I
J.
F. W O O D H A M l
and C. D. HOLLAND
Department of Chemical Engineering, A. and M. College of Texas, College Station, Tex.
A New Catalyst f o r .
..
Oxidation of Propylene with Air Propylene is oxidized primarily to acrolein at about 500' F. and 2 atmospheres of pressure O x m i Z T i o N OF OLEFINS, particularly propylene, to a,@-unsaturated carbonyl compounds has received much attention in recent years ( I , 2, 4, 5, 7, 8). Most of the published information pertaining to the catalytic oxidation of propylene in the gas phase is in patent literature, and cuprous oxide supported on various carriers is the catalyst most often mentioned. Because of the need for more information pertaining to catalytic oxidation of propylene, this project was initiated.
Preparation of Catalyst
Fifteen catalysts, sufficiently homogeneous to justify their evaluation with qualitative or semiquantitative determinations of their behavior in a flowtype reactor, were prepared (9). One catalyst studied in detail was prepared as follows: A solution was prepared which contained 0.13 gram of C u ( N 0 3 ) ~ . 3 H z O and 1.25 grams of water per gram of Al(NO3)2,9HzO. A hydrogel was prepared by simultaneously adding the solution containing copper nitrate and aluminum nitrate and a 28Yo ammonia solution to a 3-liter beaker with vigorous stirring. The rate of flow of the copper nitrate-aluminum nitrate solution was adjusted to a value of from 2 to 4 drops per second. The rate of flow of the ammonia solution was regulated to maintain the pH of the slurry in the beaker at a value of 5.5 f 0.5. After mixing, the slurry was stirred for 5 minutes and additional ammonia solution or copper nitratealuminum nitrate solution was added as needed to adjust the pH to a value of 5.50 i 0.05. Half of the slurry in the Present address, Southwestern Louisiana Institute, Lafayette, La.
beaker was withdrawn and poured into a stock bottle. The flows of ammonia and copper nitrate-aluminum nitrate solutions to the mixing beaker were readjusted to the proper values, and the process was repeated. Eight stock bottles were eventually filled with slurry. The material in each bottle was permitted to sit undisturbed for a t least 24 hours. In each case a fairly rigid gel was formed, which was dispersed in the supernatant liquid by mechanical agitation, and then left undisturbed for 7 days. The precipitate did not again form a continuous gel; rather it seemed to be gel particles of macroscopic dimensions. The contents of the 8 bottles were thoroughly blended, and the resulting slurry was left undisturbed for 7 days. This step was taken in order to ensure maximum homogeneity of the product. The solution was filtered and the unwashed precipitate was immediately cut into small cubes of about '/z inch in linear dimension and dried under 27 inches of vacuum a t 230' F. for 24 hours. For the drying operation, four 2-liter vacuum flasks were connected
to vacuum lines and placed in a conventional forced-air circulation oven. Two 100-gram samples of the dried precipitate were placed in an open crucible in a muffle furnace a t 400' F. and the temperature was raised to 1700' F. at a rate of about l o O D F. per hour. The catalyst was maintained at 1700' F. for approximately 24 hours, and then separated into two batches according to particle sizes: 6- to 16mesh and 16- to 30-mesh. A thin supporting layer of the larger particles was placed a t the bottom of the catalyst bed. The remainder of the catalyst bed was composed of particles ranging from 16-mesh to 30-mesh. The thin layer of larger particles kept smaller particles from falling into the space between the support blocks and the reactor wall. The mass ratio of copper to aluminum in the catalyst was 0.48. During heating, the color of the material changed from blue to green with the evolution of oxides of nitrogen. The green material was stable up to temperatures in excess of 1500" F. At no time was there any evidence of the formation of either cupric oxide or cuprous
Organic compounds other t h a n carbonyls were formed in greater t h a n trace amounts Acrolein was formed in yields reacted propylene
a s high
as 45%
not of
Acrolein, acetone, a n d carbon dioxide were formed a s primary products
At longer residence times, acrolein a n d l o r acetone formed additional carbon dioxide Dimer of acrolein was formed i n small amounts
VOL. 52, NO. 12
DECEMBER 1960
985
oxide. It is believed that the catalyst consisted mainly of a spinel of copper and alumina. The cocoa material, formed a t l6OO0 to 1700° F., was insoluble in dilute hydrochloric, nitric, and sulfuric acids.
