Again recyclization and cracking will give the olefinictype product distribution.
tion. Product distribution indicates that progressive scission reactions of the alkyl group predominate.
Alkyl Aromatic Cracking
Acknowledgment
A mechanism for dodecylbenzene cracking, on the other hand, should be similar to paraffin cracking. There is no way to form an olefinic carbonium ion to give cyclic isomers. The reaction below shows hydride ion abstraction from the alkyl group to yield the carbonium ion.
The author thanks C. G. Myers for advice and encouragement during this investigation.
t CI2
Rt---@
RH
t
9
cn (cH 2 ) 8 i"c H cn (ONE SPECIFIC CARBONIUM ION)
Q-Q-Q tC4"
tC3"
tc;
Probabilities of &-scissionalong the carbon chain should be the same as with n-dodecane, except for the allowance of @-scissionto occur nearer the end of the chain when the aromatic ring heads the chain. This forms some toluene and ethylbenzene. Benzene can be made through dealkylation of the whole C1?chain or by progressively splitting off fragments, followed by dealkylation of a short chain. As demonstrated in Table IX, the product distribution from dodecylbenzene cracking is not like that from dodecene cracking but is similar to dodecane products. Some toluene and ethylbenzene are produced, together with corresponding Cl0and C I 1paraffins. Dealkylation of the entire alkyl chain to form benzene and dodecene occurs, but it contributes very little to secondary olefin cracking based on carbon number distribution and the low coke concentra-
Literature Cited
Basila, M. R., Kantner, T. R., J . Phys. Chern. 71, 467 (1967). EgloiT, G., Morrell, J. C., Thomas, C. L., Block, H. S., J . Am. Chem. SOC.61, 3571 (1939). Greensfelder, B. S., Voge, H. H., Ind. Eng Chem. 37, 514, 983, 1038 (1945). Greensfelder, B. S., Voge, H. H., Good, G. M., Ind. Eng. Chem. 37, 1168 (1945). Greensfelder, B. S., Voge, H. H., Good, G. M., Ind. Eng. Chem. 41, 2573 (1949). RES. DEVELOP. 8, Sace, D. M., IND.ENG. CHEM.PROD. 24 (1969). Pickert, P. E., Rabo, J. A . , Dempsey, E., Schomaker, V., Proceedings of 3rd International Congress on Catalysis, 1964, Vol. 1, p. 714, h'orth-Holland Publishing Co., Amsterdam, 1963. Tung, S. E., McIninch, E., J . Catalysis 10, 166 (1968a). Tung, S. E., McIninch, E., J Catalysis 10, 175 (1968b). Ward, J. W., J . Catalysis 10, 34 (1968). RECEIVED for review October 24, 1967 ACCEPTED October 9, 1968 Symposium on Physical Techniques for the Study of Heterogeneous Catalysis, Division of Colloid Chemistry, 154th Meeting, ACS, Chicago. Ill., September 1967.
THERMAL DECOMPOSITION OF FIBRILLAR SYNTHETIC BOEHMITE L L O Y D
ABRAMS'
Department of Chemistr!,
A N D
M . J .
D .
L O W
,Veu York Cnicersity, Nerc York, N . Y.
10453
The physicochemical properties of the synthetic fibrillar boehmite, Baymal, were comprehensively studied using vacuum microbalance, differential thermal analysis, x-ray, infrared spectroscopy, and nitrogen adsorption techniques. The boehmite contained water in excess of stoichiometry which exerted a definite influence on the properties of the solid. Part of the excess water was incorporated between the layers of the boehmite lattice. A structural rearrangement of the lattice occurred on heating Baymal in vacuo above 360'C. An intermediate structure in the boehmite calcination was observed and identified as containing isolated AI-OH groups. The texture of the material did not change during the decomposition.
SOME, time ago we required gamma-aluminas of certain specific texture and surface properties, and it appeared that suitable adsorbents and catalyst supports might be prepared by the thermal decomposition of the synthetic boehmite, Baymal. It consequently became necessary t o consider the boehmite decomposition process in some detail Present address, Pigments Division, Experimental Laboratory, E. I. du Pont de Xemours & Co., Inc., \J'ilmington, Del. 19898 38
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
because the precursors of the adsorbent, the formation and decomposition of intermediates, and the like, might influence the properties of the desired end product. Although the conversion of hydrated aluminas has been studied extensively, the literature revealed uncertainty about the details of some of the processes. For example, the boehmite-to-gamma-alumlna transformation temperature has been variously reported as 120", 300", 360", 450", 480", or 500°C. (Bielanski and Sedzimir, 1960; El'tekov et d.,
1959; Lenne, 1961; Michel, 1957; Torkar and Bertsch,, 1961). Such uncertainties were attributed to the use of
various experimental techniques, solids of various compositions, and some lack of regard for the effects of particle size, surfaces, and ambient atmosphere. Examination of the calcination of boehmite in general and of Baymal in particular led to a detailed study using five different experimental techniques.
-I (?
