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Design and Analysis of Experiments for Obtaining High Bulk Density Sodium Tripolyphosphate Marcin Banach* and Zygmunt Kowalski Institute of Inorganic Chemistry and Technology, Cracow UniVersity of Technology, 24 Warszawska St., 31-155 Cracow, Poland
The results of experiments for obtaining granulated sodium tripolyphosphate with bulk density adjustable within 1.00-1.05 kg/dm3 and expected content of STPP crystalline phases are presented. The scope of experiments included the identification of factors with statistically significant impacts on the study object and the estimation of response surface. Because of the application of the Plackett-Burman design, 15 input factors could be evaluated regarding their impact significance and insignificant factors could be eliminated. Moreover, the Hartley design enabled the determination of a response surface based on the general regression equation in the form of a second degree polynomial with double interactions. The input factor values, determined on the basis of the prediction profile and desirability function, were used to perform a series of experiments to achieve STPP expected bulk density within the range of 1.00-1.05 kg/dm3. 1. Introduction Since 1940, we can observe the mass production of sodium tripolyphopshate used as a detergent component.1 STPP is widely used in detergents because of its advantageous properties, such as calcium and magnesium ion sequestration in hard water, buffering properties, emulsion stability, deflocculation, and dispersion.2-5 There is no other single chemical compound involving so many different functions as an active additive affecting the performance of innovative washing powders which has been found or developed so far. Until the mid-1980s, traditional washing powders with low bulk density that required high doses were the basic form of washing products. In 1987, the Kao Corporation introduced a compact washing powder onto the Japanese market for the first time. By the end of the 1980s, compact powders were already used in Europe and North America. In the 1990s, a new kind of detergent, tablets, was launched. Nowadays, “compact” and tablet washing powders have substituted traditional washing powders to a considerable extent.4,6,7 Regarding traditional washing powders, the compact products have higher bulk density (0.60-1.00 kg/dm3). They contain more surface active agents (25-50% by weight), whereas powders with low bulk density contain ca. 20% by weight. The increase in bulk density and surfactant quantity enabled a 3-fold decrease in the quantity of cleaning agent used for washing.4,6 Sodium tripolyphosphate (pentasodium triphosphate (V) STPP) appears in three crystalline forms. Salt hexahydrate (Na5P3O10 · 6H2O) is a stable form of sodium tripolyphosphate. The other two forms are anhydrous salts specified as phase 1 (high-temperature) and phase 2 (low-temperature). Phase 2 is transformed into phase 1 at ∼417 °C.1,8-12 Sodium tripolyphosphate phase 1 undergoes hydration very quickly forming small hydrated salt crystals. Its solubility reaches the value characteristic for hexahydrate, starting from an initial value of ∼32 g/100 g solution. The hydration rate in phase 2 is considerably lower. The solubility of the lowtemperature form is similar to the solubility of hydrated salt after ∼15 min. The obtained crystals are very large.1,13 * To whom correspondence should be addressed. Telephone: +4812 628 28 61. Fax: +4812 628 20 36. E-mail: marcinbanach@ chemia.pk.edu.pl.
