effective. These substances probably remove water which might act as a poison. T h e promoters were more effective for fluorinated than for nonfluorinated esters. Solvents are not essential for a smooth reaction, and in fact sometimes retard the reaction. Nomenclature
A E,, E
area of chromatogram concentration of ester a t times 0 and t, respectively, moles/cc. = fugacity of hydrogen, p.s.i. = calibration factor, mole/unit area F k = reaction rate constant in kinetic equations, mole ester/(min.) (gram catalyst) K B , K,, K F , K R = adsorption equilibrium constants for 1butanol, ester, heptafluorobutanol, and hydrogen, respectively P = pressure, p.s.i. = reaction rate, mole ester/(min.) (gram catalyst) r t = time, min. T = absolute temperature, OK. = =
Acknowledgment
Financial assistance to T. Y. Yan for this work was provided by the School of Chemical Engineering, Purdue University; the Lilly Varnish Co.; and E. I. du Pont de Nemours & Co.
literature Cited
(1) Adkins, H., “Organic Reactions,” Adams, ed., Vol. VIII, p. 8, Wiley, New York, 1954. (2) Adkins, H., “Reactions of Hydrogen with Organic Compounds,” p. 78, University of Wisconsin Press, Madison, Wis., 1937. (3) Baranaucks, C. F., White, R. R., U. S. Patent 2,911,444 (1959). (4) Church, J. M., Abdel-Geil, M. A., Ind. Eng. Chem. 49, 813 (19571. (5)’-Ho;gen, 0. A., Watson, K. M., “Chemical Process Principles,” Vol. 3, Part 3, p. 947, Wiley, New York, 1943. (6) Husted, D. R., .4hlbrecht, A. H., U. S. Patent 2,666,797 (1954). (7)’ Ibid:, 2,681,370 (1954). (8) Lazier, W. A., Arnold, H. R., “Organic Synthesis,” A. H. Blatt, ed., Coll. Vol. 11, p. 142, Wiley, New York, 1943. (9) Markley, K. S., “Fatty Acids,” 2nd ed., Past 2, p. 1270, Interscience: New York, 1960. (10) “Newer Methods of Preparative Organic Chemistry,” p. 108, Interscience, New York, 1948. (11) Nobis, J. E., “Encyclopedia of Chemical Technology,” Vol. 6, p. 761, R. E. Kirk, D. F. Othmer, eds., Interscience EncvcloDedia. New York. 1951. (12) Traphell, 8. M. W., “Chemisorption,” p. 75, Academic Press, New York, 1955. (13) Trenner, N. R., Bacher, F. A., J . Am. Chem. Soc. 71, 2352 (1949). (14) Ft‘ojick, B., Adkins, H., Zbbid., 55, 4939 (1933). ~
RECEIVED for review October 19, 1964 ACCEPTEDMarch 31, 1965
HYDRATION BEHAVIOR OF SODIUM TRIPOLYPHOSPHATE
IN DETERGENT SLURRIES C. Y . SHEN AND J. S. METCALF
Inorganic Chemicals Division, Monsanto Co., St. Louis, M o .
In preparing detergent slurries prior to spray drying, control of the amount of hydration of sodium tripolyphosphate i s of prime importance. Using a differential thermal analysis technique, the effects of various forms of sodium tripolyphosphate, seed crystals, solids concentration, temperature, and the presence of tetrasodium pyrophosphate on the hydration rate of sodium tripolyphosphate in detergent slurries were quantitatively determined. Significant changes in hydration rate due to solids concentration, temperature, and slurry pH of a detergent slurry were noted, and this technique should be a useful tool in optimizing methods of detergent slurry preparation. OUSEHOLD
heavy-duty detergents generally are near-
H optimum mixtures of organic surfactants, builders, and various minor ingredients designed for balanced functional properties. Sodium tripolyphosphate, NajP3010, because of its good cost performance on buffering and calcium-sequestration properties, is the preferred builder and often comprises the major ingredient of a detergent composition (3,6-9). Furthermore, it is known to form a unique hexahydrate (72). T h e hydrate, exhibiting very low water vapor pressure and high stability a t room temperature, helps to give the spray-dried detergent a crisp, free-flowing appearance with a relatively constant moisture content. I t follows that in manufacturing spray-dried detergents, good control of the amount of sodium tripolyphosphate hydration in a detergent slurry is a key step in producing a satisfactory product. For example, insufficient hydration of sodium tripolyphosphate frequently results in a product of poor flow properties, thus causing problems in packaging and merchandizing the product. Excessive and
