Properties of Detergent Solutions Detergent Action of the System Modified Soda-Soap-Water THOMAS H. VAUGHN, ANTON VITTONE, JR., AND LESLIE R. BACON The J. B. Ford Company, Wyandotte, Mich. and Bascom ( 8 ) . They builb ODIFIED soda has Three types of washing tests made with an arti0.25 per cent soap solutions ficially soiled cloth a t 60" C., using 0.1 per cent soap been extensively used with sodium carbonate, sosolutions built with modified soda, show that a t a in the laundry indusdium phosphate, or sodium constant pH soil removal in this system first intry as a soap builder. The pH hydroxide, and studied the characteristics of the system creases to a maximum and then decreases as the resulting pH behavior and amount of modified soda is increased. Over the modified soda-soap-water were detergent action. Results prerecently reported in the first range of soap-builder ratios used in commercial sented in graphical form inlaundry practice, soil removal is approximately paper of this series ( 1 ) ; the dicated that the maximum proportional to t h e acid titration value, which is authors showed that such sodetergent efficiency of all the in turn proportional to t h e concentration. For lutions maintain unusually builders occurred a t a pH of this system titration is therefore a much better constant pH values over wide 10.7 (measured a t room temmeans of controlling the suds bath i n laundry pracranges of concentration. The perature). tice than pH measurements. The optimum ratio present i n v e s t i g a t i o n deals Later work by Rhodes and of soap to modified soda with the type of standard with the detergent action of Wynn (10) using sodium hysoil used is approximately 1 to 2 a t a soap concenthis system. droxide as a builder showed tration of 0.1 per cent. The detergent action of a that maximum detergency ocResults obtained with soiled cloths of the same built soap solution varies with curred a t a pH of 9.66 (pH type b u t with different residual removable soil the ratio of soap to builder as measured a t 60" C.). Howcontents are correlated. Reflectivity values of well as with the soap concene v e r , solutions c o n t a i n i n g standard soiled cloth are only an indirect measuretration (8, 9). The addition soap, either sodium chloride, ment of soil content. Under the conditions used in of an alkaline builder to soap sodium sulfate, disodium hythis study and other things being equal, the rate of changes a number of the propdrogen phosphate, dipotassium soil removal is directly proportional to the residual erties of the solution, and some hydrogen phosphate, sodium removable soil content of the cloth. Two types of of these properties have been tetraborate, or sodium aceLaunder-Ometer studies have been made, and one proposed as criteria of the detate, and sodium hydroxide type is correlated with commercial washer tests. tergent action. at a pH of 9.66 (measured The relative merits of all three types of experiThe degree of alkalinity of a t 60" C.) showed differen6 mental wsshing procedures are discussed. p H of a built soap solution is degrees of detergermcy. chief among the physical Morgan (6) also studied Drooerties whichhave been conthe effect of building soap with either sodium carbonate,3 sidered in studying the detergency of built soaps (3, 8, 10). trisodium phosphate, sodium metasilicate, o r sodium hyI n addition t o being considered a criterion of detergency, pH droxide. His results indicated that optimum detergency has also been advocated and is widely used as a means of occurred between a pH of 10.5 and 11.0. The order Gf the controlling the suds bath in laundry practice (9,6). As a various builders when rated on the basis of efficiency disresult many individuals closely connected with the laundry agreed entirely with that obtained by Rhodes and Bascom. industry have come to believe that, regardless of the type of Morgan (7) also studied the detergent action of these buildbuilder and soap and the quantities used, good detergency can ers by carrying out tests in the power laundry. The same be obtained provided the pH of the suds bath is a t a certain relative order of efficiency was obtained in the field as in his definite value or within certain definite limits. The fallacy of work in the laboratory. Later results by SneH ( 1 1 ) confirm this belief becomes clearly evident when it is realiaed that Morgan's work in general. effective washing is carried out in every-day practice, depending on class of work and builder used, at pH values ranging from below 10 t o above 12, a hundred fold or more difference Rate of Detergent Action in hydrogen- or hydroxyl-ion concentration. Furthermore, That detergency could be looked upon as a problem in through the use of organic detergents, effective washing may equilibrium was recognized by Rhodes and Brainard (9). On be carried out even in nonalkaline solutions. washing soiled and unsoiled pieces of cloth together, the soir redistributed itself between the solution and the soiIed and Previous Work unsoiled pieces of cloth, which approached each other in brightness and thus could be considered t o show the same deEarly work pertaining to the effect of alkalinity or pH on gree of soiling. It is readily evident Ohat there is a limit to, the detergency of soap solutions was presented by Rhodes
