I N D U S T R I A L A N D E N G I N E E R I N G C H E 111 I S T R Y
376
I n the leach liquor from the autoclave the mole ratio of KzO to NazO is 0.425, and of COOto Clz is 4.5, so that the concentration of potassium carbonate in the final carbonate brine is very satisfactory, The flow sheet of Figure 3 falls short of realizing the maximum economic benefit because it produces a valuable saltnamely, sodium carbonate monohydrate (Na2C03HzO)and then debases it to almost nothing in value by redissolving it in the brine and circulating it back into the autoclave. SODA WELL WATEL
I
n
-1
PPtLlMlt4AF.Y CONCLHTKATIHG EVAPORATOK
LEACHING
I
SECONDAPY
SALTING-OUT
RETUPN CPYVALLILER
SOLU~ION
C A R B O N N E SOLUTION
To
pOTCSH
PLAHT
WYOMINGITE AXD RIVERSODA WELLWATER
Obviously, good plant management would demand that this slat should be removed if possible from the cycle and sold as such, or worked up into other salable compounds of sodium, such as soda ash, caustic soda, and trisodium phosphate. The flow sheet of Figure 4 has been designed with this end in view. I n Figure 4 all of the sodium carbonate monohydrate is removed from the cycle, and all of the sodium for base exchange is furnished by the soda brine which .is first concentrated so as to promote efficiency in the use of the autoclave space. There are two evaporator and two crystallizer steps-the primary and secondary. In the primary evaporator, sodium carbonate monohydrate is salted out, and pure potassium chloride is salted out in the primary crystallizer. The mother liquor from the primary crystallizer goes to the secondary evaporator where more sodium carbonate monohydrate is salted out. The secondary crystallizer produces more potassium chloride, and 80 per cent of the mother liquor from the secondary crystallizer is circulated back through the secondary evaporator. The recirculation in the
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secondary evaporator is necessary to increase the mole ratios of KzO to KazO and of COS to Clz in the final potassium carbonate brine to values substantially the same as those obtained in Figure 3 . In practice, as much sodium carbonate monohydrate will be diverted as it is possible to sell, and Figures 3 and 4 can be combined in any ratio desired, so that either none, or any part, or all the sodium carbonate monohydrate may be diverted for sale. If the latter is considered as a by-product of the mocess. Dotash beinn the main Droduct, the elastic con&ol of its Goduction s extremely favorable to its profitable sale. If all of the sodium carbonate is returned in circulation to the autoclave, about 20 per cent of the total KzO is produced as the chloride, the balance as the carbonate. If all of the sodium carbonate is removed, these percentages become 60 per cent for the chloride and 40 per cent for the carbonate. I n the latter case about 2.5 tons of equivalent soda ash (58 per cent KazO) are produced per ton of KzO. In Figure 4 only a small part of the water is e v a p o r a t e d in the secondary evaporators. These may be looked upon as regulators demanded by the phase rule relations to reduce the contents of sodium and chlorine in the final potassium carbonate brine. Both flow sheets (Figures 3 and 4) p r o d u c e pure crystals of potassium chloride and a strong brine c o n s i s t i n g principally of potassium carbonate with some sodium carbonate and only a small amount of chlorine. This potassium carbonate brine is pure enough to be utilized directly for production of f e r t i l i z e r c h e m i c a l s . By merely introducing requisite a m o u n t s of the respective acids, solutions of the sulfate, nitrate, or phosphate are immediately produced.
ECONOMIC ESTIMATES A cost estimate has been made which shows that 62 per cent potassium chloride can be produced in bulk a t Green River by the method of Figure 2 for a direct cost of $20.00 per net ton or $32.00 per net ton of contained KzO. The cost for producing KzOby the method of Figure 3 is estimated a t $25.60 per ton. If the method of Figure 4 is used, taking full advantage of the soda by-product and marketing the same in the Middle West, the cost of K20 would be reduced as low as 815.00 per net ton. These estimates do not include general overhead, selling expense, or fixed charges on the capital employed.
LITERATURE CITED (1) Blasdale, J . IND. ENQ.CHEW, 10, 344 (1918). (2) Blasdale, J. Am. Chem. Soc., 45,2935 (1923). (3) Pike, IKD. ENG.CHEM.,25, 256 (1933).
