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INDUSTRIAL AND ENGINEERING CIIEMISTRY
low volatility (boiling point, 380" C.), is apparently well fitted for use as a fixative in perfumes. The same properties, coupled with good solvent action on cellulose acetate, should make it suitable for use as a plasticizer for cellulose acetate lacquers and molding compositions. The alkyl ethers of hydrogenated cardanoi are stable liquids of high boiling point. The ethyl ether boils at about 365" C, and can be boiled at this temperatllre with no apparent change. This compound may find utility as a substitute for mercury in hi-liqiiid boilers, as well as for geueral heat transfer applications. by the reaction of cardanol &.,,janoxyacetic with chloroacetic acid, may be substituted for a portion of the phthalic anhydride in the preparation of alkyd resins and
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thereby confer greater miscibility with ordinary solvents and greater water resistance on the final resins. These and other uses await further commercial development of this material.
Li terat ure Ci I ed
u.
(I) do, Worth, 8. Pub. I i d t h Servioc, ~ ~ i e l i Lab. a c ~ d i88 . (1913). (2) Peal. K.3 el ai., J . Indian I%*t.SCi.. 5, 152 (1922). (a) Ruhwnenn. 8.. and Skinner, S., J . C h s n . Soo., 51. 663 (1887). smit, A, $, proc,A&. sei, Ama2e7hm, 34, (193,). ( 5 ) spiogei. L.,and correii. M., &r. deut. ees.,23,356-78 (1913). ( 6 ) SPieEcl. 12.. and Dobrin. C..Ibid.. 5, 309-25 (1895). (7) Stncieler. Ann. CAern. u. PFhannacie, 63, 137-64 (1847). Commoroe, 'Round World, No,5 ,
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(1838).
Evaporation Rate of Stoddard Dry Cleaning Solvent CHARLES S. LOWE AND A. C. LLOYD National Association of Dyers and Cleaners, Silver Spring, Md.
Apparatus designed by Thorn and Bowman for determining the evaporation rate of solvents at high temperature by passing a measured volume of air through solvent maintained a t constant temperature has been utilized, in a modified form, to obtain evaporation curws of dry cleaning solvents. The results with this technique correspond to those obtained under conditions similar to plant practice by following the loss in weight of fabrics containing the solvents and suspended in an oven equipped with air circulation. Evaporation rates of commercial dry cleaning solvents vary widely. Distillation curves do not provide adequak information as to evaporation characteristics. The effect of small amonnts of fatty acid and mineral oil residues on evaporation rates is shown to he negligible.
from dieerent refineries have been noted. Whcn the drying period is lengthened to provide adequate time to remove a more slowly evaporating solvent completely, more steam and electricity are required to operate the tumbler or cabinet, more stains are probably set owing to long exposure to the heat, the cleaning cycle is longer, arid production is slowed down. This investigation was undertaken to devise a laboratory test to place such variations on a quantitat.ive hasis, and
T
HE time required for tho complete evaporation of Stoddard dry cleaning solvent from cleaned garments so that no trace of solvent odor remains, is largely governed by the particular solvent being used, and by the temperature and air circulation employed in the drying operation. Under noma1 conditions for deodorizing, exhaust vapors leave the tumbler or drying cabinet at 120-1FO" F., depending on the type of garment, and are accompanied by a rapid flow of air; wide variations in the drying time of Ytoddard solvent
firoun~1. MODIFIED TXOXN-BOWMAN Am*RATUS FOR DETERMINING EYAPORATION RATEOF SOLVENT^ AT H I ~ TEMPERATURES H
~
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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not providing conditions of actual cleaning practice, has been found useful in comparing the relative drying time of cleaning solvents under arbitrarily controlled conditions. I n order to determine whether the results obtained in this way could be considered representative of evaporation rates of solvents from garments, different fabrics were “wet out” with the solvents, extracted lightly by centrifuging, and then
c
O F MODIFIED THORN-BOWMAN FIGURE 2. DIAGRAM
APPAR.4TUS
to determine the effect small residues of fatty acid or mineral oil might have on this property of Stoddard solvent. The determination of evaporation rates of solvents has engaged the attention of lacquer technologists for many years. The method most widely used is to plot curves for loss in weight or vnlume against time elapsed ( I , 3, 6, 6, IO). The techniques followed in obtaining data for these curves have been designed, for the most part, to duplicate conditions existing during the evaporation of solvents from thin coatings a t room temperature into large volumes of air. For the present purpose it is necessary to obtain similar data but under conditions as closely approaching those actually employed in evaporating dry cleaning solvent from garments as possible. Thorn and Bowman (8) described a method ol determining the evaporation rate of solvents a t high temperatures, where air is passed through the liquid sample maintained a t any desired temperature. A plot of the volume of air passed through a t any time against per cent evaporated gives the corresponding evaporation curve. This method, although
TIME IN FIGURE 4.