M
1011
1012
INDUSTRIAL AND ENGINEERING CHEMISTRY 3
Vol. 33, No. 8
s e r i e s of m u l t i p l e wash tests in which various washing times were used for each set 6 of multiple washes. As the time of each wash was decreased, the increase in bright4 ness per unit of washing time increased until the i n d i v i d u a l washing times were 2 decreased to periods of 71/2 and 33/4minutes. Inthesetwosets of multiple washes D the increase in bright0 0.1 0.2 0.3 0.4 WASHING TIME, MINUTES CONCENTRATION OF B U I L D E R , P E R C E N T ness per given wash00 I:I I:2 I:3 I:4 ing time was about RATIO SOAP TO B U I L D E R the same, since the effect of redeposition FIGURE 1. EFFECTOF WASHINGTIMEAND OF MODIFIEDSODA CONCENTRATION ON SOILREMOVAL AS MEASURED BY REFLECTIVITY had been minimized by the use of shorter single wash periods. the amount of soil which a given detergent soluton may reWhen a multiple wash test is carried out in equal washing move and retain under specified conditions. periods, the amount of soil removed per wash continually deThe time necessary to approach this condition of maximum creases as the number of washes increases. With a given soil removal may be lengthy, and the effect of variations of type of soil, it is therefore evident that the rate of soil reconcentration, composition, and temperature on this limiting moval is a function of the cloth’s removable soil content. If value or the time for attaining it may be of little practical the amount of soil removed and the total removable soil value. Much more important in general is the rate and content in grams per square meter of cloth are represented amount of soil removal through the early periods, as will beby s and c, respectively, then the rate of soil removal may be come more evident later. written as follows: For soil to be removed from a soiled cloth and redeposited on an unsoiled cloth, two opposing effects or a combination of effects must exist. Soil will continue to be removed from the cloth until the conditions tending to remove the soil are where t = time, minutes balanced by opposing conditions tending to redeposit soil on It will become apparent in the following sections that the the same cloth. data on detergency which we shall present conform to the reI n considering the results of washing tests, these effects quirements of a linear function of this type. Under these must be taken into account. When a washing test is startedcircumstances, Equation 1 may be integrated from s = 0 to in other words, a t zero washing time-the concentration of s = s and from t = 0 to t = t , leading to Equation 2. the soil in solution is zero, and the only effect possible is that of soil removal. As thewashing test continues, the opposing ‘effects gradually increase and the rate of soil removal decreases. If the washing time is of short duration (as in a multiple wash test), the soil ccncentration in suspension and its tendency f o r redepositicn will be low, and the resulting data will show almost entirely the effect of soil removal. 0.3 0.4 5 IO 15 20 0 0.1 0.2 0 This fact can be CONCENTRATION OF BUILDER, P E R C E N T WASHING T I M E , M L N U T E S clearly understood to I:I I: 2 1:3 I:4 from Figure 7 of RATIO SOAP TO B U I L D E R Rhodes and Brainard’s paper (9). O F WASHING TIMEAXD O F MODIFIEDS O D A CONCENTRATION ON SOIL R E n i o v a L .4S FIGERE 2. EFFECT MEASURED BY TURBIDITY They conducted a
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1941
-In-
c - s
=
Kt
On rearranging Equation 2 , the exponential form s = c
-
(c/fi)
(3)
is obtained; it is evident that by plotting s against l/e*' and extrapolating to where 1 / e K t equals zero (in other words, where t = m), the value of c may be obtained. Since the function is linear, the curve will be a straight line when the proper value of K is chosen; therefore in making such a plot, various values of K should be tried until an approximately straight line is obtained which will facilitate extrapolation. The same value of c would be obtained, regardless of the assumed value of K . Once the value of c is obtained, (c - s) may be calculated and by plotting the log (.c s) versus t a straight line is obtained. The slope of this line when multiplied by 2.303 will give the value of K in Equation 2. I n this treatment of detergent action, constant K has the physical significance of a specific soil removal rate. It represents, therefore, the fraction of the removable soil present at any instant which a t a steady rate of removal would come off in the next minute. The larger this fraction, the more rapid the detergent action. Therefore K may be looked upon as one important measure of detergent action. The value of K is independent both of time and the soil content of the cloth. It may be expected to vary with different detergent solutions, concentration, temperature, degree of mechanical action, type of soil, etc. This method of correlation should be applied only to multiple wash tests in which the effect of soil redeposition has been minimized by a proper selection of the washing times. The shorter the time of each wash (within practical limits) and the smaller the ratio of cloth to solution, the more suitable the data are for this correlation.
