Yol. 23, No. 7
I.VDUSTRIAL AMD ENGINEERING CHEMIXTRY
800
connections. This flexibility of operation can be and is utilized to meet changing conditions. Variations in power cost due to altering minutiae of practice in liquid cooling are not important factors in the total cost of solid carbon dioxide delivered so long as proved principles of sound refrigerating engineering are not violated. Operating advantage and kilowatt-hours purchased per ton manufactured must eventually govern development of the art even though a t variance with the thermodynamic ideal based on studies in which perfect regulation and complete freedom from leakage losses are assumed. Presses
Similar considerations governed the selection of press eauiDment. Presses are four in number, vertical, with caststkeichambers tested to 375 pounds per square inch pressure. They turn out O‘ X ‘ O X loinches, which are sawed to 10-inch cubes to meet the demands of the current trade, which in appears to prefer this size* A press line is Figure 3. Conveyor and saw is shown in Figure 4. Here again has been the principle Of and it is believed that any known type of solid may be made or any known type Of practice without presses* Patent complications forbid description, but it may be stated that maximum capacity Of 2500 pounds Of Dry-1ce per press per hour has been attained when solid is formed by the solidification practice now employed.
on account of the regeneration or, more properly, preservation of crystalline structure of the stored product when a product of controlled quality is stored under proper conditions. The regenerator (Figure 5) has attracted some interest as the coldest structure of such large size in the world. It is approximately 40 feet in diameter by 80 feet high, and when filled loses considerably less than 0.1 per cent by weight of its contents daily through evaporation. Its design has naturally involved interesting problems of insulation, ventilation, structural design to minimize effects of thermal contraction, and mechanical handling under rather unfavorable conditions for lubrication and maintenance, etc. Patents have been solicited on many phases of this development. Marketing and Distribution
will no doubt Further advances in manufacturing take place. It should be stated, however, that in the past entirely too much emphasis has been placed on methods of manufacturing solid carbon dioxide cheaply, and not enough on the development of markets adequate to support units of economical size without sacrificing much or all of the saving by ~ow-cost manufacture in the expense of shipping the product considerable distances in search of a market, Sound marketing and distribution methods have been even more important than manufacturing processes in the liquefied carbon dioxide industry since its inception than fiftyyears ago, and nothing has yet appeared to indicate that this will not be equally true of the younger, solid carbon dioxide industry for some years to come,
Storage
Literature Cited
Finished cubes are bagged by hand (Figure 4), and either loaded into special cars for shipment or hoisted into topopening season storage structure or “regenerator,” so called
Chem. M e l . sa, 677 (1925) (1) (2) Reich, Ibrd., 58, 138 (1931). (3)Woodruff, IND.END. CHBMI. is, 1147 (1927).
Activated Bleaching Clays’ 0. Burghardt BADSALZELMEN, BEZIRK(MAQDEBURQ), GERMANY
LEACHING earth or clay is a decolorizing and clarification agent that is #much used in the oil industries for the bleaching of vegetable, animal, and mineral oils, fats, and waxes. There are two types of bleaching earths-the natural or fuller’s earth and the highly active, chemically processed earth. The former, which are obtained from selected raw material and have naturally a certain bleaching power, require only simple treatment in their preparation, such as drying of the raw earth and milling to the desired fineness. Only with material containing sand or stone is it necessary to introduce, before drying, the step of water-washing to settle out the impurities from the clayey substances, The second type, or chemically activated clays of high bleaching power, are produced by a process involving treatment with sulfuric acid or, preferably, hydrochloric acid. Such chemically treated material has an efficacy considerably greater than that of the natural bleaching earths. For this reason less bleaching agent is required for a desired degree of decolorizing and less oil is lost in the process, since a certain percentage of oil is retained in the earth after filtering. In order to operate most economically and reduce this oil loss
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Received January 14, 1931. Translated by Robert Calvert.
