Thermal Activation of Attapulgus Clay EFFECT ON PHYSICAL AND ADSORPTIVE PROPERTIES
w. s. W.
McCARTER, K. A. KRIEGER’, AND H. HEINEMANN2 Attapulgus Clay Company, Philadelphia, Pa.
F
i
Data are presented on the chemical composition, strucThe main constituent of ULLER’s earth is a ture, x-ray diffraction patterns, thermal cleavage, surBttapulgus clay is a hyclay w h i c h h a s t h e face area, true, apparent, and bulk densities, water addrous magnesium aluminum property of decolorizing oils. sorption properties, void volume, pore volume, and equivasilicate which is believed t o Its name was derived from lent pore diameter for both natural and extruded samples be a distinct clay mineral (6, the earliest application in of Attapulgus clay (attapulgite) as a function of activation 31). De L a p p a l e n t sugthe removal of grease from temperature over the range 220” to 1400’ F. Water adgested the name attapulwoolen cloth. More than sorption properties are correlated with changes in strucgite (31)for the clay mineral 45% of the total tonnage of ture during activation. The effect of thermal cleavage found near Attapulgus, Ga., fuller’s earth in the United upon surface area and water adsorption is discussed. The a n d M o r m o r i o n , France, Statescomes from the southrole of extrusion in maintenance of surface area at high and gave it the empirical eastern states, more than activation temperaturesis outlined. formula (OH)2H2AI‘/ 3MgT from anv other section of the Si3HdOlo(32). Others concountry (47). The natural sider it a form of montactivity of fuller’s earth is, in morillonite ($5). Bradley (6) and Nagelschmidt (40) suggest a contrast to sub-bentonitic clays (montmorillonite), not substanstructural scheme for attapulgite which on the basis of x-ray diftially enhanced by treatment with chemicals, such as acids (42). fraction data distinguishes the mineral from mica, montmorilLarge deposits of fuller’s earth are found in Decatur County, lonite, and other clay minerals. Grim and Rowland (17) find Ga., and Gadsden County, Fla., near Attapulgus, Ga. It is with that attapulgite gives a differential thermal analysis curve unlike this Attapulgus clay that this paper is exclusively concerned. that of other minerals, supporting the conclusion that the material Industrial applications of Attapulgus clay are numerous and have often been described (36). An outstanding use is the decolorizis a distinct species. In attapulgite long double chains of composition SiaOllrun paring, deodorizing, dehydrating, and neutralizing of vegetable and allel to the fiber axis. They are joined together by magnesium mineral oils and waxes which can be accomplished either by conand calcium ions as well as through shared oxygen atoms. A tacting the oil with fine mesh clay or by percolating the oil in liqcomplete planar sheet of oxygen atoms is thus produced, aruid phase through a bed of the granular adsorbent (13,1Q,80-22, ranged exactly as in the micas and in other clay minerals (37); 41,43, 46,48). The spent clay can be regenerated by burning off however, in contrast to the micas, the silicon a t o m form long carbonaceous deposits and hence can be used through a large strips alternately on the two sides of the oxygen sheet. The magnumber of cycles. Fuller’s earth is used in the reclamation of nesium-aluminum-oxygen units are placed also in strips parallel used lubricating, turbine, and transformer oils (23). Georgiato the fiber axis. Channels, of a free cross section of 3.7 to 6.0 A. Florida fuller’s earth also h d s use in the petroleum industry as a or large enough to admit molecules of considerable size, run parcatalyst or catalyst support (4),in the treating of gasoline by the allel to the fiber axis, having no interconnections of comparable Gray process (46),and in the desulfurization (2, 16),polymerizasize. In natural clay, loosely held water molecules occupy a contion (18), depolymerization (8, 9 ) , and cracking of hydrocarbons siderable part of this space. On dehydration a t moderate tem(16). In the sugar industry, Attapulgus clay can be used for pH peratures they are removed, but the structure remains essentially adjustments of sugar liquors (30). Large amounts of the clay are used as an absorbent floor cleaner to remove oil and grease. The intact (37). earth will take up rn much as 70 to 80% by weight of oil and will The lathlike character of attapulgite particles predicted by Nagelschmidt (40) was demonstrated in the electron microscope remove stains caused by oil penetration of concrete and wooden floors (44). Fine mesh Attapulgus clay is finding increased use as (11,37,38). The fibers have a diameter of 10 to 50 mp (37) and an inexpensive, inert diluent for insecticide dusts (39, 44). One their surface has been calculated as 150square meters per gram (11). Attapulgus fuller’s earth contains, in