INDUSTRIAL AND ENGINEERING CHEMISTRY
762
I n Table V heat capacities as calculated for mono- and dimethylamines are compared with experimental values as reported by Felsing and Jessen (6). The largest deviation is about 7 per cent, but use of the higher frequencies for nitrogen bonds as given in Raman data, instead of the carbon bonding frequencies, would increase this error. This method of calculation was not expected to give very good results for ammonia, but as the values in Table V show, the differences from accepted values are less than 5 per cent. OF NITROGEN COMPOUNDS TABLEV. HEATCAPACITIES
C p , cal./(mol.)(o X.) Temp., C. Exptl. Calcd. 12.90 12.3 25 50 13.W 12.9 16.65 16.7 Dimethylamine 25 50 18.70 17.8 Ammonia 23 8.46 8.3 123 9.26 9.2 223 10.06 10.1 323 10.7b 11.0 423 11.36 11.9 0 Ex erirnental values from Felsing and Jessrr. ( 6 ) . b C a h a t e d from equations given by Bryant (3;.
Compound Monomethylamine
Almost no gaseous heat capacity data are available for any organic compounds of sulfw, and therefore it was not possible to obtain much of an experimental check on the frequencies assumed for sulfur bondings. However, these frequencies were chosen in the same manner as those for halogens and
Vol. 33, No. 6
should be of comparable accuracy. The one heat capacity value found for an organic sulfur compound (that for diethyl sulfide, 9) agreed within 2 per cent with the calculated value. The calculated heat capacity is 35.5 calories/(mol.) (” K.) and the experimental value, 36.2 calories for the range 120-223’ C. Literature Cited (1) Bennewitz and Rosaner, Z . physik. Chem., 39B, 126 (1938). ENG.CHEM.,31, 912 (1939). (2) Benning and McHarness, IND. (3) Bryant, Ibid., 25, 820 (1933). (4) Eucken and Parts, Z . physik. Chem., ZOB, 184 (1933). (5) Felsing and Jessen, J . Am. Chem. SOC.,55, 4418 (1933). ENG.CEEN.,30,1029 (1938). (6) Fugassi and Rudy, IND. (7) Glockler et al., J . Chem. Phys., 7, 278, 382, 669, 970 (1939); 8, 291 (1940).
(8) Hibben, “Raman Effect and Its Chemical Applications”, A. C. S. Monograph 80, New York, Reinhold Pub. Corp.,1939. (9) International Critical Tables, Vol. V, p. 80, New York, MoGrawHill Book Company, 1929. (10) Kemp and Pitzer, J . Am. Chem. Soc., 59, 276 (1937). (11) Kistiakowsky and Rice, J . Chem. Phys., 7 , 281 (1939). (12) Landolt-Bornatein, Physikalisoh-chemisohe Tabellen, Vol. 11, p. 1252, Berlin, Julius Springer, 1936. (13) Partington and Shilling, “Specific Heats of Gases”, p 40, New York, D. Van Nostrand Company, 1924. (14) Pitzer, J . Chem. Phys., 5 , 4 7 3 (1937). (15) Sage, Webster, and Laoey, IND.ENG.CHPM.,29, 1309 (1937) (16) Stevenson and Beach, J. Chem. Phys., 7, 25 (1939). (17) Teller and Topley, J . Chem. Soc., 1 9 3 5 , 8 8 5 . (18) Vold, J . Am. Chem. Soc., 57,1192 (1935). from a thesis presented in June, 1940, t o the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of master of science. The work was performed under the direotion of E. F. Farnau of the chemioal engineering faculty. .4BsTRAoTmD
Reclamation of Stoddard Dry J
Cleaning Solvent CHARLES S. LOWE AND ADRIAN C. SMITH’ National Association of Dyers and Cleaners, Silver Spring, Md.
FTER repeated use dry cleaning solvent becomes con-
A
taminated with dirt, fatty substances from perspiration and soap residues, grease, and oils of various kinds. The insoluble soil consists of suspended matter such as lint, grit, sand, dust, and water; the soluble impurities are usually of an organic nature, consisting of mineral oils, fatty acids, wool grease, unsaponified fats, dyes, and to some extent various chemicals used in removing stains. The color of the originally clear solvent, even though no soap or cleaning aid is employed and no dyestuff is removed from the garments, passes through shades of light yellow to dark reddish brown as the poundage of clothes cleaned inoreases. Peroxides, derived from the solvent itself by the action of light and from oleic acid (the principal fatty acid constituent of dry cleaning soaps), decompose and yield aldehydes, ketones, and lowmolecular-weight acids. Small amounts of such solvent re1 Present address, Pennsylvania Salt Manufacturing Company, Philadelphia, Penna.
