TECHNIQUE FOR REMOVING METAL CONTAM I NANTS FROM CATALYSTS H A R O L D B E U T H E R AND
Gulf Research
R . A. FLINN'
Developmen/ Co., Ptttsburgh 30, Pa.
In the catalytic processing of heavy oils, chemically combined nickel and vanadium present in the oil deposit
on the catalyst and markedly influence catalytic behavior.
Small quantities of these metals change the
selectivity in catalytic cracking, while larger deposits in residual oil desulfurization or hydrocracking cover the catalyst and lower activity. By using a dilute aqueous solution of a complexing agent, such as oxalic acid, dioxane, or acetylacetone, nickel and vanadium oxides can b e removed to obtain a substantial improvement in catalytic activity and/or selectivity. In this work, a number of complexing agents were tested, and their selectivity for removing contaminating metals, catalytic metals, and alumina was studied. A study of the state of vanadium as i t exists on the catalyst surface i s also reviewed.
HE DEPOSITION ON CATALYSTS of metallic contaminants Tpresent as metallo-organic compounds in petroleum feedstocks is a serious catalytic processing problem. O n cracking catalysts ( 7 ) > such deposition results in a considerable loss of selectivity so that the reaction tends to produce more coke and gas along \vith less of the desired product, gasoline. In residue hydrodesulfurization, the metal deposits do not greatly alter catalyst activity or selectivity (5). However, the abundance of metals in most residues results in a catalyst "blanketing" effect Lvhich completely alters the original surface components and can eventually lead to reactor plugging. .4number of approaches to solving the metal contamination problem are evident. Removal of the metallo-organic contaminants from the reactant overcomes the problem, but in many cases this becomes costly or technically difficult to accomplish \vith a high degree of selectivity. Another approach is to allow the contaminants to deposit on the catalyst and then to remove such deposits either chemically or physically without allowing a significant build-up to occur. Although the same limitations of cost and technical difficulty are applicable to this approach? i t is possible to envision a more selective system in jvhich less of the reactant is lost while removing the metals. The work reported in this paper describes some chemical techniques which have been developed for removing certain metallic contaminants from catalysts. It is believed that these can be used effecrively in combination \vith either catalytic cracking or residue hydrodesulfurization to circumvent the metal contamination problems.
Metallic Contaminants
The most common organically combined metal contaminants in heavy gas oils and residues are vanadium and nickel. 'The nature of these contaminants has received considerable attention. and one abundant class of metal-containing compound present appears to be of the porphyrin type. In the vanadium porphyrin, the vanadium exists in the plusfour valence state (V+4)). Deposition of the metal from Pa.
Present address, ;\ir Products and Chemicals Inc., .Allento\vn.
such compounds on the catalyst does not apparently result in a change of this valance. Examination of the electron paramagnetic resonance (EPR) spectra of vanadium-contaminated cracking catalysts indicates that the vanadium is deposited in the plus-four valence state (2). In addition. the presence of a bveak hyperfine splitting characteristic of porphyrins suggests that the deposited vanadium is actually still bound in the porphyrin structure. This would indicate that. on cracking catalysts a t least. the deposition of the metallic compounds may not involve dissociation but may be more akin to adsorption. Further examination of the vanadium-contaminated cracking catalysts, after varying degrees of air oxidation of the type used conventionally to remove "coke" deposits, revealed that the oxidation converts the plus-four vanadium to another oxidation state, probably plus-five. which is undetectable by EPR. The plus-five state (V'j) is diamagnetic and, thus. unresponsive to EPR. Apparently, the vanadium compounds in the oil are absorbed on the catalyst during the reaction and. at the most, only partially decomposed. IVhen the contaminated catalyst is then subjected to oxidation to remove coke. this regeneration process converts the vanadium to the pentoxide. Since \ ' a 9 5 is rather low melting (800' C . ) , it may actually fuse on the catalyst surface and combine with other metal oxides present to alter the physical and chemical structure of the catalyst. The fact that the metals are deposited in a n organically combined state is of interest in attempting to devise techniques capable of extracting these metals from the catalyst. Although still combined in an organic structure, the over-all metalloorganic is probably embedded in a coke matrix from which chemical extraction would be difficult. The porphyrins themselves are rather resistant to chemical decomposition, as is the coke; it, therefore, appears that chemical extraction of the metals from the "coked" catalyst would be quite difficult. O n the other hand, in the oxidized form. such as OS, the metals should be reasonably susceptible to chemical attack. Accordingly, the oxidized catalysts were chosen for chemical extraction studies, and hydrogenation catalysts were studied after regeneration to obtain the oxidized form of the metal. VOL. 2
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53
~~~~
Table 1.