to a minimum, one uses advantageously the most highly activated earth possible. Such highly activated, chemically processed clays are produced principally in Germany, but because of their desirable properties they are being introduced rapidly into other lands where they are being used in increasing amounts. The industry is well developed in Germany for two reasons: First, it was here that the process of increasing the bleaching power through the use of mineral acids was discovered; second, there occurs in South Germany, in Bavaria, an earth especially suitable for this process, the so-called “Isartone.” Raw Material for Activation Treatment
This particular clay varies from green, yellow, to gray in color and occurs in layers of variable thickness. The clay stratum proper is generally quite clean and seldom contaminated by sand or limestone. The layers are of variable quality. They lie a t different depths, under 2 to 20 meters of overburden. A typical analysis follows: Moisture Ignition loss SiOz FeaOa
% 12.1 11.4 53.9 3.8
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Unfortunately, the usefulness of a raw clay for the activation process cannot be forecast from the appearance and the analysis. The writer has examined many samples that in these respects appeared the equal of Isartone but which, when treated and then tested with oils, showed not the slightest decolorizing power. It is much more important that the raw material shall show susceptibility to improvement of bleaching power by treatment with acids. For this reason a definite opinion as to the value of a raw clay can be given only after laboratory experiments simulating commercial activation and bleaching tests. The analysis of German raw clays shows it to be an aluminum hydrosilicate, with a fairly high percentage of bound (hydrate) water as indicated by the loss on ignition. This content of hydrate water in activated earths has a definite relation to bleaching power. For instance, if activated bleaching earths are heated above 400" C., they gradually give up the bound water with increasing temperature, and a t the same time the bleaching power diminishes correspondingly. It might therefore be concluded that the bleaching power of an earth depends on the percentage of bound water it contains, and that the raw earths with a high content of bound water are especially suitable for the production of highly active bleaching earths. This hypothesis, however, is unfortunately not confirmed by recent activation experiments. The author has recently had an opportunity to study the activation of foreign earths which were quite similar in analysis to the German clay and contained an astonishingly high percentage (15 to 18 per cent) of bound water. These activated clays showed almost no color removal on bleaching of various oils. It is very probable that clays suitable for activation occur also in other lands, since the geological prerequisites are there present to the same extent as in Germany. This assumption is supported by the author's discovery, during the past year, of clays in two other European countries that are equally as valuable as Isartone and from which highly active bleaching earths were made. No doubt North and South America, with their known clay deposits, contain clay suitable for activation. The accompanying diagram illustrates the schematic arrangement of the plant for producing highly activated bleaching earths. There are five steps, as follows: (1) preparing the slime, ( 2 ) activating, (3) filter-pressing, (4) drying, and ( 5 ) milling. Preparing the Slime
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Water is added to the moist raw clay to form a thick slime that may still be handled by means of a rotary pump ( 5 ) . The slimeproducing unit (3) is cylindrical and is provided with a belt-driven iron agitator of special construction suitable for rubbing up the undisintegrated lumps of clay. The raw material (1) is charged into the slime apparatus (3) by means of a self-gripping, movable crane ( 2 ) . The slime is pumped through a screen (4)to remove foreign matter and then into the reaction kettle ( 7 ) . Activation
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The raw slime is treated with acids in the reaction vessel ( 7 ) . After the mineral acid has been added, live steam a t 2 to 3 atmospheres is admitted through an acid-proof distributor and the charge is brought to boiling. The acid used is carefully measured in the vessel (6). Either sulfuric or hydrochloric acid, preferably the latter, is used. Although sulfuric acid gives as high bleaching power to the earth as hydrochloric acid, nearly all German plants use the latter because the former imparts to the clay filtration properties that are bad in oil refining. I n the hydrochloric
INDUSTRIAL AND EXGINEERING CHEMISTRY
802
acid process the boiling is conducted for 2 to 3 hours, whereas twice that time is required with sulfuric acid. The temperature of boiling is about 105' C. The optimum proportion of acid to clay varies with the nature of the raw clay and must be determined by laboratory test for each raw clay used. The use of too little or too much acid has marked effect on the bleaching power of the finished product. The proper amount of acid to be added depends on its concentration and on the dry weight of clay in the charge, With Isartone 28 to 30 per cent of hydrochloric acid is used, calculated as dry hydrogen chloride, on the weight of dry substance. Thus, for a day's output of 20 metric tons of finished clay, about 20 tons of technical hydrochloric acid of 19" to 21 O Baume would be used. The reaction vessel (7) is constructed of pine wood and has a capacity of 20 to 30 cubic meters. In such a vessel 2000 to 3000 kg. of dry substance can be activated in one batch. The wooden kettle is provided with strong steel hoops with tightening screws. On the cover are various accessoriesvalves, cocks, and dampers-for withdrawing acid vapors arising from the boiling and for the introduction of the hydrochloric acid, steam, and slime. The steam distributor in the vessel, as well as the other equipment, is coated with acidproof hard rubber. At the lowest point of the vessel is a cock through which the activated charge may be withdrawn to the sieve (8). A strong agitator of pine wood, driven by pulleys and a belt, keeps the contents thoroughly mixed during the activation. Filter-Pressing
When decomposition is complete, the acid sludge is pumped into the filter press (10) by means of a rotary pump (9) connected with a wooden frame sieve (8). When the press is filled at a pressure of 3 atmospheres, washing with fresh water is begun and continued until the free acid and dissolved salts are removed and the filter cakes are neutral. Since the cakes give up the last of the acid only slowly, a long time of washing, about 6 hours, is required. The filter presses used in the manufacture of bleaching earth are of pine wood2 and the thickness of the frame is not greater than 35 mm., since cakes of greater thickness cannot well be washed. The presses have not only provision for washing, but also hydraulic closure for large sizes. After the washing is completed, the press is opened and the cakes are removed from the frames and allowed to fall onto a conveyor which carries them to the drying equipment. Drying
A rotary kiln (12), which is provided with the modern cell installation that gives to the material several exposures for each turn, is used for drying the highly activated bleaching :The pine mentioned in this article is of the variety known in Germany a s pitch pine, which probably corresponds t o the hard pine in America.