The adsorptive properties of activated carbon, magnesium silicate, and activated fuller’s earths toward fatty acids and substances associated with rancidity in dry cleaning solvent have been studied in laboratory and plant tests. Alkali absorption and mineral acid theories of dry cleaning soap decomposition are presented to account for excessive accumulation of fatty acids in Stoddard dry cleaning solvent above that derived from the garments themselves. The effect of soap on the adsorptive capacity of a powder is pointed out. maining in the cleaned garments develop unpleasant rancid odors. Eventually the solvent becomes so polluted as t o be unfit for further application as a cleaning medium. Before this condition is reached, it is necessary to clarify the solvent by alkali treatment, by pressure filtration with adsorbing powders, by vacuum distillation, or by a combination of these methods. It is generally held that distillation will yield the purest solvent, removing insoluble soil and all mineral oils, grease, and fatty acid residues having boiling ranges over 410’ F. which is the end point of Stoddard solvent.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
763
earth. The initial charge amounts to 5-7 pounds of powder for each 100 square feet of filterin area. Additional powder is added with each load of soiled clothes cleaned. Recently developed activated fuller's earths and synthetic adsorbents have been recommended for removing soluble fatty acids, which often lead to odor trouble, in addition to acting as a filtering medium for insoluble soil. These materials are added directly in the washer with the garments, as is filter powder, and are subsequently removed on the pressure filter. Distillation, as ordinarily carried out by the cleaners, is accomplished a t 30 to 40 pounds per square inch steam pressure and 26 to 28 inches of vacuum. A tra is provided to allow water to settle out and the sogent is then passed through revi ousiy dam ened cotton rags which serve to a t s o r i droplets oPmoisture and light particles of suspended matter that may have been entrained in the vapor.
Laboratory Tests
FIGURE 1. PILOPPLANT MODEL STILL
Alkali treatment in conjunction with a pressure filter removes fatty acids and insoluble soil but does not touch unsaponifiable matter such as mineral oil or grease. The purpose of this investigation has been to determine whether Stoddard dry cleaning solvent can be kept in a suitable operating condition b y use of adsorbing powders and pressure a t r a t i o n without recourse to distillation or alkali treatment. The study has involved laboratory tests to give a comparison of the efficiency of removal of fatty acids and odorous impurities by different adsorption powders now on the market, and b y alkali and distillation treatments, as well as the cleaning of over 12,000 pounds of clothes at the association's cleaning plant under controlled conditions.
Methods of Reclamation Agitation with a 10 to 15 BB. solution of sodium hydroxide in the ratio of 5 gallons of alkali solution to each 100-gallon capacity of the clarifyin tank converts animal and vegetable fatty acids from solvent-sofuble com ounds into water-soluble soaps which settle to the bottom of &e tank. Activated carbon, always used in con unction with alkali treatment, tends to remove color- and odor-forming compounds by adsorption. A layer of soapy soil forms on top of the alklai charge, providing a filtering medium for retaining the lighter particles of insoluble soil. The solvent is finally given a water wash and passed through cotton filter bags to remove particles of suspended matter and traces of moisture. Pressure filtration is carried out by forcing the solvent through a close1 woven cotton ba or metal screen covered with a finemesh done1 metal wire. %his is a continuous process, a rate of flow of 30 to 35 gallons per hour per square foot of filtering area having been found most satisfactory. Whether a cotton bag or metal screen is employed, the openings become packed with the larger soil particles, and the flow of solvent is stopped unless the retaining medium is coated with a filter aid such as diatomaceous