addition to the clay of its outstanding properties is the ability to adsorb 40y0or more of its weight of liquid active ingredients without losing its flowamineral attapulgite, some free silica, calcite, and iron minerals. bility. Sorptive properties of fuller’s earth find use in the drying Typical chemical analyses are given in Table I. of gases and liquids (28) and in poultry litters and animal bedding Spectrographic analysis of the clay shows traces of manganese, (33). In recent years, specially processed fuller’s earth (12) has nickel, chromium, zinc, copper, lead, tin, vanadium, and silver. been used as a drilling mud component for oil wells, particularly Mining and milling of the natural earth has been described in salt water regions ( 1 , 10). The colloidal properties of the mud previously (24). Briefly, the raw clay is crushed in roll crushers, are not appreciably affected by salt (46) or other electrolytes. dried in kiln-type, oil-fired, rotary dryers, and finally milled to Miscellaneous analytical uses have been developed for fuller’s desired mesh size. Clay of somewhat different physical properearth, such as a chromatographic adsorbent in the determination ties is prepared by extrusion. In plant operation, the crushed of vitamins ( 3 ) ,carbohydrates (34),and oil-soap mixtures (6,26). clay is mixed with water in a pug mill to a volatile matter content 1 John Harrison Laboratory, University of Pennsylvania, Philadelphia, of 54% or higher, passed through an auger-type extruder which Pa. forces the clay through a die plate having a plurality of holes. 2 Present address, Houdry Process Corporation, Marcus Hook, PE.
529
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
530
TABLE
I. CHEYICAL h A I , Y > I S
Total volntile matter, % Free moisture, % Volatile-free basis, % Si02
A1201
Fez02 MgO OaO
'
OF ATT.4PULGUS CLAY .IttUpLllgllS EmenDe CIiy 13ratUey dorfer Lappareut c0 (6) (85) (26) 10.93 20 49 19.86 21.25 20 01 12.10 12 8 1 9.73 10.8'3 11.83
68.43
08.32 11.30
4.94
4.1'3
ii8.67 12.77 4.40
9.82 1 , 67 0.70
10.79 2 ,:%:I
12.56
0.2.5
0.6; 0.31
0.60
O..i!l
103
1.43
67.68 12.75
67.05 10.05
4.20
...
4.31 11.00 1 , 6,3
11.31
...
0.12
I .04 0.94 0.78
0.49
1.23
13.08 0.59
... 0.49
0.76
0.66
2.53
Like natural clay, the extruded material is dried and gi~omid; it possesses improved adsorptive properties for many applications. Attapulgus clay is hygroscopic; this characteristic has suggested the use of this mineral as :in inexpensive and abundant desiccant. It readily disperses in water. This property of the clay, however, is lost with increasing temperatures of activation. While the natural clay has adsorbent properties, these are usually enhanced by thermal activation. Properties of clay vary with the temperature of activation. It has been the purpose of the authors' studies, part of xhich are reported in this paper and part of which are being preparcd for publication, to investigate the physical properties of Attapulgus clay in general and their relation to the activation temperature in particular, to enhance the understanding of its adsorptive action, and to give data on its surface and structural characteristics in conuection with a relatively simplc adsorption phenomenon such as its drying properties. METIIODS AND , w P A H . 4 m s
The clay samples used in this work TIIE~IA ACTIVATION. L were activated in 1000-nil. batches in externally gas-fired rotary kilns (7 r.p.m., 6.5-inch diameter, 13.5-inch length) fitted with flights, and having an air inlet at onc end and a vent a t the other. Air was admitted a t the rate of 385 litei,s per hour. The samples n-ere heated to temperaturcm in 30 minutes and maintained at Ehe activat,ing temperature ( A z o F.) for 30 miiiutes. The products were removed from the kilns a t 400 O F. or a t the highest temperature below 400" F. used for activation and screened to remove tines. For temperatures above 1300" F., samples were activated in an electric muffle furnace previously heated t o the specified temperature. They were kept in the furnace for 30 minutes after reaching activation temperature. The volatile matter, V.b'I., of the samples n-as determined by placing a weighed sample of about 10 grams in a crucible into a muffle furnace a t 1750" F. for 20 minutes, reweighing after cooling in a desiccator, and expressing the weight loss as per cent of the sample. Surface area, S.A., was measured by the low temperature nitrogen adsorption method of Brunauer, Emmett, and Teller ( 7 ) , using the molecular size data of Livingston (35) and apparatus described by Krieger (27). The total or bulk volume, Vb, occupied by a porous solid is composed of three parts-the true volume occupied by the solid and adsorbed material, Vt; that occupied by pores within the granules, pore volume, V p ; and that occupied by the voids between the granules, void