IV. Manufacture of Monopotassium Phosphate
B
ECAUSE of the presence of large deposits of phosphate rock in the Rocky Mountain region near Green River the manufacture of monopotassium phosphate has great technical and economic importance, the more so, because of the excellent physical characteristics of this salt which is one of the least hygroscopic of the concentrated fertilizer chemicals (2), as well as being the most highly concentrated. Monopotassium phosphate has no water of crystallization, having the formula KH~POI. The pure salt contains 34.6 per cent KzO and 52.2 per cent Pz05,giving a total of 86.8
per cent total available and water-soluble plant food. From the standpoint of an optimum combination of physical properties and concentration, monopotassium phosphate has no equal among the concentrated fertilizer chemicals. A combination of ram materials and simple processes for its low cost production, has, therefore, considerable interest. The manufacture of monopotassium phosphate from both potassium chloride and the crude potassium carbonate brine which it is proposed to manufacture a t Green River will be discussed.
April, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
L~OXOPOTASSIUM PHOSPHATE FROM POTAS~IIX CHLORIDE AND PHOSPHORIC ACID Ross and Hazen of the United States Bureau of Soils propose to decompose potassium chloride with 51 50 per cent excess of phosphoric acid (1). Their process gives a mixture of nionopotassium phosphate and phosphoric acid. I n another patent they propose to neutralize the surplus phosphoric acid remaining in the product of the reaction with ammonia, giving a final product which is a mixture of monopotassium phosphate and monoammonium phosphate. The author experimented with the Ross and Hagen process on the laboratory and semi-commercial plant scale. Laboratory work demonstrated that, when commercial phosphoric acid containing small amounts of iron and alumina was employed, the sirupy mixture of monopotassium phosphate and phosphoric acid, which results after heating to drive off the hydrochloric acid, is not susceptible to filtration even after dilution with water. Filtration is evidently stopped by the presence of colloidal iron and aluminum phosphates, because, when pure phosphoric acid is employed, a filterable product is obtained. But a t best, filtration is not free enough to present a satisfactory industrial operation. It is necessary, therefore, in practice to introduce another base to neutralize the surplus phosphoric acid. Ammonia, if available, is convenient for this purpose. Other practical bases are lime rock and phosphate rock. If either of the latter is employed, there results a mixture of monopotassium and monocalcium phosphates, containing 65 to 70 per cent total available plant food, and less than 20 per cent K20. Objections to the Ross and Hazen process appear to be: (1) Difficulties of filtration unless a base is used t o neutralize the excess acid. This objection might be minimized by the use of a pure grade of acid such as might be obtained from an electric furnace or from the burning of phosphorus, but at best the filtering problem presents difficulties. (2) Difficulties in the way of the design of a suitable furnace. (3) The slowness of the reaction at the low temperature which must not be exceeded if the formation of insoluble metaphosphates is to be avoided. hfANUFACTURE
O F ?dONOPOTASSIUM
PHOSPHATE BY
BASICh/IETHOD -4practical method has been developed which completely removes all of these objections. The general idea of the new method is to approach the manufacture of monopotassium phosphate from the basic rather than from the acid side. If one mole of phosphoric acid is mixed with three moles of potassium chloride and heated to about 700" C'. (1292" F.), only about one-third of the hydrochloric acid is driven off, and a sticky, unmanageable product results which has no value. But, if the following mixture is employed: 2.8 mole KC1 1 mole Hap04 0.9 mole H2SO4 it may be heated to about 750" C. (1382" F.) in a rotating or reverberatory type of furnace of usual design lined with fire brick, and a t this temperature all of the hydrochloric acid is quickly eliminated and the mass is liquid. At this stage of the reaction, coal is thrown into the furnace and the temperature raised to 850' C. (1562" F.). The coal quicLly eliminates the sulfur as sulfur dioxide. The material is then removed from the furnace. When allowed to cool, it is a blackishappearing clinker which deliquesces in air. I n solution it is strongly alkaline. I n preparing commercial monopotassium phosphate, a solution is made of the clinker which is then filtered free from coal and coal ash. Crude phosphoric acid is added to this solution until its pH lies between 4.4 and 6.0. Within these limits the entire solution, which will alway, contain a precipitate of iron and aluminum phosphates unless pure phosphoric acid is used, may be run to dryness without filtcation or crystallization, in suitable drying apparatus,