rapid hydration of sodium tripolyphosphate will result in a difficult-to-handle slurry containing lumps and gritty, sandlike particles. Since the process and equipment used by various detergent manufacturers differ considerably, numerous grades of sodium tripolyphosphate are provided by phosphate producers to give the desired hydration characteristics. Primary control of the sodium tripolyphosphate hydration rate is accomplished by varying the amount of Form-I iYaePsOlo in the phosphate. Form-I l\’ajPsOlo, being the metastable form of the two isomorphic forms a t temperatures below 420’ C. (70), hydrates more rapidly than the Form-I1 variety. T h e Form-I level may be measured directly by diffraction techniques (4),but routine determinations are made by an empirical temperature-rise (TR) test (7), in which the Form-I Na5P3010is estimated by the increase in temperature from the heat of hydration in a water-glycerol mixture. T h e hydration of Form-I1 Na5P3010in this case is inhibited by the glycerol (5)* VOL. 4
NO. 2
JUNE 1965
107
T h e simple temperature-rise test, however, cannot predict the true hydration behavior of sodium tripolyphosphate accurately under actual process conditions because of widely varying detergent compositions and crutching techniques encountered in the industry and the variation in chemical and physical properties of sodium tripolyphosphate derived from different raw materials and processes. To overcome this difficulty, additional controls on phosphate quality and detergent processing conditions are necessary (3, 6-9), and considerable time and expense are required to establish the desired control limits. There is a need for a test method which will permit direct measurement of phosphate hydration under conditions similar to those used in actual manufacture of detergents. The method employed in this work is theoretically sound, czn be applied to widely varying detergent compositions, and, we believe, fulfills this need.
no
A differential thermal analysis method has been developed for studying the kinetics of the hydration of sodium tripolyphosphate in detergent slurries. The rate of hydration is determined from the rate of heat release accompanying the hydration of the phosphate. T h e procedure involves the measurement of the temperature differential between two hot detergent slurries contained in identical thermos bottles with adequate stirrers and accessories for temperature and viscosity measurements. I n one slurry the phosphate is anhydrous a t the start of the test, while in the other it is completely hydrated. When hydration of the anhydrous test sample starts, the differential temperature between the two slurries begins to increase, and the rate of increase is proportional to the rate of formation of the hydrated phosphate. T h e calculation method used to convert the thermal data to the hydration rate is similar to that given by Borchardt and Daniels (2). Briefly, the relation between the hydration rate and the total heat effect is expressed by dn
[
heat transfer coefficient to the surrounding, cal./ O C./min. A T = differential temperature change, C., a t time 6, in minutes T h e amount of phosphate not hydrated is given by Equation 2, which can be solved by graphic integration. =
Table 1.
Sample Notation
Sodium tripolyphosphates LOW-TR High-TR Form-I1 Form-I Tetrasodium pyrophosphate* KasPsOlo. 6HzO a
108
As receiued.
l&EC
b
ledq+ le K
d6
(ATjdO]
(2)
Unless specifically mentioned in the text, the procedure given below was used for all work presented in this paper.
Chemical and Physical Properties of Test Samples
PH, 1%
[Cp
Differential thermocouple assembly, preferably multijunction to give greater accuracy of measurement. Bendix Ultra-Viscoson meter and probes. Stirrer motors with U-shaped agitators. Thermos bottles, 60 mm. in diameter by 100 mm. deep, Pyrex brand glass, evacuated and silvered. Thermos bottle lids, corks lined with aluminum foil, with proper holes for thermocouples, stirrers, and viscosity probes. Thermocouple for reference slurry.
c.