volume, V,. Determination of these data and their relation to apparent, true, and bulk densities (Dn, Dt,Db) and the equivalent pore diameter, d, have been d o scribed in an earlier paper (19). The dry gas capacity, D.G.C., is expressed as weight per cent and is equal to the weight of water vapor removed from a stream of humidified air by 100 grams of activated adsorbent prior t o the appearance of detectable water in the effluent. The a p p a m tus used to determine the dry gas capacity has previously been described in detail (29). Briefly, the method comprises carefully adjusting the moisture content of an air stream to a known value, passing the humidified air a t a known temperature and velocity through a bed of granular adsorbent in a suitable bulb, and finally, passing the effluent air from the adsprbent through a detector tube containining anhydrous magnesium perchlorate. Periodic weighings of the adsorbent bulb and of the detector tube permit plotting moisture sorption against time and a graphical
Vol. 42, No. 3
determination by extrapolation of the point a t which water vapor first passes the adsorbent. Determinations were made by passing gas of 75% relative humidity a t 80 F. through a bed (3.6 inches long, 1.5 inches in diameter) of l0/20 mesh adsorbent at 15 cubic feet per hour per pound of adsorbent, The equilibrium capacity, E.C., expressed as weight per cent, is equal to the total weight of water vapor which can be adsorbed by 100 grams of activated adsorbent. The apparatus used for this determination has been described (d9). The method is B dynamic one which involves passing a stream of air, which has been humidified to a known water vapor content, through a bed of activated adsorbent a t a known temperature and velocity and weighing the adsorbent periodically to constant weight,. A temperature of 80" F. and an air velocity of 175 liters per hour a t 75% relative humidity were used for a bed 3.6 inches long and 1.5 inches in diameter to obtain results reported in this papcr. X-ray diffraction data were obtained with a Norelco Geiger counter spectrometer using CuK, radiation and nickel filters. With this apparatus the intensity as well as the location of the peaks is recorded on a strip chart, and the relative intensities reported are computed from the peak heights after subtractiori of the background. In order to hecure reproducible intensiticv without the use of an internal standard, special care was taker1 in the mounting of specimens. Clay samples were first ground to pass 200 mesh, then made into a paste with collodion thinned LTith ether, and pressed into a form made by cutting a rectangular opening in a piece of 0.020-inch shim-stock and clamping it against a microscope slide. When the wafer thus produced had partially dried, it was lifted out of the form by touching it with a microscope slide coated with Duco lacquer and mounted in thr holder of the spectrometer. By this means it was possible to obtain a reproducibility of the order of * 10%; this was suficirni for the authors' purposes.
t~xscussIoN : ~ C T I V A T I O S TIG.lII'EH.4TURE O S RESIDUAL \vA'Tl';R IIESULlS AND
C T OF
COXTENTA SD DRY-INGC.WACI~TY. Attapulgus clay retains about 12'3, of water after prolonged drying at 220' F. By thermal treatment at higher temperittures, the combined watcr is partially removed and the adsorptive capacity for water is increased. In comparing the residual water content of the clay, V.M., with the differcntial thermal analysis curve given by Grim and Ronlniicl ( 2 7 ) ) Figure 1, the coincidence of four de-
@ NATURAL CLAY
0 EXTRUMD CLAY
4
0
200
600 800 1000 ACTIVATION TEMPERATUSE,'F
400
1200
1400
Figure 1. Effect of Activation Temperature on Residual Water Content and Drying Capacity
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
March 1950
b
hydration ranges is evident. These ranges are: 250" to 450°, 450" to 700°, 700" t o BOO", and 900" to 1400' F. These ranges correspond to destruction of the colloidal properties of the clay a t about 250' to 300" F., optimum drying properties at about 450" F., loss of the tendency to disintegrate in water, and development of optimum decolorizing efficiency a t 700" and higher. Optimum adsorptive capacity is obtained in the activation temperature range 400" to 700" F. at a volatile matter content of 6 to 10% (Table 11, Figure 1). The dry gas capacity reaches a maximum after activation at 450" to 500" F., then slowly declines to 600" F., and after that, declines steeply. This decline is temporarily interrupted and halted a t 800" t o 1100" F. The equilibrium capacity increases somewhat more slowly to a maximum a t 600" to 700" F., then declines sharply, the decline becoming more gradual above 900' F. (Table 11, Figure 1). The influence of activation temperature on extruded clay is similar to that on natural clay (Table 11,Figure 1).
