December 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
A pilot plant with an extractor capacity of 680 cubic feet per charge has been erected for the purpose of extracting ponderosa, sugar, and Idaho white pine lumber, stumps, and other western pine forest and mill wood waste with solvents to determine whether such extraction processes are practical on a commercial basis. ACKNOWLEDGMENT
The author is indebted t o Carl Rasmussen, George Schroeder, C. V. Zaager, George I. Garin, and Ernest Kolbe for collecting the samples and to Albert Hermann for comments and suggestions.
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LITERATURE CITED (1) Anderson, IND.ENG.CHEX.,36, 662 (1944) ( 2 ) Ibid., 38, 450 (1946). (3) Ibid., 38, 759 (1946). (4) Betts, U. S.Forest Service, Bull. 116 (1912;. (5) Bray, Paper T r a d e J . , 115, N o . 10, 2 (1942). (6) Georgi, Ibid., 100,No. 12, TAPPI See. 156-8 (1935). (7) Humphrey, IND. ENG.CHEM.,35, 1063 (1943). (8) Kurth, ISD. ENG.CHEM.,- 4 s ~ED., ~ . 11, 203 (1939). (9) Schorger, E. S. Forest Service, Bull. 119 (1913). (10) Wise, "Wood Chemistry," B.C.S. Monograph 97, pp 563-4, New York, Reinhold Publishing Corp., 1!244. RECEIVEDJune 10, 1946
Acid Pyro- and Metaphosphates Produced bv Thermal Decomposition of Monocalcium Phosphite J
W. L. HILL, S. B. HENDRICKS, E. J . FOX, AND J . G. CADY Dizrision of Soils, Fertilizers, and Irrigation, U . S . Department of Agriculture, Beltsville, M d .
Information o n the products formed by heating monocalcium phosphate a t temperatures below- 600' C. has a practical significance in connection with t h e thermal treatmeut of superphosphate to produce mineral feed of low fluorine content. 3lonocalcium phosphate monohydrate is known to undergo partial fusion when it is heated rapid? i n t h e open a t 150' to 200' C., and t h e resultant mixture is converted to stable 8-calcium metaphosphate a t 600" to 700" C. Fusion can be avoided bq first heating the charge a t 125' to expel water of crystallization, b u t further heating in the range 200' to 600" yields a n unpredictable mixture of phases, consisting of glasslike amorphous material and one or more of a t least three crjstalline phases. O n t h e other hand, t h e anhydrous salt, obtained either by drying t h e hydrate or by crjstallization from solution, readily loses water in an
atmosphere of steam a t 275" to 300' C. arid changes smoothly into calcium acid pyrophosphate with the formation of little or no amorphous material. A n es*entiall) pure amorphous material can be prepared by heating extremely thin flakes of monocalcium phosphate monohydrate., A t 325' to 350" in steam crystalliue acid pyrophosphate is converted into a mixture of two crystalline compounds with more or less amorphous material. The latter, soluble in water, can be leached from insoluble crystalline compounds. One of these compouuds is tetracalcium dihydrogen hexaphosphate; t h e other, y-calcium metaphosphate. Formation of another cr)stalline nietaphosphate from calcium acid pyrophosphate is enhanced b y t h e presence of sulfate. This modification is structurally similar to, and apparently forms a solid solution w ith, anhydrous calcium sulfate (anhydrite).
P
to which free acid was removed and represent, respectively, ( a ) material separated from mother liquor with the aid of a porcelainbasket centrifuge, suspended in acetone and centrifuged again, ( b ) the same after two suspensions in acetone with intervening centrifugation, and ( c ) the same after four similar Kashings with acetone. Sometimes monocalcium phosphate monohydrate c r i stallizes in extremely thin flakes which, being undesirable for most puiposes in commercial practice, are customarily discarded or redissolved. One crop of crystals (No. 2 ) obtained in the laboratory showed unusual uniformity in this respect and was included in the study. When this fluffy material R & S found t o change completely into the amorphous state at 300' C., conditions for its ready preparation were successfully worked out. Several lots of fluffy monocalcium phosphate that yielded good amorphous material were prepared by heating 500 ml. of 45% phosphoric acid and 200 grams of monocalcium phosphate monohydrate in a covered beaker in an oven a t 110" C. until the solution was saturated, decanting the clear hot solution into a 600ml. beaker, and allowing it to cool in air. The crust that formed a t the surface as the solution cooled was broken up by occasional gentle stirring until presently the solution turned rapidly to a
R O D C C T I O S of feed-grade phosphate by thermal defluorination of superphosphate has raised questions about compounds formed from monocalcium phosphate when it is heated alone or in the presence of calcium sulfate (4). The reactions involve loss of water Kith formation of such compounds as calcium acid pyrophosphate, CaH,P?O,, and calcium metaphosphates. As the temperature is increased pgro- and orthophosphates can be formed with accompanying loss of sulfur trioxide when calcium sulfate is present. Preliminary attempts to identify the compounds in laboratory and commerical preparations indicated a complexity to the reactions that is generally characteristic of metaphosphate salts. Further work reported here was undertaken t o obtain reliable information on the compounds that may be formed from monocalcium phosphate. Several monocalcium phosphates from various sources, thought to be typical of both laboratory and commercial food-grade preparations, were used as starting materials. These materials (Table I ) differ with respect to the nature and amounts of impurities, crystal habit, and compounds produced upon heating. The laboratory preparations v w e crystallized from aqueous phosphoric acid solutions essentially as described in a previous article (8). Materials Xo. l a , Ib, and I Cdiffer only in the extent
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 39, No. 12
ges of partially dehydrated materials, such as anhydrous monocalcium p h o s p h a t e a n d Free Acid Total Total calcium acid pyrophosphate. p 2 ~ p ,p ) 2 ~ 1C, ~ O , ma, E'. SarO[IGO1. HzOh. Tutal Prepn. 0 KO. l'repd. Character of Crystals '2 c% ,o Q 7c % "c were placed in the dry furnace l a 111lab. Euhedral, thin plates, a t 200" C. and allowed to variable 3 . 3 7 54 39 19 91
