Retention of Glycerol and Glycols by Cellophane and Cotton Cellulose RICHARD S. SHUTTAND EDWARD MACK,JR., Chemical Laboratories, Ohio State University, Columbus, Ohio 30 minutes in an oven a t 130”C. ELLOPHANE, prepared The manner in which glycerol and seceral instead of at “incipient boiling in s h e e t f o r m b y reglycols are retained when imbibed by Cellophane for 30 minutes.” This change generation of c e l l u l o s e and natural cellulose is investigated f r o m three gave check results. The two f r o m v i s c o s e (It?), b e c o m e s angles. 25-cc. p o r t i o n s of the extract rather brittle and fragile when i t The glycerol and glycols are held by adsorpwere i n t r o d u c e d into 400-cc. is air-dried. To give it the debeakers containing exactly 25 cc. sired physical properties, it has tion; and, on the assumption that the adsorbed of potassium dichromate solution been found necessary to let the layer is one molecule deep, the surface-covering (12 grams per liter) and about Cellophane imbibe a considerpower of the adsorbate molecules agrees in a 15 cc. of concentrated sulfuric able amount (10 to 20 per cent) satisfactory quantitative fashion with the sugacid. The beakers were covered of glycerol, ethylene glycol, or gestion that the adsorption occurs on the ends of with watch glasses, and, after some other glycol. These imheating in an electric oven for bibed addition agents are called the cellulose micelles. O n this basis the micelles 30 minutes a t 130” C., they were “softeners,” b e c a u s e in effect of cotton cellulose seem to be about three times as r e m o v e d ; 200 cc. of distilled they soften the brittie Cellophane long as those of the regenerated cellulose in Cetlowater were added and the soluand make it more plastic as well phane. tions allowed to cool in a pan of as more resistant to mechanical The order in which the glycerol and glycols ice water. Ten cubic centimestress. ters of 30 per cent p o t a s s i u m The manner in which the glycare adsorbed in the vapor phase is the same as the iodide solution were added, and erol and glycols are retained in adsorption f r o m concentrated aqueous solutions. the r e s u l t i n g s o l u t i o n w a s the Cellophane sheets was intitrated with sodium thiosulfate v e s t i g a t e d by three different solution (0.2 normal) until the color became appreciably lighter. procedures. - In general it was not possible to measure the amount of One cubic centimeter of starch indicator was added,and the adsorption in terms of the increase or decrease in weight of titration continued to the end point, which was a change from the adsorbent because of the complication introduced by blue green to green. The sodium thiosulfate was checked from the simultaneous adsorption or desorption of water. The day to day against the potassium dichromate solution. amounts of adsorption were determined by chemical analysis. Calculation: The general results indicate that glycerol and glycols, a t least B = NazSz03required by blank, cc. in part, are held in the Cellophane and cotton cellulose bodies A = Naz&03required by sample, cc. by adsorption; for convenience the process nil1 be referred N = normality of Na2S2O3 Mol. wt. of glycerol = 92.06 to as one of adsorption. The general method employed and 4Hz0 C3H5(OH)3 7(0) 3coz the conclusions reached would probably apply, in a broad 92.06/14 = 6.576 (factor) sense, to any form of regenerated cellulose and to the various ( B - A ) 0.006576 X N X 20 X 100 = % glycerol forms of native cellulose; Cellophane and cotton cellulose, weight dry cellulose sample respectively, have merely been chosen here as convenient specimens with which to work. The water content of the cellulose samples was variable The softeners which were used in these experiments are: and was not considered in the calculations. Calculations for the glycols were made in a corresponding Glycerol CHzOHCHOHCHzOH Ethylene glycol CHzOHCHzOH manner, although it was necessary to determine experimenTrimethylene glycol CHzOHCHzCHzOH tally the amounts of potassium dichromate and concentrated Diethylene glycol