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Filtrates from Modified Starch Process
Colic111sions
Starch slurries are treated with acids and other chemicals to modify the physical-chemical characteristics of the starch for a large range of products. Some organic solubles are created, but over 50 per cent of the solids in the sewered filtrates are inorganic in nature and of little commercial importance. For several months during 1936 these filtrates were concentrated in a vacuum evaporator, and the solids were recovered which eliminated a population equivalent of over 4000 persons from the total factory effluent. The damage to the equipment caused by the chemicals present far exceeded expectations, and the practice had to be abandoned. -1bout 25 per cent. of this effluent is used for wetting coal and cinders at the power plant. Studies are in progress to alter the present manufacturing process.
Sources of pollution load of the seivered water from the Corn Products Refining Plant at Argo have been carefully analyzed, and their respective proportions of the total load have been evaluated. Developments leading to the curtailment of these sewered waste waters and the recovery of losses, where possible, in the remaining portion sewered, have been traced over the past two decades u p to the present time. The net result has been a reduction of pollution load from a total of 250,000 to 400,000 population equivalent per day to around 40,000, with a corresponding recovery of materials and products of sufficient economic importance to more than justify the cost of the improvement in operations. Experimental work has been given to indicate that it may be commercially possible to reduce this load still further.
Other Sources
Acknowledgment The direct cooperation of the Sanitary District Laboratories has helped to make many of the described innovations possible without resorting to methods involving sewage treatment where no recovery of materials or products could be attained.
A complete survey of the factory sewer system was made in 1935 to determine the origin of the 15,000populationequivalent unaccounted for in the total factory effluent. Samples were taken daily at each sampling station along the principal sewers, and the oxygen demand was determined. These results were watched closely for any sudden “shots” which would lead to a new source of process loss. Every opening in the sewer was traced back to its origin, a list prepared of all drains or outlets to the sewers, and each one investigated individually. It was found that material from careless process spills, due to drains being located too near tanks, pumps, presses, etc , was escaping to the sewer. Removing drains, changing equipment, and treating particularly bad effluents before sewering, such as the wash waters from washing machines for press cloths, reduced this pollution te a present range of 1000 to 2500 persons.
Literature Cited (1) Berlin, H., and Kerr, R. U’. ( t o International Patents Devclopment Corp.), U. S. Patent 1,918,812 (1933). (2) McCoy, R. (to International Patentr Development Corp.). Ibid., 2,126,568 (1938). (3) Mohlman, F. W., IND.ENG.CHEM.,18, 1076 (1926). (4) Mohlman, F. W., and Beck, A. J., Ibid., 21, 205 (1929). (5) Sjostrom, 0, Ibid., 3, 100 (1911) (6) Strain, H. H., J. Am. Chem. SOC.,57, 738 (1933). PRESENTED as part of the Symposium on t h e Utilization of Agricultural Wastes before t h e Division of Sgricultural Chemistry at the 99th Meeting of the iimerican Chemical Society, Cinrinnati, Ohio.
ALUMINA FLOC-
X-Ray Diffraction Study
H-ARRI- I). WEISER, W. 0. JIILLIG.Ah7,. .iND W. R. PURCELL T h e Rice Institute, Houston, Texas
RESHLY precipitated alumina gives an x-ray diffraction pattern consisting of broad bands or lines corresponding to y-A1203.H20or y-A100H (1). The gel precipitated from aluminum sulfate solution gives much broader diffraction bands of yA1z03.HzO than the gel from chloride or nitrate (8,s). This means that the crystal size of the particles in the gel from chloride is larger than in the gel from sulfate, and hence that the gel from sulfate possesses the greater adsorption capacity. Since the alumina floc made from aluminum sulfate is widely used in water purification, additional information concerning the composition of this gel is of interest. The purpose of this paper is to report the results obtained from a n x-ray diffraction study of the constitution of the alumina floc thrown down a t varying pH values from highly dilute solutions of aluminum sulfate such as are used in water purification.
F
Effect of pH with Various Precipitants An amount of A12(S01)3.18Hz0,equivalent to a concentration of 50 p. p. m. in 5000 ml., was diluted to 1 liter in a volumetric flask and transferred to a separatory funnel. Various amounts of a standard sodium hydroxide solution correspond-
ing to 60,80, 100, 120, a n d 140 per cent of the amount equivalent to the dlz(S04)3.18H20 mere diluted to 1 liter and transferred to a second separatory funnel mounted beside the first one. The two solutions were allowed to run together at a uniform rate into a glass jar containing 3 liters of water while the mixture was stirred rapidly.
FIGURE1.