Wet-process or thermal phosphoric acid and sodium carbonate or sodium hydroxide are the most commonly used raw materials for producing sodium tripolyphosphate. Phosphoric acid is produced by wet methods and thermal methods. Wet phosphoric acid is obtained in the reaction of sulphuric acid and ground mineral phosphates at high temperature. In thermal methods for the production of phosphoric acid phosphorus is burned to obtain phosphoric anhydride, which is then hydrated. As wet-process phosphoric acid contains impurities which affect the process of STPP formation, its preliminary purification is required. Iron and aluminum ions lower, for example, the temperature of phase 2 transformation into phase 1, whereas sulphates inhibit this process. Sodium hydroxide and thermal phosphoric acid can result in forming a product of a high purity level.8,9,14,15 Sodium tripolyphosphate is usually produced by the sprayfurnace method. Sodium orthophosphates solution undergoes spray drying at the first stage of this process, and the dried mixture is calcinated in a rotary kiln at the second stage. This method is used, inter alia, by such companies as Krebs, Lurgi and Montecatini.16,17 The content of STPP crystalline phases and granulation can be widely modified as the separate drying and calcination reactors are used. However, the product’s low bulk density (0.55-0.75 kg/dm3) being the result of spray drying is the disadvantage of the process. The low content of sodium phosphates bulk density is caused by the characteristic morphology of the particles. Sodium phosphate particles obtained due to spray drying have a spherical shape and a characteristic “shell” structure with an undulating surface.18 Previously carried out studies allowed for the establishment of parameters having a significant effect on the bulk density of sodium tripolyphosphate and for the design of a model process in which medium bulk density product is obtained.19,20 The process of obtaining high bulk density sodium tripolyphophate is studied in this work. The aim of the experiments was to verify the significance of the process parameters’ impact on sodium tripolyphosphate bulk density, the estimation of response surface and the application of the created model to predict the output value, sodium tripolyphopshate bulk density.
10.1021/ie1011195 2010 American Chemical Society Published on Web 11/08/2010
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ratios in a mortar. The mass was calcinated in an electrically heated chamber furnace. The process flow sheet is presented in Figure 1. Bulk density was measured for the granulometric fractions of the obtained products mixture (10% of fraction with size >1.00 mm; 20%, 0.85-1.00 mm; 5%, 0.60-0.85 mm; 58%, 0.25-0.60 mm).21 The phase content of tested materials was identified by X-ray powder diffraction using a Philips X’Pert diffractometer with graphite monochromator PW W 1752/00. The real properties of sodium tripolyphosphate depend on numerous factors related to both raw materials’ physicochemical properties as well as their processing and product formation parameters. They were classified into the groups of input, output and constant factors. The group of input factors (independent variables), their determination and studied area defined by their variation range are presented in Table 1. Granulated product bulk density (kg/ dm3) was assumed as the output factor (y, dependent variable). The mass of sodium phosphates after spray drying (100 g) was assumed as a constant value. The scope of the experiments covered the determination of factors that have statistically significant impacts on the study object and the determination of independent variables and the level of their impact on process results, the estimation of response surface and values of input factors providing the most expected values of sodium tripolyphosphate bulk density. The input factor values, determined on the basis of prediction profile
Figure 1. Flow sheet of high bulk density sodium tripolyphosphate production process.
2. Experimental Section The process of obtaining high bulk density (1.00-1.05 kg/ dm3) sodium tripolyphosphate is the study object. The mixture of sodium phosphates and water and mesh return of the calcination product (granulation fraction below 0.25 mm) were used as raw materials. The applied mixture of sodium phosphates is an intermediate obtained as a result of sodium phosphate solution spray drying in an STPP industrial installation. Sodium tripolyphosphate samples with a predetermined bulk density were prepared by mixing reagents of known weight
Table 1. Determination of Studied Factors and Their Values at Low and High Level variable symbol
variable name
x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15
sodium phosphates temperature sodium phosphates crushing time water mass water temperature water dosing rate mixture mixing time (sodium phosphates + water) STPP mass STPP temperature STPP dosing rate STPP phase compositiona mixture mixing time (sodium phosphates + water + STPP) calcination initial temperature calcination maximum temperature calcination time at max temperature product cooling rate
a
unit
low level (-1)
high level (+1)
20 0 30 10 200 5 50 20 0.33 1 5 20 350 30 20
120 5 60 90 1000 10 100 120 100 2 10 350 550 60 50
°C min g °C µL/s min g °C g/s min °C °C min °C/min
(Phase 1, 1; phase 2, 2; phase 1/phase 2 ) 1:1, 1:5).
