3369.     TEMKIN, M. L., KIPERMAN, S., AND LUK’YANOVA, L. I.  [Flow-Circulation Method of Investigation of the Kinetics of Heterogeneous Catalytic Reactions.]  Doklady Akad. Nauk. S.S.S.R., vol. 74, 1950, pp. 763-766; Chem. Abs., vol. 45, 1951, p. 1854.

        This is an adaptation of the idea of Denbigh, subsequently utilized by Hammett for homogeneous reactions.  The reacting gas is admitted to the catalyst zone at a constant velocity v, is made to circulate through the reaction zone, and is led out at exactly the velocity v.  Provided the velocity of the circulation through the reaction zone is very much greater than velocity v of inflow and outflow, the variation of the composition of the reacting gas in each single pass is negligible, and that composition can be taken as stationary.  A check is provided by splitting the outgoing gas stream into 2 portions led out of the system just before and after the catalyst zone, with the sum of the 2 outgoing gas streams equal to v; fulfillment of the constancy of composition in each single pass is indicated by closeness of the compositions in the 2 branches of the outgoing gas.  The method was applied to the synthesis of NH₃ from a stoichiometric N₂+3H₂ gas mixture on 1 cc. of a synthetic NH₃ catalyst at 451°, with rates of circulation of 360-500 l. gas per hr., and v varies between about 9 and 110 l. gas (STP) per hr.  With U=volume of gas flowing in and out per unit time, c=concentration of the product in the total outgoing gas, W=volume of the catalyst, f=free fraction of the catalyst volume.  The rate k of the reaction can be expressed by cU/fW, or in terms of the partial pressure pA’ of NH₃ in the initial gas mixture, pA’U/fW, or, on account of the insignificant volume change, r=pAU/fW, where pA=partial pressure of NH₃ in the outgoing gas.  The previously established Temkin (abs. 3367) kinetic law for the catalytic synthesis of NH₃, r=k₁pH(pH³/pA²)^0.5-k₂(pA²/pH³)^0.5 (with the exponent 0.5 valid for the particular catalyst), gives k=y¹.⁵P^0.5 (Uο/W)x²/(1-x²), where γ=pH/^0.75pA’; P=total pressure; Uo=U reduced to 0° and 1 atm.; k=273fk₂/0.75^1.5PoT(Po=1 atm.); x=yield of NH₃ in fractions of the equilibrium NH₃ content (=0.210%).  Experimental data (Uo/W=8960, 20,000, 46,900, 69,800, 86,200, 110,000 ml. gas (STP) per ml. catalyst per hr., x=0.726, 0.603, 0.461, 0.388, 0.355, 0.302) give k(av.)~12X10³, fairly close to the previously determined k=7.8X10³ by the simple flow method.