-3 I
; 120 0 I-
r B
Experimental
w
Baymal powder (E. I. du Pont de Kemours & Co., Inc.) has been partly characterized (Barr, 1966; Bugosh, 1959, 1961; Bugosh et al,, 1962; E. I . du Pont de Semours & Co., 1961; Iler, 1961). Its typical composition (E;. I. du Pont de Nemours & Co., 1961) in weight per cent is: boehmite, 83.1; acetic acid, 9.8; sulfate, 1.7; water, 6.0; ammonia., 0.2; sodium, 0 . O i ; iron, 0.02; silica, 0.02. The loose powder was compacted for both infrared and gravimetric work. For the latter, pellets of approximately 0.3 gram were prepared by pressing Baymal in a l-inch-diameter steel die a t 1000 p.s.i. Pieces of a pellet were then used for the microbalance experiments (compacting prevented loss of sample by the "boiling" which occurs when a loose powder is evacuated). The vacuum microbalance was like that described by Gulbransen (1953). The beam displacement was measured t o 110.' cm. with a Gaertner cathetometer. The balance sensitivity was 8.995 ~-t 0.003 mg. per cm. with a 176-mg. load. The sample temperature was kept constant to within 1". To change temperature, the "leg" of the balance containing the suspended sample was surrounded by a preheated furnace. Differential thermal analysis (DTA) experiments were carried out with conventional instrumentation, a t a linear rate of lo" per minute in flowing nit:rogen. Baymal, which had been heated a t 876.C. for 283 hours. was used as reference. X-ray powder diffraction patterns were obtained with a Sorelco spectrometer, using filtered Cu K radiation, a cylindrical 114.6-mm. diameter camera, and 4-hour exposures. Samples for x-ray analysis were prepared by heating Bayinal in air a t the following temperatures (C.) and periods in hours: 14OC,68; 2543, 123; 316", 195; 362", 200; 420", 377; 660a, 200; 875', 283. These samples were also used for DTA and infrared studies. Infrared spectra were recorded with Perkin-Elmer Models 521 and 621 spectrophotometers equipped with Reeder thermocouples. Samples for infrared study in vacuo were prepared by compressing Baymal in a 0.75-inchdiameter steel die a t 5 to 10 tons per sq. inch to form self-supporting disks containing approximately 0.15 mg. per sq. mm. A sample disk was held t o a movable quartz carriage by quartz prongs. The carriage was within im infrared cell similar to that described by Peri and Hannen (1960). Nujol and Kel-F mulls were prepared by conventional means, using the same Baymal powder samples used for x-ray and DTA experiments. The Baymal disks had very low transmittances, requiring attenuation of the reference beam of the instrument. The ordinate scale expansion device of the instrument was used, as was abscissa expansion by means of the instrument's gears, frequently a t scan rates of 25 seconds per cm. ., to record spectra. Conventional techniques and apparatus were used to measure nitrogen adsorption-desorption isotherms a t 77" K. B E T surface areas (Brunauer et al., 1938) and pore size distributions (Barrett et al., 1951) were then estimated.
a
Results and Discussiort
Vacuum Microbalance. Weight loss data were obtained by heating several Baymal samples in vacuo from 30" to 800" C. with long intervals of heating a t specific constant temperatures. A portion of the results obtained with one of the samples is shown in Figure 1. The cumulative weight loss appeared to reach an equilibrium or steadystate value a t each new temperature, an observation substantiated by experiments using samples having different thermal histories. All samples had the same unit weight loss a t the end of a 48-hour period a t a given temperature. Such data were used to construct plots as in Figure 2. T h e residual weight of a sample heated in vacuo approached 70.480% of the weight of the original sample.
80
W
c
gI 2 u
$0
o
100
300
200 TIME
(HRS.)
Figure 1 . Isothermal weight loss of Baymal in vacuo
r. 700 0
200
400 TEMPERATURE
600
-
'h
-
800
("C)
Figure 2. Residual weight of Baymal heated in vacuo Weight loss data normalized for initio1 weight of 1000 mg Each point derived from plots such os those of Figure 1
This gradual approach to a constant weight-e.g., Figure 2-is in good agreement with previous results on aluminas and indicates that the dehydration of the samples tended toward completion (El'tekov et al., 1959; Peri, 1965). Assuming that the product of the 800°C. calcination was anhydrous alumina and using the equation 2A100H + ALO3 + H 2 0 , the Baymal is estimated to contain 82.93LC of boehmite, in good agreement with the claimed (E. I. du Pont de Nemours & Co., 1961) value of 83.1';. A plot of incremental weight loss (the loss brought about by raising the temperature from one constant value t o a higher one) as function of temperature is given in Figure 3, obtained from data such as those in Figures 1 and 2. Such plots, which yield information much like that obtained from thermogravimetric analysis, suggest that five distinct temperature regions were involved in the over-all calcination process. The weight losses corresponding to the various regions are shown in Table I. Region I of Figure 3 is attributed to the desorption of loosely bound water, ammonia, and acetic acid. Using Peri's results (Peri, 1965), loosely bound water is considered to desorb below lO0"C. Also, Iler (1961) reported that Baymal contained 1.8'; of physically adsorbed VOL. 8 NO. 1 M A R C H 1969
39
200
0
400 TEMPERATURE
600
800
(*C)
Figure 3. incremental weight loss 48 hours a t each
W e i g h t loss of Baymal heated in vacuo for
temperature
Table I. Summary of Weight losses of the Regions in Figure 3
Weight Loss, Mg. Lost/ Gram Baymal 87.97 31.50 21.75 115.56 32.40
Region I I1 I11 IV V
Temp. Range,
c.
30 to 100 to 175 to 225 to 350 to
100 175 225 350 800
80
c
60 I-
z 0
u a W
t-
-
40
I-
n
20
0
300 T E M P E R AT U R E
400
('C)
Figure 4. Differential weight loss D T is first derivative with respect t o temperature
of a plot of water content v s . temperoture, constructed from plots such os t h a t of Figure 2.
