Oxidation of Phosphorus with Steam LABQRATQRY SCALE RESEARCH J. F. SHULTZI, GRADY TARBUTTON, T. M. JONES, & E. 'I DEMIXG, . C. RI. SMITH, AND MARION B. CANTELOU Tennessee Valley Authority, Wilson Dam, Ala. T h e catalyzed reaction between phosphorus vapor and steam to produce phosphoric acid and hydrogen has been studied on a laboratory scale at atmospheric pressure and elevated temperature. Both platinum and palladium, supported on aluminum metaphosphate or zirconium pyrophosphate, are highly active and stable catalysts; they direct the reaction toward the formation of acid and hydrogen relatively free of phosphorous acid and phosphine, respectively. Supported copper catalysts are less stable, but their high catalytic activity and low cost justify their consideration in an industrial process.
Methods for substantial elimination of phosphine from the by-product hydrogen were developed with the object of making the hydrogen suitable for the synthesis of ammonia. The ranges of conditions suitable for a commercial process appear to be temperatures from 650" to 800" C., mole ratios of steam to phosphorus vapor from 16 to 30, and space velocities of 640 to 9500 hour-' for platinum catalysts or 640 to 2350 hour-l for copper or palladium catalysts. Elimination of contaminative phosphorous acid and phosphine is facilitated by retention of products in a heated chamber downstream from catalyst.
I
steam in the presence of various catalytic agents has been studied by several investigators, but a practicable commwcial procesq has not been developed. The reaction between phosphorus and water to form phosphoric acid (85%) and hydrogen is favorable thermodynamically a t temperatures that are reasonable for large scale operations. This conclusion results from calculations based on critically evaluated data and reasonable assumptions. The basic data are given in Table I, and the results of the calculations are shown in Table 11. The investigations described in the literature cover both the reaction of liquid white or solid red phosphorus with watw under superatmospheric pressure at relatively loa. temperatures, and the reaction between phosphorus vapor arid steam under atmospheric pressure a t high temperatures. The reaction between liquid white phosphorus and water under pressure a t temperatures as high as 420" C. was studied by Ipatiev and co-workers (27-19). Their investigations included tests of materials that might catalyze the reaction. Bushmakin and his associates (6, 7 )
Ii T H E method of maiiufa,cture of phosphoric acid that coni-
prises reduction of phosphate rock t o eletnental phosphorus, oxidation of the phosphorus to the pent,oxide, arid hydration of the pentoxide to phosphoric acid, the phosphorus is burned in air. The combustion of 1 pound of phosphorus in air generates about 10,500 B.t.u. The corrosiveness of phosphorus pentoxide and its hydrates at, high temperat,urcs makes the recovery of the hea.t of combustion difficult, and the heat is usually dissipated by the injection of a considerable excess of Tvater into the products of the combustion. The excem xater merely cools and dilutes the phosphoric acid; it, has no significant part in the over-all reaction. In the oxidation of phosphorus with water
P,
+ 16H20 +4HaP04 + 10H2
(1)
the heat of combustion of phosphorus is partially utilized in the production of hydrogen. The process is attractive, therefore, where the by-product hydrogen can be used in another process. The oxidat,ion of phosphorus both Tyith liquid wat'er and TTith 1
Present address, U. S. Bureau of Mines, Pittsburgh, Pa.
D . 4 ~ ~ON 4 PHOSPHORUS, HYDROGEK, TTATER, . ~ N DPHOSPHORIC ACID TABLE 1. THERMODYSAMIC
Heat C
-
~
a
y
AH (Form)
Temp. interval,
Substance Hydrogen, Hz Phosphorus, Pa Phosphorus, P4 Phosphorus, PI Phosphorus, P4 Phosphorus, P4, PhosDhorie acid I' 5 5 . 5 1
State Gas Solid Liquid Liquid Gas Gas
Temp.,
' K.
K.
CP
f 0.81 X
2500-2731 273-317 317-533
6.62
553
16.39
291.1 291.1
lO-3T (80) 2 2 . 0 9 (46)" 11.64 O.O3722'(46)b
+ + 3.66 X
892.677
... ...
1 O - s T (89)
4- 0.4172' (4%Ie
291.1
+ +
Entropy Temp
Cal./mole K." Cal./mole/degrse 0 . 0 1) 298.1 31.23 1 0 . 0 1 (88) 0 . 0 [ 1 ) 298.1 40.4J46) ... 317.76 43.7 553.66 56.4c ... 298.1 6 6 . 9 2 (3.9) 553.7 77.44d - 305,920 (1) 2 9 8 . 1 3 7 . 6 (58)/
30.100 0.0744T(48)e ... .. Phosphoric acid, 85% (1 aq.. approx.) 291 1 -68,730 ( I ) 2 9 8 . 1 1 6 . 7 5 * 0 . 0 3 (I8 273-373 1 8 . 0 3 (10) Liquid Water Liquid 373-573 16.873 0.003165T(IO)g ... ... Water ... 298.1 4 5 . 1 3 =t0 . 0 1 (88) 300-2500 8 . 2 2 f O . 1 5 X lO-3T-t 1 . 3 4 X 10-8T2(20) . . . Gas Water H>O(g)-+ HzO(1). AH288 = -10,520cal. (81). P4(1) --c Pa(s), AHaii.~= -600 cal. (45). H3PO4#55.51 aq. -+ H3P 1, 857, 54.55 aq., AFms.1 = 4231 ral. (11). 2.872 X 10-2t, where t = e C. Calculated from Young and Hildebrand's equation (45): Cp = 21.46 3.927 X 10-6t*,where t = 25' to 100" C., on assumption t h a t b Calculated ffom Young and Hildebrand's equation (46): Cp = 24.47 - 9.521 X 10-at equation is applicable a t temperatures up to 280' C. Calculated from data from (56 57, 46). d Interpolated from data of Ste&nson and Yost (59). e Recalculated from Volkov and Ginstling (48); unit is 1 mole of &POI. f I t is assumed t h a t Sma.1, HsPOa, 55.51 aq. = Sz88.i! HaP04. aq. 0 Recalculated from Dorsey ( 1 0 ) ; mean molar specific heat.