CH~OHCHzOCHzCHzOII Triethylene glycol CHzOHCHzOCHzCH~OCHzCHzOH sulfuric acid, and the temperature of the oven and duration of heating, required to give 100 per cent analyses for the ANALYTICAL METHODS glycols. Details are given in Table I. Two or three grams of the Cellophane (or cotton cellulose) samples to be analyzed for glycerol were cut into strips (or TABLEI. FACTORS IS ANALYSESOF GLYCOLS macerated), placed in a large Erlenmeyer flask, and extracted TriD1Trifor 30 minutes by shaking with exactly 500 cc. of distilled Glycol Ethylene methylene ethylene ethylene Cone HzSOd, cc. 15 50 50 50 water. Two 25-cc. portions of this solution were removed KgCrOO-, cc 25 25 25 25 Oven t e m p , C 150 160 160 160 with a pipet for duplicate analysis. The extracted CelloTime in oven, hours 0 5 1 1 1 97 43 97 63 98 60 phane (or cotton cellulose) was then collected in a Gooch 1: ; 97 43 97 70 98 60 crucible or a Buchner funnel, thoroughly washed with 200 -4na1ysis’ % 196 17 97 53 98 05 99 41 cc. of distilled water in five portions, dried in a n electric oven In all cases in Table I, 25 cc. of the aqueous solution of the for 2 hours a t 105” C., cooled in a calcium chloride desiccator, and weighed to determine the amount of dry cellulose in the glycol were analyzed. In the last three glycols if the sample was sufficiently concentrated to require 50 cc. of potassium original sample. The extract was analyzed for glycerol according to the dichromate, then the concentration of the sulfuric acid had Du Pont method ( d ) , which is a modification of Hehner’s to be increased to 7 5 cc. to keep its volume equal to that method ( 7 ) , with the exception that a more even heating of of the water present. Dilution with about 100 cc. of water the sample previous to titration was obtained by heating for for each 10 cc. of concentrated sulfuric acid was necessary to
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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give a sharp end point with starch indicator. The above analyses are considered as 100 per cent. The difference is probably due to water present, as all these glycols are hygroscopic.
PROCEDURE 1 Strips of Cellophane, already impregnated with glycerol, were placed in a suitable glass container in a DeKhotinsky electric oven. A stream of air, dried in a calcium chloride train and brought up to oven temperature in a copper tube preheater located in the oven, was passed over the Cellophane a t a rate of 10 liters per minute as measured by a calibrated flowmeter. Runs were made simultaneously with separate drying trains and the Cellophane samples were removed a t various time intervals and analyzed for glycerol content. TABLE 11. GLYCEROL CONTEXT OF CELLOPHANES AFTER OVEX TREATMENT CELLOPH.4NE
ORIQINAL
AFTER 1 DAY
AFTER 2 DAYS
AFTER 5 DAYS
AFTER 14 D A Y S
%
%
%
%
%
15.68 15.75 14.30 16.41 14.87 15.22 13.60 13.71
13.02 13.22 12.96 13.03 12.43 12.62 12.66 12.79
13.47 12'93 12.98 12.70 12.87 12.84 13.16
11.44 11.84 11.25 11.30 11.05 11.15 10.85 10.90
12.71 13.00 11.01 11.68 12.03 12.27 11.41 12.11
11.22 11.53 10.70 10.94 10.68 11.08 10.77 10.85
T E M P E R A T C R E . 60'
600/20
25.55 26.24 59.85 54.73 25.61 25.85 16.25 16.37
300/40 300/21 350/14
21.35 21.05 24.31 36.11 19.43 19.96 14.78 14.83
C.
15.54 17.41 23.69 28.06 16.16 16.49 14.29 14.39
T E M P E R A T U R E , 76'
600/20
25.55 26.24 59.85 54.73 25.61 25.85 16.25 16.37
300/40 300/21 350/14
16.71 16.85 16.86 17.11 15.67 16.13 14.21 14.88
C.
15.78 16.09 14.44 15.04 14.91 15.13 13.15 13.37
T E M P E R A T U R E 88'
600/20
25.55 26.24 59.85 54.73 25.61 25.85 16.25 16.37
300/40 300/21 350/14
13.64 14.10 14.27 14.85 13.70 14.25 13.16 13.41
C.
13.64 13.34 13.08 13.24 12.07 12.82 12.80 13.07
In the case of ethylene, trimethylene, diethylene, and triethylene glycols, glycerol-free Cellophane was impregnated by allowing it to absorb the glycols to the desired extent from aqueous solutions. These samples of Cellophane were dried on wire frames by exposure to the atmosphere of the room and were then treated with dry air in the oven as in the case of glycerol. I
i
i
i
I
I
b
/i
,1,
/k!
