Ethane Hydrogenation-Cracking on Iron Catalysts with and without Alkali

Abstract

The kinetics of the hydro-cracking of ethane on iron catalysts with and without alkali additions have been studied. A general expression of the form -d [C~He]/dt = k p r~.~a p s~z has been obtained. The exponent T is 1 or a fraction; s changes from negative t o positive as potash is added to fused iron oxides, containing traces of acidic impurities, from which the catalysts were prepared by reduct,ion. A general formulation of the reaction kinetics is presented to include all the data here recorded and earlier work with nickel on the hydro-cracking of ethane and propane. It postulates as a slow step the breaking of a C-C bond by interaction of an adsorbed hydrocarbon radical (CzH,), with hydrogen on the surface. The mechanism proposed suggests an interpretation of the role of alkalies in Fischer-Tropsch synthesis on iron catalysts.The catalytic hydrogenation of ethane has been studied on nicke11p2 and cobalt3 catalysts, where the reaction rate corresponds to an expression of the type N o investigation has been made so far on iron catalysts. Fused iron catalysts, of the synthetic-ammonia type, are particularly interesting because of the great importance that they have gained in the last decade for hydrocarbon ~ynthesis.~ A fundamental problem which arises in connection with these iron catalysts is the role of the alkali promoter, which is known to have great importance in the synthesis and which could therefore affect a reaction such as the present one. Accordingly it was decided to investigate ethane hydrogenation on reduced fused iron catalysts with and without alkali, mainly to determine whether and how the kinetics of such a reaction is influenced by alkali. ExperimentalApparatus.-A static system, similar to the one described by Kemball and Taylor2 has been used. The reaction vessel of about 220 cc., electrically heated, was provided with an air-jacket and a mercury regulator to keep the temperature constant within 1'.Gases .-Cylinder hydrogen was purified over palladized asbestos at 300", calcium chloride, ascarite, magnesium perchlorate and phosphorus pentoxide. Cylinder ethane was dried over calcium chloride and phosphorus pentoxide, and then doubly distilled from liquid nitrogen traps.Catalysts.-The catalysts6 were prepared by fusion of Alan Wood magnetite oren with the addition of potassium or lithium carbonate. Concentrations of the alkali promoters, determined by means of chemical analysis, were as follows (basis iron): Catalyst AW, no alkali added; catalyst FlK, 0.05% K20; Catalyst FlL, 0.6%, LizO; catalyst F2K, Analyses.-The analyses were carried out7 in a Nier-type mass spectrograph, and based on a calibration curve obtained from hydrogen-containing mixtures of ethane arid methane.Reduction Experiments.-A preliminary study was conducted on the reduction by hydrogen of catalysts AW, F2K and of two other catalysts, MW and MK, prepared, -dpcnHa/dl = kPC~HarPEin8.(1) 0.6% Kz0. (5) All the catalysts and their analyses were obtained through the courtesy of the M. W. Kellogg Company, Jersey City, N. J. (6) ...

Site requirements in the kinetics of alkane transformations catalysed by metals

“…Particular attention must be given to the interpretation of the results obtained on various transition metals [28,31]. Use was made of the kinetic analysis proposed in 1954 by Cimino et al [32] for iron catalysts, and the rate determining step was assumed to be identical on all metals where the experimental order with respect to hydrogen is negative. In 1974, Frennet et al [33] suggested an alternative to this already well accepted interpretation.…”

Catalytic specificity

“…The reactions are catalyzed by various transition metals. The simplest example is the reaction of ethane with hydrogen to yield methane, the kinetics of which were investigated originally on nickel (Morikawa et al, 1936), and subsequently on cobalt (Taylor and Taylor, 1939) and iron (Cimino et al, 1954). More recently, studies of the kinetics of ethane hydrogenolysis have been extended to platinum (Sinfelt, 1964b;Sinfelt et al, 1965), other Group VIII noble metals (Sinfelt and Yates, 1967;, and rhenium (Yates and Sinfelt, 1969).…”

Influence of the Addition of a Second Metal on the Catalytic Performance of Pt-Beta Agglomerated Catalyst in the Hydroisomerization of n-Octane

“…The presence of hydrogenolysis products, C1 and C2, were only patent in Ni monometallic catalyst and even in the bimetallic catalyst with higher content of nickel (0.75Ni0.25Pt). It is well documented by many authors in a wide variety of studies that hydrogenolysis of alkanes on Ni-containing catalysts occurs mainly at terminal carboncarbon bonds [23][24][25][26][27][28], evidencing the presence of light alkanes. Figures 5-8 show for all catalysts used the monobranched and multibranched selectivity, respectively, as a function of the n-octane conversion.…”