+
+
f
377
yielding a stable, nonhygroscopic, granular product which is mainly monopotassium phosphate. For many years trisodium phosphate has been made by the Strickler process ( 3 ) . The furnace step in the process just described may be carried out in furnaces of the same type used in the Strickler process. hlonopotassium phosphate of high concentration is made by the new process, and no other base is required. The process may be employed t o particular advantage in localities where sulfuric acid is cheap; this would be the case a t Green River. MANUF.4CTURE O F h1ONOPOTASSIUM PHOSPHATE FROM GREENRIVERPOTAssIChl CARBOXATE BRIKE By adding crude phosphoric acid to the potassium carbonate brine which it is proposed to produce a t Green River until the pH of the solution lies between 4.4 and 6.0, the entire solution can be run to dryness with production of a crude monopotassium phosphate. The material thus produced will contain a little soda, and on this account will not be quite as high grade a product as that made from potassium chloride. Each 100 pounds of solids in this brine will be made up about as follows: Lb. 1.95 77.00 16.65
If this brine is brought to a pH of about 5.5 with crude phosphoric acid and the slurry run to dryness, a granular, nonhygroscopic product is produced having about the following composition: 7c
70
70
50.00 C1 0.40 A1203 2 . ooa KlO 29.0 sos 1.70a Fen03 0.70y NalO 5.80 a These constituents result from usmg phosphoric acid made by the sulfuric acid method; they will be absent if blast furnace acid is used.
PzO~
+
In this analysis the ratio of (K20 SazO) to PZOSis greater than it would be if only the monobasic salt were present, because the pH is so controlled that from 5 to 10 per cent of the total alkali present goes to form dibasic phosphates. When the alkaline process described is employed for making crude monopotassium phosphate from potassium chloride and phosphoric acid, the analysis is substantially the same as above, except that the KazO content will be almost eliminated and the K20increased to about 33 per cent. CONCLUSIOKS Monopotassium phosphate can be made a t Green River a t a low cost because of the near availability of all of the necessary raw materials. The phosphoric acid will be obtained from the phosphate rock of southeastern Idaho. This can be produced by the sulfuric acid method, the sulfuric acid being made from sulfur obtained in Utah; but it is more promising to produce it by volatilization with wyomingite as the furnace flux and utilization of the cheap coal of the Rock Springs region as the fuel for the blast furnace. I n this way about one-third of the potash of monopotassium phosphate is obtained as a by-product a t no additional cost. The remainder of the potash is obtained from Wyomingite, either as the chloride or the carbonate by base exchange with sodium. Sodium salts suitable for base exchange are obtainable either from the carbonate brine of Green River or from Great Salt Lake. The latter presents a known inexhaustible supply of common salt, whereas the soda brine, while possessing great advantages, is not positively known to exist in very large amounts, although there is likelihood of such being the case. Therefore, it is conservative to count upon using potassium chloride, made from wyomingite by base exchange with salt from Great Salt Lake, as the source of potash for supplying the
378
INDUSTRIAL AND ENGINEERING CHEMISTRY
deficiency of potash in the phosphoric acid made by volatilization, in the manufacture of monopotassium phosphate. A simple process for effecting the combination between phosphoric acid and potassium chloride has been developed which produces an almost pure grade of monopotassium phosphate containing over 80 per cent total available plant food. It is believed that this salt can be profitably marketed in the Middle West, on the Pacific Coast, in the export trade and possibly under favorable conditions throughout the entire United States. It would also seem that the growing demand
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for fertilizers from the Middle West is a factor which favorably affects the prospects of the proposed industry a t Green River. LITERATURE CITED (1) Ross, IT. H., and Haaen, T.,U. S. Patent 1,486,851 (1923). (2) Ross, W.H., hlehring, A. L., and Merz, .4. R., IND.ENQ.CHEX., 19, 211 (1927). (3) Strickler, U. S. Patent 1,037,837 (1912).
