1170
0. A. MILLS, JAMES HOLMES, AND E. E. CORNELIUS
ACID ACTIVATION OF SOME BENTONITE CLAYS' G. A. MILLS, JAMES HOLMES,'
AND
E. B. CORNELIUS
The Houdry Laboratory, Houdry Process Corporation, Marcus Hook, Pennaylvania Received November 14, 1949 INTRODUCTION
The distinctive surface properties of clays have long been utilized in bleaching and other adsorptive processes. For such purposes, individual clays possess widely different properties. Actually, the most efficient bleaching clays have been prepared by the acid-leaching of certain bentonite clays of relatively low bleaching power. More recently acid-treated bentonites have found an important new use as catalysts in catalytic cracking (12). Although the procedure for acid-treating clays for bleaching purposes has been described (16), relatively little has been published concerning the general properties of acid-treated clays and the changes which occur in the clay structure during acid-leaching. The present investigation was directed towards the preparation of cracking catalysts by systematically acid-treating a number of different bentonite clays under conditions of varied severity. The chemical compositions and catalytic cracking activities of the clays were determined as well as their physical properties, such as surface area, porosity, and pore-size distribution. All measurements were made on calcined clay pellets. Changes of properties have been correlated with severity of acid treatment. Activable and inactivable bentonite clays have been compared for the purpose of finding distinguishing features. Since the properties of clay are known to vary from deposit to deposit, the results must be restricted to the particular bentonite clays examined. However, the fourteen clays reported here were selected as representative of a wide range of properties and thus more general conclusions can be drawn. EXPERIMENTAL
The clays were dried at 105°C. and ground to pass a 200-mesh sieve. Samples were treated with 5-20 per cent sulfuric acid solution, a t acid:clay ratios of 0.2 to 0.8, and a t 93°C. for times up to 16 hr. They were then washed at room temperature until the washings were free from sulfate ion. The acid-treated clay was dried, ground, mixed with sufficient water to fnrm a plastic mass, and extruded into 4-mm. pellets, The pellets were dried, and samples were calcined a t 565°C. in dried flowing air. The physical and catalytic properties were all measured on samples which had been pelleted and calcined. The catalytic aqtivity was measured by the Catalytic Activity Test A (l), cracking light East Texas gas oil at 427°C. The surface areas were determined by the method of Brunauer, Emmett, and Teller (3), employing nitrogen as adsorbate. Pore-size distribution was esti1 Presented before the Division of Colloid Chemistry a t the 113th Meeting of the American Chemical Society, which was held in Chicago, Illinois, April, 1948. 9 Present address: Poly-Chemicals Department, E. I. du Pont de Nemours and Company,
Wilmington, Delaware.
ACID ACTIVATION OF BENTONITE CLAYS
1171
mated from the adsorption-desorption curves for nitrogen over the relative pressure range of 0.4 to 1.0. In some cases the macropore distribution was measured by mercury penetration by the method described by Ritter and Drake (20). The latter procedure was modified in that, instead of an electrical arrangement, the mercury level in the dilatometer was read directly by visual observation through the thick glass window of a Jerguson gage. One such gage allowed a maximum pressure of 1000 and another, used later, 10,OOO lb./sq. in. TABLE 1 Deucription of clays CLAY
A B
C
D
DZSCCPIMION
SOURCE
Fairly pure, white bentonite
Nye County, Nevada Monroe County. Mississippi
Calcium bentonite; a light brown powder said t o be from the Tombigbee sand of Eutaw formation of the Upper Cretaceous age; 85 per cent montmorillonite, the rest largely glauconite White bentonite with yellow-brown streaks, from the Montgomery lower Ripley formation County, Alabama Yellovish brown bentonite, believed to be that described Navarro County, by P. G. Kutting on page 150 of U. S. Geological Survey Texas Bulletin 928-C (1943) as lying in the Nacatoch sand of the Kavarro group i Sodium bentonite procured as a light yellow-green powWeston County, Wyoming der; this swelling-type bentonite is from the Black Hills region in the Upper Cretaceous i “White acid bentonite” 1 Light green bentonite (with some rust streaks and other Phillips County, Kansas , impurity) Wallace County, Light green bentonite Kansas Jessamine County, Light green bentonite (some rust streaks) lying in the * upper part of the Tyrone limestone Kentucky Grey-brown, very impure bentonite (some rust streaks Sumter County, South Carolina , and mica impurity) Sumter County I Very impure (adjacent t o J) i Grey, fairly pure bentonite (overluin by wmge and grey Thomas County, Georgia gritty clay), found near the Ocklocknee River Inyo County, Light brownish pink to white, impure bentonite California ~~
E
F G. H
I.