-
1013
For the measurement of reflectivity, a Hunter multipurpose reflectometer equipped with filters was used. All reflectivity measurements were made with a green filter on one thickness of fabric using a background with a reflectivity of 53.8 er cent. In making the measurements, the pieces of cloth were pyaced so that the warp and filling ran pmallel to the axes of the illuminated ellipse. The Lange reflectometer, model MU, was used to measure the optical transmission of the detergent solutions for the determination of soil content. For this purpose the absorption scale was used. To hold the solutions during this measurement, a special cell was made by cutting the top off a 100-ml. beaker and grinding down the edges to define a horizontal plane about a/4 inch (19 mm.) from the bottom. The outer surface of the cell was coated several times with a lacquer pigmented with magnesium oxide and finally painted with an ordinary white enamel. In making transmission measurements, 10 ml. of the suspension were pipetted into the cell, the photoelectric cell housing was placed on the ground surface, and the reading taken. For this purpose the Lange reflectometer was standardized with the black standard of the instrument (0 per cent Lange reflectivity standard) set at 100 and a ray enameled plate (32.5 per cent Hunter reflectivity, green Ater) set at 35. For the purpose of drying the samples of cloth between washes, a commercial gas-heated tumbler was used. The samples of cloth were ironed with a 24-inch home ironer of the rotary type and allowed to come to moisture equilibrium with the atmosphere before reflectivity measurements were made. Whenever soft water was used, Wyandotte city water (7 grains of total hardness) was softened to 0-1 grain total hardness with a Permutit base-exchange water softener. Commercial grades of both soap and modified soda were used. The com osition of these materials has already been iven by Bacon, gensley, and Vaughn (I), and they will be referred to merely as soa and modified soda throughout this aper. I n the figures and tatles modified soda is abbreviated to S. Degomma 80A, a commercial starch solubilizing enzyme, was used in desizing the cloth previous to soiling.
%.
Experimental Methods
An artificially soiled cloth was prepared using Indian Head muslin, Norit C, lubricating oil (S. A. E. 30), Crisco, and Stoddard solvent. This soil is similar to, although not identical with, that used by Mack and co-workers at PennsylEquipment and Materials vania State College (4). Before soiling, twenty yards af I n conducting the washing tests, a Launder-Ometer, type LHD, Indian Head muslin were cut into yard squares and desized and a small 24 X 40 inch (60.9 X 101.6 cm.) Monel metal comby soaking overnight twice in a 1 per cent solution of Demercial washer were used. The washer was equipped so that gomma 80A. They were given two suds in the commercial speeds of 30 and 15 r. p. m., which will be referred to as high and washer described previously, using 40 liters of solution prelow speeds, respectively, could be obtained. -pared by dissolving- 40 grams each of soap and modified soda in 40 liters of Wyandotte city water (7-grain hardness) at 110120' and 140-150" F. (43.3-48.9' and 80-65.6" C.), respectively. Following the two suds, they were rinsed, extracted in a commercial extractor, ironed, and hung vertically overnight, in order to attain moisture equilibrium with the atmosphere. To prepare the standard soil, a solution consisting of 128 liters of Stoddard solvent, 1600 grams of melted Crisco, and 800 ml. of lubricating oil was prepared in a commercial wash wheel. One-half of this solution was withdrawn for use in the rinsing operation. The soiling suspension was completed WASHROOM IN A COMMERCIAL LAUNDRY
1014
Vol. 33, No. 8
INDUSTBIAL AND ENGINEERING CHEMISTRY
c z w
0
LT
EO 12
1
1 50
I
I IO0
I 150
100
150
1
2
I
W K
:= >
+ W
05:
I
w a
=k! lvJ4
0 s m a
a W
0
0
50
200
T O T A L WASHING T I M E , M I N U T E S
FIGURE3. SOIL REMOVAL BY REFLECTIVITY AND BY WEIGHT AS FUNCTIONS OF THE TOTAL WASHING TIMEIX MULTIPLEWASH TESTSWITH STANDARD SOIL21 by adding to the solution in the washer 240 grams of 200mesh Norit C and agitating the mixture by running the washer a t high speed for 10 minutes. To the soiling suspension twenty of the original 1-yard squares of desized and washed Indian Head muslin mere added, and the washer was run a t high speed for 30 minutes, being stopped a t 10-minute intervals for manual segregation of the pieces. The soiling suspension was withdrawn from the washer and the rinsing solution added. The cloth was rinsed for 5 minutes at high speed, after which the washer speed was reduced and the rinsing solution withdrawn. The soiled cloth was allowed t o remain in the washer for 10 minutes, the washer being rotated every minute or bo in order to facilitate draining. The soiled cloth was then removed from the washer and hung horizontally t o dry for 48 hours. Following the drying period the soiled cloth was washed in the commercial wash wheel previously mentioned at high speed for 5 minutes with a solution prepared by dissolving 40 grams each of soap and modified soda in 40 liters of Wyandotte city water (7-grain hardness) a t 65" F. (18.3" C.). It was rinsed in 40 liters of Wyandotte water for 3 minutes; the water was brought from 65' to 100" F. (18.3' to 37.8" C.) during this time by the admission of live steam. The washer was reduced to low speed, and 40 liters of water were added at 70" F. (21.1" C.); the water was brought u p to 140" F. (60" C.) by adding steam for 7 minutes. The load was then run for 2 minutes and drained. Each yard of soiled cloth was removed separately and rinsed by hand twice in 10-liter volumes of Wyandotte water, extracted lightly by hand, and hung vertically to dry but not ironed. This procedure allowed for the build-up of a uniform amount of hard-water soaps which are a part of this standard soil. The cloth was cut into 3.25 X 2.5 inch (83 X 64 mm.) test pieces with pinking shears for use in Launder-Onieter studies.