1
I
I
k
'
-0
K 3 10 8
4;
1
e! z/ 27 Days in Oven at 88'C Air 10 Litem p e r m i n u t e
FIGURE1. EFFECTOF TIMEOF EXPOSURE TO DRYAIR ON RETENTION OF GLYCEROL AND GLYCOLS
Such treatment was carried on a t several temperatures and the results are listed in Tables I1 and 111. Experiments were also conducted with absorbent cotton (Johnson-Johnson product) and with wood pulp. The loss of glycerol or the glycols by Cellophane a t room temperature proceeds so slowly
Vol. 25, No. 6
TABLE 111. GLYCEROL AND GLYCOL CONTENTS OF CELLOPHANE AND COTTON AFTER OVENTREATMENT BASIC
SCESTAKCE
(At 88' C.) AFTER ORIGIXAL 1 DAY
%
2DAY0
AFTER
AFTER 5DAYS
%
%
%
%
AFTER 14 DAYS
GLYCEROL
Cellophane, 300/17.5
21.50 22.10
13.57 13.69
12.10 12.71
11.10 11.08
11.42 11.51
Cellophane, 300/25
30.22 30.74
13.22 13.35
12.93 13.54
11.84 12.05
11.56 11.66
Cellophane, 250/12
14.67 14.91
11.67 11.94
11.86 11.78
11.08 11.32
10.79 10.81
Cellophane, 350/12.7
14.56
..
12.02 12.36
11.61 11.80
11.21 11.31
9.44 10.02
Cellophane, 256
15.37 15.43
12.29 12.35
11.64 11.66
10.70 10.82
9.93 10.15
Cellophane, 160
16.84 16.86
12.13 12.59
10.95 11.75
10.61 10.68
10.39 10.67
Cellophane, 350/11.6
13.20
11.43 11.62
10.66 11.03
10.39 10.80
9.97 10.06
..
Cotton
100.5 111.4
5.44 5.55
4.81 4.93
4.58 4.72
4.12 4.22
Cotton
145.9 170.8
5.42 5.62
5.01 5.06
4.51 4.56
4.32 4.44
5.88 9.10
5.23 5.62
5.13 5.42
4.82 4.88
6.89 7.11 2.09 2.10
6.39 6.55 1.84 1.97
4.76 5.65 1.75 1.85
Wood pulp
14.28 15.43
Cellophane
10.72 16.00 11.83 11.98
ETHYLENEGLYCOL
Cotton
7.88 8.01 2.30 2.30
T R I M E T H Y L E N E GLYCOL
Cellophane
10.76 30.88
8.25 8.62
8.37 8.52
7.71 7.79
7.82 7.81
Cotton
13.30 15.27
3.20 3.19
2.92 2.95
2.83 2.93
2.64 2.68
Cellophane
28.36 28.97
9.07 9.18
8.44 8.62
7.82 7.97
7.57 7.63
Cotton
20.48 21.04
3.28 3.46
3.14 3.18
2.68 2.85
2.54 2.63
D I E T H Y L E N E GLYCOL
T R I E T H Y L E N E GLYCOL
Cellophane
10.42 11.36
9.20 9.29
9.27 9.32
8.45 8.59
8.48 8.59
Cotton
23.38 26.59
3.66 3.79
3.54 3.66
3.28 3.29
3.16 3.17
that it would have been out of the question to carry out the tests a t ordinary temperatures. For instance, the loss of glycerol by Cellophane a t room temperature is almost negligible over a period of months. In the first column of Tables I1 and I11 the numerator, or gage, represents the weight in grams of one square meter of Cellophane multiplied by 10; the denominator, or percentage, is the Du Pont standard glycerol content calculated on the basis of glycerol plus cellulose in Cellophane. Every datum number is the average of two analyses for one sample, given as percentage glycerol in water-free and glycerol-free cellulose. I n Tables I1 and I11 the glycerol and glycol contents drop off rapidly during the first part of the aeration treatment and finally after about 14 days reach a practically constant value for a given sample. Since such a treatment a t temperatures of 60", 75", and 88" C. causes a perceptible volume shrinkage of the Cellophane and cellulose, it might be supposed that the final constant values represent glycerol and glycol entrapped and held mechanically by the shrunken fibers of the cellulose body. To determine whether this was the case, several samples of Cellophane which had been treated a t 88" C. for 14 days and which had reached a constant glycerol content were resoftened or allowed to expand by exposure of the separate samples, respectively, to the saturated vapors of water, benzene, ethyl alcohol, and ethyl ether for 24 hours. The samples were again placed in the oven and treated with air as before for 14 days. Results are given in Table IV.
June, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEIV. GLYCEROL COXTENTOF GLYCEROL CELLOPHANE 300/21 AFTER RESOFTESINQ AFTER14 AFTER RESOFTENINQ AND S U B S E Q ~ E N T D a m IN OVEN O V E N TREATMEVT Ethyl Ethyl Water Benzene alcohol ether 25.61 10.38 9.47 10.29 9.84 10.24 25.85 10.84 10.56 10.37 10.08 10.29
ORIGI-
TABLEV. CELLOPHANE ADSORPTIONSFROM AQCEOUS SOLUTIONS -ETHYLESE
NAL
The results shorn that the glycerol content was not appreciably lowered by the second period of aeration, even when the cellulose structure had been loosened by the various vapors. The results therefore seem to indicate that the glycerol molecules are adsorbed by the cellulose, or that they are bound in a close association uniformly throughout the cellulose body, and that their escape is not prevented by a mere shrinkage and hardening closure of the surface.
PROCEDURE 2 Weighed sheets of glycerol-free Cellophane were suspended in a wire basket over a dish of pure glycerol placed in a closed brass box kept in an oven a t 88" C. At various time intervals two sheets were removed, reweighed, and analyzed for glycerol. While the amounts of glycerol taken up by different samples of Cellophane in the early stages of this adsorption were not reproducible, the final values obtained in the latter stages, when equilibrium had evidently been nearly reached, were in agreement for the different samples. The equilibrium glycerol content for 300-gage Cellophane a t 88" C. was about 30 per cent. The results of a systematic study of the adsorption isotherms for glycerol and the glycols-that is, of the amounts of these substances adsorbed by Cellophane in equilibrium with the vapors a t various pressures-would have been valuable. But it was not feasible to make such studies because of the relatively large amounts of water vapor present in the gas phase of the adsorbate. For example, the vapor in equilibrium with 98 per cent glycerol at 88" C. has a pressure of about 23 mm., and only 1.7 per cent by weight of the vapor is glycerol. This means that the pressure of the glycerol itself would be only about 0.07 mm. The difficulties introduced by the presence of even small amounts of water in glycerol and the glycols were so formidable that no further work along the line of procedure 2 was undertaken.
PROCEDURE 3 I n order to compare the amount of adsorption by Cellophane from aqueous solutions of glycerol and glycol with the adsorption in the vapor phase, sheets of glycerol-free cellophane were immersed in solutions of various concentrations. The experiments were carried out in large dishes covered with glass plates to prevent appreciable evaporation of water. The Cellophane sheets were covered with wire gauze to keep them below the surface, and the solution was kept thoroughly mixed with motor-driven stirrers. After 24 hours of stirring, the Cellophane sheets and aliquot portions of the solution were removed and analyzed for glycerol or glycol. To remove excess solution adhering to the Cellophane, the sheets were pressed between the rollers of a wringer. Equilibrium between the solution and Cellophane was reached before about 5 hours. Brass and Frei (1) state that equilibrium is reached between cellulose, or cotton, and solutions of aliphatic acids in 1 to 2 hours. The data indicating the various solution concentrations and the equilibrium amounts adsorbed by the Cellophane are given in Table V. Every number is the average of two analyses for one sample; x / m is the percentage (glycerol/ cellulose) calculated for Cellophane free of water and of glycerol and glycol.