I. B a y m a l 11. Synthetic boehmite of low crystallinity ( P a p e e et a/., 1958) Ill. Highly crystolline synthetic boehmite ( P a p e e et a/., 1958)
40
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
water-Le., 18 mg. for a 1-gram sample. A loss of 2 mg. is attributed to the desorption of ammonia (E. I. du Pont de Nemours & Co., 1961). The remaining 68 mg. of the total loss of 88 mg. of Region I is attributed to the desorption of loosely bound acetic acid. The loss of 18 mg. of water below 100°C. implies that the sample retained 32 mg. in a more strongly bound state. Also, the loss of 68 mg. of acetic acid below 100°C. indicates that the solid retained approximately 30 mg. Assuming that these two components would be desorbed in the order of their boiling points, one would expect water to desorb before acetic acid. The weight loss of Region I1 of 31.5 mg. is in good agreement with the value of 32 mg. expected for bound water on the basis of the analysis (E. I. du Pont de Nemours & Co., 1961). Similarly, the weight loss of approximately 28 mg. can reasonably account (E. I. du Pont de Nemours & Co., 1961) for the desorption of bound acetic acid. Regions I1 and I11 are therefore attributed to the desorption of water and acetic acid, respectively. The initial composition of the Baymal samples may differ slightly from batch to batch, so that the weight losses of Regions I, 11, and I11 would show some slight variations. Region I may be especially influenced by the physical adsorption of water from the ambient atmosphere. However, the assignments are reasonable and are supported by DTA and infrared results. Region IV is attributed to the decomposition of boehmite. If the solid obtained after heating to 225°C. were taken to be stoichiometric boehmite, an additional weight loss of 124.53 mg. on heating to 800" C. would be expected. However, the observed weight losses of Regions IV and V exceed the expected value by 23.45 mg., indicating that the material was not stoichiometric a t the start of Region IV. Assuming that the 23.45-mg. weight loss was caused by a loss of water initially incorporated in the boehmite structure, the approximate formula AlOOH. (0.075H20) is indicated for the material calcined a t 225" C. This would mean that the boehmite in Baymal was hydrated. The existence of nonstoichiometric boehmite hydrates has been reported (El'tekov et al., 1959; Eyrand et al., 1955), Arakelyan and Chistyakova (1962b) suggesting that the excess water was incorporated in the boehmite lattice. However, various workers have reported different degrees of hydration. If the boehmite formula is written as A l p O J o ( l+ X ) H 2 0 , where X is the amount of water in excess of the formula AlOOH, estimates of X values were 0.01 (Wanek and Wankova, 1965), 0.22 (de Boer et al., 1954), and 0.25 (Erdley et al., 1956; Papee et al., 1958). There apparently was a relation between the stoichiometry of the synthetic boehmite and the method of preparation, processes involving autoclaving yielding products with X close to zero, the degree of crystallinity increasing with decreasing values of X (Glemser and Rieck, 1957; Torkar and Bertsch, 1961; Torkar et al., 1961). The value of X = 0.15 for the boehmite of Baymal falls in the range of X values considered, and it is useful to compare the decomposition kinetics of Baymal boehmite and two other synthetic boehmites. This can best be done by considering the rate of change of water content as a function of temperature-i.e., the derivative (DT) of the reciprocal of a plot such as in Figure 2. Such rate plots are shown in Figure 4 for Baymal (plot I ) and for two other synthetic boehmites, I1 (X = 0.22;
low crystallinity) and I11 ( X = 0; highly crystalline), prepared by de Boer et al. (1954). Comparison of the plots must be qualitative because the conditions of the decomposition of the materials were not identical (the same Baymal sample was used over the entire temperature range in vacuo, whereas a fresh sample of boehmite I1 or I11 was used a t each dehydration temperature, the calcination occurring in air under a small partial pressure of water). The absence of a maximum in plot I1 indicated a continuous decomposition, which de Boer et al. attributed to the poorly defined crystal structure of boehmite 11. Similarly, the broad rnaximum of curve I, in contrast to the sharp maximum caused by the well-crystallized boehmite 111, can be taken as an indication that the crystal structure of Baymal was not well developed. Region V of Figure 3 represents the final decomposition stages of the boehmite structure and the dehydration of the alumina products. Region V might be subdivided because of the formation of transition aluminas and their hydrates, but the gravimetric data are not extensive enough to permit further differentiation. Attempts were made to express the weight loss kinetics of the boehmite decomposition (Region IV) by a suitable rate equation. However, expressions such as that of Ginstling-Brounstein as well as others reviewed by Brindley et al. (1964) did not fit the data well. The present data were consequently plotted according to the equation used by Callister et al. (1966),
f=kt where f is the fraction of boehmite reacted a t time t and h is a constant. The plots are shown in Figure 5. The data deviate from the straight lines after about 5 hours of heating. Using Bretsznajder's (1964) analysis of decomposition mechanisms, the deviations indicate that a second phase was controlling the decomposition reaction. Using only the initial slopes of the plots of Figure 5, the activation energy can be derived in the usual fashion (Figure 6).
0041
03
02
Y
.01
005 1.800
I600
I / T X 10-3
Figure 6. Arrhenius plot for Boehmite decomposition
The activation energy of 10 kcal. per mole derived from Figure 6 is considerably lower than that of 42 kcal. per mole reported by Eyrand and Goton (1954), who decomposed 50-micron-diameter boehmite particles in a vacuum of about torr, and also that of 70 kcal. per mole reported by Callister et al. (1966), who carried out the decomposition in the 430" to 495°C. range in the presence of water vapor. In an attempt to reconcile their results with those of Eyrand and Goton, Callister et al. suggested that the reaction in vacuum occurred via a different mechanism and that the rate appeared to be proportional to surface area. The present value of 10 kcal. per mole, obtained with a high surface area powder decomposing in vacuum under a partial pressure of water of the order of torr, thus follows the trend suggested by Callister et al. Differential Thermal Analysis. Four different samples were examined (Figure 7 ) , the DTA traces indicating the
0 24
I-
0
a
16
W
c 0
a w
a
I-
v
a
08
a LL
100
300
500
T E M P E R A T U R E ('C)
Figure 7. DTA traces of four Baymal samples
"
0
4
0
12
TIME (HRS)
Figure 5 . Boehmite decomposition kinetics