Preliminary work with contaminated solvents indicated that two types of impurities would have to be considered-those resulting from changes in the solvent itself by the action of light, and those derived from the breakdown of oleic acid through peroxide formation. Rancid solvent of the first type was repared by exposing new solvent in an unstopperef bottle to atmospheric conditions over a period of 3 weeks. A t the end of this time the originally clear and sweet solvent was brownish yellow in color and had a marked rancid odor. Solvent containing impurities of the second t pe was repared by dissolvin a technical ade o?oleic a d , through which air ha8 been bubblerfor several days, in new solvent. Portions (200 ml.) of the solvents thus prepared were placed in pint jars with accurately wei hed amounts of adsorbent, and thorou hly agitatef for 3 hours on a shaking machine mafing 420 to 430 2.5-inch strokea per minute. They were then allowed to stand overnight to reach equilibrium before filtering and examination. Four commercially available adsorbing powders representing two different brands of activated Florida-Georgia fuller's earth, a dry cleaner's grade of activated carbon, and synthetic ma esium silicate were investigated. The amount of acid removed E m solvent originally containing approximately 0.5 and 1 per cent oleic acid, respectively, with increasing concentrations of adsorbent was determined, as was the amount removed by a 1 per cent concentration of adsorbent from solvent containing varying amounts of fatty acid. Distillation was carried out in a small model still (Figure 1) a t 100 mm. pressure, the distillate coming over a t 225' to 250' F. Alkali treatment consisted of thoroughly mixing 250-ml. portions of the solvents with 50 ml. of 10 per cent sodium hydroxide, allowing to settle, decantin and filtering. Tests and observations inauded: determination of acid number (mg. potassium hydroxide per gram of sample); determination of peroxide content by titrating iodine liberated in the presence of glacial acetic acid with thiosulfate; Schiff rea ent test for aldehydes; modified Kreis test for epihydrin Jdehyde (g); observation of color and turbidity of solvent; estimation of odor remaining on desized and chloroform-extracted cotton cloths after wettin out with the solvents and d ing at 140" F.; in the case of pfant tests, determination of resirue remaining from a 100-ml. sample after evaporating to constant weight on a steam bath.
Plant Tests A 36-inch diameter, grounded, wooden cylinder washer, 54 inches long with reversing drive and rated capacity of 75 pounds of garments, was used for all plant runs with adsorption powders (Figure 2). This was connected with a 3000-gallon-per-hour filter having a capacity of 115 gallons and a total Monel metal screen filtering area of 85 square feet. The washer and connectin lines when filled to the normal o erating level establishedfor these test runs held 103 gallons ofsolvent. I n testing activated carbon, to eliminate the ossibility of this coming in contact with the clothes a n z t o ensure better a d 8 of the filter aid used with the carbon, a by-pass was installed so that the solvent could be continuously circulated on the filter without enterin the washer. The filter was thorou hly cleaned out after compkting each series of runs with the &fferent adsorbent owdem tested, and the screens were steamed. The washer, storage tanks, and extractor employed for this work
dter,
~
~
~
~
764
INDUSTRIAL AND ENGINEERING CHEMISTRY
constituted a complete system entirely separate and distinct from any other operating units in the plant. No work other than that set aside for these experimental runs was cleaned in this system during the course of the investigation. Only wool garments were cleaned in this series of test runs since they make u the lar er part of the volume of work handled 8y the cfeaner and were more readily obtainable. I t is customary t o use more soap with silk garments than with wool, since traces of dirt remaining on light-colored silk garments are more noticeable than on dark wools. Therefore two series of runs were carried out: in one, 3 pints of soap were used to a load, representin the amount of soap for silks, in the other, onqy 0.5 pint of soap to a load, which is customary with wool garments. By this procedure it was possible t o determine, under plant conditions, whether an undesirable condition of the solvent was related to the amount of soap used. A widely used commercial ammonium soap, containing roughly 19 per cent soap, 8 per cent free fatty acid (calculated as oleic acid), 67 per cent Stoddard solvent, and 15 per cent water, was utilized on all plant runs during which adsorption tests were carried out.
TABLE I. REMOVAL O F IhlPURITIEs FROU STODDARD DRYCLEANINQ SOLVENT BY ADSORPTIOX, ALKALI, AND DISTILLATION TRE.4TMENTs Treatment Original solvent Magnesium silicate Activated carbon Activated fuller’s earth No. 1 No. 2 Distillation Alkali Original solvent Magnesium silicate Activated carbon Activated fuller’s earth No. 1 No. 2 Distillation Alkali a Blank, 0.1 m!.
