July, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
NOTE. I n the above example, the log mean partial-pressure difference was used for the driving force. This method is not applicable to the design of towers employing acid of an appreciably different concentration from that used in the experimental determination of KGU. I n such cases the equilibrium curve for air and phosphoric acid should be plotted and Kaa determined by graphical integration (8).
Acknowledgment Credit is due L. H. D. Fraser for the vapor pressure determinations and correlation of the vapor pressure data, and R. A. Wilson for assistance in the experimental work.
Nomenclature a = area of interphase contact, sq. ft./cu.
.
ft. of packed volume b = constant in equation, p = HC b C = concentration of acid G = air rate, lb./(hr.) (sq. ft. total cross section) H = proportionality constant in equation, p = HC b KQU= over-all coefficient of mass transfer, lb. moles/(hr.) (cu. ft.) (atm.)
+
+
915
= as-film coeffcient of material transfer uid-film coefficient of material transfer L = aci rate, lb./(hr.) (sq. ft. total cross section) 11 = exponent in equation,koa = G,, p = equilibrium partial pressure of water over acid Y = Proportionally constant in equation, = Y G”
‘3
Literature Cited (1) Chilton, T. H., and Colburn, A. P., IND. ENQ.CHBM.,23, 913 (1931). (2) Greenewalt, C. H., Ibid., 18, 1291 (1926). (3) International Critical Tables, Vol. 111,p. 61,New York, McGrawHill Book Co., 1928. (4) Kablukov, I. A., and Zagvoadkin, K. I., 2. anorg. allgem. Chem., 224, 315 (1935). (5) Keenan, J. H., and Keyea, F. G., “Thermodynamic Properties of Steam”, New York, John Wiley & Sons, 1936. (6) Perry, J. H., and Duus, H. C., C h m . & Met. Eng., 41,74 (1934). (7) Ibid., 41, 127 (1934). (8) Roas, W. H., and Jones, R. M., J. Am. Chsm. Soc., 47, 2165 (1925). (9) Sherwood, T. K., “Absorption and Extraction”, New York, McGraw-Hill Book Co.,1937. PRHIS~NTPD before the Division of Industrial and Engineering Chemistry a t the 1Olst Meeting of the American Chemioal Society, St. Louis, Mo.
Diatomaceous Earth Base for Chemical Pigments E.
c. BURWELL, The Dicalite Company, New York, N. Y.
D
IATOMACEOUS earth has developed from a position of obscurity to one of value in industry today. Its utility will be apparent from the process literature and patents (2). Processing and refining has accounted for its increased value. The paint industry is one of those which has come to recognize the value of a process-refined diatomaceous earth. I n the research laboratory and later in the development laboratories of paint manufacturers, it was observed that this refined diatomaceous earth seemed to increase the hiding or opacity of pigmented paint products materially even though it has a refractive index of 1.45, which is very near that of the paint vehicles and thus imparts no hiding power or opacity in itself. It was thought that this increase in opacity was due to the diatom particles being coated over by the other pigment so that they did not merely occupy space within the paint film, which is characteristic of the usual paint extenders. Microscopic examination of mixtures containing diatomaceous earth and paint pigments showed that virtually every diatom particle did have attached to it the particles of pigment with which it was mixed. Based on this experience, it was reas6ned that diatomaceous earth would be an excellent base upon which t o precipitate chemical pigments. Accordingly, a research program was instituted to determine any possible advantage and value of such phenomenon. Obviously the first thought would be to use this material as a base for the more expensive pigmentsfor example, the organic dyes to make lake colors. However, in order to take advantage of the characteristics imparted to the paints by the diatomaceous earth in the larger
volume of the business, it was decided to start first with the lead pigments as a type of the white, next the iron blue pigments, then chrome yellow, and later the chrome greens, titanium pigments, zinc sulfides, and chromium oxides.