Trace Trace Trace Trace made
1. Baymal, as received
2. After heating in vacuo at 100" C. 3. Heated in air at 110" C. far 68 hours 4. Heated in air at 200" C. for 66 hours. Treatments prior to DTA experiment
VOL. 8 NO. 1 M A R C H 1969
41
Table II. Summary of DTA Results
Temp. Region, C. 105,120 155 200 to 310 280 310 to 400 400 to 500 500 to 600
Type Endotherm Endotherm Endotherm Exotherm Exotherm Endotherm Exotherm
Process Desorption of loosely bound water Desorption of loosely bound acetic acid Desorption of bound water Unknown (see text) Pyrolysis of acetic acid Boehmite transition Possibly amorphous alumina
occurrence of several processes (Table 11). I n general, the DTA traces agree well with the proposed decomposition regions of Figure 3 and Table I . Trace I of Figure 7 shows two endotherms between 30" and 200°C. These, in view of the weight loss and other data, are correlated to Region I of Figure 3. Generally, loosely bound or physically adsorbed material will desorb a t a temperature near the material's boiling point. An apparent shift in the temperature a t which desorption occurs may be expected because of the kinetic nature of the DTA experiment. I t is thus reasonable to attribute the endotherm centered near 105°C. to the desorption of loosely bound water, and that centered near 155"C. to the desorption of acetic acid. Using these assignments, the absence of the 105" C. peak in Trace 2 would indicate that most of the loosely bound water has been removed by degassing a t 100°C. The degassing was not efficient, however, and a relatively high final pressure of 1 torr was obtained a t 100°C., probably caused by the desorption of acetic acid; the appearance of the 155°C. endotherm in Trace 2 confirms this. Similarly, Traces 3 and 4 show large endotherms a t 110"C., indicating that the samples had adsorbed water from the ambient atmosphere prior to the DTA experiments. The absence of a distinct peak near 150°C. in Trace 4 indicates that much of the acetic acid had desorbed; a shoulder in the 125" to 175°C. region on the 110°C. endotherm of Trace 3 shows that some acetic acid had been retained by the sample. The wide endothermic region between 200" and 310°C. (Figure 7) is taken to correspond to Region 11-Le., to the loss of tightly bound water by the samples. This assignment agrees with the results of Rufimskfi (1959) on the thermal analysis of alumina gels. Traces 1, 2. and 3 of Figure 7 show small exotherms near 280" C., similar to those previously reported (Arakelyan and Chistyakova, 1962a; de S. Santos, 1963; Krais, 1963; MacKenzie, 1957). DTA traces of naturally occurring, highly crystalline boehmites showed an exotherm near 280°C., but its origin was not explained (MacKenzie, 1957). Krais (1963) attributed a similar exotherm to a small amount of organic impurity present in his synthetic boehmite, but Arakelyan and Chistyakova (1962a) found similar behavior occurring in experiments with materials free of organic impurities. The 280°C. exotherm therefore does not seem to be connected with the presence of organic materials or with the degree of crystallinity of the sample, because it has been observed with amorphous and crystalline boehmite. The cause of the 280°C. exotherm is uncertain, but may be a transformation of the boehmite structure. 42
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
The exotherms between 310" and 400°C. shown by all traces in Figure 7 are attributed to the pyrolysis of acetic acid bound to the surface, and thus would correspond to Region 111. As pointed out by Arakelyan and Chistakova (1962a), the pyrolysis of organic compounds generally produces an exothermic effect in the region of 360" C. The trace of sample 4 also showed an exotherm smaller than that of the other samples, indicating that some of the acetic acid had been removed by heating a t 200°C., in agreement with the proposed scheme of Figure 3. T h e large endotherms a t 470" C. correspond to Region IV, the boehmite transition. Similar endotherms have been found in previous work with boehmite (Arakelyan and Chistyakova, 1962a; Krais, 1963),but, as with the present work, these have occurred a t temperatures appreciably higher than the 225" to 350°C. range of Region IV. However, the difference in the transition temperatures, as observed in experiments under different conditions and by means of different instrumental techniques, could be brought about by several factors. For instance, DTA experiments have an inherent tendency to shift recorded transition points to higher temperatures, the shift increasing with increasing heating rate. Conversely, the microbalance data were obtained isothermally. Also, as water vapor inhibited the boehmite decomposition (Callister et al., 1966; Eyrand et al., 1955), the continuous removal of water during microbalance work would have a pronounced effect on the boehmite transition. Thus, it is not unreasonable that the transition temperature observed in the microbalance study was lower than that found by means of DTA techniques. The 470°C. endotherm is therefore attributed to the boehmite decomposition. However, it is also of interest to consider some earlier results. Some DTA curves of naturally occurring, highly crystalline boehmites and one curve of a fine-grained, synthetic boehmite are included in MacKenzie's (1957) summary of DTA traces of various hydrated Fe, Al, and Mn oxides. The DTA trace of the synthetic boehmite showed rounded endotherms a t 120" and 45OoC.,whereas that of the natural boehmite showed one sharp endotherm centered a t 550" C. Similar behavior was exhibited by boehmites I1 and 111. The DTA traces of these and of Baymal are shown in Figure 8. A single sharp endotherm was produced by the highly crystalline boehmite I11 (Trace 111, Figure 8), whereas boehmite I1 (Trace 11, Figure 8) produced three poorly defined endotherms attributed t o the desorption of loosely bound water and strongly bound water, and to the boehmite transition. I n comparison, the boehmite transition endotherm of Baymal (Trace I , Figure 8) is sharper than that of boehmite 11. The same trend is thus apparent in DTA traces and the derivative plots (Figure 4). I n general, such results suggest that the presence of water in excess of stoichiometry has a significant effect on the boehmite transition, the transition endotherms becoming less well defined and occurring a t lower temperatures as the degree of nonstoichiometry increases. The exotherms occurring above 500" C. subsequent to the boehmite transitions in the traces of Figure 7 correspond in part to Region V of Figure 3. I n analogy to the effects observed with lepidocrocite (Gheith, 1952), the boehmite in Baymal might decompose to form a partially amorphous intermediate. The transformation of the latter into a more stable form of alumina then would result in the observed 500" to 600" C. exotherms.
