Table 111. Removal of Crs+ by 2-Stage Pilot Plant
mium, mercury, copper, and ammonia from various wastewater streams have been quite encouraging.
Feed to test unit; wastewater containing 100 ppm Cr6+ from plating process
Literature Cited
Test no.
1
Test no. 2
(1) PAT Report, Enuiron. Sci. Technol., 10, 127 (1976). 3
LM emulsion
Membrane (A) Reagent solution (B) BIA
Flow rates, cclmin Wastewater Emulsion Treat ratio Mixing speed, rpm Concn of Cr6+ After treatment In effluent In emulsion
10% NaOH 20% NaOH 20% NaOH 112 112 112 300
300
300
280
105
064
114.85 200
114.85
113.40 300
(2) Bell, A. V., ibid., p 130. (3) Leitz, F. B., ibid., p 136. (4) Chem. Eng. News, 54,14 (April 20,1976). (5) Li, N. N., Shrier, A. L., in “Recent Developments in Separation Science”, N. N. Li, Ed., Vol 1, pp 163-74, CRC Press, Cleveland, Ohio, 1972. (6) Li. N. N.. U.S. Patent 3.410.794 (1968). i7j Li; N. N.: AICHE J.,ii, 459 (1971). ( 8 ) Li. N. N., Cahn. R. P.. Shrier. A. L., U S . Patent 3,779,907 ‘(1973). (9) Cahn, R. P., Li, N. N., Sep. Sci., 9 (6), 505 (1974). (10) Matulevicius, E. S., Li, N. N., Sep. Purif. Methods, 4, 73 (1973). (11) Mohan, R. R., Li, N. N., Biotechnol. Bioeng., 16,513 (1974). (12) Mohan, R. R., Li, N. N., ibid., 17, 1137 (1975). (13) May, S.W., Li, N. N., “Enzyme Engineering”, E. K. Pye and L. B. Wingard, Eds., Vol 1, p 77, Plenum Press, New York, N.Y., 1974. (14) May, S. W., Li, N. N., Biochem. Biophys. Res. Commun., 47 ( 5 ) , 1179 (1972). (15) General Mills Corp., “Chromium”, Tech. Bull. CDS1-61, 1961. (16) Moore, F. L., Enuiron. Sci. Technol., 6 (61, 525 (1972). (17) Lewis, C. J., in “Recent Developments in Separation Science”, N. N. Li, Ed., Vol2, p 47, CRC Press, Cleveland, Ohio, 1972. (18) McDonald, C. W., Moore, F. L., Anal. Chem., 45 (61, 983 (1973). (19) Cotton, F. A., Wilkinson, G., “Advanced Inorganic Chemistry”, 3rd ed., p 514, Interscience, New York, N.Y., 1966. (20) Irving, H. M. N. H., Al-Jariah, R. H., Anal. Chim. Acta, 74,321 (1975). ’
200
1 PPm 1 PPm 1 PPm 35 800 ppm 108 000 ppm182 000 ppm
At present, there is no good process that can efficiently and economically remove heavy metals and ammonia from wastewater. Therefore, a considerable incentive exists to develop a process to fill such a need. Pilot plant tests and economic analyses on the liquid membrane process are continuing to achieve final commercialization. Emphasis in these tests is on regeneration of the membrane and recovery of valuable metals. The results obtained thus far on the removal of cad-
Receiued for review September 17,1976. Accepted January 26,1977. Presented a t the Division of Industrial and Engineering Chemistry, Centennial Meeting, ACS, New York, N.Y., April 1976.
Photooxidation of n-Hexadecane Sensitized by Xanthone Hyman D. Gesser”, Timothy A. Wildman, and Yadu
B. Tewari’
Department of Chemistry, University of Manitoba, Winnipeg, Man., Canada
The photosensitized oxidation of hexadecane on water is studied as a model system for the solar dissipation of oil spills. Xanthone acts as a sensitizer forming hexadecanol with a quantum yield, at 313-335 nm, of 0.60-0.16 depending on intensity. Yields of peroxides are about 1%of the alcohol produced. A mechanism is proposed consistent with the alkylperoxy radical detected by ESR. The possibility and probability of oil spills in remote inaccessible regions must be anticipated. Normal methods ( I ) are ineffective for areas such as the Arctic, and it is with this aspect in view that this work was undertaken. It is believed that the addition (from an aircraft, for example) of a suitable sensitizer to an oil spill should accelerate the solar photosensitized oxidation and solubilization of the oil. Recently, it has been shown (2-6) that certain compounds can be used as sensitizers to accelerate the photochemical oxidation of hydrocarbons. The primary requirements of a suitable sensitizer are: stability in the oil-water system, strong absorption in the visible or near UV region, a triplet state of sufficiently high energy so that a free radical chain reaction
Present address, Frederick Cancer Research Center, Frederick, Md. 21701.
