THE ADSORPTION OF THE VAPORS OF CERTAIN KETONES AND ESTERS BY ACTIVATED CHARCOAL1 J. N. PEARCE
AND
A. C. HANSON
Physical Chemistry Laboratory, The State University of Iowa, Iowa City, Iowa Received September 17, 1934
Previous investigations (4)have dealt with the adsorption of vapors of various types by activated charcoal. These have been studied with special reference to the in%uenceof the position and the nature of substituent groups in the vapor molecules upon adsorption magnitudes. In this paper we present the results obtained in the study of the adsorption of certain ketone and ester vapors by charcoal. If these are considered in conjunction with the vapors of ethers previously studied (6), we have three types of oxygen compounds to consider, namely,
R’
I Ether
Ketone
I1 Ester
The mobility of the molecules on an adsorbing surface supports the view that adsorption is a phenomenon due to physical attraction. These forces may be simply van der Waals forces or they may be of an electrical nature, depending upon the dipole nature of the vapor molecules. Under the influence of the powerful surface forces the molecular dipoles will be definitely oriented and attracted by the surface atoms. According to Eucken and Meyer (2), the dipole moment of a molecule is the vector sum of the partial moments of the individual linkages of the 1 A brief extract of a dissertation presented by Arthur C. Hanson to the Graduate College of the State University of l o m in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 679
680
J. N. PEARCE AND A. C. HANSON
atoms in the molecule. They have calculated the moments of the follow ing typical linkages : Linkages.. . . . . H-C p
X lo1*E.S.U.
0.4
H-0 1.6
C-0 C-C 2.3
0.7
C-OH 1.6
C-CH0 1.0
They have added vectorially the four moments in the ester molecule, R.COO.R', and they have found the moments for formulas I and I1 to be 3.4 X and 1.1 X 10-l8 E.s.u.,respectively. Since the moment of the H-(C) should be the same as that of CH3-(C), or of CH1. [CH2In-(C), the moments should be independent of the nature of the radical R, provided it consists of hydrogen atoms, or of alkyl groups only. Except as modified by the remaining linkage moments, the C=O moment is the one specifically active in the adsorption of ketone vapors. Its value should be affected considerably by the presence and the manner of rotation of the R-0dipoles in the ester molecule. The moments of the fatty acids are approximately 1.4 X 10-ls and of most esters about 1.8 X lo-'' E.S.U. According to Debye (l), the two possible angles between the two H-0 linkages of the water molecule are 64" and llOo, respectively; the corresponding moments calculated for these angular dimensions are 1.34 X 10-l8 and 4.34 X 10-l8 E.S.U. The actual observed moment lies between these at about 1.8 X 10-l8. It is conceivable that by repulsion between substituted groups the moments of the ether molecules, RzO, should be different from that of their prototype, HzO,and yet be only slightly affected by the size of the alkyl groups. With these considerations in mind, it should be quite evident that whether we consider the ethers, the ketones, or the esters separately as a class, the magnitude of the adsorption due to the dipole moment will be but slightly modified by the complexity of the molecules of the given type. While the moments of the molecules are undoubtedly effective in adsorption, the relative amounts adsorbed for the different vapors of any one class 7NiU depend to a large degree upon certain other physical properties. Among these are the cross-sectional area of the molecules, the ease of condensation, or the boiling points of the pure liquids, and the van der Waals constants "a." If it is assumed that the vector moment is the same in the ether and ketone molecules oriented at the surface, it is evident that the surface covering power of dimethyl ether should be practically the same as that of dimethyl ketone. The surface covering power of either one must be less than that of the corresponding diethyl compound. With either type the covering power must increase with increase in the complexity of the substituted alkyl groups.