Apparatus In the flow-type, tubular, fixedbed reactor used, thermocouples were placed in the thermocouple well at 1to 2-inch intervals throughout the catalyst bed. Copper cooling coils, not illustrated, were wound around the outside of the reactor at about 2-inch intervals. Also? electrically insulated coils of resistive wire were wound between the rounds of copper tubing in each section. The flow of air through
each section of cooling coil and the rate of heating in each section of resistive wire were individually controlled. This arrangement permitted close control of the temperature of the gas phase in each section of the catalyst bed. Ordinarily, point temperatures in the gas phase were maintained at the desired values by manual manipulation of the voltage impressed across each section of the resistive wire. O n occasions when the rate of rise of the temperature within an increment of the catalyst bed could not be controlled by varying the heating rate, air was admitted at a measured rate to the cooling coil surrounding that section. Maximum deviation of the temperature of the gas phase from the control value did not exceed 16' F. for the runs reported in this paper.
GASKET
A L L FLANGES
.EL PREHEAT SPIRAL
ATALYST B E D
SUPPORT GRID
CER BLOCKS
NLESS STEEL
I
The reactor. Air flow through each section of heating coil and heating rate in each section of resistive wire were individually controlled
986
INDUSTRIAL AND ENGINEERING CHEMISTRY
The rates of flow of propylene and air to the reactor were measured by use of rotameters which had been calibrated by means of a wet-test meter. A proportional pneumatic controller was employed to control the total pressure of the reactor. Carbonyl compounds ivere rrmoved by passing the effluent gas from the reactor through a scrubber which contained chilled water and then through several scrubbers that were charged \vith 2.4-dinitrophenylhydrazinereagent. The rate of flow of the effluent gas, M hich had been scrubbed, was measured with a wettest meter.
Analytical Procedures Compositions of the feed gas and the scrubbed effluent gas were determined with an absorption apparatus, a Burrell premier model gas analyzer. Determinations for propylene, oxygen, carbon monoxide and carbon dioxide were made. For comparison, samples of the effluent gas from six runs were analyzed with a mass spectrometer (Model 102; Consolidated Engineering Co.). The carbonyl compounds recovered in the water scrubber were converted to their 2,4-dinitrophenylhydrazonederivatives. The chromatographic procedure of Gordon and others (6) was modified slightly ( 9 ) and employed to resolve the 2,4-dinitrophenylhydrazone derivatives obtained from the 2,4dinitrophenylhydrazine scrubbers and those formed from the samples taken from the water scrubber. The chromatographic procedure gave two mobile bands and one stationary band. A third very faint band, believed to be the 2,4-dinitrophenylhydrazone of acetaldehyde was observed in several samples. The first mobile band eluted from the chromatographic column contained the 2,4-dinitrophenylhydrazone of acrolein. The second band eluted from the column contained the 2,4-dinitrophenylhydrazone of acerone. The 2,4-dinitrophenylhydrazonesof acrolein dimer and higher polymers of acrolein and unreacted 2,4-dinitrophenylhydrazine constituted the stationary band found at the top of the column. No effort was made to elute the unreacted 2,4-dinitrophenylhydrazineand the 2,4-dinitrophenylhydrazonesof the various polymers of acrolein. Melting points and mixed melting points were used to identify the 2,4dinitrophenylhydrazones of acrolein and acetone. The solvent, petroleum ether, was scurbbed Tvith concentrated sulfuric acid? washed, and distilled in the presence of the activated adsorbent. The 2,4-dinitrophenylhydrazone was recrystallized once from alcohol by cooling a hot, saturated solution and then
OXlDlZlNG PROPYLENE adding enough water to causc more than 90% precipitation, The melting points were determined by using a calibrated micro melting-point apparatus. The identity of the first mobile band was further confirnled by showing that the melting point of the compound obtained from this band was not depressed by an authentic sample of the 2,4dinitrophenylhydrazone of acrolein. Additional proof of the identity of the second mobile band, the 2,4-dinitrophenylhydrazone of acetone, was established in a similar manner. I t was observed that the 2,4-dinitrophenylhydrazone of the dimer of acrolein (2H-pyran-2-carboxaldehyde-2, 3dihydro-) was soluble in chloroform to the extent of only 0.05 gram per liter. Although no effort was made to determine the solubility values for the 2,4-dinitrophenylhydrazones of higher polymers of acrolein, it seemed probable that the solubilities in chloroform of such