable nutrients, other carbohydrates, including most of the simple sugars, are fermented by C1. acetobutylicum. More recently molasses has become an important industrial raw material for the production of butyl alcohol and acetone; a different organism has been used, however, from the one mentioned here. Robinson (11) and Speakman (Id)found that xylose and arabinose were fermented by the butyl-acetone organism; Peterson, Fred, and Schmidt (IO)reported a more detailed investigation of the butyl-acetonic fermentation of pentoses. Hydrolyzates from cottonseed hulls, peanut husks, corncobs, and sawdust from five different kinds of wood were fermented with C1. acetobutylicum by Weinstein and Rettger (17). None of these workers attempted t o determine optimum conditions or to use commercially feasible concentrations of carbohydrate. Hence, preliminary to the more exhaustive investigation of the possibility of utilizing xylose-containing hydrolysates in the butyl-acetonic fermentation, a study was made of the fermentation of pure xylose. The results were published by Underkofler, Christensen, and Fulmer (16). Data were given on the influence of physical and chemical conditions and the treatment of the cultures to bring about maximum yields of solvents from xylose. Using the optimum conditions, final yields and ratios of solvents from a semisynthetic medium containing 6.25 grams xylose and 1gram corn gluten meal per 100 cc. were practically the same as from corn mash. It is interesting to note that, although as much as 80 per cent of the usual corn mash could be replaced by glucose and 90 per cent by starch (the yields of solvents remaining normal), only 40 per cent replacement of the corn mash was possible with pure xy-