ADSORPTION
OF VAPORS OF CERTAIN KETONES AND ESTERS
681
p ...... 0.00 0.00 0.20 0.55 1.24 3.52 5.16 12.41 28.19 33.69 44.87 50.58 x / m . . 12.23 25.40 60.8875.4585.4894.2097.94 102.80 109.06 110.64 114.59 116.90
.
p . . . .. . 61.00 64.58 70.08 x / m . . . 120.87122.74 131.67
p . . . . . . . . 0.10 0.35 0.55 0.69 0.79 1.55 2.28 3.52 4.46 9.03 12.02 x / m . . . . . . 6.33 20.17 25.48 31.10 34.74 45.57 60.65 67.59 72.28 83.13 86.93
p . . . . . . . . 18.02 24.07 27.00 37.72 52.12 78.42 89.89 154.47243.51 288.68 x / m . . , . . . 91.83 95.28 96.10 99.34 101.45 104.36 105.49 109.62 114.48 116.51
.
p . . , . . , . 337.92 388.26 420.91 421.50 412.17 x / m . ,. . . , 119.29 121.26 128.10 129.74 122.93
I
p ....... . . . . . . 0.30 0.89 1.89 4.25 6.70 12.57 16.88 17.22 24.8037.6745.54 x / m ... , . . . . . 10.01 19.12 31.05 49.98 58.97 70.50 75.06 75.20 80.5786.3088.65
.
. . . , . . 56.14 80.38 112.92 158.29 164.64 228.62 281.32 421.51 437.04 . . . , . . . 91.12 93.93 96.64 99.37 99.81 102.21 103.84 108.90 109.07
p . . ..... x / m . .,
p .... . 1.09 1.84 4.17 8.79. 15.29 17.52 32.61 39.21 56.58 58.72 75.6086.82 x / m . . 5.88 7.76 13.77 22.90 31.36 33.68 44.74 47.57 53.85 56.05 62.8066.15
.
p . . . . 88 .OO 88.45 112.77 137.49 169.01 183.60 204.10 233.59 288.09 358.12 422.64 x / m . . 66.56 66.56 71.38 75.06 77.94 79.21 80.73 82.35 84.49 86.95 89.58
At 138.27"C.
lI lI l l Il Il I I I I 1I 1 I -
. . . . 2.00 7.69 10.32 35.24 66.11 112.72 161.56 248.53 297.72 315.48 405.97 419.95 . . . . 4.38 10.68 13.21 25.63 36.32 46.48 52.98 60.66 63.38 64.24 68.93 71.50
p.., . x/m.
At 183.10"C.
Here, also, the cross-sectional area exerts a specific influence. The first molecules admitted to the surface are adsorbed without definite arrange-
.
682
J. N. PEARCE AND A. C. HANSON
ment with respect to the surface atoms. Before the surface can become completely covered at saturation there must be a movement of the molecules along the surface, or a rotation about their points of attachment. For this reason more time is required for the attainment of adsorption equilibrium ( 5 ) , and this influence will be greater, the greater the crosssection and the complexity of the molecules.
p ..........
x/m.. ......
1
I
0.00 0.00 0.25 0.74 0.86 2.45 3.92 6.50 8.2812.25 17.99 21.21 43.47 44.22 60.98 83.50 83.72 89.39 91.91 94.26 96.17 98.40 102.79 105.85
p . . ........ 24.93 25.27 x / m . ...... 108.43 112.91
p ........
0.15 0.60 1.85 5.75 8.42 9.32 19.2829.6852.77 105.47 172.40237.20
x / m . . . . . . 9.98 19.6635.3450.0456.5457.0065.2769.4472.95 76.80 80.00 81.88 p ......... 279.27 297.43
x / m . . . . . . 83.33 85.57
p.....
x/m..
4.71 13.33 24.25 43.31 62.69 63.23 91.97 98.11 98.56 125.56 165.56 184.94 16.86 27.6036.4545.63 51.2451.31 55.9756.9657.36 59.95 62.94 64.11
p .........274.34 298.22 x / m . . .... 68.45 76.65
p
........
x / m......