O
2
Apparatus and Procedure
where n = moles of phosphate hydrated no = moles of phosphate added initially AH = heat of hydration of the test sample, cal. C, = heat capacity of the test vessel and contents, cal./
K
-
(11
-I- R ( A T ) ]
C,
= no
The heat capacity of the test equipment and the heat transfer coefficient are determined from known slurries. The value d(AT)/dB is the slope of the curve at a given 0 from a plot of A T us. time. T h e most difficult part of this test is to arrange the stirrer in such a way that the test powder sample can be rapidly and uniformly dispersed into the detergent base slurry. For this reason, a n efficient stirrer is required. The hydration rate study is not carried out under isothermal conditions. T h e temperature of the test slurry will increase as much as 10' C. above the starting temperature in the case of Form-I sodium tripolyphosphate because of its very rapid rate of hydration. This, however, is not considered a drawback, since the results obtained will simulate closely the actual behavior of phosphates in a commercial crutching operation. The test temperatures reported are the starting temperatures of the detergent slurries prior to the addition of room temperature phosphate. T h e heats of hydration of Form-I and -11 NaSP3OI0used were those determined by McGilvery (5), -18.1 and -16.6 kcal. per mole, respectively. T h e heat of hydration of Na4P207 was calculated from the heats of formation of Na4P207 and Na4PzO7.10H20 (77) to be -14.3 kcal. per mole. The heat capacities of Na5P3Ol0 and Na4P207 were estimated from Kopp's rule as 0.24 cal./(g.)(O C.). In each test, the heat of hydration of the test sample is calculated from the weighed average of Form-I, Form-I1 sodium tripolyphosphate and tetrasodium pyrophosphate present in the sample or test mixture. A heat balance was made after each test, and the amount of heat unaccounted for was consistently less than 5%. This amount was attributed a t least in part to the tripolyphosphate dissolved in the liquid phase. The heat of crystallization of sodium tripolyphosphate hexahydrate is -2.6 kcal. per mole.
Method and Test Procedure
- - = - no do (AH)
-n
Soh.
TR, "C. Na6PaOla-Z
9.80 9.75 9.70 10.00 10.30 9.60
5.6 13.1 7.7 28.3 ca. 1 3 . 5
...
XRD Analysis, yo NasP&oZZ Na4P207 NaP0,-Z
4.9 27.8 0.0 88.6
*..
...
86.9 62.5 96.9 8.7
... ...
4.9 7.2 2.9 1.8 99.5 4.3
3.2 2.5 0.1 0.9
...
1.2
Sizing,
CR-200
CR-270
2.3 0.6 0.3 0.1 5.4 0.0
22.8 6.4 7.2 0.3 23.3 5.5
28.7 14.5 16.2
Anhydrousphosphate samples heated at 160' C. for 24 hours to remove any water of hydrationpresent.
PRODUCT RESEARCH A N D DEVELOPMENT
yo
R-700
...
...
...
70 H20 (Loss at 550" C.). 0.27 0.13 0.26 0.08 0.05 24.0
Heat the reference slurry to about 5' C. above the desired test temperature and place a known \\eight (150 to 200 grams) in the reference vessel. Start the stirrer. Heat the test slurry (all ingredients but the phosphate sample and any ingredients to be added after the addition of phosphate if so desired) to about 5' t o 10' C. above the desired test temperature. Place in the test vessel a n amount of precursor slurry siich that the weight and composition of the final slurry (after phosphate and other ingredients are added) will be the same as the reference slurry. Start stirrer. Insert thermocouple and viscosity probe assemblies and thermos lids. The temperature and viscosity of the slurries will be iecorded on the rrcorder. \Vhen the temperatures reach dynamic equilibrium conditions, as noted by an essentially constant AT between the two slurries, add the requiwd amount of phosphate sample and other ingredients to the test slurry by lowering the vessel SO that the agitator is barely submerged rather than raising the agitator and lid. Then gently shake the vessel to aid rapid dispersion of test sample into the slurry, and return to its original position immediately. \\Then the reading of the differential thermocouple has gone through a maximum and has started to decrease a t a uniform rate, the hydration of the phosphate sample is considered to be complete. The rate of hydration is then calculated from the data taken from the recorder chart. Observe the final test slurry carefully to detect any irregularity in appearance from the reference slurry. Phosphate Test Samples
'The chemical and physical properties of the test phosphate samples are given in Table I. T h e so-called low-TR and high-TR sodium tripolyphosphate samples ivere commercial grade loa.-Form-I (containing lesr than 5% Na5PsOlo-I) and high-Form-I (containinq between 20 and 4070 Na5P ~ O I 0 - Isodium ) tripolyphosphate samples randomly obtained from the market. T h e special Form-I1 sample was prepared in the laboratory and \\as unusual in that its TR value was higher than the value calculated from its Form-I content by the empirical equation (7).
1
60
'\
\ \
\
\
\
90°C.
I
I I
I
I
I \ I
I
I
3
1
Hydration Conditions: 659. Anhydrous NasP,Olo into Solution of 3 5 9 Na,SO, and 100g.H2O
[
! 70' ! and ! 95'C
1.ines:
I I
I
20
40
Form I
Na5P3010
- 2 0 - 4 0 % Form I ---- 0 - 5 % Farm I I
I
60 00 Time, rnin.