TITRATION CURVES SULFATE
ALrJMrNmf
FOR
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DE
4.81 4.96
6.15
i
I a I I I
’
4.93
6.53
7.54
I
FIGURE2. X - R A ~DIFFRACTION PATPEENS FOR y-Aizos .Ha0 PaECIPITATED WlTU SODIUM HYnRoxrnE
The pH value of the solution was determined with a glass electrode after an arbitrary period of 30 minutes. Preliminary experiments showed that uniform mixing and equilibrium between the solution and glass electrode were obtained in a much shorter interval than 30 minutes. After the pH was measured, the stirrer was stopped and the alumina d l o w d to settle. After 24 hours the supernatant liquid was decanted, and the precipitate was washed four times with 200-ml. portions of distilled water, using a centrifuge, and dried in air a t room temperature. Additional series of samples were prepared by the same procedure using ammonium ,hydroxide, sodium carbonate, and sodium sulfide as preclpitants. The pH valuea are plotted against amount of precipitant in Figure 1. X-radiograms of the several ssmples were obtained with filtered CuIL x-radiation. The exposure time was 30 miuutes, using “No-screen” film. Figure 2 shows the x-radiograms of the samples precipitated with sodium hydroxide. Since the photographic reproductions of the hand patterns are much less satisfactory than the original negatives, diagrams made from examination of the original negatives are shown in Figure 3A. The x-radiograms show that the freshly formed alumina floc thrown down in the pH range from ahont 5 to S consists of small particles of y-A120a.Hz0, and there is no indication of the formation of a basic sulfate ( I ) . The primary particles vary in size from crystals so sma11 that the y-M1Oa.Hn0pattern consists of two or three broad bands, to crystals large enough (pH 7.5) to give very sharp hands. The gel prepared by adding 140 per cent of the equivalent amount of sodium hydroxide (pH 8) was transformed into a-Al10s.3H,0 during the time required for washing. This is in accord with the wnal behavior ory-A120s.H10 in contact with dilute alkali (4). The effect of pH on the primary crystal size of y-A120s.Hs0 with other precipitants is similar to that with sodium hydroxide. Diagrams of the x-ray ditrfaction patterns constructed from the original negatives, using ammonium hydroxide, sodium carbonate, and sodium sulfide as precipitants, are
4.62
4.62
P.74
5.11 6.39
6.71
-
F I G U3.~ DIAGKAMS OF X-RAYDIFFRACTION PAl”I’ERN8 FOR Y-A]zoa.HeO A. Precipitated with NsOH B. Precipitated with NH&W C . Precipitated with N&COCO, D. Precipitated with N d
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FZGURE 5. X-RAYDZFFUC~ON PATTERNS OF r-AlaOz.HsO AaEn FOR VARYINQ PERIODS
A.
Precipitated with NELOH at
&
pH of ahout G
range from about 5 to 8 are so small, their x-ray daraction pattern consists of hands which may make i t impossible to detect the possible presence of weak interference from another oxide hydrate or basic salt. Convincing evidence that the usual floc consists only of minute crystals of y-AlzOa.H20 is furnished by the electron diiTract i o n p a t t e r n of a floc t h r o w n down by ammonium hydroxide a t a pH of approximately 6 (Figure 4A). Unlike the x-ray diffraction pattern f o r t h e f l o c t h r o w n down a t this pH value, the electron diffraction pattern consists of sharp rings in the same position a8 the rings obtained from a standard y-ALOs.E~Owhich gives sharp x-ray interference rings (Figure 4B).
Wect of Time on Aging of Gel To determine the effect of aging of gel on the primary particle size, four samples were prepared exactly as described above except thst in each case 120 per cent of the equivalent amount of sodium hydroxide was employed. The wet unwashed gels were aged for 1,8, 16, and 24 hours, respectively, before washing, and particular care was taken to ensure a constant time for washing and drying the samples. X-radioprams of these samples showed a progressive increasein sharpness of bands for ssmples aged from 1 to 24 hours. Diagrams of the diffraction pattern constructed from the original negatives are given in Figure 5.
Effect of Aluminum Sulfate Concentration
To show the effect of dilution on primary particle size, samples were prepared as described above except that the concentration of DIFFFLACTION PATPEBNS FOR r-Al,Oa.H*O FIGWE 4. E~~ECLF~ON AI2(SO,)&3H2O was varied in nine steps from 4570 to 4.57 D. D. m., and an equivalent amount of sodrum hydroxide was used. Xradiograms were obtained of the samples from each conshown in Figure 3, B , C, and D . For the various precipitants, centrationexcept themostdiluteone,from whichaninsufficient the primary crystal size decreases in the follo\ring order: amount of precipitate was recovered. These x-radiograms sodium hydroxide, ammonium hydroxide, sodium carbonate, show a continuous but not marked decrease in primary parand sodium sulfide. tick size as the concentration of aluminum sulfate is increased Since the crystals of y-M2O1.H,Othrown down in the pH B. Standard @tern
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from 20 to 4570 p. p. m. The higher the dilution, the greater is the primary particle size in accord with the von Weimarn rule and with the expected decrease in the adsorption of sulfate ion as the concentration decreases.