689
Molarity 4.16
GLYCOLMillimoles gram % x/m cellulose 27.4 4.41 27.7 4.46
--TRIMETHI-LENE
Molarity 4.17
GLYCOL.lfillimoZes pram % x/m cellulose 31.9 4.20 41.5 4.14
3.15
23.2 23.4
3.74 3.77
2.07
2.08
17.1 18.2
2.76 2.94
1.06
1.04
9.51 10.3
1.53 1.66
0.526
5.81 6.43
0.764 0.845
0.556
4.95 5.36
0.798 0.864
0.263
3.09 3.43
0.406 0.451
0.269
2.16 2.83
0.348 0.455
0.131
1.52 1.52
0.199 0,200
0.137
1.39 1.39
0.223 0.223
0.071
0.81 0.83
0.107 0.109
0.069 0.71 1.06 -GLYCEROL 4.23 42.8 43.3
0.114 0.17
4.64 4.70
17.6 18.2
2.31 2.39
10.5
1.38 1.51
11.5
0,037 0.47 0.061 0.54 0.071 -DIETHYLENE GLYCOL4.01 40.1 3.78 40.4 3.80
3.14
33.1 34.0
3.59 3.69
3.27
33.0 33.1
3.11 3.12
2.07
23.1 23.1
2.51 2.51
2.18
22.9 23.5
2.16 2.22
1.06
12.8 13.6
1.39 1.48
1.09
13.1 13.3
1.23 1.25
0.529
7.60 8.00
0.82 0.86
0.545
6.57 7.30
0.619 0.688
0,267
3.98 4.51
0.433 0.489
0.256
2.93 3.00
0.278 0.282
0.127
2.02 2.11
0.219 0.229
0.143
1.61 2.01
0.151 0.190
0.071
1.11 1.13
0.122 0.120
0.070
0.98 1.02
0.092 0.096
EFFECT O F AIR
TRE.4TMENT
When Cellophane with a considerable content of glycerol (about 20 per cent) is exposed to a stream of dry air (as in procedure l), part of the glycerol is removed, as shown by results in Tables I1 and 111. The glycerol which is retained by the Cellophane can hardly be considered in equilibrium with the vapor phase, since the air which is circulated is itself practically free of glycerol vapor. Probably. all of the glycerol, or glycols, would be removed if the air were passed for a long period of time. The results of procedure 1 clearly demonstrate that a certain portion of the glycerol (or glycols) is held by the Cellophane very loosely and (at the temperatures employed) is easily and quickly removed, but that a certain portion is also held in the Cellophane body quite tenaciously. KO doubt the glycerol and glycols are held in Cellophane with various degrees of tenacity corresponding to a free, capillary, and adsorbed state. The final values after 14 days of exposure listed in Tables I1 and I11 and indicated graphically in Figure 1, show that the tightly held quantities are for glycerol and a few glycols in Cellophane.
EFFECT OF THICKKESS OF CELLOPHAKE FILM The fact that the final value for glycerol content a t the end of 14 days, as well as the value after 1 day, is independent of the thickness of the Cellophane film (160 to 600 gage) shows that the glycerol which is retained is not held because of viscous resistance to its escape. Rather it is held uniformly throughout the body regardless of the distance to the outside surface. This view is also confirmed by the results listed in Table IV, and the remarks previously made in con-
690
INDUSTRIAL AND ENGINEERING
nection with the resoftening of the Cellophane by vapors of water, benzene, ethyl alcohol, and ethyl ether.
CHEMlSTRY
Vol. 25, No. 6
by the surface. We would expect that a larger number of the smaller glycerol molecules could be packed into a given area of active surface than the much larger triethylene glycol EFFECT OF MOLECULAR STRUCTURES molecules, as indeed is the case (column 3, Table VI). It seems hardly likely that the molecules of glycerol (and The tenacity with which the various molecules are held on glycols), which are taken up by the cotton cellulose and Cello- the cellulose surface a t a given temperature (88" C.) might phane bodies, combine chemically with the cellulose mole- also be expected to play a role in determining the covering cules; if this were true, one would expect stoichiometric power. For example, we would expect that glycerol with relationships among the quantities of the glycerol and glycols the lowest vapor pressure would be held more tenaciously held by the cotton and Cellophane, and such relationships than ethylene glycol with the highest. The lack of suitable data, either vapor pressures or heats of adsorption, makes impossible any quantitative predictions from this point of view. =/AI/A rough semi-quantitative treatment may be given the surface-covering power of the absorbed glycerol and glycol molecules in terms of the recent deductions regarding the structure of cellulose itself (2, 3, 6-9, 12-14). These deductions, based on x-ray examination of native cellulose, are summarized graphically in Figure 2, which is taken from a recent paper by Clark ( 2 ) . The bricklike units are colloidal micelles which are piled together in such a way that they lie FIGURE2. COMPLETE MODELOF CELLULOSESTRUCTURE AS parallel to the long fiber axis of the native cellulose threads. DEDUCED FROM X-RAYDATA,SHOWING A NUMBER OF CELLU- The micelle is about 50 A. wide and deep, and has a length LOSE MICELLES, THE INTERIORONE OF WHICH Is IN PART varying from about 500 to about 150 A., depending upon the EXPOSED AND ENLARGED TO SHOWTHE CHAINSOF GLUCOSE nature of the natural cellulose. An individual micelle is RESIDUEUNITS made up of long chains of C6HI0O5residues joined together a , primary valence forces b , secondar association forces e, tertiary micellar forces (diagram g y Seifriz) end