M. J. D. Low AND A. M. KAMEL
450
--
The Thermal Decomposition of Cadmium Hydroxide
by M. J. D. Low and A. M. Kame1 School of Chemistry, Rutgers, The State University, New Brunswiek, New Jersey
(Received July 21, 1964)
Differential thermal and thermogravimetric analyses of CdO .65H20 showed that four processes were involved in the thermal decomposition. Isothermal weight loss determinations showed that, a t 300' and above, the decomposition to CdOo.80 was continuous. The composition of intermediates is uncertain because of the rapid and continuous reaction. Some oxide was formed as low as 265'. The decomposition was accompanied by marked textural changes of the solid. Surface areas of pure hydroxide as well as samples containing 1 atom yo Li+, Znf2, Mgf2, or Alfa were measured after heating in vacuo for various times at temperatures from 150 to 500'. Alf3-addition inhibited and Lif-addition enhanced oxide sintering up to 400', through the destruction or creation of oxygen vacancies. At 450 and ZOOo both Alfa and Lif additions increased sintering, suggesting that a cation vacancy mechanism became dominant. 9
During a study of the surface properties of CdO, it became necessary to prepare well-defined CdO samples by various means, including the thermal decomposition of the hydroxide. Although some work has been reported on the isobaric and isothermal dehydration of cadmium hydroxide,1s2 the information available was incomplete. Additional work was required and, consequently, the thermal decomposition of doped and undoped cadmium hydroxides was studied.
Experimental Details Cadmium hydroxide was precipitated from the nitrate with a m m ~ n i a thoroughly ,~ washed and dried a t 100' in air. A portion of the powder was mixed with enough LiOH, Zn(NO&, Mg(N0&, or Al(N03)a solution to yield a stiff paste, which was dried a t 110'. The amounts of solutions and their concentrations were sufficient to result in hydroxide samples that, when converted to CdO, would contain 1 atom % of foreign cations. Differential thermal analyses (d.t.a.) were made a t linear heating rates of 10°/min., using Pt-10% Pt.Rh thermocouples. A slowly moving stream of purified nitrogen passed over the nickel detector block. Thermogravimetric analysis (t.g.a.) was made in air with a modified Ainsworth automatic recording balance, a t linear rates of 4.6'/min. from room temperature to 500°. Isothermal weight loss (i.w.1.) was measured in air with a modified analytical balance. Sitrogen adsorption isotherms and B.E.T. surface The Journal of P h y e h d Chemistry
1
areas4 were obtained with an apparatus of conventional desigm6 The initial degassing of each sample was carried out overnight a t room temperature because of the instability of the hydroxide. Surface areas were then measured for a sequence of heat treatments of various durations in vacuo {at each temperature. The surface areas, 'each calculated from data a t six relative pressures, are given in m.2/g. of starting material.
Experiments and Results D.t.a. Experiments. These experiments are described in somewhat greater detail than would normally be warranted, because electrical disturbances of the instrument brought about by CdO can be used to deduce information about the extent of the decomposition. In studying the hydroxide-oxide transformation, it seemed reasonable to use CdO as a reference substance. A sample of Baker Company C.P.material which had been heated in air to 300' for 2 hr., and which (1) G. F. Hlittig and R. Mytyzek, Z. anorg. allgem. Chem., 190, 353 (1930). (2) G. F. Hiittig, "Hydroxyde und Oxyhydrate," R. Fricke and G. F. Huttig, Ed., Akademische Verlagsgesellschaft m.b.H., Leipsig, 1937, p. 413 ff. (3) A. Cimino and M. Marezio. J . Phys. Chem. Solids, 17, 57 (1960). (4) 9.Brunauer, P. H. Emmett, and E. Teller, J . A m . Chem. SOC., 60, 309 (1938). ( 5 ) P. Faeth, "Adsorption and Vacuum Technique," Report N o . 66100-2-X, University of Michigan, 1962.