+
+
-
August 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
studied the reaction between solid red phosphorus and water under similar conditions. Although these workers reported some success, their methods entail operation under pressure with highly corrosive materials. Also, the methods yield dilute and impure phosphoric acid and by-product hydrogen that is contaminated with phosphine. The vapor-phase reaction between phosphorus and steam to form phosphoric acid and hydrogen was proposed by Liljenroth; his early patents (27, S I ) covered the oxidation of phosphorus with steam a t about 1000" C., and other patents (23-26, 28-30,32-34) described catalysts t h a t could be used to lower the temperature of the process from 1000" to 700" C., suggested methods of oxidizing the phosphine that was formed as an impurity in the hydrogen, and indicated various operating details. The patented catalysts include all the nonalkaline metals of the first group of the periodic table and all the metals and phosphides of the metals of the sixth, seventh, and eighth groups. Among the materials claimed by other authors to be catalytically active in promoting the phosphorus-steam reaction are ferrosilicon (8),ferric oxide (46), Nichrome (a), silver alloy containers in combination with binary, ternary, or quaternary silicates ( 8 ) ,finely divided copper and nickel phosphides (9), potassium metal (36), and fire clay (16). The uncatalyzed reaction between phosphorus and steam at 1000° to 1200' C. was studied by Britzke and Pestov (4).Similar studies were made by Brunauer and Shultz a t 1000" to 1 1 0 0 O C. (5). These investigators found that from 3 to 17% of the theoretical yield of hydrogen was lost as phosphine and that the phosphoric acid always contained phosphorous acid. Britzke and Pestov (4) tested a number of potential catalysts but found none that was effective in the absence of a large excess of steam. Brunauer and Shultz (5) obtained complete reaction in the presence of phosphate rock; the rock absorbed the phosphorus pentoxide as it was formed. Although conditions are thermodynamically favorable for the reaction between phosphorus and steam to form phosphoric acid and hydrogen, the rate of the uncatalyzed reaction is slow below 1000" C., and the products contain phosphine and phosphorous acid that probably result from reactions intermediate to that represented by Equation 1. Previous investigators failed to find a satisfactory catalyst for the reaction, but the process appeared to be suffciently promising to warrant further study, This paper describes laboratory scale studies in which an efficient catalyst was found for the reaction between phosphorus vapor and steam to form phosphoric acid and hydrogen and in which a reasonable basis was established for starting pilot plant work. The pilot plant development is described in a companion paper (14). MATERIALS
White phosphorus was obtained either from a chemical supply house or from selected samples from the TVA plant. It was found that high purity of the phosphorus was not required. Although it is possible to study the phosphorus-steam reaction with mixtures containing only the two reactants, it is more convenient in the laboratory to transport the phosphorus into the reaction vessel by means of a carrier gas. Nitrogen, carbon monoxide, and hydrogen were used as carrier gases in this investigation. The nitrogen and hydrogen, from commercial cylinders, were freed of oxygen by passage over copper wool at 450" C. Carbon monoxide was obtained from the TVA phosphate-reduction furnaces or it was prepared by decomposition of formic acid with hot phosphoric acid (41). The carbon monoxide from both sources contained less than 0.2% carbon dioxide; the furnace gas contained several per cent of nitrogen and a trace of hydrogen sulfide. I n investigations of the effect of hydrogen sulfide on certain catalysts, this gas was obtained from a commercial cylinder. All carrier gases were dried before use.
1609
TABLE11. THERMODYNAMIC DATAFOR OXIDATIONOF PHOSPHORUS WITH WATER
- dH, Gal.
- A F , Cal.
K
25 100 300 500
118,950 125,300 138,400 143,250
160,150 169,800 187,400 203,200
... ... ... ...
25 100 200 300 500 700 727 827 1000 1100
300,100 292,400 279,650 263,900 225,200 175,900 168,600 139,500 83,600 55,400
198,650 174,000 143,800 117,500 70,800 36,600 32,800 20,640 6,000 1,200
Temp.,
O
C. P4(1)
+ 16Hz0(1) 4- 4 aq. = 4HaPOa(85%) + 10Hl(g)
,
4.98 x 9.14 X 2.75 X 2.87 X 1.08 x 1.65 X 1.50 x 1.27 x 1.08 x 1.56
10145 10'0' lOee 1044 10"
108 107 104 10
About sixty materials, including ma?y suggested in the literature, were tested as fixed-bed catalysts for the phosphorus-steam reaction. The materials included metals, alloys, phosphides, oxides, and salts. The massive metals and alloys were used as either turnings or wire gauze; other materials were used in the form of 7- to 12-mesh pellets or irregular pieces. Most of the metal phosphides were prepared in the laboratory; those of aluminum, copper, nickel, and cobalt were prepared by heating pellets of mixtures of the powdered metals and finely divided red phosphorus in hydrogen a t atmospheric pressure. Platinum diphosphide was prepared by a method similar to t h a t described by Biltz and coworkers ( 2 ) . The metal, either in massive form or dispersed on the surface of a supporting material, was placed in a boat in one end of a quartz tube that contained red phosphorus in the other end. The tube was evacuated and sealed, and the red phosphorus was heated to 450" C. The metal was heated, successively, a t 550" C. for 48 hours, a t 650" C. for 48 hours, and a t 750" C. for 24 hours. The apparatus then was cooled t o room temperature in 6 hours. Supported catalysts were prepared by soaking the support in a solution of either the chloride or the nitrate of a metal, evaporating the solvent from the wetted support, and decomposing the absorbed salt with heat. The oxide obtained by heating a nitrate sometimes was reduced with hydrogen and sometimes was placed directly in operation. Pumice, silica gel, aluminum silicate gel, activated alumina, aluminum ortho- and metaphosphates, zirconium and titanium pyrophosphates, and several other phosphates were tested as supports for various catalysts. APPARATUS AND PROCEDURE
Apparatus. The apparatus, Figure 1, was similar t o that used by Brunauer and Shultz ( 5 ) . Reaction vessels of silver and of porcelain were used. The silver tube was 32 mm. inside diameter and 46 em. long, and the catalyst bed was supported by a perforated silver plate placed midway between the ends of the tube. Two sizes of porcelain tubes were used, each shaped as shown in Figure 1. The larger tube was 44 em. long by 32 mm. inside diameter a t the top and 14 mm. a t the bottom. The smaller size was 44 em. long; its inside diameters a t top and bottom were 13 and 6 mm., respectively. The catalyst bed was supported on a perforated porcelain plate that rested on the shoulder in the tube. The larger tubes were connected t o the glass parts of the apparatus by ground spherical joints. The smaller porcelain tubes were sealed directly t o the glass. Operating Procedure. The carrier gas was passed through the saturator over a stagnant pool of white phosphorus In most of the runs, the temperature of the wax bath surrounding the saturator was maintained at 165 C. to provide a vapor pressure of phosphorus approximately equal to the partial pressure of phosphorus vapor, equivalent to about 6% P4 by volume, in the gas produced in the electrothermal reduction of phosphate rock. The p h o ~ phorus saturator was calibrated a t various rates of flow of carrier gas. The steam generator was calibrated a t several rates by varying the electrical current in the heating coil. The steam w w mixed with the gases from the phosphorus saturator in the reaction vessel just above the catalyst bed. Tests of catalytic activity O
1610
INDUSTRIAL AND ENGINEERING CHEMISTRY
were made a t temperatures, measured by a thermocouple on the outside of the reaction-vessel wall, in the range between 300" to 900" C. The reaction products passed downward into two C-tube condensers, where the condensable products were collected. The first condenser usually was cooled with ice and the second with a mixture of solid carbon dioxide and acetone. In some tests, the first condenser was operated a t 100" t o 400" C. to collect concentrated acid. In a few runs, in which exact analyses for phosphine were made, an electrostatic precipitator was placed downstream from the condensers.
