October 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
(10) Panzer, 2.physiol. chem., 94, 110 (1915). (11) Papazogli, 2. anal. chem., 36, 715 (1896). (12) Pinoff, Ber., 38, 3316 (1905). (13) Reich, Arch. Pharm., 50, 293.
415
(14) Rosenbach, 2. anal. chem., 31, 724 (1891). (15) Sieben, Ibid., 13, 248 (1873). RDCEIVEDApril 22, 1932.
Sulfite Digester for Research and Instruction W. L. BEUSCHLEIN AND FRANK H. CONRAD,University of Washington, Seattle, Wash.
C
HEMICAL engineering laboratory equipment should be selected on the basis of usefulness. Too frequently, expensive apparatus to be used a t best part time is purchased, whereas a slightly modified form would have lent itself to a variety of experiments. Conversely, a special piece may be purchased for a limited but important investigation and then with a few and relatively inexpensive accessories, used for basic studies in class work. I n such cases, one can justify the initial expense. This discussion has to do with the design of a special KA 4 metal rotary digester for sulfite pulping studies, and also its use in class work.
to the one described are installed and all may be rotated from a main drive a t 4.7 r. p, m. The speed of rotation is not so great but that temperatures and pressures may be read without stopping the apparatus. Three electrical resistance coils, which are used for heating, are connected through three commutator rings, and hence no switches need be on the rotating drum. There is little danger of heating interruptions due to shorting with this arrangement.
OPERATION Before use of this digester for sulfite pulping studies, two series of heating rates were obtained. One was made with the KA 4 digester insulated only with the electrical packing normally placed around the heating elements and in running position. The other was obtained after packing "85 per cent magnesia" between the digester and the steel carriage. In these runs 18 kg. (39.6 Ib.) of water were heated. The results, given in Figure 3, show that 0.56 kw. maintained a
FIGURE 1. D~GESTER SHOWING KA 4 METALCASTINQ
The preparation of sulfite pulp in the laboratory is usually limited to working with heavy glassware and rare-metal containers. Such limitations frequently permit working with only small samples. At the University of Washington, a digester of 25 liters capacity has been in operation for several months, and because of the ease of control and wide limits of operation and application, a detailed description has been prepared. Those interested in such equipment may find use for this apparatus and many can add, no doubt, to its applicability. I n the digestion of wood chips by a solution, variables such as size and composition of chips, temperature, concentration, and composition of solution are usually studied. Uniformity of operating conditions is always desirable: Apparatus for such work should withstand corrosion, allow for simple but accurate control, be of the rotating or tumbling type; and externally heated. DESCRIPTION OF DIGESTER The digester is shown in Figure 1. The body of KA 4 metal was cast from the pattern of a standard 6-inch steel steam drip pocket. The flanged opening was fitted with stud bolts which, in conjunction with a solid KA 4 metal plug in the bottom, were used for mounting the casting in a steel drum. The side openings intended for gage cocks in the drip pocket were used for thermometer well, pressure gage, sampling, and blow-down fittinge. The apparatus was given a 24.6 kg. per sq. cm. (350 lb. per sq. in.) hydrostatic test. Figure 2 shows the mounting of the casting in the steel cylindrical drum which rotates at right angles to its axis. The sprocket, chain drive, and commutator rings for ellectrical heating are evident. Two steel digesters similar
FIGURE 2. ASSEMBLY OF DIGESTER
constant temperature of 132" C. (270" F.) before and 146" C. (295" F.) after packing with 85 per cent magnesia. The usual maximum temperatures used in the sulfite cooking process are 143" to 149" C. (290" to 300" F.). The additional insulation had little effect upon the rate of temperature rise to 149" C. (300' F.) when 2.07 and 1.12 kw. were used. EXPERIMENT IN RATEOF HEATING Charges may be heated having heat capacities other than that equivalent to 18 kg. of water, and then the heating
ANALYTICAL EDITION
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Vol. 4, No. 4
