Compressibility of Liquid Naphthalene
F. R. RUSSELL' A N D H. C. HOTTEL Massachusetts Institute of Technology, Cambridge, Mass.
nected to a vacuum pump, to an open-end sampling or vent line (either directly or through a condensing coil in a hot water bath), and to the top of a hot naphthalene chamber. This chamber, in turn, was connected a t the top to a naphthalene melting pot and at the bottom to an oil system separated from the naphthalene by mercury. The oil system consisted of a pressure gage, an open-end oil release line, and an injector. The injector was merely a threaded rod which could be turned by hand through a packing gland into a cylinder of heavy oil, displacing 0.836 * 0.0008 cc. of oil per revolution; the ail, in turn displaced an equal amount of the mercury and the molten naphthalene. The data were obtained in a series of five runs. For each run the reactor was cleaned, evacuated, filled with molten naphthalene (by means of the injector) to atmospheric pressure, and heated to the desired temperature. When, during the heating, the pressure had risen to the desired value (either 3030 or 5800 pounds per square inch), sufficient naphthalene was continuously released from the reactor to
I
N THE course of an investigation of the rate of polymerization of ethylene dissolved in molten naphthalene, it became necessary to know the temperature-density relation of naphthalene a t temperatures up to about 800" F. and pressures u p to 400 atmospheres. Inasmuch as density (or specific gravity) data (1) existed only for atmospheric pressure, determinations of specific gravities a t several temperatures were made a t pressures of 3030 and 5800 pounds per square inch in the apparatus used for the polymerization studies, The apparatus was described in detail in a recent publication (2) of the results of the investigation of polymerization. Briefly, i t consisted of a reactor in which a known quantity of molten naphthalene could be heated at constant pressure to the desired temperature, together with the necessary equipment for measuring the quantity of naphthalene required to fill the reactor and the quantity expanded out during the heating of the reactor. The reactor was con1
Present address, Standard Oil Development Company, Elizabeth, N. J.
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a
2L .90 z
c
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t
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I-
.75
.70
I i i i i i i i i i i i i i i i i i 1 i i i i i i i i i i i i i i i ii iNi I 200
400
TEMPERATURE,
600 ' F.
0
800
1500 ABSOLUTE
3000 PRESSURE,
4500
6000
POUNDS PER SQUARE INCH
FIGURE 2. SPECIFICGRAVITYOF NAPHTHALENE vs. PRESSURE AT CONSTANT TEMPERATURE
FIGURE 1. SPECIFICGRAVITY OF NAPHTHALENE vs. TEMPERATURE AT CONSTANT PREBSURE
(By interpolation from Figure 1)
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INDUSTRIAL AND ENGINEERING CHEMISTRY
344
TABLEI. SUMMARY OF DATA Run A Reactor bested from 220' to S55O F. Reactor volume at 220' F., cc. Reactor volume at 855" F., cc. Naphthalene expanded out of reactor (calcd. from measured quantity of oil) at 194O F. and 3030 lb./sq. in., oc. Run B Reactor heated from 218' to 759O F. Reactor volume at 218' F cc. Reactor volume at 759' F:: cc. Naphthalene expanded out of reactor, grams
100.3 101.66 29.6 100.3 101.46 23.8
Run C Reactor Temp., ' F. Reactor Vol., Cc. Naphthalene Out, Grams 100.3 0.0 217 101.1+ 16.05 612 101.3 19.33 679 101.5 23.03 766 27.75 101.7 862 Absolute pressure 3030 lb./sq. in. Run D Reactor Temp., Reactor Vol., Naphthalene Out (Calcd.), O F. cc. cc.0 0.0 100.3 210 100.8 9.95 459 15.15 101.1 578 21.70 101.4 713 30.60 101.7 884 Absolute pressure 3030 Ib./Rq. in. Xaphthalene left in reactor = 68.8 * 0.5 grams
-
Run E Reaotor Temp.. Reactor Vol., Naphthalene Out (Calcd.), O F. cc. Cc.b 222 100.25 0.0 459 100.75 8.35 595 101.05 13.15 744 101.35 18.80 852 101.60 22.85 Absolute pressure 5800 lb./sq. in. Compressibility Data. Vol. of reactor at 222' F., cc. Vol. of tubing in reactor system, cc. Naphthalene added= t o reactor system (by aompresvion from 15 t o 30301b./aq.in.) at 253' F.and 30301b. ( p = 10.973),cc. Naphthalene add?dC to reactor system (by compression from 3030 to 5800 lb,/sq, in.) at 250' F. and 5800 lb., cc. Reactor maintained at 222O F. in both cases.