SPHERICAL JOINT
REACTION VESSEL
Vol. 42, No. 8
Bone-Wheeler gas analysis apparatus ( 3 ) as a check on the thermal conductivity measurements. The volume of dry exit gas from each experiment was measured TTith a calibrated wet-test meter. I n the analyses of the solid and liquid products, the elemental phosphorus was extracted in benzene, converted to copper phosphide with aqueous copper nitrate, oxidized with nitric acid, and determined as orthophosphate by the volumetric molybdate method (15). One portion of the aqueous condensate was analyzed for hypophosphorous and phosphorous acids by the method of Wolf and Jung (4.9). Another portion was treated with nitric acid and the total phosphorus determined by the volumetric molybdate method (15). The amount of phosphorus delivered to the reaction chamber, as calculated from the saturator calibration curve and the volume of carrier gas, usually checked closely with the total phosphorus found in the products when the catalyst was not acted upon chemically. The amount of hydrogen produced agreed well with the amount calculated from the quantities of phosphoric and phosphorous acids in the condensate. Catalyst Tests. Exploratory tests of experimental catalysts yere made a t 700" C. with a steam ratio of about 22 and a space These conditions were selected arbivelocity of 640 hour-'. trarily but were found to be suitable for making comparative tests of the catalysts; they appeared to be within the practical range of operation of a commercial process. The tests were carried out in periods of about 7 hours each; materials that were unstable or that failed to shov satiqfactory activity within three such periods were discarded. 12 catalyst was considered to bc satisfactorily active when it effected oxidation to water-soluble oxides of a t least 95% of the phosphorus throughput. Catalysts that showed high activity in exploratory tests were subjected t o performance tests in n-hich the temperature was varied from 300" to 900" C., the steam iatio was varied from 15 to 75, and the space velocity was varied from 640 to 12,750 hour-'.
Figure 1. Apparatus for Oxidation of Phosphorus with Steam
RESULTS A h D DISCUSSION
Definition of Terms. The ratio of steam to phosphorus in a reaction mixture is defined as the number of moles of water per mole of phosphorus and is termed steam ratio for convenience. The space velocity, expressed in reciprocal hours (hour-'), is defined as the combined volumes a t standard temperature and pressure of phosphorus vapor, water vapor, and carrier gas passed through the converter per hour per unit apparent volume of catalyst. Because of the difficulty of maintaining either the steam ratio or the space velocity constant while the other was being varied, both of these factors varied somewhat during each run. The effects of these minor variations on the experimental results, however, probably were small. The values given for these conditions are rounded averages. The amount of phosphorus oxidized is defined as the phosphorus equivalent of the water-soluble oxides of phosphorus that were recovered in the condensate from the reactant gases and is expressed as per cent of the total phosphorus. The phosphine content of the hydrogen is expressed as the percentage of the volume of hydrogen plus the volume of phosphine. The phosphorous acid content of the acid condensate is expressed as the percentage of the total phosphorus equivalent of the water-soluble oxides of phosphorus in the condensed acids that was present as H3P03. Analysis of Products. The gas leaving the condensers was analyzed for phosphine by reaction either with copper wool a t 450" C. or with silver nitrate solution a t room temperature. The phosphine was determined from the gain in weight of the copper wool or by analysis of the contents of the silver nitrate scrubber. The gas was dried and analyzed for hydrogen in thermal conductivity cells. Occasional grab samples of gas were analyzed with a
Initial Evaluation of Catalysts. At first, catalyst studies were made with massive materials in a silver tube with nitrogen as the carrier gas for the phosphorus vapor. I t was known that silver would catalyze the phosphorus-steam reaction (4), but it was assumed that the effect of the vessel would be small because of the relatively small amount of surface exposed, and it was found that the relative catalytic activities of the materials under test could be determined in the silver vessel. The physical and chemical stabilities of the catalyst materials were indicated also by these tests. Copper phosphide, nickel phosphide, and platinum diphosphide were found to have high catalytic activities, but best results were obtained with physical combinations of two or more materials. Binary mixtures of aluminum phosphide with platinum gauze, platinum phosphide, copper phosphide, or nickel gauze showed high activity. Of these, however, only the catalysts that contained platinum diphosphide or nickel gauze appeared to be stable. Kickel phosphide appeared to be stable but its catalytic activity was low. Plat,inum metal was attacked and removed from the catalyst bed as a subphosphide, probably the eutectic between platinum and PtzoP?which melts a t 588" C. ( 2 ) . Copper, present as the metal, an alloy, or a chemical compound, was removed from the catalyst bed, and aluminum phosphide apparently underwent chemical change. The acids produced in these tests always contained silver, and after several hundred hours of use the 3-mm. wall of the silver tube corroded through. A number of pinholes appeared just above the catalyst bed. McDanel porcelain was found to be attacked only slightly and to have no measurable catalytic activity a t about 700' C. Subsequent tests were made in porcelain reaction vessels. Copper, copper compounds, and silver were highly active
August 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
1611
catalyst that consisted of 3% platinum metal on aluminum metaphosphate also was highly active; x-ray examination of the used catalyst did (Tests made at 700° C. in porcelain reaction vessel with nitrogen as carrier gas) Catalyst-not show platinum phosphide. Six platinum Analysis of Products Active catalysts supported on aluminum phosphates Ingredient Space P in acid Steam Velocity, PHs in Hz, as HsPOs, Pa were tested; of these, two were prepared from Support Material Ratio Hour-' vol. % % oxidized,% metallic platinum and four were prepared from Alp04 PtPs 13 22 640 Trace 21 . 63 9 9 . 27 platinum diphosphide. Each of these catalysts AlPOi Pt 10 22 3?50 0.06 Al(P0a)s Pt 3 22 2050 0.08 2.4 99.3 was examined by x-rays after use. One of the Cu 14 22 640 0.01 1.3 99.0 Alp04 640 - 0 . 0 5 (trace) 1 . 1 - 1 . 6 99.7-100 , platinum catalysts and two of the diphosphide Al(P0a)a CU 1 22 0.26 22 640 0.025 1.6 99.6 cu catalysts were found to contain platinum metal, Ag 10 22 2530 0.04 2.1 99.7 ZrP107 Pd 5 28 580 - 0 . 