INDUSTRIAL AND ENGINEERING CHEMISTRY
Xovember, 1930
The values for the latent heat of vaporization of moisture from lignite (20" to 40" C.) as calculated by this equation are given in Table VII. The mean value (20' to 40" C.) of the latent heat of vaporization of water from a plane surface, calculated by the same equation, equals 580.9 calories per gram. From Table VI1 we note that the heat of vaporization is greater than this value and increases as the moisture content of the lignite is reduced. The average of the calculated values amounts to 609.1 calories per gram. It is evident from the foregoing that the use of the normal latent heat of evaporation of water in calculating heat losses due to drying of lignite in boiler tests is not strictly accurate. Literature Cited (1) Allmand and Others, J . Phys. Chem., 33, 1151, 1161, 1682, 1694
1231
(2) Anderson, 2. phrsik. Chem., 88, 191 (1914). (3) Bemmelen, van, Z. anorg. Chem., 13, 233 (1897); 18, 14 (1898); 30, 265 (1902). (4) Gauger and Iverson, Quart. J . U n i v . N . D a k . , 20, No. 4 (1930). (5) Hawley and Wise, "The Chemistry of Wood," Chemical Catalog, 1926. (6) International Critical Tables, Vols. I and 111, McGraw-Hill, 1928. (7) Katz, Kolloidchem. Beihefte, 9, 5 (1918). (8) Kreulin and Ongkiehong, Brennstof-Chem., 10, 319 (1929). (9) Larian, Lavine, Mann, and Gauger, IND.END.CHBM., 22, 1231 (1930). (10) Lowry and Hulett, J . A m . Chem. Soc., 42, 1393 (1920). (11) Paul, Bur. Mines, Tech. Paper 410 (1928). (12) Pidgeon and Maass, J . A m . Chem. Soc., 62, 1053 (1930). (13) Porter and Ralston, Bur. Mines, Tech. Paper 113 (1916). (14) Thiessen, Bur. Mines, Bull. 38 (1912). (15) Thompson, Phil. Mag., 141 42, 448 (1871). (16) Zsigmondy, Z. anorg. Chem., 71, 356 (1911); 76, 189 (1912); 79, 202 (1912).
(1929).
11-Sorption of Water Vapor by Lignite, Peat, and Wood' Maurice Larian,2 Irvin Lavine,$ C . A. M a n n , 4 a n d A. W. Gauger6 UNIVERSITY OF MINNESOTA, MINNEAPOLIS, MINN., A N D CNIVBRSITY OF NORTHDAKOTA, GRANDFORKS,hr. DAK.
Foreword
vapor, etc., have been studied in great detail and the results have led to a better understanding as to the structures of these colloidal substances. In most of the published work dealing with such adsorption isotherms the investigators have excluded foreign gases by using some kind of vacuum technic. Recently, however, Lavine and Gauger ( 2 ) used the desiccator method in studying the fundamental characteristics of the water in lignite from North Dakota and were able to draw many conclusions as to the colloidal nature of this fuel. It was thought advisable to extend this study to peat and wood, and the results of this investigation, together with the results for a sample of h'orth Dakota lignite, are presented herein. It is clearly understood that the desiccator method of following an adsorption isotherm has its inherent difficulties. However, the results so obtained can serve for industrial applications as well as for theoretical considerations and, in particular, may be well applied for a critical comparison of different materials subjected to identical conditions of experimentation.
A s t u d y of t h e sorption of water by N o r t h Dakota lignite, Minnesota peat, a n d birch wood shows t h e characteristics of t h e desorption a n d adsorption process t o be the s a m e f o r the t h r e e materials. Hysteresis is f o u n d to be present w i t h t h e t h r e e m a t e r i a l s investigated. Pore radii have been calculated by m e a n s of t h e T h o m p s o n equation a n d in t e r m s of pore size we o b t a i n t h e following classification in order of decreasing pore size: peat, birch wood, lignite, a n d brown coal.