duced in calculating by means of Equation 2 the time required to heat 10 kg. (22.0 lb.) of water from 25" C. (77" F.) to any temperature below 149' C. (300" F.) is illustrated by selection of the temperature 164" C. (327"F.). The error for this temperature is 9.0 minutes, or 6 per cent. Similar calculation for a charge of 5 kg. (11 0 lb.) of water shows the same error. MEASUREMINT OB HEATLOSSES When the temperature of the digester charge becomes steady, and after allowing for the energy required for any change takipg place, the electrical input will be equivalent to the heat losses, Measurement of such losses can be accomplished easily with the usual electrical meters. Since heat leaves the steel jacket by radiation and convection,
Before /nsu/ut'/oon- o Affer 4
/Z
8
-
/b
/osu/atton 20
z+
-
b
2
TIM€ HOURS
FIGUI~E 3. DIGESTER HEATING RATES
time required to bring to a given temperature is desirable. A method for such calculations is given below. Assuming that each temperature represented on the 2.07kw. input curve of Figure 3 gives the average temperature of the metal digester and the water, the total heat loss, Q2, in lagging and radiation up to a given time, 8 hours, is ghen by:
r
(1000)(2.07)(3600)0- (22.7)(454) 4185 looo
+ 20 I
I
0 0
2
T/M€
The total heat capacities in Calories per 0C. or B. t. u. per " F. of the metal parts and of the water are (22.7) (454)/1000, or 22.7 and w, respectively, depending on the units. Equation l is for metric and la for English units. Room temperature, Tr, is taken as 25" C. (77" F.), while T represents the average temperature of the water. Corresponding values of time and temperature have been taken from curve 1 of Figure 3, and Equation 1 solved for Q2. Values of Qz so calculated have been plotted against T - T7on log-log paper and result in the equation: Qz = 2.45 (T Tr)1.36 in metric units QZ = 4.40 (T - Tr)1,35 in English units
-
I
I
/
- HOURS
3
FIUURE 4. COMPARISON OF CALCULATED AND OBSERVED HEATINGRATES
the quantitative determination of either loss separately is rather complicated, and simplifying expressions have been suggested. Although the transfer of heat by radiation from a body is proportional to the fourth power of its absolute temperature, the net exchange between two bodies at approximately room temperature, having a small temperature difference, may be approximated closely by assuming it proportional to only the temperature difference as in heat transfer by conduction. Heat transfer due to radiation and convection may be estimated from the equation
where T, is the room temperature and Q 2 is expressed in Calories or B. t. u., respectively. Substituting this value of Q 2 in Equation 1 and simplifying, 8 = (0.00578 0.00000056w)(T- T,.) 0.000137(T - Tr)l.'6 (2) e = (0.00321 0.000141 w)(T - T,) O.O00622(T - T,)l.35
where
where 0 represents the hours required to heat a charge of w grams or pounds of water from 25" to T oC. (77" to T oF.). I n Figure 4, Equation 2 has been solved for values of w equal to 5 and 10 Calories per "C.(11.0 and 22.0 B. t. u. per OF.) corresponding to charges of 5 and 10 kg. (11.0 and 22.0 lb.) of water. Experimental results for such charges are also indicated in Figure 4. The maximum error intro-
The application of this equation in work with the digester can be exemplified by measuring the heat input required for maintaining steady charge temperatures and recording the temperature of the steel-jacket surface and of the room. An input of 0.56 kw. (481 Calories per hour) was found t o maintain the temperature of the charge at 146" C. (295" F.). The skin temperature of the steel jacket averaged 45' C.
+ +
+ +
(24
Q = (hc ' 0
hc
e
+ hrA
AT
= = = =
+ hr)A AT
(3)
heat transferred per unit of time gas film radiation coefficient area of hot body temperature difference
+
October 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
(113' E'.) and that of the room 25" C. (77" I?.). The value of (hc f hr) A, using Equation 3, is found to be 24.1 Calories per hour per C. (53.2 B. t. u. per hour per O F.). Heat capacities of solutions and mixtures, in particular those used in the pulping industries, can be determined by the use of Equation 1.
CHEMICAL PREPARATIONS Undergraduate laboratory courses in industrial chemistry have inany uses for rotating autoclaves. The preparation of wood pulp is but one of the digestion processes which
417
familiarize the student with important phases of the chemical industry. Other processes, especially those peculiar to geographical location, suggest themselves. The object of this paper has been to show that expensive research equipment can be also used for undergraduate instruction in industrial chemistry and chemical engineering, The intensive and general application of apparatus can justify the installation of equipment developed for special investigations. R E C E ~ VJune ~ D 15, 1932.
