SUPERPHOSPHATE MANUFACTURE Composition of Superphosphate Made from Phosphate Rock and Concentrated Phosphoric Acid R. H. NEWTON AND R. L. COPSON Tenneesee Valley Authority, Wilson Darn, Ala.
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HE first paper of this series (1) described the preparation of superphosphate by mixing finely ground phosphate rock with concentrated phosphoric acid (70 to 85 per cent H3P04). Although sufficient analytical data were given to indicate the chemical composition of the products, the first paper was concerned primarily with the physical characteristics of the superphosphate during and after mixing. It was shown that, by using phosphoric acid of concentration above approximately 75 per cent HsP04, a product could be obtained after a few minutes of mixing which was sufficiently dry so that subsequent artificial drying was unnecessary. Analysis of the products after curing for one month indicated that high percentage conversion of the phosphate content of the rocks into citrate-soluble form was accomplished. A more detailed investigation of the composition of superphosphate prepared from concentrated phosphoric acid is described in the present paper. The principal variables studied were the quantity of acid used, the concentration of the acid, and the grade of the phosphate rock. Preparation of Superphosphate Samples Four different samples of Tennessee brown phosphate rock were used in preparing the various superphosphates.
The chemical reaction between three different Tennessee brown phosphate rocks with concentrated phosphoric acid, containing 60 to 80 per cent HZP04, is studied. The percentage conversion of nonavailable to available PzOj is presented as a function of quantity of acid, acid concentration, and grade of rock. The Fez03 and A1203 present in phosphate rock are almost completely converted into citrate-soluble compounds, and dicalcium phosphate is not formed in appreciable quantities. The data presented permit prediction of the analysis of the product resulting from the reaction of various grades of Tennessee phosphate rock with concentrated phosphoric acid.
These are designated throughout the paper as A, B, C, and D, respectively. A and B were samples of washed rock and were the highest in P?O6 content; C was a sample of intermediate grade; and D mas a low-grade material, consisting of the soft matrix which surrounds the lump rock in the deposits. Care was taken to grind all of the phosphate rock samples as closely as possible to the same particle size. Screen analy*es (Tyler standard screens) of the four samples fell within the following limits: 95 t o 98 per cent through 100 mesh; 75 to 82 per cent through 200 mesh; and 60 to 64 per cent through 325 mesh. Chemical analyses of the samples are given in Table I. The methods used in analyzing the phosphate rock samples were, in general, those described by Jacob and eo-workers ( 5 ) . The phosphoric acid used in making the superphosphates was prepared from crude acid produced by the electric furnace process in the T. T'. A. Fertilizer Works at Tilson Dam. It was purified by allowing it t o settle until clear. The concentration of the acid was checked by specific gravity determinations, by acidimetric titiation using sodium alizarin sulfonate indicator, and by determination of the P205by ammonium molybdate precipitation. The three methods were found t o agree satisfactorily. The fluorine content of the acid, as determined by the Willard and Winter method ( 7 ) v-as found to vary from 0.04 to 0.10 per cent. The sulfuric acid used in the experiments wit,h phosphoricsulfuric acid mixtures was commercial 66" BB. acid. As in the first paper of this series (1j , the theoretical amount of phosphoric acid was calculated as that quantity required to react with the CaO and P205in the rock to form monocalcium phosphate. In calculating the theoretical requirement, no allowance was made for reaction of the acid with iron and aluminum compounds present in the rock. However, in some cases quantities of acid were used as much as 25 per cent in excess of the calculated theoretical requirement, and this excess was more than sufficient to react with all of the iron and aluminum present. A sigma-blade mixer, with a bowl capacity of 6 gallons, was used to mix the phosphoric acid and phosphate rock. The procedure was the same as that described in the first paper of this series (1). Briefly stated, the required quantity of acid was placed in the mixer and 10 pounds of phosphate rock were added. The mixing was continued until a fairly dry, granular product was obtained. In the great majority of cases. this required from 3 to 5 minutes. With the most dilute acids and Tvith the largest excess of acid, longer mixing was required, in a few cases as much a$ 30
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l \ D L S ' l ' I ~ l . ~. ~i X, D E\GI\EKl1-10o-c 28 ... .. 0.1 0.3 O., 2.6 1.1 3.4 the sample a t the end of 28 &I-110-c 28 ... .. 0.0 0.0 3.2 0.7 1.8 1.0 XI-125-C 28 1 . 2 . . . . . 0 . 0 0.0 1 . 0 2 . 9 0.9 days of storage a p p e a r e d to >I-90-D 28 4.6 ... .. 0.5 2.0 1.2 3.2 4.7 M-100-D 3.4 1.2 26 ... 0.5 2.1 . . 3.1 4.5 be the same, r e g a r d l e s s of M-110-D 28 2.7 2.9 4.3 1.1 ... . . 1.4 0.4 whether curing was normal or XI-125-D 1.7 1.2 26 ... 2.8 4.1 0.3 1.1 i5-75-A e 2.2 28 3.6 0:24 0.2 0.1 2.2 2.6 0.3 reversed. This was shown by 80-60-B e 8 4 6.6 0.W 3.06 3.0 56 0.31 80-75-B e 56 3.i 3.1 4.9 the fact that the results for 0.6d 2.76 0.30 the above-mentioned runs fell on s m o o t h c u r v e s with the other runs in which normal curing occurred.