~~
Treatment of Contaminated Hydrogenation Catalyst with Aqueous Oxalic Acid Catalyst particle size: 10-20 mesh
Washing Treatmenta
Cafalyst Properties
Soh. concn.;
Surjace Time. Temp., Composition, W t . % area, sq. wt. % hr. a F. i'\' W V meters/gram Fresh catalyst 3.8 8.5 0.0 238 __Contaminated catalyst4.0 8.4 9.2 -2 1. o 0.17 80 4.1 8.1 7.4 112 1. o 0.5 80 4.2 8.0 5.9 9: 1 .o 1 .o 80 4.4 8.2 5.2 117 1.o 4.0 80 4.4 8.8 4.0 139 1. o 8.0 80 4.4 8.5 4.5 134 1 .o 24.0 80 4.4 7.8 2.6 156 1 .o 0.5 40 4.3 8.3 7.2 100 1 .o 0.5 150 4.3 8.9 6.1 134 5.0 0.5 80 4.4 9.1 6.2 131 a Solution pumped upJoru overjxed bed of catalyst granules at 96 volume space velocity. b Parentheses indicate gain. ~
Removal Techniques
Consideration of the inorganic chemical problem involved indicates that a reagent is needed which is fairly selective for the reaction with vanadium or nickel oxides in the presence of oxides of aluminum and silicon for cracking catalyst applications, and also in the presence of molybdenum, tungsten. and cobalt oxides for use with hydrogenation catalysts. Actually, with hydrogenation catalysts the removal of nickel contaminants is not a serious problem, since nickel is relatively active for the hydrogenation reaction and is also generally the less abundant of the two metallic contaminants. Organic reagents capable of forming water-soluble metal complexes appeared to offer a reasonable hope for giving the selectivity desired. ,4 cursory examination of several of these revealed that aqueous oxalic acid, which had previously been reported to remove iron ( 3 ) ,also removed VzOj rapidly from catalyst surfaces. Unfortunately, it also attacked MoOz and A1203. For use with silica-alumina cracking catalysts and nonmolybdenum-containing hydrogenation catalysts, the oxalic acid appeared promising, nonetheless. since the loss of alumina did not appear to be too great. Furthermore, the slow dissolution of some of the alumina appeared in some cases to increase the surface area, which could actually prove beneficial.
yo Remooalb i'\.
W
...
...
...
..
'(2)
4 5 2 (4) (1) 8 1 (6)
2c 36 44 56 51 72 22 34 33
(4) (12) (12) (12) 112) ( 4 (8) (12) ~
(8)
V
These thoughts led to a closer examination of the oxalic acid technique. The experimental treatment used consisted of an upflow percolation of the acid solution through a fixed bed of catalyst a t approximately atmospheric conditions. .4 nickel-tungsten-alumina catalyst which had been contaminated with vanadium and nickel during residue hydrodesulfurization was washed with oxalic acid solutions under varying conditions (Table I). N o conditions gave a significant change in the nickel content of the catalyst, but the vanadium level could be substantially reduced. The acid concentration and washing temperature appeared to have little effect upon the degree of vanadium removal, but time had a significant effect. '4 rapid initial removal of vanadium was followed by a period of decreasing removal rate. One hour of washing removed 44y0 of the vanadium while 24 hours removed 72%. The rate of removal could be accelerated by interrupting the acid washing with a water washing or with a water washing and drying (Table 11). For example, while 8 hours of continuous washing removed 51% of the vanadium, two 4-hour washings separated by a rinsing and drying removed 69%. T o obtain 69% removal by continuous washing required about 2 1 hours. The surface area improvement brought about by washing was substantial. The contaminated nickel-tungsten catalyst area of 72 square meters per gram was increased to 134 by
Table II.
Acceleration of Vanadium Removal by Interrupted Washing Washing Treatment LHSV,. Tfmp., vo1.lhr.l -Vl F. vol. Technique
Soh concn., wt.
a
54
%
Time. hr.
1. o 1 .o
8.0 8.0
1 .o 1 .o
4.0 4.0
1 .o
4.0
Liquid hourly space velocity.
