Conclusions
1
C
A
I
6.40
' I
5.95
I
d
5.25
b
Acknowledgment
I
4.70
The authors thank Clara McGrew for the elemental analyses.
Figure 1. NMR spectra of 6% solutions of four products in DMSO-& A.
B. C. D.
The chlorohydrination of allyltrimethylammonium chloride at 25" to 32OC. affords a mixture of MCC in nearly quantitative yield and of DCC by-product in only slight amounts. At about 45"C. and higher temperatures, from 32 to 43% of DCC is produced, which would be expected to decrease the efficiency of the over-all product in subsequent reactions. The structure and composition of the products were confirmed by N M R spectroscopy. I t was also shown that concentration of the unsaturated precursor was not critical for obtaining optimum results a t the lower temperatures of reaction. The procedure developed shows promise for use in the commercial production of cationic starches and ion exchange cellulose.
Allyltrimethylammonium chloride Lower temperature chlorohydrination product Higher temperature chlorohydrination product N-(2,3-Dichloropropyl)trimethylammonium chloride (DCC)
isomer 11. The ratio of primary to secondary hydroxyl in B is approximately 3 to 2. The spectrum of C has the same general pattern as that of product B, but the multiplet signal a t 65.25 is much stronger and clearly indicates the presence of a significant quantity of' DCC in product C. The absence of the olefinic line position in the spectra of both chlorohydrination product mixtures shows that complete reaction of allyltrimethylammo nium chloride had occurred.
literature Cited
McKelvey, J.B., Benerito, Ruth R., J . Appl. Polymer Sci. 11, 1693 (1967). Partheil, A., Ann. 268, 152 (1892). Paschall, E. F. (to Corn Products Co.), U. S. Patent 2,876,217 (March 3, 1959). Shildneck, P. R., Hathaway, R. J. (to A. E. Staley Manufacturing Co.), U. s. Patent 3,346,563 (Oct. 10, 1967). Weiss, J., Ann. 268, 143 (1892). RECEIVED for review December 19, 1968 ACCEPTED April 28, 1969 The Northern Laboratory is part of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture. Mention of firm names or commercial products does not constitute an endorsement by the U. S. Department of Agriculture.
PLASTICIZING EFFECT OF PERMEATES ON THE SELECTIVITY OF POLYMERIC MEMBRANES NORMAN
N .
L I
Corporate Research Laboratories, Esso Research and Engiwering Co., Linden, N . J . 07036
POLYMERIC membranes have long been used to separate hydrocarbon mixtures. The separation, however, cannot be predicted from the permeation data of single compounds, for the reason that the permeates plasticize the membrane (Li and Henley, 1964; Li and Long, 1969; Long, 1965; Reilley, 1965; Robeson, 1967; Vetter and Kim, 1967). Plasticizing of the membrane changes the solubility and diffusivity of the permeate. This paper presents the solubility results of both single gases and gaseous mixtures and shows how plasticizing effect can be quantitatively defined from the solubility data. Experimental
Materials. All gases were of the C.P. grade made by the Matheson Co. The plastic films contained no additive
or filler. The Teflon film was Du Pont's Teflon F E P with a density of 2.1056 grams per cc. The cellulose acetate film was the reverse osmosis membrane manufactured by Aerojet General, with a density of 0.2362 gram per cc. The polyethylene and polypropylene films were made by Enjay Polymer Laboratory. Their respective densities were 0.9288 and 0.8920 gram per cc. and crystalline contents were 55 and 64%. The polyolefin films (polyethylene and polypropylene films) were preannealed to ensure their structure stability by the procedure described by Li and Long (1969). Briefly stated, the film was submerged in a solvent and held a t 85°F. for 24 hours. The solvent used in annealing polyethylene was isopropyl alcohol. For polypropylene, three solvents (n-heptane, xylene, and isopropyl alcohol) VOL. 8 NO. 3 SEPTEMBER 1969
281
In permeation through polymeric membranes, plasticizing of the film by the permeates reduces membrane selectivity. This effect is evaluated as the solubility difference of a permeate between its pure state and the state where it is mixed with another compound. The solubilities of methane, ethylene, nitrogen, and methane-ethylene mixture in polyethylene, polypropylene, and Teflon, the permeabilities of methane and ethylene through polyethylene, and the separation of methane-ethylene mixture by permeation through Teflon and cellulose acetate films were determined and discussed.