compounds would be even less. The quantity of dimer and higher polymers of acrolein was computed from the knowledge of the weight of insoluble material in the sample taken for chromatographic analysis and from the knowledge of the solubility in chloroform of the 2,4-dinitrophenylhydrazone of the dimer. All polymeric forms of acrolein were reported as the dimer. T h a t the chloroform-insoluble mixture of the 2,4-dinitrophenylhydrazones consisted mostly of acrolein dimer along with smaller quantities of higher polymers was demonstrated by a comparison of its melting range with that of a chloroform-insoluble sample prepared by reacting a n excess of 2,4-dinitrophenylhydrazine reagent with acrolein dimer. Melting ranges of the chloroform-insoluble mixtures obtained from the various scrubbers were not altered b y admixture with the synthetic sample. The following quantitative determination for the 2,4-dinitrophenylhydrazones of acrolein and acetone was used. The solution corresponding to each eluted band was evaporated to dryness in a Petri dish by passing a stream of air a t room temperature over t h e solution. T h e residue from each cut was dissolved in 100 ml. of chloroform and suitable dilutions were performed to obtain a solution which had a transmission in the range of from 20 to 80%. The percentage transmission in a 1-cm. cell at a 356-mp wave length was obtained by means of an ultraviolet spectrophotometer (DUR-Beckman model, modified to accommodate conventional sample cells). The concentration of the particular carbonyl of 2,4-dinitrophenylhydrazone was read from a calibration curve. T h a t organic compounds other than carbonyls were not formed in greater
than trace quantities was established within reasonable accuracy by a combustion procedure and by qualitative tests. One extended run was made which involved operation over the entire range of operating variables employed in this research. Carbonyl compounds were removed with aqueous, acidified 2,4-dinitrophenylhydrazine reagent from a 1-liter sample obtained from the water scrubber. T h e residual solution was distilled into a combustion tube which contained cupric oxide and which was maintained a t 1700' F. Air, free of carbon dioxide, was admitted simultaneously. The gases from the combustion tube were passed through several scrubbers which were charged with a barium hydroxide solution saturated with barium carbonate. Comparison of the amount of barium carbonate precipitate obtained from the analysis of the sample with that from a blank containing a solution of the 2,4-dinitrophenylhydrazine reagent under the same conditions indicated that organic compounds with boiling points below the decomposition temperature of the 2,4-dinitrophenylhydrazine reagent, other than carbonyls, were not formed in quantities detectable by this procedure. Under the conditions of this test, ethyl alcohol was detectable in quantities less than 2 parts per thousand. A second portion of the sample taken from the water scrubber was subjected to the qualitative tests of Feigl ( 3 ) for the detection of alcohols, ethers, esters, and organic acids, and negative tests were obtained. A qualitative test (3, 9) for formaldehyde was made on each 2,4-dinitrophenylhydrazone sample prior to its separation by the chromatographic procedure and no trace of i t was found. The limit of identification for the modified test was 2 r n ~grams of the 2,4dinitrophenylhydrazone of formaldehyde.
are the ones which are generally of primary interest in the partial oxidation of propylene. Analyses for carbon dioxide and other effluent gases were not so reliable as those for the carbonyl compounds. I n the case of carbon dioxide, small quantities could not be determined accurately with the equipment available. For example, the mass spectrometric analysis differed from the absorption analysis by as much as 0.9% for a sample containing 5% carbon dioxide. The quantity of water formed was taken as that which would be given stoichiometrically in the formation of the carbonyl compounds and of the carbon dioxide. All of the reaction products formed were attributed to the presence of the catalyst because several blank runs ( W =0) were made a t the reaction conditions and no detectable reaction to carbonyls occurred. The problem of establishing with a minimum of doubt the exact mechanism followed by a complex system of reactions is ordinarily difficult and generally more data are required than were obtained in this investigation. Although a mechanism sufficient to explain the experimental data which were obtained in the present study has been proposed (9), it should be pointed out that the proposed mechanism is not necessarily the only one consistent with the data. Since the primary objective of this research was to determine the product distribution as a function of W / F , rather than the reaction mechanism, only the product distribution and stoichiometry are discussed herein. The mass of catalyst in grams employed for each experiment is denoted by W and the rate of flow of the total feed in grammoles per hour is represented by F. The plot shown in Figures 1 and 2 is convenient for the demonstration of the stoichiometry of a system of reactions. For example, consider the single unidirectional reaction, A