TABLE11. DRYGAS AND EQUILIBRIUM CAPACITIES OF ATTAPULGUS CLAY .4ctivation Temp., F. 300 350 100 450 500
600 700 800 900 1050 I100 1200 1400
Attapulgus Clay, Natural V.M., D . G . C , E.C.,
%
%
10.6 10.1 9.9 8.6 8.3 7.0 6.3 4.6 2.8 2.5 2.0 1.8 0.8
11.1 12.3 12.2 12.7 12.6 11.3 6.9 5.0 4.8 4.3 4.4 3.9 1.7
Attapulgus Clay, Extruded V.M., D.G.C., E.C.,
% 16.0 16.8 17.3 18.0 18.2 18.6 18.5 14.9 10.9 10 4 10.2 9.6 5.3
%
%
%
10.4 10.0 9.6 8.5 8.1
10.4 11.4 11.7 12.5 12.0 11.5 8.9 6.4 5.4 4.5 4.3 3.7 2.5
16.8 17.1 17.4 18.3 18.6 17.8 17.2 14.0 11.3 10.9 10.7 10.1 8.3
6 7
6.0 4.5 3.1 23 2.0 15 1.1
There is little difference between the equilibrium capacity of natural and extruded clay (Figure 1). The optimum value is obtained at a slightly lower activation temperature for extruded than for natural clay. This equivalence of performance of natural and extruded clay is not reflected in the surface area values as will be shown later. Regeneration of the clay for drying purposes is carried out best by heating the spent clay a t 300" F. for a period of 4 hours. Complete regeneration is obtained during this period of time and no advantage is gained by longer heating. Lower temperatures frequently do not give complete regeneration, while higher temperatures reduce the adsorptivity (Table 11). The clay can be taken through a large number of adsorption-regeneration cycles without suffering in adsorptivity (Table 111).
TABLE 111. DRYGASCAPACITY OF REGENERATED ATTAPULGUS CLAY Reactivation Temp., 300° F. D.G.C., % of initial
7%
iinitia4 D.G.C. After Prst regeneration After-second regeneration .'After ,bhird regeneration ..After daurth regeneration .ifter,f&h regeneration .:Afterfhth regeneration After saventh regeneration After.eighth regeneration After,ninth regeneration Average .aegeneration
11.8 12.2 12.5 12.1 12.1 12.0 11.6 11.9
12.1 12.4 12.1
D.G.C. 100.0 103.3 105.9 102.5 102.5 101.7 98.3 100.8 102.5 105.1 102.5
Reactivation Temp., 400° F. D.G C., yo of initial 3' % D.G.C. 11.8 100.0 11.1 94.1 10.6 89.8 10.5 89.0 10.5 89.0
...
...
... ...
10.7
90.7
I
I
.
.
.
I
.... ..
... ...
an investigating the influence of mesh size on adsorptivity in a laboratory size apparatus, it was found that adsorbents finer than about 10 mesh showed substantially the same capacity. The capacity for producing dry gas decreases with decreasing
531
TABLE IV. DRYGASCAPACITY OF ATTAPULGUS CLAY Relative humidity, % a t 80' F Dew oint of air, F. D . G . ~ . ,%
10 53 6.3
75 74 12.5
97 79 27.5
TABLE V. X-RAYDATAFOR ATTAPULGUS CLAY Intensity, dhkl,
dhkl,
Obsvd. Bradley 10.51 10.5 6.45 6.44 5.46 5.42 4.50 4.49 4.28 ... 4.16 4.18 3.70 3.69 3.35 3.25 3.23 3.05 3.03 2.62 2.61 2.56 2.55 2.28 2.23 ... 2.15 2.15 1.920 .*. 1.874 ... 1.828 1.82 1.718 1.675 1.546 1.56 1.509 1.50 1.422 1.376 ... 1.300 1.2Qa 5 Not given by Bradley, de Lrtpperent (Sf).
