Change in Solvency during Evaporation of Thinners E. H. MCARDLE, Standard Oil Development Company, Elizabeth, N. J. boiling materials, such as mineral spirits, are evaporated from pools in sufficient quantity for sampling during the progress of the evaporation, too much time is required. Further, it seems reasonable that evaporation as a film should more nearly simulate actual conditions than evaporation from a pool, in some cases inches deep. During the setting and drying of a protective coating film the effect of solvent retention occurs. Dorsch and Stewart (3)
A .rapid film evaporator for “mineral spirits” and related naphthas permits the measurement of change in solvency of hydrocarbon thinner blends as 100 ml. are evaporated in the form of a film during less than 3 hours at room temperature.
0
LEORESIKOUS protective coatings are frequently cut hot with a high-solvency naphtha and later thinned with a material of considerably lower solvency-e. g., “mineral spirits.” When a difficultly soluble resin forms a part of the coating, it is important that solvency should not fall away too rapidly during application and setting. Maintenance of solvency during evaporation also makes possible a better leveling of the film and generally improves the physical characteristics of the coating. An apparatus has been devised wherein 100 ml. of a thinner or a mixture of thinners, which boil within or near the mineral spirits boiling range, can be evaporated in less than 3 hours, at room temperature, and as a film. Characteristics of the evaporation differ from those accompanying actual coating application in two respects-viz., the film is in motion, and no nonvolatile component is present. A number of evaporation methods whereby changes in solvency during evaporation can be determined have been described ( I , 4, 6-8). Most were designed to deal with lacquer thinners, and have provided for evaporation and sampling from pools of liquid contained in a beaker, paintcan cover, or crystallizing dish. When comparatively high-
FIGURE2. APPARATUS have shown that the retention of hydrocarbons by nitrocellulose fdms differs from retention of esters and alcohols of the same evaporation rate. For most oleoresinous and synthetic resinous coatings, however, hydrocarbons alone are employed as thinners, and thus the error introduced by the total absence of nonvolatile vehicle may be assumed to be fairly constant and of lower magnitude in the case of mineral spirits than with lacquer volatiles.
FIGURE 1. SOLVENT FILMEVAPORATOR 450
ANALYTICAL EDITION
AUGUST 15, 1939
451
Estimation of Solvency A convenient method of determining solvency as the thinner evaporates is t o abstract small samples (1 ml.) after one half, three quarters, and seven eighths are off, and take the aniline points. Aniline point is so generally accepted as a measure of solvency of a hydrocarbon thinner of a given boiling range that several large producers and consumers of naphthas use it as a specification solvency test. It requires neither temperature control nor costly equipment. To abstract three I-ml. samples, and yet not greatly upset the composition of the fractions, it is desirable to evaporate 100 ml. of naphtha. Since most oleoresinous or resinous coatings retain considerable thinner after reaching their set point (d), no measurements of a residual portion less than one eighth were taken.
Precision of Method The precision attainable in the apparatus was originally tested by making two runs with the same thinner mixture under different conditions. Run 1 was made with 200 ml. during 207 minutes for seven eighths evaporated, and in a steam-heated room without other temperature or humidity control. Run 2, and subsequent runs detailed below, were made with 100 ml., in about half the time (112 minutes for seven eighths evaporated in run 2), in a room maintained a t 25' C. and 50 per cent relative humidity. That time and temperature, within fairly narrow limits, were not factors affecting the operation of the apparatus is indicated in Table I. Thinner mixture, of 31.4' C. aniline point, was blended from two volumes of Stoddard solvent and one volume of No. 2 aromatic naphtha (Table 111). The rate of evaporation is not considered. The method is limited to the determination of change in solvency during evaporation at a speed of the same order of magnitude as that encountered in the setting of oleoresinous varnishes and enamels.
Run 1 Run 2
Last Quarter
Last Eighth
c.
c.
c.
47.2 47.6
55.5 55.8
61 .O 61.0
O
FIGURE 3
TABLE 11. ANILINEPOINTS Thinner or Blend
Original
c.
Stoddard solvent Varnish spirits Stoddard solvent 4 volumes No. 1 naphtha: 3 volumes Stoddard solvent 4 volumes No. 3 naphtha '2 volumes Stoddard solvend, 4 volumes No. 2 naphtha 1.6 volumes Nq.3 naphthi,0.4volume Varnish spirits 4 volumes No. 2 naphth;, 0.5 volume No.3naphtha,0.5volume
Apparatus It may be found convenient t o modify the apparatus (Figures 1 and 2), but the present setup is quickly assembled, sufficiently rapid for most purposes, and automatic. The small glass-sealed air jet may be replaced by a Neoprene-connected T-tube arrangement. The funnel need not necessarily be of glass, although liquid level reading is thus facilitated. The flared overhead discharge tube should be large enough, and close enough to the watch glass, t o prevent spattering as the bubbles break. The fan should be
58.0 44.0
Last Half O
c.
61.3 50.4
Last Quarter
Last Eighth
64.2 54.0
66.0 57.2
c.
c.