Comparative Efficiency of Methods The data in Table I show the effect of treatment with 3 per cent by weight of various adsorbing agents, alkali treatment and vacuum distillation on color, odor, and impurities found in solvent containing rancid oleic acid and in solvent exposed to light. Hydrocarbon peroxides formed by the action of light are difficult to remove completely by any of these treatments. Distillation appears to give the best removal, followed closely by activated carbon. For fatty acid peroxides the case is somewhat different, distillation, alkali, or magnesium silicate being equally effective. Activated carbon did not remove this type of peroxide so effectively as the hydrocarbon peroxides. Alkali treatment completely neutralizes all acids present, as would be expected. Distillation is very effective in remov-
FIGURE 2.
Vol. 33, No. 6
TvASHER AND F I L r E R
Peroxides o Aldehydes (AIL 0.058’N Acid (Schiff NaZStOa) Number Reagent) Odor Solvent Exposed t o Light 19.5 0.197 Trace Bad 8.0 4.0
0.000 0.000
Neg. Traoe
14.9 0.041 Neg. 10.0 0.066 Trace 2.7 0.180 Present 7.4 0.000 Trace Solvent Containing Rancid Oleio 1.2 2.21 Present 0.1 1.15 Neg. 0.8 0.999 Present 1.2 0.4 0.2 0.2
1.47 1.80 0.115 0.000
Present Neg. Present Neg.
Slight Slight
Color Brownish yellow Clear Clear
Bad Bad Bad Bad Acid Rancid Sweet Sweet
Pale yellow Faint yellow Slight Pale yellow
Slight Sweet Bad Sweet
Cloudy Clear Clear Clear
Cloudy Clear Clear
Kreis Test
, , .
...
... ...
.., ...
... POS.
Neg. Neg. Pas. Pas. POS.
Xeg.
ing acidity due to fatty acids. Of the adsorbents studied under these conditions, activated carbon is the most effective in removing acids, followed closely by magnesium silicate. Distillation showed a tendency t o produce aldehydes in the solvent containing hydrocarbon peroxides and did not remove those present in the solvent containing rancid fatty acid. A positive Kreis test with the latter distilled solvent showed that epihydrin aldehyde was not removed. Activated carbon did not remove aldehydes from solvent containing rancid fatty acids, but they were removed by magnesium silicate. The brownish-yellow color of the solvent exposed to light was completely removed by activated carbon and magnesium silicate, but not entirely by distillation. The same adsorbents improved the odor while distillation and alkali treatment had no effect. The rancid odor of oleic acid was removed by all adsorbents and by alkali, but not by distillation. The odor noted after distillation was not that of a rancid fatty acid but resembled odors resulting from the decomposition of the solvent itself. The amount of fatty acid removed (measured by the difference in titration of 50-ml. samples with 0.057 N alcoholic potassium hydroxide) by treatment with various concentrations of adsorbent powders is shown in Figure 3. Two different concentrations of rancid oleic acid in solvent, 0.5 and 1 per cent, respectively, were employed. AU of the powders tested removed slightly more acid from the more concentrated solution. The decreasing order of efficiency of removal is as follows: activated carbon, magnesium silicate, activated fuller’s earth No. 1, and activated fuller’s earth No. 2. Figure 4 shows the results obtained with 1 per cent by weight of the four adsorbents in Stoddard solvent of varying acid concentration. The greater adsorption capacity of activated carbon and of magnesium silicate is again apparent. These adsorbents follow the exponential adsorption equation:
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1941
766
x / m = kc”n
where k, l/n = constants x/m = amount of solute adsorbed by 1 gram of adsorbent c = concentration of solute in solution
T A B L11 ~. ACIDAND RESID^ ACCUMULATION IN EXPERIMENTAL PLANT TESTSWITEI ADSORPTION POWDERS Total No. of Loads
Adsorbent
Figure 5 shows that the logarithmic plots, log x / m = log k
+ l/n log c
for activated carbon and magnesium silicate, respectively, are approximately straight lines with the slopes l/n = 0.35 and 0.39 intercepting the log x / m axis a t log k close t o -0.53 and -0.78. The shape of these curves shows that, for a given weight of powder, a greater percentage of the total amount of acid present will be removed, the greater the dilution. By comparing the amount adsorbed with the corresponding equilibrium concentration, it is noted that for small values of c this ratio is more favorable to the amount adsorbed.
Efficiency of Powders during Plant Tests
Garments Total Cleaned, Powder, Lb. Lb.
Final Final Acid Residue No. C./lOO GI.