I
~
J
K L
~
’
~
M
Porosity, pellet density (sometimes called apparent density (13)), and real density were measured by water adsorption, employing a technique similar to that specified in A.S.T.M. C-20-46. Bulk density was also measured. However, values for bulk density have been omitted, since it was found that the packing factor remains fairly constant from sample to sample, bulk density being equal to pellet density times 0.6. Chemical analyses were obtained on some of the raw and acid-treated samples. In addition, a measure of the basic constituents which were dissolved during
The clays described in table 1 are of the subbentonite or nonswelling type for the most part and were identified principally by x-ray, chemical, and thermal analyses. RESULTS AND DISCUSSION'
Chemical composition of raw and acid-treated clays The acid solubility of the basic constituents of bentonite clays has been reported by Nutting (16) for a wide range of systematically varied conditions.
1173
ACID ACTIVATION O F BEXTONITE CLAYS
Comparisons in chemical composition for clays in raw and acid-treated conditions (presumably optimum for bleaching) have also been published (4,6, 8, 22). Similar results were obtained here for the changes in the prhcipal basic constituents during acid treatment. Data are given in tables 2 and 3. It is evident that different bentonite clays are attacked to different degrees by the same acid treatment. The effect of acid concentration on the “R203” removal is shown in figure 1 aa a function of time. It is obvious that, within limits, the same “R203” removal may be achieved by different acid strength-time combinations. The progressive solution of each of the individual basic constituents is shown in figure 2 for increasing severity of acid treatment. I t is of interest to examine the relative removal of each constituent. For instance, based on the original amount of each constituent present, the following amounts are found to have been dissolved: ~~
I
PER CENT OF CONSIITUENT DISSOLVED
NEYADA CLAY SAMPLE
-
A13. . , . . . . . . . . , . . . , . . . . . . . . . , . , , , A14................... . . . .. .. . . ..
, -____
CaO
97
Considered from the viewpoint that aluminum, iron, and magnesium occupy the same position in the montmorillonite lattice (19, 21), it is not surprising that these are removed at approximately the same relative rate. I n these experiments all the calcium sulfate formed by the sulfuric acid treatment is dissolved by the extensive washing, a circumstance not usual in commercial activation. Comparisons have been made in the last two columns of table 2 between the “R203”removal as determined from analyses of the spent acid solution and as determined from analyses made on the acid-treated clay. Considering the fact that the values from the clay are arrived at by difference, the agreement is reasonably good, particularly for higher values where the accuracy is greater. The “R20s”removal value obtained directly from the spent acid liquor is believed more accurate, although there may be small amounts of magnesia included, owing to the procedure used.
Physical properties of raw and acid-treated clays The physical properties of clays, particularly when in colloidal dispersion, are well known to display wide variations. The surface areas and porosities reported here for the raw calcined clays also show wide ranges of values. Examination of the pellet density, porosity, and real density reveals a good deal about the structure of clay pellets and the behavior of both the raw and the acid-treated clays. The measured real density of acid-treated clays was found from water absorption to lie between 2.6 and 2.4 g./cc., in general agreement with values calculated by taking an arithmetic average of the densities of the individual oxides weighted according to the composition of the clay. The measured real density decreased with increasing severity of acid treatment as the basic con-
1174
G. A. MILLS, JAMES HOLMES, AND E. B. CORNELIUS
TABLE 3 Physical and catalytic properties of raw nnd acid-treated clays
I
I
ACID TREATMENT
tble’
A. “Act
PBYSICAL PROPERTIES
I
CATALYTIC PROPERTIES
,entl itea
- __
&C.
5.0
Ash Meadows, Nevada : Al. . . . . , . . . , . . A2. . . . . . . , . . . A3. . , . . . . . . . . A4. . . . , . . . . . . . A5. . . . . . . . , , . . A6. . . . . . , . . . . . Ai, .. . . . , . . . , , A8, , . . , . . . . . . , rig. . . . . . . . . . . A10. . . . . . . , . . . A1 1. . , . , . . . . . , A12. . . . . , . . . , . .413. . . . . . . . . , . A14. . . . . . . , . . A15. . . . . . , . . . . Pant her Creek , Monroe County, Miaaissippi : B1. . . . . . . . , . . . B2, , . , . . . . . . . B3. . . . . . . . . . , . B4. . . . . . . . . . . . B5. . . , , . . . . . . . B6. , . . . , . . , , . . B7. , . . . . . . . , . . B8. . . . . . . . . . . . B9. . . . . . . . . . . . B10.. . . . . . . . . . Bll.,.. ., , ... , Montgomery County, Alabsma:
c1. . .
