NOTES
1604
T H E DETERMINATION OF SOLUBILITY CONSTANTS FOR GASES I N POLYMERS BY A. S. MICHAELS AND R. B. PARKER, JR. Department o,t Chemical Engineering, Massachusette Innlitute of Technology, Cambridge, Massachusetts Received August 1 , 1968
The study of gas-polymer sorption equilibria is of interest since valuable information can be gained regarding transport processes in high polymer materials, polymer structure, and the interactions bettween gas molecules and polymer chains. The direct determination of solubility constants for the lighter gases in polymers is made difficult by the fact that the amount of gas taken up by the polymer at ordinary pressures is extremely small. Solubility constants for gases in rubber have been determined by dynamic However, it is often desirable to have an accurate, independent method of measuring the solubility coefficient directly. Venable and Fuwa4 and van Amerongen6 have made direct determinations of the solubility constants for gases in rubber. In both instances, the determination qf a rather small gas volume difference is involved, particularly for the very slightly sorbable gases. A novel method, giving very satisfactory results, has been developed by the authors and employed to determine the solubility constants for gases in polyethylene, where the values were found to be as little as one-fifth as much as for the same gas in rubber. The problem is thus somewhat more difficult with gases in polyethylene than in rubber. Results have indicated that this method should be applicable t o the study of sorption equilibria for any gas-solid system where the rate of diffusion of the gas in the solid is sufficiently low. Experimental Solubility determinations were carried out in a glass vacuum system. A weighed quantity (about 150 9.) of the polyethylene in pellet form was placed in a sample bulb which was attached to the system by a ground glass joint. The sample was allowed to come to equilibrium with the test gas a t a known pressure, atmospheric pressure being used in the runs cited here. After equilibrium (usually about 12 hours), the system was exhausted rapidly by way of a large-bore stopcock. Using a 600 r.p.m. Megavac pump, a pressure of less than 0.05 mm. of mercury easily could be attained in a one-minute pumping interval, as determined with a thermocouple gage. After a pumping interval of about one minute, the system consisting of the sample bulb and associated tubing was sealed and allowed to come to final pressure equilibrium (usually about 12 hours). The final pressure was read on a precision mercury manometer equipped with a Vernier scale. By keeping the free gas space in the system small (approximately 200 cc.), i t was found possible to attain a final pressure of from 10 to 15 mm. of mercury for nitrogen, and from 15 to 25 mm. of mercury for oxygen depending on the olyethylene studied. The solubility constant, k (cc. at S.F.P. per cc. polymer per atmosphere), was obtained from the expression
k[?]
[TI [TI+ [Y]
-k P2VB
=
P,V,
k
where W is the weight (grams) of polymer used, p its density (g./cc.), PI the pressure (atm.) a t the initial equilibration, (1) R. M. Barrer, Trans. Faraday Soc., 36, 628 (1939). (2) G. J. van Amerongen, J . Polvmer Sci., 6, 307 (1950). (3) A. 8. Carpenter, Trans. Faraday Soc., 43, 529, 822 (1947). (4) C. 8. Venable and T.Fuwa, J . Ind. Eng. Cham., 14, 139 (1922). ( 5 ) G. J. van Amerongen, J . A p p . Phys., 17, 972 11946).
Vol. 62
PZ the pressure s;fter one minute of pumping, and Pa the final pressure. I' is the gas temperature (OK.) in the system and V. the gas space volume (cc.). Usually the second terms on both the left and right sides of the equation are small in magnitude, and neglecting them would cause an error of about 1%.
Results Table I summarizes some results for a linear polyethylene (Grex Olefin Polymer, W. R. Grace and Co., Polymer Chemicals Division) and two low density branched polyethylenes. It is seen that the solubility constants are indeed small, being several times less than for the same gases in rubber. The results obtained are believed accurate to within 3% for the low density polyethylenes, and 5% for the linear polyethylene. The accuracy should be subject to considerable improvement through the use of a more sensitive measuring device for reading thd final equilibrium pressure. Apart from the accidental reading errors associated with the manometer, the accuracy of the method is well within 1%. Since values for the diffusion constants were available from other studies, it was possible to estimate the extent of the gas loss from the polymer during the one-minute pumping interval, and apply this as a correction t o the first term in the equation. For oxygen and nitrogen in the polyethylenes cited, the magnitude of the correction is less than 10% of the sorbed gas originally present. Since the amount lost can be estimated to within lo%, no serious error in the determination arises from this source. TABLE I SOLUBILITY CONSTANTS IN cc. STP/cc. X ATM.AT 25' Polyethylene
Alathon 14 Alathon 34 Grex olefin polymer
0 2
NP
0.040 f O . O O 1 .033 zk .001 022 f . O O l 0.012 f 0.0006
:
Conclusions Results obtained with the described method of determining sorption equilibria have led to the conclusion that a useful tool is at hand for studying any gas-solid system where the solubility constant and the diffusion constant for the gas in the solid are small. Through further refinement of the measurement of the final equilibrium pressure, it should be possible to attain accuracies of better than 1% in this manner. ALTERATION I N SURFACE AREA OF CARBONIZED COALS ON OXIDATION BY N. C. GANGULI, K. A. KINIAND A. LAHIRI Contribution from Central Fuel Research Institute, Jealgoro, Biha., India Receiued July PO, 1068
In a recent paper,' values were given of the surface area (by the BET hod using argon atmet - 183") of high rank Jharia and low rank Raniganj coals carbonized at several temperatures between 200 and 1000" i n vacuo. It was found that the BET surface area with the high rank coal de(1) s. P. Nandi, K. A. Kini and A. Lahiri, Brennstoff Chem., in press.