Table 2. Plackett-Burman Design (Factors Screening Design) independent variables
dependent variable
no.
x1
x2
x3
x4
x5
x6
x7
x8
x9
x10
x11
x12
x13
x14
x15
y
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
20 120 20 120 20 120 20 120 20 120 20 120 20 120 20 120 70 70 70
0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 2.5 2.5 2.5
30 30 30 30 60 60 60 60 30 30 30 30 60 60 60 60 45 45 45
10 10 10 10 10 10 10 10 90 90 90 90 90 90 90 90 50 50 50
1000 200 200 1000 1000 200 200 1000 1000 200 200 1000 1000 200 200 1000 600 600 600
10 5 10 5 5 10 5 10 10 5 10 5 5 10 5 10 7.5 7.5 7.5
100 50 100 50 100 50 100 50 50 100 50 100 50 100 50 100 75 75 75
120 120 20 20 20 20 120 120 120 120 20 20 20 20 120 120 70 70 70
100 100 0.33 0.33 100 100 0.33 0.33 0.33 0.33 100 100 0.33 0.33 100 100 50.2 50.2 50.2
2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 1.5 1.5 1.5
5 10 10 5 10 5 5 10 5 10 10 5 10 5 5 10 7.5 7.5 7.5
20 350 350 20 20 350 350 20 350 20 20 350 350 20 20 350 185 185 185
350 550 350 550 550 350 550 350 550 350 550 350 350 550 350 550 450 450 450
30 30 60 60 60 60 30 30 60 60 30 30 30 30 60 60 45 45 45
50 20 20 50 20 50 50 20 20 50 50 20 50 20 20 50 35 35 35
0.990 0.984 0.964 1.032 1.020 0.954 1.050 0.964 0.996 0.954 0.916 1.022 0.992 1.066 0.990 1.078 0.998 1.010 1.010
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Table 3. Effect Estimates confidence limit -95%
factor
effect
standard error
t(4)
p
mean/intercept x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15
0.99947 0.01700 0.00750 0.03200 0.00700 0.02700 -0.01450 0.03950 0.00500 -0.00800 0.02750 -0.02850 0.01350 0.03900 0.00050 -0.00500
0.00209 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454 0.00454
479.4171 3.7415 1.6507 7.0428 1.5406 5.9424 -3.1913 8.6935 1.1004 -1.7607 6.0524 -6.2725 2.9712 8.5834 0.1100 -1.1004
0.00000 0.03331 0.19737 0.00588 0.22106 0.00953 0.04966 0.00320 0.35152 0.17651 0.00905 0.00818 0.05901 0.00332 0.91932 0.35152
+95%
0.99284 1.00611 0.00254 0.03146 -0.00696 0.02196 0.01754 0.04646 -0.00746 0.02146 0.01254 0.04146 -0.02896 -0.00004 0.02504 0.05396 -0.00946 0.01946 -0.02246 0.00646 0.01304 0.04196 -0.04296 -0.01404 -0.00096 0.02796 0.02454 0.05346 -0.01396 0.01496 -0.01946 0.00946
and desirability function, were used to conduct a series of experiments to achieve the expected STPP bulk density value within the range of 1.00-1.05 kg/dm3. The predetermined partially saturated Plackett-Burman design and the predetermined poly section Hartley design were considered as optimal designs regarding selection criteria (feasibility, informativity, efficiency).22,23 Because of the application of the Plackett-Burman design, 15 input factors could be evaluated regarding their impact significance and insignificant factors could be eliminated. Moreover, the Hartley design enabled the determining of the response surface based on the general regression equation y ) b0 + b1x1 + ... + bkxk + b1,2x1x2 + b1,3x1x3 + ... + bk-1,kxk-1xk + b1,1x12 + ... bk,kxk2 3. Results X-ray diffraction analysis demonstrated that monosodium and disodium orthophosphate double salt (NaH2PO4 · Na2HPO4) present the basic crystalline phase of the applied raw material. The accompanying phases for double salt are disodium orthophosphate (Na2HPO4), disodium orthophosphate dihydrate (Na2HPO4 · 2H2O), sodium pyrophosphate (Na4P2O7), and monosodium orthophosphate (NaH2PO4). Adding water to sodium phosphates and returning a part of the product results in forming a mixture of the following phase Table 4. Analysis of Variancea factor