100
300
500
T E : M P E R A T U R E ('C)
Figure 8. [ITA traces of three different boehmites I. Baymal 11. Poorly crystallized boehmite (Papee et ai., 1958) Ill. Highly crystalline boehmite (Papee et a i . , 1958)
X-Ray Analysis. The x-ray results and discussion are based on the nomenclature and diffraction patterns summarized by Kewsome et al. (1960). The results of the present work can be summarized as follows. Baymal sainples heated a t 110", 254", and 316°C. showed only the presence of boehmite. However, the patterns were much more diffuse than those of boehmite reported by Newsome et al. (1960), suggesting that the sample was not highly crystalline throughout. The presence of boehmite was not evident in the 362O C. sample, and the pattern showed rather diffuse lines characteristic of gamma-alumina. Also, a broad line centeled a t 4.5 A. indicated the presence of an amorphous alumina constituent. The presencl? of eta-alumina could not be confirmed bacause of the diffuseness of tlie pattern. The patterns of the 420" and 362°C. samples were identical. The pattern of the 550' C. sample was sharper than those of the 362" or 420' C. samples, indicating a greater degree of crystallinity. The presence of eta-alumina was confirmed. The sample also appeared to have an amorphous constituent. The pattern of the 875"C. sample was sharp and matched the pattern typical of theta-alumina. There was no indication that any other alumina form was present. The results of the present study, which indicate the formation of some eta- and amorphous alumina in addition to gamma-alumina, contradict earlier reports that Baymal decomposed solely to gamma-alumina (E. I. du Pont de Kemours & Co., 1961; Iler, 1961). The cause of Iler's (1961) failure to observe the other aluminas formed from Baymal is uncertain. Also, there is disagreement with some of the results obtained with other synthetic or natural boehmites, but the earlier reports themselves show some conflicts. Some of those were considered by Sewsome et al. (1960) and were brought about in part by varying
nomenclature, differences in sample purity, misinterpretation of x-ray data, and the like. Extensive comparison and discussion of present and prior data are consequently not attempted. However, the conversion of boehmite to eta-alumina has been reported several times (Eyrand and Goton, 1954; Ginsberg et a / . , 1957: Glemser and Rieck, 1955, 1957; Torkar and Bertsch, 1961) and appeared to occur when a poorly crystallized boehmite was calcined, while a highly crystalline sample yielded gamma-alumina. Also, Arakelyan and Chistyakova (1962b) reported that an amorphous alumina was formed by decomposing a boehmite prepared from hydrargillite, and that the experimental conditions used in the boehmite preparation influenced the microstructure of the boehmite and consequently its physicochemical properties (1962a). Extending their observations to Baymal, the poorly developed structure of the boehmite can be expected to lead to the formation of an amorphous decomposition product. However, the amorphous product could also arise from amorphous boehmite gel in the Baymal. The existence of an amorphous gel in the boehmite lattice has been suggested (Oomes et al., 1961; Yamaguchi, 1956). Also, when the water associated with the boehmite structure is in excess of the stoichiometric amount, the properties of the nonstoichiometric material are apt to be somewhat different from those of the stoichiometric material. Relatively low crystallinity, small particle size, gel inclusion, a n d / o r excess water could thus account for the diffuse pattern of the boehmite of Baymal and the formation of a partially amorphous calcination product. However, in the 420" to 530°C. region the surface area did not decrease appreciably (Figure l 5 ) , indicating that no substantial increase in particle size occurred. The sharpening of the pattern in going from a 420~.to 550'C. sample suggests that a part of the structure became more crystalline. This could be caused by a conversion of some of the amorphous alumina to either gamma- or etaalumina, the transition occurring in the same temperature range as the 530°C. DTA exotherm. Also, the fact that delta-alumina was not observed after the conversion of Baymal boehmite to gamma-alumina may be explained by considering the decomposition schemes of Kewsome et al (1960):
Scheme B indicates that eta-alumina is completely converted to the theta form before gamma-alumina can convert to the delta form. The present results suggest, therefore, that the presence of the theta-alumina produced via scheme B may inhibit the formation of the delta form via scheme A. Considering Baymal to be a mixture of highly crystalline and poorly crystalline boehmite then leads to the decomposition scheme outlined in Figure 9. Infrared Spectra. The samples prepared for DTA and x-ray study were also examined by infrared spectroscopic techniques. The spectra of the mulls of these samples are shown in Figure 10. Bands were observed a t 3700 to 2600, 3300, 3070, 2100, 1700, 1625, 1560, 1500, 1460, 1415,1340,1270,1150,1060,750, 610, 470, and 360 cm.-'. The general features of these and other spectra of the present work were similar to those previously reported (Bernstein, 1958; Glemser and Rieck, 1957; Frederickson, 1954; Kolesova and Ryskin, 1962; Orsini and Petitjean. VOL. 8 NO. 1 M A R C H 1969
43
niGnLY CRYSTALLINE BOEHMITE
L
I
I
1
EAYMAL
-\
heated above 3 6 P C . contained a large amount of water, confirming the DTA results. The presence of a band a t 1625 cm.-' also indicated the presence of adsorbed, molecular water. Baymal samples were heated and maintained in vacuo to prevent the readsorption of water. Some of the spectra obtained are shown in Figure 11. Perhaps the most striking feature of the spectra of samples heated below 360°C. is the apparent absence of the OH bands characteristic of boehmite. However, the bands were present but were indistinct because of their intensity and width, and their presence could be shown by recording the spectra using somewhat unusual instrument operating procedures. The spectra of Figure 12 were obtained by judicious use of reference beam attenuation, scanning speed, and other instrument parameters. Portions of the spectra of four Baymal samples heated and maintained in vacuo are given in Figure 13 and show a band a t 3660 cm.-' not observed in the mull spectra of Figure 10. The 3660-cm.-' band increased in intensity in the range 195' to 297°C. and then declined and disappeared. The formation of individual bands in the OH region of spectra of aluminas is unique and has not been previously observed [for a discussion of the surface hydroxyls of aluminas, see Little's review (1966) and Peri's work (1965)l. The band is relatively sharp, appears in the OH region, and bears great similarity to hydroxyl bands found with silicas (Little, 1966; Low and Ramamurthy, 1968) and porous glass (Low and Ramasubramanian, 1966), and, in analogy to surface Si-OH, B-OH, P-OH, and Ge-OH (Low and Ramamurthy,
THETA ALUMINA
GAMMA ALUMINA
AMORPHOUS ALUMINA
H I
POORLY CRYSTALLINE EOEHMfTE
THETA ALUMINA
ETA ALUMINA
I
1
150
350
I 550 TEMPERATURE, C '
I
I
750
950
Figure 9. Schematic decomposition scheme
1953; Wickersheim and Korpi, 1965) and consequently need not be considered in detail. However, some of the details of the present mull spectra and spectra of samples in vacuo differed significantly from previously reported spectra, and attention will be focused on those aspects of the work. In general, spectra of mull samples heated below 360°C. showed the characteristic boehmite OH stretching and bending bands a t 3300, 3075 and 1150, 1060 cm.-', respectively. These bands disappeared on heating above 360° C., showing that the boehmite had decomposed. However, the broad bands in the OH region showed that samples
Figure 10. Mull spectra of baymal Samples heated in air ot following temperatures and times in hours:
A. B.
110°C.,68
C.
254" C., 123 316"C., 195
D.