The reflectivity of each small test piece was measured on both sides, and the average value recorded on the cloth with marking ink. Three types of washing experiments were conductednamely, single and multiple, washes in the Launder-Ometer, and single washes in the washer. I n carrying out the single wash experiments in the LaunderOmeter, ten rubber balls, 0.375 inch (9.5 mm.) in diameter and weighing 12.9 grams, and eight steel balls, 0.25 inch (6.35 mm.) in diameter and weighing 8.2 grams, were placed in a pint fruit jar with 100 ml. of the proper solution; jar, balls, and solution were all preheated to 140" F. Two pieces of soiled cloth and two pieces of unsoiled cloth were added to each jar; each piece was 3.25 X 2.5 inches in size, and the total weight of the cloth was 3.65 to 3.70 grams. The jars were immediately placed in the Launder-Ometer, run for a definite period, and removed. The washing solution was collected, and the cloth was rinsed in running Wyandotte water, extracted by hand, and ironed. Soil removal was determined by measuring the reflectivity of the soiled cloth with the Hunter reflectometer. The soil content of the s o h tion was measured with the modified Lange reflectometer, a calibration curve of soil concentration us. reading having been made by methods to be discussed. The turbidity of the solution was measured immediately after its removal from the jar; any lint present was first removed by passing it through a 50-mesh screen. The multiple wash test is a series of single washes. The length of the consecutive washes was varied in order to remove approximately the same amount of soil during each wash. The pieces of cloth were dried for 4 minutes in a commercial tumbler (at approximately 180" F. or 82" C.) after each wash and then replaced in a fresh solution for the next re
.
0
0.2
0.4
e -ut
0.6
0.8
I .o
FIQURE4. EXTRAPOLATION O F DATA T O DETERMINE MAXIMUM AMOUNTOF REMOVABLE SOILFROM STANDARD SOIL21 wash. One complete set of samples was removed from t h e Launder-Ometer after each wash, rinsed in running Wyandotte water (7-grain hardness), extracted by hand, and ironed. All reflectivity measurements after washing were made on ironed cloth. In no case was the soiled cloth ironed before washing, since the effect of thus heating the standard soiled fabric is unknown. In carrying out the washer tests, a square yard of standard soiled cloth was ruled into forty-two 3 x 4 inches (7.6 X 10.2 om.) areas, and the average reflectivity of both sides of each area was recorded on the cloth with marking ink. A solution consisting of 60 liters of softened water a t 140" F. with the desired amount of soap and modified soda was prepared in the commercial washer. To this solution 30 pounds (13.6
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
August, 1941
kg.) of clean, dry, white rags were added, and the wash wheel was rotated a t high speed for 1 minute. A yard of standard soiled cloth was next introduced and the washer run a t high speed. Small amounts of live steam were occasionally run into the washer to hold the temperature a t 140" F.; the amount, however, was sufficiently small so as to cause only a negligible dilution. This procedure was followed in all washer experiments, and therefore practically identical conditions existed. At the end of 5-minute washing intervals the washer was stopped, and a strip of standard soiled cloth containing seven squares was cut off with scissors. The strip so cut was rinsed in running Wyandotte water (7-grain hardness), extracted by hand, and ironed, and the average reflectivity was determined. Soil removal results as measured by the reflectivity method are expressed as per cent change in reflectivity. If A is the soil removal exmessed as Der cent change in reflectivity,.B the reflictivity afterwashing t h e soiled cloth, D the reflectivity of the original soiled cloth, and E the reflectivity of t h e unsoiled cloth (75 j=1 per cent), A =
(B
- D ) (100) ( E - D)
FINISHING ROOM IN
(4)
The soil removal by weight is given by two methods. In the single wash experiments it is expressed as soil concentration (grams per liter of detergent solution); in the multiple wash experiments it is expressed as grams of soil removed per square meter of standard soiled cloth. In this study of the detergent action of the system modified soda-soap-water, a soap concentration of 0.1 per cent, representative of usual commercial laundry practice, was used in all experiments, while the modified soda concentration was varied from 0 to 0.4 per cent. All of the built soap solutions used had the same pH value-namely, 9.60 * 0.05 a t 140"F. Solutions will be referred to on the basis of their modified soda content, with the understanding that they also contain 0.1 per cent soap. All experiments were conducted a t 140"F. with Wyandotte city water softened by base exchange. Detergent solutions were prepared in enameled pails by :adding to weighed amounts of soap and modified soda the
A
COMMERCIAL LAUNDRY
correct amount of softened water and heating to 140' F. All solutions were used within 1 hour of their preparation.