451
THERMAL DECOMPOSITION OF CADMIUM HYDROXIDE
was the material it had been intended to use as reference, was subjected to d.t.a. using a y-alumina reference. Near 200' a voltage indicating an endothermic process was produced that rapidly increased with increasing temperature. Cadmium hydroxide was examined in another experiment using alumina as the reference; in addition to endothermic peaks of dehydration processes, a large and increasingly endothermic signal began near 400'. On holding the temperature constant at 600' for 107 min., the signal remained at a constant value, then progressively became smaller as the temperature was decreased, and vanished near 350'. Figure 1 shows the results of another experiment in which the positions of hydroxide and alumina were reversed. The decomposition processes appeared as exothermic peaks. Xear 265' the signal indicated an endothermic process. After keeping the temperature constant near 300' for 30 min., the temperature was decreased, and the signal declined. The results of these and similar experiments suggest that the large endothermic signal appearing in the presence of the oxide was an artifact produced by electrical "leakage" between thermocouples and the detector block permitted by the relatively high electrical conductivity of CdO. More important is the deduction that CdO was formed at temperatures in the vicinity of 265'. This is in agreement with the observation that the white hydroxide turned brown within a few minutes at 300'. Figure 2 shows the details of typical d.t.a. curves. All of the curves pertain to the Mg-doped sample, and were obtained under different conditions of packing of the sample into the heater block. The peak near 110' is ascribed to the desorption of water. An alumina reference was used with these and all other samples because of the electrical disturbance produced by a CdO reference substance. There were no significant differences in the d.t.a. curves ascribable to the effects of doping. The data are summarized in Table I. T.Q.u.Ezperiments. Each of the samples was subjected to t.g.a. with reproducible results. The doping of the hydroxide was without effect. There was no increase in sample weight on cooling the samples from 500' to room temperature in air, suggesting that oxygen sorption was negligible. The d.t.a. peak of Figure 2 near 260' split into peaks centering a t 255 and 275', and the shoulder near 325' appeared as weak shoulders centering near 230, 260, and 300' of a large shoulder of the t.g.a. curve. The data are summarized in Table I. I.w.1. Experiments. A fresh sample was used at each temperature. With the exception of the plot of the Li-doped .sample, marked Cd(OH)z/Li, all plots of Figure 3 are for the decomposition of the undoped hy-
200
300
300
200
100
Temperature, y
Figure 1. J3.t.a. of AllOa us. cadmium hydroxide. The alumina reference material was placed in the position normally used as sample position, the cadmium hydroxide being in the reference position of the detector block of the d.t.a. instrument.
I
Ternprolure, *G
Figure 2. J3.t.a. curves of cadmium hydroxide
droxide. The following observations are noteworthy i (a) a t and above 300', a weight loss of about 21% occurred, indicated with arrow P ; (b) decomposition a t 300 and 350', although much slower, was as effective as decomposition a t 750'; (c) there was a change in slopes after about an 8% weight loss, indicated with arrow Y ; (d) there was a pronounced arrest in some plots after about 12% weight loss, indicated with arrow Z. The various plots suggest that the decomposition Volume 69, Numher d
Fehruury 1,966
M. J. D. Low AND A. M. KAMEL
452
Table I Temp., OC.
.
Initial
T.g.8. Center
Final
Initial
D.t.8. Center
Final
Composition at end of process
I
25
...
I90
..,
110
170
Cd0.1.65H20
I1 I11
190 240
230 260
240 270
170
255 275
IV V
270 370
300 410
340 430
Process
350
Desorption Dehydration
CdO.1 .03Hz0
325 420
350 450
Cd0.0.76H20 Cd0o.m
Process
1
Dehydration and deoxygenation
Time (hours)
Figure 3. Isothermal weight loss of cadmium hydroxide.
at and above 350' was continuous, the various processes indicated by d.t.a. and t.g.a. experiments not being clearly distinguishable. Sequential decomposition is indicated a t and below 300'. Product C'ompositions. The interpretation of t.g.a. and i.w.1. curves was based on the final weights of the samples, in order to avoid errors in initial sample weights caused by fortuitous water loss or gain. To permit this, and also to check on the conipleteness of the decomposition, 11 samples of end decomposition products of pure and doped samples obtained a t temperature from 350 to 750' were analyzed. Cadiniuin The J o u r w l of Physical Chemistry
was estimated by the method of Fernando and Freiser.6 As the dissociation pressure of CdO is small7 and the formation of cadmium mirrors was never observed, the empirical formulas of the final decomposition products were calculated on the assumption that the samples consisted only of cadmium and oxygen and that loss of water and oxygen accounted for the observed weight decreases. This resulted in the formula (6) A. Fernando and H. Freiser in "Treatise on Analytical Chernistry," I. M. Kolthoff and P. J. Elving, Ed., Part 11, Vol. 111. Interscience Publishers, Inc., New York, N. Y . , 1961, p. 199. (7) I. G. F. Gilbert and J. P. Kitchener, J . Chem. Soe., 3919 (1956).
