I
CHARLES POTTER' and
M. V. SUSSMAN2
Department of Chemical Engineering, Columbia University, New York, N. Y.
Gas Adsorption on a Copper-Magnesia Catalyst Surface area as an index of catalytic activity can be misleading. A more sensitive measure may be extent of hydrogen adsorption
BECAUSE
ACTIVITY and adsorptive capacity of a heterogeneous catalyst are often related, adsorptive behavior was studied for catalytically active and inactive forms of a particular hydrogenation catalyst. The catalyst was coppermagnesia, whose preparation and kinetic behavior in ethylene and propylene hydrogenation have been described (24, 25, 27). The gases chosen for the adsorption study were those used in the earlier kinetic studie-ethane, ethylene,
Present address, Amersil Go., Inc., Hillside, N. J. Present address, Experimental Station, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.
propane, propylene, and hydrogen. Also, butane was used. Adsorption isotherms were determined for each of these gases on a single sample of the catalyst in its active (reduced) and inactive (oxidized) forms. The information obtained supplements earlier kinetic studies and has been used to examine some adsorption correlation techniques reported in the literature. Method of Experimentation
Equipment for obtaining pure gas isotherms a t various temperatures was of the volumetric type where extent of adsorption was determined by changes in the volume of gas within the apparatus (2, 6, 9, 70, 75). Capillary tubing, 2
Table 1.
Temp., OC.
Ethane Adsorotion, Press., mole/g. cm. Hg adsorbent
mm. in diameter, was used wherever possible to keep volume of the system to a minimum. Stopcocks were precisionground vacuum type, lubricated with a minimum quantity of Apiezon N stopcock grease. Attempts to use other means of lubrication such as graphite, fluorocarbons, silicone, and carbowax which would absorb less test gas, were unsuccessful because of inadequate lubrication, sealing, or both. After once equilibrating with the test gas, the Apiezon grease was found satisfactory. The apparatus permitted the test gas to circulate through the adsorbent in a positive fashion. This was accomplished by placing two small glass check valves, i, at the top of the gas buret and arranging the capillary tubing in a closed cir-
Gas Adsorption on Copper-Magnesia
(Summary of experimental data) Ethylene Propane Propylene n-Butane AdsorDAdsorpAdsorpAdsorption; tion, tion, tion, Press., mole/g. Press., mole/g. Press., mole/@;. Press., mole/g. cm. Hg adsorbent om. Hg adsorbent cm. Hg adsorbent cm. Hg adsorbent Active Catalyst
0
79.08 65.48 54.90 48.57 39.21 29.53 19.16 11.70
1. 60a 1.40 1.23 1.13 0.96 0.78 0.65 0.36
79.06 61.37 53.97 43.35 38.31 28.10 15.67 4.09
1. 68a 1.45 1.32 1.18 1.07 0.89 0.65 0.31
78.59 68.01 59.51 49.91 38.64 19.38 10.23 3.08
4.43' 4.11 3.80 3.43 2.94 1.98 1.39 0.71
79.07 66.55 50.29 38.59 31.44 22.89 13.00 2.74
4.42' 4.06 3.51 3.07 2.79 2.37 1.79 0.86
67.42 54.69 48.40 36.56 23.67 27.79 12.69 5.40
13.48a 8.56 7.28 5.82 4.56 4.89 3.35 2.01
56
79.30 67.36 58.08 45.15 31.86 22.73 12.98 5.64
0.53 0.47 0.42 0.33 0.24 0.18 0.11 0.05
76.08 65.46 50.78 45.65 35.76 22.63 15.98 5.53
0.54 0.48 0.38 0.37 0.28 0.19 0.14 0.05
76.76 65.79 55.26 44.12 32.00 26.05 10.38 4.46
1.47 1.32 1.16 0.98 0.78 0.69 0.36 0.18
