Heat of Wetting of Activated
Bauxite and Attapulgus Clay JOHN G. MILLER’, HEINZ HEINEMANN2, AND W. S. W. M C C A R T E R Attapulgus Clay Company and Porocel Corporation, Philadelphia, Pa.
A
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The calorimeter was surrounded by a constant temperature bath regulated to *0.01“ C., the bath level being brought to within 0.75 inch from the top of the Dewar. The circuit used to control the heater current and to determine the electric power input was of the conventional design described by Sturtevant (9). The storage battery was discharged into the ballast resistor for at least 20 minutes to stabilize its voltage before the heater was switched into the circuit. This ballast resistor was of nearly the same resistance as the heater coil. The standard resistor was a Rubicon 1-ohm unit. On calibration, it showed a value of 1.0000 international ohm. The heater resistance was checked periodically throughout the studies. The 25 O C. value originally was 3.205 international ohms and increased slightly with aging until after 6 months, when it had reached the value 3.212 ohms and showed no further change. Its value was determined at the appropriate temperature for each experiment. About 0.7 ampere was used in the electrical heating periods, the current being steady to 1 part in 10,000. A stop watch was used for timing. The potentiometer was a Rubicon type B instrument. The sample tubes ordinarily used readily held 9 to 11 grams of bauxite or 5 to 7 grams of fuller’s earth. To prepare a tube for use, its dome was blown to an optimum thickness so that it could AUXITE and fuller’s earth (Attapulgus clay), both natusupport the breaker rod when in position in the stirrer and yet be rally occurring materials of large surface area, are important broken readily when desired. I n sealing, the solids were protected industrial adsorbents (8-6). I n the percolation filtration or conby wrapping the tubes with moist asbestos paper. I t was not necessary to seal the solids under vacuum to obtain rapid wetting tact treatment of liquids the amount of heat evolved when the and no detectable chanze in the heat of wetting resulted when liquid wets such solid adsorbents is of sufficient magnitude to consuch treatment was trie& stitute an important factor in the design and operation of the apAn amount paratus used. Few data of use in predicting the quantity of this of wetting heat of wetting for these two solids have been available up to the liquid was present. added to the D e w a r sufiThis paper presents values of the heat of wetting of activated cient to cover bauxite and Attapulgus clay with a large group of liquids chosen the coil, therto include many of the most important types of substances enmometer, and countered in industrial adsorption processes. The results indisample tube &s shown in Figcate that selective or preferential adsorption of liquids by fuller’s u r e 1. T h e earth or bauxite may be determined by the amount of heat genliquid had erated during wetting. been brought This work is part of a program of study of the fundamental to proper temperature in adchemical and physical properties of bauxite and Attapulgus clay vance in the related to their various industrial applications (2-6). constant-t e m perature bath. APPARATUS T h e Dewar was then The calorimeter is shown in Figure 1. The Beckman thermomclamped to the eter, A , and heating coil B, were held in place in the wooden suptop support port, C, by corks, while the glass stirrer, D, passed through a and the calowooden bearing, E . The vessel, F, was a 1-pint silvered Dewar rimeter placed bottle and was supported firmly in the sealing groove, G cut in C. in the bath. The figure shows a sample tube, H , held in place in the stirrer, For use with and the breaker rod, J , above it. The stirrer was constructed so very volatile or that by the window at D the rod was readily manipulated for obnoxious breaking the dome of the sample tube. The bottom part of the liquids, the stirrer, which held the aample tube, waa made of brass. The mospecial alltor attached t o the top of the stirrer was controlled by a variable glass t u b e s transformer, a disk stroboscope serving as constant-speed indicator. shown in Fi,gThe Beckman thermometer was calibrated b y the National ure 2 were deBureau of Standards. A vibrator attached to the motor support signed. These mounted on C served to prevent the thread of the thermometer tubes s e r v e d from sticking. both as samThe heating coil, 3 feet of chrome1 A wire was wound in 26 ple tubes and turns on a lathe and was supported b y the heavy leads, K , of o l e as stirrers, and u: P 0.08-inch tinned copper wire. fitted the INCHES 1 Harrison Laboratory, University of Pennsylvania, Philadelphia, Pa. wooden bearFigure 1. Calorimeter * Present address, HoudrV Process Corporation, Marcus Hook, Pa. ing readily to 151
method for determining the heat of wetting of adsorbents is described and heat of wetting data of a series of organic liquids and water are given for activated bauxite and Attapulgus clay. The influence of the activation temperature o€ the adsorbents and of their residual water content on the heat of wetting was studied. In the case of bauxite, the heat of wetting follows the trend of the surface area with change in activation temperature. With Attapulgus clay, the residual water content exercises a more pronounced effect than the surface area. Comparison with some wetting data for silica gel and charcoal indicates that the area available to the wetting liquids is variable for any one solid, depending on the shape and size of the wetting molecule. The electric moment of the Iiquid does not appear to be an important factor. Close similarities in the molecular structure of wetting liquids cause nearly equal heats of wetting, especially with bauxite.