No,P3010 NQSP~O,~ I
100
I
120
I
140
Figure 1 . Effect of temperature on rate of hydration of anhydrous sodium tripolyphosphate in sodium sulfate solution
yo Form-I. Ka5P3Ol0=
4 (TR-6)
I t is believed that the high TR value of this special sample was due to high surface energy such as a much smaller than usual crystallite size. This was partially substantiated by a slight line broadening effect in the x-ray diffraction test. Earlier, McGilvery had shown that Form-I1 sodium tripolyphosphate with high surface area would give a n abnormally high TR value. T h e Form-I sodium tripolyphosphate was prepared by heating a commercial Monsanto sodium tripolyphosphate to 550' C. for 24 hours. Since tetrasodium pyrophosphate is sometimes used with sodium tripolyphosphate in building heavy-duty detergents, t h r hydration rates of some tetrasodium pyrophosphate and sodium tripolyphosphate mixtures were studied and are reported. T h e tetrasodium pyrophosphate sample was obtained from Monsanto's commercial production unit. T h e SahP3010.6Hz0used for seeding purposes was prepared by hydrating a sodium tripolyphosphate sample placed on a pool of water in a n evacuated desiccator. I t was believed that the hrxahydrate crystals produced in this manner would closely resemble in size and shape those produced in commercial sodium tripolyphosphate on absorption of moisture from the air. T h e hexahydrate used to make reference slurries was prepared by crystallization from aqueous solution with alcohol. All Test samples except the sodium tripolyphosphate hexahydrates were heated in a n oven a t 160' C. for 24 hours to remove all traces of moisture and thus to eliminate any effects due to traces of seed crystals. Mechanism of Hydration of Sodium Tripolyphosphate
A detergent slurry may be considered to consist of two principal phases-a continuous liquid phase and a discontinuous suspended phase. T h e latter Lvould be composed of undissolved phosphate, solid or liquid organic-actives, etc. I t is generally agreed that the continuous phase is the aqueous phase. Although the organic materials present in the suspended phase contain some water, it is not believed that such water is readily available for hydration. T h e aqueous continuous phase, therefore, can be considered to control the rate of hydration of sodium tripolyphosphate in detergent slurries and the crystal habit of the resulting hydrated crystals. If this assumption is correct, the hydration of a sodium tripolyphosphate detergent slurry may be evaluated from a study of the hydration in a n aqueous solution containing those chemicals present in the aqueous phase. As a first approach, the hydrztion rate of sodium tripolyphosphate in a sulfate solution \\as studied. T h e test procedure used for this study is described above. T h e ingredients consist of 65 grams of Na5PsO10,35 grams of h-a,SO,, and 100 grams of HzO. T h e sodium tripolyphosphate is added in the sodium sulfate solution at temperatures of about 70' or 90' C. For anhydrous sodium tripolyphosphate samples, Figure 1 shows the hydration rate of various types of sodium tripolyphosphate. A long induction period is required for sodium tripolyphosphate containing large amounts of Form-I1 Sa5P3010 before hydration starts, T h e hydration rate apparently follows first-order kinetics and is not affected by temperature. This indicates that the rate of diffusion is probably the controlling step. T h e induction period was found to increase with temperature and to decrease with the amount of Form-I S a 5 P 3 0 1 0 or of hexahydrate seed crystals present (Figure 2). T h e effect of N a j P 3 0 1 0 . 6 H z 0is less when the amount of added seed crystals is over 5% in the test phosphate. VOL. 4
NO. 2
JUNE 1 9 6 5
109
,
,
&Admix
with N a 5 P 3 0 1 0 * 6 H 2 0
g IO Q
Hydration Conditions:
c U
.-e
a
65p. Na5P3OI0 sample into 70'C. solution o f 359. Na2S04 and loop H 2 0
*I
E Q
.-E
l
,
lo
IO
0
2
I-
,
I
I
20 30 40 Na5P3010-I, Ye 4
6
a
I
I
50
60
IO
12
Na5P3010.6 H20 , %
Figure 2. Effect o f increase in Na6P3010-I or Na5P3010.6Hz0content on hydration rate of low temperature form Na5P3010
T h e above studies in general agree with available data on hydration of sodium tripolyphosphate in plant crutchers and with results obtained in our laboratory. Preliminary successes indicate that studying sodium tripolyphosphate hydration in a liquid medium containing the more probable ingredients in the dissolved state is a feasible approach. Hydration of Sodium Tripolyphosphate in Anionic Detergent Slurries