. .. ..., , c2. , . . . , . . . . . . Navarro County, Texas: D1.. . , . . . . . . . . D2. , , . . . . . . . . . ,
0 Raw calcined clay 0.2 4 5 1.6 0.2 5 2.0 8 5 0.2 2.0 16 10 0.2 8 3.4 4.2 10 0.4 4 5 0.4 5.2 8 15 6.0 4 0.4 10 6.6 0.4 8 5 7.3 0.6 8 15 7.2 4 0.6 0.4 10 16 8.0 15 0.6 8 10.7 0.8 8 14.9 20 0.4 10 8$ 15.3
5.7 40.6 36.2 43.9 51.0 53.6 53.8 56.4 57.5 54.5 1.oo 60.0 1.05 57.8 0.95 60.8 0.87 63.0 0.81 67.0
9 7.1 1 . 2 71 34.9 4.2 117 34.0 4.5 40.5 4.5 41.4 4.5 146 46.8 4.6 44.9 5 . 1 44.4 4 . 3 236 43.9 4.4 43.0 4.6 45.9 4.4 236 43.0 4 . 3 282 42.5 4.1 279 37.5 2.9 348 38.7 3.2
1.1 4.8 5.7 6.6 6.3 8.4 7.8 8.2 8.7 9.1 8.0 7.7 8.1 6.9 6.5
1.29 1.42 1.48 1.47 1.47 1.58 1.59 1.54 1.56 1.57 1.57 1.53 1.55 1.49 1.50
0.4 4.9 5.0 4.3 5.3 4.4 4.5 3.8 3.0 4.1 3.8
0.6 6.3 5.3 5.8 7.0 7.3 7.3 4.9 5.0 6.3 6.2
1.24 1.36 1.40 1.33 1.38 1.40 1.51 1.38 1.33 1.42 1.38
7.1 0 . 6 1.78 18.4 22 1.05 57.0 180 36.1 3.0
0.8 5.2
0.8
1.92 16.7 8 . 2 5.4 0 1 . 5 1.32 48.9 155 34.1 4.0 1.29 49.5 l i 9 34.2 7.6 1.20 54.6 229 35.0 36.4 1.36 51.4 1.16 54.6 35.0 6.0 1.05 61.0 250 41.2 9.5 1.03 59.6 253 31.6 10.0 0.95 63.0 250 32.8 1.10 58.3 32.8 34.0 1.03 60.5
Raa calcined clay 10 1 0 4 ’ 4 10 4 15 15 15
1.95 1.55 1.55 1.45 1.26 1.19 1.19 1.08 1.07 1.15
0 6 8 06 10 1 0 6 116
1
0.2: 0.3 1 . q
I
Raw calcined clay lo
I
0.4
I
0
1.57
j l2
Raw calcined clay 15 1 0.6 I 8
’
0 5.3
1.96 1.26 _ _
1
li.8 I 2 i 4 . 4 1 . 2 0.8 0.57 2.9 5.4 1.12 51.2 188 127.2 -
1175
ACID ACTIVATION OF BENTONITE CLAYS
TABLE 3-Continued
1
1
ACID TREATMENT
PEYSICAL PROPERTIES
1
CATALYIIC FKOPERIIES
A. “Activable” bentonites-Continued
-
1 Wyoming bentonite : El,. . . . . . . . . . E2. . . . . . . . . . . “White acid bentonite” : F1. . . . . . . . . . . F2. . . . . . . . . . .
i
volume
1
I
__ I
1
1
5 . 3 0.4 42.5 1109 129.6 3.7 Raw c’alcined’clrcy 20 I 0.8 1 4
___ ~-
I
1
I 1 l
0 7.5
l
I
0.7 4.0
1.2i
1.46
!
1.3 2.8
1.67 1.54
1.2 0.93 4 . 1 1.38
B. “Inactivable” bentonites Phillips County, Kansas : G1, . . . . . . . . . . . G2, . . . . . . . . . . . G3, . . . . . . . . . . . G4. . . . . . . . . . . . Wallace County, Kansas : H1, . . . . . . . . . . . H2, . . . . . . . . . . . H3. . . . . . . . . . . . H4, . . . . . . . . . . . Jessamine County, Kentucky: 11, . . . . . . . . . . . . I2 . . . . . . . . . . . . Sumter County, South Carolina: J1 . . . . . . . . . . . . . 52 . . . . . . . . . . . . Sumter County, South Carolina : Kl... . . . . . . . . . K2. . . . . . . . . . . . Thomas County, Georgia : L1. . . . . . . . . . . L2. . . . . . . . . . . .