capable of proceeding a t low temperatures may be initiated, lipophilic and hydrophobic properties, and stability under conditions which prevail during the oxidation of the oil. We have studied the following compounds as sensitizers: chloranil, anthraquinone (62), carbazole (70), xanthone (74), 1-naphthol (58),triphenylamine (70),2’-acetonaphthone (59), l-cyanonaphthalene ( 5 7 ) , and thioxanthone (65) (the energies in kcal/mol of the corresponding triplet state are indicated in parentheses). Based on results of GLC analysis of the oil layer and on the UV spectra of the aqueous layer of the irradiated samples as compared to control samples (not irradiated) of n-hexadecane saturated with sensitizers, xanthone was found to be most effective and thus was selected as the sensitizer in the study of this model system. In the photochemical oxidation of hydrocarbons ( 7 ) , the products are generally alcohols, ketones, aldehydes, acids, peroxides, and hydroperoxides. Klein and Pilpel have shown (2-5) that alcohols were the major product from n-hexadecane and that peroxides and hydroperoxides accounted for about 10% of the products. We have also examined the photosensitized reaction using ESR. Based on the product analyses, quantum yields, and the ESR results, a mechanism (Type I) is proposed for the oxidation in which xanthone (triplet) abstracts a hydrogen atom from the hydrocarbon to initiate a free radical chain reaction. Volume 11, Number 6, June 1977
605
Experimental The hydrocarbon used was n-hexadecane, 99% pure from Aldrich Chemical Co. It was further purified by oxidizing the impurities with concentrated sulfuric acid with a small amount of potassium permanganate and chromatographing the hydrocarbon twice through an activated silica gel column. The purified hexadecane was then checked for impurities by GLC and UV absorption spectroscopy. All water used was freed of organic contaminants (distilled from alkaline permanganate and acidic dichromate) as evidenced by far UV absorption spectrum. Xanthone from Aldrich was used without further purification. The saturated sample solutions of sensitizer in n-hexadecane contained about 10 mmol/L of xanthone. The alcohol standards were prepared from hexadecanols obtained from Sample Chemical Co. with minimum purities of 99%. A Westinghouse 400-W mercury lamp (#H33-1-CD) with a Nonex glass envelope and an Hanovia S500 lamp (8) were used as UV sources. Various filter combinations were used to isolate different wavelengths for irradiation. Radiation intensities were determined with the potassium ferrioxalate actinometer (9). Quantum yields a t 313-335 nm were made using the filter combination (10) of Corning #7-54 and NiS04 in a Pyrex cell. A solution of n-hexadecane saturated with sensitizer (1mL) was added to the cell (4cm diameter) containing 40 mL of water (organic phase about 1 mm in thickness). During the photolysis, air was passed through the cell above the oil film at a flow rate of 20 mL/min while the temperature was maintained at 24" f 1 "C with a continuous flow of water through the cell jacket. Aliquots of oil film were obtained a t various time intervals with a 10-pL Hanilton syringe. The increasing alcohol concentration in the sariple was monitored by GLC. The gas chromatograph (equipped with flame ionization detector) was a Hewlett-Packard Model 402 fitted with a 6-ft copper column (yS in. 0.d.) packed with chromosorb W (80-100 mesh AW-DMCS) coated with 10% OV-17 a t 175 "C. The concentration of xanthone in the n-hexadecane was also determined periodically by GLC a t 190 "C. The trace Cli component in hexadecane (corrected for partial reaction by the yield of alcohol) was used as the internal standard since the exact volume of the sample, which often contained water, was not known. Separation of the various isomeric hexadecanols was not complete, and total integration of the peaks was used to indicate total alcohol. Alcohol concentration in the oil after 96 h of photolysis was also determined by acetylation (2).The agreement between the two methods was within 2%. Peroxides and hydroperoxides were determined iodometrically ( I 1 ). , The cavity of a Varian E-3 ESR spectrometer was rotated through 90" to allow the insertion of a quartz tube (11 mm 0.d.) horizontally in the cavity. This tube contained a quartz boat with a raised platform to allow only a thin water film in the center of the cavity (Figure 1). The hydrocarbon film containing the sensitizer was floated onto the water layer in the boat and irradiated in the cavity from above. A continuous flow of air (saturated with water) was maintained during the photolysis. The UV light source (8)was used in conjunction with a Vycor filter. The buildup of free radicals during irradiation, their decay in the dark, and their dependence on oxygen were determined for hexadecane solutions of xanthone and 1-naphthol. The g-values of the radicals were determined relative to DPPH. Chromatograms of the alcohols in the irradiated boat were similar to the products obtained during the irradiation in the cell.