THERMAL DECOMPOSIT~ON OF CADMIUM HYDROXIDE
CdOo.so+o.or. There was no correlation between decomposition temperatures or doping and the small variation in formula, and consequently the average formula was used to compute the compositions given in Table I. If the end product at P in Figure 3 was taken as CdOo8, then a t points corresponding to Y of that figure a product CdO-HZOwas formed. At points corresponding to 2, the product had the approximate composition Cd0.0.6Hz0. Process I, indicated by an endothermic peak near 110' in d.t.a. curves and by a plateau in t.g.a. curves, is considered to be a loss of adsorbed water. Processes 11, 111, and IV are taken as dehydration steps. In view of the rapidity of the decomposition and the continuous weight loss indicated by the i.w.1. curves, it is probable that the compositions of intermediate products indicated in Table I are'subject to some error. Also, the production of brown coloration a t 300') the continuous i.w.1. curves, and the electrical disturbance of the d.t.a. apparatus suggest that some oxide is produced near 265' and that some loss of oxygen occurs a t stages of decomposition very far from completion. Nitrogen Adsorption. The surface areas of pure and doped samples are shown by the plots of Figures 4 to 8. Some nitrogen adsorption-desorption isotherms at liquid nitrogen temperature were made with undoped samples after heating in vacuo and are shown in Figure 9. The adsorption-desorption cycles shown there as plots A, B, and C were made in sequence with one sample. A second sample was used for plot D. The color changes that occurred during such heat treatments are of interest. The original hydroxide was a white powder and became yellowish after heating a t 150' for 9 hr., suggesting that a small amount of decomposition had occurred. At 200°, however, the sample turned brown after about 1 hr., suggesting that substantially more decomposition had occurred than a t 150'. At 300' the sample was within the furnace for 15 min. and emerged totally brown.
453
14
-
12
-
10
-
0.2
04
-PR
0.6
OB
1.0
Figure 4. Nitrogen adsorption-desorption isotherms. The direction of the arrows indicates the order in which the various points were obtained: A, after degassing overnight a t room temperature; B, after heating a t 300" for 30 min.; C, after heating a t 300" for 12 hr. displaced by - 1 ml.; D, after heating a t 500" for 1 hr., displaced by -2.5 ml.
Discussion T h e Decomposition Process. The present observations agree, in general, with those of Hiittig and Mytyzek,lp2 who studied the isobaric dehydration of cadmium hydroxides. Their samples, ranging in comto Cd0.2.207Hz0, were position from CdO.1.041Hz0 stated to lose water continuously and irreversibly without a change of phase until CdO.HzO was formed. A second phase, termed "hydro-oxide," of approximate composition CdO.0.4Hz0 was then formed, which could undergo further dehydration. On heating a cadmium hydroxide sample with a Teclu burner, they obtained a material of composition CdOo 87, not inconsistent with
I
I
2
4
6
I I
10
2
Time I h w d
Figure 5. Surface area isotherms of cadmium hydroxide.
that reported presently. These observations are borne out by the continuous dehydration shown by the V o l u m e 69, Number 2
February 1966
M. J. D. Low AND A. M. KAMEL
454
t e II
1
IO
Tme ( h u l l
Tim. Ikounl
Figure 6 . Surface area isotherms of Cd(OH)zLi+.
Figure 9.
5
MZ
;4
E
f{ 4 3
2
2
6 T8mc (howsl
4
10
Figure 7 . Surface area isotherms of Cd(OH)z-MgC2.
‘
O
1
8
1 7
j 1 6 Y
4
3
2
4
Figure 8. Surface area isotherms of Cd(OH)z-Zn+z.
i.w.1. experiments. The points Z, corresponding to a composition Cd0.0.6Hz0, as well as process IV of d.t.a. and t.g.a. experiments, corresponding to a forThe Journal of Physical Chemietry
Surface area isotherms of Cd(OH)z-AI+a.
