Gardner, R. P.. Austin, L. G., Proceedings 1st European Symposium on Comminution in Dusseldorf: DECHEMA Monogr., 232-248 (1962). Hardgrove, R . M.. Trans. Am. SOC.Mech. Eng., 54, 73 (1932). Jindal, V. K., Ph.D. Thesis, The Pennsylvania State University, University Park, Pa., 1974. Klimpel, R. R., Austin, L. G., "BackCalculation of Specific Rates of Breakage and Non-normalized Breakage Distribution Parameters from Batch Grinding Data." submitted for publication, available from authors, 1974. Klimpel. R. R., Austin, L. G..Proceedings 3rd European Symposium on Comminution in Cannes; DECH€MA Monogr., 69, 449-473 (1972). Luckie, P. T., Ph.D. Thesis, The Pennsylvania State University, University Park, Pa., 1972. Luckie, P. T., Austin, L. G., Min. Sci. Eng., 4, 24-51 (1972). Mika, T., Ph.D. Thesis, University of California at Berkeley, 1971. MSA Staff, "MSA Particle Size Analyzer Operating Procedures and Applications," Mine Safety Appliances Co., Pittsburgh, Pa., 1966.
Reid, K. J., Chem. Eng. Sci., 20, 953 (1965). Savage, K. I., Ph.D. Thesis, The Pennsylvania State University, University Park, Pa., 1971. Savage, K. I., Austin, L. G.. Sun, S.C.. Trans. AIM€, 255, 89-96 (1974). Sedlatschek, K.. Bass, L., PowderMet. Bull,, 6, 148 (1953). Shoji. K.. Ph.D. Thesis, The Pennsylvania State University, University Park, Pa., 1974. Shoji, K.. Austin, L. G..Powder Tech., 10, 29-35 (1974). Whitby, K. T., Heat. Piping, Air Cond., 27, 139-145, 231-237 (1955).
Received for review June 2, 1975 Accepted September 22,1975
Presented at the Joint AIChE/GVC Meeting, Munich, Germany, September 1974.
Effect of Surfactant Addition upon Packed Distillation Column Performance Anthony 6. Ponter;
Pierre Trauffler, and S. Vijayan
ChemicalEngineeringInstitute, Swiss Federal Institute of Technology of Lausanne, Ecublens, Switzerland
Column performance data are reported for the separation of dilute butylamine-water mixtures, a surface tension positive system, at atmospheric pressure and total reflux conditions using either glass or polytetrafluoroethylene Raschig rings. The effect of the introduction of ndecanol on performance has been ascertained, and contact angles of the binary and ternary mixtures on glass and polytetrafluoroethylenehave been measured under total reflux conditions. With glass, high HOGvalues were observed at near-terminal compositions of butylamine and the addition of surfactant caused a significant reduction in HOGto a limiting value. Using polytetrafluoroethylene rings, improved performance was observed at low concentrations and inferior behavior at higher butylamine compositions. The addition of decanol produced no change in efficiency at near-terminal compositions but caused a reduction in performance at higher concentrations. The behavior was explained satisfactorily by considering the liquid flow regimes existing on surfaces of high and low wettability.
Introduction The effect of surfactant addition on packed distillation performance has been studied by Francis and Berg (1967), who noted that surfactants significantly improve the efficiency of the distillation of negative binary mixtures, both aqueous and organic. They suggested that the improved efficiency was caused by a stabilization of the liquid film so providing an increased interfacial area for mass transfer. The increase in efficiency was found to be much greater for the aqueous mixtures than for the organic systems. No improvement was evident when surface active agents were added to positive systems. However, when surface tension positive systems were distilled in film contacting devices, it was observed by a number of workers (Jackson and Geaglske, 1950; Vanwijk and Thijssen, 1954; Liang and Smith, 1962; Norman et al., 1963; Pritchard, 1963; Sawistowski and Smith, 1959; Boyes and Ponter, 1969) that at low compositions significant changes occurred in the values of the Height of a Transfer Unit and Ponter and co-workers (Ponter et al., 1973; Boyes and Ponter, 1972) by measuring the contact angles under total reflux conditions, demonstrated the large wetting changes which resulted a t near-terminal compositions and were able to explain the phenomenon satisfactorily with simple wetting theory. I t was established that the anomalous wetting behavior would only exist on high energy surfaces such as glass or copper and that low energy surfaces such as polytetrafluoroethylene could not produce this effect. 196
Ind. Eng. Chem., Process Des. Dev., Vol. 15, No. 1, 1976
A severe pollution problem facing the chemical industry in Base1 has been the disposal of dilute aqueous amine solutions which interfere with the water treatment processing. Attempts have been made to distill the mixtures in packed columns but very poor separation performances were achieved. The research program now described was undertaken to investigate if the addition of a surfactant would produce a significant increase in column performance for these systems since amine solutions are surface tension positive in nature.