SS
df
MS
F
P
x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x15 x15 error total SS
0.00116 0.00023 0.00410 0.00020 0.00292 0.00084 0.00624 0.00010 0.00026 0.00303 0.00325 0.00073 0.00608 0.000001 0.00010 0.00025 0.02946
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 18
0.00116 0.00023 0.00410 0.00020 0.00292 0.00084 0.00624 0.00010 0.00026 0.00303 0.00325 0.00073 0.00608 0.000001 0.00010 0.00008
13.9987 2.7247 49.6010 2.3735 35.3117 10.1842 75.5762 1.2110 3.1001 36.6316 39.3442 8.8279 73.6750 0.0121 1.2110
0.03331 0.19737 0.00588 0.22106 0.00953 0.04966 0.00320 0.35152 0.17651 0.00905 0.00818 0.05901 0.00332 0.91932 0.35152
confidence limit coefficient standard error coefficient 0.99947 0.00850 0.00375 0.01600 0.00350 0.01350 -0.00725 0.01975 0.00250 -0.00400 0.01375 -0.01425 0.00675 0.01950 0.00025 -0.00250
0.00209 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227 0.00227
+95%
0.99284 1.00611 0.00127 0.01573 -0.00348 0.01098 0.00877 0.02323 -0.00373 0.01073 0.00627 0.02073 -0.01448 -0.00002 0.01252 0.02698 -0.00473 0.00973 -0.01123 0.00323 0.00652 0.02098 -0.02148 -0.00702 -0.00048 0.01400 0.01227 0.02673 -0.00698 0.00748 -0.00973 0.00473
content: Na2HPO4 · 2H2O, Na2HPO4, NaH2PO4 · 2H2O, Na5P3O10 · 6H2O, and depending on the phase content of the recirculated product, Na5P3O10 phase 1, Na5P3O10 phase 2, or a mixture of both phases. STPP phase 2 is the product of calcination conducted at 350 and 450 °C, and STPP phase 1 results from calcination at 550 °C. 3.1. Study of Process Parameters’ Impact Significance. The effect of 15 input variables on the output variable in the area with the limits presented in Table 1 was tested. The matrix of the experiment eliminating sodium tripolyphosphate bulk density and measurement results are presented in Table 2. The matrix has been supplemented with three systems of the central plan, where all input data are mean values. These systems are a partial iteration of the plan. The evaluation of analyzed independent variables’ effects on the dependent variable at 5% and 2.5% significance levels was performed on the basis of presented data (Table 3). Also, the analysis of variances was conducted (Table 4). The effects indicate changes in STPP bulk density at an extreme change of a given factor and invariable values of other input factors. The effects, for which the test probability level (p) defined in Table 3 assumes values lower than the accepted significance level (5% or 2.5%) are statistically significant. The obtained results enabled the selection of x3 (water mass), x5 (water dosing rate), x7 (STPP mesh pass mass), x10 (STPP phase content), x11 (sodium phosphates, water and STPP mixture grinding time), and x13 (calcination maximum temperature)
a
SS, variance; df, degrees of freedom; MS, mean square effect; F, F test value; p, significance level.
-95%
Figure 2. Pareto chart of standardized effect.
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Table 5. Hartley Design (PS/DS-P:Ha6) independent variables
dependent variable
standard deviation
no.