mula Cd0.0.76H20, can be taken as being reasonably close in composition to the hydro-oxide of Huttig and Jlytyzek. That the dehydration is not, in reality, continuous but occurs in four rather than two stages is shown by the present experiments. The precise nature of the structural changes occurring in the solid during the dehydration is not known and, in the absence of supporting data such as X-ray diffraction, speculation on the changes is fruitless. That considerable textural changes of the solid occur, however, is indicated by the changes in surface areas and in nitrogen absorptiondesorption isotherms. The surface areas of pure hydroxide increased by almost 20% on heating for 15 or 30 min. a t 150 or 200°, respectively. Although some decomposition occurred a t 150°, it is more plausible to ascribe this increase to an opening of a previously blocked pore system than to a generation of new surface through decomposition because the amount of decomposition occurring in 15 min. was small. This suggests that the overnight degassing a t room temperature was incomplete, and that the untreated hydroxide had a system of small pores. Presumably, water molecules blocked the pore system and were desorbed above room temperature. This is in agreement with the existence of a system of cylindrical or ink bottle-shaped pores than can be deduced froin the hysteresis* and from the smooth closing of the hysteresis loop of plot A of Figure 9. The curves of Figure 4 of areas a t 200, 250, 300, and particularly 350’ show that rapid declines in areas occurred. This, as well as the disappearance of hysteresis and decline in area shown by plots B and C of Figure 9, suggests (8) S. Brunauer, “Physical Adsorption of Gases and Vapors.” Oxford University Press, Oxford, 1944.
THERMAL DECOMPOSITION OF CADMIUM HYDROXIDE
that the original structure was subject to drastic change, the system of small pores and pore openings being destroyed or converted to one having relatively large pores. Increases in area occur at higher temperatures, shown by the 350 to 450’ plots and in Figure 9 by plot D. The reappearance of a hysteresis loop in the latter indicates the reformation of a network of fine pores. Similar information can be derived from Figures 5 to 8, and also more clearly from isochrones or plots of surface area as function of temperature a t constant heating times. The various decomposition processes cause minima in surface areas near 350 and 450’ and a maximum near 400’. This is shown schematically by the generalized isochrone in part A of Figure 10. The various data suggest that several general trends occur. (a) There was a,rapid decline in surface area on heating to 300’, ascribable to the destruction of an original system of small pores. There was little change a t 300’ after this had occurred. (b) A new pore system began to form a t 350°, but the new system also was subject to slow change. (c) The degree of porosity of the second system depended on the velocity of formulation of the pores. (d) The new pore system, if formed rapidly, was relatively stable. These data, in conjunction with those derived from d.t.a., t.g.a., and i.w.l., suggest four general processes: (1) loss of water with attendant destruction of the texture of the hydroxide; (2) formation of CdO, attended by increase in area; (3) sintering of CdO; and (4) deoxygenation of cadmium oxide. These are indicated schematically in part B of Figure 8, and result in the composite C. The surface area and stability of the solid were, in general, greater the higher the temperature of decomposition. This may be connected with the change in crystal structure attending the hydroxide-oxide conversion. Cadmium hydroxide forms a layer structureg in which every Cd is surrounded by 60H. Every OH forms three bonds to Cd atoms in its layer and is in contact with 30H of the adjacent layer. The characteristic feature of such a layer structure is unsymmetrical environment of the OH groups, which have their Cd neighbors all to one side and on the other side are in contact only with OH groups, in marked contrast to the rock salt structure of CdO. Two over-all steps are involved in the rearrangement from layer to rock salt structure: dehydration, whereby HzO is lost, 0-2 is formed. and OH vacancies are made in the anion sublattice; and rearrangement, whereby the depleted layer lattice collapses to form the rock salt lattice. In view of the larger surface areas found with increasing temperature, it is not implausible to suggest that this effect was in part brought about by a reten-
455
(B) I
1
I
300
400
500
T (*c)
I /
(C )
I
I
I
300
400
XH)
T(.Q
Figure 10. Schematic decomposition mechanism.
tion of the gross structure of the hydroxide crystallites by the newly formed oxide. Although local rearrangement‘could occur rapidly over regions of a few unit cells, the densification resulting from the diffusion and rearrangement of 0-*and C d f 2 ions attending the recrystallization of an entire crystallite could lag beyond the dehydration. The surface area of the original material could then be retained or increased a t high decomposition rates. The Efects of Doping. It is recognized that the foreign cations could not be distributed throughout the host lattice but were, initially, at least, on the surface of the hydroxide crystallites. Yet several effects of doping were discernible, appreciable changes in surface areas occurring even a t low temperatures. As the “sintering curves’’ reflect the summation of the changes occurring in the solid, some attempt must be made to separate the effects of the two major over-all processes, i e . , the hydroxide-oxide conversion, and the oxide sintering and deoxygenation. This can be (9) G. Natta, Gazz. chim. ital., 58, 344 (1928) : Atti Accad. Lincei, (6) (1926).
