December, 1929
INDUSTRIAL A N D ENGINEERING CHEMISTRY
waste showed greater total acidities but lower H-ion concentrations than the corresponding effluents of the lownitrogen waste on storage for 2 days a t 20" C. This is due to the greater buffer action in the former. It is assumed that an effluent which will not develop an acidity greater than p H 7.0 on anaerobic storage for 2 dags at 20" C. may be safely added t o municipal sewage. Such effluents were produced by filtration of a 4 per cent skim milk through 3 feet, and 7 per cent skim milk through about 4.5 feet. Wastes containing the same quantities of lactose but considerably lower nitrogenous constituents required about 0.5 foot greater filter depths to yield a non-acid-developing effluent. Summary 1-The development of germicidal or inhibitory acidities due to the anaerobic decomposition of lactose 1s responsible for the disruption of the protein digestion activities of bacteria in septic and Imhoff tanks. 2-The activated sludge process has been shown to be capable of eliminating lactose and other acid-producing con-
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stituents from milk wastes, but the process is not considered feasible or economical for the average small creamery. 3-Trickling filters may be depended upon to oxidize lactose quickly. The upper 2 feet of an experimental lath filter effected reductions of over 90 per cent in lactose when receiving skim milk solutions containing from 1700 to 3250 p. p. m. of milk sugar. 4-Wastes (simulating cheese factory sewage) which contain a much lower proportion of nitrogen required about 0.5 to 1 foot greater filter depth to effect the same reductions of lactose as were obtained with skim milk solutions. 5-An effluent which remains neutral or alkaline on anaerobic storage will not interfere with septic action in municipal sewage plants. Such effluents were produced from a 4 per cent skim milk by filtration through 3 feet and from a 7 per cent skim milk by treatment on 4.5 feet of an experimental lath filter. Literature Cited (1) Levine, Burke, and Soppeland, Iowa Eng Expt Sta , Bull 68 (1923) (2) Levine and Soppeland, Ibzd , Bull 82 (1926)
Effect of Temperature upon Chrome Tanning' Henry B. Merrill and Howard Schroeder 'ORATIOK, M I I . W A V K U ~ Ei s, A. F. GALLUX&? Solis CORI
H E effect of temperature on the rate of fixation of conipounds of chromium by hide substance seems to have received no study whatsoever. This is the more surprising because the variations in temperature that can easily occur during chrome tanning are rather large. As chrome tanning is commonly carried out skins are tumbled in a drum with the chrome tan liquor. Since the volume of the liquor is generally insufficient to float the stock, the skins are subjected t o a rather vigorous pounding, which causes the temperature of the skins and of the liquor to rise. The temperature finally attained may be considerably above room temperature. If bicarbonate is added during tanning to neutralize the skins in part, the heat of neutralization contributes to the elevation of the temperature. The temperature finally attained depends upon many factors, including the initial temperature of the skins and liquor, the dimensions of the drum and the quantity of stock placed therein, the ratio of skins to liquor, the rate and duration of drumming, and the temperature of the room. As some of these factors frequently are allowed to vary from lot to lot, the final temperature of the tan liquor may vary by as much as 30" or 40" F. (17" to 22" C.) in extreme cases. Experience has shown that the higher the temperature reached in actual chrome tanning the more chrome is fixed by t h e skins in a given time. Increasing the temperature facilitates the hydrolysis of chromic salts, with concomitant changes in the structure of the chromium nucleus. Such changes may affect the character of the leather produced more than small differences in the degree of chrome tannage. To determine the effect of temperature upon chrome tanning, we tanned strips of calfskin in a large excess of chrome liquor at temperatures of from 10" to 50" C. and for periods of from 4 hours to 5 days. The results of these experiments show that the weight of chromic oxide fixed by a given w i g h t of hide :substance in a given time increases enormously with tempera-
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] Presented before the Division of Leather and Gelatin Chemistry a t t h e 78th Meeting of the American Chemical Society, Minneapolis, L f i n n , September 9 to 13, 1929.
