Hydrogen Fluoride-Boron Trifluoride Extraction of Xvlene Isomers J
D. A. MCCAULAY, B. H. SHOEMAKER,
AND
A. P. LIEN
Standord Oil Company (Indiarca), Whiting, Ind. Batch extraction experiments show that m-xylene may
be selectively removed from its isomers by extraction with (I hydrogen fluoride-boron trifluoride (HF-BFa) mixture. The extracted m-xylene may be recovered from the extract eolution by vaporizing the HF-BFe therefrom at moderately low temperatures. Vapor pressure measurements involving each of the individual xylene isomers show that all the xylenes react extremely rapidly and reversibly with HF-BFa to form a complex in which the mole ratio of boron trifluoride to hydrocarbon ie one. Thio complex is soluble in excess hydrogen fluoride, but uncomplexed xylene is aubstantially insoluble. Equillbrium constants, representing the stability of each of the xylene complexes, were calculated from the vapor pressure measurements and were found to be in the ratio: metarorthorpara = 20:2:1. These values show that the rn-xylene complex is much more stable than the other two and explain the preferential extraction of m-xylene into the acid layer.
A
LTHOUGH the xylene mixture distilled from coal tar has been commercially available and haa been used as a solvent for nearly 100 years, the individual isomers have always been much more expensive chemicals. Analyses of coal tar xylene ( 4 9 ) and of the xylenes occurring in the product from catalytio refining processes, such as hydroforming and catalytic cracking (I$), have shown that xylenes from all these commercial sourcea have similar compositions and contain large amounts of ethylbenzene (10 to 20%). The similar physical propertie of this group of aromatic hydrocarbons has been one major deterrent to isomer separation. For example, the boiling pointa (7) of +xylene, m-xylene, pxylehe, and ethylbenzene are 144.4, 139.1, 138.3, and 136.2' C., respectively. Although o-xylene can now be separated from ita isomers by fractional diatillation through modern fractionating columns, the problem of separating the remaining three isomers is much more difficult. In the past, m-xylene has been separated from the isomeric mixture by selective sulfonation (94,8). This separation is based on the principle that the rate of sulfonation of m-xylene ia faster than that of o-xylene, p-xylene, or ethylbenzene and that the rate of hydrolysis of mxyleneaulfonic acid is faster than that of the other xylenesulfonic acids. pXylene has been separated by freezing (I, 10, 11), since it has a much higher melting point than the other Ci aromatics. The existence, however, of a m,pxylene eutectic mixture (12.6% para) limik the amount of p xylene recoverable by this technique. Although these methods and various combinations of them have been successfully adapted to the laboratory and commercial scale production of xylene isomers, it waa evident that improved and cheaper methods of separation would increase enormously the demand for the individual
isomers. The hydrogen fluoride-boron trifluoride (HF-BFI) extraction procesa discussed here gives promise of being a method for Separation of the meta isomer. When used in combination with other methods, for example, fractionation or crystallization, it provides a possible method for separation of each of the xylene ispmers in a state of high purity. Two methods of attack were used in the study of this problem. One involved a series of batch-extraction experiments, using the reagent H??-BF, on synthetic xylene mixtures, designed to give quantitative separation data. The other employed a series of vapor-preeaure measurements which were made on the three xylene-HF-BFI systems to gain information concerning the mechanism of the selective solvent action. EXTRACTION STUDIES
Experimental. All the work described in this paper waa carried out with Eastman Kodak Company xylenea with the exception of run 1, Table I, which was made with a closely fraotionated cut of CI alkylbenzenes obtained from the hydroforming unit of the Standard Oil Company (Indiana). The hydrogen fluoride and boron trifluoride were commercial grades of 99.6 and 96% purity, respectively, obtained from the Hershaw Chemical Company. The 4y0 impurity present in the boron trifluoride consisted mainly of an inert noncondensable gar. This impurity was separated by evacuation from the boron trifluoride, which waa maintained a t liquid nitrogen temperaturn during the pumping period. The batch-extraction runs were carried out in a 1570-ml. carbon-steel autoclave fitted with a 1725-r.p.m. mechanical stirrer (6). A schematic drawin of the reactor and acceaeory equipment is shown in Fi w 1. &e xylene mixture to be extracted wan charged t h o u y a n opening in the closure plate, after which liquid hydro en iuoride was added from the metering bomb. The volume o f hydro en fluoride was measured b the amount of mercury displace1 from the visual-ty liquid-fevel gage. hydrogen fluoride was charged origin$ to the meterin bom by dhtillstion from a commercial 1Wpound cylinder.) %oron tnfluoride was pressured into the reactor through a valve on the line to the pressure gage from a small cylinder, which was weighed
bThe
Figure 1. Reactor and Accemories
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2104
Vol. 42, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY
into higher boiling producb tends to remain in the refhate phase. The separation factor between ethylbenaene and the xylenes can be calculated as follows:
(uEB
VAPOR PRESSURE MEASURING FLASK
Figure 2.