Figure 1. Quartz boat in ESR cavity (schematic diagram-not scale)
A: 1 1-mm 0.d. quartz tube. B: Quartz boat with raised platform P. C: ESR cavity. W: Water. 0:Oil film with sensitizer. F: Cavity window for UV beam
ImQMTmharr)
- -
Figure 2. Yield of hexadecanoi as function of irradiation time Curve A: Vycor filter, xanthone 10 mM. Curve B: 313-335 nm, xanthone 6.37 mM. Absorbed intensity 1.2 X lo-' Einstein/min
t
4n
P 10
606
Environmental Science & Technology
ID
5
0 Irradaltlon
Results and Discussion The yields of total alcohols as a function of irradiation time are shown in Figure 2 for xanthone in n-hexadecane. The
to
Tim
!-I
-
Figure 3. Yield of hexadecanol as function of irradiation time
-
Curve C: Bright sunlight, xanthone 4.43 mM. Absorbed intensity 6 X lo-' Einstein/min. Curve D: 313-335 nm, xanthone 3.77 mM. Absorbed intensity 7.25 X lo-' Einsteinhin
-
initial rate of formation of the alcohol at 313-335 nm is 7.3 X mol/min. The intensity of the lamp a t this wavelength region as determined by actinometry was 1.2 X Einsteidmin. The absorption at these wavelengths by xanthone M) is complete (OD = 4) and gives a quantum (6.37 X yield for alcohol formation of about 0.60. At higher intensities of incident radiation, corresponding more closely to the solar flux, the rate of formation of alcohol is much higher. This is shown in Figure 3 for unfiltered bright sunlight (Curve C) and for filtered UV (313-335 nm) a t 7.25 X Einstein/min (Curve D) where the quantum yield for alcohol formation was calculated to be about 0.16. The effect of irradiation time on the xanthone concentration is shown in Figure 4.After irradiation for a period of 25 h (Curve A, Figure 2 and Curve X, Figure 4),the extent of decomposition of xanthone is about 1.5 pmol which corresponds to the formation of about 200 pmol of alcohol. At higher intensities (Curve D, Figure 3 and Curve Y, Figure 4) the corresponding values after 5 h of irradiation are 1.5 pmol of xanthone decomposed and 52 pmol of alcohol formed. This shorter chain length a t higher intensities is probably due to radical-radical reactions which would also account for the lower quantum yield for alcohol formation. This implies that a long free radical ch,ain reaction is producing the alcohol and/or that the xanthone is being regenerated after initiating the reaction.
-
Irradiation Time (hwrr)
10
;rri
v
'
50
'
9
7
8
'm
The falloff in rate of formation of alcohol at low intensities (Figure 2) may be due to the formation of di- and trihydroxy hydrocarbons, though this explanation is inconsistent with the agreement between the results obtained in the two methods for alcohol analysis. Figure 5 shows the yields of peroxides and hydroperoxides as a function of irradiation time. The ratio of peroxide/alcohol from xanthone is about %O that obtained by Pilpel from 1naphthol and implies a different reaction mechanism is operative especially in view of the greater susceptibility of the 1-naphthol to oxidative destruction compared to xanthone. This was verified by the ESR spectra obtained from the two systems. The photolysis of xanthone in a n-hexadecane film on water in the presence of air gives a single line (g = 2.015, line width 9G) which decays in the dark in a few seconds. The radical could not be detected in the absence of oxygen. This radical is believed to be the alkylperoxy radical (RO',) (12, 13). A different single line spectrum was obtained in the 1naphthol system (g = 2.002, line width 10G). This radical, which has not as yet been identified, decays slowly in the dark ( t 112 = 1 h) and was also observed when nitrogen, instead of air, was passed over the boat. When both sensitizers were present in the hydrocarbon film, the free radical due to 1-naphthol appears first followed, after prolonged irradiation, by the RO; radical. In the dark the RO:, radical disappears in seconds, whereas the radical 1-naphthol decays slowly. The Type I photosensitized oxidation mechanism (14) can best account for the results, viz., X + hu-*X*
X* + RH
+02R. + 0 2
X
XH-
+ RH RO; + XH.