Discussion Feed rates were calculated on the basis of the rotameter readings and the analyses of the feed. The effluent rates were computed on the basis of the analyses of the product streams and on the total flow rates as measured by the wet-test meter. The amount of propylene which reacted was calculated on the basis of the analyses of the effluent streams. All of the experiments were carried out with a large excess of propylene, and a n operating pressure of 2 atm. The quantities of the carbonyl compounds in the effluent stream were established from analyses with a high degree of reliability. These compounds
-+
2B
When this is the only reaction occurring in the system, a plot of the moles of B formed per mole of A reacted us. W / F would give a horizontal line with an ordinate of 2. If two reactions occurred, such as A
--t
2B
A-.C
plots of the moles of B and C formed per mole of A reacted would yield horizontal lines having ordinates proportional to a certain combination of the rate constants. If B further reacts to a secondary product D, B-+D VOI. 52, NO. 12
DECEMBER 1960
987
?,GRAMS
OF CATALYST PER G R A M - M O L E O F FEED P E R H O U R
Figure 1 . The primary product, acrolein, was further oxidized to carbon dioxide as ratio of catalyst mass to flow rate was increased
then the molm of R formed per mole of A reacted decreases as W I F increases. Also, the plot of the moles of D formed per mole of A reacted begins a t the origin and increases as W / F increases. Figures 1 and 2 suggest that acrolein, acetone, and carbon dioxide were formed as primary products. T h e negative slopes of the curves for the production of acrolein and acetone shoivs that a t the larger residence times, these compounds underwent further reaction to form compounds such as carbon dioxide. T h e positive slope of the curve for the production of carbon dioxide supports this contention. The intercept of 1.2 of the curve for the producrion of carbon dioxide infers that this compound was also formed by a primary reaction. Thus, the stoichiometric equations are proposed : C3H6
r '
1 D 0.10
.-
I
W
c
I
PRESS,=2 ATM B 500" F. 525" F.1 - '
I
1 I
W
z
w 0.06 1
a > [L
0.04
L
0
w
0.02 I
-I
0
= 0.0
I
,
40
50
1
10
0
:,GRAMS
20
30
60
OF CATALYST P E R G R A M - M O L E OF F E E D P E R H O U R
Figure 2. Reaction rate was independent of temperature over the range of 500' to 525' F.
I
7
5.0
PRESS = 2 ATM I I 500' F.
t-
~
0
525' F. l
1-
A 5 0 0
" I
k z w
a:
::
F,
G R A M S OF C A T A L Y S T P E R G R A M - M O L E OF F E E D PER HOUR
Figure 3.
988
Small amounts of acetone and the dimer of acrolein were produced
INDUSTRIAL AND ENGINEERING CHEMISTRY
0 2
+ HpO
CHSCOCHB
+
3COg
+ 3.5
+ 3H2O
0 2 +
+ 2H90 3C02 + 3HzO 3COz
CHaCOCH3
+ 4.009
+
I n the case of the dimer of acrolein, the curve of Figure 2 indicates that this compound was formed by a primary reaction. However, because such a small amount of the compound \vas formed and because the analysis for it was approximate, the dimer may have been formed b y the secondary reaction of acrolein. T h e results shown in Figure 3 indicate that lvithin the temperature range of 500" to 525" F., the effect of temperature was oi" a smaller order of magnitude than was the reproducibility or experimental res :.Its.
V
R
Og +
CHzCHCHO
3a 0.08 0
CHyCHCHO
0 2 -
+ '/z C3Hs + 4.5 C3He
literature Cited (1) Andrianona, T. I., Roginskii, S. C., Z h u r . Obshchei. Khim.24, 605 (1954). (2) Bataafsche, N. V. de (to Petroleum Maatschappij), Dutch Patent 640,383 (1950). (3) Feigl, F., "Qualitative Analysis by Spot Tests," (3rd ed.), New York, Elsevier Publishing Co., Inc., New York, 1946. (4) Goodings, E. P., Hadley, U. J., (to Distillers Co. Ltd.), British Patent 625,330 (1949). (5) Zbid., 658,179 (1951). (6) Gordon, B. E., Wopat? Fred, Jr., Burnham, H. D., Jones, L. C., Jr., Anal. Chem. 23, 1754 (1951). (7) Hearne, G. W., Adams, M. L. (to Shell Development C o . ) , U. S. Patent 2,486,842 (1949). (8) Margolis, L. Ya., Roginskii, S. Z., Gracheva, T. A., Zh'hur. Obshchei Khim. 26, 1368-71 (1956). (9) \Voodham, J. F., Ph. D. dissertation, A. and M. College of Texas, College Station, August 1959.
RECEIVED for review June 16, 1960 ACCEPTED September 6, 1960 Work was supported in part by the Gulf Oil Corp. and by the Texas Engineering Experiment Station.