White Lead I n the case of basic-carbonate white lead the present trend in manufacture is away from the old corroding process. As a result, chemical and electrically precipitated white leads are now available which have better color, better hiding power, better control of oil absorption, and consistency in the finished paints. I n our experiments a lead nitrate solution was used, from which the lead was precipitated in the form of a basic lead carbonate by a mixture of sodium carbonate and sodium hydroxide, according to the following formula: 3Pb(NOs)a
+ 2NalCOa + 2NaOH +
2PbCOs.Pb(OH)a
+ 6NaN08
Other salts of lead, such as lead acetate or chloride, dissolved in hot salt brine could have been used with comparable results. Pure solutions of these salts were used and molecular proportions taken. Yields were checked in each case to determine the completeness of reaction. Batches of the 100 per cent white lead were compared with a first-grade commercial product for color, brightness, Gardner-Coleman oil absorption ( I ) , and hiding power as determined by a Pfund Cryptometer. After several runs were made on the 100 per cent products and constants were determined, mechanical mixtures were
Vol. 33, No. 7
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
916
Before the hiding power was determined, the sample used in the oil adsorption test was placed on a marble slab and given one hundred mulls with a weighted muller; a representative sample was taken for hiding power determination (expressed as square centimeters per gram of pigment). Calculation is made according to the following formula:
x = where X V M K L
= = = = =
V
K xL x M hiding power volume of pigment and oil weight of sample (pigment) wedge constant Cryptometer scale reading
Figure 1 shows the relative hiding powers as well as what would normally be expected of a mixture of diatomaceous earth and white lead. Diatomaceous earth has are fractive index of 1.45, less than that of linseed oils or POWER OF WHITELEAD-DIATOMACEOUS EARTHMIXTURE FIGURE 1. HIDING Daint and varnish vehicles, and when combined with themimparts no opacity or hiding power. Therefore, a straight line plotted from the made with the process-treated diatomaceous earth, and hidpoint of zero hiding power for the diatomaceous earth to the ing power determinations were run on them. point of 53.6 sq. cm. per gram on laboratory-precipitated Definite quantities of the diatomaceous earth were added white lead will show what would normally be expected in hidto the solutions of lead salts to produce the same ratios of ing power for any mixture of these two materials. precipitated lead carbonate to diatomaceous earth as were That the structure of the diatom is such that it becomes used in the mechanical mixtures; the lead salt was then precoated easily with pigments when admixed with them and to cipitated by the addition of the alkali solution, and a coating an even greater extent when pigments are precipitated upon of basic lead carbonate was thus produced upon the diathe diatoms, is evident; otherwise such a n increase in hiding tomaceous earth. power as found in this work would not occur. The usual decantation, repulping, washing, drying, and grinding procedure was followed on all precipitated pigments so that they were in the same condition as the commercial Prussian Blue products. Again in the case of Prussian blue, a much greater hiding Table I shows the figures obtained on the tests of white power was obtained when the blue was precipitated on the lead pigments. diatomaceous earth. This pigment was in reality what is known as Chinese blue, since it was precipitated and oxidized at high tem,perature. The color produced was deep TABLEI. REEULTSWITH WHITE LEAD AKD DIATOMACEOUSwith a clear top tone and good strength. The color was EARTH made according to the following formula: Specific Oil Hiding Commeroial Lab. precipitate Mechanical mix 85% lead, 15 D. E. lead 26$ D. E. lead: 50% D. E. 25% lead, 75% D. E. Coated pigments 85% lead on ,574 D: E. 75% lead on 25 o D E. 50 lead on 50'7 D. E. 26% lead on 75% D. E.
Gravity 6.8 6.8
Adsorption 14.9 24.0
Power 37.0 53.6
5.24 4.48 3.42 2.66
32.0 40.0 57.0 80.0
54.6 64.8 58.0 44.9
5.24 4.48 3.42 2.66
43.0 60.0 70.0 104.0
66.4 76.6 70.2 46.9
The specific gravity of each of the mixtures and coated products was calculated from the known specific gravity of the diatomaceous earth (2.28) and that of the basic lead carbonate (6.8). For example, 15% Dicalite L grade: 1.5 grams at 2.28 = 0.66 cc. 85% white lead: 8 . 5 grams at 6 . 8 = 1 2 cc. 1.91 cc. = Total wt. = T O grams total vol. 10 Sp. gr. = wt : vol. 1.91 3
5.24
+
K4Fe(CN)6.3H20 2FeS04.7H~O-+ FezFe(CN)a 2K2SO4 17H@ (white base) (1) 3FezFe(CN)e 2KClOa 2H2S04.+ Fea[Fe(CN)elg 2FeSOl 2KC1+ 4H20 0 2 (Chinese or Prussian blue) (2)
+ +
+ ++
+
+
As in the case of white lead, molecular proportions were taken of potassium ferrocyanide and ferrous sulfate with a 5 per cent excess of the ferrous sulfate to promote settling. Uniform conditions as to concentration of salts in solution, time, temperature, and rate of reaction were carefully controlled in order to obtain uniformity of color, mass tone, tinting strength, and hiding power in the c. P. or 100 per cent precipitates as well as the let-downs. The precipitation of the Prussian blue on the diatomaceous earth may be carried out by adding the earth to the potassium ferrocyanide or the ferrous sulfate solution. Experimentation revealed that the mass tone and undertone of the coated products more nearly approached that of the c. P. pigment when the diatomaceous earth was added to the hot cyanide solution. Table I1 and Figure 2 show the value of coating Prussian blue upon diatomaceous earth from the point of view of hiding power.