VOL. 30, NO. 3
Inasmuch as absolute specific gravities or densities were more desirable than relative expansion data, compressibility tests were made by compressing a reactor full of naphthalene at one atmosphere and 222' I?. (where the density was known from data in International Critical Tables, 1) first to 3030 and then to 5800 pounds per square inch. I n each case the injector system was brought to the final pressure with the valve separating it from the naphthalene closed. The valve was then opened and the screw turned in to restore the pressure to its desired value. The quantity of naphthalene added during the compression was measured by the number of injector revolutions and the temperature of the naphthalene. I n this way density data for these two pressures could be based on the accurately known densities a t one atmosphere The data are summarized in Table I. The results are shown in Figure 1 where specific gravity (density) is plotted against temperature for different constant pressures. The line for atmospheric pressure represents the data from the International Critical Tables extrapolated by the equation given there to temperatures above the boiling point. The lines for 3030 and 5800 pounds per square inch represent the data obtained in this investigation. The line for 1000 pounds per square inch comes from an interpolation pIot (Figure 2). Figure 2 shows the variation of density with pressure for various temperatures; it was constructed from the lines of Figure 1 corresponding to pressures of 1 atmosphere, 3030 pounds and 5800 pounds per square inch. T a b b I1 gives the summarized results as calculated from the data of this investigation. Table I11 is a table of compressibility factors.
100.20 3.90 3.05
TABLE11. RESULTS CALCULATED FROM EXPERIMENTAL DATA"
1.35
F.and 3030 lb./sq. in. F. and 5800 lb./sq. in. The temperature given for the added naphthalene is the temperature at which it was measured-that existing in the hot naphthalene reservoir. a At 211' b A t 223' 0
maintain the pressure constant. I n runs D and E (the most accurate and therefore the most important runs) the naphthalene expansion was accommodated and measured by backing off the injector screw; the volume increase of the injector was measurable to 0.01 cc. I n calculating the amount of naphthalene expanded from the reactor, corrections were made for the -thermal expansion of the reactor (expansion due to the pressure was negligible), for the holdup of the lines, for the leakage (less than 0.1 cc. per hour), and for the changes in temperature in the liquid system outside of the reactor. Runs A , B, and C were of a preliminary nature. The quantity of naphthalene released during the heating period was not accurately measured by the release methods used, because of the relatively large holdups of the open-end release lines. I n run A the expansion was measured as the volume of heavy oil released (at atmospheric pressure) from the oil release line, corrected back to its volume at the pressure in the reactor (3030 or 5800 pounds per square inch). I n run B it was measured as the weight of naphthalene actually released through the naphthalene release line. I n run C it was measured as the weight of naphthalene actually released through the naphthalene release line and hot water condenser.
Temp.
* F.
855 759 612 679 766 862
Data from Run
Naphthalene Data Naphthalene PresSp. Gr. from PresSp. Qr. sure (Density) Temp. Run sure (Densitv) Lb./sp. in. Gram/cc. O F. Lb./sq.in. Gram/oc. A 3030 0.6825 222 n 3030 0.9855 B 0,7410 459 3030 3030 . 0.8875 C 3030 0.8200 578 3030 0.8340 8030 0.787713 3030 0.7670 3030 0.7490 884b 3030 0.6780 3030 0.7010 222 0.9985 E 5800 459 0.9102 5800 595 0.8607 5800 0.8027 744 5800 852 5800 0.7608
0 All values are based on density at 222' F. and atmospheric pressure of 0.957 gram per cc. b 9 ' F.above critical temp.
DEAD- WClGHT RELEASL
FIQURE 3.
DIAQRAM OF APPARATUS
MARCH, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE 111. COMPRESSIBILITY FACTORS Temp.
F. 176 (m. p.)
Pressure Range (-4bs.)
Bav.
Per megabar
X 106* Per lb./sq. i n . 8.84
Megabars
Lb./sq. in.