were used to test the effect of solvent on the permeation characteristics of the film. N o significant difference was observed in the permeability data. Apparatus and Procedure. Both the permeation cell and the solubility cell and their operating procedures have been described in detail (Li and Long, 1969). The permeation cell was made from a Mity-Mite backpressure regulator with its diaphragm removed to enable insertion of the polymeric film. The volume of gas permeated was measured by the volume of water it displaced in a manometer. The solubility cell was made by modifying a high pressure rotameter. The cell contained a quartz spring from which a polymer sample was suspended. Gas was sent into the cell a t a controlled pressure. The solubilities of single gases and the total solubilities of gaseous mixtures in polymer were determined by measuring the extension of the quartz spring with a cathetometer. The composition of the *gaseous mixture dissolved in polymer was determined by the commonly used desorption method (Michaels et al., 1963; Robeson, 1967; Stannett et al., 1962). The experimental setup involved chiefly a high pressure solubility cell connected to a vacuum bomb (Figure 1). The gaseous mixture was fed into the cell containing a plastic film until a certain pressure was reached. The film was submerged in the gas for a sufficient length of time, usually 48 hours, to reach sorption equilibrium. The remaining feed gas a t the end of sorption was quickly released to 0 p.s.i.g. and completely flushed out by helium gas. The desorbed gas was then drawn into the vacuum bomb. When the vacuum gage on the bomb indicated no further pressure increase, helium gas was sent into the bomb to equalize the pressures inside and outside. Samples of gas were then taken from the bomb by a hypodermic needle for gas chromatographic analysis. If the residue feed gas is not flushed, the determined composition of the gas in the bomb is the combined composition of the desorbed gas and the residual feed gas in the solubility cell. The following equation of mass
/ POLYMER FILMS
t
TO VACUUM PUMP
Figure 1. Schematic diagram of desorption apparatus 282
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
balance is needed to calculate the composition of the desorbed gas.
c,=
( W p
+ Wr)Cd - WrCr
~
WP
(1)
Both methods were used and no significant difference in the solubility results was found. Results and Discussion
The plasticizing effect in single gas permeation was previously shown (Li and Henley, 1964; Li and Long, 1969) to affect the membrane permeability defined by Equation 1.
P=DH
(2)
Substituting Equation 2 and Henry’s law Equation 3 into Fick’s law Equation 4, and carrying out the integration, one gets a rate equation describing the permeation process through a plastic membrane.
C = Hp J =
(3)
-D-dC dx
(4)
I n the subcritical pressure range, Henry’s law in general holds; P varies as an exponential function of pressure.