80 80
Catalyst I: 4.070 Ni, 8.4yo W , 9.270 V 96 Continuous 8-hr. washing 96 Dried after 4 hr.; then washed for another 4 hr.
Catalyst II: 5.0% Ni, 15.5% lV, 2.8% V Continuous 4-hr. washing 18 Dried after 2 hr.; then washed for 18 another 2 hr. Washed for 2 hr.: water rinsed 2 80 18 hr., then washed 2 hr. Parentheses indicate gain. 80 80
b
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
(12) (19)
12
Removalb W
Y
(t'
51 69
17 13
46
J
7
13
60
65
Treatment of a Molybdenum-Containing Catalyst with Aqueous Oxalic Acid
Table 111.
Catalyst particle size: 10-20 mesh
Washing Treatment ~-
Soh. concn., wt. %
Temp.. a F.
T i m e , hr. Fresh catalyst-Contaminated catalyst0.0 2.0 80 1.25 0.08 150 1.25 0.33 150
5.00 1.o Parentheses indicate gain.
150
Catalyst Properties Composition, W t . % Ni .Mo 0.0 10.1 0.7 8.5 0.8 8.9 0.8 6.9 0 8 4 8
Go
2.5 1.9 2.0 1.8 1 7
1 .o
1.6
2.1
a n 8-hour treatment removing 51y0of the vanadium (Table I ) . The oxalic acid technique did not appear to be applicable to molybdenum-containing catalysts (Table 111). .4 series of experiments on washing a contaminated cobalt-molybdenumalumina catalyst showed that molybdenum was removed a t least as fast as vanadium. In the case of contaminated silica-alumina cracking catalysts. oxalic acid removed vanadium and also a substantial portion of the nickel present (Table IV). The fact that a significant percentage of nickel is rcamoved in this case is attributed to the rather low level of metals contamination. A small portion of nickel removed in such a case has a larger percentage effect. However, rather small quantities of vanadium and nickel are sufficient to poison a cracking catalyst. It seems significant that changes in the washing conditions varied the degree of vanadium removal over a fairly wide range but altered the nickel removal very little from the 30 to 40% range. Since a portion of the nickel is removed more easily than the remainder, it is possible that this may be related to the concept of “aged” us. ”fresh” metal contaminant deposits ( 7 ) . The removal of vanadium from a contaminated cracking catalyst also appears to occur most rapidly in the initial stages of the washing. Extended washing periods seem to have virtually no effect compared with the initial period. It seems likely that a relatively short washing period a t elevated temperatures would suffice to remove most of the vanadium. Unfortunately, some aluminum is extracted along with the vanadium. This could ultimately lessen the catalyst activity.
Table IV. Washing Treatments
Soh. comn., ut.
?&
Time, hr.
-Contaminated
-
V 0.0 5.4 5.7 3.6 3 0
1.9
Surface area, sq. meterslgram 255 50 62 77
% Removala Co
n-1
Mo
V
...
... ...
...
...
19 43
i4j
(5) 34 45
76
66
ti j
(8) 141
5
116
10
118 162
9 14
(34)
From these initial experiments with oxalic acid, it appeared that vanadium could be effectively removed from contaminated catalysts by oxalic acid washing, but several problems remained. First, the inability to remove nickel in substantial amounts limited the applicability, particularly in the case of cracking catalysts where nickel contamination is even more serious than vanadium contamination. Second, the tendency to remove molybdenum was also problematical, since many effective hydrodesulfurization catalysts utilize molybdenum. And finally,’the marked increases in area and the loss of alumina from silica-aluminas indicated that the catalyst supports themselves wrre attacked by the oxalic acid, and an understanding of the extent of this attack was of importance. To discover other washing compounds \vhich might overcome some of these problems, an exploratory series of possible complexing agents was studied. From this series (Table V), glycolic acid appeared unusual since it removed vanadium effectively and did not remove molybdenum. ,411 of the materials tested removed substantial amounts of nickel, with oxalic acid removing the most. This is not consistent with the earlier results on cobalt-molybdenum and nickel-tungsten catalysts and a t present is inexplicable. Some nonacidic complexing agents which removed vanadium effectively appeared worthy of further study. since it seemed possible that these might not attack alumina to the same extent as the acids. To determine this, several such agents were compared with tartaric acid, which had also proved effective in the washing of a contaminated cracking catalyst (Table V I ) .