3 Pints of Soap per Load
Aotivated fuller’s earth No. 1 Magneaium silicate Nonaotive filter aid Aotivated no mo ti^^ carbon filter *id} Aotivated fuller’s earthNo. 2 Filter aid
1
20 20 20 20
1353.25 1326.75 1406.25 1306.50
20
1234.75
112 108 57
{it) {$I
0.663 0.524 1.001 0.736
0,3683 0.3662 0.6187 0.4802
0.802
0.5394
0.317 0.298 0.347
0.4568
0.6 Pint of Soap per Load
Aotivated fuller’s earth No. 1. Nonaotive filter aid Magnesium silicate
71
I
I
39 10 37
2649.75 745.75 2620.00
1
i
123 32 83
I
1
I
I
I
I
....
0.6760
1
Laboratory tests were followed by experimental plant runs. I n addition t o series of runs with the four adsorbent agents studied in the laboratory, a nonactivated dry cleaner’s grade of diatomaceous earth having no adsorptive action was used on one series for purposes of comparison. Three pints of soap were used on each load cleaned in these series. Figure 6 gives the acid build up as a function of the number of
---FILLER’S 13.51 --.-ACTIVATED
EARTH N 0 . 2 CARBON .---.-MAGNESIUM SILICATE
ov 0
1
3
I
6
I
I
9 12 15 IS 21 ACID REMAINING f ML. 0.057 N KOH I
24
27
FIGURE 4. FATTY ACID R~MOVBD BY ONE PERCENT ADSORBENT FROM SOLVBNT OB VARYING ACIDCONCENTRATION
PER CENT ADSORBENT BY WEIGHT
ACIDRDMOVED BY INFIGURE 3. FATTY CREASING AMOUNTSOF ADSORBENT
pounds of garments cleaned. Figure 7 gives similar data for series with three of the powders during which only 0.5 pint of soap was added with each load. The marked increase in acid accumulation when the larger amount of soap was used is elearly evident. Table I1 lists the total amount of powder used, total poundage of clothes cleaned, final acid number, and final residue. With respect to fatty acid removal the powders rank in the same order as determined from laboratory tests, with the
exception of activated carbon. This exception was due to the fact that a much smaller concentration of the carbon powder was used during the plant runs than in laboratory tests -4.14per cent by weight as compared with 1 per cent. This concentration represents 2 pounds of powder per load cleaned. After the carbon particles become embedded in the layer of filter aid on the screens, their adsorptive action is greatly diminished. The effective concentration must therefore be based only on powder in intimate contact with the solvent and not on the total accumulated powder additions. The high cost of this material would prohibit, from a practical standpoint, a greater charge than 2 pounds per load. It should also be pointed out that the order of efficiency for fatty acid removal of the other powders is given on a pound basis and does not involve the cost factor. Determination of peroxide content on samples from the last run of each series and from intermediate runs indicated this quantity to be negligible in all cases. Tests for aldehydes and odors remaining on conditioned cotton cloths as well as the Kreis test were negative. The results of these tests indicated that, under these conditions, products associated with rancidity had not formed, since negative tests were also obtained on samples from the series using a nonactivated filter aid. The color of the solvent was found to depend to a great extent on small amounts of dyestuffs removed from the garments and could not be correlated with poor cleaning or the
INDUSTRIAL AND ENGINEERING CHEMISTRY
766
-1.6
-14
-12
-1.0
-OB
-06
o to2 -12 LOG c ( 0 /ZOO M L I
-0.4 -02
-1.0
-a6
-0.8
-0.4
-0.2
o
Vol. 33, No. 6
to.2
+04 +ob
FIGURE 5. LOGARITHMIC PLOTOF EXPONENTIAL EQUATION APPLIED TO ACTIVATED CARBON (left) AND TO MAGNESIUM SILICATE (right)
acid content. After long usage the solvent always takes on a yellow to reddish-brown color. On the other hand, one garment out of a single load may lose sufficient dyestuff to give an originally clear solvent a pink or bluish-green cast, as the case may be, and thus invalidate a color test as an index to the condition of the solvent. At present the only suitable criteria for judging the condition of Stoddard dry cleaning solvent quantitatively are the acid content, representing potential rancidity, and the amount of residue left on evaporation. Although from the information now available, it is impossible to set any definite limits above which a solvent may be considered unfit for further use, the smaller these quantities are, the less chance there is for development of odor trouble or grease swales on the garments. It is generally held among progressive cleaners today that an acid number of 0.3 or a residue of 0.5 per cent represent control points which, if exceeded, may lead to odor trouble or poor cleaning.