74.54 62.51 53.83 43.04 34.55 25.31 15.70 3.93
1.54 1.40 1.23 1.09 0.94 0.76 0.57 0.22
68.52 56.44 45.08 37.39 28.49 13.65 10.73 6.72
2.76 2.43 2.09 1.83 1.51 1.00 0.86 0.63
77.62 64.96 54.79 42.27 32.81 27.83 13.10 4.30
0.75 0.65 0.57 0.45 0.39 0.35 0.19 0.07
75.10 62.79 52.92 40.87 31.97 22.74
0.85 0.75 0.67 0.56 0.47 0.36
65.9 61.3 49.3 27.7 21.8 16.1 10.7 3.3
10.97 9.33 7.32 4.57 4.08 3.54 2.85 1.39
100
Hydrogen Adsorption, PresB., mole/g. om. Hg adsorbent 78.8 63.8 54.4 41.8 29.1
0.56' 0.57 0.57 0.54 0.53
75.8 75.5 59.7 45.8 31.8
0.02 0.02 0.03 0.02 0.02
Inactive Catalyst 0
78.7 65.4 57.6 46.3 33.8 27.9 14.2 2.8
1.46 1.28 1.15 0.98 0.76 0.65 0.38 0.08
79.4 69.1 56.9 45.8 33.4
1.66 1.54 1.38 1.18 0.98
79.3 63.8 53.3 41.0 30.5 24.2 15.3 6.75
4.04 3.57 3.20 2.51 2.24 1.93 1.41 0.80
77.1 65.5 54.3 41.5 37.4 26.5 17.4 9.1
4.06 3.74 3.39 2.93 2.85 2.39 1.91 1.39
Adsorption values must be multiplied by 10.--p
VOL. 49, NO. 10
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1763
I
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I
study of adsorption equilibrium for gas mixtures. It also simplified the catalyst deactivating procedure. Adsorption was studied at 0", 56", and 100" C. The 0" C. temperature was maintained by immersing the adsorbent tube in an ice and water mixture. The higher temperatures of 56" and 100" C. were attained with a saturated vapor heating jacket and vapor pressure controller which maintained temperature constant to 1 0 . 0 5 " C. Acetone and water vapors were used at 56" and 100" C., respectively, in order to maintain the heating jacket pressure a t 1 atm.
Materials PRESSUREiCm H g l
Figure 1. Adsorption isotherms on active catalyst at 0" C.
Figure 2. Adsorption isotherms on active catalyst at 56" and 100" C.
cuit comprising the buret and adsorbent tube. Gas was circulated through the adsorbent by slowly raising and lowering the mercury level in the buret. Iron inserts within the valve balls per-
mitted opening of the valves with a n external magnet prior to reading pressure and volume. T h e circulating feature was incorporated in the system to ensure homogeneous gas composition in a later
Except for two gases supplied by the Air Reduction Co.-hydrogen which was electrolytic grade and helium which was XXX grade-all gases were Phillips Petroleum Co.'s research grade.
Specifications for Test Gases Analysis, Gas
%
Ethane Ethylene Propane Propylene n-Butane
99.9
Hydrogen Helium I
Impurities 0.04% Cot
100.0
99.9
99.70 99.78
Propane, ethane, Isobutane 02,
Hz0
99 I99
The adsorbent, 50 mole 7 0 each of copper and magnesium oxides prepared according to Wynkoop (27), was activated in situ by passing a stream of hydrogen over it for 24 hours at 250" C. Heat and hydrogen were shut off and the system was evacuated to mm. of mercury. Prior to determining an isotherm, the system and adsorbent were flushed with the subject gas and again evacuated to IOw5 mm. of mercury. Hydrocarbon gases and helium were used without additional purification. Hydrogen was passed through palladized asbestos held a t 250" C. and activated alumina to remove traces of oxygen and water.
I
l
e
Procedure
@
f
This volumetric equipment, where adsorption i s determined b y gas volume changes, was used to obtain pure gas isotherms at various temperatures a.