B
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INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
352
replace the usual stirrer and sample holder, The weighed solid was placed in the lower chamber and sealed as shown in the figure. Then, the liquid was added to the upper chamber, the breaker rod was put in place, and the upper chamber was sealed. This breaker rod had a soft iron top so that it could be manipulated by a magnet. The seal on the solid chamber was shaped in such a way as to act as a stirrer. When these tubes were used, the calorimeter was filled with 95y0 ethyl alcohol, which was chosen for its low heat, capacity and good thermal conductance. PROCEDURE
The stirrer was run at a constant speed of about 200 r . p m being started a t least 20 minutes in advance of the measurements to ensure a steady rate of temperature change in the fore rating period. The stirrer was stopped for about 15 seconds in advance of the measuring period so that the breaker rod could be readied and thrust into the sample tube to start the wetting process. The brief cessation of stirring never caused any appreciable error because the heat input due to stirring was small. The electrical measurements used to determine the heat capacity of the calorimeter and its contents in each determination were carried out after the wetting measurements. Thus, the assumption was made that the heat capacity of the system was the same after the wetting process as before. This assumption was checked by a run in which determination of the heat capacity was made. both before and after t h e wettine Urocess. The values agreed within 0.1%. The measurements were all carried out in the temperature range 25' to 30" C., with the exception of the butane determination which was run at 0 O C. I
*
CALCUIA'I'IONS
The heat loss corrections were calculated by the ItegriaultBfaudler method in a simple form presented by White (11). In the determinations using the special sample tubes, a small but appreciable correction was made for the vaporization of some of t h t liquid which took place m h n the liquid flowed into the chamber containing the solid. In 13 cases, two or more dupllcate cletcrminations of the specific heat of wetting were made. For all of these cases, the deviations of the individual values from the means averaged 2.4%, which is taken as an indication of the over-a11 accuracy of Ihe measurements. MAl'EKIALb
Arkansas and South American bauxites, socii as deacribed b j Heinemann, Krieger, and hlcCarter ( d ) , were used. The Attapulgus clay used is a fuller's earth of the Georgia-Florida typti, comprising predominantly the mineral attapulgite ( 7 ) . Both tltr natural and extruded f o r m ( 7 ) wele studied. The activaled silica gel and the activated charcoal were commercial productb. dried a t 400" F. All the solids were stored in small hatches in glass containers sealed from the atmosphere. The liquids were all of high quality arid were dried carefully before use. RESULTS
The values of the specific heat of wetting, expressed 111 defined calories per gram, for several samples of bauxite and for Attapul-
TABLE 1. EFFECT OF
AcrrIvAi310NTEMPERATURE AND
gus clay, with different liquids are listed in Table I t o show the effect of activation temperature and per cent residual volatile mat,ter ( % V.M.) for the solid. It, is well knoxn that the absolute surface area cannot be calculated froin the heat of wetting without knowledge of the adhesion tension arid its temperature coefficient'( 1 , 8, 10). Severtheless, it might be expected that two solids of the same chemical composition but of different surface areas would, with the same liquid, have specific heats of wetting proportional to their specific surface areas. The bauxite values in Table I show the behavior nxpected in this way, the heats of wetting follow the known illcrease in surface area with activation t,empera,turt!lip to 700' F and t,he decrease a t higher temperatures (W,b). With the clays, the surface area is relatively constant a t activitt,ion temperatures above 400 ' F. arid below 1300 F., while the raw dried material shows H lmwr brit rather unpredictable area ( 7 ) . For these reasons it appears that, in contrast to bauxite, only a relatively small part of (he total surfaoe area of t,he clay is actively nlei by the liquids and that a large fraction of t,hir available or active S U I face is affected by change in activation temperature, The increase i r i heat of wetting by extrusion treatment of the clay i s a l s o d e m o n strated. Further COIIsideration of the availability of the surface area of the clays in relation to the wetting liquids i c given below. ORDINARY The values of Table I SAMPLE TUBE suggest, that the per ceili residual volatile matter is an additional important factor in determining the lieat of wetting SCALE: At, any activation tem. perature, the lower the per cent residual volatile SPECIAL matter, the greater the SAMPLE TUBE heat of w e t t i n g witti water. Figure 2. ,All-Glaua Tube for I'se w i t h Very Volatile o r The efi'ect of riitrati Ohnoxious Liquid (i size was riot determined Most of (.he samples Mere 6/14 mesh, while d fefi tiere 10/30 mesh. Arkansas bauxite, activated at 700" F. to 7% residual volatile matter, and natural Attapulgus clav, nctivated at 550" F to O
RESIDUAL ~OL,.%TlLJ2
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hTTAPULGlE C L A Y
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A t t a j d g u s Clay----.-.--
Extruded
Natural
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Sieaifio heat of wetting, oal./g. Water Motor gasoline Benzene Ethyl alcohol
Dried ram 14.9
Below
10.6
17.7 ..