The rate equation then becomes
(7) In the supercritical pressure range, Henry’s law in general does not hold. The variation of P with pressure becomes more complicated and can no longer be represented by an exponential equation. Additional data recently obtained show that P also varies with Ap, because of the plasticizing effect (Figure 2). When Ap was increased, P decreased a t constant P I and increased a t constant p 2 . I n this case, keeping P Z constant means increasing p l and the plasticizing effect on the upstream side of the membrane, resulting in an increase of film swelling and permeability. On the other hand, keeping pi constant means decreasing p 2 . This leads to a decrease of the plasticizing effect and film permeability. In multicompound permeation, the presence of the plasticizing effect usually means that the sorption of the more soluble compound in polymer increases the solubility of
0 1 m i l POLYETHYLENE, GAS: CH4
~l m i l POLYPROPYLENE, G A S : C2H4
ic Ijo
:I
,( 3 )
4'
5 3
--m t
=
2 2 -
-
1 CHq & N2
200
00
A P Ips11
I 1000
800 G A S PRESSURE (psigl 600
-
1 1200
1400
Figure 3. Solubilities of methane, ethylene, nitrogen, and methane-ethylene mixture in polyethylene
Figure 2. Permeability as a function of A f
the less soluble compound. Therefore, the plasticizing effect can be best studied from the solubility point of view. I n this work, the gases used in the solubility study were methane, ethylene, nitrogen, and their binary mixtures. The polymers were polyethylene, polypropylene, and Teflon. However, complete solubility data were obtained only for methane, ethylene, and methaneethylene mixture in polyethylene and Teflon. These include the solubilities of pure methane and pure ethylene, and the total solubilities of methane-ethylene mixture, and the solubilities of methane and ethylene in the presence of each other a t various feed gas pressures. The solubilities of pure methane, ethylene, and nitrogen in polyethylene films, measured a t pressures up to 1400 p.s.i.g., were discussed in detail by Li and Long (1969). The data, summarized in Figure 3, were used in this work to predict the solubilities of methane and ethylene in the presence of each other. The solubilities of these gases in polypropylene and Teflon were measured at pressures up to 5000 p.s.i.g. (Figures 4 and 5 ) . The solubilities of methane and ethylene in both polymers increased asymptotically toward a saturation value, whereas that of nitrogen increased asymptotically toward a saturation value in polypropylene but linearly with pressure within the pressure range investigated in Teflon. The solubility curves of methane and ethylene in both polymers and of nitrogen in polypropylene can be approximated by a straight line a t least up to the critical pressure of these gases. This means that, in these cases, Henry's law holds in the subcritical pressure region, whereas appreciable deviation occurs a t higher pressures. Similar results were obtained with molten polyethylene (Durrill and Griskey, 1966; Lundberg et ai., 1962). I n the case of nitrogen dissolving in Teflon, Henry's law holds throughout the pressure range investigated (0 to 5000 p.s.i.g.). The over-all solubilities of methane-ethylene in all three polymers were also determined. The solubility curves
400
6.0 A
CH4
O
N2
-4
/-
5.0
a
w E
CH4/C2H4 PREDICTED
> 4.0
I 0
-. 3
Y)
5
-I
3.0
cd
9
2.0
Y) 0
Y 1.0
y/--I
I
I
1
2000
3000
4000
5000
0
1000
G A S PRESSURE (psig)
Figure 4. Solubilities of methane, nitrogen, and methaneethylene mixture in polypropylene
obtained were much higher than those calculated from the solubilities of the individual gases a t their partial pressures in the mixture. Such a large difference means a strong plasticizing effect of the permeating compounds. The composition of the dissolved methane-ethylene mixture in a polymer was determined by a desorption experiment, from which the separation factor, a, was calculated. a is defined as the concentration ratio of the more soluble compound to the less soluble compound in the product to the ratio in the raffinate. I n the case of polyethylene, the separation factor predicted from the solubility data of pure methane and ethylene increased with increasing pressure, whereas the actual separation V O L . 8 N O . 3 S E P T E M B E R 1969
283
3.0
I
I
I
I
I
I
GAS PRESSURE (psigl
Figure 5. Solubilities of methane, nitrogen, and methane-ethylene mixture in Teflon
T E M P E R A T U R E , 25'C.