2, 495
Valunze 69,Number 8 Februar 2/ 1966
M. J. D. Low ANI? A. M. KAMEL
456
done by considering relative surface area, i e . , the actual surface area measured after a heat treatment divided by the surface area of the unheated sample. Table I1 summarizes the sintering data, using the simplified symbolism indicated. In each vertical column the samples are arranged in decreasing order of surface area, e.g., a t 300' the highest and lowest actual surface areas are given by E and C, respectively. ~~
~
~~~
Table 11: Actual and Relative Surface Areas after 12 Hr."
300
E A D B C
c e a b d
350
E D A C D
c e a b d
Temp., 'C. 400
E C A D B
c e a b d
7
450
A D E C B
c a d e b
500
c* c A E D* B
a d e b
a, A = Cd(0H)Z; b, B = Cd(OH)?-Li+; c, C = Cd(OH)2-Mg+2; d, D = Cd(OH)t-Zn+2; e, E = Cd(OH)z-Al+a; C*: 12.5 m.2/g; D*: 4.9 m 2 / g . Capital letters indicate the actual areas, lower case letters the relative surface areas.
There is little regularity in the order of actual surface areas, implying that doping had a random effect, but the order of relative areas is more consistent. Also, there appears to be a change in order in going from 400 to 450'. Reference to the postulated mechanism schematically shown in Figure 10 shows that this region is near that a t which the hydroxide-oxide conversion is coniplete and also near the maximum of the range of existence of stoichiometric cadmium oxide. Although it thus seems possible to separate the effects of doping on the two major processes, only the sintering of the oxide will be considered because no supporting data such as electrical conductivities are available for the hydroxide. Haul and Justlo and Dumbgen" studied the disorder and oxygen transport in CdO by measuring the 0 l 6 0l8exchange between gaseous oxygen and CdO crystals from 630 to 855'. They found that Li+ addition resulted in a marked increase in the diffusion coefficients of oxygen in the oxide lattice, while In+3addition had the reverse effect. The doping effects and the increase of diffusion coefficients with decreasing oxygen pressure furnished strong evidence for a transport mechanism involvirlg vacancies in the anion sublattice, This is in agreenlentwith the of ~ ~ and wagner,12 ~ who found a decrease in the electrical conductivitv of CdO with increasing oxygen pressure, and does not conflict with the results of Engell's study13 of doping on CdO electrode potentials. Cimino and Marezio' The Journal of Physical Chemistry
studied the effect of Ag+ and I n f a doping on the lattice parameter of CdO and explained the results in terms of interstitial metal. However, as pointed out by Haul and Just, Cimino and Marezio's results are equally well in agreement with the concept of oxygen vacancies. Acceptance of the oxygen vacancy mechanism suggests that vacancies are also involved in the sintering of cadmium oxide. The various sintering data suggest that up to 400' the oxygen vacancy mechanism could account for the increased loss of surface area of the Li+-doped samples, Li+ incorporation causing an increase in oxygen vacancies, O(V) Liz0 (CdO) +2Li+ (Cdf2)
+ 0-2+ O(V)
and the decreased loss of area of the Alf3-doped samples through the destruction of vacancies A1203(CdO) -+-2Al+3 (Cd+2)
+ 30-2 - O(V)
At 450 and 500°, however, the Al+3-doped samples exhibited smaller surface areas than undoped samples, suggesting that the effect of A1203addition had brought about an increased rate of material transport. This does not necessarily mean that the oxygen vacancy mechanism ceased to operate, but merely suggests that that mechanism was no longer the dominant one above about 400'. An additional mechanism could become operative or dominant A1203(CdO)
---)
2Alf3 (Cd+2)
+ 3Cd0 + Cd(V)
where Cd(V) symbolizes a cadmium vacancy. This is based on the premise that the incorporation of 2A1+3 would result in the displacement of 3Cd+3 with the creation of one Cd(V). The postulated cation vacancy mechanism does not conflict with the anion vacancy or with changes of electrical conductivity of the solid. The effects of cation vacancies on the lattice parameters cannot be assessed.3 An adequate explanation for the effects of Zn+2 and Mg+2 additions is not a t hand. In terms of a substitution mechanism, the presence of Znf2 or Mg+z a t Cd+*lattice positions should be without effect. The fact that large sintering effects have been found, however, suggests that the incorporation of the homovalent impurities brings about significant changes in the elec(10) R. Haul and D. Just, J. Phys., 33, 487 (1962). (11) R. Haul, D. Just, and G . Diimbgen, "Reactivity of Solids." ~ Proceedings~ of the 4thbInternational ~ Symposium ~ on Reactivity h in the Solid State, J. H. deBoer. Ed., Elsevier Publishing - CO.. New York. N. Y., 1961, p. 65 ff. (12) H. H. Baumbach and C. Wagner, 2. physik. Chem., B22, 199 (1933). (13) H. J. Engell, 2. Elektrochem.. 60, 905 (1956).