T h e hydration rates of various types of sodium tripolyphosphate were measured in an anionic detergent slurry in which the ratio of organic actives to polyphosphate to Na2S04 was about 1 : 2.2: 0.7. To reduce the number of variables, the composition of the organic-active mixture used to prepare the base slurry was kept constant. Anionic active compositions vary widely in the industry and this variation can cause differences in behavior of sodium tripolyphosphate; however, the limited amount of data available indicates that these differences will be small in comparison with those observed on changing the type of tripolyphosphate used. T h e active mixture used in this tvork consisted of sodium alkylaryl sulfonate and sodium alkyl sulfate. Sodium silicate, sodium carboxymethylcellulose, and dye were added to simulate a commercial detergent formulation. Effects of Solid Concentration. I n the initial tests, the temperature and slurry solids concentration were kept moderately low, 65" C. and SO%, respectively. As shown in Figure 3, the hydration rate of the low-TR sodium tripolyphosphate is comparable to that of the high-TR sample, with the advantage that the low-TR sodium tripolyphosphate does not form as many hard, slowly soluble lumps. Under these test conditions, about 10% of the high-TR sodium tripolyphosphate appears to cake and complete hydration of this caked material within a few hours is nearly impossible. The special Form-I1 sodium tripolyphosphate hydrates somewhat faster than the high-TR sodium tripolyphosphate and without caking. T h e hydration rate of Form-I sodium tripolyphosphate was extremely fast (less than 5 minutes for complete hydration) 110
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N 1
Types of Sodium Tripolyphosphate
4-
s
f
2
$
'1
Special Form-II H i g r R L ] 1 % For;-I A Low-TR 0 - 5 % Form-I 0 High-TR 20-40% Form-I 0 LOW-TR 0 5 'Ye Form-I A Special Form-II
3
2O
-
5
10
15
20
il
Percent S o l i d s Concentrotion
25
60 60
30
Time, m i n .
Figure 3. Effect of high solids concentration on hydration of Form-ll Na5P3OI0in anionic formulations at 65" C.
and a n accurate measurement of the actual rate was difficult because many hard lumps formed when the test sample was mixed with the slurry. O n increasing the solids concentration from 50% to 60%, the hydration rate of low-TR sodium tripolyphosphate was greatly reduced as shown in Figure 4. T h e apparent fasthydrating characteristic of the special Form-I1 material was not observed at this solids concentration and, moreover, an induction period of 5 minutes occurred before actual hydration started. Complete hydration of the special Form-I1 sodium tripolyphosphate required about 200 minutes. T h e hydration rate of Form-I sodium tripolyphosphate was again fast, and formation of a large amount of hard lumps could not be avoided under test conditions. The most noticeable effect of increased solid concentration on the hydration of anhydrous sodium tripolyphosphate is that high solids concentration tends to inhibit the hydration of Form-I1 sodium tripolyphosphate, but has little effect on the hydration rate of Form-I sodium tripolyphosphate. T h e rate for a mixture of Form-I and Form-I1 (as in high-TR sodium tripolyphosphate) was retarded a n intermediate amount, as was expected. Effects of Temperature. Theoretically, the hydration rate of a n inorganic salt a t some elevated temperature can be expected to approach zero or negative values (dehydration) because the anhydrous salt becomes the stable phase. O n the other hand, a t temperatures below the transition point, the hydration rate may increase with temperature because of such factors as reduced liquid viscosity and higher specific hydration rate constant. The true transition temperature of anhydrous sodium tripolyphosphate and the hexahydrate is not known, though a rough extrapolation of the hydration rate of sodium tripolyphosphate in water a t different temperatures indicates that it is somewhat above 100' C. This was also indicated from the apparent vapor pressure of NasP3Olo.6 H z 0 a t various temperatures. The purpose of this investigation was to determine how temperature affects the hydration