7
F I L M : 1 0 m ~ POLYETHYLENE l =
(C2H4 / CH4) POLYMER /(C2H4/CH(I
RAFFINATE
b-
-
5PREDICTED (ASSUMING PLASTICIZING EFFECT)
NO -
4-
EXPERIMENTAL
' 0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2 4 0 0 2500
FEED GAS PRESSURE ( p s i g )
Figure 6. Effect of plasticizing on separation by selective sorption in polyethylene
factor increased at a slower rate up to about 1000 p s i . , then began to decrease, apparently because of severe film swelling at high pressures (Figure 6). The difference between these two separation curves is a definitive measure of the plasticizing effect, which increases rapidly with pressure (Figure 7 ) . I n the case of Teflon, plasticizing had about the same influence on the solubilities of methane and ethylene, as demonstrated by the fact that the separation factor calculated from the composition of the absorbed methaneethylene mixture is the same as that predicted from the solubilities of the individual gases (Figure 8). These results for Teflon film indicate that high upstream and downstream pressures and large Ap may be used 284
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
without affecting the membrane selectivity. This is verified by the constant separation obtained within the pressure range studied (0 to 1200 p.s.i.). Similar results were also obtained with cellulose acetate film (Table I ) . The permeation results with polypropylene, Teflon, and cellulose acetate thus show that plasticizing effect of hydrocarbon gases may be reduced by using polymers with rigid structure such as Teflon or hydrophilic polymers such as cellulose acetate. In these cases, high upstream and downstream pressures may be used when necessarye.g., in the separation of natural gas-and high pressure drop across the membrane may be applied to increase the permeation rate without reducing the membrane selectivity.
TEMPERATURE = 25’C. F I L M = 10 m i l POLYETHYLENE
A n = a (PREDICTED ASSUMING NO PLASTICIZING E F F E C T b a ( E X P E R I M E N T A L L Y DETERMINED)
s 4
-0
0
200
I
600
400
800
I 1000
1
1200
I
1400
1600
1800
1
2000
1 2200
I
1
24002500
F E E D GAS PRESSURE (psig)
Figure 7. Increase of plasticizing effect in polyethylene with pressure
a
P R E D I C T E D A S S U M I N G NO P L A S T I C I Z I N G E F F F r 7
A = MEASURED EXPERIMENTLY
TEMPERATURE = 2 5 T .
U
F I L M = 5 mil TEFLON F E P
z t
2 500
1000
rn
1500
2000
2500
3000
3500
4000
F E E D GAS P R E S S U R E lpsig)
Figure 8. Effect of plasticizing on solubilities of methane and ethylene in Teflon
Nomenclature Table 1. Separation of Methane-Ethylene Mixture by Permeation through Teflon and Cellulose Acetate Films Temperature. Film thickness. Feed composition.
25” C. 1 mil CH,/CzH, = 45/55
C,H, Concentration, (Wt. 5%) in Permeate
Film Teflon Cellulose acetate
PI, p.s.i.g./ p2, p.s.1.g. = 100 0
66101500
1200 ’1100
59.7 66.0
60.2 66.8
59.3 67.5
a = parameter characterizing pressure dependence of C C = concentration D = diffusion coefficient H = Henry’s law constant, cc. (STP)/cc. polymer, cm. Hg H , = Henry’s law constant independent of pressure J = mass transfer rate, cc. (STP)/sec., sq. cm. L = film thickness p = gas pressure P = permeability or permeation constant defined by Equation 2 Po = permeability independent of pressure W = weight of gas X = distance between film surface and any point inside film
SUBSCRIPTS Acknowledgment
The author thanks R. B. Long for his helpful review of the manuscript arid T. Hucal for his assistance with the experimental work.
d = mixture of desorbed gas and residual feed gas in a solubility cell p = gas desorbed from a polymer r = residual feed gas in a solubility cell (after sorption of gas by polymer is completed) 1, 2 = upstream and downstream side of film VOL. 8 N O . 3 S E P T E M B E R 1 9 6 9
285
Literature Cited
Durrill, P. L., Griskey, R. G., A.1.Ch.E. J . 12, 1147 (1966). Li, N . N., Henley, E. J., A . I . C h . E . J . 10, 666 (1964). Li, N. N., Long, R. B., A.1.Ch.E. J . 15, 73 (1969). Long, R. B., Ind. Eng. Chem. Fundamentals 4, 445 (1965). Lundberg9 J‘ L., Wi1k9M‘ B‘’ Huyettt M’ J’, J . Sci. 57. 275 (1962). Michaels: A. S., Vieth, W. R. Barrie, J. A., J . A p p l . Phys. 34, 13 (1963). Reilley, J. W., Sc.D. dissertation, Stevens Institute of Technology, Hoboken, N. J., 1965.