Apparatus for Vapor Pressure Determinations
before and after addition. After the boron trifluoride addition the mixture was stirred for about E~~minutes a t 20’ to 25’ C . and allowed to settle for another 15 m u t e s . The acid phase was withdrawn from the bottom of the reactor into a dry ice-cooled flask after which the hydrocarbon phase was removed and washed with ammonium hydroxide to remove traces of dissolved hydrogen fluoride and boron trifiuoride. The extracted xylenes were recovered from the acid phase by displacement with water. About 300 grams of water were added slowly to the extract-containing copper flask immersed in a dry ice-acetone bath. After all the water was added, the flask waa shaken until it warmed to room temperature. The contents were then transferred to a copper separatory funnel, where the supernatant h drocarbon was separated from the lower aqueous acid phase. ‘$his method was used because of ita simplicity, although I t was demonstrated in other experiments thbt the components of the extract phase could be readily separated b distilling the boron fluoride and hydrogen fluoride from the hyJocarbon. The hydrocarbon extracts and raffinates of all runs were fractionated on a column of 30 theoretical plates, and the CSalkylbenzene fraction of each was analyzed by the ultraviolet-absorption technique (19). Results and Discussion. The resulta of the batch-extraction runs are given in Table I. A comparison of the raffinate and extract compositions for all four runs shows that nt-xylene is selectively extracted by the hydrogen fluoride and boron trifluoride mixture. A quantitative meaaure of the selectivity is given by the alphas (Table I, last three lines) which are singlestage separation factors defined by the following equations:
where Nto, N‘,,,, and N’, are the mole fractions of 0-, m-, and pxylene in the r a f i a t e phase and No, N,, and N , are the corresponding mole fractions in the extract phase. The u thus defined is analogous to the relative volatility used in vaporliquid distillation terminology. An a value of six means that in a countercurrent extraction system about four stages would be required to separate 95% m-xylene from an equimolar mixture of the three isomers. The fractionation analyses of the r a f i a t e and extract of run 1 disclose that benzene and Ct0 alkylbenzenes are present in the products. These must have resulted from the migration of an ethyl group from the ethylbenzene to a xylene or to another ethylbenzene molecule. Since no toluene or COaromatics were detected in this run and also since no products other than CS alkylbenzenes were found in runs 2, 3, and 4, where little ethylbenzene was present in the feed, it is apparent that a methyl group does not migrab from xylene under these conditions, Run 1 also shows that any ethylbenzene which is not converted
-/-
-/
1 - N’EB 1 - NEB = 1 - 0.26 N‘EB NEB 0.26
km 0.001
o,oo3
I
Although the true value of a is extremely uncertain because of the occurrence of the ethylbenzene conversion reaction, the above calculated value gives an idea of its order of magnitude, It is so much smaller than the xylene a that an effective separation could be made between ethylbenzene and the xylenes in a onestage extraction process. The results of the vapor-pressure measurements (described in the next section) show that, in the presence of hydrogen fluoride, boron trifluoride and xylene form a mole-for-mole complex which is soluble in the acid phase. Hence the number of moles of xylene taken into the extract layer should equal the number of moles of boron trauoride used in forming the complex. The extract yields of runs 1 and 4 (Table I) agreed with this prediction whereas runs 2 and 3 gave 1.3 and 1.6 times the theoretical extract yields. This leads to the conclusion that another force is operating besides the