+ R.
(2)
+ HOi
(3)
XH-
-+
+
(1)
RO;
+ R* R02H + X R02H RO. + *OH ROH + R. RO. + RH RO2H + R. RO- + ROH RO;
-*
RO2H
+
+
+
-*
5
0
ImM!n Time
b.rs)
x)
Figure 4. Proportion of xanthone undecomposed as function of irradiation time Curve X: (Upper abscissa-filled circles) Conditions as in curve A, Figure 2. Curve Y: (Lower abscissa-open circles) 313-335 nm, xanthone 4.43 mM. Absorbed intensity 7.25 X lo-' Einstein/min
-
Y
.
f I 0
I
I
50 ImdDthn T m
Kx)
( t u . &
Figure 5. Yield of peroxide as function of irradiation time (condition as in Curve A, Figure 2)
(4) (5) (6) (7) (8) (9)
where X = xanthone, X* = xanthone triplet, and RH = n hexadecane. Reaction 1 represents the formation of triplet xanthone via the excited singlet. The activation energy for Reaction 2 is small [approximately 3 kcal/mol for benzophenone (15)].Reactions 3 and 6 result in the regeneration of the sensitizer. The remaining reactions are well known and have been studied extensively (7, 12,13). Radical-radical interaction (other than Reaction 6) leading to chain termination and the decomposition of the xanthone also occur. When xanthone was added to a crude oil film on water, the RO; radical was not observed, probably due to the high absorption of the oil a t the sensitizing wavelength. However, a noticeably different chromatograph was obtained for a GC analysis of the irradiated oil sample as compared to the control. The effect of temperature at constant irradiation intensity was studied for the xanthone photosensitized oxidation of n-decane since this hydrocarbon is liquid a t 0 "C. The results showed that under identical irradiation intensities and xanthone concentration, within experimental error (about f 5 % ) , there was no difference in the rates of formation of alcohol at 2 and 25 "C. The practicality of the method is thus not restricted by temperature but by the competitive absorption of light between the crude oil and the sensitizer. Further work Volume 11, Number 6, June 1977 607
is in progress on a sensitizer which will absorb a t longer wavelengths.
Acknowledgment We gratefully acknowledge the assistance of C. W. Turner with the low-temperature experiments. Literature Cited (1) Proceedings of Joint Conference on Prevention and Control of Oil Spills, No. 4172, American Petroleum Institute, Washington, D.C., 1973. (2) Klein, A. E., Pilpel, N., J . Chem. SOC.Faraday I , 69, 1729 (1973). (3) Klein, A. E., Pilpel, N., ibid., 70,1250 (1974). (4) Klein, A. E., Pilpel, N., Water Res., 8,79 (1974). (5) Pilpel, N., “Photo-oxidationof Oil Films Sensitized by Naphthalene Derivatives”,Institute of Petroleum Report 75-007,London, England.
(6) Pilpel, N., New Sci., 59,636 (1973). (7) Emanuel, N. M., “The Oxidation of Hydrocarbons in the Liquid Phase”, Chap. 1, Pergamon Press, London, England, 1965. (8) Jones, P. W., Gesser, H. D., J . Chem. SOC.,3,1873 (1971). (9) Hatchard, C. G., Parker, C. A., Proc. Royal SOC.A , 253, 518
(1956). (10) Sili, C. W., Anal. Chem., 33,1585 (1961). (11) Johnson. R. M., Siddiai, I. W., “The Determination of Organic Peroxides”,Chap. 3, Pergamon Press, London, England, 1970. (12) Bennett, J. E., Brown, D. M., Mile, B., Trans. Faraday SOC.,66, 386 (1970). (13) Bennett, J. E., Eyre, J. A., Summers, R., J . Chern. SOC.Perkin Trans. II, 797 (1974). (14) Gollnick, K., Schenck, G. O., Pure Appl. Chem., 9, 507
(1974). (15) Topp, M. R., Chern. Phys. Lett., 32,144 (1975).