to end by the strong primary valence forces of oxygen atoms. Such a micelle contains from 3000 to 6000 glucose are not found. This conclusion is made more obvious by residues. The native cellulose molecules are held together the treatment of the data (in Table 111)to be given in Tables laterally within the micelle by secondary valence forces (van VI and VII. I n column 3 of Table VI the final 14-day values der Waals forces). The micelles are supposed to be held are expressed as moles per mole of cellulose. together by somewhat weaker forces, which might be called '[tertiary" forces. It seems likely that adsorption occurs TABLEVI. CONSTANT ADSORPTION VALUESOF GLYCEROL AND on the surfaces of these micelles. GLYCOLS B Y COTTON CELLULOSB Furthermore, it is not improbable that the ends of the TOTAL micelles exert stronger adhesive forces than the sides of the AREA COVERED micelles. Certainly the ends of the micelles correspond to B Y ADMOLES AREACOVERED SORBED terminal oxygen-bearing groups of the long threadlike celluPER PER MOL. MOL.PER lose molecules, and such a surface coated with oxygen-bearing MOLE BOILFrom GRAM CELLU- :NO MOL. mol. From CELLUgroups would be expected to exert a rather strong field of GLYCOL z/m LOSE POINT VOL. vol. model LOSE~ unbalanced adhesive forceo On the other hand, the oxygenc. sq. A . sq. A . % 0 . 0 7 6 290 73.05 24.4 29 GI cero1 4.3 0.68 bearing groups in the cellulose molecule lying in the side 55.7 22.5 0.50 Et1 ylene 197 1 . 8 0.068 20 surfaces of the micelle would be expected, as is usual with 72.4 214 Trimethylene 2 . 6 6 0.055 2 4 . 3 27 0.48 94.7 36 Diethylene 0.039 0.42 2.6 29 245 highly polar groups, not to occupy positions in the surface but 142.6 49 Triethvlene 0 . 0 3 4 276 3.2 38 0.49 to turn themselves inward by a rotational twisting of the a Times 106 sq. om. (from column 6) cellulose molecule chain, so that the surface energy would be The whole behavior of that portion of the glycerol and a minimum. As a matter of fact, this rotation of the glycols retained most tenaciously by the cellulose after the oxygen group into and out of the micelle surface has been removal of the more loosely held portions suggests strongly postulated by Urquhart (15) as the mechanism which is that these materials are in reality adsorbed. Unfortunately operative in the well-known hysteresis effect which has been this view must go unsupported, for the present, by adsorption observed when water vapor is adsorbed by cotton, although isotherm data, for reasons already stated. But such a view the work of Grace and Maass must be considered in this conoffers the most consistent explanation of the experimental nection (5). In cotton fibers (assuming micelles of dimensions 300 X results. cc., The values in column 3 fall off. Glycerol a t the top of this 50 x 50 A.), the volume of a micelle is about 0.75 X list is most strongly and triethylene glycol a t the bottom the number of micelles per cubic centimeter of fiber is about and the number of micelles per gram of cotton least strongly adsorbed. We may suppose that all of these 1.35 x Since adsorbed molecules are fastened by their hydroxyl groups or fiber (density about 1.5) is approximately 0.9 X oxygen atoms to the cellulose surfaces. We may also sup- the two end surfaces of such a single micelle have a combined pose that certain regions of the cellulose surfaces possess area of about 5 X 10-13 sq. cm., the total micellar end area or 0.45 X lo6 stronger powers of adsorption than other regions. The per gram would be 0.9 X 10l8 X 5 X number of molecules of glycerol and the various glycols which sq. cm. It is interesting to note that this is about the surface can occupy these highly active cellulose spots will be depend- area which could be covered by the glycerol and glycol moleent to some extent upon the sizes of the adsorbed molecules, cules adsorbed by one gram of native cellulose (cotton), if as well as upon the extent to which the exposed surface of we suppose that these adsorbed molecules are held in a layer cellulose can be covered by adsorbate molecules. This one molecule deep, as shown by the values given in column 8, would undoubtedly be a function of the geometrical arrange- Table VI. In Cellophane the micelles are probably arranged ment of adsorbing spots on the cellulose surface as well as in a chaotic (brush heap) manner; that is, the micelles are of the geometry of the glycerol and glycol molecules retained not joined together end to end, Such an arrangement would
probably favor a full and effective exposure of the micellar end surfaces to invasion and occupation by the glycerol and glycol molecules. Table VI1 gives similar data for Cellophane. TABLEVII. ADSORPTION OF GLYCEROL AND GLYCOLS B Y REQENERATED CELLULOSE SHEETS (CELLOPHANE) TOTAL AREA COVERED BY
ADAREACOVERED SORBED PER PER MOL. MOL. PER MOLE From GRAM CELLP-BOILIXQMOL. mol. From CELLUz / m L 0 0 E POINT vOL. Vol. model LOSEn MOLES
GLYCOL
691
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1933
%
c.