selective, complex-forming reaction of boron trifluoride with xylene. It is believed that the stable xylene complex in the acid layer acta as a “solutizer” to bring about the nonselective physical solution of additional amounta of uncomplexed xylene. In other words, more xylene is physically soluble in a solvent comprising hydrogen fluoride plus a m-xylene-boron trifluoride complex than is soluble in hydrogen fluoride alone. Thk theory accounts for the fact that increased concentration of m-xylene in the feed in runs 2 and 3 resulted in lower a than in run 1. Furthermore, run 1, which waa identical to run 3 except that an inert countersolvent was used, gave a theoretical extract yield and a much higher a than did run 3 (6.8 against 2.8). This shows that the physically held, uncomplexed xylene differs from the chemically held, complexed xylene in that it is easily extractable from the acid layer by an inert hydrocarbon such as hexane. The reaction rate between xylene, hydrogen fluoride, and boron triiluoride is extremely rapid. In all the runs, hydrogen fluoride and xylene were charged to the reactor and boron trsuoride was then added under prassure above the liquid so that three distinct phases were present: a bottom liquid hydrogen fluoride layer; a middle xylene layer; and a top layer of gaseous boron trifiuoride under about 30 to 40 atmospheres preasure. As soon as the mixture was stirred, an immediate drop in preasure to eero indicated an almost instantaneous reaction between the three components. It appears, therefore, that the rate of reaction is governed only by the rate of mixing of the three components. VAPOR PRESSURE STUDIES
In order to obtain more information concerning the nature of the boron trifluoride-xylene-hydrogen fluoride interaction, vapor-pressure measuremenb were made on the three xylene systems. Experimental. A schematic drawing of the apparatus is shown in Figure 2, The manifold waa constructed of */&cb copper tubing and was connected to a glass vacuum system by means of a copper-to-glass seal, The indicated valves were ‘/Finch Hoke brass needle valves packed with Teflon. The flasks for metering the boron trifluoride and for holding the liquid hydrocarbon-HF-BFa mixture were copper Kjeldahl flasks of 1200-ml. and 600-ml. capacity, respectively. The latter flask was attached to the system by a helix of */Finch copper tubing to allow agitation of the flask. Weighed amounts of hydrogen fluoride and hydrocarbon (about 5 moles of h drogeii fluoride and 0.4 mole of xylene) were introdured into d e flask. The flask waa attached to the vacuum sys-
October 1950
2105
INDUSTRIAL AND ENGINEERING CHEMISTRY
from the amount added the approximate amount in the Run No. 1 2 3 4 gas phase aa computed from a knowledge of ita partial presReactor oharge, grama 348 255 344 239 Hydrocarbon sure and its volume, with the 821 603 80 1 354 Hydrogen fluoride 112 82 113 95 Boron trifluoride assumption that it obeyed the .. .. 203 Petroleum ether 95 99 95 88 Hydrocarbon recovery, wt. 5% ideal gas law. The partial Product distribution, wt. % pressure of boron trifluoride 34.7 24.5 500 42.4 Rafftnate 65.3 75.5 50 57.6 Extraat was calculated by subtracting Ratio :moles extract per mole 1.3 1.6 1.0 1.0 BFI wed from the total pressure the partial pressure of hydrogen fluoRaff. Ext. Raff.6 Ext. Fractionation analyses, mole % Rrrff. Ext. Raff. Ext. ride, which was computed to 0 0 0 0 0 1 0 3 Benmene 0 0 0 0 0 0 0 0 Toluene change from 36 om. of mercury 100 100 85 100 100 100 100 97 CI alkylbensenes 0 0 0 0 0 0 0 0 Cc alkylbenzeneu for 100% hydrogen fluoride to 0 0 14 0 0 0 0 0 CM dkylbenzenes 32 cm. of mercury in the most Ultraviolet analyses, mole % Feed Raff. Ext. Feed Raff. Ext. Feed Raff. Ext. Feed Raff. Ext. concentrated solution. 