x3
x5
x7
x10
x11
x13
y1
y2
y3
ymean
S(y)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
60 60 60 60 30 30 30 30 30 30 30 30 60 60 60 60 30 60 45 45 45 45 45 45 45 45 45 45 45
1000 1000 1000 1000 1000 1000 1000 1000 200 200 200 200 200 200 200 200 600 600 200 1000 600 600 600 600 600 600 600 600 600
100 100 100 100 50 50 50 50 100 100 100 100 50 50 50 50 75 75 75 75 50 100 75 75 75 75 75 75 75
2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 1.5 1.5 1.5 1.5 1.5 1.5 1 2 1.5 1.5 1.5 1.5 1.5
10 10 5 5 10 10 5 5 10 10 5 5 10 10 5 5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 5 10 7.5 7.5 7.5
550 350 550 350 550 350 550 350 550 350 550 350 550 350 550 350 450 450 450 450 450 450 450 450 450 450 350 550 450
1.020 0.978 1.010 0.982 0.938 0.834 0.926 0.930 0.960 0.912 0.958 0.910 0.946 0.948 0.964 0.930 0.928 0.982 0.994 0.984 0.944 1.008 0.974 0.976 0.970 0.978 0.972 1.008 0.958
1.018 0.978 1.010 0.978 0.944 0.836 0.920 0.926 0.964 0.904 0.936 0.920 0.948 0.946 0.966 0.936 0.908 0.986 0.998 0.980 0.940 1.004 0.966 0.972 0.968 0.978 0.974 0.998 0.966
1.024 0.982 1.006 0.986 0.926 0.826 0.916 0.940 0.952 0.900 0.936 0.914 0.950 0.946 0.958 0.928 0.912 0.986 0.998 0.978 0.940 1.004 0.968 0.964 0.964 0.972 0.984 1.002 0.960
1.021 0.979 1.009 0.982 0.936 0.832 0.921 0.932 0.959 0.905 0.943 0.915 0.948 0.947 0.963 0.931 0.916 0.985 0.997 0.981 0.941 1.005 0.969 0.971 0.967 0.976 0.977 1.003 0.961
0.0031 0.0023 0.0023 0.0040 0.0092 0.0053 0.0050 0.0072 0.0061 0.0061 0.0127 0.0050 0.0020 0.0012 0.0042 0.0042 0.0106 0.0023 0.0023 0.0031 0.0023 0.0023 0.0042 0.0061 0.0031 0.0035 0.0064 0.0050 0.0042
Table 6. Regression Coefficients confidence limit coefficients
value
standard error
t(23)
p
-95%
+95%
b0 b3 b5 b7 b10 b11 b13 b3,5 b3,7 b3,10 b3,11 b3,13 b5,7 b5,10 b5,11 b5,13 b7,10 b7,11 b7,13 b10,11 b10,13 b11,13 b3,3 b5,5 b7,7 b10,10 b11,11 b13,13
0.52022 0.01456 0.00000 0.00075 0.21591 -0.00875 -0.00071 0.00000 0.00004 -0.00129 0.00015 0.00000 0.00000 0.00004 -0.00001 0.00000 -0.00023 0.00010 0.00000 0.00337 -0.00017 0.00003 -0.00013 0.00000 -0.00001 -0.03736 -0.00123 0.00000
0.09766 0.00125 0.00004 0.00075 0.04398 0.00880 0.00026 0.00000 0.00001 0.00013 0.00003 0.00000 0.00000 0.00000 0.00000 0.00000 0.00008 0.00002 0.00000 0.00228 0.00006 0.00001 0.00001 0.00000 0.00000 0.00988 0.00040 0.00000
5.3268 11.6191 0.0854 0.9998 4.9099 -0.9950 -2.7305 -4.5714 5.0096 -10.2090 5.8274 -4.8635 -2.4683 8.8945 -5.3893 3.0233 -3.0233 6.5285 1.6212 1.4751 -3.0233 2.4975 -11.7380 3.7742 -2.4307 -3.7796 -3.1051 4.1788
0.00000 0.00000 0.93221 0.32150 0.00001 0.32382 0.00833 0.00003 0.00001 0.00000 0.00000 0.00001 0.01649 0.00000 0.00000 0.00370 0.00370 0.00000 0.11031 0.14550 0.00370 0.01532 0.00000 0.00037 0.01813 0.00037 0.00292 0.00010
0.324801 0.012051 -0.000075 -0.000753 0.127920 -0.026349 -0.001222 -0.000003 0.000023 -0.001548 0.000097 -0.000004 -0.000001 0.000033 -0.000007 0.000000 -0.000382 0.000069 0.000000 -0.001200 -0.000287 0.000006 -0.000151 0.000000 -0.000018 -0.057139 -0.002019 0.000001
0.715635 0.017065 0.000081 0.002256 0.303907 0.008848 -0.000188 -0.000001 0.000053 -0.001041 0.000199 -0.000002 0.000000 0.000052 -0.000003 0.000000 -0.000078 0.000130 0.000001 0.007934 -0.000058 0.000051 -0.000107 0.000000 -0.000002 -0.017581 -0.000437 0.000002
variables having a significant impact on STPP bulk density at 2.5% significance level. At the assumed 5% significance level, x1 (sodium phosphates temperature) and x6 (sodium phosphates and water mixture grinding time) additionally demonstrate the significant impact on the dependent variable. Figure 2 is a graphic illustration of the elimination plan results. The statistical analysis also allowed the determination of the input factors variability effect on the result factor. Because of