Treatment of Contaminated Fluid Cracking Catalyst with Aqueous Oxalic Acid Catalyst Properties Surface Composition, Wt. yo area, sq. ?& Remooalb Temp., ’ F. &Vl ‘4 1 meterslgram .Vl
v
catalyst-
0.29 0.1 12 80 0.20 0.1 24 80 0.18 0.1 48 80 0.19 1 .o 12 150 0.10 1 .o 24 150 0.12 5.0 12 80 0.14 5.0 24 80 0.13 5.0 48 80 0.14 Slurry washing technique using 70grams of catalyst in 200 ml. of
...
v
0.07 16.9 0.05 17.0 0.05 16.8 0.05 16.6 0.04 14.3 0.05 14.0 0.05 15.3 0.04 14.9 0.04 15.6 solution a i t h agitation follomed by
49 .. 51 31 50 38 49 35 85 66 82 59 62 52 68 55 a2 52 rinsing and drying.
VOL. 2
..
b
A1
‘1’
29 29 29 2 41 15 29 17 29 10 41 12 41 8 Parentheses indicate gain.
NO. 1
MARCH 1963
55
Table V.
Other Chemicals Capable of Extracting Contaminant Metals
Catalyst: N i 0 - C o 0 - M a 0 - A 1 2 0 ~contaminated in residue hydrodesulfurizatian aqueous solution, 4 hours, 80' F. Washing conditions; 1.0 wt. Washing technique: Recycled 1000 ml. of solution upflow over 15 grams of catalyst at 500 ml./haur, then rinsed and dried
70
Catalyst Properties Composition, Wt. Chemical
Fresh catalyst Contaminated catalyst Oxalic acid Lactic acid Citric acid Glycolic acid Phthalic acid (0.570 s o h . ) Malonic acid Succinic acid Salicylic acid Tartaric acid Salicylaldehyde 0 - Aminophenol Ethvlenediamine Acrtylacetone Pnrentheses indicate gain.
Table VI.
V 0.0 1.9 1 .o 1.1 1.o 1.2 1.2 1.1 1 .?I 1.2 1.2 1.3 1.4 1.2 1.4
Surface
yo
co
)Vi
:Mo
area, sq. rnettrslgram
1.o 1.o 0.4 0.5 0.8 0.8 0.5 0.6 0.8 1.1 0.4 0.9 1.2 1.1 0.8
0.5 0.9 0.4 0.5 0.5 0.7 0.7 0.6 0.8 0.7 0.5 0.8 0.8 0.7 0.8
7.7 7.6 3.1 4.8 6.6 8.0 6.5 5.6 6.9 5.4 3.6 5.4 5.4 5.2 4.9
102 92 109 106 107 103 104 105 99 101 108 100 99 101 105
Nonacid Reagents for the Removal of Vanadium Contaminants
Catalyst: aged SR Flltrol Washing Conditions: 5.0 wt. % aqueous solution, 4 8 hours, 80' F. Washing technique: Slurry washed, 10 grams of catalyst in 2 0 0 ml. of solution
Catulyst Properties S117fure
arpa, sq.
Composition, Wt. % mettrs/ 7 0 Chemical V Si A1 gram V Contaminated catalyst 0.29 0 . 0 7 1 6 . 9 49 -4cetylacetone 34 0 . 1 9 0 . 0 4 1 7 . 3 53 Diosanr 0 . 1 4 0.05 1 8 . 1 46 52 Tartaric acid 0 . 1 7 0 . 0 5 1 6 . 5 61 41 Parenlheses indicate gain.
Removnln AVi AI 43 20 29
i2) (7) 2
Table VII.
Effect of Chemical Decontamination of a Fluid Cracking Catalyst Erp ilibrium Surne Catalyst Cutalyst bffore V ajter Dtcontavunated Poisoning Poisoninq Cufdysl" Conversion, vol. 70 2 2 . 8 28.2 31.4 Carbon factor 1.3 2.80 1.20 Hydroqen factor 4.0 18.0 7.42 Vanadium, wt. % 0,011 0.195 0.061 Nickrl, wt. % 0.024 0.019 0.017
TVoshen' {our times-48 oncc with 7.070citric. '4
Table VIII.