Source of Fatty Acid Accumulations Since the acid content of the solvent plays such an important role in determining the condition of the solvent, further experiments were made t o ascertain its nature and relationship to the soap used. The average increase in acid number per load when 3 pints of soap and a nonadsorbing powder were used was 0.050. Soap runs carried out with the same amount of soap but without attempting to clean any garments gave an average acid number increase of only 0.012. A load of wool garments weighing 67 pounds was cleaned without any soap, and the acid number increased 0.024. These facts would indicate that acids from the garments contributed more t o the total acid build up per load than the soap, but the combined increase from the two sources accounts, roughly, for only two thirds of the total average accumulation. The remaining portion of the acid comes from the soap as the result of two separate and distinct reactions. Whether one or the other reaction predominates depends upon the kind of fabric being cleaned, the mineral acid content of the garments, and the amount of moisture present in the garments and in the particular soap employed. The first of these reactions involves the pronounced affinity of protein fibers for alkali (1). The experienced cleaner knows that white wools, such as white flannel pants, must be soured after going through a normal wet cleaning treatment if a yellow cast is to be prevented from developing during subsequent pressing operations. This yellowing on heat treatment is caused by the presence of alkali absorbed during the suds, the alkali becoming so firmly attached to the fibers that it is difficult to remove completely by rinsing. A similar
action takes place in dry solvents; protein fibers such as wool and silk adsorb the alkaline portion of the hydrolyzate from a completely saponified and neutral soap, and leave fatty acid residues to accumulate in the solvents. T o illustrate this effect more clearly, several different kinds of cloth were extracted with chloroform and washed with a dilute ammonia solution to neutralize any acidity present. On shaking two 7 X 30 inch samples, treated in this way in Stoddard solvent for 10 minutes on the shaking machine, no change in acid number could be detected. If a neutral soap containing a considerable amount of water was added in the ratio of 10 ml. soap t o 700 ml. solvent, the following acid numbers were obtained : Wool Regenerated cellulose rayon Cotton Cellulose acetate rayon Silk
0.131 0.082 0.000 0.000 0.221
A soap containing a relatively small amount of water and higher percentages of alcohols and esters gave increases in acid numbers with silk and wool, but not of the same magni1.0
P
0.7 0.6
0.5
3 z 0
04
U 0
0.3
-FULLER'S
EARTH NO. I FULLER'S EARTH N0.2 INACTIVE FILTER AID ACTIVATED CARBON MAGNESIUM SILICATE
0.2
0.I 0.0
0
200
400 600 800 1000 1200 POUNDS GARMENTS CLEANED
FIGURE 6 . ACIDBUILD-UP, USIXG3 PINTSOF SOAPPER LOAD(PLANT TEST)
INDUSTRIAL A N D ENGINEERING CHEMISTRY
lune, 1941
II
tude. This would indicate that the extent of hydrolysis and hence of alkali adsorption, and ultimately of fatty-acid buildup in the solvent is dependent on the amount of water present. Thus the excess accumulation of fatty acid above that derived from the fatty acid content of the soap itself and the garments during plant runs may be attributed to the water content of the soap or garments, the hydrolysis equilibrium being displaced as the alkaline product of dissociation is removed. The second reaction liberating fatty acid involves the displacement of the fatty acid combined in the soap when in contact with comparatively strong mineral acids held on the garments and insoluble in the dry cleaning solvent. This conception presupposes two types of acids in the soiled garments: (a) organic acids soluble in the solvent, originating in perspiration and food stains, and therefore varying in kind with the individual and in amount with the season and with the quality and frequency of cleaning; (b) mineral acids insoluble in the solvent and tightly held a t the surface of the fibers or in the interstices of the fabric, derived from the sulfur dioxide content of the air and thus varying with the season @)and with country or industrial city location, or derived from acid soils floating in the air or from products of perspiration. FROM SOILED TABLE 111. INCREASE IN ACIDCONTENT DERIVED GARMENTS AND FROM SOAPCONTAINING EXCESSFATTYACID
Acid Numbers wt. of Increase due to Garments, 801. acids Lb. Start Break Soap from garments 0.032 76.0 0.074 0.106 0.164 0.024 71.5 0.164 0.188 0.254 0.024 50.011 0.254 0.278 0.344 0.017 58.0 0.384 0.401 0.458 0.025 84.0 0.458 0.483 0.515 break 0.344,soap 0.384. (I On cleaning second time:
Increase due to aoap 0.058 0.066 0.066 0.057 0.032
Further data illustrating the breakdown of the total acid increase into that derived from soluble organic acids present in the soiled garments and that derived from the soap by the above reactions are given in Table 111. The cleaning cycle is usually separated into three distinct runs: a “break” run of about 10 minutes to loosen and carry away particles of insoluble soil in the garments, a soap run of 20 to 40 minutes, and a rinse run. The figures under “break” and “soap” in Table I11 give the acid numbers of solvent samples removed at the end of the respective intervals in the cleaning cycle.