FIGURE 3. APPARATUSUSED IN OVEN-BALANCE METHOD OF DETERMINING EVAPORATION RATE
suspended from a balance arm in a large constant-temperature oven equipped with air circulation. By following the loss in weight a t time intervals, curves were obtained showing actual evaporation of the solvent from specific fabrics.
Apparatus and Method The apparatus used for determining evaporation rates by passing air through the sample is shown in Figures 1 and 2. Essentially it is the same as that employed by Thorn and Bowman (8)with certain additions :
MINUTES
EVAPOR.4TION C U R V E S O F SOLVENT FROM FABRICS
1
FIGURE 5. REPRODUCIBILITY BY OVEN-BALANCE METHOD AND EFFECT OF CIRCULATION (SOLVENT 1, WOOLCLOTH)
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8"r
'
I
I
I
I
TIME IN MINUTES
LITERS OFAIR FIQURE 6. EVAPORATION CURVESBY BUBBLING AIR SOLVENTS
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THROUGH
A return line, A , direct from condenser t o heating flask, was provided to avoid any cooling effect the condensed liquid might have in flowing past the tube containing the sample. The air supply was held at approximately constant pressure by means of water column B and manometer C; marked variations in barometric pressure were thus eliminated. A thermometer, D, inserted in the vapor chamber, indicated that the temperature variation during the evaporation process was not greater than *0.5' C. Vapor from an azeotropic mixture of 75 mole per cent carbon tetrachloride and 25 mole per cent n-propyl alcohol, boiling a t 72.8" C. (Q), was used as a heating medium. A correction factor t o allow for expansion of the solvent at this temperature and the volume occupied by the capillary was applied t o all volume readings of samples. The rate of air flow was adjusted to 360 ml. per minute, although variations in this factor are not critical, as Thorn and Bowman (8) stated. Simultaneous readings on wet test meter E and on conical sample tube F were taken at intervals. Milliliters of solvent remaining from an original 100-ml. sample were plotted as a function of liters of air (corrected to 0 ' C. and 760 mm. pressure) bubbled through the solvent. In following the evaporation from fabrics, an analytical balance was placed over a vent on top of a drying oven with inside dimensions of 24 X 24 X 26 inches (61 X 61 X 66 cm.), Figure 3. A hole was drilled through the base of the balance and a cloth sample, approximately 6 X 6 inches (15.2 X 15.2 em.) in the case of wool, was suspended from one arm of the balance by a light copper wire. For the lighter fabrics such as pure silk and regenerated cellulose rayon, larger samples were used, approximately 12 X 16 inches (30.5 X 40.6 cm.) in size. Seams were made on the upper and lower edges of the samples from which small-gage aluminum wires protruded. When set between upright rods, these wires served to prevent the suspended samples from swinming excessively from the air circulation. Temperature was herd at 38" C., just below the flash point of the solvents. The cloth sample was dipped in the solvent t o be tested, extracted for 1 minute in a small garment centrifuge, and hung in the oven as quickly as possible. Weighings t o the nearest milligram were made every 2 minutes. Results were plotted with loss in weight as a function of time. Distillation curves for the solvents studied were obtained by the method outlined in Commercial Standard CS3-38 (9).
Accuracy of Method The method and apparatus described for determining evaporation rates of dry cleaning solvents by bubbling air through them have been used in this laboratory for over two years. During this time a large number of solvents have been tested, and consistent and reproducible results have been obtained. The maximum deviation in volume of air required t o evaporate a definite volume of solvent has never been over 2 per cent.