Preparation of Standard Soiled Cloth Two separate batches of standard soiled cloth were prepared by the method previously given. A portion of the second batch was given an additional wash of 3 minutes with a 0.1 per cent bath of modified soda and soap and rinsed as before. These three lots of soiled fabric will be referred to as etmdard soils 1,2, and 21, respectively. In the preparation of standard soil I, the cloth was allowed t o come to equilibrium with the atmosphere a t a relative humidity of 40 per cent and a dry-bulb temperature of 71 " F. (22" C.) prior to soiling. For standard soils 2 and 21, the cloth was allowed to come t o equilibrium a t a relative humidity of 22 per cent and a dry-bulb temperature of 70" F. (21" C.). Standard soil 21 was the same as soil 2 except for its lower soil content. The reflectivities of the various soils are as follows (with a maximum deviation of * 2 per cent) : Standard soil 1 2 21
I-
g% 21
After the preparation of standard soil 2, the soiling suspension was filtered, and the Norit, containing Crisco, oil, and solvent, was air-dried for 48 hours. This soil was considered very similar to that on the cloth and was used to standardize the method of determining the soil content of the detergent solutions.
1.0
f
w
I2 0 0
2
1015
0.5
i5 v)
Single Wash Experiments
2
2 P
VI W
O
,a cl
3 -0.50 FIGURE
20 40 T O T A L WASHING TIME,
60 80 MINUTES
5. CORRELATION O F MULTIPLI W A S H TESTS CONDUCTED WITH STANDARD SOIL21
To study the effect of variable amounts of modified soda on the initial rate a t which the detergent capacity is a p proacbed, a series of single wash experiments was made. The @&tseries was carried out on standard soil 1, and the soil removal was evaluated by reflectivity measurements. The results are plotted in Figure 1. Curves at the left are for each fixed concentration, and soil removal always increases as a function of the washing time over the range considered. However, as the concentra-
I N D U S T R I A L AND ENGINEERING CHEMISTRY
1016
tion of modified soda increases, the amount of soil removed per unit time increases to a maximum and then slowly decreases. This is more clearly shown a t the right where soil removal (data obtained from left-hand graph) is plotted against the concentration of modified soda a t constant washing time. Maximum soil removal occurs a t a modified soda concentration of 0.2 per cent, or at a soap-builder ratio of 1 to 2, and is independent of the washing period. For short washing periods the adjustment of soap-builder ratio is more critical for maximum efficiency than for longer washing periods. 0.04.
I 1 I 1 tI i1 - 1 I
I
1 H 4
i
1
I
I
I
I
I
0.0 K
I
I
,
I
I
Single wash experiments were also conducted on standard soil 21 in which the soil removal was determined b y measuring the concentration of soil in the wash solution by ineans of the Lange reflectometer and cell previously described. To measure soil concentration in this way, it was necessary first to obtain a quantity of soil similar t o that removed from the cloth so t h a t standards might be prepared, and a calibration curve relating soil concentration and Lange reflectometer readings was developed. The Norit filtered from the soiling suspension and dried after the preparation of standard soil 2 was considered to be similar t o the soil on the cloth; this was confirmed in the following manner: Two pieces of standard soiled cloth 2 were washed for 50 minutes with a solution containing 0.2 per cent modified soda and 0.1 per cent soap. The wash solution was diluted with a solution of 0.2 per cent modified soda and 0.1 per cent soap until the Lange reflectometer gave the same reading as i t did with a suspension prepared by adding 0.05 gram of filtered Norit to 100 ml. of a solution of 0.2 per cent modified soda and 0.1 per cent soap and agitating in the Launder-Ometer for 30 minutes. Thus, as determined by turbidity, the two solutions had the same content of soil. The soil deposition tendency of the two solutions was determined by placing 100 ml. of each solution in separate Launder-Ometer jars with ten rubber balls, eight steel balls, and two pieces of white Indian Head muslin. The jars were agitated in the Launder-Ometer for 30 minutes, the cloths were rinsed, extracted by hand, ironed, and the reflectivity was determined to be as follows: % Reflectivity Before soil deposition After soil deposition Difference
Norit from Soiled Cloth 74.5 5 G 18.0
Norit from Filtration 74.2 55 0
19.2
From these results it was concluded that the two soils behave similarly and thus are in the same physical state. A calibration curve of Lange reflectometer readings us. soil concentration, using the Norit-oil-Crisco mixture obtained by filtering after the preparation of standard soil 2, was pre-
Vol. 33, No. 8
pared by adding various weighed amounts of soil to 100 ml. of soap solution built as indicated in the next paragraph. These mixtures were placed in Launder-Ometer jars, agitated for 30 minutes, and removed from the Launder-Ometer, and the turbidity of the suspension was immediately determined. Two sets of measurements were made, one on an unbuilt 0.1 per cent soap solution, and the other on a 0.1 per cent soap and 0.4 per cent modified soda solution. The results in Table I and the average value were used in preparing a calibration curve. Although the soil used in preparing the calibration curve may not be identical with that removed from the cloth, the constituent mainly responsible for decreasing the light transmission of solutions is the same in both cases, and the results, if not absolute, are relative and can for many purposes be treated as if absolute. Returning now to the single wash experiments on standard soil 21, in Figure 2 (left) the soil removal is given as a function of the washing time. These data were obtained by the use of a calibration curve prepared from the data reported in Table I. At the right, soil removal is plotted as a function of modified soda concentration. The results are closely analogous to those obtained by reflectivity measurements on standard soil 1. As before, maximum soil removal occurs a t an approximate concentration of modified soda of 0.2 per cent, independent of washing time. As the left-hand graphs of Figures 1 and 2 show, none of the solutions had attained its capacity for soil removal a t the end of 20 minutes.