U-tube adsorbent container
b. Gos buret consisting of a precision bored, calibrated cylindrical portion with a 1 0-ml. capacity, joined t o a series of four small calibrated spheres with a total capacity of 59.10 ml. was housed in a water jacket to stabilize its temperature c. Manometer having a capacity of 80 cm. of mercury d. Gold foil mercury vapor traps e. Mcleod gage, mercury diffusion pump, and Cenco Megavoc vacuum pump f. Gas pressure operated mercury leveling bulbs g. Storage bulb for holding test gas
1764
INDUSTRIAL AND ENGINEERING CHEMISTRY
The entire buret
Stopcocks on the adsorbent U-tube were closed and a sample of gas was admitted to the evacuated apparatus, exclusive of the adsorbent. Temperature, pressure, and volume of the sample were measured and then again after the gas was admitted to the adsorbent. Since the volume of void or dead space within the system had been previously measured, the quantity of gas adsorbed on the catalyst was determined by the apparent decrease in total volume of test gas. The adsorption isotherm was determined by raising the mercury level in the gas buret in discrete steps to compress the gas. Conversely, the desorp-
GAS A D S O R P T I O N lion isotherm was obtained by lowering the gas buret mercury level to decrease the gas pressure. Volume and temperature readings taken a t each new pressure supplied data for points on the isotherm. Measured parts of the original gas sample were removed from the system to permit examination of the low pressure end of the isotherm. Dead space in the system was determined in two stages. First, the volume bounded by the fixed mercury level in manometer c, the uppermost calibration in buret b, the stopcocks leading to the adsorbent U-tube, a, and stopcocks k, was determined by admitting helium to this evacuated space and noting variations in pressure accompanying a series of volume changes made by changing the mercury level in buret b. This information was then fitted by regression analysis to the equation, pV'/T = -k'p/T
f constant
where k' is equal to the desired void volume. The dead space within the adsorbent tube, which includes the adsorbent void and pore volumes, was then determined by repeating this procedure with the stopcocks on the adsorbent U-tube open. Further details on this
method are available (23). Helium adsorption was assumed negligible, Measurements were made on both catalytically active and inactive adsorbent. The adsorbent was activated by hydrogen reduction in situ, and deactivation was accomplished by admitting an excess of air to the reduced adsorbent which rapidly oxidized and darkened. When the adsorbent appeared to be fully oxidized-Le., when it came to equilibrium quickly with a newly admitted air sample-the system was pumped down to mm. of mercury and absence of activity checked by admitting an equimolar mixture of ethylene and hydrogen Table II.
Mole Adsorbed"
Gas
(v
- b)
=
The results of experimental runs are plotted in Figures 1 through 4, and a condensed tabulation of experimental data is shown in Table I. Complete tables of experimental data are available elsewhere (23).
+I53 92.3 95.6 9.7 32.1 -239.9 -267.9
...
+;)
Results
Order of Adsorbability and Physical Properties van der W a d Constantsb Mol. BbPt., T, P,, wt. O C . Atm. U b C.
%-Butane 9.90 X 58.1 -0.6 Propylene 3.88 42.1 -47.0 Propane 3.82 44.1 -42.2 Ethylene 1.42 28.1 -103.9 Ethane 1.32 30.1 -88.3 Hydrogen 0.56 2.02 -252.8 Helium 4.00 -268.9 At 0 ' C. and 60 om. of mercury. (p
to the adsorbent. If the mixture came to equilibrium rapidly with only a small apparent loss in volume and a slight temperature rise, deactivation was assumed complete. Earlier kinetic studies (24) revealed that catalyst activity was sensitive to oxygen poisoning.
36 45 43 50.9 48.8 12.8 2.26
14.47 8.379 8.664 4.471 5.489 0.244 0.034
0.1226 0.0827 0.0844 0.0571 0.0638 0.0266 0.0237
20
40
AH vap. C al./ G , Mole - 5342 - 4402 - 4487 - 3237 -3517 -216
.
..I
RT.
,
I
4
8 1 0
6
I
1
60
80
PRESSURE(Cm.Hg.)
Figure 3. at 0" C.
Adsorption isotherms on oxygen-poisoned catalyst
_ - -- Isotherms of
paraffin gases on active catalyst
Figure 4.