... ... ,..
...
Kkh. 1.00 0.17 0.14 0.39 0.33 0.22 0.11 0.55 0.33 0.22 0.33 0.44
Index, Bradley 110 200 130 040 ,..
310 240
Identification Attapulgite Attapulgite Attapulgite Attapulgite Quartz dttapulgite Attapulgite Quartz ~
,..
Attapulgjte Attapulgite calcite Attapulgite Attapulgite Quarta calcite ... Quartz ... 0.22 Attapulgite 600 ... Calcite ... ... Calcite ... 0.11 390 Attapulgite quarta 0.1 ... Unidentified 0.06 Quartz 0.08 Attapulgite 680 quarta 0.11 0120 Attapulgite __ ... , . Quartz ... .. Quartz 0.11 ,.. Attapulgite but reported by Endell ( f f ) , Kerr (86),and 0
400 420 440 510
+
+
.
0
+ +
.
~~
humidity, but not in direct proportion to the moisture content of the gas. This is demonstrated in Table IV for operation at 80" F. and air velocities of 15 cubic feet per hour per pound of adsorbent. ADSORBENT PROPERTIES AND STRTJCTURE. Table V summarizes the x-ray data for Attapulgus clay. The particular sample chosen was kiln-dried a t 250" F. for 30 minutes and is typical of this clay except for the changes resulting from high temperature activation discussed in the following section. Extrusion does not change the pattern. Values of diameter, d h k t , found by Bradley (6)have been given for comparison. Using an iron target tube it is possible, under favorable conditions, to obtain a few additional lines, probably due to small quantities of an iron-containing mineral--e.g., lepidocrocite. Unfortunately, the lines so found are too few and too weak for positive identification. There can be no doubt that the principal mineral present here is attapulgite, identical with that studied by Bradley, with the admixture of small amounts of calcite, quartz, and possibly another substance. The line a t d,,,l = 14, reported in the A.S.T.M. card index, was not found, although the authors' experimental arrangement would have detected it if it had been present. The variation of surface area with activation temperature is shown in Figure 2, B. The most striking feature of this curve is the long, nearly flat portion extending from about 400' to about 1300" F. The constancy of area over this range is the more remarkable when contrasted with the considerable changes in equilibrium capacity (Figure 2, A ) and in relative intensity of lines in the x-ray diffraction pattern (Figure 2, C) which occur in the same region. It is apparent that area as measured by nitrogen adsorption is only indirectly related to water adsorption for this material, a result which is not surprising since the mechanism of water absorption is unquestionably different on this surface from that of nitrogen. Equilibrium capacity is not, however, the quantity most responsive to structural changes, greater sensitivity being exhibited by dry gas capacity, as the following section will show. Tbe invariance of total surface area in the face of rather profound structural changes is a second noteworthy feature of these data. The structure proposed by Bradley (6) is instructive in explaining these relationships. The lattice is a rather open one,
INDUSTRIAL AND ENGINEERING CHEMISTRY
532
ile
I
I
I
-
510.
E
-
2 8 -
0
5 6-
-
g 4 -
L
s
-
2-
do
j
(C)
Figure 2. Effect of Activation Temperature on Surface Area, Equilibrium Capacity, and X-Ray Diffraction
Vol. 42, No, 3
Although all of the data reported above were obtained with samples activated for only 30 minutes, the authors believe that, except at the highest temperatures, longer activation periods would produce little additional change. This is clearly true of the surface area, which, as Table VI shows, is substantially constant even a t 1100" F. for prolonged periods of activation, though it decreases fairly rapidly at 1300" F.
TABLEVI. NATURAL CLAY,SURFACE AREAAS FVXCTIOX OF TIMEAND TEMPERATURE OF ACTIVATION -Temp. 600
of Activation, 1100
-.