The apparatus, charcoal, and the technique involved are the same as that employed in all of the previous work. The ketones and esters were Eastman's products of highest purity. They were further purified according to approved standard methods and several times fractionally distilled, using the apparatus designed by Loveless (3). Only the final middle frac-
ADSORPTION OF VAPORS OF CERTAIN KETONES AND ESTERS
683
tions distilling over within a range of 0.01' to O.lO°C. a t the correct boiling point were used. The complete experimental data, including all duplicate series, are collected in the following tables. In these p is the equilibrium pressure TABLE 3 The adsorption of diethyl acetone vapor b y charcoal at various temperatures A t 0°C.
p . . . . . . . . 0.00 0.10 0.35 0.70 2.61 4.4311.68 16.93 21.3928.1330.08 x / m , . . . 24.09 34.39 50.18 55.09 65.31 68.68 74.22 76.19 77.31 78,8379.23
..
.
p . . . , . . . 31.87 53.02 56.14 63.74 68.45 70.49 95.20 120.15 120.68 x / m . . . . . 79.60 83.61 84.32 85.62 86.35 87.35 90.85 95.30 97.72
.
p . . . . . . . . 0.35 0.84 1.78 1.95 4.02 5.43 9.8110.7914.4223.06 x / m . . , . , . 28 .OO 35.19 42.34 43.16 49.57 52.45 57.65 58.36 60.29 62.93
..
p . .. . . 24.89 36.22 69.28 93.90 115.46 119.77 x / m . . . . . 63.28 65.11 67.87 69.25 70.15 72.62 I
.
p ....... 0.40 1.55 2.79 5.85 5.92 6.95 8.6811.0114.4216.6719.00 x / m . . . . 10.34 21.19 28.68 37.25 39.66 39.66 42.57 45.62 48.57 49.66 51.38
. p . . . . . . . 21.82 34.0439.15 59.0290.00 117.94 118.68
x / m . . . . . 52.49 55.02 55.48 57.36 60.30 62.26 64.37
p ........ 0.80 1.88 4.08 5.49 9.0610.4015.6122.3026.2239.6250.64 x / m . . . 9.73 15.43 21.58 24.58 29.87 31.01 34.95 38.03 39.06 43.60 45.64
..
p . . . .' . . . . 77.31 102.03 114.08 119.70 x / m . . . 49.17 51.38 53.09 55.40
..
in millimeters and x / m is the number of cubic centimeters (N.T.P.) of vapor adsorbed by 1 g. of charcoal. For want of a better method we have made use of the Langmuir equation for adsorption on a plane surface and we have plotted the values of p/(z/m) against the corresponding pressures, p . The Langmuir isotherms thus obtained for low pressures at various temperatures are shown in figures 1
684
J. N. PEARCE AND A. C. HANSON
and 2; those for the boiling points at higher pressures are shown in figure 3. Within the range indicated by the experimental points, the Langmuir equation satisfactorily expresses the adsorption relations. At still higher pressures, however, the experimental points deviate widely from the straight line plot. The influence of the structure and molecular complexity of the ether, ketone, and ester vapor molecules is perhaps best shown by the natural boiling point isotherms, xlm = up". At the boiling point the tendency
p ....... 0.10 0.20 0.60 2.98 7.2512.91 21.94 30.58 40.95 50.33 59.47 69.94 x / m .... 37.79 60.69 82.01 92.61 96.96 99.47 102.39 104.74 107.65 110.27 112.53 114.55 p . . ..... 73.41 x / m . . .. 117.88
p ......... 0.05 0.25 1.25 3.57 6.66 7.89 13.10 17.62 29.63 44.77 89.89 x / m ...... 16.89 30.56 44.06 59.54 71.13 74.50 79.47 81.27 85.79 88.86 93.14
..