Dec., 1958
NOTES
creases with increase in the temperature of carbonization to a minimum in the residue obtained a t 400°, rises to a maximum in the sample obtained a t 800" and then decreases. With the low rank coal, the surface area decreases to a minimum a t about 400°, rises to a small maximum a t about 600" and then decreases to a second minimum a t about 800". The surface area of the 1000° char, however, is higher than that of the sample obtained a t 800". The peculiar behavior observed with the low rank coal suggested that it might be due to a fine structure in the carbonized samples. Recent work a t the British Coal Utilization Research Association2 has shown that the cokes obtained a t high temperatures exhibit an increase in surface area on oxidation. It was decided to investigate this phenomenon with the carbonized samples obtained from the coals mentioned above. Experimental The coals had the analyses indicated in Table I.
TABLE I ANALYSISOF COALS
Coal
Moisture,
%
Ash,
%
Carbon
Ultimate ?'.A d.a.f. Sulfur Hydro- Nitro- (orgen gen ganic)
oxygen
1605
is no general relation between reactivity (toward steam) and surface area applicable to cokes made from different coals. Walker and c o - ~ o r k e r s ~have - ~ noticed a similar increase in surface area in the oxidation of carbons and Bastick, e t aLI8 in the gasification of cokes with carbon dioxide and water. The above conclusions were based on results obtained with samples oxidized to the same percentage "burn off." It is possible the surface area a t this "burn off" does not represent the maximum value. Further work is in progress to ascertain this factor. TABLE I1 REACTIVITYA N D SURFACEAREA (BET) CHARS Temp. of carbonieation, OC.
Orig. coal 500 800 1000
Surface area B E T sq. m./g. d.a.f. Before After oxidation oxidation
The coals or chars were oxidized in a current of air until a loss in weight of about 11-15% occurred. The temperature and duration of oxidation are given in Table 11. These data incidentally give a measure of the reactivity of the fuel, the low temperature coke or char being more reactive than the corresponding coal or the high temperature carbonization product. The surface area was measured as previously.1
Results and Discussion The BET surface areas of the original and the oxidized carbonization samples are presented in Table 11. It is seen that there is a phenomenal increase in the surface area as a result of oxidation. The important features of the study are: (1) the surface area after oxidation of the carbonization products obtained with the high rank coal decreases with increase in the temperature of carbonization of the parent sample; (2) the surface area after oxidation of the carbonization products obtained with the low rank coal, on the other hand, increases with increase in the temperature of carbonization of the parent sample; (3) the explanation given in the previous paper that the high reactivity of a low temperature coke or char is due t o contributions from surface area and from the active groups is further confirmed. With the high rank coal, the surface area increases on oxidation with all the carbonized samples but the reactivity does not correspond to the increase in surface area. The low temperature char from the low rank coal which has the highest reactivity also has the lowest BET surface area. The results show that surface area by itself is not enough to explain reactivity and that other factors such as active groups also play their role. Investigations carried out a t the Fuel Research Stationa also have,shown that there ( 2 ) Brit. Coal Utilization Research Assoc. Quart. Gazette, 1957.
Original coal 400 800 1000
COKESA N D
Duration and oxidation temp..of
% loss in wt.
1.7 2.0 7.9 2.9
Jharia coal 1.8 95 hr. (250") 234.6 0 . 5 hr. (400") 221.8 4 . 5 hr. (400') 207.2 hr. (400')
10.9 10.5 12.2 15.2
19.8 19.8 1.3 0.9 11.7
Raniganj coal (i) 2.5 (i) 148 hr. (200') (ii) 178.8 (ii) 1.5hr. (300') 99.9 1 hr. (300') 275.4 0 . 5 hr. (400") 452,8 2 . 5 hr. (400")
13.8 16.2 14.6 13.4 15.4
d%)
Jharia (XIV seam) 1 . 2 15.7 88.16 5.04 1.95 0.65 4.20 Raniganj (Jambad Bowlah) 8 . 0 15.4 79.00 5.39 1.68 0.42 13.51
08%
(3) Fuel Research Board Ann Rep. London, p. 19 (1956). (4) P. L. Walker, Jr., R. J. Forcsti, Jr., and C . C . Wright, Ind. Eng. Chem., 46, 1703 (1953). (5) P. L. Walker, Jr., and C. C. Wright, ibid., 46, 1715 (1953). (6) P.L. Walker, Jr., F. Rusinko, Jr., and E. Raats, THISJOURNAL, 69,245 (1955). (7) P.L. Walker, Jr., and F. Rusinko, Jr., ibid., 89, 241 (1955). (8) M.Bastick, M. Montaah and H. Guirin, Compt. rend., 243, 1764 (1957).
FORMATION OF ETHYL ETHERATES OF DICHLOROBORANE AND DEUTERIODICHLOROBORANE BY T. ONAK,H. LANDESMAN A N D I. SHAPIRO Research Laboratory. Olin Mathieson Chemical Corporation, Pasadena, California Received Auoust 1 , 1968
A recent investigation of the diborane-boron trichloride system in the dimethyl ether of diethylene glycol ("diglyme") indicated the formation of both mono- and dichloroborane etherates.' I n studying this same system in ethyl ether we observed the preferential formation of the dichloroborane ethyl etherate. Results are based on infrared and BI1 nuclear magnetic resonance spectra which are reported here for dichloroborane etherate and deuteriodichloroborane etherate. Experimental Boron trichloride gas (obtained from Matheson Co.) was fractionated through a 30 cm. glass helices packed column; infrared analysis indicated the presence of only trace amounts of phosgene. Diborane and deuterodiborane were prepared in the conventional manner as described pre(1) H. C.
Brown and P. Tierney, J . Am. Chem. Soc., 80, 1552 11958).
.