Multiple Wash Experiments Multiple wash tests were conducted with standard soil 21, and the soil removal was evaluated both by reflectivity and by turbidity. The data obtained in this series of tests are given in Figure 3. Above, the soil removal by reflectivity is plotted against the total washing time at constant concentrations; below, the soil removal by weight is plotted against the total washing time. Both sets of data indicate that soil removal increases with increasing concentration of builder over the range of 0 to 0.2 per cent concentration.
0
50
100
150
T O T A L WASHING T I M E , M I N U T E S
FIGURE 7. 'SOIL R E M O V A L BY W E I G H T AS A FUNCTION OF THE TOTAL WASHING TIMEIN MULTIPLE WASHTESTSWITH STANDARD SOIL2
In Figure 4 the weight of soil removed from standard soil 21 by 0.1 per cent soap built with 0.05 per cent of modified soda is plotted against e--Kt, using values of K equal to 0.015 and 0.020, and extrapolated to e-=' = 0, corresponding to an infinite value of t. The first trial with a value of K equal to 0.015 gives a curve; the second trial with a K value of
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1941
1017 K,
C o y n . of
Standard Soil 2 0 019 0.022
Modified Soda 0 0.025
K
Standard'Soil 21 0.017
0.020
The agreement between the two sets is exceedingly good.
A slightly larger value of K should have been expected in the case of standard soil 2, since in this case the length of each wash was shorter than in the case of standard soil 21, and the effect of redeposition therefore smaller on standard soil 2.
Washer Tests
0
0.2
0.4
0.6
0.8
e- Kt
1.0
The reliability of data obtained with a Launder-Ometer has often been questioned. Consequently, a set of experiments was carried out in which soil removal was determined in a commercial washer by the single wash method with standard soil 21. The procedure for these experiments was described earlier in this paper.
FIGURP~ 8. EXTRAPOLATION OF DATATO DETERMINE MAXIAMOUNTOF REMOVABLE SOIL FROM STANDARD SOIL 2
MUM
0.020 gives a straight line. From this extrapolation the total removable soil content for standard soil 21 is determined. I n Figure 5 the log of the residual removable soil content is plotted against the total washing time, and the best straight lines are drawn through the points. The slope of these lines when multiplied by 2.303 gives the value of K in Equation 2. K is plotted as a function of concentration in Figure 6; it is evident that the rate of soil removal increases with the concentration of modified soda up to a concentration of 0.2 per cent a t least.
TABLE I. CALIBRATION OF MODIFIEDLANGE .REFLECTOMETER Lange Reflectometer Reading Soil Concn., G:am/ Liter 0.05 0.1 0.2 0.3 0.4
0.5
0.1%
Boap-
0.4%
M. S. soln. 9 33 56 70.5 79.0 85
08:z
soln. 9 32.5 57 70.5 80.0 86
Average 9 32.2 56.5 70.5 79.5 85.5
0
50
IO0
I50
Lange Reflectometer Reading
Soil Concn., Gram/ Liter 0.6 0.7 0.8
0.9
1.0
0.1%
soap0.4% M. S . soln. 90 93.5 96.5 97.5 98.0
%z soln. 89.5 92.5 95.5 97.0 99.0
Average 89.7 93.0 95.8 97.2 98.5 0.1% SOAP
1-0.000%M.S. 2-0.05 0 " '
Multiple wash experiments were also conducted on soil 2 using modified soda concentrations of 0 and 0.25 per cent. The data, calculated to grams of soil removed per square meter, are presented in Figure 7 as a function of the total washing time. They indicate that practically the same amount of soil will be removed a t different builder concentrations by sufficiently prolonged multiple wash tests. This amount of soil corresponds t o the removable soil content, determined by extrapolation in Figure 8. The rate of soil removal increases with concentration of modified soda throughout the range investigated. I n Figure 8 the soil removed from standard soil 2 a t a concentration of 0.1 per cent soap is plotted against e--Kt and is extrapolated to an infinite value of t. The total removable soil content in grams per square meter was determined by this method and found to be 13.7 grams. I n Figure 9 the log of the residual soil content of standard soil 2 is plotted against the total washing time, and the best straight line drawn through the experimental points. From the slope of these lines the value of K was determined. It is interesting to compare the values of K obtained in Figure 9 .on standard soil 2 with those read from Figure 6 for standard soil 21 :
P W AI-
a w
g?
ts: ~a W -IP
z m ma? a
a
0
20
40
60
T O T A L WASHING T I M E , M I N U T E S
80
.