x 0 A
Freundlich isotherm
A
CZH4 C3H6
0
Cans n-C4Hlo
C3HE
VOL. 49,
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OCTOBER 1957
1765
Discussion Adsorption Isotherms. Isotherms of all gases studied resemble Type I or Type I1 isotherms of Brunauer and others ( 3 ) and are typical for physical adsorption. In addition, adsorption decreases as temperature is increased, which is also characteristic of physical adsorption. Chemisorption of olefins, suggested by results of the prior kinetic study (24, was not observed under conditions of this investigation. The slope of the butane isotherm at 0" C. begins to increase rapidly at pressures above 40 cm. of mercury. This probably marks the beginning of capillary condensation because vapor pressure of butane is only 1 atm. at this temperature. The catalyst pore diameter capable of causing condensation at these conditions was estimated to be 50 A. (23). Order of Adsorbability. The relative ease with which a given hydrocarbon gas is adsorbed on copper-magnesia appears related to its molecular weight. Thus, four carbon gases are adsorbed in greater quantity than three carbon gases which, in turn, adsorb more readily than two carbon gases. Between gases having the same number of carbon atoms, the adsorbent shows a greater affinity for unsaturates than for paraffins. Adsorption of hydrogen is only slight, and of helium negligible. Preferential adsorption of unsaturates appears unrelated to the common characteristic physical properties of gases listed in Table 11. Adsorption a n d Catalytic Activity. Interrelationship between catalysis and adsorption prompted an examination of adsorption on catalytically inactive, as well as active, adsorbent. Inactive adsorbent isotherms (Figure 3), with the possible exception of hydrogen, have the same general order and appearance as the active adsorbent isotherms (Figures 2 and 3). Deactivation decreased adsorbent capacity for the hydrocarbon gases by aproximately 10% (at 0" C. and 60 cm. of mercury). This was true for both olefin and paraffin gases and was somewhat disappointing because the observed olefin affinity had been presumed to be associated with both activity and chemisorption. From the foregoing, it appears that the inactive adsorbent simply presents a copper oxide-magnesia instead of a copper-magnesia surface, and both surfaces have similar affinities for the gases studied. Chemisorption, if present, is probably obscured by the relatively large physical adsorption. A marked sensitivity to catalyst poisoning was demonstrated by hydrogen whose adsorption decreased 95%-from 0.56 X IO4 mole on the active adsorbent to 0.02 X 10" mole on the inactive-at 0" C. and 60 cm. of mercury. This result is similar to Pease's observation (79) that reduced copper oxide when poisoned
1766
with mercury, lost 95% of its adsorptive capacity for hydrogen and only 22% of its capacity for ethylene. Hydrogen adsorption may, therefore, be more sensitive than catalyst area as a n index for activity of a hydrogenation catalyst. This result warrants further study. Evaluation of Common Correlation Techniques. The classical equation relating pressure to moles adsorbed is the Freundlich equation, N = k,n
where k and n are constant. I t states that a simple logarithmic relationship exists between pressure and quantity of gas adsorbed, which appears as a straight line on a log-log plot. The equation was originally empirical, but it was later derived from theoretical considerations (77, 22). Experimental data obtained in this study are plotted as log N us. log p . (Figure 4). Almost all experimental points fall directly on smooth curves and, with the exception of high pressure data for n-butane, these curves are all nearly straight lines. Information read from these curves was used in the correlating techniques subsequently described. Adsorption Potential Correlation. Polanyi (20) suggested that "adsorption potential" is independent of temperature and only a function of the volume of gas adsorbed. Adsorption potential defined as
i 4
2
-
0.01
Ee 68
L$
E $
2
0.001 8
6 4
2 IO
20
30
40
Figure 5. Polanyi-type correlation of olefin adsorption OR active catalyst a t various temperatures
0 C2H4, '0 c.
INDUSTRIAL AND ENGINEERING CHEMISTRY
C2H4, 56' C.
A CaHa,
x
A
O°C. CaHs, 56' c. c 3 H 6 , 1 O O 0 C.