Raw calcined clay 10 0.4 4 15 4 20 4
1 ~
1.88 1.45 1.31 1.25
30 9 1 66 L1.3 43.1 1 133 13.9 45.4 163 14.1 51.0 183 10.4
0 1.73 6.4 1.41 9.1 10.1 1.24
7.5
5.1
1 . 7 0.73
144 9 . 8 10.3
2.6 1.7
1 .o 1.1
0.57 0.65
I 5 0 8.9 1.9) 1.38 49.6 105 9.2
2.9 1.5
1.9
0.39
4.7 1.3
2.0 0.32 1 . 5 0.66
0 5.2 8.7 10.3
~
Xi
5.6 2.3 2.4 1.5 2.5 1.5 1.9 0.9
0.52 0.65 0.64 0.66
I
I Raw calcined clay 10 1 0.4 15 I O 6 20 0.8 4
i
~
I
1
I
I
I
0 5.0
Raw calcined clay 20 1 0.8 4
1
1.1 1.01
1
i
l
Raw calcined clay 10 1 0.4 8
1
I
0
1.28 48.5 1.19 50.4
58.8 60.0
~
8.4 115 13.9
!
Raw dalcined ‘clay
I
0.95 0.92
I
I
l5
0
0.6
I
Raw dalcined’clay 10 1 0.4 1 8
~
9.6 3 . 5 100 17.1 1.4
1.6 1.6
0.48 0.77
,
I
0 (13)
1.67
35.3
1.24 49.6 -
~
75 16.7 4.0 2.3 0.66 161 L8.2 2.6 2.1 __ 0.85
1176
G. A . MILLS, JAMES HOLMES, A N D E. B. CORNELIUS
-
TABLE 3-Concluded ACID TRKATMEXT
PEYSICAL PROPEPIIES
1
CATALYTIC PROPEPTIES
B. “Inactivable” bentonites-Continued
California :
M1.. . . . . , . . . .
Raw calcined clay
1.67
34.2
i
8.0 3.2
0.9
0.61
* Pellet density = weight of dry pellets/volurne of pellets; volume of pellets 3 pycnometer volume minus volume of water added t o fill pycnometer containing water-filled pellats. t Porosity = (volume of pores/volume of pellets) X 100; volume of pores = weight of water t o fill pellets X density of water. 1Blank test for Catalytic Activity Test A; no catalyst present. 5 Hydrochloric acid instead of sulfuric acid. stituents were removed from the less dense silica. For certain raw clays the measured real density was low (for example, 2.08 for sample Al), owing to the existence of closed pores not accessible to the penetrating liquid. The measured porosity was only 5.7 volume per cent in this instance, whereas the volume per cent porosity has a calculated value of 26 (which happens to be that for close packing of spheres) when the real density is assigned a reasonable value of 2.6. The porosity of a clay pellet depends in part upon the colloidal behavior of the clay slip. A great variation in drying shrinkage occurs for different clays. This shrinkage is believed to be a lining up of the montmorillonite platelets due to the action of the water on the surface and the forces exerted during drying when the water film is progressively lessened. In the case cited above (sample Al), the great drying shrinkage results in a pellet having smaller external dimensions and consequently a high pellet density (column 4, table 3A). Moreover, the shrinkage has made most of the pores inaccessible to liquid. With increasing severity of acid leach the pellet porosity increases, as shown in figures 3 and 4 and in column 5 in table 3. The effect of the removal of rather moderate amounts of basic constituents is to cause a large increase in the measured porosity. The increase in porosity is greater than can be accounted for by the volume of basic materials removed. The reason for the increased porosity is believed to arise from the circumstance that the porosity is to a degree dependent on the extrusion conditions, which partly depend upon the changes in the plasticity of the clay brought about by acid treatment. This effect is large in some cases. The effect of extrusion Conditions on the porosity of a single clay was investigated for an acid-activated bentonite manufactured by the Filtrol Corporation
1177
ACID lCTIVATION OF BESTONITE CL.4YS
for use in Thermofor catalytic cracking. With increasing pressure, effected by having less water in the extrusion mix, increasing pellet density and decreasing I
C
I
i 4 t
'
'
'
'
'
'
'
"
'
'
'
'
' I
' 1
/P
:eElEEl 3 0
HOURS O f I C 1 0 T R E A T M E N T
"RIOI"
REMOVAL ,cmS/lOO
OMS. CLAY
FIG. 2 FIG. 1 FIG. 1. Effect of time and acid concentration on "R20a" removal from Nevada bentonitic clay, A, acid-treated a t 93°C. FIG. 2. Chemical composition of clay remaining after acid treatment (ordinate) calculated on the basis of constant Si02 = 100. 0, Nevada clay, A; 0 ,Mississippi clay, B. L
300
3260
'
:
I
* "b 'R,O