2.2 2.6 9.0 19 6 26.1 19.4 16.8 21.2 11.9 2.2 2.7 1.0 o-Xylene Plots of the partial pressure 83.6 79.5 91.5 60.7 59.2 30.4 69.5 83.6 80.2 95.9 41.2 17.7 m-Xylene 5.8 10.8 13.7 16 7 23.3 12.5 27.7 44.8 17.1 10.8 11.4 1.8 of boron trifluoride against its 0.6 2.4 3.4 0.7 3.4 1.3 1.6 2.1 2.4 1 9 . 7 2 6 . 1 0.1 E-Xy1ene thylbenzene mole fraction in solution for 7.2 5.2 2.8 5.8 am 2.3 6.4 6.0 9.1 a mlp each of the systems: HF-BF8 1.5 4.6 4.1 3.a a m/o alone, HF-BFa with m-xylene, a Solvent-free. HF-BFa with o-xylene, and HF-BFa with . w x v-l e n e a r e given in Figures 3 to 6. tem, its contents frozen in li uid nitrogen, and the whole system Figure 3 (HF-BF, done) shows that boron trifluoride in hyevacuated. The valve to t l e flask was closed and boron tridrogen fluoride obeys Henry's law, and a t 0" C. ita partial presfluoride as was passed into the system and allowed to fill the sure may be expressed as, calibrate5 metering flask to a definite pressure. The valve of the va r-pressure meaaurin flask was opened and the boron trifluoPBF, ~OONBF, r i g w a s condensed in t k s flask. After several increments were where PBF~ partial preseure of boron trifluoride in cm. of added in this manner, the valve of the metering flask waa closed and the va or-pressure flask was allowed to warm to 0" C. in an mercury, and NBF:= mole fraction of boron trifluoride in soluice bath. h$)e' flask wan agitated by hand a t this temperature tion in hydrogen fluoride. The straight l i e drawn through the until a constant pressure was reached; this usually required from points crossea the abscissa a t 0.005 instead of a t aero aa expected. 1 to 2 bours. After this reading was taken, the contents of the This is probably because there are present in the hydrogen Bask were again frozen in li uid nitrogen and another increment of boron trifiuoride waa add&. This cycle was repeated until the fluoride m a l l amounts of impurities, such as water, which form partial pressure of boron trifluoride in e uilibrium with each liqstable complexes with boron trifluoride. There is no evidence for uid phase had reached about 150 am. ogf mercury, which is the the formation of the often postulated compound, fluoboric acid safe working-pressure limit of the apparatus. (HBF,). If such a compound were formed and it were stable, Results and Discussion. The results of the vapor-pressure the partial pressure of boron trifluoride a t NBF:= 0.5 would be measurements are &own in Table 11. The weight of boron close to aero; actually an extrapolation of the graph shows that trieuoride in the liquid phase was calculated by subtracting ita partial preaaure is nearly 2300 cm. of mercury a t this composition. Fluoborate salts are known, and there is probably some fluoborate ion formed in an HF-BFa system. However, its concentration must be low and the equilibrium indicated below must lie far to the left. HF BFs e HfBFIFigure 4 (m-xylene HF-BFI) shows that, in the presence of hydrogen fluoride, boron trifluoride and m-xylene form a
TABLEI. BATCHEXTRACTION OF XYLENEMIXTURESWITH HF-BFa
I
.
+ +
TABLE11. VAPOR PRESSURES OF THREEHF-BF~-XYLENI SYSTEMS AT 0 O C. Partial
Hydrocarbon Wt., HF, Name g. g. None
.,
rn-Xylene
44
93.5
o-Xylene
44
99.5
p-Xylene
MOLE FRACTION OF BF3 IN HF
Figure 3. HF-BFs System at 0' C.
41
106
109.6
BFs BF: in Solution Added, Mole G. Grams fraction 0 3.8 7.0 10.5 0 10.7 21.3 28.4 32.0 35.5 0 12.5 25.0 33.3 87.5
0
10.7 21.4 28.5
0 2.8 5.0 7.2 0 10.6 21.2 27.5 30.3 32.2 0 12.1 23.5 30.4 34.4 0 10.0 19.4 25.4
0 0.008 0.014 0.020 0 0.033 0.067 0.086 0,095 0 102 0 0.036 0.070 0.090 0.102 0 0.027 0.052 0.068
pzi$\,
Cm. of Hg 38 67 122 176 36 42 39 75 100 129 36 62 117 171 199 36 67 126 173
PCm.r gbf r Hg
e
29 84 138 0 6 3 42 68 97 0 27 84 138 167 0 32 92 139
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2106
B
MOLE FRACTION OF BFs IN HF I I J
I 0
0.35
0.76
1.0
MOLE RATIO: BF* TO M-XYLENE
Figure 4.