.IriCoMo Catalyst FrrJh
Coniaminated
Decontaminated"
... 0.5 87
12.5 3.3 64
4.6 1.6 81
Contaminant, wt. % 70
ll'ashed with 7 yo aqurous glycolic acid at 200' I;. and liquid hourly sface velocity = 7 j o r 24 hr., lollowed by rinsing and drying. a
~~
56
47 42 47 37 37 42 32 37 37 32 24 38 29
.vi
.MO
...
.. .. 56 44 44 22 22 33 11 22 44 11 11 22 11
...
... 60 50
20 20 50 40 20 (10) 60 10 (20) (10) 20
... 59 37 13 (5) 14 26 9 29 53 29 29 32
35
The results obtained do seem to support the possibility that nonacidic vanadium and nickel extractors remove less aluminum. I\:hile tartaric acid removed a small amount of aluminum (2%) and increased surface area markedly, acetylacetone and dioxane apparently removed no aluminum while extracting substantial amounts of vanadium and nickel. At this point it was of interest to consider the means by which contaminating metals are dissolved. T o study this, vanadium \vas chosen as the prototype contaminant because of the ease ivith which its valence changes can be follo\ved using EPR. By complexing pure l74O5 with aqueous solutions of the complexing agents oxalic acid, tartaric acid, and acetylacetone, it was found that the dissolution process changes the valence of vanadium from the plus-five of the pentoxide to the plus-four state. This suggested that a portion of the treating reagent may perform as a reducing agent. Oxalic acid is known to be a reducing agent, but whether acetylacetone or perhaps dioxane could act in this manner is unkno\vn. I n other experiments it \vas found that reduction of a vanadium-contaminated catalyst with hydrogen (800' F., 4 hours) prior to treatment with aqueous acetylacetone or tartaric acid actually reduced the extent to which vanadium could be dissolved. This suggests that the reduction step is an integral part of the disso.ution process. Activity of Treated Catalysts
Catalyst particle size: 10-20 mesh Evaluation charge stock: Kuwait vacuum residue (5.5% sulfur) Evaluation conditions: 1 0 0 0 p.s.i.g., 790' F., 0.5 liquid hourly space velocity
Desulfurization, wt.
..
CO
hr. a / 80' F., three limes with 5.0% oxalic,
Effect of Chemical Decontamination on a Residue Hydrosulfurization Catalyst
V Si
Yo Rernorula V ..
~
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
The main purpose in removing metallic contaminants from catalysts is to maintain or restore activity or selectivity (4: 6). Accordingly, several of the catalyst \vashing techniques were applied to contaminated catalysts \vhich \\'ere then re-evaluated in processing. '4 vanadium-contaminated equilibrium cracking catalyst evaluated before and after a chemical ivashing in a small catalytic cracking activity test (7) gave the results shown in Table VII, Both the selectivity and activity of the vanadiumpoisoned catalyst were improved by the treatment. Ib'hile the noncontaminated equilibrium catal>-st had given 23% conversion and the contaminated catalyst 28Yc',,the washed catalyst gave 317,. Thus, activity \vas actually enhanced by the chemical treatment. Furthermore, selectivity was largely
restored to the level of the original catalyst, as shown b) the improvements in h>drogen factor from 18.0 to 7.4 and in carbon factor from 3.3 to 1.6. From these results it is apparent that such a chemical treatment can largely overcome the detrimental effects metal contaminants have on cracking catalysts. i\'ith h\ drodesulfurization catalysts. the results are also attractive. T o determine the effects of the washing procedure in this case. a nickel oxide-cobalt oxide-molybdenum oxidealumina (NiCoMo) \vas tested in residue hydrodesulfurization before and after processing a very high metals-content stock and then re-evaluated following a chemical treatment with aqueous g1)colic acid (Table 1-111). While the fresh catalvst gave 87% desulfurization of a Kuwait residue and the contaminated catalyst gave 04y0,the washed catalyst gave 81%. .4gain the results indicate a definite beneficial effect caused by the washing procedure. Similar results have been obtained with nickel oxide- tungsten oxide-alumina hydrodesulfurization catalysts.
Acknowledgment
T h e authors thank 1M. M. S m i a r t . who participated in the early stages of this work. Literature Cited .\PI Preprint, (1 ) Grane. H. K.. Conner. .J. E.. Masologites. G. P., 26th Midyear Meetin%. Division of Refining. Houston, Tes.,
Mav 1961.