ture. The greatest increase in the rate of fixation of chromium is between 20" and 30" C., which is just the range met in the early stage of chrome tanning. The weight of chromic oxide fixed in 8 hours a t 30" C. is over 60 per cent greater than the weight fixed in the same time a t 20" C. Conversely, the time required to fix a specified weight of chromic oxidc per 100 grams of hide substance is more than twice as long a t 20" as a t 30" C. Leather tanned a t 40" C. withstood the action of boiling water after only an 8-hour tanning, while leather tanned a t 20" C. did not stand the boiling test until after 48 hours. The apparent acidity of the chromium salt fixed by collagen is markedly higher at 20" than at 30' C. Procedure
CHROME LIccuoR-We dissolved 260 grams of a commercial chrome-tanning compound in 10 liters of water and allowed the solution to stand 7 days before use. The liquor contained the following: chromic oxide, 1.50 per cent; acid sulfate as SOS, 1.20 per cent; sodium sulfate, 1.52 per cent. The acidity of the chromium salt was 0.51, the pH value of the liquor was 3.23, and the precipitation figure wa? 10.2 cc. of 0.05 S sodium bicarbonate per 10 cc. of liquor. CALFSICIS-A whole calfskin was limed and bated in the usual way and then pickled with a solution containing 12 per cent of sodium chloride and enough sulfuric acid to give a pH value between 1 and 2 after equilibrium was established. Strips approximately 2 by 6 inches J\ ere cut from the butt and hack, with the longer dimension parallel to the backbone. Each strip was trimmed to weigh 30 grams in the wet state. AfANIPULATIOiY-FiVe strips, suitably marked, were placed in each of 5 large bottles with 1900 cc. of the chrome liquor. Each bottle was immersed in a thermostat, one a t lo", one a t 20", one a t 30", one a t 40", and one a t 50" C. The temperature was maintained constant to 0.1" except in the 50" C. thermostat, in which it varied by about *0.5" C. The liquor and skins were stirre& by hand a t 15-minute intervals during the first 8 hours and three times a day thereafter. One
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Figure 1-Effect of Temperature u on Quantity of Chromic Oxide Fixed in 8 i f ferent Time Periods
Figure 2-Rate of Fixation of Chromic Oxide a t Different Temperatures
Figure 3-Effect of Temperature on Time Required for Fixation of Specified Quantities of Chromic Oxide
I n Figure 1 the weight of chromic oxide fixed by 100 grams of collagen is plotted as a function of temperature for each of the different tanning periods employed. The curves are sigmoid, showing that the effect of temperature on the rate of tanning is not uniform over the whole range studied. The greatest increase in rate with temperature occurs between 20" and 30" C. I n Figure 2 the weight of chromic oxide fixed is plotted as a function of time for each temperature. All the curves are of the usual shape, apparently tending toward convergence at some very prolonged tanning period. The effect of temperature upon degree of tannage a t any given time is shown by the vertical distances between the curves. Figure 3 shows the effect of temperature upon t h e time required for the fixation = so of a definite quantity of chromium. T h e 8 quantities of chromic :1.26 oxide for which curves 5 are shown are 5.07, $ l . m 6.76, and 10.14 grams k of Cr20sper 100 grams 2 o,,l of hide substance. If : the combining weight of collagen be taken io,% as 750, these quanti- 8 ties correspond to 1.5, 4 0 . 2 5 2, and 3 equivalents Table I-Composition of Chrome Liquors ACIDITY OF PH PRECIPITATIONof c h r o m i u m per VALUE' C O N D I T I O N O F LIQUOR Cr?Oa Cr SALT VALUE e q u i v a 1e n t of colla2a &, me: Per cent Per cent gen. M o s t of t h e 3.23 10.0 Before using 1.50 0.51 Figure 4-Rate of Change of Apparent chrome leathers ana- Acidity After 24 hoirs at: of t h e Chromium Salt Fixed b y 0.49 3.02 1.40 9.2 100 c. lyzed in this labors- Collagen a t Different Temperatures 0.60 3.21 11.0 1,36 200 c. 0.51 3.22 10.5 1.26 30' C. t o r y have contained 0.50 1.25 3.08 9.5 40' C. percentages of chromium between the lowest and the high0.54 1.20 3.20 10.3 50' C. After 120 hours at: est values given. The enormous effect of temperature upon 0.42 3.14 10.7 100 c. 1.28 the time required for fixing a specified quantity of chro3.20 11.0 0.45 200 c. 1.26 10.2 0.51 3.22 30' C. 1.1s mium, particularly when the quantity to be fixed is large, is 3.20 10.3 1.17 0.52 40' C. 50' C. 1.16 0.50 3.14 9.5 apparent. a Cc. 0.05 N NaHCOa per 10 cc. liquor. The effect of temperature upon the apparent acidity of the chromium compound fixed by the leather is shown in Figure 4. Results The values for acidity are the ratios of equivalents of acid The effect of temperature on the rate of chrome fixation, as sulfate in the leather to equivalents of chromium in the determined by the analysis of the tanned strips of skin, is Leather. Since part of the hydrolyzable sulfate is combined with collagen, all the values shown are too high. This probashown in Figures 1, 2, and 3.