0 1 (trace) 1.1 99.9 but no platinum phosphide was detected, after use; the other three catalysts contained platinum diphosphide, but no metallic platinum- was detected. Platinum subphosphide was not detected in any of the catalysts. KO reason for the changes catalysts, but they were rapidly lost from the catalyst beds. from platinum metal to the diphosphide or from the diphosPlatinum diphosphide was both highly active and stable, but the phide to the metal is apparent. Platinum diphosphide has a small specific surface of massive platinum diphosphide was an small dissociation pressure a t 1400" C. ( 2 ) , and the conversion of economic disadvantage, and a search was made for a support that this compound to metallic platinum a t 700' C. probably is not a would increase the effective surface of the catalysts. The supported catalysts investigated were copper supported on pumice or simple decomposition. The changes may result, however, from an calcium metaphosphate; and platinum diphosphide supported undetected reaction, as with water molecules on the surface of the catalyst. It was concluded that it made no difference whether the on silica gel, aluminum silicate gel, activated alumina, or alunplatinum was phosphided in the preparation of supported dum. The siliceous materials and calcium metaphosphate discatalysts. The data obtained with supported platinum catalysts integrated rapidly, but the activated alumina and alundum are summarized in Table 111. underwent little physical change. The catalytic activity of the It was found that massive platinum metal, such as gauze, was alumina- and alundum-supported platinum diphosphide was low. converted to a low melting subphosphide, which drained from the Subsequent tests of catalyst supports were made with nonsiliceous catalyst during use, but that platinum metal supported on compounds, especially phosphates. Aluminum, titanium, and zirconium phosphates were the only aluminum phosphate was not removed. It was assumed that aluminum phosphates would retain copper or silver or their phoscompounds found to be sufficiently stable for use as catalyst supports. Aluminum metaphosphate, titanium pyrophosphate, and phides in the catalyst bed. Copper, probably converted in use t o copper phosphide, supported on aluminum phosphate was an zirconium pyrophosphate, prepared in the laboratory, were hard, porous solids with bulk densities of about 0.6 to 0.7. Copper s u p active catalyst and about as effective a t low space velocities as metallic platinum or platinum diphosphide, but the activity of ported on titanium pyrophosphate showed high catalytic activity the copper catalyst decreased more rapidly than that of platinum a t first, but its activity decreased rapidly with use in initial tests, and this material was not studied further. When supported on catalysts as the space velocity was increased. Both copper and aluminum metaphosphate or on zirconium pyrophosphate, silver were continuously removed from supported catalysts during catalysts retained their activities with use. Nickel supported on operation. Although the condition of the catalyst during operaaluminum orthophosphate, however, exhibited an unexpected low tion was not observed, it is assumed that the product acid may have condensed on the catalyst a t 700" C., and that a part of the activity. Aluminum orthophosphate alone, in the form of friable lumps made from powdered material, catalyzed the reaction sigcopper and silver lost may have been removed by solution in the nificantly, but it reacted with the products of the oxidation, alacid. Because of the high cost of silver, catalysts containing this most doubling its weight, to give a product that contained about metal were abandoned, but the less expensive copper catalysts a p 78% PzOs (aluminum metaphosphate contains 80.68% PZOS). peared to be economically feasible for commercial use. Samples of aluminum metaphosphate that had been used as As little as 0.26% by weight of copper supported on aluminum catalyst supports were found to contain from 75 to 7801, P205, and metaphosphate is more active catalytically than the same amount x-ray examination showed that the material was substantially of copper supported on aluminum orthophosphate. The rate of aluminum metaphosphate. The pyrophosphates of titanium and removal of copper from catalysts of low copper content was only zirconium probably underwent changes in composition with use, about 32 parts of copper per million parts of PzO6 formed. but these materials were not analyzed after they had been used. The specific surface area of one aluminum metaphosphatesupported copper catalyst that had been subjected to extensive Most of the later tests were made with aluminum phosphate tests was found by the gas-adsorption method to be less than 0.2 supports. The activities of the more important catalysts are square meter per gram. shown in Table 111. The catalyst consisting of 13% platinum diphosphide supPalladium supported on zirconium pyrophosphate was a stable catalyst; it was somewhat less active a t high space velocities than ported on aluminum orthophosphate was highly active a t 700" C. supported platinum catalysts but was about as active as supported After this catalyst had been in use for several hundred hours, copper catalysts. it was steamed, cooled in dry nitrogen, and removed from the Performance Tests of Active Catalysts. A supported platinum reaction chamber. X-ray examination of portions of the catalyst diphosphide catalyst was tested extensively to determine the showed that the aluminum orthophosphate had been converted effect of variations in temperature, space velocity, and steam to the metaphosphate; the examination showed also that ratio on the catalyzed reaction. The catalyst comprised platinum platinum metal was present, but platinum diphosphide was not diphosphide, equivalent to 10% platinum, supported on alumidetected. The conversion of the platinum diphosphide to metallic num orthophosphate. platinum suggested that the platinum in the supported catalyst need not be converted to the phosphide before use, and a catalyst Table IV shows that the oxidation of phosphorus with steam in the presence of a supported platinum catalyst is nearly complete that consisted of platinum metal supported on aluminum orthoa t temperatures between 700" and 850" C. The low apparent phosphate was found to have about the same activity as the platinum phosphide catalyst. X-ray examination of this catalyst activity a t 650" C. was due largely to the accumulation of reacafter use showed the presence of platinum diphosphide. A third tion products in the catalyst bed, and this effect was found at
TABLE 111. ACTIVITY OF SUPPORTED CATALYSTS
7 -
M&y;:,
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1612
temperatures as low as 300" C. The decrease in activity at 900 O C. is characteristic of all the highly active catalysts that were tested. The noncatalytic gas-phase reaction becomes appreciable at 900" C., but this does not compensate for the decrease in catalytic activity. The amount of phosphorous acid in the acid product increased regularly with increase in temperature, as shown in Figure 2, and the data indicate that an equilibrium, involving trivalent and pentavalent phosphorus compounds, exists in the catalyst bed. At catalyst temperatures below 900" C. the percentage of phosphine in the hydrogen did not change greatly with changes in temperature. I
I
600
700
800
900
TEMPERATURE, 'C.