362" C., 200
E. 550" C.,
200
After heating, samples were cooled in air and mulled with Nujol and Kel-F. Spectro are precise composites, so that bands of the mulling agents were removed. Ordinates are displaced to avoid overlapping. Number at left of each trace is percentage transmittance of spectrum at 4000 cm.
c
I
Figure 1 1. Baymal heated and maintained in vacuo Baymal samples heated in vocuo a t following temperatures and times in hours:
A. 255O C., 150 D. 360"C., 87 B . 275" C., 120 E. 439"C., 91 C. 297" C., 134 F. 507"C., 88 Atmospheric CO? bonds deleted in 2300-2400 -I cm. region (dotted lines). Ordinates displaced to avoid overlapping. Each spectrum had 4% transmittance at 4000 cm.-'
I
4000
44
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
, ,
,
,
I
,
3000
,
,
,
I
,
1
I
,
I
I
2000
,
,
,
I
,
,
,
',o'oo
I
1
Cm!,'
1
s
o.zj! 0
3500
,
\ d 1 A
3400
50X
I
I
1
3300
3200
3100
GM-f
Figure 12. Highly expanded spectra Each spectrum recordecl with same sample used for spectrum A, Figure 11, but at 50-fclld or 500-fold ordinate scale expansion
1966) structures, is attributed to the 0-H fundamental of A1-OH groups,
stretching
OH
I
___
boehmite decomposition process leads to a smaller increase in the number of free A1-OH groups and the dehydration and dehydroxylation processes become dominant, so that the net effect is a decrease in the intensity of the 3660cm.-' band. The free surface A1-OH structure probably represents an intermediate state in the boehmite-gamma-alumina transition. Also, the disappearance of the free A1-OH structures in spectra of samples heated above 360°C. can be taken to indicate that a structural rearrangement may have occurred in the 360" to 439°C. range. Such a rearrangement of the boehmite lattice would involve the coalescence of adjacent layers, and this breakdown of layered boehmite would destroy the geometry necessary for the existence of free A1-OH groups. This could produce the changes noted in the x-ray and DTA studies and also account for the infrared bands characteristic of transition aluminas. The mull and vacuum spectra showed a band near 1700 cm.-' which decreased in intensity on heating the samples in vacuo, and was not observed above 316°C. I n direct analogy to work on the adsorption of carboxylic acids (Low and Inoue, 1965; Low et al., 1967), the 1700cm.-' band is ascribed to the C = O stretching vibration of adsorbed acetic acid. The infrared results thus are consistent with those of the microbalance study, which indicated that about half of the acetic acid was desorbed in vacuo a t 30" C. The bands a t 2100 and 1980 cm.-' have been observed previously, but were not explained (Bernstein, 1958; Glemser and Rieck, 1957; Kolesova and Ryskin, 1962; Orsini and Petitjean, 1953). The 2100-cm.-' band declined and was replaced by a band a t 1580 cm.-' when boehmite was deuterated. The 1980-cm.-' band similarly disappeared upon deuteration (Bernstein, 1958; Glemser and Rieck, 1957; Kolesova and Ryskin, 1962; Orsini and Petitjean, 1953), but only Bernstein (1958) reported the formation of a band a t 1460 cm.-' a t the position expected for an analogous deuterated species. The 2100- and 1980cm.-' bands can therefore be attributed to hydrogencontaining species, but the precise structures responsible
%'a
___
)--boehmite lattice
which are "free" or isolated-i.e., do not interact extensively with their neighbors on the boehmite surface. Multiple bands in the OH region of spectra of aluminas are well known (Little, 1966; Peri, 1965). The changes in intlensity of the 3880-cm.-' band with the boehmite content of a sample may be attributed to the loss of water from the boehmite lattice. Coalescence of neighboring hydroxyls and dehydration result in the formation of free A1--OH groups. The dehydroxylation and dehydration of the alumina lattice occur simultaneously with the boehmite decomposition. The former two processes proceed a t slower rates than the bbehmite decomposition below 300" C.. with the net result that the number of free A1-OH groups increases. Above 3OO0C., the
Figure 13. Baymal heated in vacuo Portions of spectra of four Baymal samples heated in vacuo at following temperatures and times in hours:
195"C., 48 255"C., 150 C. 2 7 5 " C . , 120 D. 297" C., 134
A. 6.
VOL. 8 NO. 1 M A R C H 1969
45
for the bands are unknown. Comparison with the boehmite OH stretching bands, however, shows that the ratios 2100/ 3300 and 1980/3100 are almost identical and, as the bands disappeared in concert upon thermal treatment of the boehmite, suggests that the corresponding bands were brought about by the same structure. The 2100- and 1980-em. bands were therefore probably caused by vibrations of OH or A1-H groups within the boehmite lattice. The 1580- and 1480-cm.-' bands have not been reported previously. Their intensities decreased and the band positions shifted slightly with increasing dehydration of the sample-e.g., a t 439°C. the positions were 1557 and 1472 cm. I , respectively (Figure 14). The disappearance of the bands coincided with the removal of water from Baymal. As noted earlier, the boehmite may be represented as A120i.1.15H20, and the excess water was incorporated in the boehmite structure (Arakelyan and Chistakova, 1962b). If the water were occluded between the boehmite layers, it might be bonded to the structures, giving rise to the 3300- and 3100-em. I bands. The similarity of the ratios 1480/3100 and 1580/3300 lends some support to this supposition. Also, deuteration caused only slight decreases in the intensities of the 1580- and 1480-cm. ' bands, suggesting that the structures causing them were not readily accessible to deuterium. Such effects suggest that the 1580- and 1480-cm. bands were caused by intraglobular OH or H 2 0 groups. The bands near 1340 and 1260 cm. ' occurred over the entire temperature range, but the intensities declined