An economical supply of fuel for industrial and d o m e s t i c u s e s is a major problem of Minnesota and the Dakotas, which is rendered more baffling, and a t the same time alluring, by the e x i s t e n c e in North Dakota of a tremendous tonnage of lignite. The fact that chis lignse has only one bad quality which prevents its use on a large scale has long been recognized. The high content of water renders some form of dehydration imperative. The water removal must not only be sufficiently complete and cheap to make lignite acceptable as a fuel, but its qualities as to storage, spontaneous ignition, and utilization must be satisfactory. Various phases of this problem have been the subject of prolonged and intensive research in the School of Mines of the University of North Dakota; first under the direction of the late E. J. Babcock and later under his successor, A. W. Gauger, the present director. On account of the importance of the problem to the entire Northwest region and of the benefits which its solution would bring, it appears most fitting that the University of Minnesota should cooperate in the work. The present publication represents a part of this work, which was carried out jointly during the past year under the direction of A. W. Gauger a t the University of North Dakota and under Charles A. Mann in charge of chemical engineering in the University of Minnesota. The results of other investigations in this cooperative program will appear in later papers of the present series. It is gratifying to realize that through this cooperation a further step has been taken toward the ultimate goal, which will be reached, if the same spirit of perseverence and cooperation is maintained. S. C . LIND,Director, School of Chemistry University of Minnesota
T
HE adsorption of water vapor by solid adsorbents has engaged the attention of many investigators. Such systems as silica gel-water vapor, charcoal-water
* Received August 11, 1930. Presented before the Division of Gas and Fuel Chemistry a t the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8t o 11, 1930. * Graduate student in chemical engineering, University of Minnesota. Assistant professor of chemical engineering, University of North Dakota. 4 Chief, Division of Chemical Engineering, University of Minnesota. Director, Division of Mines, University of North Dakota.
Samples Used
The following samples were used in these experiments: Lignite. A sample of lignite from Velva, N. Dak., was shipped directly from the mine in a sealed container. Upon reaching the laboratory it was immediately pulverized and sized between 80 and 100 mesh under conditions whereby a minimum amount of moisture was lost by air-drying. Samples of approximately 1 gram of the pulverized material were used in the experimental work. Peat. A 2-quart sample of peat was obtained from a peat bog located a t the Northwest Terminal, hlinneapolis. This was immediately sized between 20 and 40 mesh and samples of approximately 1.5 grams were taken for the experimental work. Birch wood. The sample of birch wood was obtained through the courtesy of the Forestry Division of the Agricultural College, University of Minnesota. A section of a freshly cut birch tree (approximately 40 years old) was first debarked and then thin shavings of about 1 cm. in length were planed from the outer
INDUSTRIAL AND ENGINEERING CHEMISTRY
1232
5 WATER
IO
15
20
25
IN GRAMS PER 100 GRAMS OF DRY MATERIAL
section. Samples of approximately 1.5 grams of shavings were used in the work.
The moisture content of the samples as determined by drying over concentrated sulfuric acid (sp. gr. 1.84) for approximately 50 days is as follows:
Vol. 22, No. 11
desorption process for lignite, peat, and birch wood shows the same characteristics as the moisture is reduced below its saturation value-namely, a gradual decrease in vapor pressure from 100 per cent to 85 per cent, a rapid decrease from 85 per cent to 15 per cent, and a gradual change from 15 per cent to 0 per cent. Although the desorption curves for the three materials follow the same general characteristics in the reduction of vapor pressure, we find, however, that the vapor pressuremoisture equilibrium relationships for these materials are quite different. Thus, in an atmosphere of 60 per cent relative humidity a t 20" C., North Dakota lignite, as mined, .i?-ill dry to approximately 23 per cent moisture (dry basis) while Minnesota peat under identical conditions will dry to 12 per cent (dry basis). Birch wood under these conditions will dry to 13.0 per cent water (dry basis). It is evident that the vapor pressuremoisture equilibrium relationship is of practical importance in the commercial drying of these materials. A 4 ~ s o PROCESS-The ~ ~ ~ ~ o adsorption ~ process may be followed from the curves in Figures 1 to 3 that are indicated by the ascending arrows. These curves show that in each case the adsorption process follows a smooth S-shaped curve which corresponds closely to the adsorption isothermal of a swelling gel. On the basis of the gel theory we may interpret this to mean that as these materials adsorb moisture the first traces are adsorbed on the surfaces and the vapor pressure increases but slowly. The further adsorption of moisture consists in filling the smaller capillaries. As more moisture is taken up the vapor pressure increases rapidly owing to the change in the radius of curvature of the water meniscus. The last stage consists in filling the largest capillaries until saturation is reached.