rate of sodium tripolyphosphate. A temperature of 90" C. >vas chosen, because it was difficult to maintain the test slurry a t higher temperatures. T h e test results are suinmarized in Figure 4. At temperatures around 90' C., a n induction period is required before actual hydration starts for anhydrous sodium tripolyphosphate other than the straight Form-I modification. T h e induction period appears to increase with slurry solids concentration, and for the special Form-I1 m d the low-TR sodium tripolyphosphate a t 607, solids concentration and 90' C. is a t least 75 minutes. T h e tests were stopped a t this point because it was feared that appreciable amounts of sodium tripolyphosphate had hydrolyzed and that the hydrolyzed products from sodium tripolyphosphate could inhibit nucleation. Once hydration did start, hou ever, the hydration rate apparently followed a first-order relationship until only a small amount of sodium tripolyphosphate was left. T h e small amount of unhydrated sodium tripolyphosphate varied somewhat from batch to batch and is believed to represemt the portion either dissolved in the aqueous phase or enclosed in lumps which resisted hydration. T h e hydration rates of low-TR and high-TR sodium tripolyphosphate n e r e about the same once the hydration started. At 90' C. and 50% solids concentration (and a t 65" C.) the special Form-I1 sodium tripolyphosphate hydrated faster than either loiv-TR or high-TR sodium tripolyphosphate (Figure 3). Form-I sodium tripolyphosphate hydrates very fast a t both 50 and 60% solids concentrations, regardless of the change of temperature. T h e striking phenomenon for the Form-I sodium tripolyphosphate slurry produced around 90' C. was the low apparent viscosity and uniformity in contrast to the hard, lumpy slurry observed a t 65' C. I n summary, a n increase in temperature from 65' to 90" C. appears to decrease the hydration rate for Form-I1 sodium tripolyphosphate as well as the induction time before actual hydration starts. However, the hydration rate of Form-I
sodium tripolyphosphate is not affected by the temperature increase. Effects of NaSP3010.6H,0Seed Crystals. The hydration of anhydrous sodium tripolyphosphate containing a substantial quantity of the Form-I1 Na5P3010 in a detergent slurry frequently shows an induction period characteristic of a nucleation process. Therefore, it was expected that the hydration rate of a Form-I1 sodium tripolyphosphate could be increased by incorporating a few per cent of N a 5 P 3 0 1 0 . 6 H z seed 0 crystals in the test sample. Indeed, as shown in Figure 5, the induction period disappeared with the addition of 2% Na6P3010.6Hz0 to the Form-I1 or low-TR sodium tripolyphosphate. T h e presence of these Seed crystals caused a n increase in hydration rate a t the test solids concentration and temperature employed. Smoother slurries of lower viscosity were produced from either low-TR or high-TR sodium tripolyphosphate when 2% Na6P3010.6H~0seed crystals were added to the test samples. No appreciable change in the consistency of the slurry or change in the hydration rate was noticed when 2y0 Sa5P3010.6H20 seed crystals were added to Form-I sodium tripolyphosphate. This appears to be of importance, since it indicates that the hydration characteristics of NasP3010-1 would be relatively unaffected by absorption of trace quantities of water from the air. This is not the case for commercial low-TR and high-TR sodium tripolyphosphate. I n certain cases the formation of larger hexahydrate crystals and thinner slurries was claimed with the use of anhydrous sodium tripolyphosphates because of their ability to form supersaturated solutions (7). Effects of Tetrasodium Pyrophosphate. Tetrasodium pyrophosphate is sometimes used with sodium tripolyphosphate as a detergent builder. Because the effect of tetrasodium pyrophosphate on the hydration rate of sodium tripolyphosphate has not been thoroughly investigated, a mixture consisting of 507, NaSP3010-Iand 507, Sa4P2Oi was prepared and its hydration rate was evaluated as shown in Figure 6. Tentative conclusions drawn from these tests are as follows : Tetrasodium pyrophosphate did not hydrate above 79.5' C., the transition temperature to anhydrous form, as was expected. I t seems that, under the test conditions, it will not hydrate completely a t a solids concentration above 60%; even a t lower temperatures.
\
'.
B 30L CT : 0
.E 20+
3l 2O
Firm-I ;!
------7 --5 6
IO
Lo;-TR, 0,-5 % H i g h - T R , 20-40% Form-] L o w - T R . 0 - 5 96 Form-I Special F o r m - X
20
s
" '-1L .U
,
E
:
E
8
=0 30 Time, min.
40
50
60
Figure 4. Effect of combination of high temperature (90" C.) and high solids concentration (6OyO) on hydration of Form-11 Na5P,OIo
'With W i t h Seeds, 65'C,
10 10-
j
,
,
5
IO
,
, 15
, 20
, 25
30
Time, min.