strip of skin was removed from each bottle after the lapse of 4, 8, 24, 48, and 120 hours. At the same time one-fifth of the liquor was removed, so that the ratio of skin to liquor remained constant. The strips of tanned skin were washed for 1 hour in running tap water. A boiling test was made by boiling a piece about by 1 inch for 5 minutes and noting whether or not contraction occurred. Each leather was cut up, air-dried, and analyzed for chromic oxide, hide substance, and acid sulfate by the methods of the American Leather Chemists Association. Each sample of liquor removed was analyzed for chromic oxide, acid, precipitation value, and pH value. REMARKS-The ratio of skin to liquor in these experiments was much lower than is usual in chrome tanning. This was necessary in order to obtain uniform exposure of each piece of skin to liquor. To obtain this uniformity with the usual ratio of skin to liquor would have required the use in each thermostat of a tumbling device, which was not available. Because of the high ratio of liquor to skin the liquors were-not nearly exhausted. A large excess of chromium was present a t all times, and the acidity, pH value, and precipitation value of the liquor changed very little. This is a further departure from practical tanning conditions, but an advantage from the experimental standpoint, as the temperature was practically the only variable factor. The composition of the liquors before using and a t the end of 24 and 120 hours is given as a matter of record in Table I. It was not thought worth while to record the values for 4, 8, and 48 hours.
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December, 1929
bly does not affect their significance for comparative purposes, however. At all temperatures there is a rapid drop in acidity during the first 8 hours of tanning. This probably reflects the displacement of sulfuric acid from combination with collagen by chromi-complexes. The higher the temperature, the more rapidly does the acidity decrease, up to 30" C. Above 30" C. temperature has practically no effect on the acidity of the chromium salt. After the apparent acidity has fallen to about 0.46 it remains practically constant throughout the remainder of the tanning period. At temperatures of 30" C. or over this equilibrium acidity is reached in 24 hours, but a t lower temperatures it was not reached up to 120 hours. After 24 hours the acidity of a leather tanned a t 20" C. is about 33
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per cent higher than that of leather tanned a t 30" or higher, while the acidity of leather tanned a t 10" C. is 100 per cent higher. After tanning for only 4 hours the leather tanned at 50" C. almost stood the boiling test; that is, it showed only a slight contraction and remained soft and supple. The leathers tanned a t 40" and a t 50" C. stood the boiling test after an 8hour tannage; that tanned at 30" C. after 24 hours; and those tanned a t 10" and 20" C. after 48 hours. That a leather is produced a t all at 50" C. shows that the tannage at that temperature must be very rapid, as raw skin is rapidly converted into gelatin on exposure to a solution of p H 3 a t that temperature.
Studies in Liquid Partial Oxidation-I'z' E. P. King, Sherlock Swann, Jr., and D. B. Keyes I i N I V E R s I T Y O F I L L I N O I S , U R B A N A , ILL.