Robeson, L. M., Ph.D. dissertation, Universitv of Marvland, College Park, 1967. Stannett, V., Szwarc, M., Bhargava, R. L., Meyer, J. A., Myers, A. W., Rogers, C. E., “Permeability of Plastic Films and Coated Paper to Gases and Vapors,” TAPPI Monograph Series, No. 23 (1962). Vetter, A. F., Kim, S. N., Separation Sci., 2, 625 (1967).
RECEIVED for review December 23, 1968 ACCEPTED April 16, 1969
ORGANOPHOSPHORUS COMPLEXES OF COBALT CARBONYL AS HY DROFORMYLATlON CATALYSTS EDMOND
R .
TUCCI
Gulf Research and Development Co., Pittsburgh, Pa.
15230
Cobalt carbonyl-organophosphorus complexes have been investigated as olefin hydroformylation catalysts for improving linear-product formation. The organophosphorus ligands found to be most effective included tetraalkyl( aryl)diphosphines, PzR4 or PZAr4; dialkyl( aryl)chlorophosphines, RzPCI or ArzPCI; cyclic organophosphines, PH[CH( R) O]zCHR; bicyclic organophosphines, P( CHZO)~CR; and bicyclic organophosphites, P( 0CHz)XR. Although these organophosphorus ligands possess characteristics different from trialkylphosphines( PR3), their carbonyl complexes were still selective in forming linear products (ca. 85 to 88%) at optimized olefin-oxonation conditions. The optimum P to Co ratio for high linear-product formation did not necessarily follow the PR3modified oxo system, but depended more on the type of organophosphorus complexing ligand. Cobalt carbonyl complexes of arylphosphorus derivativese.g., PzPh4 or PhzPCI-generally yielded less linear products and were poorer hydrogenation catalysts than the corresponding alkyl derivatives. The lower oxonation and hydrogenation activity of the RzPCI-cobalt carbonyl catalyst system suggests possible interactions between CI and Co leading to the formation of a stabilized [Co(CO)3(RzPCI)]~dimer. Hydroformylation of olefins with a bicyclic tertiary organophosphite-cobalt carbonyl catalyst system indicated that bicyclic organophosphites behaved more like trialkylphosphines than trialkylphosphites.
THE hydroformylation
of 1-olefins with trialkylphosphine-cobalt carbonyl complexes was reported in the literature (Slaugh and Mullineaux, 1963, 1968; Tucci, 1968a,b) to be superior to the conventional H C O ( C O ) ~ oxo catalyst in lessening branched-product formation. T o determine if trialkylphosphine ligands were unique in improving the selectivity of the oxo reaction, the author investigated other classes of organophosphorus modifiers and found several different types which, upon complexing with cobalt carbonyls, favored the stereoselective formation of linear products (Tucci et al., 1966). The most effective catalyst systems which we investigated consisted of cobalt carbonyl complexes of tetraalkyl(ary1)diphosphines-Le., P2R4, PnArr-dialkyl(aryl)chlorophosphines-Le., R2PC1, ArsPC1-cyclic secondary organophosphines (I), bicyclic tertiary organophosphines (11), or bicyclic tertiary organophosphites (111). 286
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
P RHC”\CHR I I 4H/O
k
I
A\ CH2 I CH2 l CH2 l 0 0 0
\I / L R
II
A\
?CH2 ?CH2 ?CH2 \A/ L
R
m
This paper illustrates the effectiveness of these novel oxo catalysts in improving linear-product formation in the oxonation of propene, and attempts to differentiate between these catalyst systems and the simple PR3modified oxo catalyst system. Experimental
Materials. The tetrabutyldiphosphine, tetraphenyldiphosphine, and diphenyldibutyldiphosphine were obtained