or the free energy change accompanying transport of a gas from the gas phase to a point near the adsorbent surface where saturation conditions prevailed. Dubinin and others (5) expanded the concept by assuming that adsorption potentials of similar type gases were equal when adsorbed volumes were equal. Adsorbed volumes were calculated as the product of moles adsorbed and molar volume of the adsorbate considered as a saturated liquid. Lewis and others (78) modified the Dubinin relationship by substituting fugacities for pressures and basing adsorbed volume on molar volume of the adsorbate considered as a liquid whosr vapor pressure equals adsorption pressure. Their equation took the form (.VRT In f~/f)l = ( N R T InfI/f)? when ("VI, = ( N V h O r dividing each side by NV, ( T / V In fsislfh = ( T / V In / ~ / f h (A) The molar volume, V, used by Lewis and others has a practical advantage over the molar volume suggested by Dubinin, because it is applicable to isotherms measured a t temperatures above critical temperatures of the gases studied. However, Vis a function of pressure and must be determined for each point on the isotherm. Equation (A) was applied to this work and also in a simplified form using a constant, V,, the molar volume at the boiling point, instead of the variable molar volume V. The equation based on I/, was as adequate as that based on V, both for these data and samples of data from Lewis (78) and Jelinek (74). Results of applying the simplified correlation are demonstrated by Figures 5 through 7. Adsorption on the active catalyst is represented by Figures 5 and 6. Data for the olefins, ethylene and propylene, are fairly well correlated between 0" and 100' C. by a single line (Figure 5). A single line also represents paraffin data (ethane, propane, nbutane). Data for adsorption on the inactive adsorbent (Figure 7) may be shown as straight lines for the paraffin and olefin gases. They appear, however, in Figure 7 as two series of closely grouped curves, to emphasize distribution of data for each test gas. I t is evident that the Polanyi-type correlation permits estimation of adsorption isotherms at temperatures beyond or between the range of available data. The equation should, therefore, be useful for engineering design purposes because, for example, low pressure data for butane can be used to estimate the high pressure data for ethane or data token at one temperature can be used to estimate the isotherm a t another temperature. Langmuir Equation. Shortly after the Polanyi equations were proposed, Langmuir (17) proposed an adsorption
GAS ADSORPTION isotherm equation based on the assumption that adsorption involves a reaction between the gas molecules and sites on the adsorbent surface. This equation is 1/N
f
= (lIbNm11IP
1/Nm
Low pressure data for ethane, ethylene, propane, and propylene produce straight lines when plotted in accordance with this equation. As pressures increased, the plots curved downward. Following the assumption made in deriving this equation, the intercept of the plot corresponds to N,, adsorbate concentration a t monolayer coverage. This intercept was taken as the extrapolation of the straight-line portion of the curves rather than the part of the curves nearest the ordinate. Values of monolayer adsorption range from 0.9 X l o 4 to 6.4 x IO4 gram mole per gram of adsorbent (Table 111). Brunauer, Emmet, and Teller Equation. Brunauer, Emmet, and Teller (4) extended the Langmuir monolayer concept to multilayer adsorption and derived the equation, P/Nm(Ps
- P)
= 1/Nmc
PIP.
+
(C
-
1)I"mC
which also permits estimation of N,,, (monolayer concentration) and, therefore, surface area of the adsorbent.
h
I
I
I
I
I
Surface areas of the copper-magnesia adsorbent in its active and inactive states were computed from propane and nbutane isotherms a t 0' C. Area for the active adsorbent as calculated from isotherms of both gases, was 98 square meters per gram, that for the inactive adsorbent, 96 as determined from the propane isotherm and 84 from the butane isotherms, averaged 90 square meters per gram. Surface areas of the poisoned and catalytically active adsorbent differ, therefore, by only 10%. Also, the value of constant c, for the active adsorbent is close to that for the inactive adsorbent (Table 111); this suggests that heats of adsorption on the active surface and on the poisoned surface are equivalent, and further emphasizes similarity of adsorption on the active and inactive catalyst surfaces. Monolayer concentrations of propane and butane were essentially equivalent. Rpssel and Cochran (27), when reporting BET measurements on alumina catalysts with these gases, made the same observation which led to the supposition that both gases occupy the same surface area, calculated as 39 square A. This quantity was therefore used to calculate the copper-magnesia surface area. Figure 8 shows the BET correlation for propane on the active and inactive catalyst. Monolayer concentration was estimated from the slope of the straight portion of the curve a t a relative pressure of 0.1. The method is similar to that used by Russel and Cochran (27). Fugacities were substituted for pressures in this correlation. This slightly improved the agreement. between values of N,,, calculated for propane and butane. Use of fugacities in the BET equation appears consistent with their uge in the previously mentioned Polanyi equation. Table I11 summarizes th'e constants calculated from the BET and Langmuir correlations. Values of monolayer concentration, as calculated by either equation, are only slightly affected by activity. These findings support Emmet's theory (7) that catalyst area is not directly related to catalyst activity. Langmuir N , values are more dependent on the gas adsorbed than are BET values. Table 111.
Figure 6 . Polanyi-type correlation of paraffin adsorption on active catalyst at various-temperatures 0 cZH6, 0" c. 0 CzHa, 56' c. A Cans, ' 0 C.
x A
Cans, 56' c. C3Hs. 100' C. 0 n-ChHio, 0" C. W n-CaHlo, 56" C.