507
OC
439 ' C 360 'C
297OC 22 22 22
and the band positions changed (Figure 14). For example, the bands occurred a t 1352 and 1264 cm.-' with a sample degassed a t 255"C., and shifted t o 1380 and 1273 cm.-' when the sample was degassed a t 507°C. Deuteration appeared to diminish the 1340-crn.-l band slightly. The two bands are tentatively assigned to OH groups within the alumina lattice. Some support for this comes from the microbalance work, which indicated that the alumina product contained water even after outgassing a t 500" C. Nitrogen Adsorption. The adsorption of nitrogen a t -196" C. was measured on samples which had been heated t o various temperatures. The isotherms were much like those shown by Fluid Filtrol (Ries, 1952) and had hysteresis loops with sloping adsorption and desorption branches. As pointed out by de Boer (1938), such loops could arise from a capillary system of open slit-shaped capillaries together with wedge-shaped capillaries with a closed edge a t the narrower side. The adsorption measurements were used to estimate the B E T surface areas (Figure 15) and the pore size distributions (Gregg and Sing, 1967) (Figure 16). The surface areas agree for the most part with those of Iler (1961) (Figure 15). The increase in area up to 250°C. is attributed to unblocking of the pore system by the desorption of loosely held materials. The difference in areas above 500" C. is attributed to enhanced sintering of the calcination products in vacuo. The areas remained nearly constant over the 250" to 500°C. range and there were no marked changes in the pore systems of the samples (Figure 16). The 250°C. sample had a rather narrow pore size distribution centered a t a pore radius of 18 A., while the 500°C. sample showed an additional pore system centered near 22 A. The 18-A. system disappeared on heating a t 700°C. and was replaced by a system centered near 24 A. The results then show that, over the temperature region in which the boehmite was decomposed and the sample lost approximately 25% of its weight, the texture of the material did not change significantly . The surface area data were also used to compute surface coverage - by . water. Peri (1965) recently examined several aluminas and found the correlation shown in Figure 17 300
5 \ W
5
g
200
U
w
a a
=t
u"
100
U LL
a v)
0
1700
1500
1300
1100
Figure 14. Baymal heated in vacuo
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
I
8
400
cm"
Samples heated in vacuo a t following temperatures and times in hours: 255O C., 150; 275" C., 120; 297" C., 134; 360" C., 87; 439" C., 91; 507" C., 88. Ordinates displaced to avoid overlapping. Number at left of each trace i s transmittance a t 1700 cm.
46
I
0
I
1
800
TEMPERATURE
b 1200
("C)
Figure 15. Surface area of Baymal 0 Data of ller (1961)
1 Present data. Heating temperatures and times (hours) in vacuo: 25" C., 9; 25" C., 12; 250" C., 19.5; 300" C., 15.5; 350" C., 22; 400" C., 48; 500" C., 24.5; 600" C., 15; 700" C., 16
content than would be expected on the basis of the correlation. The latter would predict that the 350°C. sample contained 28.2 mg. of water on the surface. As data such as those of Figure 2 showed that that sample, after losing 5.2 mg. after 5 hours a t 350°C., contained a total of 46.8 mg. of water, the results indicate that 18.6 mg. of water was within the bulk of the material. However, a sample a t 350” C. would contain about 7 5 undecomposed boehmite, the decomposition of which would release 9 mg. of water (of which 5.2 mg. was lost during the first 5 hours a t 350°C.). The results thus suggest that 18.6 - 3.8 or 14.8 mg. of water was within the bulk of the material but not associated with boehmite p e r se-Le., was present as intraglobular water.
a 0.2-
0.1 -
I
I
I
I
I
I
I
r,~. Figure 16. Pore size distributions Boymol samples heated in vacuo at following temperatures and times in hours:
A.
250°C., 19.5
Acknowledgment
The DTA experiments were carried out a t the laboratories of the Minerals and Chemicals Phillips Corp. with the assistance of T. D. Oulton, who also supplied valuable advice in the interpretation of data. X-ray results were obtained a t the M. W. Kellogg Research Laboratory with the valuable assistance and advice of E. W. Kell and C. C. Kang.
B. 500’ C., 24.5 C. D.
6OO0C., 15 700°C.. 15.8
T E M P E R A T U R E (‘C)
Figure 1 7 . Dehydration of Aluminas Peds ( 1 965) correlation
A
Present study
between the surface coverage and the temperature of dehydration. The monolayer coverage was calculated on the basis of the number of water molecules per 100 sq. A. of surface, assuming that 6.25 water molecules per 100 sq. A. approximated a filled monolayer. Similar estimates of water coverage were made using the water content of Baymal after 5 hours of evacuation a t specific temperatures (Figure 17). The two plots show good agreement above 400”C., indicating that the effects of the dehydration process of the transition products of the Baymal calcination are similar to those of the dehydration processes occurring with the other aluminas. I t is therefore reasonable to expect the surface characteristics of the Baymal calcination products t o be similar to those of other transition aluminas. The point for the 350” C. sample deviates considerably from the plot of Figure 17, indicating a higher water
Literature Cited