Summary 1. Alumina floc consists of a hydrous mass of minute crystals of y-Al&.H& (y-A100H). This has been established by x-ray diffraction and electron diffraction studies. 2. The size of the primary crystals in the y-&O3.Hz0 floc increases with increasing pH value of the solution from which it separates. In alkaline solution the transformation of yA120a.Hz0to a-Al2O3.3H20is fairly rapid. 3. At a given pH value with different precipitants, the size of the primary crystals falls off in the order: sodium hydroxide, ammonium hydroxide, sodium carbonate, sodium sulfide. 4. The primary crystals of y-MZO3.H2Oshow a progressive increase in size on standing in contact with the mother liquor for periods of 1 to 24 hours. 5. Under otherwise constant conditions, the primary crystals of y-A120a.Hz0increase in size with decreasing concentration of aluminum sulfate, in accord with von M7eirnarn’s rule
VOL. 32, NO. 11
and with the expected decrease in adsorption of sulfate ion as t’he concentration decreases. 6. By suitable changes in the p H value, time of aging, and concentration of aluminum sulfate, the floc of r-A1203.Hz0 can be varied from primary crystals so small that the x-radiogram consists of two or three broad bands to primary erystals large enough to give well-defined lines. 7. The use of aluminum sulfate and sodium carbonate a t a pH value between 5.5 and 6.5 in the precipitation of the aluminum floc is favorable for the formation of the most highly dispersed crystals of y-&03.H20.
Literature Cited (1) Weiser, “Inorganic Colloid Chem.”, Vol. 11, pp. 97, 400, New York, John Wiley & Sons, 1935. (2) Weiser and Milligan, Chem. Rev., 25, 1 (1939). (3) Weiser and Milligan, Div. of Water, Sewage, and Sanitation Chem., Baltimore Meeting, A. C. S., April, 1939. (4) Weiser and Milligan, J . Phys. Chem., 38, 1175 (1934). PRESENTED before the Division of Water, Sewage, and Sanitation Chemistry at the 39th Meeting of t h e American Chemical Society, Cincinnati, Ohio.
Carbon Monoxide as an Inhibitor for Stainless Steel H . H. UHLIG
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass.
Stainless steel ordinarily corrodes in dilute hydrochloric acid with hydrogen evolution. Illuminating gas, because of its carbon monoxide content when passed through the acid, appreciably reduces such corrosion. The quantitative behavior of carbon monoxide as inhibitor in hydrochloric acid of various concentrations and temperatures is presented. Use is made particularly of electrochemical potential data to explain the mechanism of the inhibition.
I
iK A STUDY of the solution rates of 18 per cent chro-
mium-8 per cent nickel steel in dilute hydrochloric acid, using various gases above the acid, it was observed that illuminating gasinhibited the reaction of the acid with the steel. This was an unexpected result which deserved further investigation and explanation. Additional experiments were accordingly planned to determine the nature of the inhibitor in illuminating gas and, in addition, to learn the possible explanation for the effective action of this inhibitor in retarding corrosion. The original corrosion or solution rate experiments consisted in immersing strips of commercial 18-8, which had been cleaned in organic solvents and measured 12.7 X 2.5 X 0.36 cm. (5 X 1 x 0.14 inch), in 2.45 N hydrochloric acid at room temperature. The acid was contained in 500-cc. glass-stoppered bottles with greased stoppers, and the air dissolved in
the acid was displaced by either hydrogen, oxygen, nitrogen, or illuminating gas by bubbling the gas for some time through the acid. After 24 hours the specimen was removed from the bottle, washed in water and alcohol, dried, and weighed. The results are given in Table I. TABLEI. EFFECTOF GASATMOSPHERE ON RATEOF CORROSION OF STAINLESS STEELIN HYDROCHLORIC ACID Weight Loss of
Atmosphere Air oxygen Hydrogen Nitrogen Illuminating gas
18-8 in
2.45 N HC1, G./Sq. Dm./
Day 0.40 0.50
0.35 0.40
0.08
The behavior of the alloy steel in hydrochloric acid containing illuminating gas was markedly different from that in acid containing other gases. Experiments were next undertaken to determine the constituent of illuminating gas responsible for this inhibition. The first was an experiment in which illuminants and less volatile constituents were condensed out of illuminating gas in a solid carbon dioxide trap. The condensate added to the acid did not inhibit reaction with 18-8, whereas the gas residue was still effective. This left the possibility of hydrogen, methane, carbon monoxide, and any lesser constituents such as ammonia. Since hydrogen had already been run, i t was eliminated; ammonia, added as a salt in another experiment, was found to have no effect. Since methane is inert, carbon monoxide was left as the remaining substance probably responsible. Pure carbon mon-