The catalytic oxidation of ethylbenzene and acetalo r g a n i c liquids. It is also HE partial oxidation of dehyde in the liquid phase has been studied. Catalysts necessary that the catalyst for organic compounds usused for the vapor-phaseoxidation of hydrocarbons have liquid phase oxidation shall ing air as the oxidizing been tried as catalysts for the oxidation of ethylbenoperate a t a much lower temagent, and in the presence of zene. The oxidation of acetaldehyde was carried out perature than is customary a c a t a l y s t , h a s been the in aqueous solution and substances capable of changing for the vapor phase in order foundation of several successvalence were used as catalysts. The effect of obtaining ful commercial r e a c t i o n s . that the reaction may go withbetter contact between gas and liquid phases by means Oxygen may be substituted out the use of pressure. This of a high-speed stirrer was studied for both oxidations. for hydrogen in a hydrocarnecessitates the development The conversion of ethyl alcohol to acetic acid in two bon. for example. bv a mocof a special type of catalyst. ess ilivolving s e v e r a l s t e p s steps was also carried out. There are many processes and utilizing relatively costly involving the oxidation of an oxidizing agents. It is apparently difficult to make the sub- organic liquid by means of air, some of which are commercial stitution directly. Examples of such a reaction are the well- and others which might well become commercial processes known partial oxidation of naphthalene to phthalic anhy- if the general problem of bringing the two phases into contact dride and the partial oxidation of anthracene to anthra- efficiently were solved. The oxidation of acetaldehyde to quinone ( 5 ) . In these cases specially prepared catalysts are acetic acid is an example of such a reaction which is already used and the reactions are carried out in the vapor phase. carried out on a commercial scale. The importance and use Since all oxidations are exothermic, it is necessary to main- of acetic acid is ever increasing with the growth of industrial tain very precise temperature control. Otherwise the oxi- organic chemistry. Acetic acid is used in the manufacture dation would continue and only the end products of the of lacquers, cellulose acetate, and various solvents. Anreaction be obtained-namely, carbon dioxide and water. other example is the oxidation of ethylbenzene to acetoExperience has shown that temperature control is an ex- phenone. Acetophenone is now prepared by the Friedelceedingly important factor in this type of reaction. Crafts reaction, which is quite expensive. The use of acetoIf such a reaction is carried out in the vapor phase with a phenone in the manufacture of resins and as a reagent in solid catalyst, the heat is, presumably, liberated a t the sur- the preparation of various organic compounds is increasing. face of the catalyst, because this is where the reaction is It was the object of this investigation, therefore, to study supposed to take place. The heat is transmitted to the the effects of different catalysts on the oxidation of ethyl walls of the reaction tube by means of the gases, the solid benzene and acetaldehyde, and also to show the effect of catalyst, or both. Since the heat capacity of the reacting increase in the efficiencyof contact between the gas and liquid gases is small, usually an inert, diluting gas is added to make phases on the products of these reactions. The conversion up for this deficiency. Steam is often used because of its of alcohol to acetic acid was tried in a continuous process relatively high specific heat. The solid catalyst, though it involving two steps. may have a fairly high heat capacity, is often a poor conductor Historical of heat, and as it is usually stationary is of little value. On the other hand, if the reaction could be run in the There has been a great deal of investigation on oxidation liquid phase, the higher heat capacity and better heat conductivity might make the matter of temperature control in the liquid phase by means of air. Stephens (11) has more simple. However, it is difficult to obtain good contact done some notable work on the oxidation of liquid aromatic between a gas and a liquid, especially when that gas is not hydrocarbons, including the oxidation of ethylbenzene in very soluble in the reacting liquid, as in the case of air and the liquid state. Many investigators have studied the oxidation of alcohol Presented by D. B. Keyes before the Division of Industrial and Ento acetic acid by means of air, and a great number of methods gineering Chemistry at the 78th Meeting of the American Chemical Society, for carrying out the reaction have been suggested, as well Minneapo!is, Minn , September 9 to 13, 1929. as many catalysts for hastening the reaction. Although some Published by permission of the director of the Engineering Experiment Station, Uni\ersity of Illinois investigators have obtained acetic acid in the direct oxida-
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