CATALYTIC VAPORPHASE OXIDATION OF 0-METHYLBENZYL ALCOHOL
tronic nature of the solid which then make themsehres felt as changes in rates of surface and bulk diffusion. Acknowledgment. Support of this work by the Government of the United Arab Republic by means of a Fellowship for A. M. K., the Petroleum Research
457
Fund of the American Chemical Society, and the Research Council of Rutgers, The State University, is gratefully acknowledged. We are also grateful to the Phillips Minerals and Chemicals Company, Metuchen, N. J., for making the d.t.a. experiments possible.
The Catalytic Vapor Phase Oxidation of o-Methylbenzyl Alcohol
by Theodor VrbaLki and Walter K. Mathews Sinclair Research, Inc., Harvey, Illinois
(Received August 3, 1964.)
A study was made of the oxidation of o-methylbenzyl alcohol over fused vanadium oxide catalyst from 280 to 460' in a flow system. The reaction course consists of four parallel routes: (1) the formation of phthalic anhydride by way of o-tolualdehyde, o-toluic acid, and phthalide as intermediates; (2) the simultaneous direct oxidation to phthalic anhydride ; (3) the formation of carbon oxides by way of maleic anhydride; (4) the direct oxidation to carbon oxides. A minor portion of both maleic anhydride and carbon oxides is formed from phthalic anhydride and its precursors. The activation energy for the over-all reaction is 20.0 kcal./mole in the range from 300 to 350")and the order of reaction with respect to the concentration of o-methylbenzyl alcohol is 0.48. The oxidation rate shows a square root dependence of the oxygen concentration below 0.2 atm. Both the reaction order and the activation energy for the formation of o-tolualdehyde were also determined.
Introduction The vapor phase oxidation of o-xylene has gained considerable importance in the past decade as a commercial method for producing phthalic anhydride. The however, is scanty and deals published literature, primarily with obtaining high yields. About 70 mole % of phthalic anhydride is attainable from o-xylene, whereas yields in the naphthalene oxidation are 85 to 90 mole 70.8f9 This discrepancy combined with the fact that about 85 mole % of o-toluic acid is converted to phthalic anhydride under conditions similar to those used in the oxylene oxidation10 tends to indicate that in the o-xylene oxidation different branching reactions in the interniediate steps are taking place. Such reactions could be, for instance, decarbonylation of o-tolualdehyde and de-
hydrogenation of o-methylbenzyl alcohol followed by decarbonylation. Both of these reactions would lead, via toluene and benzoic acid, eventually to additional formation of carbon oxides. o-Methylbenzyl alcohol is
-'
(1) W. G . Parks and C. E. Allard, Ind. Eng. Chem., 31, 1162 (1939). (2) I. B. Gulati and S. K. Bhattacharyya, J . Sci. Ind. Res. (India), 12B,450 (1953).
(3) G. L. Simard, J. F. Steger, R. J. Arnott. and L. A. Siegel, Ind. Eng. Chem., 47, 1424 (1955). (4) S. K. Bhattacharyya and I. B. Gulati, ibid., 50, 1719 (1958). (5) G. Ibing, Brennstof-Chem., 42, 357 (1961). (6) T. P. Forbath. Chem. Eng., 69, No. 19, 98 (1962). (7) S. K. Bhattacharyya and R. Krishnamurthy, J . Appl. Chem., 13, 547 (1963). (8) A. B. Welty and W. F. Rollman, U. S. Patent 2,489,346 (1949). (9) UT.F. Rollman, U. S. Patent 2,489,347 (1949). (10) C. E. Morrell and L. K. Beach, U. S. Patent 2,443,832 (1948).
Volume 69, Number 8
February 1966