the positive effect and at increasing their values, x1, x3, x5, x7, x10, and x13 variables cause increase in STPP bulk density. The increase in x6 and x11 variables values results in decreasing the value of the dependent variable. 3.2. Estimation of Response Surface. On the basis of the evaluation of 15 independent variables’ significance impact on sodium tripolyphosphate, the following items were regarded as significant: water mass (x3), water dosing rate (x5), STPP mesh
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Figure 3. Profiles for predicted values (1.05 kg/dm3) and desirability (D). Table 7. Bulk Density Analysis at Optimum Values of Parameters bulk density (kg/dm3)
parameters
standard deviation
x3 (g)
x5 (µL/s)
x7 (g)
x10
x11 (min)
x13 (°C)
y1
y2
y3
ymean
S(y)
60 60 60 60 50 50
1000 1000 1000 200 200 200
100 100 100 100 100 100
2 1.5 1 2 1.5 1
10 10 5 10 10 5
350 450 550 350 450 550
0.994 0.992 1.020 1.032 1.038 1.052
0.986 0.996 1.006 1.036 1.044 1.044
0.996 0.990 1.002 1.040 1.042 1.044
0.992 0.993 1.009 1.036 1.041 1.047
0.00529 0.00306 0.00945 0.00400 0.00306 0.00462
pass mass (x7), STPP phase content (x10), sodium phosphates, water and STPP mixture grinding time (x11), and the maximum temperature of mixture calcination (x13). These parameters were classified to be independent variables in the experiment aimed at determining the approximating polynomial. The group of constant values was expanded with parameters having an insignificant impact on tripolyphosphate bulk density. Their values were assumed arbitrarily low level values for x1, x2, x4, x6, x8, and x9 and high level values for x12, x14, and x15 (Table 1). The experiments were conducted in accordance with the Hartley design (PS/DS-P:Ha6) at the area variation on the cube (Table 5). Table 6 presents the values of complete model regression coefficients. The approximating polynomial explains about 98% of dependent variable variability. 3.3. Prediction of Dependent Variable. The important process parameters and the results of a series of experiments confirming the possibility of obtaining sodium tripolyphosphate with a bulk density of ∼1.00 and 1.05 kg/dm3 and various crystalline phases content in STPP are presented in Table 7. The values of input factors providing the most expected output factor values were defined on the basis of the prediction profile and desirability function for bulk densities of 1.00-1.05 kg/ dm3. Figure 3 presents the prediction profile of output value and the exemplary of desirability profile for which the following utility values of output factor were defined: 0.0 for STPP bulk density below 0.95 kg/dm3 and 1.0 for STPP bulk density equal
to 1.05 kg/dm3. XRD analysis of products demonstrated that STPP phase 2 was obtained at temperatures of 350 and 450 °C, and STPP phase 1 was obtained at 550 °C. 4. Discussion The formation of powder prior to calcination is carried out to preliminarily concentrate particles to ensure the efficiency of the processes in which high bulk density sodium tripolyphosphate is obtained. During the preparation of the mixture for calcination, particles of sodium phosphates are exposed to external forces causing the destruction of their “shell” structure, the breaking of week bonds between grains and the subsequent destruction of granules, aggregates and agglomerates. This leads to a more concentrated arrangement of grains resulting from their relocation and deformation. Prior to the calcination process sodium phosphates are dispersed in water. Water absorption modifies their rheological properties and causes the transformation from dispersed powder to plastic solid body. This confirms the importance of mass proportions in the studied system (water mass, STPP mass). Because grains are of small size, the dissolution in water can concern whole grains. The increased speed at which water is dosed intensifies the process of sodium phosphates dissolution and at the same time affects the consistency of batch mixture and the final effect of concentration.