RECEIVED August 3, 1932
Manufacture of Printing Ink WOODFORD F. HARRISON The California I n k Company, Inc., San Francisco, Calif.
T
HE printing ink industry, small and almost unknown, is entirely dependent on its parent, the printing industry. Rapid developments in printing machinery have necessitated like progress in ink making, such machinery modifications often having been devised with little regard to ink problems. Originally, pressmen made their own inksconcoctions of pigments and oils, which were simple in comparison with the carefully controlled products of today which are formulated with the precision that is essential for the modern high-production press. The many kinds of printing presses and paper and the innumerable uses for printed materials have made ink manufacture a variety business as well as largely a specialty business. Printing processes can in general be classified under three headings: typographic, or printing from surfaces in relief; lithographic, or printing from plane surfaces; and intaglio, including gravure processes and engraving, steel die, etc. This seems simple for the ink maker, and would be so, were it not true that each of the above classifications is extremely general and includes printing by numerous processes using many kinds of press mechanisms. Again calling attention to the huge variety of papers and other materials on which printing is done, and to the many purposes for which printed materials are to be used, it becomes clear that these factors, coupled with the many printing processes, necessitate a multiplicity of modifications in ink formulation. It is not within the scope of this paper to explain in detail the various printing processes, but a cursory description of the principal ones will aid in providing a clear understanding of the printing ink manufacturer’s problems. Printing from surfaces in relief is so common that it need only be mentioned. Practically all small job printing is so done. There is a great variety of printing presses using this principle, and it is adaptable for almost any printing purpose. Under printing from plane surfaces comes the important lithograph process. Modern lithography is usually done from specially grained zinc or aluminum plates. The design on the plate is not in relief but is simply prepared to make it accept ink while the surrounding area of grained plate is wettable by water and not by ink. Thus the inking process applies ink to the design but not to the surrounding area, whereas this specially grained and water-adsorptive surrounding area is wet with water from damping rolls that have no power to wet the design. In general there are two types of lithography: direct, in which printing is directly from plates to paper; and offset, in which a rubber blanket first contacts the plate and then the paper. Offset lithography has practically displaced direct. Under printing from below the surface, come the
popular rotogravure processes. The design is etched into a copper cylinder. The cylinder revolves in a fountain of ink, and the excess is scraped off. The paper literally absorbs ink from depressions in the cylinder, as i t is brought into close contact by the impression cylinder. The ink sets initially by absorption. and is finally dried by evaporation of solvents as the paper passes over a steam-heated drum. XEEDFOR RESEARCH IN INKMAKIKG Although printing ink manufacture is essentially a chemical industry, it is only recently that the chemist has had an opportunity to organize properly the ink experience of many years past and to build a scientific foundation of fundamental information. The ink maker of today still employs many materials simply by rule-of-thumb; good scientific reasons for their uses are not always known. To be more explicit, lithographic inks have practically always been made of pigment, oxidizable oils (chiefly linseed oils), driers, and possibly waxy materials. The pigment is ground into heatpolymerized oils to obtain an ink of proper consistency which is considerably more viscous and plastic than an enamel paint. It is known by experience that the correct combination of pigment, viscous polymerized oils, and drier will work reasonably well on a lithographic press; that is, it will distribute properly on inking rolls, take readily on the lithographic plate without adhering to the dampened portion of the plate, transfer sharply to the rubber blanket and then likewise to the paper or other material being printed. After being so printed it must dry with the desired finish in proper time, and perhaps take well over other colors, or accept other inks afterwards, or both. The adjustment of the ink to do all of these things was a t one time accomplished by purely rule-of-thumb methods. It may always have been common sense to avoid use of a vehicle that can emulsify readily with water or the water solutions used on lithographic damping rolls. The ink chemist, however, is thinking of the picture as one largely influenced by surface tension of vehicle and interfacial tension between vehicle and water, between pigment and water, and between pigment and vehicle. Exploration of such fields not only provides a better understanding of the functions of the materials used, but also brings to light untried materials having more favorable properties than those now in use. Methods developed in the past few years for measurement of preferential wetting of pigments by liquids and of adhesion tension are of great value in contributing toward a better understanding of ink formulation. These are tools with which the printing-ink research chemist must become more familiar.