p . , , , . . 129.01 172.24 238.75 300.01 322.99 377 -64 397.49 448.37 448.72 x / m . . .... 94.90 96.83 99.41 102.18 103.12 105.68 106.24 108.64 110.85
p ......... 0.30 0.50 1.09 1.24 2.43 3.91 4.21 7.53 10.40 12.8217.08 x / m . . ..... 9.50.13.52 22.90 24.01 35.30 44.28 46.42 56.76 61.63 65.5269.75 p ......... 25.05 33.52 47.53 63.08 80.80 88 .08 176.56 224.94 243.25 370.85 x / m ....... 74.74 78.55 81.51 84.75 86.27 87.55 91.13 92.62 93.68 96.40 p .........371.84 464.97 580.33 x / m . . ..... 96.82 98.21 100.55
of the vapors to condense is practically eliminated. The only forces prevailing are those between the adsorbent and the vapor molecules and the van der Waals forces between the molecules in the vapor phase. The natural boiling point isotherms, figure 4, show definite characteristic regularities. Ethyl formate is less adsorbed at all pressures than is methyl acetate. At pressures below 0.2 mm. the order of increasing adsorption for the acetate vapors is: methyl < ethyl < propyl. At higher pressures the order is exactly reversed. Methyl propionate is less adsorbed than are ethyl and propyl acetates a t pressures below 0.8 mm.;
ADSORPTION
685
OF VAPORS OF CERTAIN KETONES AND ESTERS
it is more highly adsorbed than methyl acetate below 1.5 mm. The higher boiling n-propyl acetate is the most highly adsorbed of all the esters TABLE 5 The adsorption
01methyl acetate vapor by charcoal at various temperatures
0.10 0.20 0.35 0.40 2.38 6.16 16.08 16.63 33.31 48.50 55.40 38.94 59.99 71.1078.71 92.6697.61 102.94103.05108.75 114.11 115.95
p.... x/m
.
p ........... 59.56 63.04 63.34
x / m ........116.65 123.81 123.12
...... x / m ...... p..
p
.
0.20 0.30 1.29 5.91 7.15 23.08 26.9154.2678.43125.84 20.85 35.51 54.07 75.42 77.59 87.98 88.6492.9195.25 97.88
........190.51 234.80 309.78 332.67 360.69 391.44 394.94
x/m..
.... 101.62 103.49 108.22 109.58 110.26 112.65 121.08
p ........ x / m ......
0.10 0.94 3.67 7.13 17.39 24.91 40.96 71.22 109.26 258.99 6.52 35.96 55.88 65.24 76.4981.4185.8288.79 91.29 96.59
p ........ 351.66 428.08 447 -96 573.13 754.03 x / m ...... 99.08101.21 101.89105.66110.91
........ ....
p x/m..
1.04 3.20 12.75 16.0328.69 43.18 60.46 76.14 129.40 184.25 13.12 22.70 41.50 43.75 52.66 58.91 63.74 66.81 72.20 76.55
p ........ 244.16 310.98 380.27 402.26 x / m ...... 79.01 81.56 82.98 85.52
I I I I I I I 1 I I I
I
p . ...... 6.16 10.92 15.88 38.07 68.35 135.91 177.65 221.47 261.34 327.06 376.55 405.43 x/m 16.14 21.84 26.06 38.11 45.76 56.26 60.41 64.10 65.93 68.97 70.07 72.50
....
a t low and least a t high pressures. The order of adsorption of all the esters a t pressures below 0.8 mm. is Ester.. ........ .n-AcOPr
.
a X 10S(atms.)2.. .5144 p x (E.S.U.). .I.78
.
> AcOEt > PrOMe > AcOMe > FOEt 4076 1.81
4027 1.69
3137 1.76
3128 1.92
The van der Waals constants, a, were taken from or calculated by formulas given in Landolt-Bornstein, Physikalische-Chcmische Tabellen, 5th edition, Vol. I, p. 253. Springer, Berlin (1923).
. .
686
. .
J N PEARCE AND A C HANSON
p ........ 0.00 0.05 0.10 0.30 0.40 2.63 2.98 6.30 9.5810.8215.88 x / m ...... 17.06 34.28 40.13 66.88 75.21 81.59 82.36 85.08 87.69 88.60 91.97 p ........ 17.37 20.50 24.47 . . . . . 92.85 94.09 99.01
x/m
p
. . . . . . . . . . . 0.00
x/m . . . . . . . . .