Arakelyan, 0. I., Chistyakova, A. A., Zh. Prihl.Khim. 35, 1396 (1962a) (English trans.). Arakelyan, 0. I., Chistyakova, A. A., Zh. Prihl. Khim. 35, 1591 (1962b) (English trans.). Barr, M., Am. J . Pharm. 137, 127 (1965). Barrett, E. P., Joyner, L. G., Halenda, P. P., J . Am. Chem. Soc. 73, 373 (1951). Bernstein, R . B., U.S. Atomic Energy Commission Rept. ANL-5889, 1958. Bielanski, A . , Sedzimir, A., “Reactivity of Solids,” Proc. International Symposium on Reactivity Solids, 4th Amsterdam, p. 301, 1960. Bretsznajder, S., in “Catalysis and Chemical Kinetics,” A. A. Balandin et al., Eds., pp. 207ff, Academic Press, New York, 1964. Brindley, G. W., Sharp, J. H., Sarahari, B. K.,“Thermodynamics and Kinetics of the Dehydroxylation of Hydrous Minerals,” NASA Accession No. h-65-11789, Rept. AD 607879,1964. Brunauer, S.,Emmett, P. H., Teller, E., J . Am. Chem. SOC.60, 309 (1938). Bugosh, J., J . Phys. Chem. 65, 1789 (1961). Bugosh, J., U. S. Patent 2,915,475 (Dec. 1, 1959). Bugosh, J., Brown, R . L., McWhorter, J. R., Sears, G. W., Sippel, R. J., IND. ENG. CHEM. PROD.RES. DEVELOP. 1, 157 (1962). Callister, W. D., Cutler, I. B., Gordon, R. S., J . Am. Ceram. Soc. 49, 419 (1966). de Boer, J. H., in “The Structure and Properties of Porous Materials,” 0. H. Everett and F. S. Stone, Eds., p. 85, Butterworths, London, 1958. de Boer, J. H . , Fortuin, J. M. H., Steggerda, J. J., Koninkl. Nedl. Akad. Wetenschap. Proc. B57, 170 (1954). de S. Santos, P., Bol. Dept. Eng. Quim., Escola Politechnica Uniu.,Suo Paulo, KO.17, 39 (1963). du Pont de Nemours & Co., Inc., E. I., Wilmington, Del., “Baymal Colloidal Alumina,” 1961. El’tekov, Yu. A., Akimov, V. M., Rubinshtein, A. M., Izc. Akad. Nauk S S S R , Otd. Khim. Nauk 1959, 1947 (English trans.). Erdley, L., Paulik, F., Paulik, J., Acta Chim. Acad. Sci. Hung. 10,61 (1956). Eyrand, C., Goton, R., J . Chim. Phys. 5 1 , 430 (1954). VOL. 8 NO. 1 M A R C H 1969
47
Eyrand, C., Goton, R., Trambouze, Y, Hun The, T., Prettre, M., Compt. Rend. 240, 862 (1955). Frederickson, L. D., Jr., Anal. Chem. 26, 1883 (1954). Gheith, M. A., Am. J . Sei. 250, 677 (1952). Anorg. Allgem. Chem. 293, 33 (1957). Glemser, O., Rieck, G., Angew. Chem. 67, 652 (1955). Glemser, O., Rieck, G., Trabajos Reunion International Reactividad Solides, 3rd Madrid, 1956, Vol. I , p. 361, 1957. Gregg, S.J., Sing, K. S. W., “Adsorption, Surface Area and Porosity,” Academic Press, New York, 1967. Gulbransen, E. A., Aduan. Catal. 5 , 120 (1953). Iler, R. K., J . Am. Ceram. SOC.44, 618 (1961). Kolesova, V. A., Ryskin, Ya. I., Zh. Strukt. Khim. 3, 680 (1962). Krais, S., Silihaty 7, 52 (1963). Lenne, H.-U., 2. Krist. 116, 190 (1961). Little, L. H., “Infrared Spectra of Adsorbed Species,” Academic Press, New York, 1966. Low, M. J. D., Brown, K. H., Inoue, H., J . Colloid Interface Sei. 24, 252 (1967). Low, M. J. D., Inoue, H., Can. J . Chem. 43, 2047 (1965). Low, M. J. D., Ramamurthy, P., Chem. Commun. 1966, 733. Low, M. J. D., Ramamurthy, P., J . Phys. Chem. 72, 3161 (1968). Low, M. J. D., Ramasubramanian, N., J . Phys. Chem. 70, 2740 (1966). MacKenzie, R. C., in “The Differential Thermal Investigation of Clays,” pp. 299ff, Minerals Group, London, 1957.
Michel, M., Compt. Rend. 244, 598 (1957). Newsome, J. W., Heiser, H. W., Russell, A. S., Stumpf, H. C., “Alumina Properties,” Tech. Paper 10 (2nd revision), Aluminum Co. of America, 1960. Oomes, L. E., de Boer, J. H., Lippens, B. C., “Reactivity of Solids,” Proc. International Symposium on Reactivity Solids, 4th Amsterdam, 1960, p.317, 1961. Orsini, L., Petitjean, M., Compt. Revd. 237, 326 (1953). Papee, D., Tertian, R., Biasis, R., Bull. SOC.Chim. France 1958, 1301. Peri, J. B., J . Phys. Chem. 69, 211, 220, 231 (1965). Peri, J. B., Hannen, R. B., J . Phys. Chem. 64, 1526 (1960). Ries, E . H., Aduan. Catal. 4,121, 122 (1952). Rufimsk;, P. V., Kolloid Zh. 21, 351 (1959). Torkar, K., Bertsch, L., Monatsh. Chem. 92, 746 (1961). Torkar, K., Egghart, H., Krischner, H., Workel, H., Monatsh. Chem. 92, 512 (1961). Wanek, W., Wankova, J., Chem. Prum. 15, 562 (1965). Wickersheim, K. A., Korpi, G. K., J . Chem. Phys. 42, 579 (1965). Yamaguchi, G., Kogyo Kagaku Zasshi 66, 770 (1956). RECEIVED for review August 1, 1968 ACCEPTED January 4, 1969 Supported by a contract from the Sun Oil Co. and a grant from the National Center for Air Pollution Control and NSF grant GP1434.
DEVELOPMENT OF A BENCH DETERGENCY TEST FOR AUTOMOTIVE OILS AND ITS CORRELATION WITH THE
MS SEQUENCE V ENGINE TEST E.
S. FORBES A N D J. M. WOOD,
B P Research Centre, The British Petroleum Co., Ltd., Chertsey Road, Sunbury-on-Thames, Middlesex, England A laboratory bench test has been developed for evaluation of the low-medium temperature detergency properties of automotive crankcase lubricating oils and for use as a research tool for studying the mechanism of action of detergent additives. In the test, which simulates the mode of sludge formation in gasolinefueled engines, the lubricating oil is mixed with synthetic sludge precursors, and gases containing oxides of nitrogen are passed through the mixture at 100’ C. The resultant sludge deposits are finally rated to assess the oil‘s detergency properties. Descriptions are given of the method of preparation, and subsequent modification, of the sludge precursors together with the techniques used to obtain test ratings. In its ultimate form, this bench test has given excellent correlation with the MS Sequence 5 engine sludging test for a range of oils of widely varying detergent quality.
THEproblems
of sludge formation and deposition in gasoline-fueled engines, when operated under lowmedium temperature conditions, have received considerable attention in recent years owing to the rapid growth of stop-start driving. Although modern oil formulations have been largely successful in solving these problems, the trend toward 48
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
longer oil drain intervals and more severe usage means that even better additives will be necessary in the future. From the oil chemist’s point of view, the development of suitable additives has been made difficult because of the lack of reliable techniques, other than engine testing, for the initial evaluation of experimental materials. This is undoubtedly due to the complexity of the mechanism