FIQURE 9 (Above). CORRELATION OF MULTIPLE WASHTESTSCONDUCTED WITH STANDARD SOIL 2 FIGURE 10 (Center). CORRELATION OF MULTIPLE WASHTESTS WITH WASHER TESTS FIGURE 11 (Below). COMPARISON OF A SINGLEAND MULTIPLEWASHTEST
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Vol. 33, No. 8
Reflectivity as a Measure of Soil Removal The fact that the reflectivity of soiled cloth is not directly proportional to the soil content was early realized by Rhodes and Brainard (9). The data obtained in the multiple wash experiments (Figure 12) show how reflectivity varies with the removable soil content. F o r this type of soil, reflectivity is not a good criterion of soil removal over the range below 30 per cent; similarly, the residual soil content is not a sensitive criterion of reflectivity; over the range above 35 per cent. The two methods used to express soil removal-namely, by per cent change in reflectivity and by weight-are compared in Figure 13. The soil removal as measured by the two methods is cohsistent under the range of experimental conditions of this work.
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FIGURE 12. REFLECTIVITY AS A MEASURE OF SOILCONTENT
S O I L REMOVAL
% CHANGE I N REFLECTIVITY
FIGURE13. COMPARISONOF S O I L REMOVAL BY W E I G I i T AND BY REFLECTIVITY
I n Figure 10 the soil removal data obtained in the washer are plotted as a function of time and correlated with the Launder-Ometer data read from the upper curves of Figure 3. The time axis of Figure 3 was transformed by multiplying by the factor 0.7.
Comparison of Single Wash, Multiple Wash, and Commercial Washer Experiments The discussion of results obtaiiied by laboratory methods and in commercial equipment and practice may now be carried further. A single wash and multiple wash curve based on Figures 2 (left) and 3 (below), respectively, are shown in Figure 11. During the later stages they deviate considerably, since the soil removal capacity of the solution is being approached in the single-wash experiment. I n laundry practice the soil in suspension is always very low (otherwise whiteness retention would be extremely poor). I n the washer tests 1 square yard of soiled cloth was washed in GO liters of solution, with the soil concentration in suspension kept low. Soil removal was therefore practically unopposed by counterprocesses, and the results correlate better with the multiple wash than with single wash experiments, as indicated previously. I n rating the detergent ability of various materials, the numerical rating is dependent on the washing time, if the detergent action is considered a t constant time periods. However, by using the correlation previously given for multiple wash experiments, it is possible to obtain a correlation independent of the washing time. The method used to determine the soil content of the cloth as a function of the total washing time in the multiple wash experiments does not yield accurate values a t long washing periods. It consists of the addition of separate soil removal determinations and subtraction of the sum from the total value. Separate and systematic errors thus become additive and allow for larger discrepancies with increased washing time. The soil removal as measured by reflectivity in the single wash tests (Figure 1,left) is greater than that in the multiple wash tests (Figure 3, above) a t the end of a 5-minute washing period. This is attributed to the greater soil content of standard soil 21 in comparison with soil 1 (approximately 11 grams per square meter for No. 21 against approximately 7 for No. 1). As previously stated, the cloth was brought to equilibrium a t different relative humidities in the preparation of the standard soil, which fact is believed to account for the different soilload.
pH and Detergency Data presented by Bacon, Hensley, and Vaughn (1) definitely show that, over the range of concentration of modified soda from 0.006 to 0.4 per cent (soap concentration 0.1 per cent), the pH is 9.60 * 0.05 (140" F.). I n other words, over this entire range the pH is substantially constant.