Figure 2. Effect of Catalyst Temperature on Proportion of Phosphorous Acid in Acid Products
Table V shows that platinum diphosphide supported on aluminum orthophosphate, which was converted to the metaphosphate in use, is a highly active catalyst, even a t a space velocity of 12,750 hour-', and that the amount of phosphine formed is not affected greatly by variation in space velocity below about 9500 houi -I. The proportion of phosphorous acid in the product, however, increases linearly Ivith space velocity, as is shown in Figure 3. The effect of varying the steam ratio at several temperatures is shovvn in Table VI. The degree of oxidation of phosphorus was not changed greatly by variation of the steam ratio from 15 to 30 at temperatures between 700" and 800" C. A steam ratio of 15 supplies less water than is required for the formation of orthophosphoric acid, according to Equation 1, but it is sufficient for the formation of metaphosphorlc acid:
P1
+ 12H20 +4HP08 + lOHz
(2)
In one or two experiments the steam ratio was adjusted to the stoichiometric requirement of Equation 2, and the percentage oxidation of the phosphorus decreased appreciably. These results shoTV that the mass-action effect of the water is important and indicate that hydration of the oxide is involved in the reaction. The low degree of oxidation of phosphorus obtained with steam ratios of about 20 a t 650" C. is attributed to the adverse effect of accumulated reaction products in the catalyst bed. A steam ratio of 78 was effective in removing these products and restoring the high activity of the catalyst. Increase in the steam ratio at temperatures of 850" and 900" C. caused an increase in
Vol. 42, No. 8
t,he degree of oxidation of phosphorus, a decreasc in the phosphorous acid content of the acid product, and a decrease in the percentage of phosphine in the hydrogen. Quenching Tests. In evaluating the results of the catalyst tests, it became evident that the temperature and time of retent,ion of the reactants and products in parts of the apparatus other than the catalyst chamber have important, effects on the over-all reaction. To determine the effect of quenching the products of the catalytic reaction, experiments were made in an apparatus, shown in Figure 4, that was designed to provide sharp temperature gradients in both sides of the catalyst chamber. The catalyst chamber was made by joining sections of the larger portions of two porcelain tubes, grinding t,hem to fit, and cementing the joint with phosphoric acid. The joint became gastight xhen heated to a high temperature. Several turns of 3/1a-inch stainless st,eel tubing were wrapped firmly about the outlet tube from the ratalyst chamber; air passed through this coil 'ivas an effective cooling agent. The temperature of the reactants entering the catalyst chamber was held below 700" C., a t which little reaction occurs in the absence of a catalyst; the catalyst was maintained a t 700", 800", or 900" C.; the steam ratio was 22; and the space velocity was 210 hour-'. The exit gases were cooled quickly to temperatures ranging from 225 to 400' C. a t a point about 6 mm. downstream from the catalyst; the products then were cooled slo~vlyto 0' C. in the usual traps (Figure 1). When the gases leaving the catalyst bed were cooled quickly to about 225" C., the proportion of the oxidized phosphorus present as phosphorous acid increased from about 7.1 to 9.5% as the catalyst temperature was increased from 700' to 900" C. On slow cooling from t'he same temperatures (Table IV), however, the acid contained only 1.3 and 4.97, phosphorus as phosphorous acid, respectively. When the gases leaving the catalyst bed were quenched to about 400" C., however, the phosphorous acid content of the condensed acid mas about the same as when the usual slow cooling was imposed. In previous experiments, interpolated from Figure 3, with a space velocity of 9500 hour-' and a cat,alyst temperature of 700 C., the acid product cont~ainedphosphorous acid equivalent to about 6.87, of the total phosphorus in the acid. The phosphorous acid content of the product's obtained with drastic quenching is similar to that obtained a t high space
TABLE
IT. EFFECTO F TEXPERCTURE
ON ACTIVITY O F
SUPPORTED PL.4TINVX CATALYST (Tests made in porcelain reaction vessel with nitrogen ai: carrier gas; steam ratio, 22; space velocity, 640 hour-') Analysis of Products P in acid Temp., PHI in Hz, P1 c. vol. % as HsPOa, % Oxidized. c/'o 650 700 750 800 850 900
0.0 Trace 0.1 0.2 0.1 0.7
1.2 1.3 2.0 2.7 3.9 4.9
76.4 99.7 99.8 99.5 99.2 97.4
OF SPACEVELOCITY ON ACTIVITYOF TABLE V. EFFECT SUPPORTED PLATINUM CATALYST
(Tests made a t 700' C. in porcelain reaction vessel with nitrogen a? carrier gas; steam ratio, 22) Bnalysis of Products Space Velocity, PHs in Hz, P in acid Pa vol. % as H ~ P O J% , Oxidized, % Hour -1 640 1,275 2,550 3,250 3,800 4,400 5,100 5,800 6,400 7,000 9,500 12,750
Trare Trace 0.1
Trace 0.1 0.1 0.1 0.2 0.2 0.2 0.3 0.9
1.3 2.4 2.5 2.8 3.2 3.8 4.3 4.5 5.2 5.0 5.5 8.9
99.7 99.9 99.4 99.3 99.8 99.8 99.7 99.5 99.4 99.5 99.2 97.8
August 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
1613
The results of the quenching experiments show that the oxidation of phosphorus with steam comprises a t least two steps; in the first step the phosphorus is oxidized to the trivalent state, and in the last step it is oxidized t o the pentavalent state. The first step is accelerated by the catalysts used in the study, whereas the last step proceeds, although more slowly, without the aid of a catalyst. The data shaw that an equilibrium exists between the two stages of oxidation, and that the over-all reaction cannot go to completion under the conditions maintained in the catalyst bed. Equilibrium values were not determined in this study, but it was shown that the equilibrium shifted toward higher proportions of trivalent phosphorus with increase in temperature. Data obtained in tests in the secondary reactor showed that the last step of the over-all reaction can be carried nearly to completion by maintaining the products from the catalyst chamber at some temperature lower than that of the catalyst bed, preferably about 400 O C., for a few minutes. The process may be carried out in a system with a small catalyst bed and operated a t high space velocity if the products are allowed to remain for a sufficient period in a larger ohamber immediately afterwards. Catalyst beds in large scale installations probISTEAM a b l y should be PHOSPHORUS VAPOR IN operated a t tem1 kkq NITROGEN peratures of 650 ' to 800" C., with PORCELAIN-TOs t e a m r a t i o s beGLASS SEAL tween 16 and 30, LAGGING-4 I and with space velocities between 640 a n d 9500 hour-l with platinum catalysts, or b e t w e e n 640 and 2500 hour-' with copper or palladium catalysts. Purity of Produ c t s . Under the PER FORATED o p e r a t i n g conditions that probably would b e maintained in a large s c a l e installation, the phosphoric acid kTHERMOCOUPLE might contain 1 t o WELL 2%phosphorous TO CONDENSERS acid, and the hyFigure 4. Reaction Vessel for drogen might conQuenching Tests t a i n a b o u t 0.2% DhosDhine. SuDerTABLE VI. EFFECT OF STEAM RATIOON ACTIVITY OF SUPPORTED phosphates were prepared with phosphoric acids in which as much PLATINUM CATALYST as 5.9% of the phosphorus was present as phosphorous acid, and (Tests made i n porcelain reaction vessel with nitrogen as carrier gas: space these fertilizers showed no evidence of toxicity to plants in greenvelocity varied inversely with steam ratio-for example, the space velocities corresponding to steam ratios of 15 and 30 were 750 and 660, respectivelv) house tests. If the hydrogen is to be used in the manufacture Analysis of Products of ammonia, it should be freed of phosphine, because concentraPHs in Hz, Steam P in acid Temp. P4 vol. % tions as low as 0.005% (2 mg. per cubic foot) poison the waterRatio c. as HsPOa, % Oxidized, % 0.0 20.3 650 1.2 75.4 gas conversion catalyst used in ammonia plants. 