FIGURE 7. EVAPORATION CURVES BY BALANCE
THE
METHOD ON WOOL CLOTH
OVEN-
Figure 4 shows evaporation curves of dry cleaning solvent from various fabrics of ordinary construction and weight, considered typical of the garments made from those fibers that the dry cleaner handles. Pure silk, regenerated cellulose rayon, and cellulose acetate rayon fabrics are similar in their evaporation characteristics, whereas the solvent evaporates more slowly from cotton and is retained longest on wool fabrics. For this reason a wool cloth was selected for following evaporation of the solvent by the oven-balance method. The technique of following the evaporation of a volatile solvent from a cloth is not so accurate as the air evaporation method of obtaining evaporation rates since weighings must be made rapidly. However the same relative results are obtained in less than a n hour as compared with 16 to 20 hours by the latter method. The reproducibility which may be expected and the effect of the air circulation used on the evaporation rate, as determined by the oven-balance method, are shown in Figure 5 .
Discussion of Results Figure 6 shows evaporation curves obtained by bubbling air through samples of five different dry cleaning solvents which are now commercially available and conform to Stoddard specifications (2). The wide variation in the time required to evaporate the samples completely under identical conditions is evident. Thus solvent 3 requires almost twice as long for complete evaporation as does solvent 2. That the same results are obtained under conditions more nearly approaching plant practice is shown in Figure 7 . I n this instance solvent 3 required 40 minutes for complete evaporation whereas solvent 2 was completely evaporated in 20 minutes. A difference in the rate of evaporation of these solvents might be expected from the distillation curves for the solvents (Figure 8). Thus we might expect solvent 3 to evaporate more slowly than solvent 2 from the respective positions of the curves and the difference in end points. However, on the basis of the distillation curves alone, we would not predict that one solvent would evaporate twice as fast as the other. Also the relative positions of curves and end points of solvents 3 and 1 and the fact that they required 40 and 30 minutes, respectively, for complete evaporation indicate that either the first part of the distillation range is of primary importance or that other factors such as the type of hydrocar-
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FIGURE 8 (Top). DISTILLATION CURVES FIGURE 9 (Center). EFFECTOF 2 PER CENT OLEICACID AND 2 PER CENT MINERAL OIL ON EVAPORATION RATE BY BUBBLING AIR THROUGH SOLVENT 6 FIGURE10 (Bottom). EFFECTOF 2 PER CENT OLEIC ACIDAND 2 PERCENTMINERAL OIL ON EVAPORATION RATE BY THE OVEN-BALANCE METHOD (SOLVENT 6, WOOLCLOTH)
TEMPERATURE 'F.
bons present affect the evaporation rate considerably. Wetlaufer and Gregor (9) showed that for solvents having distinctly different chemical compositions, distillation curves may not occur in the same order as evaporation curves, even within rather wide limits. These investigators also noted instances where petroleum naphthas, used in formulating quick-drying enamels, had low distillation end points but evaporated much more slowly than naphthas with high distillation end points. Although distillation curves may permit a gross estimate of the length of time required for evaporation, they do not furnish a complete picture with quantitative comparisons and may be misleading. After dry cleaning solvents have been used for some time without adequate clarification, residues of mineral oils and fatty acids tend to build up (7). Figures 9 and 10 show evaporation curves for dry cleaning solvent containing 2 per cent by volume of both oleic acid and mineral oil. Both techniques of determining evaporation rates point to a slightly longer time for complete evaporation in each case, as would be expected. Although the percentages of fatty acid and mineral oil used in these tests may be considered excessive as compared with the average condition of dry cleaning solvent in plant use, the increase in time required for complete deodorization, as shown by these methods of testing, has been found insignificant.
Literature Cited
LITERS OF AIR
TIME IN MINUTES
(1) Bent and Wik. IND.ENO.CHEY.,28, 312 (1936). (2) Bur. Standards, Stoddard Solvent, Commercial Standard CS3-38 (1938). (3) Hofmann, IND.ENG.CHEM.,24, 135-40 (1932). (4) International Critical Tables, Vol. 111, p. 318, New York, McGraw-Hill Book Co. (5) Lowell, IND.ENO.CHEM.,Anal. Ed., 7, 290 (1935). (6) Rubek and Dahl, Ibid., 6, 421 (19341. (7) Smith, Lowe, and Fulton, IND. ENG.CHEM.,32, 464 (1940). (8) Thorn and Bowman, Ibid., Anal. Ed., 8, 432 (1936). (9) Wetlaufer and Gregor, Zbid., 7, 290 (1935). (10) Wilson and Worster, IXD.ENQ.CHEM.,21, 592 (1929).