1.014-209 209-400 1.014-400
15-3030 3030-5800 15-5800
125 64 96
300
1.014-209 209-400 1.014-400
15-3030 3030-5800 15-5800
167 81.7 126
11.5 5.63 8.69
400
1.014-209 209-400 1.014-400
15-3030 3030-5800 15-5800
227 112 172
15.6 7.71 11.8
209-400 209-400 209-400
3030-5800 3030-5800 3030-5800
217 402 502
14.9 27.7 34.6
600 800 875 (IC)
* Bav.
1
-
vg)
=
4.40 6.01
compressibility.
Because of the accuracy with which the injector could be read in runs D and E, the absolute values of the specific
345
gravity should be accurate to 0.002 and the relative values to 0.001 (the atmospheric pressure data upon which the absolute values are based are given as accurate to 0.001). The temperatures are reliable to 1’ F. and the pressure to 1 per cent. The naphthalene did not show any signs of cracking a t the temperatures used (no color produced and no gas produced). The compressibility factors shown in Table I11 should be reliable even in the event that the atmospheric pressure data upon which the absolute values of specific gravity (or density) are based were seriously in error.
Literature Cited (1) International Critical Tables, Vol. 111, p. 30, New York, MoGraw-Hill Book Co.,1928. (2) Russell and Hottel, IND. ENG.CHEM.,30, 183 (1938).
R ~ C I U I VAugust D D 21,1937. Presented as part of the Symposium on Characteristic Properties of Hydrocsrbons and Their Derivatives ae Related t o Structure before the Division of Petroleum Chemistry at the 94th Meeting of the American Chemical Society, Rochester, N. Y.. September 6 to 10. 1937.
Polymerization of Methyl Methacrylate in Organic Solvents D. E. STRAIN E. I. du Pont de Nernours & Company, Inc., Wilmington, Del.
R
ECENT developments have made commercially available a series of resins based on polymethacrylic esters; because of their outstanding properties, these resins are finding a wide variety of industrial applications. Studies of the reactions involved in converting these liquid monomers to resinous polymers afford information which, in supplementing available data, may ultimately lead to a clearer understanding of the nature of polymerization reactions. The polymerization of methacrylic esters is most readily explained by assuming a chain reaction with the production of a linear-type polymer. The activation of a monomer molecule through some agency, such as heat, light, active oxygen, or a combination of them, is thought to be the trigger that initiates the formation of a chain. The activated monomer unites with all other monomer molecules properly encountered while in the active state. The time during which a molecule remains activated is so exceedingly short that the growth of a polymer chain can be considered almost instantaneous. Whatever the size of a polymer molecule when it becomes deactivated, it is thought to remain inactive, in that it will not again enter into polymerization reactions to produce polymers of higher molecular weight. Numerous specific polymerization methods are described in the literature, but those most commonly used fall into the following groups : 1. The monomer is polymerized without solvent or diluent. 2. The monomer is dispersed in a nonsolvent and polymerized. 3. The monomer is dissolved in a solvent and polymerized. The first method involves the various casting technics; the second is typified by emulsion processes. This paper, dealing with methyl methacrylate, discusses certain variations in the third method as they affect the rate of polymeri-
zation and the molecular weight of the resulting polymer.
It is important to distinguish clearly between what is called “rate of polymerization” and the actual rate of chain growth which, as stated above, is thought to be exceedingly rapid and comparatively independent of external conditions. “Rate of polymerization” is used here to express the amount of polymer produced in a given time; this amount is thought to depend largely on the rate of initiation of polymer chains and the molecular weight attained. Minute traces of various impurities have marked effects on polymerization reactions in general; it is thus difficult to obtain consistent results unless very pure materials are used. The methyl methacrylate employed in this work was very pure and uniform, and all solvents used in connection with the monomer were carefully purified. Various factors which influence the polymerization of methyl methacrylate in solution are discussed in the following paragraphs.
Temperature and Catalyst When polymerizations are conducted in solution, the effect of temperature and catalyst concentration is, in general, the same as in massive polymerizations; the higher the temperature the shorter will be the induction period, the more rapid the polymerization, and the lower the molecular weight of the polymer. Benzoyl peroxide, a commonly employed polymerization catalyst for vinyl compounds, acrylates, and methacrylates, is relatively inactive in the dark a t low temperatures. However, at 65” C. as little as 0.1 per cent of this catalyst exerts a marked effect in increasing polymerization rates and reducing the molecular weight of the resulting polymers. When the catalyst concentration is increased by