( 2 ) Gulf Research 8r Dei.elopment Co.. Pittsburgh. Pa.. un-
published data. 1959. 1 3 ) Herman. .J.. Scafe. E. T. fto Soconv-Mobil Oil C o . ) . U. S. Patent 2,380,731 (July 31. 1945). ( 4 ) Leum. L. N.,Connor. J . E.. Ind. En?. Chrm. Prod. R P S .Drwlofi. 1, 145. (1962). ( 5 ) McAfee. J.. Montgomerv. C. I$'.. Hirsch. J . H.. Horne. IV. .I., Summers. .Jr.. C. R.. Prtrol. R e f . 34, No. 5. 156-62 (1955). ( 6 ) Sanford. R. A . Erickson. H . Rurk. E. H.. Gossett, E. C., Van Petten. S. L.. Ibid..41, No. 7. 103 (1962). ( 7 ) il'hitaker. .A. C.. Kinzer. A. D.. Ind. En?. Chem. 47, 2153 (1955).
RECEIVED for review October 4, 1962 ACCEPTEDDECEMBER 20, 1962 Division of Petroleum Chemistry. 142nd Meeting. ACS. .4tlantic City. N. J . ? September. 1962.
END OF SYMPOSIUM
OXIDATION OF BUTANE T O MALEIC ANHYDRIDE T. C. BISSOT A N D K . A. BENSON Electrochemicais Department, E. I. du Pont de .Vemours 3 Co., Inc., .Vzaqara Falls, S. Y.
Kinotics of maleic anhydride formation via partial oxidation of n-butane over CoMo04 catalyst i s controlled b y two consecutive first-order reactions: dehydrogenation of n-butane and decomposition of maleic anhydride. The intermediate oxidation of butene to maleic anhydride i s so rapid that it has no influence on the kinetics of the over-all reaction.
the lowest cost four-carbon molecule, is potentially one of the best raw materials for production of maleic anhydride. Most commercial processes, however, are based on the catalytic oxidation of benzene, over vanadium oxide cata1y:ts. T h e benzene process does not utilize all of the carbon atoms, as would Oxidation of a molecule [vith only four carbon atom:. I t is no surprise, then. to find many patents on the catalytic oxidation of butane, butene. and butadiene to maleic anhydride (7, 4: .5. 6, 8. 70. 7 7). Some academic work has also been published on the subject (2, 9 ) . These efforts have recently led to the commercial production of maleic anhydride from butene ( 3 ) . Very few of the above references touch on the partial osidation of butane. and only Hartig (4) has reported appreciable yields of maleic anhydride from this starting material. H e employed an unsupported cobalt or nickel molybdate catalyst in a fluidized solids reactor. Carbon dioxide and carbon monoxide were the only by-products formed in greater than trace quantities. The work reported here was undertaken to extend the discoveries of Hartig by investigating the effect of reaction variables on conversion of butane to maleic anhydride and, if possible, to define the mechanism and kinetics of the reaction. ORMAL B U T A N E ,
Apparatus and Catalyst
T h e reaction \vas studied in fluidized solids reactors. Initial experiments \yere made in a column 1 inch in diameter and 3 feet long. .4 column 2.5 inches in diameter and 8 feet long \vas used for more precise data. Both were made of borosilicate glass and heated Lcith closely spaced windings of Nichrome ribbon. -4 thermoiiell was centered throughout the reactor. It was studded a t close intervals with baffles of slass rod which cstended from the thermoivell to the \call of the reactor. T h e reactants. butane of 99Yc purity and air. \cere metered by dry gas meters and by rotameters and \\-ere premised just before entering the fluidized solids bed. T h e off-gases from the reactor \cere firs1 filtered to remove catalyst fines and then passed into a Lvater scrubber to remove the product as maleic acid. X portion of the off-gas \vas dried and analyzed at this point and the remainder metered and ventcd. Per cent oxygen \cas measi:red continuously \vith a Pauling oxygen analyzer. Butane and carbon dioxide \cere determined by vapor chromatography usirie; a Perkin-Elmer Model 154B L'apor Fractometer ivith a 1-meter silica %el column a t 100' C . Periodic Orsat analysrs for 0,. CO.. and CO were made? to obtain complete carbon and oxyyen balances. T h e catalyst was an unsupported cobalt or nickel molybdate modified by addition of boric acid. Its prrparation was based on the method of Hartig (-7). I n a typical preparation of the cobalt molybdate catalyst, VOL. 2
NO. 1
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57
