INDUSTRIAL AND ENGINEERING CHEMISTRY
44
stant was 0.234. With either sulfuric or hydrochloric acid the was found to be practically o.2 Of a pH unit lower than for juice obtained in the ordinary manner. The data presented in this paper cannot be expected t o apply to any juice having a composition greatly different from those of the juices used in the work here reported.
Vol. 24, No. 1
LITERATURE CITED (1) Jackson, Silsbee, and Proffitt, Bur. Standards (1926).
Sci. Paper 519
(2) McGlumphy, Eichinger, Hixon, and Buchanan,
CHEM.,23, 1202 (1931).
IND. ENQ.
RECEIVED September 30,1931.
Available Phosphoric Acid Content of Ammoniated Superphosphate FRANKG. KEENEN,Ammonia Department, E. I . d u Pont de Nemours and Co., Inc., Wilmington, Del.
N
EARLY two years ago sistent r e s u l t s . H o w e s a n d T H E E F F E C T qf temperature and time of it was found that am( 3 ) indicated the effect Jacobs storage, of moisture content, and of grade of of i n c r e a s i n g t h e acidity of mo n i a t e d superphosmixed fertilizers on the availability of the phoscitrate solutions, as well as of phate exhibited analyticalirreguphoric acid in ammoniated materials has been changing the citrate phosphate larities no t e xis t e n t in unamdetermined. Comparative data were obtained by moniated phosphates. The inratio, o n t h e i n s o l u b l e P206 found in ammoniated materials. vestigation of these peculiarities both the oflcial method of analysis and the proT e c h n i c a l phases of the amand subsequent vegetation tests posed method tentatively adopted in October, moniation process, including diaunder the direction of the United 1930, by the Association of Oficial Agricullural grams and photographs of facStates Department of AgriculChemists. T h e rate at which ammoniated prodture and several state agricultory installations, have been preucts reach final equilibrium can be varied f r o m tural experiment stations led the sented (7, 8). Association of Official Agricul12 months at low temperatures to 5 days at tural Chemists in October, 1930, PLANOF INVESTIGATION elei5ated temperatures. The moisture content is tentatively to adopt a modified also of importance in determining this rate. P r e v i o u s work (6) had remethod of analysis for available P205in fertilizers. The signifisulted in fairly definite conclucance of this change with respect t o industrial ammoniation sions as to the chemical reactions in ammoniated supertechnic and factory data on the reversion of phosphates under phosphates. Little was learned of the controlling factors, the proposed method were practically unknown. however, beyond the general knowledge that temperature This paper contains data on: (1) Comparative analyses and moisture are the most important. The 3-year industrial of ammoniated materials under both official and proposed development of the process resulted in widely varying methods methods; (2) influence of temperature, length of storage, of handling and storing ammoniated goods, which brought moisture, and degree of ammoniation on the rate and ex- about correspondingly discordant results. A final note of tent of phosphate reactions in ammoniated superphosphates; uncertainty was added by the proposed change in analyti(3) effect of mixture grade (ratio of ammoniated super to cal control method. It was not known whether the limittotal weight) on the analytical determinations of insoluble ing factor of ammonia addition would remain the reversion Pz05;(4) results of factory tests to determine mechanical of phosphate or would become a mechanical problem inciaspects of significance in the addition of larger amounts dental to the introduction of larger amounts of ammonia. The first requisite in obtaining information on these probof ammonia; ( 5 ) correlation of previously derived theoretilems was small-scale, controlled, storage equipment which cal equations and data with present results. could duplicate factory conditions and a t the same time RECENTLITERATURE accelerate the reactions. This apparatus was developed. Two major series of experiments were made, one using The patent and journal literature up to 1930 has already been reviewed (6). The calcium phosphates formed by ammoniated superphosphate alone and the other a 4-8-4 ammoniation reactions were shown by Jacob et a1 (4)to mixed fertilizer in which the superphosphate was ammoniated be hydroxy or basic compounds of characteristics different to compositions corresponding to the unmixed samples. from those of the naturally occurring rock phosphates. The procedure involved ammoniation of a 50-pound batch Ross and Jacob (IO) reported that preliminary pot and field 01 material and immediate placing of 4 to 6 one-pound samtests indicated these basic phosphates to be a t least 75 per ples in the storage equipment. The samples were removed cent efficient (water-soluble phosphates, 100 per cent ef- individually a t the desired time intervals and analyzed. ficient). Comparative analytical behavior, with respect t o Most of the 50-pound batch was cooled, bagged in ordinary solubility in neutral ammonium citrate solution, of all types fertilizer bags, and stored in a relatively open shed. Samof phosphatic fertilizer materials was determined by Jacob ples of the cooled material, as well as that from the storage e t a1 ( 5 ) . Haskins (6), Salter (ff), Buie ( f ) , and Parker apparatus, were analyzed again a t intervals of about 2 (9) described experiments on the agricultural availability months to determine the stability of the products. The of the less soluble forms of calcium phosphates. Salter (12) storage tests were made over periods of from 1 to 30 days also showed the citrate solubility of calcium phosphates t G a t 60' C. and 80" C. with ammoniated superphosphate conbe strongly influenced by the presence of other soluble cal- taining between 2.5 and 5.5 per cent N. The official methods of analysis consist essentially in excium compounds, and suggested the addition of ammonium oxalate to the citrate solution as a means of obtaining con- tracting a water-washed 2-gram sample of superphosphate
January, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
with 100 cc. of neutral ammonium citrate a t 65' C. for 30 minutes. The proposed method requires the use of a 1gram sample and extraction with neutral citrate for 1 hour a t 65" C. All the experimental batches were analyzed by both methods. The factory operating problems in connection with higher ammoniation were found by experiments in several typical fertilizer mixing plants. The fine cooperation and free exchange of information between the fertilizer industry
STORED AT 80 O C. (176" F.) FIGURE 1 . SUPERPHOSPHATE
and industrial, state, and federal research laboratories have been primarily responsible for the rapid and successful growth of the ammoniation process. STORAGE TESTING EQUIPMENT Anhydrous ammonia was added to the fertilizer materials in a small drum mixer which had been used for the past 21/2 years in the experimental work. The storage tests were made in an apparatus similar to that described by Schucht ( I S ) , consisting of an oil-filled thermostat and several containers. The containers were short sections of a 4-inch iron pipe with a head Relded in one end and fitted with a removable piston. The piston was a secticln of smaller iron pipe with welded oversize head fitting close t o the 4inch container. A 1- or 2-pound sample of fertilizer was introduced in the container placed upright in the oil bath. The piston was inserted and putty was pushed into the annular space between piston and cylinder walls to prevent loss of moisture from the sample. From 3 to 4 pounds pressure per square inch was applied to the piston in most of the tests by merely placing bags of lead shot on top of it. In a few cases 15 to 20 pounds per square inch was obtained by hanging the shot bags from the end of a &foot horizontal bar passing across the top of the piston. Increasing the pressure beyond about 3 pounds did not significantly affect the reaction.