Experimental Section Materials. Butylamine was redistilled to give 99.9% purity with boiling point 75.8"C at 725 mmHg and surface tension 24.6 dynlcm a t 20°C. Water was double distilled in a quartz still and gave a reproducible surface tension value of 72.6 dynlcm at 20°C using the Du Nouy ring electronic Prolabo tensiometer. n-Decanol, which is miscible with butylamine, was selected as surfactant. In the wetting studies optical glass plates were cleaned by immersion in chromic acid solution followed by thorough washing with distilled water before the test solution was introduced. Teflon (polytetrafluoroethylene) surfaces were prepared by polishing with a series of compounds and cleaned by the procedure described by Boyes and Ponter (1973). Apparatus and Procedure for the Measurement of Contact Angles. The apparatus comprised a 1-1. flask, a glass wetted-wall column, and a condenser where vapor was
.
0 uolQlo
o
n
3
0
n-decanol
IO2 lo-'
~
20 10
5
10
15
20
25
30
1 B u t y 1 a m r e toncentration
35
40
I
10
5
20
15
Figure 1. Wetting data for n-decanol-n-butylamine-water glass system at total reflux.
30
25
35
40
n-Butylamine concentration (mole %I
i moIeOio1
Figure 2. Wetting data for n-decanol-n-butylamine-water-poly. tetrafluoroethylene system at total reflux. 100
returned to the column as a liquid film. The details are described elsewhere (Boyes and Ponter, 1970). Contact angles were measured under total reflux conditions using a travelling microscope fitted with a goniometer eyepiece. The reported values, an average of a t least five readings, are accurate to within f0.5'. Distillation Column Efficiencies under Total Reflux Conditions Using Teflon and Glass Raschig Rings. Apparatus and Procedure. The column consisted of five cylindrical glass sections of internal diameter 5 cm, fitted with silver-plated vacuum jackets. Details of the equipment are described elsewhere (Trauffler, 1975), but basically the reboiler had a capacity of 20 l. and the packing heights could be varied from 15 to 75 cm. Two sampling points were situated immediately above and below the packed section, and special precautions were taken to eliminate mass transfer occurring a t the sampling points. Both the polytetrafluoroethylene and glass Raschig rings were carefully machined to give sharp edges and uniform size of 5 X 5 mm with wall thickness 1 mm. The heat input to the reboiler was controlled by an electronic Normag 68 unit and the boil-up rate was maintained such that the vapor velocity remained constant throughout the experiments. Experiments were carried out for reboiler concentrations 0.0049-3.5 mol % butylamine and with rz-decanol additions ranging up to 0.1 mol %. Three packing heights, 15, 30, and 45 cm, were investigated. A Normag 5000 equilibrium cell was employed and data obtained for the butylamine-water system were found to be in very close agreement with reported values of Komarov and Krichevtsov (1966). Further measurements were made to assess the influence of surfactant addition upon the equilibrium. Analysis. For the middle range of butylamine concentrations, refractive index measurements gave reproducible values with errors of less than 1%.However, a t concentrations both below 5% and above 5096, refractive index determinations were not satisfactory and a titration procedure was undertaken involving the addition of standard sulfuric acid with back titration using sodium hydroxide, the indicator being bromothymol blue. The reproducibility of the analyses was very satisfactory, the error being less than 0.5% for concentrations down to 0.01 mol % butylamine. Below this value, however, the titration error increased rapidly to 50% a t 0.0007 mol % which led to an error of less than 10% in the HOG values a t the lowest concentrations considered.
90
-
80
b
-
70
G
>
60
50 4C
30 M 10 0 0
10
20
30
40
50
60
x
70
80
90
1W
i mole 010 I
Figure 3. Equilibrium data for n-butylamine-water system.