WF-BF-rn-Xylene System at 0' C.
complex containing I mole of boron trifluoride per mole of xylene. This complex is not completely stable since the partial pressure of boron trifluoride does not remain a t zero until the mole ratio of boron trifluoride to hydrocarbon reaches 1. With a completely stable complex, the partial preasure of boron trifluoride would follow along the line, OA, and then would rise along the line, A B , in accordance with Henry's law. Instead, the asymp totic approach to line A B indicates that complex formation is 100% complete only under excess boron trifluoride prmure. L i e AB has a slightly smaller slope than the line (transposed from Figure 3) representing the partial pressure of boron trifluoride over hydrogen fluoride alone. This is to be expected because the presence of 8 complexed aromatic in solution would slightly increase the solubility of boron trifluoride in hydrogen fluoride. Figure 6 (+xylene HF-BFa) shows that &xylene, hydrogen fluoride, and boron trifluoride also form a complex containing 1 mole of boron trifluoride per mole of xylene. That this complex is much less stable than the m-xylene complex is evident from the curve, because the boron trifluoride partial pressure for a given composition ratio is considerably greater. Figure 6 (pxylene HF-BFI) shows that pxylene forms a similar mole-for-mole complex, but ita stability is even lees than that of the +xylene complex. The partial-pressure curve approaches line A B only a t a relatively high prassure. In order to obtain a rough quantitative comparison of the stability of the xylene complexes, it was assumed that the following reaction occurred: BF8 HF xylene ~ = E = SBFrHF.xylene
Vol. 42, No. 10
in defining the equilibrium constant that the activities of the components of the liquid phase are proportional to the mole fractions. This may be far from the truth, but it was hoped that deviations from the perfect-solution laws would be the same for each of the xylenes and hence that mutually comparable constants could be obtained. The quantities NaFand PBF& of the above equilibrium constant c a n be obtained directly from the curves of vapor pressure against composition. Noornplax is equal to the total mole fraction of boron trifluoride in solution (the abscissa of the vapor-pressure curves) minus the mole fraction of uncombined boron trifluoride in solution. The latter quantity can be calculated from P B F a and Henry's law as given by the asymptote to which the vaporpressure curve approaches. Thus, for the m-xylene system, it can be seen in Figure 4 that,
The last of the four quantitias, Nwiane, is more difficult to evaluate. I n the lower part of the vapor pressure curve, where two phases are present, it is constant but unknown. In the upper part of the curve, where only the one acid phase is prwent, it is equal to the mole fraction of the total xylene in the system minus Noompiel.In order, therefore, to get a numerical value for NWisne, the latter method of computation and the measurements at high boron trifluoride concentrations were used. The results of the calculations of these four quantities and the equilibrium constants for the three xylene systems are shown in Table 111. The average values of the equilibrium constants express semiquantitatively the observation that the m-xylene complex is much more stable than either of the others and that the ortho complex is more stable than the para. From the definition of a given previously and from the assumption that the isomer ratio in the hydrocarbon phme is equal to the isomer ratio of uncombined xylenes in the acid phase-that is, the partition coefficient expressing the distribution of uncombined xylene between the acid phase and the hydrocarbon phase is the same for all three xylenes-it can be seen that the ideal single-stage
+
+
+
+
Equilibrium constants were calculated from the vapor-pressure data by use of the following equation:
where N,,,,,, = mnle fraction of the complex in the acid phase; E mole lrnctioa of uncompiexed xylene in the acid phase; N a p P mole froc*tic~iiof hydrogen fluoride; and PBF,= partial preseure of htirriri trifluoride in cm. of mercury. I t was assumed
1
0
MOLE FRAGTION BFa IN HF I I 0.5
1.0
MOLE RATIO: BF3 TO 0-XYLENE
Figure 5. HF-BFm-Xylene System at 0' C.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
October 1950
-
separation factor for any two isomers is equal to the ratio of their equilibrium constants. Thus, the between m-xylene and 0-xylene is:
s
Likewise, u rnlp and Q o l p are: u m / p = 0.38/0.018 a o / p = 0.038/0.018
-
-
20 2
These relationships are true only for the ideal C&BB in which substantially all of the xylenes present in the acid phase exist in the form of an HF-BFa complex and also in which the partition COe5icients of all three xylenes are the same. The actually obeerved separation factors are lower than the calculated ideal valuea probably because both the above conditions are only approximated.