Q3
0.2
- - INACTIVE FILTER
0.I
0 01
0
300
I
600
I
I
I
I
AID
I
900 I200 1500 1800 2100 POUNDS CARMENTS CLEA
FIQURE 7. ACID BUILD-UP, UEIING 0.5 LOAD(PLAN’P TEST)
BREAK RUNS
0.5
Y
m I 0.4
2
g
z
0.3
w
3 0.2 u
0:
z
0.I
1,
0.0
I
125
I
250
I
375
I
500
I
525
I 750
I
875
I 1000
I
1125
I
POUNDS GARMENTS GLEANED
FIGURE 8. BUILD-UP OF ACIDDURINQ BREAK AKD SOAP RUNS, USINGA NEUTRAL SOAP
On recleaning a load of garments previously cleaned, there is no increase in acid number; i. e., all of the soluble organic acid is removed during the first cleaning. The comparatively slight increase on the second soap run beyond that derived from the fatty acid content of the soap itself was due either to the effect of residual mineral acids in the garments which were not completely neutralized during the first cleaning or to the adsorption of alkali by the garments; since all mineral acidity had been neutralized, fatty acid residues were left to accumulate. Similar effects were obtained when a neutral soap was used in plant runs in place of the ammonium soap containing excess fatty acid. I n this case no increase in acid number OCcurred when soap was added to the system without garm The increase in acid number which did occur in the presence of garments was due, therefore, to the combined effects of soluble acids in the soil and to the breakdown of the soap by one or both of the reac during soap runs using a only that the acid conte
Acid-activated clays, containing comparatively large amounts of residual mineral acids, will also decompose soaps and increase the rate of acid accumulation in the solvent. That mineral acids tightly bou about a breakdown of a neutral by the fact that invariably the a tracted from the garments by centrifugal action is higher than that remaining in the wash m which the clothes were taken before extraction: , Solvent Remaining Solvent Extd. Solvent Remaining Solvent Extd. in Washer from Garments in Washer from Garments 0.417 0.434 0.882 0.908 0.671 0.703 0.957 0.973 0.810 0.834 0.957 0.990 0.867 1.072
-.--MAGNESIUM SILICATE
I
I
0.71
p
’267
I
2400
The soap is decomposed on the fabric where it comes in contact with mineral acids. Fatty acid decomposition products from the soap remain in the voids of the fabric or adhere to the fibers until torn away by the force of extraction, thus giving rise to the higher acid number of the solvent recovered from the extractor. This effeot cannot be attributed to a
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Vol. 33, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
natural affinity of wool garments for fatty acids, since a new piece of wool, free from mineral and organic acids, did not change the acid number of a dry cleaning solvent solution of oleic acid when percolated over it for 30 minutes.