Results and Discussion The wetting properties of butylamine-decanol-water mixtures under conditions of total reflux on both glass and polytetrafluoroethylene surfaces are presented in Figures 1 and 2. For the glass surface it was observed that in the absence of surfactant the wetting changed markedly a t nearterminal compositions, behavior which has been reported previously for the ethanol-water system and explained in terms of simple wetting theory by Ponter et al. (1973). The effect of surfactant addition was to increase the wettability of the system. With the polytetrafluoroethylene surface there were no equivalent wetting changes a t low butylamine concentrations, again as expected, but at higher concentrations, the effect of surfactant addition was to slightly decrease the wettability. The vapor-liquid equilibrium data presented in Figure 3 demonstrated that the addition of small quantities of decano1 had no effect on the equilibrium, and it was seen that the results agreed very closely with those reported by Komarov and Krichevtsov (1966). In Figure 4 the column efficiency expressed in terms of HOG values are presented for various average concentrations of butylamine for the high energy surface, glass. No surfactant had been added during these investigations. It was observed that for a given average concentration the column efficiency decreased with increasing packing depth. Similar behavior is exhibited in Figure 6 for the corresponding polytetrafluoroethylene surface. This can be exInd. Eng. Chem., Process Des. Dev., Vol. 15,No. 1, 1976
197
l
1
15cm 30crn
a
10
20
30
40
45cm
50
Height olpacktng 15 cm
I
Height olpacking
60
0 voI
,
. 6
010
n-decanol
10-2
2 x 10-2
4 x 10-2
70
n-Butylamine concentrailon (mole %I
10
Figure 4. Influence of packing depth on column performance,
20
30
40
50
60
70
n-Butylamine concentration lmole%l
using glass rings for the n-decanol-n-butylamine-watersystem.
Figure 6. Effect of n-decanol addition upon column performance /o
using glass rings.
I
*! Helght 01 packing
. D
..
15cm
45cm
162vol% n-decanol
2x102
4xm2
30 -
20
L 10
2C
10
40
n B u t y l a i ne
50
60
70
ConcentrwtioP 'mole 'lo1
Figure 5. Influence of packing depth on column performance, using polytetrafluoroethylene rings for the n -decanol-butylaminewater system
'0
20
30 I I
40
50
bO
70
B v t y amineconcentration l r n a l ~ % 1
Figure 7. Effect of n-decanol addition upon column performance plained by considering that maldistribution and wall-flow increase with increasing packing depth as has been observed by a number of workers and reviewed by Porter and Templeman (1968). Figure 5 illustrates the effect of the addition of n-decanol on HOGvalues as plotted against ?. It is evident that an increase in n-decanol addition results in an improvement in column efficiency using high energy packing. For example, without the surfactant present, with ? = 2.7%, HOG = 57.3 cm for z = 15 cm while with an n-decanol concentration of 0.1 mlfl. of solution HOG = 32 cm. It is interesting to note that increasing the surfactant concentration did not decrease appreciably the HOGvalues. Thus, for E = 2.7% and decanol concentration of 1 ml/l. of solution, HOG = 28 cm for the same column height. In Figure 7, it is 198
Ind. Eng. Chem., Process Des. Dev., Vol. 15, No. 1, 1976
using polytetrafluoroethylene rings.
observed that a t near-terminal compositions without decano1 addition, the performance of the column packed with polytetrafluoroethylene rings was better than when using glass rings. This is because the liquid does not flow in a filmwise manner on poorly wetted surfaces, as has been reported by Charpentier et al. (1968) and Ponter et al. (1975), but breaks up into a series of rivulets and droplets which result in increased liquid mixing and vapor turbulence. With decanol addition there was no effect a t low concentrations but at higher ? values a small increase in HOG was noted. This is expected since in Figure 2 the wettability decreases i n this composition range.
Finally, independent of the nature of the surface, HOG values will be expected to fall off at concentrations of around 2% amine since the slope of the equilibrium line changes rapidly and the contribution of the liquid-phase resistance will be significantly reduced.