0.0 29.7 650 0 5 98.3 Removing Phosphine from Hydrogen. A search was made for 78.0 Trace 650 0.4 99.9+ 14.3 0.5 700 2.3 98.5 a suitable method of removing phosphine from hydrogen-phos21.9 Trace 1.3 700 99.7 Trace 29.4 0 6 700 99.9+ phine mixtures. It was assumed that a commercial process in 15.1 0.8 3.1 750 97.5 which phosphorus is oxidized with steam would operate under 21.3 0.1 2 0 750 99.8 27.1 Trace 1.3 750 99.8 conditions that would yield concentrated phosphoric acid. The 15.2 1.3 800 87 2 4.4 0.2 21.4 800 2.7 99:5 operation would then entail acid condenser temperatures of 200 Trace 31.7 1.7 800 99.9+ 1.7 to 300" C. A study was made of the catalytic steam-oxidation 5.8 14.7 850 94.1 0.1 23.6 3.9 850 99.2 of phosphine in nitrogen, in nitrogen-carbon monoxide mixtures, 0.1 30.5 850 2.8 99.8 2.0 15.1 7.1 900 93.2 and in hydrogen a t 200°, 300°, and 400" C. The catalyst was 0.7 21.8 4.9 900 97.4 0.2 29.7 copper or platinum supported on zirconium pyrophosphate. The 4.2 900 99.4 unoxidized phosphine was determined by scrubbing the exit gas
E
'
velocity, whereas the acid obtained by slow cooling c o n t a i n s about as much phosphorous acid as acid obtained by moderate quenching. To determine the effects on the over-all reaction of the temperature and time of retention of the reaction products leaving the catalyst, experiments were made in an apparatus having a secondary reaction chamber inserted between the c a t a1y s t Figure 3. Effect of Space Velocity c h a m b e r a n d 'Onin Catalyst Bed on Proportion of PhosDhorous Acid in Acid Products densers. The secondary reactor was an e m p t y vessel having a volume about 120 times that of the catalyst chamber and provided with a heating element that permitted control of its temperature independently of other parts of the apparatus. The catalyst was operated a t 700" C. with a steam ratio of 22 and a space velocity of about 210 hour-'. On leaving the catalyst chamber, the products were cooled quickly to the temperature of the secondary reactor, held a t that temperature for various periods, and then cooled t o 0" C. By varying the amount of catalyst and the rate of gas flow in the apparatus simultaneously, the space velocity in the catalyst bed was held constant, but the time of retention of the reaction products in the secondary reactor was varied. The temperature of the secondary reactor was varied from 100' to 500' C. Since the acid components of the products were condensed largely in the secondary reactor, the actual time of retention in the reactor could not be measured. The results indicated, however, that a low rate of flow through the secondary reactor is required to obtain acid practically free from phosphorous acid and hydrogen practically free from phosphine. The temperature of the secondary reactor affected markedly the amount of phosphorous acid in the product. N7ith the longest retention time, a minimum phosphorous acid content, less than 1% of the acid product, was obtained a t a temperature of about 400' C. Under these conditions, the phosphine content of the hydrogen was about 0.2%, and it varied only slightly from this value with variation in temperature over the experimental range.
dr
1
-
-
1614
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE VII. Train Cnit
DISTRIBUTIOX OF PHOSPHORUS IX PRODWTS WHEP* P q WAS OXIDIZED Weight % of Initial Pr Appearing as Hap02 H3POa HaPOi
.
P4
P Hr
With Air in Presence of Steam a t 300" C .
With .4ir in Presence of Steam a t 700° C. 1
2 3 4
0.0 tr. 0.0
0.0 0.2 0.0
..
*.
0,4
0.2 0.1
..
80.7 17.6 0.6
..
..
.. ..
0.11
With .4ir a t 700' C. and Products Mixed with Steam a t 200' C.
with a solution of silver nitrate and analyzing the contents of the scrubber. T h e n the gas was passed over the catalyst a t 300" to 400" C., its phosphine content was reduced from initial values of 0.1 to 0.5% to less than 0.0003% (0.1 mg. per cubic foot). The gas mixture should contain about 1000 moles of steam per mole of phosphine, and the space velocity (total gas basis) should not exceed 2000 hour-'. The high ratio of steam to phosphine probably would be maintained in an installation in which an initial steamto-phosphorus ratio of about 20 was used, the acid condenser was operated to produce an acid containing a t least 75% PZO6,and t.he hydrogen entering the phosphine-removing catalyst contained not more than 0.2% phosphine. Another method of purifying the hydrogen was devised, whereby the impure hydrogen was mixed with the tail gas from a nitric acid plant and passed over a catalyst a t about 400 a C. The t,ail gas was a mixture of nitrogen, about 4% oxygen, and a small amount of oxides of nitrogen; both the tail gas and the hydrogen contained water vapor. The catalyst consisted of 5y0 copper suppxted on zirconium pyrophosphate. The oxides of nitrogen reacted completely with the phosphine when the impure hydrogen and the tail gas were mixed a t room temperature; passage of the mixture over the catalyst, a t 400" C. a t space velocities (tot'al gas basis) of 1800 to 3200 hour-'result,ed in substantially complete removal of both phosphine and oxygen. I t is postulated that the phosphine reacted with the oxygen and that the residual oxygen reacted with hydrogen. The large amount of steam present kep't the catalyst surface free of phosphorous acids. This method can be used for t,he direct preparation of a nitrogen-hydrogen mixture for use in the synthesis of ammonia. Effect of Carrier Gas. In most of this work, nitrogen was used for convenience to transport the phosphorus vapor into the reaction apparatus. On a large scale, however, it might be economically advantageous t o oxidize phosphorus with steam by t,reat,ing the gases directly from the electric phosphate-reduction furnace. Tests were made to determine whether carbon monoxide, a major constituent of gas from the electric furnace, would interfere wit,h either the reaction or the catalyst and to determine rvhether materials that catalyze the phosphorus-steam reaction would promote the water-gas conversion reaction.