1101. 23, No. 7
earth. A coke furnace (11) supplies the heat. The hot gases from this furnace are forced by a fan (13) through the rotary kiln in a direction parallel to the flow of material being dried. The dried activated earth is very soft and friable. There is therefore much dust in the kiln, which is carried out with the exhaust gases. In order to collect this valuable material, an electrical precipitator (14) is placed after the exhaust fan to deposit the dust in dry form. The dust flows out of the chamber (14) to a screw conveyor (15), at the end of which the dust falls through a pipe (22) and is proportioned into the milled finished product. The material comes from the drier in pieces about the size of hazelnuts. They fall from the lower end of the drier automatically into a screw conveyor (16), go then to the elevator (17) and the screw (18), and finally to the storage for dry material (19). Milling
From the storage dry material is brought to the mill in such quantity that a day's production can be undertaken without interruption to the drying and other connected operations. The mill (21) is of a high-speed hammer type, which pulverizes easily the soft material to a degree that is determined partly by the sieve plate selected for the mill. In general, bleaching earth for oil refineries or breweries is milled so that the residue on a 180-mesh screen is about 10 to 15 per cent. Finer grinding increases the bleaching power somewhat, but it has an unfavorable effect on the filtration properties. The material is fed to the mill by a continuous discharge mechanism (20). The resulting powder is withdrawn from below the mill by the screw conveyor (23) and then carried through the powder elevator (24) and the screw (25) to the storage (26). From this storage it is withdrawn by the packing screw (27) and filled into the sacks (28). The finished product is tested in the control laboratory for bleaching power, water content, percentage of acid, and fineness. Generally, bleaching power is tested with linseed or soybean oil. The amount of earth used in making the test varies from 3 to 6 per cent, according to the quality and color of the oil, and the time of bleaching is hour at 90-95" C. After the bleaching is finished, the oil is freed from the earth by filtering through paper. The color of the clear oil is determined with a colorimeter, usually with a Lovibond tintometer. Although the production of activated bleaching clays a p pears simple from the sketch and description, long years of experience and operating practice, as well as a broad knowledge of the necessary machines and apparatus, are required to produce an unobjectionable bleaching earth in a smoothly operating process.
Potash in 1930 Potash produced in the United States in 1930 amounted to 105,810 short tons of potassium salts equivalent to 61,270 short according t o the United States Bureau of Mines. tons of K20, Sales by producers amounted to 98,280 tons of potassium salts, with an equivalent of 56,610 tons of KzO, valued at $2,986,157 f. 0.b. plants. About 20,550 tons of potassium salts, with an available content of 10,800 tons of KaO, remained in producers' stocks December 31, 1930. The output decreased 2 per cent in gross weight with a decrease of less than 1 per cent of K10 content, The sales of salts decreased 3 per cent with a decrease of 1.6 per cent in KzO content. The total value of the sales decreased less than 1 per cent. More crude salts remained in the hands of producers a t the end of 1930 than a t the end of
1929. The production was chie5y from natural brines in California and distillery residue from molasses in Maryland. Alunite was shipped from Sulphur, Nevada, to California, ground, and sold as- fertilizer. The potassium salts imported for consumption into the United States in 1930 amounted t o 978,974 short tons, representing an increase of 5 per cent in gross weight over imports for 1929. Exports amounted to 1256 short tons of potassium compounds (not fertilizer), and 17,042 short tons of potash fertilizer material. These figures represent a decrease from 1929 of 17.5 per cent in quantity and 14.5 per cent in value for potassium salts (not fertilizer), and an increase of 10 per cent in both quantity and value of potash fertilizer material shipped.