0.05 0.10 0.50 0.98 1.24 1.54 8.49 14.7415.1932.41 6.90 20.39 21.6847.54 50.86 63.69 64.57 71.92 75.2675.5578.50
p
............ 43.09
p
. . . . . . . . . . . .43.29 166.58 183.66
49.64 50.1383.39 104.34 111.58 117.14 135.36 141.81
x / m ......... 79.26 79.99 80.3383.12 84.60 85.62 85.37 87.83 87.88 x / m ......... 88.36 89.91 91.29
p . . . . . . . . 0.05 0.20 0.25 0.35 0.89 3.18 4.67 9.7818.4748.15 x / m . . . . . . 7.93 18.25 21.85 29.46 38.56 52.32 55.63 61.39 66.03 70.30 p . . . . . . . . 50.48 100.37 115.06 160.30 180.88 184.95 x / m ...... 70.54 73.49 74.15 75.21 76.50 77.48
p . . . . . . . . 0.40
1
1.54 3.97 8.3420.9533.0141.4067.21115.80132.08
x / m ...... 19.24 31.02 40.41 47.49 55.35 58.67 60.28 63.27 66.03 66.64
p
........ 153.68 174.03186.64
x / m ...... 67.27 67.89 69.24
p ........ 0.30
2.98
6.16 13.01 22.2440.7548.2548.6058.2287.51
x / m ...... 13.55 22.61 28.15 34.51 40.83 46.25 48.33 48.76 50.20 53.23
p
........ 122.90 142.86 167.33 178.59 189.66
x / m ...... 55.56 57.07 58.08 58.37 61.57
p ........
x / m .....
This is exactly the order of decreasing boiling points of the liquids; it is also the same order as that of the van der Waals constants .
ADSORPTION OF VAPORS OF CERTAIN KETONES AND ESTERS
687
The order of adsorption at higher pressures is Ester.. . . . . . . . . .AcOMe a X lo5 (atms.). .3137
>
FOEt 3128
>
AcOEt 4076
>
>
PrOMe 4027
AcOPr 5144
With slight variations due to cross-sectional influences the order here is the reverse of the order of increasing values of the van der Waals a. TABLE 7 The adsorption of n-propyl acetate vapor by charcoal at various temperatures At 0°C.
p ........ 0.00 0.00 0.20 0.30 0.50 1.04 2.03 5.2610.6717.27 x / m . . . . . . 19.72 26.13 37.94 52.34 54.63 58.17 59.86 63.33 65.23 66.70
p . ....... 22.63 28.09 34.50 38.77 44.5255.19 58.27 67.60 69.09 71.08 x / m . . . . . . 67.88 68.86 69.72 70.79 71.21 73.25 73.72 74.74 75.17 76.95
At 181.54"C. p..
......
x/m .....
Similar relations also were found to exist for the adsorption of ketone and ether vapors. The order of adsorption a t low pressures is Ketones ..................... Et2C0 a X lo6 (atms.) p x 10'8E.S.U.......................
>
Ethers.. ........................... l o 5 . ........................... p x 1018.. .........................
Pr20
a X
EtCOMe
>
Me&O
2.74
>
Et20 3464 1.14
2.74
>
Me20 1609 1.29
. . PEARCE AND A . C. HANSON
688
J N
p ........ 0.00 0.05 0.10 0.15 0.25 0.70 0.75 2.98 7.89 9.7814.00 x / m ..... 14.94 29.99 55.85 64.05 67.87 76.68 77.77 82.23 86.43 87.59 90.26 p ........ 17.72 18.8121.94 22.14 x / m ..... 92.79 93.26 95.74 98.51
p ........ 0.05 0.10 0.20 0.84 3.90 7.1526.0137.2854.5574.6598.08 x / m ..... 16.41 33.31 48.30 61.16 70.02 73.33 78.21 79.63 81.47 83.32 85.63 p ........ 127.72 156.21 168.91 xlm 88.25 90.63 93.18
.....