31.6
42.0
48.9
53.7
34.0
32.6
33.3
35.1
32.4
44.0
49.0
52.2
31.4
37.9
41.1
43.2
TABLE 111. INSPECTIONS Stodd& Solvent Gravity a A: P. I. specific 'gravity Initial boilingpoint, C. off
g%
E%
50% Dry point
49.4
0.782 155 162 163 172 192 201 208 210 41
Varnish Spirits 45.6 0.799 154 159 161 170 185 191 202 202 41
Aromatic Naphths No. 2 No, 3 35.9 33.6 29.8 0.845 0.857 0.877 133 131 175 142 137 178 143 139 180 152 147 186 171 163 197 177 169 202 183 176 210 184 177 210 28 28.0 29 17.6 22.4 55
No. 1
Finalboilingpoint C. Tag o1osed:oup fla;hhb O Mixed aniline point, C. Aromatics,b % 73.5 91.8 89.2 0 A control test now run in several laboratories, measuring the critical solution temperature of a mixture of 10 ml. of anhydrous andine, 5 ml. of sample, and 5 ,ml. of any naphtha whose aniline point is 60' C. b As determined by method of Philadelphia Paint and Varnish Production Club (6).
C,. . . .
...
TABLE I. ANILINEPOINTS Last Half
PERCENT EVAPORATED
... ...
of such power and distance from the apparatus (20 cm. in the present instance) that no droplets of liquid are carried away. An air current which requires only a 2" or 3' tilt of the watch glass toward the fan for equal film distribution over the surface appears to be satisfactory. The lower speed of a conventional rubberbladed automobile defrosting fan is used in this laboratory. Air current should be directed underneath the watch glass, to scavenge vapors inside the funnel, as well as above. The funnel is graduated, with the fan shut off, while the air lift is in operation. Liquid holdup of the apparatus as shown amounts to 9.5 ml.
452
INDUSTRIAL AND EKGINEERING CHEMISTRY
Opera tion Air from the laboratory line is admitted before the 100 nil. of thinner are poured into the funnel. The air lift is regulated, conveniently with the aid of a constant-pressure by-pass, to supply a smooth, equally distributed flow of bubbles. After the first three quarters of the thinner have evaporated it may be necessary to increase the air slightly, owing to loss of liquid head. When the 50-ml., 25-ml., etc., marks have been reached, a few milliliters are run out into a small beaker and 1 ml. is pipetted into a test tube which is corked tightly. The remainder is poured back into the funnel at once. Aniline points, using equal volumes of thinner sample and anhydrous aniline, were taken at the end of each run and read to 8.1"C. with the same thermometer. Fractional Solvencies Table I1 lists solvencies of fractions remaining from the evaporation of two typical mineral spirits, and of several
VOL. 11, NO. 8
blends of these with commercial high-solvency naphthas. The solvency corresponding to an aniline point of about 32" C. was taken as typical of that of the total thinner present in many current industrial oleoresinous finishes. Figure 3 illustrates the changes in solvencies. Table I11 shows pertinent inspections of the commercial thinners used.
Literature Cited (1) Bent, F. A, and Wik, 5.N., IND.ENG.CHEW,28, 312 (1936). (2) Bogin, C., and Wampner, H. L., Ibid., 29, 1012 (1937). (3) Dorsch, J. B., and Stewart, J. K., Ibid., 30, 325 (1938). (4) Lowell, J. H., Ibid., Anal. Ed., 7, 278 (1935). (5) MoArdle, E. H., Moore, J. C., Terrell, H. D., Haines, E. C., et al., Ibid., 11, 248 (1939). (6) Metzinger, E. F., Paint, Oil Chem. Reu., 99, No. IO, 9 (May, 1937). (7) Rubek, D. D., and Dahl, D.W., I N D . ENG.CHEM.,Anal, Ed., 6, 421 (1934). (8) Stewart, J. K., Dorsch, J. B., and Hopper, C. B., IND. Exc. CHEM.,29, 899 (1937).
A New Style of Chemical Heater W. MASTER, Consolidated Edison Company New York, Inc., Brooklyn, N. Y.
A
of
KEW style of electric heater, developed several years ago by the Research Bureau of the Consolidated Edisoii
Company, has proved very satisfactory in severe chemical laboratory service. It may be used as an ordinary hot plate or as an "air bath" when provided with a removable heat-reflecting jacket. In the latter form, shown in the photograph,
it is a n excellent substitute for water, oil, or glycerol baths with the added advantage of eliminating liquids. Under ordinary conditions the air-bath temperature may be maintained within a few degrees by means of a rheostat, transformer, or thermostat. I n a draft-free location or by the use of a double jacket, regulation within a fraction of a degree is possible. It is exceptionally rugged and to date no trouble has been experienced from corrosion so frequently encountered in chemical heaters. Various sizes may be made using stock heating units. The diagram shows the construction of a good general-purpose heater built around a 500-watt Chromalox A-20 ring unit. This type of unit is inherently resistant to corrosion and is further protected from spilled chemicals by the lip around the bottom of the casting and the transite clamping plate which holds it in intimate contact with the casting. Prongs of nickel silver are substituted for the wire-holding nuts on the unit, care being taken not to disturb the nuts next to the sheath. The holding rod is 18-8 stainless steel 0.5 inch in diameter and the jacket is anodized 25 aluminum alloy tubing of 4-inch diameter.