InUUSTRIAL AND ENGINEERING CHEMISTRY
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a small proportion of
the i r o n o x i d e and alumina remained in t h e citrate-insoluble residue. It is noteworthy that, although r e v e r s i o n had been noted in t h e case of sample 75-76d, the citrate-insoluble PzOs apparently was in the u same form as in the x XP,O, IN ROCK other runs, apparently FIGURE 3. EFFECTOF GRADEOF being present as fluorROCKON CONVERSION TO AVAILapatite. ABLE PHOSPHATE The mole ratio of the citrate-soluble Pz05 (total PzO5 minus water-soluble P,O5 and citrate-insoluble P&) to the citrate-soluble Fen03 plus A1203is given in the last column of Table IV. In all except the last three runs, this ratio is approximately unity, indicating that citrate-soluble compounds such as trialuminum phosphate and triferric phosphate are formed.
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In the last three runs of Table IV reversion was observed. I n these runs the mole ratios of citrate-soluble PzOF,to citratesoluble Fez03plus AlpOa were 2.2, 3.0, and 3.1, respectively. This may indicate that the cause of reversion was the formation of di- or monoaluminum and ferric phosphates, thus causing a greater proportion of the acid to be combined with the iron and alumina, and causing a reversion of the monocalcium phosphate to fluorapatite. This phenomenon was especially marked and rapid when superphosphate samples were heated to about 300" F. (150" C.) for an hour or so, indicating that the formation of di- and monoaluminum and ferric phosphates undoubtedly proceeds, although a t a slower rate, a t room temperature.
Literature Cited (1) Copson, Newton, and Lindsay, IXD. ENO.CHEM., 28,923 (19363. (2) Hill and Beeson, J. Assoc. Oficial d g r . Chem., 18,244-60 (1935). (3) Hill and Hendricks, ISD. ESQ. CHBM.,28, 440 (1936). (4) Hill and Jacob, J . LIssoc. Oficial Agr. Chem., 17,487-505 (1934). (5) .Jacob, Hill, Marshall, and Reynolds, U. 8. Dept. Agr., Tech. Bull. 364 (June, 1933). (6j Marshall. Rader, and Jacob, IND.ESG. CHEU.,25, 1253 (1933). (7) Willard and Winter, IND. ESG.C H E K ,.%rial. Ed., 5, 7-10 (1933). RBCEIVED July 2, 1936
TERTIARY ALKYL ETHERS PREPARATION AND PROPERTIES
@I
N 1907 the Belgian chemist Reychler (8) heated trimethylethylene, methanol, and sulfuric acid together in a sealed tube and found that methyl tertiary amyl ether was produced: CH,OH
+ CsHlo +CH30CjHn (tertiary)
Regchler performed only this one experiment, and little attention was paid to the reaction, probably because the tertiary olefins requisite to the synthesis have not been readily accessible. Thus to secure trimethylethylene, it was necessary to isolate isoamyl alcohol from fused oil and then dehydrate the alcohol; the preparation of isobutylene necessitated the similar isolation of isobutanol as a first step. In recent years, however, the advances in the cracking and distilling arts in the petroleum ndustry have made these olefins readily available as major constituents of the hydrocarbon fractions of appropriate boiling point. These fractions consequently afford a conlenient source of the two lowest tertiary olefins, although in the form of solutions in other hydrocarbons. However, tertiary butanol and pentanol are likewise cheaply available a t present from petroleum. Hence they serve as ready sources of pure isobutylene and trimethylethylene when required. The availability of these materials led t o the present investigation of Reychler's reaction. The authors have endeavored to determine the scope of this reaction with regard to both alcohols and olefins, and to determine the most suitable conditions for producing these ethers in good yields
Starting Materials OLEFINS. Starting with methanol, the general reaction may be written: CHsOH CnH?, C- CHsOC,Ha,+i
+
T.W.EVANS AND K. R. EDLUND Shell D e v e l o p m e n t C o m p a n y , Emeryville, Calif
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This reaction reaches an equilibrium which varies with the olefin used. By observing the change in yield, the suitability of the different olefks for this synthesis can be determined. In this reaction isobutylene reacts very rapidly and the equilibrium lies well on the ether side. Trimethylethylene is slightly less favorable than isobutylene, and the tertiary hexylenes derived by dehydrating tertiary hexyl alcohols are only moderately suitable. By the time diisobutylene is reached in the series, practically no reaction takes place. illso the introduction of chlorine into the isobutylene molecule inhibits the reaction, so that @-methyl allyl chloride is not suitable. On attempting t o use secondary olefins such as 2butylene, much higher reaction temperatures and catalyst conccntrations are required and lower yield.; otitained than wit8hi-obutylene. ALCOHOLS. Similarly, to evaluate the alcohols used in this reaction, a fixed olefin, isobutylene, can be reacted with various alcohols and the change in yield noted. By this means it is found that, the more acid or labile the hydrogen in the hydroxyl group, the faster the reaction and the better the yield. Thus, as a class, the priinary alcohols are much inore suitable than the secondary alcohols, and the tertiary alcohols react slightly if a t all. [The existence of tertiary dibutyl ether is doubtful, although Pet'rov (8) claims t o have secured it.] Of these alcohols, methanol is the most reactive. However, the primary alcohols, a t least as high as isoamyl, may be employed. Of the secondary alcohols, isopropanol and secondary butanol give only moderate yields, while the secondary pentanols are only slightly reactive. Similar considerations apply to the polyhydric alcohols. If the acidity of the hydrogen atom is taken as the controlling factor, it is interesting to observe that, although methanol adds to 2-butylene a t only a slow rate to give low yields of methyl