Per cent Velva lignite.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1 Minnesota p e a t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.6 Birch wood (sap) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57.3
90
Experimental Procedure
c
The procedure used in this investigation is essentially that adopted by Lavine and Gauger ( 2 ) and consisted in following the desorption +adsorption cycle by observing the variation of the aqueous tension of the samples with varying water content a t 20' C. The samples were kept in desiccators where definite humidities, ranging from 100 to 0 per cent,, were maintained by means of aqueous saturated salt solutions. Loss or gain of moisture was determined by meighing to constant weight. When equilibrium was attained, the samples were completely dehydrated by drying in desiccators over pure sulfuric acid (sp. gr. 1.84). The adsorption process was then followed by replacing the completely dried .samples in their original desiccators and weighing, as before, t o constant weight. A detailed description of the procedure, 'as well as a list of the various salts used in maintaining the humidities, is given by Lavine and Gauger in Part I of this series. Discussion of Results
c,
The results of these experiments showing the effect of dehydration as well as hydration on the vapor pressure of the moisture in Minnesota peat, birch wood, and North Dakota lignite a t 20" C. are tabulated in Table I, and graphically represented in Figures 1 to 3. DESORPTION PROCESS-For purposes of comparison there are plotted in Figure 4 the desorption curves for the three materials investigated. A study of this figure indicates that in each case there occurs a decided decrease in the vapor pressure as the moisture content is reduced below its equilibrium value a t a relative humidity of 100 per cent. I n general the
5 80 a:
2 70
z w
60 3
v, v) w 50
&
a
CY
o 40
a < > Lu
2
30
I-
5u 2 0
cc
10
30 40 10 20 WATER IN GRAMS PER IO0 GRAMS OF DRY MATERIAL
HYSTERESIS-Figures 1 t o 3 also indicate that hysteresis is present in peat and birch wood as well as lignite. However, under identical conditions of experimentation the region of hysteresis (hysteresis spread) is greatest for lignite and least for birch wood (sap) I n the case of lignite and birch mood we find the desorption + adsorption isothermals to be reversible at moisture
INDUSTRIAL AND ENGINEERING CHE.MISTRY
Xovember, 1930
1233
I n order that a direct comparison might be made as to pore size of the materials investigated by the present authors with the pore size of brown coal as determined by Kreulin and Ongkiehong ( I ) , the per cent moisture held within certain pore radii, mas calculated. These data are given in Table I11 and Figure 5 .
RADIUS OF CAPILLARIES IN I D - ~ c ~ . 10
20
30
40
Table I-Sorption
WATER IN GRAMS PER 100 GRAMS OF ORY MATERIAL
contents of 0 to 2.5 per cent, which would indicate that over this range the adsorption is a true surface phenomenon. I n the case of peat, however, we find the two processes are not reversible over any range of moisture content, and for this material the first adsorption of moisture consists in capillary condensation and not true surface adsorption. CAPILLARY RADIus-From the vapor-pressure relationships shown in Figure 4 it is possible to calculate the pore radii in lignite, peat, and birch wood by means of the well-known Thompson equation (8). Table I1 gives the pore radiimoisture relationships as calculated by this equation for North Dakota lignite, Minnesota peat, and birch wood.