p ........ 0.15 0.45 1.74 3.03 7.00 8.8411.1718.9633.2145.7760.26 x / m ..... 11.20 24.85 43.87 49.78 57.25 59.10 60.90 64.30 67.52 68.92 69.99 p . , ...... 93.47 108.90 123.80 153.13 168.22 x l m ..... 71.82 72.63 73.09 74.04 76.52
p ........ 0.25 0.35 1.04 2.98 7.5512.4124.9230.7848.5067.3685.13 x/m 12.14 20.61 27.10 38.68 47.98 52.48 58.30 60.22 63.16 65.06 66.60
.....
p . , ...... 116.90 152.29 168.87 x / m ..... 68.03 69.11 70.41
p ........ 0.25 0.75 2.13 4.27 6.35 12.56 17.7725.0731.2237.0348.25 x / m ..... 8.2512.30 18.54 24.51 27.87 34.97 38.1641.9644.0746.0048.31 p ........ 53.06 87.16 100.22 103.10 146.53 147.42 174.87 x / m ..... 49.3053.46 54.69 54.98 57.54 58.22 59.48 TABLE 9 Heats of adsorption calculated from the isosteres VAPOR
AH caE
Acetone .................... Methyl ethyl ketone ....... Diethyl ketone ............. Ethyl formate ..............
VAPOR
.
-10690 -11224 -11020 -13140
AH
cal
Methyl acetate ............ Ethyl acetate .............. n-PropyI acetate ........... Methyl propionate .........
.
-11520 -11960 -13200 -14030
ADSORPTION OF VAPORS OF CERTAIN KETONES AND ESTERS
689
Pmn.
FIQ.2. LANGMUIR ISOTHERMS FOR CERTAIN KETONES AT DIFFERENT TEMPERATURES THE JOURNAL OF PHYSICAL CHEMISTRY, VOL. 39, NO.
6
FIG.3. LANQMUIR BOILINGPOINT ISOTHERMS 1, Acetone; 2, methyl ethyl ketone; 3, diethyl ketone; 4, methyl acetate; 5, ethyl formate; 6, ethyl acetate; 7, methyl propionate.
FIQ.4. NATURAL ISOTHERMS AT THE BOILINQ POINTS 690
ADSORPTION OF VAPORS OF CERTAIN KETONES AND ESTERS
691
For both the ketones and the ethers the order is'again reversed a t high pressures. The values of a for the ketones are not available, but they should increase with increase in molecular complexity. The relations obtained from the study of the natural boiling point isotherms appear to permit two definite conclusions: first, for all vapors of any one class the magnitude of the adsorption is directly dependent upon the van der Waals constant a ; second, the magnitude of adsorption is independent of the dipole strength of the vapor molecules, or their influence is masked by other factors. The isosteres were plotted for the ketone and ester vapors. With the exception of the lowest concentration, the experimental points fall exceedingly well upon straight parallel lines. The heats of adsorption calculated from the slopes of the isosteres are given in table 9. SUMM A R Y
The adsorption of certain ketone and ester vapors by activated charcoal has been measured a t several temperatures between 0°C. and 182°C. The Langmuir equation for adsorption on plane surfaces applies for pressures up to approximately 200 mni. For any series the amount of vapor adsorbed a t low pressures is always greatest for the vapor having the highest boiling point; it is less for the simpler low-boiling liquids. At higher pressure's the order of adsorption is reversed. Adsorption increases with increase in the value of the van der Waals a, and it appears to be independent of the dipole strength of the vapor molecules. The heats of adsorption have been calculated from the slopes of the isosteres. REFERENCES (1) DEBYE:Polar Molecules. The Chemical Catalog Co., New York (1929). (2) EUCKEN AND MEYER:Physik. Z. 30, 397 (1929). (3) LOVELESS:Ind. Eng. Chem. 18, 826 (1926). (4) PEARCE AND EVERSOLE: J. Phys. Chem. 38, 383 (1934). (5) PEARCE AND TAYLOR: J. Phys. Chem. 36, 1091 (1931). (6) PETERS, PAUL E.: Master's Thesis, University of Iowa, 1930.