73.05 290 11.3 0 . 2 Glycerol 55.7 197 Ethylene 5 . 0 0.19 214 72.4 Trimethylene 1 7 . 8 0 . 1 6 8 0 0 . 1 2 245 94.7 Dlethylene 8 . 5 0.09 276 142.6 Triethylene a Times 106 sq. cm. (from column 6).
24.4 20 24.3 29 38
29 22.5 27 36 49
1.8 1.4 1.4 1.3 1.3
The values for the total area covered by the adsorbed molecules, in column 8, are about three times as large as the corresponding values in the case of cotton cellulose given in Table VI. We can therefore deduce, still assuming that these molecules are disposed one layer deep and are all on the ends of micelles, that there is about three times the end area surface in the case of tJheregenerated cellulose of the Cellophane as there is with cotton. Consequently it must follow that the length of the regenerated celluloee micelle is only about one-third the length of the cotton micelle. This is one of the most interesting conclusions to be drawn from these experiments. No doubt the natural cellulose micelle is reduced in length by the chemical treatment to which it is subjected in the manufacture of Cellophane, and the degree of degradation probably depends on the severity of the chemical treatment. To obtain the covering power, or the area occupied by a molecule in the adsorbed film, the molecular volume (column 5 ) was divided by the Avogadro number, and the resulting volume of an individual molecule was raised to the "3 power to obtain approxiniately the average cross-sectional area of a molecule. The values for the glycerol and glycol molecules obtained in this way are listed in column 6 . In the second method, models of the glycerol a n t glycol molecules were made to scale, 1 crn. representing 1 A., using atom balls with the interatomic center distances as follows: C-C 1.54, C-H 1.08, C--0 1.25, 0-H 1.0, and a hydrogen atom domain radius of 1.3 (11). These models were then placed flat on a table surface with the oxygen-bearing groups as near the surface as possible, and the covering power in square $entimeters measured. The corresponding values in square Angstrom units are listed for the glycerol and glycol molecules in column 7 . The agreement between the two estimates (columns G and 7 ) is reasonably good. The areas occupied (column G ) were multiplied by the actual number of molecules adsorbed per gram of cellulose, and the resulting values which represent the total surface occupied in the adsorbed film are given in column 8, Tables VI and VII. It seems likely that the glycerol, or glycols, adsorbed in this manner on the surfaces of the micelles, and more especially the glycerol, or glycols, retained in the Cellophane body in a capillary state and in a free condition, could easily soften and plasticize the Cellophane and effectively rid it of its tendencies toward brittleness and friability. Table V presents the data for the adsorption by Cellophane of glycerol and glycols from aqueous solutions of various concentrations (procedure 3). The amount of adsorption is calculated both as percentage and as millimoles per gram of cellulose. Figure 3 shows the data graphically.