I SALT SOLUTION
Data
~ I O I S T U (DRY R E BASIS)
RELATIVE HUMIDITY
HYDRATION
DEHYDRATION
S . Dak. hIinn.
lignite
peat
Birch wood
g. Dak. hlinn.
lignite
Birch wood
peat
7 0 7 0 % 34.00
Pb (Kod2 ZnSOn.7HzO KBr NH4C1 SaCl K2CrzOi.2WzO NaN02
KNOB MgCh 6H20 KCzH30z H?SO+(sp. gr. 1,5098) H&04 (sp. gr. 1.5524) H&04 (sp. gr. 1.6240)
14.93 9.17 3.54
I
25.35 23.60 20.40 17.38 15.80 11.60 8.38
-,
l2:65
...
20.60 17.9C 16.75 13.37
...
9.70 6.90 4.60
...
8.90 6.71 4 00
4.25
4.48
6.35
3.00
4.00
5 62
3 92
3.60
5.00
2.90
3.20
4.04
2.03
2.00
3.42
1.23
1.92
Radius =
Radius a t 20' C. ZYM Ps SRTln P ,
= surface tension = 72 75 dynes per cm. = molecular weight = 18.02 = density = 0.99823 = gas constant = 8 316 X 10-7 erq per C. = saturated vapor pressure = 1 754 cm. Hg
hIOISTURE (DRY SALT S O L U T I O K
Water Pb(N0dz ZnSO4.7HnO KBr "aC1 NaCl NaNOz KzCr20,.2H?O KNOz MgC12.6H20 KCaHsO? H2S04 (sp. gr. 1 5098) HtSOa (sp. gr. 1 5524) H&OI (SP.gr. 1 6240) 0
31.00 26.40
7.60
Table 11-Capillary
3f S R Pa
21.00
zi:is i4:io
pw
1.754 1.719 1.5790 1.4730 1.3890 1.3330 1 1580 0.9128 0.7893 0.Z790 0.3508 0.2620 0.1610 0.0622
N. Dak. hlinn. lignite peat
BASIS)
Birch wood
.....
56,734 10,3055 6.19518 4.6463 3.93416 2.5987 1.6307 1.3509 0.9734 0.66995 0.5676 0,4517 0.32317
Values taken from curves in Figure 4.
Figure 5 shows that 50 per cent of the bound water is held in capillaries less than 7.4 mp in Minnesota peat; 5.6 mp in birch wood; 3.7 mp in Xorth Dakota lignite; and 1.8 mp in
INDUSTRIAL AND ENGINEERING CHEMISTRY
1234 Table 111-Moisture
Cm.
X 10-7 Cm. X 10-7 56.73 > 56.73 1 0 . 3 1 10.31-56.73 6 . 2 0 6.20-10.31 4 . 6 5 4.65- 6 . 2 0 3 . 9 3 3.93- 4 . 6 5 2 . 6 0 2.60- 3 . 9 3 1 . 6 5 1.65- 2 . 6 0 1 . 3 5 1.35- 1 . 6 5 0 . 9 7 0.97- 1 . 3 5 0 . 6 7 0.67- 0 . 9 7 0 . 5 7 0.57- 0 . 6 7 0 . 4 5 0.45- 0 . 5 7 0 . 3 2 0.32- 0 . 4 6 0.00 0 . 0 0 . 3 2
Held within Various Pore Radii
1
LIGNITE
I
%
1
PEAT
I %
%
I
BIRCHWOOD
I % 14.30 24.75 8.57 6.26 3.38 7.5 8.34 3.10 6.26 4.45 2.43 2.10 3.81 4.76
-
% 14.30 39.05 47.62 53.88 57.26 64.76 73.10 76.20 82.46 86.91 89.34 91.44 95.25
German brown coal. The data for brown coal are taken from the work of Kreulin and Ongkiehong (1). It is evident that, on the average, peat contains capillaries of larger radii than lignite and brown coal. I n terms of pore size we obtain the following classification: peat, birch wood, lignite, and brown coal, named in the order of decreasing pore size. The classification of North American fuels has been a problem of continuous discussion. The results of the present research indicate that a possible classification might be had in terms of pore size from sorption studies. It is the intention of the Division of Mines of the University of Korth Dakota to continue this study with the other ranks of coal, to obtain, if possible, such a classification.