45
anhydrous ammonia. 4-8-4 (3 per cent K Super)-22.5 pounds super; 6 pounds ammonium sulfate; 4 pounds potassium chloride; 17 pounds sand; 0.8 pound anhydrous ammonia. Duplicate batches were made of practically all series to avoid freak data and minimize sampling and analytical errors.
FACTORY EXPERIMENTS Early in the development of ammoniation i t was realized that the addition of ammonia to superphosphate must be carried out in the present plant equipment with very little additional capital expenditure and with no decrease in the hourly production. Experiments were recently made in five widely separated fertilizer mixing plants to determine the maximum amount of anhydrous ammonia that could be mechanically introduced under the above criteria. Smallscale experiments had shown (6) that the chemical absorption limit was 5 to 5.5 per cent nitrogen, but it requiied 5 t o 8 minutes in a relatively tightly enclosed mixer for ccmplete absorption of the maximum quantity using anhydrous ammonia. The use of an aqueous solution such as ordinary aqua ammonia (25-30 per cent XH3) made it possible t ) add an equivalent amount of ammonia in a shorter time, but the water so introduced caused excessive dampness in the mixture when more than about 2.5 per cent N was S J added to the superphosphate. Increasing the ammcnia concentration of such solutions, of course, obviates this difficulty, but more than 35 per cent NH3 concentratioLi produces pressures which demand the same type of equipment as anhydrous (100 per cent) ammonia. As the reversion of phosphate has been found to be practically independent of the moisture content of the goods as long as it lies in the region of 6 per cent water or above, the limit of ammoniation with concentrated ammonia solutions is on the same basis as anhydrous ammonia (reversion of Pz06).
1
2
4
b DAYS
8 STORED
1
0
1 I2
1 I4
FIGURE 2. 4-8-4 MIXTURE STOREDAT 80" C. (176" F.)
The factory tests included mixed goods and cured and fresh superphosphates from Tennessee and Florida rock sources. The mixers Jyere ordinary rotary batch machines of the Sturtevant or Stedman type. It was found that 3.5 per cent N (4.25 per cent XH3) was an average maximum MATERIALS limit of ammoniation with anhydrous ammonia. The limit The same commercial source of superphosphate was used is sharply defined for a given material and attempts to introfor the entire 6 months of the tests and the four shipments duce more than this amount of ammonia within a reasonable of superphosphate involved closely approximated the follow- time (3 to 4 minutes) resulted in excessive losses. The ing average analyses: moisture, 7-8 per cent; total Pz05, condition of the superphosphate and the presence of other 18.7 per cent; insoluble PzOS, 0.25 per cent; free acid, 3-4 ingredients in mixtures had relatively little effect upon this per cent. The potassium chloride and sulfate of ammonia limit, although it varied as much as 0.5 per cent N between used in the 4-8-4 mixture were obtained from stock piles in different plants. a fertilizer mixing plant. No organic nitrogenous material The fresh superphosphate was appreciably dried and was used in the mixtures, as previous experiments had shown granulated by the ammonia treatment. Although interestthis to have no specific influence on the ammoniation reaction. ing possibilities of development along this line were indiThe 4-8-4 mixtures were made on the basis oi 4 per cent cated, addition of ammonia stopped the action of the free nitrogen. Typical formulas were: 4-8-4 (4.5 per cent N acid resulting in a phosphate availability somewhat lower Super)--22.5 pounds super; 5 pounds ammonium sulfate; than that from cured super. The highly ammoniated mixed 4 pounds potaqsium chloride: 17 pounds sand; 1.1 pounds goods were comparable to present ammoniated materials
,
8
h-
$
I
I
/-
I
I
I
I
---- +==,
* ,, 2-
36
//
M= - 1 6=
I
I
I
= =='f
hi-I5
,
8
b
1
I
I
I 4
,OFFICIAL
N
__
= =*==
PROPOSED
1
/ 2
3.7b N
I