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The importance of the phase composition of the recirculated sodium tripolyphosphate results from the difference between hydration times for phase 2 and phase 1 STPP. The hightemperature phase, hydrating rapidly may cause caking of the batch mixture and concentration of grains. The formation stage should be focused on ensuring adequately high homogeneity of grain arrangement, and homogeneity of batch mixture in terms of chemical and phasic composition. During preliminary preparation of the mixture for calcination there is the highest probability of modifying the arrangement of calcinated grains, and adequate design of the starting system is the key determinant for the final result of the process, which is the obtained bulk density of sodium tripolyphosphate. During calcination the processes of mass transfer in the grain set cause the increase of their size, leading to the transformation of the particle set into a solid polycrystal. Mass transfer is possible because of specific driving forces present in the grain set. Forces acting on the perimeter of grain contacts and in the contact center create a state equivalent to the one achieved after the set is exposed to external hydrostatic pressure, as observed in the process of sodium tripolyphosphate compacting. Mass transfer is the process based mainly on the diffusion mechanisms in the solid phase. The importance of the maximum calcination temperature on the bulk density of sodium tripolyphosphate results from the fact that the intensity of diffusion mechanisms becomes significant only at high temperatures. 5. Conclusion The performed experiments result in elaborating the methods of obtaining sodium tripolyphosphate with bulk density adjustable within the range of 1.00-1.05 kg/dm3. Moreover, this product has an advantageous granulometric content and expected content of STPP phase 1 and phase 2. The effects of sodium tripolyphosphate with adjustable bulk density production process are determined by the following parameters: sodium phosphates, water and STPP mesh pass mass ratio, water dosing rate, sodium tripolyphosphate phase content, mixture mixing (grinding) time, and calcination maximum temperature. The determination of the prediction profile and desirability function enabled the selection of the most favorable parameters for obtaining sodium tripolyphosphate with bulk density within the range of 1.00-1.05 kg/dm3. Literature Cited (1) Van Wazer, J. R. Phosphorus and Its Compounds; Interscience Publishers: New York, 1958. (2) Ko¨hler, J. Detergent Phosphates and Detergent Ecotaxes: A Policy Assessment, A report prepared for the Centre Europe´en d’Etudes des