4:2 .,
400' 15-20
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4500
550"
9.3
8.5
6.2
900" 3.2
21.8
23.2 5.9
25.6
4:3 17.1
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450'
8.5
10.9
24.5
2.4
1:4
24.8 6.9
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12.9
21.8
0.1 I .
1200O
700' 7.5
3 0
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Bauxite
Arkansas
900" 3.2
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9.0
4.7
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Activation Temp.,
Vol. 42, No. 3
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South American Dried raw 700" 1200'
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INDUSfRIAL AND ENGINEERING CHEMISTRY
taauary 1950 f
TABLE11. SPECIFICHEATOF WETTINGOF ACTIVATED SOLIDS WITH SEVERAL ALCOHOLS .4lcoho1 CHaOH CzHsOH n-CaHIOH n-CdHoOH ~so-C~HBOH tert-C4HoOH
Arkansas Bauxite 16.2 12.8 12.6 12.3 11.0 9.1
Attapulgus Clay 20.6 17.1 15.0 13.4 12.1 6.5
Charcoal 25.7 27.0 26.5 27.0 23.0 20.2
Silica Gel 34.9 31.7 29.2 28.5 25.5 21.9
‘TABLE111. EFFECT OF STRUCTURE OF WETTINGLIQUID ON HEAT OF WETTINGOF ACTIVATEDBAUXITEAND ACTIVATED ATTAPULCIJS CLAY Bauxite 10.1” 36.5“ 18.6a 10.5” 5.9” 11.9“ 7.4a 5.5“ 8.3“
b C
d
*
Acetone Propionaldehyde Propionic acid Ethyl acetate Bromobeneene Aniline Nitrobenzene Benzene Furan 5.66 Cumene 4.1b n-Butane Commercial paraffin 3.5b Cs fraction gasolinec 11.0d Pyridine 5.W Thiophene 12.8d n-Butyl mercaptan Arkansas bauxite, 7.0% V.M, Arkansas bauxite, 7.5% V.M. Obtained from a sulfuric acid alkylation plant. South American bauxite, 8.4% V.M.
Attapulgua Clay 17.9 22.1 10.9 14.2 8.2 9.7 9.3 4.3 13.4
.... *. .. .. I .