6 4
a
001
%
e
0
4
g 6 1
E $
2
0001
e 6
lllzEm 10
1 V, In+
%/MI
40
50
)
Other Correlation Equations. Equations from Williams (26) and Harkins and Jura (72) did not give satisfactory correlation of the data collectedplots of these produced curved rather than the required straight lines. Correlations from Sips (22) and Koble and Corrigan (76) could not be adequately evaluated; the data produce reasonably straight lines on log N us. log p plots, and the subject correlation is designed to eliminate isotherm curvature on just such a plot. Heat of Adsorption. Isosteric heats of adsorption were estimated from the isotherms by applying a modified Clausius-Clapeyron equation,
QN decreases as amount adsorbed and temperature increase. Also, it has the same magnitude as the heat of condensation. These are both indications of physical adsorption. QN values do not
Monolayer Adsorption and Adsorbent Surface Area
Nm,0' C.
Active
(0-Mol
30
Figure 7. Polanyi-type correlation of adsorption on oxygen-poisoned catalyst a t ' 0 C. 0 C2H4 A cIH8 0 C2H6 n-C~Hlo A C3H6
Langmuir Values (1
20
Inactive
N m , 0'
Active
n-Butane 6.4" 5.6" 4.2" Propylene 2.6 2.6 4.2 Propane 2.7 2.7 4.2 Ethylene 0.9 0.9 3.3 Ethane 1.2 1.9 4.0 Given values must be multiplied by 10. -4
C. Inactive 3.6"
5.0 4.1 2.9 3.5
BET Values Surface Area, Sq. M./G. Active Inactive Active 98
... 98 ... ...
84
... 96 ... ...
C
Inactive
10.8 18.7 12.8 24.7 10.0
13.2 14.2 10.1 31.1 10.5 -
VOL. 49, NO. 10
OCTOBER 1957
1767
1
I
004
I
! 012
OOE
I
016
020
1. f.
Figure 8. BET correlation of propane adsorption on active oxygen-poisoned catalyst at 0” C.
agree with the heats of adsorption calculated from the kinetic study (24) (Table
IV). Summary and Conclusions Catalytic Activity and Adsorption Capacity. Adsorption capacity and adsorbent area can be misleading indexes of catalytic activity, because for the system described herein, these properties are only slightly affected by loss of catalytic hydrogenation activity. In both its catalytic active and oxygen poisoned form, copper-magnesia adsorbent has a n affinity for olefins over paraffins. Its capacity for either gas is only slightly decreased by poisoning. Hydrogen adsorption, however, was a n exception to this behavior and was sensitive to catalyst poisoning. This eff‘ect deserves further investigation, because it might provide an index for determining hydrogenation catalyst activity. Physical Adsorption. The observed adsorption has been classified as physical on the basis of the shape of the isotherms, their temperature dependence, and the similarity between calculated heat of adsorption and heats of condensation. Chemisorption of olefins, suggested by kinetic analysis of hydrogenation data on the active adsorbent, was not detected, possibly because it is masked by
Table IV. Q.v,
much larger physical adsorption. This, in turn, suggests that reactant chemisorption and activation during hydrogenation probably occur from a physically adsorbed gas film rather than directly from the gas phase. Correlating Techniques. The Freundlich equation gave the closest fit to the isotherm data. A Polanyi-type equation, which is a simplification of that used by Lewis and others (78), acceptably correlated data for similar gases a t temperatures between 0’ and 100 C. This equation should be useful in extending adsorption data for engineering design. T h e BET equation was used to determine adsorbent areas based on butane and propane adsorption. T h e areas of the active and oxygen poisoned surfaces differed by only 10%. Adsorbent monolayer concentrations estimated from the Langmuir equation are also relatively insensitive to activity and are not as consistent as those estimated by the BET method. Correlations from Williams (26) and Harkins and Jura (72) did not apply satisfactorily to the data and that from Koble and Corrigan (76) could not be tested adequately. Nomenclature
constant in Langmuir equation constant in BET equation (heat of adsorption - heat of liquefaction) f = fugacity a t adsorption pressure, cm. of mercury fs = fugacity of saturated liquid adsorbate a t adsorption temperature, cm. of mercury AF = thermodynamic free energy change, calories per gram mole = constant in Freundlich equation k n = constant; exponent in Freundlich equation iV = adsorbate concentration, moles per gram of adsorbent = monolayer adsorbate concentration, moles per gram of adsorbent p = adsorption pressure. cm. of mercury p s = saturated vapor pressure of liquid adsorbate a t adsorption temperature, cm. of mercury QAT = isosteric heat of adsorption, calories per gram mole R = gas law constant, calories per gram mole b
c
= =
Heat of Adsorption
Cal./G.