GO
+ HzO --+ COz + Hz
(3)
Carbon monoxide slightly poisoned an aluminum met'aphosphate-supported platinum diphosphide catalyst, and t'he poisoning effect was not eliminated when nitrogen was used subsequently as the carrier gas. Only a small amount of carbon monoxide was oxidized. An aluminum metaphosphate-supported copper catalyst was subjected to intermittent 7-hour tests totaling 155 hours in which electric-furnace carbon monoxide was the carrier gas under the standard conditions for catalyst com-
Vol. 42, No. 8
parison. The activity of the catalyst remained unchanged, during the first 90 hours of operation, and more than 99.5% of the phosphorus was oxidized; it appears that carbon monoxide does not poison this catalyst. The activity of the catalyst decreased slowlv after 90 hours, however, and at the end of the test about 98% oxidation of the phosphorus was being obtained. The decrease in activity as the test progressed beyond 90 hours may have been due to depletion of copper in the catalj-st. None of the carbon monoxide was oxidized in these tests. The aluminum met,aphosphate-supported coppcr catalyst showed no decrease in activity when nitrogen that contained 1% by volume of hydrogen sulfide was used as t,he carrier gas. The use of hydrogen as a carrier gas for the phosphorus resulted in an increase in the phosphine and phosphorous acid contents of the products and lowered the over-all efficiency of the catalyst, b u t this probably was due to the mass-action effect of the hydrogen. I n subsequent tests with nitrogcn as the carrier gas, the catalyst exhibited its initial high activity. Comparison of Steam- and Air-Oxidation Processes. When phosphoric acid is produced commercially by oxidizing phosphorus Tvith air and hydrating t,he products with a water spray, a considerable amount of the acid is entrained as mist in the off-gas. The recovery of acid mist requires special equipment and close control of operations. In laboratory experiment,s it was observed that only a small part of the acid produced by the catalytic oxidation of phosphorus with steam was entrained as mist in the exit gases from the condenser. T o obtain data more directly comparable, the air-oxidation process was studied in the laboratory. A gaseous mixture of phosphorus and nitrogen that contained 6% Pa by volume was burned with 30% excess air, and the product was hydrated with 18 volumes of steam per initial volume of phosphorus under various conditions. The products leaving the reaction chamber were passed into a train that consisted, successively, of a trap a t 300" C., a trap a t -78" C., an electrostatic precipitat,or, and a bubble-type scrubber t,hat contained a 5% soIution of silver nitrate. The conditions imposed and the distribution of phosphorus in the products and in the separate units of t,he train are shown in Table VII. In the tests in which phosphorus was burned with air and the phosphorus oxides were subsequently hydrated, the usual fog of phosphoric acid was formed. Under similar conditions, however, the acid produced by the catalytic oxidation of phosphorus vapor with steam was condensed almost completely in simple apparatus a t 300" C. The data show also that the burning of the phosphorus vapor is incomplete, even with an excess of air, in the presence of steam a t 300" C. or in the absence of steam a t 700" C. Water assists in driving the over-all reaction to completion. The presence of measurable amounts of hypophosphorous acid in the products obtained by the oxidation of phosphorus with dry air indicates that the over-all oxidation reaction proceeds in several steps. Mechanism of Over-All Reaction. Brunauer and Shultz suggested that the oxidation of phosphorus with steam at 1000" to 1100" C. proceeds through two successive retictioris: P4
-
+ 8HnO +2P204 + 8112 + 2H2O + 2Hr
2P204
2P205
(4)
(5)
With steam rat,ios of 24 or more, they found that no elemental phosphorus remained in the gas; this indicates that reaction 4 is close to completion a t equilibrium. Reaction 5 was not complete and apparently not a t equilibrium, since calculations of the equilibrium constant from the experimental data gave variable values. Also, the ratio of Pz04 to PzOs tended to shift toward higher values as the steam ratio was increased, which appears contrary to the mass-action law. Emmett and Shultz ( l a ) showed that phosphorus can be oxidized completely with carbon dioxide a t 1000" C., but that an
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1950
equilibrium between PzOr and P206 is quickly established. They calculated the equilibrium constant for the reaction
Pzo4
+ coz = Pzo6 + co
(6)
at 1000 O C. to be 0.43. If the hypothesis of Brunauer and Shultz (5) is assumed t o be correct, one may combine the equilibrium constant for the reaction COz
+ Hz = CO + HzO
(7)
at 1000” C., calculated by Emmett and Shultz (13) to be 1.669, with that for reaction 6 and obtain an equilibrium constant of 0.253 for reaction 5 a t 1000° C. This value for the constant indicates that, a t equilibrium, more than 25% of the phosphorus in the acid obtained in the present study should have been present as phosphorous acid, whereas much smaller proportions were obtained. The data obtained in the experiments a t high space velocity, the experiments with quenching, and in the tests with the secondary reactor are inadequate for a determination of equilibrium values. They show, however, that an equilibrium exists between trivalent and pentavalent phosphorus compounds and that the equilibrium shifts toward higher percentages of the trivalent compounds as the temperature is increased, The fact t h a t the oxidation of the trivalent phosphoru‘s to the pentavalent state on cooling proceeds quite rapidly may explain why true equilibrium values were not obtained. The inconsistencies in the data of Brunauer and Shultz (5) probably can be ascribed to the same rapid reaction. The experimental data obtained in the present study are in accord with the hypothesis of Brunauer and Shultz (6) in that two, and probably three or more, steps are involved in the overall reaction. Consumption of the elemental phosphorus was substantially complete in many of the tests, and both hypophosphorous and phosphorous acids were found in the products. The experimental conditions imposed in this study are thermodynamically unfavorable for the formation of phosphine from the elements (44),and the presence of phosphine in the product of the phosphorus-steam reaction probably is due to a secondary reaction such as
4HsPOs +3H3POa
+ PHI
(8)
Reaction 8 occurs when phosphorous acid is heated (44). The data obtained in this study are inadequate for a determination of the mechanism of the catalyzed phosphorus-steam reaction, but they serve as a basis for certain reasonable postulates. It is postulated that the reaction is a heterogeneous one in which the metal catalyst takes part. A dynamic equilibrium probably exists in which phosphorus vapor reacts with the metal to form an activated unit of phosphorus, possibly Pz,which, in turn, reacts with water adsorbed on the catalyst or the support in juxtaposition to the phosphorus. The postulation of Pn as the activated unit of phosphorus produced by the catalyst is supported by the fact that the uncatalyzed phosphorus-steam reaction proceeds a t a measurable rate a t temperatures above 850” C., and a t these temperatures the thermal dissociation of P d into Pzis appreciable (40). Oxidation of phosphorus with air follows a different mechanism, for oxygen may be added directly to the P4 molecule. ACKNOWLEDGMENT
K. L. Elmore, chief of the research section, was responsible for initiation of this study and contributed much to its progress. Significant contributions were made by other members of the TVA staff, particularly C. M. Mason, A. D. Jones, and T. D. Farr, who made many of the thermodynamic calculations, and R. B. Burt, who supervised studies of the effect of phosphine on water-gas conversion catalysts. W. H. MacIntire of the University of Tennessee Agricultural Experiment Station, Knoxville, directed the greenhouse tests to determine the toxicity of phosphites to growing plant.1.