F 1300
Surface Area, Sq.M /G. so that adsorption of small molecules like water and nitrogen Time of Activation, Hr. could occur in the undamaged structure. M7hen a partial breakdown of the structure occurs with rising activation temperature, 117 23 little new surface is produced, since the areas now exposed on external faces were in fact already accessible through the large pores running parallel to the c axis. (If the surface area were -.... ... measured with a molecule too large to enter the pores, an increase in measured surface area would be anticipated following activation above about 800" F.) I t should be pointed out, however, that natural and extruded clay show differences in this respect. DENSITIESAND RELATEDPROPERTIES. The true density, The authors' results confirm Bradley's observation that cleavage D,, apparent density, D,, bulk density, D,,void volume, pore should be easy parallel to 110 planes, as Figure 2, C shows, and volume, per cent voids (per cent of bulk volume), per cent indeed this cleavage does not appear to produce any measurable pores (per cent of particle volume), and equivalent pore diameters effect upon either surface area or equilibrium capacit,y. as functions of activation temperature and volatile matter are The 110 cleavage is, however, reflected in a small but distinct shown in Table VII. These quantities have been computed by methods described earlier (19), and present data useful for rise in dry gas capacity (Figure 1). I t seems probable that this increase is not so much the result of an increased capacity for engineering design. The authors have also computed the water adsorption as of an increased rate of adsorption, since it is certain that diffuTABLE VII. DENSITIESAND RELATED PROPERTIES sion of water molecules through Equivthe undamaged pore structure AotiPore alent vetion Void VolSurface Pore m u s t be v e r y s l o w a n d Temp., Da D5 Dt Volume % ume Area, Diam% Adsorbent F. G./Cc. G./Cc. G./Cc. &ds Cc./G: Pores Cc./b Sq. M./G. eter V.M. cleavage would increase this rate. Although it is substanAttapulgus clay 220 0.633 1 . 0 5 2 . 4 8 39.7 0.628 5 7 . 7 0.549 ... . . . 12.5 Natural tially impossible to assess the 400 0 , 5 8 3 1 . 0 1 2.46 42.3 0.725 60.5 0.599 126 190 9.8 30-60 mesh 500 0.548 0 . 9 8 2.63 44.1 0.805 62.7 0.640 123 208 8.4 i m p o r t a n c e of the various 600 0.546 0.97 2 . 6 8 4 3 . 7 0.801 63.8 0.658 124 212 7.0 ... 120 ... 6.3 700 2.64 possible factors which deter800 0:576 0.96 2 . 6 5 40.0 0:694 63'.8 0.'665 121 220 4.6 900 0.578 0 . 9 6 2 . 6 6 39.8 0.688 64.0 0.667 118 226 2.8 mine quantities w complex as 1050 . . . . . . . . . 119 ... 2.5 dry gas capacity, it seems 1100 0 : 5 i 4 0.92 2.69 42.0 65.9 o : i i s 119 241 2.1 1300 0,578 0 . 9 5 2.56 3 9 . 1 0.677 62.9 0.662 119 223 1.3 reasonably clear that rates of 1400 0.583 0 . 9 5 2.54 38.6 0.662 62.6 0.659 78 338 0.8 adsorption and diffusion will Extruded 220 0.564 1 . 0 1 2.47 44.2 0.783 59.1 0.585 115(300°) 203 11.5 0.96 2.59 4 5 . 5 0.870 63.0 0,656 126 208 9.6 400 0.523 play more important roles here 30-60mesh 500 0.526 0.95 2.67 44.6 0.848 64.4 0.678 137 198 8.1 600 0 , 5 2 3 0 . 9 4 2.66 4 4 . 4 0 , 8 4 8 6 4 . 8 0.689 137 201 6.7 than is the case with equilib700 ... 6.2 136 zOi 4.5 0,'s'~ 2.B5 42.'5 01803 6 i . B o : i i o rium capacity, and the greater 800 o:bic~ 0.747 136 220 3.1 0.900 66.5 44.5 2.65 900 0.494 0.89 0.884 67.0 0.761 134 227 1.9 sensitivity of dry gas capac1100 0.495 0 . 8 8 2 . 6 6 43.8 0.939 6 6 . 0 0,750 134 224 1.2 45.3 1300 0,482 0 . 8 8 2.59 ity to structural factors may 1400 0.478 0.88 0.956 6 5 . 8 0.748 82 389 1.1 2 . 5 8 45.7 be explainable on that basis. O
March 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