Estimation of Thallium after Oxidation with Bromine PHILIP E. BROWNING, Yale University, New Haven, Conn.
0I?
T H E reagents employed for the oxidation of thallium, bromine has received little attention, although its action is rapid and complete. Sponholz (3) recommended it for the volumetric estimation of thallium, using the color of excess bromine to indicate when the reaction was complete. I n the description of this method he called attention to the necessity of frequent standardization of the bromine solution. The difficulties of such a volumetric procedure are quite obvious, If, however, the oxidized solution is treated with an alkali hydroxide in sIight excess, the immediate and complete precipitation of thallic hydroxide is effected. The delicacy of this reaction was first tested qualitatively, and it was found that in a volume of 10 cc., 0.1 mg. of thallium could be detected by the dark coloration of the thallic hydroxide, a delicacy which was rarely exceeded by such reagents as potassium iodide, chloroplatinic acid, or sodium cobaltinitrite. Sodium peroxide proved to be much less satisfactory as a means of detection. This test cannot be made in the presence of such elements as iron, manganese, cobalt, or nickel which give similar color changes due to oxidation. Quantitatively the results were as follows: A solution of thallous nitrate was made up and standardized by oxidizing four portions of 10 cc. each with potassium ferricyanide in the presence of potassium hydroxide (1, 2 ) , filtering off the thallic hydroxide on a weighed asbestos felt, and weighing the oxide after bringing it to constant weight a t a temperature
of 150" to 200" C. The mean of four closely agreeing results gave 0.1345 gram of thallic oxide Portions of 10 cc. each of this same solution were oxidized with bromine water in slight excess, the oxidized solutions precipitated, with or without gentle warming, with sodium or ammonium hydroxide, and the precipitates filtered off, heated, and weighed in the same manner as the precipitate from the ferricyanide treatment described above. Four closely agreeing results, ammonium hydroxide having been used as the precipitant, gave as a mean 0.1334 gram of thallic oxide; and another four, sodium hydroxide having been employed as the precipitant, gave a mean of 0.1344 gram of thallic oxide. The method was rapid, easy of manipulation, and certainly, when sodium hydroxide was used, of satisfactory accuracy. Obviously, those elements whose hydroxides are insoluble in excess of sodium or ammonium hydroxide must be absent when this method is applied. This necessitates the previous removal of thallium from most of the other elements, a procedure not unusual before the application of many gravimetric processes to the estimation of a single element.
LITERATURE CITED (1) Browning and Palmer, Am. J. Sci., 27, 379 (May, 1909). (2) Hillebrand and Lundell, "Applied Inorganic Analysis," p. 377, Wiley, 1929. (3) Sponholz, 2. anal. Chem., 31, 519 (1894); Chem. News, 67, 187 (1894). RECEIVEDMay 20, 1932.
An Improved Flask for Van Slyke Protein Analysis RAE PATTON, University of Minnesota, St. Paul, Minn. HE flask shown has been found to be an improved form for hydrolysis of proteins according to Cavett's modified Van Slyke nitrogen distribution method ( I ) . It consists of a 300-ml. Kjeldahl flask to which has been attached a side neck, in the manner of a Claissen flask. Several operations are performed in the flask, saving time and increasing accuracy. The protein sample is hydrolyzed, the hydrochloric acid is distilled off, the ammonia nitrogen is determined, and the total nitrogen in the humin fraction is determined, all in the same flask on the same sample. The advantages of this Kjeldahl-Claissen flask over the 250-ml. distilling flask recommended in the original method, are: (1) The double neck prevents foam from bubbling over into the standard acid during the ammonia determina-
/ E
U
tion. (2) The additional s t r e n g t h of t h e K j e l d a h l flask makes it more suitable for t h e KjeIdahl digestion, etc.
0
LITERATURE CITED (1) Cavett,
J. W., J.
Bid. Chem., 95, 335-43 (1932). RBCEIVED July 22,1932.