1615
LITERATURE CITED
Bichowsky, F. R., and Rossini, F. D., “Thermochemistry of Chemical Substances,” New York, Reinhold Publishing Corp., 1936. Biltz, W., Weibke, F., May, E., and Meisel, K., 2. anorg. u. allgem. Chem., 223, 12943 (1935). Bone, W. A,, and Wheeler, R. V., J . SOC.Chem. Ind. (London), 27, 10 (1908). Britzke, E. V., and Pestov, N. E., Trans. Sci. Inst. Fertilizers (U.S.S.R.), 59, 5-160 (1929). Brunauer, S., and Shults, J. F., IND.ENG.CHEM.,33, 828-32 (1941). Bushmakin, I. N., Ruisakov, M. V., and Frost, A. V., J . Applied Chem. (U.S.S.R.), 6, 577-87 (1933). Ibid., pp. 588-606. Compagnie nationale de matiPres colorantes et manufactures’ de produits chemiques du nord reunies (Etablissements Kuhlmann), French Patent 635,432 (June 2, 1927). Ibid., 635,501 (June 3, 1927). Dorsey, N. E., “Properties of Ordinary Water-Substance,’’ Kew York, Reinhold Publishing Corp., 1940. Elmore, K. L., Mason, C. M., and Christensen, J. H., J . Am. Chem. SOC.,68, 2528-32 (1946). Emmett, P. H., and Shultz, J. F., IND. ENG.CHEM.,31, 105-11 (1939). Emmett, P. H., and Shultz, J. F., J . Am. Chem. SOC.,55, 1390-5 (1933). Hein, L. B., Megar, G. H., and Striplin, M. M., Jr., IND.ENC. CHEM.,42, 1616 (1950). Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” pp. 560-70, New York, John Wiley & Sons, 1929. I. G. Farbenindustrie A.-G. (Gustav Wietzel, Ferdinand Haubach, and Rudolf Hiittner, inventors), German Patent 485.068 (Aue. 16.1928). Ipatiev, V.‘ N.- (to Bayerische Stickstoff-werke A.-G.), U. 8. Patent 1,848,295 (March 8, 1932). Ipatiev, V. N., and Freitag, C., U. S. Patent 1,895,329 (Jan. 24, 1933). Ipatiev, V. N., and Freitag, C., Z . anorg. u. allgem. Chem., 215, 388-414 (1933). Kelley, K. K., U. 8. Bur. Mines, Bull. 371. Ibid., 383. Ibid., 434. Liljenroth, F. G., British Patent 252,952 (Sept. 22, 1925). Liljenroth, F. G., Canadian Patent 231,570 (June 5, 1923). Ibid., 247,164 (Feb. 24, 1925). Liljenroth, F. G., French Patent 508,901 (April 24, 1923). Ibid., 565,471 (April 29, 1924). Ibid., 595,987 (March 31, 1925). Liljenroth, F. G., German Patent 406,411 (April 24, 1923). Ibid.. 409.344 (Ami1 23. 1924). Liljenroth, F. G.- (to Phosphorus Hydrogen Co.), U. S. Patent 1,594,372 (Aug. 3, 1926). Liljenroth, F. G., and Larsson, M., Canadian Patent 246,431 (Jan. 27,1925). Lilienroth. F. G.. and Larsson. M.. (to PhosDhorus Hydrogen bo.), U: S. Patent 1,605,960 (NoV.‘9, 1926): Ibid., 1,673,691 (June 12, 1928). MacRae, D., and Van Voorhis, C. C., J . Am. Chem. SOC.,43, 547-53 (1921). Miner. C. G. (to Phosohorus Hydrogen Co.), U. S. Patent 1,686,873 (Oct. 9, 1928). Smits, A., and Bokhorst, S. C., Proc. Acad. Sci. Amsterdam, 18, 106-16 (1915). Stephenson, C. C., J . Am. Chem. SOC.,66, 1436-7 (1944). Stevenson, D. P., and Yost. D. M., J . Chem. Phvs., 9, 403-8 (1941). Stock, A,, Gibson, G. E., and Stamm, E., Ber., 45, 3527-39 (1912). EKG.CHEM.,21,389-90 (1929). Thompson, J. G., IND. Volkov, V. L., and Ginstling, A. M., J . Chem. I d . (U.S.S.K.), 13,987-91 (1936). Wolf, L., and Jung, UT., 2. anorg. U. allgem. Chem., 201, 337-46 (1931). Yost, D. M., and Russell, H., Jr., “Systematic Inorganic Chemistry,” p. 199, New York, Prentice-Hall, Inc., 1944. Young, F. E., and Hildebrand, J. H., J . Am. Chem. SOC.,64, 839-40 (1942). Zawadzki, J., and Borucki, T., PrzemusE Chem., 15, 76-82 (1931). RECEIVED August 13, 1949. Presented before the Division of Physical and Inorganic Chemistry at the 116th 34eeting of the .khrsn~cAr CHEMICAL SOCIETY, Atlantic City, N. J.