adjusted volumes (19) derived from the densities, but it has not seemed worth while to tabulate these data since V,‘, V,‘, V,’, and V,’ prove to be practically constant over the whole temperature range and Vb’ is nearly so except for a rather broad maximum running from about 350” to 750” F. This increase in bulk volume probably corresponds to the disarrangement of particles accompanying the 110 cleavage, Vb’,returning again to approximately its original value as the particles become small enough t o fit into a new closely packed configuration. Some data comparable with the present authors’ data have been presented recently by Granquist and Amero (16). While the present authors’ results are in general agreement with those of Granquist and Amero, a few points of divergence are worth noting. The surface areas for natural clay between activation temperatures of 220’ and 1300” F. of McCarter et al., are somewhat more constant than those of Granquist and Amero although the difference is small and might easily be accounted for by minor differences in clay composition. Perhaps more important is the fact that extruded clays show rising rather than falling arem with increasing activation temperature over the 400 a to 500” F. range. This fact was not observed by Granquist and Amero and leads to a slightly fuller interpretation of the effect of extrusion. While the present authors agree that a major effect of extrusion is to produce an initial increase in pore volume by disordering the array of lathlike particles in the raw clay, it must be pointed out that the extrusion is performed before activation and that the noticeably higher areas found in extruded clay after activation at higher temperatures are not observed a t sufficiently low temperatures--e.g., a t 400’ F. (Table VII). The fact that extruded clays show areas higher than natural clays only after activation a t temperatures above 400” F., taken in conjunction with the observation that cleavage along planes parallel t o 110 begins at about this temperature, strongly suggests that the disarray produced by extrusion prevents the cleaved fragments from falling back into a closely packed arrangement is the case with a natural clay, and that it is this cleavage, rather than an actual increase in area due to extrusion, which accounts for the observed increase a t higher temperatures in extruded samples. The equivalent pore radii calculated by Granquist and Amero by two methods, R,,, from the volume of liquid nitrogen sorbed a t p = pa and Rd from the Kelvin equation, are consistently 25 to 35% smaller than those of the present authors. This difference is to be expected since McCarter et d.obtained their radii by a mercury displacement method which arbitrarily counts &s pores all spaces with an equivalent diameter of less than 2 X 10-8 cm. and, therefore, gives somewhat high values. Considering the difference in methods the agreement is actually rather good.
=
ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of J. B. Sanborn and A. B. Chady who made some of the measurements reported in this paper and of W. A. La Lande, Jr., under whose direction this work was begun. LITERATURE CITED ( 1 ) Alexander, J., “Colloid Chemistry,” Vol. V I , New York, Reinhold Publishing Corp., 1946. (2) Amero, R. C., and Wood, W. H., Oil Gus J., 46,82-5,99 (1947). (3) Andrews, J. S.,Boyd, H., and Terry, D., IND.ENG.CHEM., ANAL.ED.,14, 271 (1942). (4) Berkman, S.,Morrell, J. C., and Egloff, G., “Catalysis,” New York, Reinhold Publishing Co., 1940. (5) Bradley, W. F., Am. Mineral., 25, 405-10 (1940). (6) Brooks, F., Peters, E. D.. and Lykken, L., IND.ENG.CHEM., ANAL.ED.,18, 544 (1946). (7) Brunauer, S., Emmett, P. H., and Teller, E., J . Am. Chem. SOC.,60,309 (1938). ( 8 ) Ciapetta, F. G., Macuga, S. J., and Leum, L. N., Anal. Chem., 20,699 (1948).
533
Ciapetta, F. G., Maeuga, S, J., and Leum, L. N., IND.ENG.
CHEX., 40,2091 (1948). Cross, R., and Cross, M. F., U.5. Patent 2,044,758 (1936). Endell, J., Z . Naturforsch., 1, 646-9 (1946). Fitasimons, O., U. 5. Patent 2,231,328 (1941). Funsten, 8. R . , Refiner Natural Gasoline Mfr., 13, 201-7, 215-16. (1934).
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Solvent Extraction-Correction In the article on solvent extraction [Elgin, J. C., IND.ENG. CHEM.,42, 47 (1950)l several minor errors occurred. I n Table I (page 48) the temperature for the system allyl alcohol-water with triphloroethylene and carbon tetrachloride should be 25’ not 20” C. Under the heading “methyl ethyl ketone-water” should be added butyl Cellosolve, 25 O C. (85). The system water-nitric acid-sulfuric acid, listed at the end of the table, does not have two conjugate liquid layers. This should be noted and the system deleted from the table. Under Literature Cited, (37)should read: ChBdin, J., Fbnbant, S., and Leclerc, R., Compt. rend., 224, 1058 (1947); (48) should read: Hands, C. H. G., and Norman, W. S., Trans. Inst. Chem. Engrs., 23, 76 (1945). J. C. ELGIN