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DETERGENCY, pH, AND TITRATION
COMPARISON O F
I n laundry practice pH is usually not measured with an accuracy better than 0.1 pH unit. This was borne out by the field tests conducted by Bacon, Hensley, and Vaughn, in which samples of modified soda solutions were submitted to various commercial laundries for pH measurements. The pH values reported varied from 9.2 to 11.0, the correct value being 9.92 (77' F.). The average deviation from the true value in the series studied was * 0.3 pH unit. Blthough the pH of the system studied is substantially constant over the modified soda concentration range from 0.006 to 0.4 per cent, the detergent action is by no means constant but increases with the concentration of modified soda up to approximately 0.2 per cent. This has been brought out by a multiplicity of tests conducted in various ways. A solution which contains 0.2 per cent modified soda has a rate of soil removal approximately twice that of a solution containing
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August, 1941
.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
‘0.006 per cent modified soda (Figure 6); yet both concentrations have almost the same p H value. The lack of any simple correlation of detergency with the properties of the washing solutions investigated is brought out in Figure 14. Here the 10-minute wash curve of Figure 2 (right) is replotted with a portion of the pH data of Bacon, Hensley, and Vaughn and with data on the acid titration values of 0.1 per cent soap solutioos built with modified soda. While the pH values of the system undergo only minor changes, both titration and soil removal over the range 0 t o 0.2 per cent modified soda are approximately linear functions of concentration. Accordingly, the amount of soil removed is reasonably well reflected by simple titration values under t h e conditions of this work. The work presented clearly shows that for the system modified soda-soap-water the initial p H of the solution is no criterion of concentration or detergent action, but the concentrations of the builder and the soapbuilde; ratio have definite and measurable effects on detergency. Detergency is improved up to about 0.2 per cent modified soda (soap-builder ratio 1 to 2 ) but thereafter it decreases.
Conclusions At a constant soap concentration of 0.1 per cent in the system modified soda-aoapwater, soil removal is a function of the soap-builder ratio. Over the commercially important portions of this system the solutions maintain practically a
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constant pH value, which renders pH valueless as a method of suds bath control. The acid titration values vary directly with the concentration of modified soda and should be used in controlling the suds bath in laundry practice. Multiple wash experiments may be effectively correlated with commercial washer tests by transforming the time axis. The rate at which soil is removed is of great importance, and by proper treatment of detergency data a specific soil removal rate may be obtained. With the type of standard soil used, soil removal can best be determined by turbidity measurements. The rate a t which the soil removal capacity of a detergent solution is approached can be effectively studied by the use of a single wash Launder-Ometer experiment.
Literature Cited (1) Bacon, Hensley, and Vaughn, IND. ENQ.CHEM.,33, 723 (1941). (21 Hall. J. S.. L a u n d r u A m . 20. No. 2. 24-5. 72 (1940). (3j Jano‘ta, J., and Huh, H. H.,’OiZ & Soup, 17,96-100 (1940). (4) Mack, P.B.,private communication, June 14, 1939. (5) MacMahon, J. D., T h e L a u n d r y m a n , June, 1940,7-8, 13 (6) Morgan, 0.M.,Can. J. Research, 8,429-34 (1933). (7)Ibid., 8,583-91 (1933). (8) Rhodes, F.H., and Bascom, C. H., IND.ENG.CHEM., 23,778-80 (1931). (9) Rhodes, F.H., and Brainard, S. W., Ibid.,21, 60-8 (1929). (10) Rhodes, F.H., and Wynn, C.S., Ibid., 29, 55-7 (1937). Ibid., 25,1240-6 (1933). (11) Snell, F.D., PREBENTED before the Division of Industrial and Engineering Chemistry at the lOlst Meeting of the American Chemical Society. St. Louis, &lo
BINARY LIQUID MIXTURES Use of a Third Component to Improve Fractional Distillation
D.B. KEYES University of Illinois, Urbana, Ill.
The use of a third component to improve the fractional distillation of binary liquid mixtures, such as two hydrocarbons with approximately the same boiling point, has attracted considerable interest recently. The basis for the selection of a satisfactory third liquid and the proper design of the process for commercial operation are briefly reviewed. The relative importance of the various factors is shown, with the hope that a clearer understanding may be had of the basis of the operation and more applications can be made, especially in the petroleum industry.
~
ONSIDERABLE confusion seems to exist in the minds of many regarding the use of a third liquid component or “entrainer”, as it is commonly called, in the fractional distillation of binary or more complex liquid mixtures where simple fractional distillation is either very inefficient or impossible. The purpose of this paper is to review the
C
fundamentals of this problem as they apply on a commercial scale to the more simple case of binary mixtures with the hope that the basis of such a process may become more comprehensible. Investigators in the United States were the first to make effective use on a large commercial scale of a third liquid component in the continuous fractional distillation of azeotropic (constant-boiling) mixtures, such as ethyl alcohol and water (6, $1, 8). Benzene, now commonly used as a third component in this process, forms a ternary azeotropic mixture which separates into two liquid phases. This separation into two liquid phases is essential; otherwise, neither the alcohol nor the benzene could be recovered from the condensate by distillation. On the other hand, the existence of an azeotropic ternary mixture with a low boiling point is a disadvantage from a commercial standpoint since it carries some of the alcohol with the water out of the top of the column. A similar process has been used for the separation of hydrocarbons whose boiling points and corresponding vapor pressures are very close together (1, I, 11, 1.6, 16, 17). Likewise, a third component has been used in the separation of acetic acid from water by fractional distillation (12). Acetic acid and water do not form an azeotropic mixture, but the partial pressures of the two constituents are so close together that fractional distillation is difficult and expensive. The use of
