After the aluminum had been dissolved from the welded plate by treating with 20% NaOH solution, this activated nickel plate was investigated by the same technique. It may be concluded (Table I ) that the boundary layers, which were formed between the nickel sheet and aluminum sheets, consist mainly of KiAlj and N i A l r , with little NiAl and NiAl, similar t o ordinary Raney nickel alloy (Raney, 1940). Results obtained on the activated nickel plate catalyst show that its surface consists only of fine crystals of nickel.
Literature Cited
Bogoslowski, B. M., Kasakowa, S. S . , “Skelett-Katalysatoren in der organische Chemie,” VEB Deutscher Verlag der Wissenschaften, Berlin, 1960. Bradley, A. J., Taylor, A., Proc. Roy. Soc. A159, 56 (1937). Nelsen, F. M., Eggertsen, F. T., Anal. Chem. 80, 1387 (1958). Raney, M., Ind. Eng. Chem. 32, 1199 (1940). Yasumura, J., Yoshino, T., Keg-yo Kagahu Zasshi 69, 602 (1966).
Acknowledgment
The authors are indebted to Taketo Ohki, Director, Research Department, Nikki Chemical Co., Ltd., for invaluable advice.
RECEIVED for review April 3, 1967 ACCEPTED April 12, 1968
CATALYTIC DEHYDROGENATION OF HIGHER NORMAL PARAFFINS TO LINEAR OLEFINS OVER
MOLY BDENA-ALUMINA CATALYSTS B. A B E L L , A N D A . R . S C H A E F E R Central Research Department. Monsanto Co., St. Louis, Mo. 63166
J .
F .
ROTH,
J .
The dehydrogenation of n-dodecane to linear dodecenes over molybdena-alumina catalysts was investigated. Selectivity to mono-olefin is about 65% a t a total p a r a f i n conversion of 12 to 13% after the catalyst has been deactivated by substantial coking. Data on catalyst coking were obtained using thermogravimetric analytical techniques. The rate of coking depends on physical properties of the alumina, and on the type and concentration of hydrocarbon present. Initially the fresh molybdena-alumina catalysts studied display high acidity, but most of this acidity is not due to the intrinsic acidity of the alumina support.
IN
T H E past few years considerable interest has been focused on Cs and higher linear olefins as intermediates for the possible manufacture of a variety of products, including biodegradable detergents, alcohols, homopolymers, and copolymers. A t first the most readily available olefins were those with terminal double bonds and these have been derived principally from thermal cracking of paraffins or from controlled oligomerization of ethylene. However, the recent availability of higher normal paraffins a t low cost has now stimulated several investigations of the possible formation of higher linear olefins via direct catalytic dehydrogenation of’ the corresponding normal paraffins (Abell et a/..1967a,b; Haensel and Hoekstra, 1966; Moore and Roth, 1966: Roth and Schaefer. 1966, 1965; Shuikin et a/.. 1964). I t is reasonable t o expect that most of the olefins produced by direct dehydrogenation of‘ the higher paraffins would consist of‘ internal olefins, but as pointed out by Shuikin et al. (1964). the position of the double bond may not he of importance in certain applications. This would be true whenever secondary processes employing the olefins require reaction conditions that promote facile bond isomerization. Both chromia-alumina and molybdena-alumina catalysts
254
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
promote a variety of hydrocarbon reforming reactions, including dehydrogenation. A good general description of their catalytic properties is given by Greensfelder et al. (1947). A more recent study by Usov et al. (1965) examines specifically the reactions of C , to C i h n-alkanes over molybdena-alumina. However, in most of the previous work the reactions were investigated over relatively fresh molybdena-alumina compositions and at relatively high levels of total paraffin conversion. These regimes are not conducive t o producing mono-olefins in high selectivity and, instead, lead to enhanced formation of aromatics. I n contradistinction to past studies with molybdenaalumina, the present investigation is directed specifically at defining conditions leading to selective dehydrogenation of‘ normal parafins t o linear olefins. Experimental
Xlaterials. The n-dodecane of 98‘0 or higher purity was obtained from Humphrey-Wilkinson and n-hexane was Phillips pure grade material. Some of the catalysts and all of the supports used were obtained from commercial suppliers. Their designation. source, and description are as follows:
.Lluteria 1
.'Manu/uc,turcJr
F I 10 alumina
Alcoa
AI 1404 alumina
Harshaw
KA 101 alumina
Kaiser
A I 0104 alumina
Harshaw
'I' 1% alumina
Girdler Harshaw
,LlO-O.~O:!
Oescription Commercial alumina. 36 -inch balls Gel alumina, 36-inch tablets Commercial alumina in the form o f 5 x &mesh nodules Gamma alumina, %-inch tablets Alumina, %6 -inch tablets Commercial molybdena-alumina catalyst, -inch tablets
Catalyst Preparations. A number of molybdena-alumina catalysts with and without Co or C u were prepared as tollows. A portion of' preformed alumina was tumbled in a rotating flask with a solution of ammonium molybdate. T h e amount o f solution was l o c , excess over that actually absorbed by the alumina. T h e mixture was then poured into a Bdchner funnel and the excess solution allowed to drain off. An 80-ml. portion of distilled water was then poured over the wet catalyst very rapidly. T h e pellets were allowed to drain for 30 minutes. then the surtaces dried hy rolling on a n absorbent cloth. T h e resulting catalyst was dried a t 120OC. for 6 to 12 hours. followed by calcination in air at 5003C. for 12 hours. Portions of the above were then impregnated with cobalt or copper by tumbling for 1 hour with a lOIi excess solution of the nitrate of the metal. T h e mixture was then poured into a Bdchner funnel and treated as in the preparation of molybdena alumina. T h e catalysts were prepared to have these nominal compositions: molybdena-aluminas, 10'1 MOO, on alumina; CoMo, 3.5:; Co + lo', M o o t on alumina; and CuMo, 4 3 ; C u + 10'; MOO on alumina. Apparatus. DEHYDROGENATION REACTORS. T w o tixed-bed reactor systems were used to study the dehydrogenation of n-dodecane at atmospheric pressure. Each reactor was constructed of stainless steel and was 22 inches long and l i a - inches in I.D. A '.,,-inch thermowell positioned in the center of the reactor was used to determine axial temperature profiles. T h e standard charge of catalyst was 145-ml. hulk volume. T h e remaining volume .of the reactor. above and below the catalyst bed, was filled with inert Alcoa T-162 alumina halls of nominal !,