Figure 5. Effect of addition of 2% NaSP3010.6Hz0 seed crystals on hydration rate of low temperature form sodium tripolyphosphate at high solids concentration (60y0) VOL. 4
NO. 2
JUNE 1 9 6 5
111
Oool
I
I
10
20
1
I
30 40 Time, min.
I
I
50
60
Figure 6. Hydration of 50% Na4PZ07and 50% NajP3010-l mixture in anionic detergent slurry
(t2L2-L
I ooo
20
40
60
00
100
Percent Na5P3010Hydrated Figure 7. Relation between degree of hydration of Form-ll NajP3010and apparent viscosity of detergent slurry Hydration condition. 65’ C., 50% solids
At low temperatures and solids concentration, tetrasodium pyrophosphate hydrates in the test slurry, but a long induction period is required and hydration proceeds a t a much slower rate than for low-TR sodium tripolyphosphate. ‘The presence of tetrasodium pyrophosphate in a Form-I sodium tripolyphosphate sample apparently reduces the hydration rate of the latter, when the test slurry solids concentration is high. The reason for this behavior is not entirely clear. I t could not be due to occlusion of test sample, because under all test conditions, the resultant test slurries were thin and uniform. \.Vhen tetrasodium pyrophosphate did hydrate, as in the case of low temperature and low concentration, the apparent viscosity of the resulting slurry was lower than that of a slurry made with low-TR sodium tripolyphosphate. This may have been the result of air entrainment, since the slurry was noticeably more voluminous than other sodium tripolyphosphate slurries. Relation between Amount of Sodium Tripolyphosphate Hydrated and Apparent Viscosity of Detergent Slurry. In most of the low-solids-concentration tests (50y0 solids), apparent viscosity increased continuously with time. The apparent viscosity was measured by a Bendix Ultra-Viscoson probe in conjunction with a n Ultra-Viscoson computer and a millivolt recorder. The probe was calibrated and rechecked with air, water, and oil of known viscosity before and after each test. At high solids concentration (above 60% solids), the Ultra-Viscoson probe could not be used continuously because stirring of the slurry tended to damage the probe blade. T h e data indicated that the apparent viscosity follows the amount of hydration very well, as shown in Figure 7. T h e surprising fact was that the apparent viscosities of detergent slurries prepared from different types of sodium tripolyphosphate varied as much as tenfold. A plausible explanation is that the shape and size of hexahydrate crystals produced from each type of sodium tripolyphosphate differ under different test conditions. This has been partially substantiated by examining the hexahydrate crystals under the microscope. The thin slurry obtained from Form-I sodium tripolyphosphate 112
I&EC
P R O D U C T RESEARCH A N D D E V E L O P M E N T
a t 90’ C. had much bigger and blockier hexahydrate crystals than those prepared from sodium tripolyphosphate containing large amounts of Form-I1 Na5P3OI0. A summary of test results is given in Table 11. Since the rate of hydration of samples containing a substantial quantity of Form-I1 sodium tripolyphosphate decreases with a n increase in temperature, the “activation energy” calculated by the conventional Arrhenius equation is a negative value of 18 kcal. per mole of NasPsOlo. I
TI W c
0 L
TI
z c 3 W e
0 c
In CL
c a h
-0
.-a
s
.TI
0 u)
c
c
W
E
a Time, min. Figure 8. Hydration of sodium tripolyphosphate in nonionic detergent slurry
Table II.
Summary of Hydration Rate of Various Types of Sodium Tripolyphosphate and Apparent Viscosity of Final Test Slurries
Tvpe of Phosphate
Low-TR
Test Sluyy Temp,, C.
Solids Concn.,
65 90 65
50 50 60 60 50 50 60
90
High-TR
65 90
Pure Form-I1
65 90 65 90 65 90
Low-TR plus 2% NajPsOlo.6Hz0
65 90
Form-I
65 90 65 90 65
507, Form-I, 507, Na4P207
Form-I plus 2% NaaPsOlo.6H20
90 65 90 65 90 65 90
wt.%
Approx. Induction Time, M i n . 0
750 510 20,000+
50 50 60 60 50 50
0
...
...
1 .o
0 10 0
10
60 50 50 60 60 50 50 60 60 60 60
Apparent Viscosity, Centipoise
2.5 15.0 37.5
10 5 75
60
60
Approx. Half Lqe, Min.
...
18.0
2,000 20,OOOf 15,000
6.0
33.0 0.7
...