Received for review J u n e 25, 1976. Accepted January 27,1977. Financial support from Imperial Oil of Canada and the National Research Council of Canada.
Analytical Method for Calculation of Deposition of Particles from Flowing Fluids and Central Force Fields in Aerosol Filters Josef Pich The J. Heyrovsky Institute of Physical Chemistry and Electrochemistry, Czechoslovak Academy of Sciences, Prague, Czechoslovakia
The methods applied for calculation of the deposition rate of particles depositing on a cylinder or in aerosol filters under the influence of external forces (limiting trajectories, Duchin and Deryaguin, and Natanson methods) are briefly discussed. By combining the Natanson method with dimensional analysis and with the concept of generalized (Friedlander’s) variables, a new method is developed. This method not only enables the calculation of the deposition rate but in certain cases also enables the formulation of the general similitude law. Under certain assumptions about the flow field and field of external forces, the deposition of particles due to the simultaneous action of external forces and direct interception on a cylinder and in aersol filters can be described by one single-valued function of one variable having a universal character for the treated two-mechanism problem. As an application example, the problem of deposition of Stokes finite size particles on a cylinder due to the action of attractive coulombic forces for the case of potential flow is solved.
One of the basic problems in the theory of aerosol filters is the determination of the deposition rate of particles @ (number of particles deposited in unit time on the unit length of the cylinder transverse to the fluid flow). This rate can be expressed by @J = 2
anoUoE,yR
(1)
where a is the cylinder radius, no is the number concentration of particles a t infinite distance from the cylinder, UOis the fluid velocity a t infinite distance, and E X K is the capture coefficient of the cylinder due to the simultaneous action of mechanism X and direct interception. Deposition of monodisperse, spherical particles of radius r is treated as the deposition of point particles on a coaxial cylinder of radius a r . Deposition of particles takes place on the part of the cylinder surface where the condition
+
u,,(p = a 608
+ r , 0) s 0
EnvironmentalScience & Technology
(2)
is satisfied, where p , 8 are the polar coordinates (0 is measured from the positive x-axis), and u,,(p, 0) is the radial component of the particle velocity. Let us define the quantity 00 by u,(p = a
+ r, 0 = 00) = 0
(3)
so that 00 decides which part of the cylinder surface deposition occurs. Consequently, the limiting trajectory, separating the trajectories of depositing and not depositing particles, goes through the point p = a r, 0 = 00. It will be shown below that in the case of deposition due to the action of external forces and direct interception, Condition 2 is satisfied; consequently, deposition occurs in the range 00 2 0 s H . In the case of pure direct interception, 00 = 7r/2 so that deposition occurs in the range ~ / 2 0 2 T . Moreover, if there are attractive external forces between the particles and the cylinder, the part of the cylinder surface where the deposition occurs increases so that 00 decreases, being in the interval 0 0” 5 ~ / 2 If . the attractive interaction is sufficiently large, then 00 = 0, and the deposition takes place on the whole cylinder surface 0 0 2 H , In the case of repulsion forces, the part of the cylinder surface where the deposition occurs decreases so that 00 increases, being in the interval ~ / 22 Bo 2 T . If the repulsive interaction is sufficiently large, then 00 = H , Condition 2 is never satisfied, and there will be no deposition. For determination of the deposition rate @, essentially three methods have been developed, all based on the assumption that inertia of the particles can be neglected. Analytical formulation and justification of this assumption are dependent on the type of interaction between particles and the cylinder. The first and the oldest method follows.
+
Method of Limiting Trajectories The motion_equation of the inertialess particles with external forces F ( p , 0 ) is given by n p , 0) =
Ob,0) + B R p , 0)
(4)
where is the vector of the particle velocity, 0is the vector of fluid velocity, and B is the particle mobility. Solution of the differential Equation 4 is p = p ( 0 , C), representing a system