-
CONCLUSIONS
m-Xylene may be extracted from its isomers by means of ti mixture of hydrogen fluoride and boron trifluoride. The reactions involved are sufficiently rapid and selective that 95% mxylene can be separated from mixed CSalkylbenzenes in a countercurrent extraction tower of four or five theoretical plates. The use of an inert h drocarbon diluent such as a light naphtha or petroleum ether [urther improves the extraction selectivity by reducing the amount of xylene “physically” dmolved in the acid layer. The extracted m-xylene may be recovered from its complex by vaporidng the hydrogen fluonde and boron trifluoride therefrom at moderately low temperatures-for example, 40” to 70” C. If the process is carried out on a small scale where recovery of reagents is unimportant, the m-xylene may be separated by dilutin the complex with water. Sthylbeneene may be separated from the remainin Csaromatics merely by adding, in the presence of an inert hyfrocarbon wlvent such as petroleum ether, enough boron trifluoride at a sufficiently high pressure to combine with all of the x lenes. Under these conditions all of the x lenes will dissolve in d e acid hase and the ethylbeneene will eitier remain in the hydrocarbon Payer or will be converted into benzene and CN aromatics which boil well outside the xylene range. Vapor pressure measurements have shown that the xylenes in hydrogen fluoride golution react with boron trifluoride to form complexes containing 1 mole of boron trifluoride per mole of xylene. The measured values of the e uilibrium constant repreeenting the stability of each of the xyyene complexes are in the ratio : Meta:ortho:para = 20:2:1
MOLE FRAGTION 6% IN HP
0
1.0
MOLE RATIO: BF, TO P-XYLENE
Figure 6. HF-BFpp-Xylene System at 0’ C.
The extraction results and the vapor pressure data have been used to formulate a theory concerning the mechanism of the acidbase interaction between aromatics and HF-BFI. This theory will be presented with subsequent work. ACKNOWLEDGMENT
The authors wish to thank R. F. Marschner and E. W. Thiele of thii laboratory for advice and encouragement during the course of this work and to express their appreciation to F. W. Powhe and R. M. Teeta, also of this laboratory, for ortrrying out the ultraviolet analyses of the xylene mixtures. LITERATURE CITED
(1) Arnold, J. C., Brit. Patent 585,076(Jan. 29,1947). (2) Clarke. E. T., and Taylor. E. R.. J . Am. Chem. Soo., 45, 830 (1923). (3) Cole, P. J., U. 8.Patent 2,393,888(Jan. 29,1946). (4) Cole, P. J., and Butt, 0. W., U. 8. Patent 2,348,329(May 9, 1944). (5) Crafts, J. M., Conapt. rend., 114,1110 (1892). The large differences in the equilibrium constants show that the (6) Evering. B. L., and d’ouville, E. L., J . Am. Chsm. SOC.,71, 440 HF-BFI system is extremely sensitive to differences in structure (1949). among aromatics and should be particularly useful as a medium (7)Foroiati, A. F., Glasgow, A. R., Willingham, C. B., and Rolleini, for separating the components of other aromatic hydrocarbon F. D., J . Reeearch Nall. Bur. Standurda, 36, 129 (1946). mixtures. (8)Jscobeen, O.,Bar. 10,1009 (1887). (9) Kishner. N..and Krasova. V..J . QBR. C h : (U.S.S.R.). 6, 748 (1936). (10) MoArdle, E. H.,and Mason, D. M., U. S. Patent 2,435,065 (January TABLE111. CALOULATION 01 EQUILIBRIUM CONSTANTB POB XYLBINEI-COMPLEIX 1948). FORMATION (11) Spannagel, H.,and Tschunkur, E., Mole Mol? Mol? U. 8. Patent 1,940,065(December Fraation Fraotion Fraction Average 1933). Xylene ,.P N=F Total BF: Free BFa Noomptnx Total Xylene NxyIaa Keq. Rea. (12) Streiff, A. J., and Roeaini, F. D., J . 9 0.93 0.07 0.0014 0.0686 0.0888 0,0202 0.41 Reeearch Natl. Bur. Standards, 39, 0.92 0.08 0.0038 0.0762 0.0888 0.0128 0.27 0.91 0.09 0.0075 0.0825 0.0~88 o.oo~a 0.80 0.88 303 (1947). 85 0.90 0.10 0.0132 0.0868 0.0888 0.0020 0.56 (la) Tunnioliff, D. D., Brattain, R. R., and Zumwdt, L. R., Anal. Chon., 84 0.93 0.07 0.0130 0.0570 0.0834 0.0264 0.028 0.92 0.08 0.0168 0.0632 0.0834 0.0202 0,032 21,890(1949).
.-,
I
185
0.91 0.90
0.09 0.10
0.C209 0.0257
0.0691 0.0743
0.0834 0.0874
0.0143 0.039 0.0001 0.055
RBODXVED Maroh 11, 1950. Preaeated before the Division of Petroleum Chemistry, H o w tan, Tex., and the Division of Phyaicd and Inormnio Chemistry, Detroit, Mioh., 117th AL Meeting, Ardnruc4w C E ~ M X OSWIBTY.