11 .o
5 5 75 0 0
850 20,OOOf
37.5
...
0 0 0 0
2.0 12.0 7.5 27.0 1. o 2.0 2.0 2.0
0
...
0 0
... ...
320 20,000 20,000
+ +
...
0
...
520 350+ 10,000=
0
1 .o 1 .o
Many hard lumps 6,000
0
t
0 0
.
.
8,000”
Na‘aaPz07does not hydrate.
Effects of pH. When the p H of a detergent slurry (based on a solution of 2 grams of slurry per 100 grams of water) is increased from 9 to 10 to 11 to 12, the hydration rate of sodium tripolyphosphate also increases, and the resultant slurry a t the higher p H is noticeably thinner even after the completion of hydration of sodium tripolyphosphate. T h e increase in hydration rate probably is due to the decreased solubility of sodium tripolyphosphate a t the higher p H . T h e fact that the apparent viscosity is lowered by increasing p H indicates that part of the water or solution which is trapped in the solids agglomerates and organic actives may be released in a manner similar to the well known deflocculation action. A drop in p H on addition of a small amount of H2SO4-for example, a change of slurry pH from 10 to 8.5 based on a solution containing 2 grams of slurry per 100 grams of wateroften results in a slower hydration rate of tripolyphosphate and changes in slurry viscosity. T h e drop in hydration rate may also be explained by the increase in sodium tripolyphosphate solubility a t a lower pH. T h e effect of slurry p H on the hydration rate of sodium tripolyphosphate appears to hold for detergent slurries containing either anionic or nonionic actives, and also for a simple sodium sulfate-water slurry. I n other words, the p H of the slurry may be used for controlling the sodium tripolyphosphate hydration rate. Hydration of Sodium Tripolyphosphate in Nonionic Detergent Slurries
T h e behavior of sodium tripolyphosphate in a nonionic detergent slurry is similar to that in a n anionic detergent slurry. For example, Figure 8 shows the hydration of highTR and Form-I NabP3010 in a nonionic detergent slurry consisting of 11 parts of Sterox AJ-100 (polyoxyethylene ether), 5.5 parts of sodium silicate, 0.8 part of sodium carboxymethylcellulose, 30 parts of sodium carbonate, and 50 parts of Nab-
P3010 on
a dry basis.
Again, the induction period of the high-
TR material can be reduced by addition of hexahydrate seed crystals. Conclusions
T h e relatively sophisticated techniques of differential thermal analysis and continuous measurement of viscosity during the hydration of sodium tripolyphosphate have shown vast differences in both rate or amount of hydration and the apparent viscosity of finished slurries through manipulation of variables largely controllable by detergent manufacturers. Use of this tool will permit optimization of crutching conditions for any of the common detergent formulations to achieve higher slurry solids, increased water content in the finished product, and reduced caking tendency. Moreover, the bulk of the experimentation can be done in the laboratory. literature Cited
(1) American Society for Testing Materials, ASTM Designation D501-55T, June 1955. (2) Borchardt, H. J., Daniels, F., J . Am. Chem. 5’06. 79,41 (1957). (3) Hizer, E. S., U. S. Patent 2,622,068 (Dec. 16, 1952). (4) Mabis, A. J., Quimby, 0. T., Anal. Chern. 25, 1814 (1953). (5) McGilvery, J. D., ASTM Bull. 191 (July 1953). (6) McNaught, J. P., U. S. Patent 2,897,155 (July 28, 1959). (7) Martin, J. B., Zbid., 2,961,409,2,961,410 (Sov. 22, 1960). (8) Metcalf, J. S., Zbid., 2,904,513 (Sept. 15, 1959). (9) Mills, V., Hromberg, H. B., Kemp, C. B.. Zbid., 2,712,529 (July 5, 1955). (10) Morey, G. W., J . A m . Chem. SOC.80, 775 (1958). (11) Natl. Bur. Standards, “Selective Values of Chemical Thermodynamic Properties,” Circ. 500. (12) Shen, C. Y., Metcalf, J. S., O’Grady, E. V., 2nd. Eng. Chem. 51, 717 (1959). RECEIVED for review September 24, 1964 ACCEPTED March 18, 1965 Division of Industrial and Engineering Chemistry, Symposium on New Processes in Synthetic Detergents, 148th Meeting, ACS, Chicago, Ill., September 1964. VOL. 4
NO. 2
JUNE 1965
113