When Cellophane containing even a large amount of glycerol is washed continuously with a stream of water, the glycerol is rapidly and practically completely removed in the course of a few hours. This behavior is quite different from that observed when air is passed over Cellophane. If we assume that water has the power of penetrating into the body of the nonmoisture-proofed Cellophane, as it certainly has, the glycerol adsorbed as has been suggested on the end surfaces of the micelles will probably not be held so tenaciously as in the absence of water. The solubility of glycerol in water is far greater than its solubility in air, and, in the competition for glycerol between the micelle surface and the water, the water will certainly obtain a considerable share of the glycerol. If the water within the Cellophane is constantly renewed by diffusion, it will not take long to remove the major portion of the adsorbed glycerol. The effect which the water also undoubtedly exerts in enlarging and opening the structure of the Cellophane, will also increase considerably the rate a t which glycerol and the glycols can be transported into and out of the Cellophane. Experiments showed that it required only several hours to establish adsorption equilibrium in the case of the glycerol and glycol solutions listed in Table V. The curves of Figure 3 seem to be true adsorption isotherms, although the curves have not flattened I
IO
I
I
PO
30
,
40 425
E n o l M o l a r i t y of S o l u t i o n
FIGURE3. ADSORPTIONOF GLYCEROL AND GLYCOLSFROM AQUEOUSSOLUTIONS
appreciably a t the higher concentrations. S o doubt a flattening would occur in more concentrated solution, but the rapidly increasing viscosity presents experimental difficulties. Figure 3 indicates the amount of adsorption in terms of per cent. If the data are expressed as moles of adsorbate per gram of cellulose, the order of adsorption of glycerol and the glycols from a 4-molar solution is the same as with the air treatment of procedure 1. At somewhat small concentrations, however, the order of the glycerol and ethylene glycol is reversed. S o eatisfactory explanation of this reversal has suggested itself.
ACXXOWLEDGMENT The authors wish to express their grateful appreciation to W. H. Charch, of the Du Pont Cellophane Company, both for material assistance and for helpful advice and suggestions during the course of this study.
LITERATURE CITED Brass and Frei, Kolloid-Z., 45, 244 (1928). Clark, G. L., IXD. ENC.CHEW,22, 4 7 4 (1930). Clark, Farr. and Pickett, Science, 71, 293 (1930). Du Pont Cellophane Co., "Glycerol and Moisture in Cellophane," method 2276. Grace and Maass, J . Phys. Chem., 36, 3046 (1932). Hegstenburg and Mark, 2. Krist.,69, 271 (1928). Hehner, J . SOC.Chem. Ind., 8, 6 (18891.
I N D U ST R I A L A N D E N G I N E E R I N G CH E MI ST R Y
692
(8) Heraog, J. Phys. Chem., 30, 457 (1926). (9) Hess, “Die Chemie der Zellulose und ihrer Begleiter,” p. 647, Akademischen Verlagsgesellsohaft, Leipzig, 1928. (10) Hyden, IND.ENQ.CHEM.,21, 405 (1929). 54, 2141 (1932). (11)’ Mack, J. Am. Chem. SOC., (12) Mark, Scientia, 51, 405 (1932).
Vol. 23, No. 6
(13)
Mark and Meyer, Ber., 61, 593 (1928); 2. phvsik. Chem., B2,
(14) (15)
Sponsler, Plant Physiol., 4, 32.9 (1929). Urquhart, J. Textile Inst., 20, 125 (1929).
115 (1929).
RECEIVED November 28, 1932.
Equilibrium Conditions in Continuous Recycle System R. BARLOW SMITH, Sinclair Refining Company, East Chicago, Ind.
ORIGINAL
LIQUID CONDENSATE FROM COMPRESSOR
GAS
HYDROCARBONS-Mu METHANE 39.8064 ETHANE 19.8211 PROPANE 11.SOOO BUTANE IP.0110 PENTANE 8.3200 HEXANE 2.2805 T O T A L 100.0000
hYOROCARBONS-MOLS
,,
WETHANE
,0064
ETHANE
.02II
PROPANE BUTANE PENTANE HEXANE TOTAL
,0800 I420
.moo
,3005 l.0000
n =
G A S LEAV NG
RESIOUE GAS
the recycle part. The composition and quantity of liquid and gas that will result from compression can be calculated from the following well-known equi-
CCYPRESSOR -0TAL
GAS
ABSCRBER I,
HYDROCAR ON)
MOL5
HYDROCARBONS METHANE ETHANE PROPANE
MAS 39.6000 19.8000 17.8?00
RECYCLE SA5 hYDRCCARBJ\S
YOLS
\I
Where 2 n = N
XO