Effect of Garments on Adsorption Powder Efficiency The adsorptive action of the powders is further complicated by the marked tendency of fabrics to pick up moisture and soap. This effect is illustrated by the following series of experiments: An oleic acid solution in Stoddard solvent was prepared and its acid content determined by titration. Portions (200 ml.) of this solution were then treated as outlined below, agitated on the shaking machine for 30 minutes, and filtered, and the acid content ivas again determined:
1. Original solvent solution 2 . Treated with 3.5y0 magnesium silicate 3 . 2 ml. of neutral soap added, treated with 3.5% magnesium silicate 4 Same a8 3, with addition of 44 g. wool 5. 6. PER CENT MAGNESIUM SILICATE BY WEIGHT
FIGURE9. EFFECTOF SOAPON FATTYACIDREMOVAL BY MAGNESIUM SILICATE
It is also probable that a neutral ammonium soap will break down and liberate fatty acid more readily than a potassium or sodium soap, particularly during summer heat. Where crude oils or fats are used in formulating a completely saponified or neutral soap, lower molecular weight acids may be released by the process of mineral acid displacement or alkali adsorption which contribute to odor difficulties. This aspect of the problem, as well as the effect of adding agents during the break to neutralize organic and mineral acids from the soiled garments and to eliminate static-charge accumulation which attracts lint and loosened soil, is undergoing further study. Effect of Soap on Adsorption Powder Efficiency The importance of the composition and amount of soap added with respect to fatty acid accumulation, as well as its removal by adsorption powders, cannot be overemphasized. The removal of fatty acid by an adsorbing agent may be exceedingly variable in the presence of soap as shown in Figure 9. A 1 per cent solution of oleic acid in Stoddard solvent was divided into two parts, and to one was added 1 per cent of a neutral dry cleaning soap. The amount of acid removed, expressed as ml. of potassium hydroxide solution per 50 ml. sample, by different amounts of magnesium silicate after agitation on the shaking machine for 20 minutes and filtering, was determined and plotted as a function of the amount of adsorbent employed, Solutions containing soap and no powder, and soap with 3 per cent by weight of a filter aid were included for comparison. The results show that the soap itself removed the fatty acid to a marked extent and that increasing amounts of adsorbent, in the presence of soap, prevented this removal up t o a point where sufficient powder had been added to neutralize this soap effect-3.5 per cent in this instance. These facts may be explained as follows: I n the absence of an adsorbing powder the soap forms a loose combination with the oleic acid which is easily broken down during pressure filtration in actual practice. However, when an active powder is present, the soap is preferentially adsorbed before the fatty acid itself is touched. Under actual operating conditions in the pressure filter, the curve for fatty acid removal in the presence of soap with increasing amounts of adsorbent would be a straight line along the x axis until all soap had been adsorbed, a t which point fatty acid would begin to be removed and the curve would begin to rise.
Ml. 0.057 N Alcoholic KOH/50 RI1. Sample Titration value Acid removed 26.3 19.1 7.2
fabric 2 ml. of neutral soap and 44 g. wool fabric Same as 5 , followed e y 20-min. shaking with 3.5% magnesium silicate
...
25.5
0.8
25.2
1.1
26.7
0.6
23.3
3.0
The effect of soap in preventing removal of acid by the powder is again apparent (steps 2 and 3). I n the presence of wool fabric a greater amount of acid is removed (step 4),which may be attributed to a tie-up of part of the soap on the fabric; it is thus prevented from interfering with the action of the powder. I n the absence of powder (step 5 ) , a part of the soap is held by the fabric and prevented from removing oleic acid, as illustrated in Figure 9. If step 3 is carried out by first shaking the soap and fabric in the solvent as in step 6, allowing sufficient time for the affinity of the fabric toward the soap to become exhausted, and then treating with the adsorbent powder, much more acid is removed. I n other words, in the presence of garments the action of the soap in preventing adsorption of acid by the powder is greatly diminished; the break in the soap curve (Figure 9) showing an increase in acid removal, after sufficient powder has been added to take care of the soap present, will then come a t a concentration of powder lower than 3.5 per cent.
Conclusion Laboratory and plant tests carried out under controlled conditions have shown that the use of adsorbent powders retards accumulation of fatty acids in Stoddard dry cleaning solvent, and will remove odorous impurities to some extent. Of the adsorbing agents studied activated carbon ranked first in this respect, followed by magnesium silicate, activated fuller’s earth No. 1 and activated fuller’s earth No. 2. Alkali adsorption and mineral acid displacement theories of dry cleaning soap decomposition have been advanced to account for fatty acid accumulation derived from the soaps employed. The effect of soap and the presence of garments on the power of adsorbing powders to remove fatty acids has been shown. Literature Cited (1) Neville. H. A.. and Harris. M., J . Research Natl. Bur. Standards,
14,765 (1935). (2) Smith, A. C., Lowe, C . S.,and Fulton, G. P., IND. ENG.CHBM., 32,454 (1940). (3) Wilkie, J. B.,B u r . Standards J . Research, 6 , 593 (1931).
Liberty Rubber-Correction Our attention has been directed to the fact that the designation ‘