July, 1941
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
917
facture. The most convenient method consists in stirring the filler into the lead salt solution before adding the bichromate solution. This method produces a more intimate mixture, the kieselguhr particles be. coming enveloped for the most part in a coating of lead chromate. Pigment intensity and covering power are corTHEORETICAL respondingly increased. The drying X----X MIXTURE process is also accelerated, owing to the greater ease with which moisture can escape from the voluminous mass with a coarser structure. Accelerated drying is particularly advantageous in the pale sulfochromates, * FIGURE2. HIDINGPOWER OF PRUSSIAN BLUE-DIATOMACEOUS EARTHMIXTURES which tend to form highly compact masses owing to the extremely fine particle size. Chrome yellow should not be incorporated with WITH PRUSSIAN BLUEAND DIATOMACEOUSkieselguhr containing a high proportion of calcium oxide, as TABLE 11. RESULTS EARTH the slightest trace of alkali leads to subsequent darkening of Oil Hiding Speoific this pigment.” Power Gravity Adsorption Three different shades of the chrome yellows were made 111.8 1096 1.82 Commeroial 93.2 1061 1.82 with somewhat disappointing results as compared to those Lab. ppt. (100% Pigment) 63.2 1022 1.82 Lab. precipitate of the white lead and Prussian blue. The shades produced 74.6 1125 1.82 Lab. precipitate were orange chrome yellow, medium chrome yellow, and Mechanical mixes 1.87 205 1177 light chrome yellow. 8 5 9 blue 169 D E 1.92 221 1116 75’$ blue: 25$ D: E: The formation of the orange chrome was divided into two 2.07 363 978 blue 50 D. E. 2.15 363 365 blue: 7 5 d D.E. stages. In the first, a normal chromate was formed. The Qmted aismenta _._.. second stage consisted in boiling the normal chromate with an 1575 1.87 65.2 85 blue on 15% D. E. alkali and converting it to a basic chromate of lead. 1707 1.92 65.2 75 blue on 25 .
I
E:g:
50$ blue on 5 0 8 2 5 % blue on 75 o D. E.
2.07 2.15
93.2 93.2
1357 709
Another observation was made in connection with the precipitation of Prussian blue on diatomaceous earth-that is, the rate of flow in the filtration of the pigment from the liquor and the clarity of the filtrate. Figure 3 shows the comparative flow rate at which the 100 per cent or c. P. blue rapidly plugs the filter medium and the flow rate decreases, whereas the flow rate of the liquor containing the pigment precipitated on the diatomaceous earth flows much more uniformly throughout the cycle of operation. Figure 3 does not tell the whole story, however. The extremely fine particle size of the Prussian blue precipitate allows much of this blue to pass through the closest filter paper; even towards the end of the filtration cycle of the c . P. pigment, the filtrate was so deeply colored with blue that one could not see through it. I n filtering the coating TIME--MIN. suns. the filtrate cleared within the first two minutes of operaO F PRUsSI.4N BLUEFIGURE 3. FLOWRATEO F FILTRATION tion ’and remained clear and transparent to the end 02 the DIATOMACEOUS EARTHPRECIPITATES operation. Under normal operating conditions this difference in filtration rate and retention of fine particles of TABLE111. RBSULTS WITH CHROME YELLOWS AND DIATOMACEOUS E.4RTH pigment would do much toLight Chrome Yellow Medium Chrome Yellow Pale Orange Chrome Yellow Oil Oil Oil ward lowering production Specific adsorp- Hiding Specific adsorp- Hiding Specific adsorp- Hiding gravity tion power gravity tion power gravity tion power
6OStS.
Chrome Yellow Mention has been made of the use of Kieselguhr (a natural, unrefined diatomaceous earth) in chrome ( 3 ): yellow manufacture “Kieselguhr can be incorporated with chrome yellow in the wet state during manu-
Commercial Lab. preoipitate Mechanioal mix 85% yellow 1 5 7 D E.
509
759 ye110w‘2543 50% yellow’ D: D ‘ E: E 25% yellow: 75% D. E. Coated pigments 8 5 7 yellowon 1 5 9 D. E. 75 yellow on 25$ D. E. 5 0 1 yellow o n 6 0 D. E. 25% yellow on 75Y0 D. E.
5.82 5.82
46.6 a7.3
168 159
6.0 6.0
55.9 93 2
234 216
6 53 6.53
46.6 37 3
197 192
4.65 4.32 3.31 2.81
37.3 55.9 74.5 93.2
154 129 109 73
4.82 4.28 3.31 2.87
74.5 93.2 121.1 158.4
150 172 142 106
4.86 4.33 3.34 2.93
37.3 55.8 65.2 102.5
152 125 87 69
4.65 4.32 3.31 2.81
60.5 55.9 65.2 74.6
144 145 111 73
4.82 4.28 3.31 2.87
83.8 74.6 121.1 121.4
186 164 144 104
4.86 4.33 3.34 2.93
27.9 27.9 65.2 93.2
251 219 132 73
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