8.2% residual volatile matter were compared with a commercial activated silica gel and a commercial activated charcoal in experiments with several alcohols, the results being listed in Table 11. These results indicate a similarity in the availability of the surfaces of the silica gel and the clay and a similarity of the bauxite to the charcoal. With the normal alcohols, starting with ethyl alcohol and increasing the chain length, the heat of wetting of the silica gel and clay decreases markedly, the bauxite and charcoal values remaining fairly constant. If one assumep equal adhesion tensions for the different alcohols with any solid, ;he length of the wetting molecule appears to determine the available surface for the clay and silica gel. The width appears important for all four of the solids in view of the decrease shown in the heat of wetting in going from n-butyl alcohol b the iso- and tertbutyl alcohols. The methanol values show the combined effects of small size and compact shape for the molecules of that liquid, except in the case of charcoal. With charcoal, the similarity of methanol to water overrides these factors (IO). One may conclude that the areas available to the wetting liquids are variable for any one solid, depending on the shape and size of the wetting liquid molecules. This study, based on the alcohols, has the advantage of eliminating effects due to variation of the electric dipole moment of the wetting liquid, the moments of the alcohols all being nearly equal (1.7 debyes in benzene solution). The measurement of the heat of wetting of bauxite with ethyl ttlcohol showed a great sensitivity to traces of water. Unless oare was taken to keep the alcohol very dry, the values were noticeably high, showing strong selective adsorption of the water. Consistent results were obtained only when some bauxite was placed in the bottom of the calorimeter to maintain dryness of the Ltlcohol. The specific heat of wetting by 95% alcohol was measured and found to be 16.5 calories per gram, a value higher thau that predicted on the basis of the mole fractions of the alcohol and water present, 13.8 calories per gram, also showing the selective adsorption of the water. I n Table I11 are presented the values of the specific heat of wetting of bauxites activated at 700” F. and of natural Attapulgus clay activated at 550“ F. to 8.2% residual volatile matter, using a variety of wetting liquids. In general, the 550” F. Attapulgus clay shows a higher value of
153
the specific heat of wetting than the 700” F. bauxite with any liquid. Exceptions are propionaldehyde, propionic acid, aniline, tert-butyl alcohol, and benzene. I n the case of the first two it may be that chemical reaction takes place a t the bauxite surface. The behavior of tert-butyl alcohol has been discussed above. The low values for benzene and motor gasoline, the only nonpolar liquids studied with clay, point to the fact that the clay values are high only if the wetting liquid contains oxygen bound to a much more electropositive element such as carbon or hydrogen. The dipole moment-i.e., the polarity of the liquid molecules-plays a secondary role. For example, furan with one of the lowest momente in the list (0.6 debye in benzene solution) has a higher heat of wetting with clay than that of nitrobenzene which has t)he highest moment (4.0 debyes in benzene). With benzene or gasoline, neither oxygen nor a permanent dipole is present to produce a high heat of wetting with the clay. The bauxite values show that close similarities in the molecular structures of wetting liquids cause nearly equal heats of wetting. Beyond the fact that more liquids were studied with this solid, the parallelism8 are more pronounced in this respect than those that exist for the clay, probably because the availability of the bauxite surface is less dependent on the size of the molecules of the liquid and does not, therefore, modify the effects of the other factors active in determining the heat of wetting-via., the presence of certain atoms or structural groupings in the liquids. The fact that the fuller’s earth has a greater mean pore diameter than the bauxite ( 7 ) is not expected to affect the relative availability of the surfaces of these solids in processes as slow as those studied here, in view of the large value of the mean pore diameter for both of the solids. Examples of the structural parallelisms with bauxite are found in the near equality of the values for benzene, bromobenzene, thiophene, and cumene; n-butyl mercaptan and the higher normal alcohols; acetone and ethyl acetate; aniline and pyridine. The speed of wetting of the bauxite was in general greater than that of the clay, t o judge by the speed of evolution of the heat of wetting. Only with propionaldehyde was the heat evolved slowly for the bauxite, and in this case the amount of heat was extraordinarily large and chemical reaction may have taken place. In wetting the silica gel with the three butyl alcohols, the evolution of heat was slow and increasingly slower with branching of the structure of the alcohol. This is another indication of the effect of size and shape of the molecules of the liquid upon the availability of the surface of that solid. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of Knut, A. Krieger who designed the calorimeter. LITERATURE CITED
(1) Bikerman, J. J., “Surface Chemistry,” pp. 204,264, New York, Academic Press, Inc., 1948. (2) Heinemann, H., Krieger, K. A., and McCarter, W. S. W., IND. ENG.CHEM.,38,839(1946). (3) Hubbell, R. H.,Jr., and Ferguson, R. P., Refiner Natural Gasoline Mfr., 17,104 (1938). (4) La Lande, W.A., Jr., IND. ENG.CHEM.,33,108 (1941). (6) La Lande, W. A., Jr., McCarter, W. S. W., and Sanborn, J. B.. Ibid., 36,99 (1944). (6) La Lande, W.A., Jr., Sanborn, J. B., Aepli, 0. T., and McCarter, W.9. W., Zbid., 34,988(1942). (7) McCarter, W. S. W., Krieger, K. A., and Heinemann, H.. Ibid., submitted for publication. (8) Razouk, R.I., J. Phys. Chem., 45,179 (1941). (9) Sturtevant, J. M., in Weissberger, “Physical Methods of Organic Chemistry,” Vol. I, p. 331, New York, Interscience Publishers, Inc., 1945. (10) Weiser, H.B.,“Colloid Chemistry,” p. 63, New York, John Wiley & Sons, Inc., 1939. (11) White, W.P., “The Modern Calorimeter,” p. 41, equation 12, New York, Chemical Catalog Co., Ino.,1928. R ~ C E I V EJuly D 7, 1949.