Conclusions Contrary to the statement of Francis and Berg, i t has been shown that the addition of a surfactant can improve the column performance when separating surface tensionpositive systems, a t near-terminal compositions. The results indicate that surfactant addition has definite industrial potential for separating pollutants which are present a t low concentrations in water and which are surface tension-positive in character. Acknowledgment One of us (P. Trauffler) acknowledges financial assistance from Fonds d’Encouragement aux Recherches Scientifiques, Berne. Nomenclature = average concentration of the higher volatile component in the packing (mole fraction)
HOG = height of overall gas phase transfer unit, cm y = mole fraction in vapor x = mole fraction in liquid
Literature Cited Boyes, A. P., Ponter, A. B., Chem. Roc. Eng.. 50, 70-73 (1969). Boyes, A. P., Ponter. A. E., A.6Ch.E. J., 18, 935-940 (1972). Boyes, A. P., Ponter, A. E., Chem. hg. Tech., 45, 1250-1256 (1973). Boyes, A. P., Ponter, A. E., J. Chem. Eng. Data, 15, 235-238 (1970). Charpentier. J. C., Prost, C., Van Swaaj, W., Legoff, P.. Chim. h d . G n i e Chim., 99, 803 (1968). Francis, R. C., Berg, J. C., Chem. Eng. Scb, 22, 685-692 (1967). Jackson, M. L.,Geaglske. N. H., Ind. Eng. Chem., 42, 1188-1198(1950). Komarov, V. M., Krichevtsov, E. K., Z.Prik/. Khim., 39, 2834-2838 (1966); 43, 112-115(1970). Liang, S.Y., Smith, W., Chem. Eng. Sci., 17, 11-21 (1962). Norman, W. S., Cakalor. T., Fresco, A. Z., Sutcliffe, D. H.. Trans. Inst. Chem. Eng.. 41, 61-71 (1963). Ponter. A. E.. Boyes. A. P., Houlihan. R. N., Chem. Eng. Sci.. 28, 593-596 (1973). Ponter, A. B., Hassanien, S.,Landau, J., Chem. hg. Tech., 47, 775 (1975). Porter, K. E., Templeman, J. J., Trans. Inst. Chem. Eng., (part /I), 46, T86T94 (1968). Pritchard. M. L.. Ph.D. Thesis, University of Birmingham, 1963. Sawistowski, H., Smith, W., Ind. Eng. Chem., 51, 915-918 (1959). Trauffler, P., D.Sc. Techniques Thesis, Swiss Federal Institute of Technology, Lausanne, 1975. Vanwiik, W. R.. Thijssen. H. A. C., Chem. Eng. Sci., 3, 153-160 (1954).
Receiued f o r reuiew June 6, 1975 Accepted August 26,1975
Aerosol Scrubbing by Foam Tlbor G. Kaldor and Colin R. Phillips’ Department of Chemical Engineeringand Applied Chemistry, University 01 Toronto. Toronto, Canada M5S l A 4
Extraction of particles from an air stream by foam was evaluated by varying throughput rate, residence time, and particle concentration. Dusty air was bubbled into a pool of surfactant solution (0.3 g/l. of ethylhexadecyldimethylammonium bromide). The dust/foam system travelled up a 4 in. diameter by 4.5 ft Plexiglas column, and was then broken centrifugally. The concentrations and size distributions of both the input fly-ash and the particles extracted into the foamate were measured and an efficiency of extraction was calculated. Qualitative comparison of results with the mechanisms postulated was good. Sedimentation was fully effective on particles greater than 2 p , and diffusive deposition accounted for about 30% extraction in the 0.5-1.0 p range. At the cross-over (1-2 p ) from the sedimentation mechanism (coarse particles)to the diffusive mechanism (fine particles), removal was about 5%. Aggregation in the foamate is a probable cause of the apparent low extraction of small (0.3-0.5 p ) particles and the high extraction of large ones. Extraction increased with residence time (1-3 min), and decreased with gas rate (5-15 Wmin). Heavier dust loading resulted in poorer extraction, leading to a hypothesis of interfacial saturation and/or repulsion.
Introduction It is of interest to examine, theoretically and experimentally, the application of foam to the removal of particulates from an air stream. The large surface-to-volume ratio and low pressure drop of such a system, combined with the fact that when a foam is broken, the particulates are concentrated into a small volume, make the process promising. The surfactant film inside the bubble also aids in wetting hydrophobic particles. On the other hand, the static atmosphere inside the bubble is not ideal for dust precipitation: also, work must be expended in breaking the foam. Few systematic studies of foam scrubbing exist in the literature. Bransky and Diwoky (1940) scrubbed sulfuric acid mist (particle size 2-11 w ) in foam bubbles (diameter 0.6-1.2 cm)
produced from a sulfuric acid solution. About 93-95% of the total H&Ol was removed in 10-11 sec. The acid concentration of the incoming mist had very little effect on the efficiency of removal, which was found to be directly related to contact time. Pozin et al. (1955) correlated the fractional removal of dust, F , in a foam produced above a perforated plate with the Stokes number defined as
-
Nst = D P V
gdo% where D , is the particle diameter, pp is the particle density, V is the gas velocity, do is the perforated plate orifice diateter, g is the acceleration due to gravity, and vg is the gas viscosity. The correlation was of the form F = a(N& Ind. Eng. Chem.. Process Des. Dev., Vol. 15, No. 1, 1976
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