100.00
a Bound water P E , where T = moisture in equilibrium at 100 T per cent relative humidity, and E = equilibrium moisture in any other atmosphere.
Vol. 22, No. 11
Literature Cited (1) Kreulin and Ongkiehong, Brennslof-Chem., 10, 319 (1929). CHEM., 221 1226 (lg30). (3) Thompson, Phil. Mag., [4] 42, 448 (1871). (2) Lavine and Gauger, IND.
Effect of Copper and Lead Ions upon the Rate of Decomposition of Hydrogen Peroxide at Various Acidities' Harry W. Rudel with Malcolm M. Haring UNIVERSITY O F MARYLAND, COLLEGE P.4RK, M D .
A
S IS well known, hy-
drogen peroxide tends to decompose s l o w l y at room temperature according to the equation: 2H202 = 2Hz0
+ 01
The rate of decomposition of 30 per cent hydrogen peroxide at varying acidities in the presence of varying concentrations of copper and lead ions has been investigated. The rate of decomposition increases with increasing pH. Copper ion has a marked catalytic effect on the decomposition, even in traces, while lead t ion has ~ a slight h inhibitory ~ effect. ~ Explanations for the various curves are offered.
hiaas a n d ~ ~ (18) claim that pure a q u e o u s solutions of hydrogen peroxide in suitable containers will keep indefinitely. However, commercial peroxide is seldom absolutely pure, so a study of the catalysts and inhibitors for this reaction is very desirable. Many such studies have been made (1, 3, 4, 6, 8, 9, 10, 18, 20), usually with relatively large amounts of the catalyst in dilute solutions. The evidence points to metallic ions, notably iron, as the active catalyst and to the formation of unstable intermediate compounds as the mechanism, However, the work of Elissafoff ( 7 ) on the rate of decomposition of hydrogen peroxide in the presence of glass wool, both with and without traces of copper sulfate, seems t o show that, in this case a t least, we are dealing with adsorption and not diffusion. This view is supported also by the work of Rice (16). The stability of hydrogen peroxide is likewise notably affected by its acidity, being least in alkaline solutions. Little work has been done to obtain comparative data on the stability of hydrogen peroxide in solutions of varying acidity in the presence of metallic ions. Furthermore, commercial hydrogen peroxide is now being made in a concentration of 30 per cent. Therefore, it was thought that a study of the effect of minute quantities of copper and lead ions, such as would be encountered in Dractice. uDon the decompoI
-
1 Received August 29, 1930. Abstracted from a thesis submitted by Harry W. Rudel in partial fulfilment of the requirements for the degree of master of science in the Graduate School of the University of Maryland,
sition of c o n c e n t r a t e d hydrogen peroxide a t varying a c i d i t i e s , would be of interest. Experimental Method
The gasometric m e t h o d developed by Walton (21) and Bohnson ( 2 ) was employed in this study. Decomposition rates were measured by observing the volume of oxygen liberated from 2200 cc. of the peroxide while maintained a t constant temperature. The mercury filled gas buret was connected to t h e decomposition flask by means of capillary tubing. Pressures were continually adjusted to atmospheric with t h e aid of a water manometer. The temperature of the thermostat was 32" C. and decomposition rates were never observed until the reaction mixtures had stood in the bath for 24 hours. All apparatus was scrupulously cleaned to prevent decomposition by unknown catalysts. The peroxide used was a pure 30 per cent product. The mixtures were made up by adding the required amount of catalyst solution to 2500 cc. of peroxide and then adjusting the acidity with normal sulfuric acid or sodium hydroxide. Hydrogen-ion determinations were made with indicators. To guard against fictitious results in such strong oxidizing solutions, two different indicators were always used. Effect of Acidity
Before a comparative study of the effect of metallic ions could be made, i t was necessary to determine the effect of varying concentrations of hydrogen ions upon the hydrogen Of this study are given in The perolji* 1 and F'lgUre 1.