Heat of Condensation
Kinetic Heat of Adsorptionb
Molea -4480 (2.0) -3517 3237 f1107 - 5 5 6 0 (2.0) Propane -6250 (4.0) - 4487 - 1870 -6650 (4.0) - 4402 i-2490 Propylene n-Butane -66860 (5.0) - 5342 Calculated from 0’ and 56” C. isotherms at N equal t o quantity in parenthesis multiplied by
Ethane Ethylene
...
...
a
10. - 4
Obtained from (24)based on hydrogenation kinetics.
1768
INDUSTRIAL AND ENGINEERING CHEMISTRY
?’ = absolute temperature, O K. = molar volume of saturated liquid adsorbate a t a vapor pressure equal to adsorption pressure, cc. per gram mole V, = molar volume of saturated liquid adsorbate a t its boiling point, cc. per gram mole V‘ = gas buret reading, cc.
V
Refere nce s
Berenyi, L., Physik. Chem. 94, 628 (1 920). Brunauer, S., “Adsorption of Gases and Vapors,” vol. 1, Princeton University Press, 1943. Brunauer, S., Deming, C. S., Deming, W. E., Teller, E., J. Am. 62, 1723 (1940). Chem. SOC. Brunauer, S., Emmet, P. H., Teller, E.,Ibid.,GO, 309-20 (1938). Dubinin, M. M., Raduskevich, L. V., Doklady Akad. hTauk, S.S.S.R. 5 5 , XO.4, 327-9 (1 947). Ernmet, P. H., “Advances in Catalysis,” (W. G. Frankenburg, V. I. Komerewsky, E. K. Rideal, editors), vol. 1, p. 65, Academic Press, New York, 1948. Emmet, P. H., “Catalysis,” vol. 1, p. 53, Reinhold, New York, 1954. Emmet, P. H.., IND.EXG. CHEM. 37, 639-44 (1945). Farkas, .4., Melville, H. W., “Experimental Methods in Gas Reactions,” Macmillan, London, 1939. Frankenburg, W. G., J . Am. Chem. Soc. 66, 1827 (1944). Halsey, G. D., Taylor, H. S., J . Chem. Phys. 15,624 (1948). Harkins, W. D., Jura, G., J. Am. Chem. Sod. 66,366-70 (1944). Hill, T. L., Ibid., 17, 520-35 (1 949). Jelinek, R. V., Ph.D. dissertation, Dept. of Chem. Eng., Columbia University, 4953. Joyner, L. G., “Scientific and Industrial. Glass Blowing and Laboratory Techniques” (W. E. Barr, V. J. Anhorn, editors), Instruments Publishing Co., Pittsburgh, 1949. Koble, R. A.,Corrigan, ’r.E.,IXD. ENG.CHEM.44. 383 (1952). Langmuir, I., J.‘ Am. ‘Chem. Soc. 38, 2221 (1916) Lewis, W. K., Gilliland, E. R., Chertow, B., Cadogen, W. P., IND. END. CHEM. 42, 1326-32 (1950). Pease, R. N., J . Am. Chern. SOC.45, 1197 (1923). Polanyi, M., Verhandl. deut. physik. Ges. 18, 55 (1916). Russel, -4.S., Cochran, C. N., IND. ERG.CHEM.42,1332-5 (1950). Sips, R., J . Chem. Phys. 16, 490 (1948). Sussman, M. V., Ph.D. dissertation, Dept. of Chem. Eng., Columbia Cniversity, 1957. Sussman, M. V., Potter, C., IND. END.CHEM.46,457-65 (1954). Wilhelm, R. H., Wynkoop, R., Chem. Eng. Progr. 46, 300-10 (1950). Williams, Proc. Roy. SOC.(London) 96A, 287-311 (1920). Wynkoop, R., Ph.D. dissertation, Dept. of Chem. Eng., Princeton University, 1948. RECEIVED for review September 4, 1955 ACCEPTED April 19, 1957 Division of Industrial and Engineering Chemistry, 128th Meeting, ACS, hfinneapolis, September 1955. This work was supported by an AEC fellowship.