PolyphosphatessA European Chemical Industry Council (CEFIC) sector group; Centre Europe´en d’Etudes des Polyphosphates: Bruxelles, Belgique, 2001. (3) Ko¨hler, J. Detergent Phosphates: an EU Policy Assessment. J. Bus. Chem. 2006, 2, 15. (4) Tsoler, U. Handbook of Detergents: EnVironmental Impact; CRC Press: Boca Raton, FL, 2004. (5) Yangxin, Y.; Jin, Z.; Bayly, A. E. Development of Surfactants and Builders In Detergent Formulations. Chin. J. Chem. Eng. 2008, 4, 517. (6) Showell, M. S. Powdered Detergents; CRC Press: Boca Raton, FL, 1997. (7) Arai, H.; Maruta, I.; Kariyone, T. Study of Detergency. II. Effect of Sodium Tripolyphosphate. J. Am. Oil Chem. Soc. 1965, 43, 315. (8) Kijkowska, R.; Kowalski, Z.; Pawłowska-Kozin´ska, D.; Wzorek, Z. Effect of Aluminium on Na5P3O10 (Form-II-Form-I) Thermal Transformation. Ind. Eng. Chem. Res. 2004, 43, 5221. (9) Kijkowska, R.; Kowalski, Z.; Pawłowska-Kozin´ska, D.; Wzorek, Z. Quantitative Determination of Crystalline Na5P3O10-I (Form I) in Commercial Tripolyphosphate Rusing X-ray Diffraction Patterns. Cryst. Res. Technol. 2002, 10, 1121. (10) Corbridge, D. E. C. The Crystal Structure of Sodium Triphosphate, Na5P3O10, Phase I. Acta Crystallogr. 1960, 13, 263. (11) Davies, D. R.; Corbridge, D. E. C. The Crystal Structure of Sodium Triphosphate, Na5P3O10, Phase II. Acta Crystallogr. 1958, 11, 315. (12) Dymon, J. J.; King, A. J. Structure Studies of the Two Forms of Sodium Tripolyphosphate. Acta Crystallogr. 1951, 4, 378. (13) Toy, A. D. E. The Chemistry of Phosphorus; Pergamon International Library of Science, Technology, Engineering and Social Studies: Woburn, MA, 1973; Vol. 3. (14) Kijkowska, R.; Kowalski, Z.; Pawłowska-Kozin´ska, D.; Wzorek, Z.; Gorazda, K. Tripolyphosphate Made from Wet-Process Phosphoric Acid with the Use of a Rotary Kiln. Ind. Eng. Chem. Res. 2008, 18, 6821. (15) Kijkowska, R.; Kowalski, Z.; Wzorek, Z.; Pawłowska-Kozin´ska, D. Otrzymywanie Tripolifosforanu Sodu (TPFS) z Ekstrakcyjnego Kwasu Fosforowego Produkowanego z Apatytu Kola Oraz z Przemysłowego Roztworu Fosforano´w Sodu. Przem. Chem. 2006, 85, 837. (16) Kowalski, Z.; Kijkowska, R.; Pawłowska-Kozin´ska, D.; Wzorek, Z. Sodium Tripolyphosphate and Other Condensed Sodium Phosphates Production Methods. Pol. J. Chem. Technol. 2002, 3, 27. (17) Raskovic´, P. Step-by-Step Process Integration Method for the Improvements and Optimization of Sodium Tripolyphosphate Process Plant. Energy 2007, 32, 983. (18) Banach, M.; Kowalski, Z.; Wzorek, Z.; Gorazda, K. A Chemical Method of the Production of “Heavy” Sodium Tripolyphosphate with the High Content of Form I or Form II. Pol. J. Chem. Technol. 2009, 2, 13. (19) Banach, M.; Wzorek, Z.; Gorazda, K. Statystyczna Analiza Wyniko´w Badan´ Otrzymywania Tripolifosforanu Sodu o Podwyz˙szonej Ge˛stos´ci Nasypowej. Przem. Chem. 2010, 89, 282. (20) Banach, M.; Wzorek, Z.; Gorazda, K. Wpływ Parametro´w Procesu Wytwarzania Tripolifosforanu Sodu na Jego Ge¸stos´c´ Nasypowa¸. Przem. Chem. 2010, 89, 286. (21) Procter & Gamble. Manufacturing StandardssEuropean Operations, Raw Material Specification, Granular Sodium Tripolyphosphate, High Density, 10072234, 1998. (22) Hill, T.; Lewicki, P. STATISTICS Methods and Applications; StatSoft: Tulsa, OK, 2007. (23) Hartley, H. O. Smallest composite designs for quadratic response surfaces. Biometrics 1959, 15, 611.
ReceiVed for reView May 18, 2010 ReVised manuscript receiVed September 22, 2010 Accepted October 21, 2010 IE1011195
