Chemical Engineering Journal 184 (2012) 303–307 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal j ourna l ho mepage: www.elsevier.com/locate/cej Avaliation of gas phase kinetics of the carburization and deactivation reactions aimed to produce NbC F.A.O. Fontes a , J.F. de Sousa b,∗ , C.P. Souza b , M. Benachour c , M.B.D. Bezerra b a Universidade Federal do Rio Grande do Norte, Centro de Tecnologia, Departamento de Engenharia Mecânica, Campus Universitario, 59072-970 Natal, RN, Brazil b Universidade Federal do Rio Grande do Norte, Centro de Tecnologia, Departamento de Engenharia Química, Campus Universitario, 59072-970 Natal, RN, Brazil c Universidade Federal de Pernambuco, Centro de Tecnologia, Departamento de Engenharia Química, Cidade Universitária, 50740-521 Recife, PE, Brazil a r t i c l e i n f o Article history: Received 7 October 2011 Received in revised form 2 January 2012 Accepted 4 January 2012 Keywords: Gas phase kinetics Methane Deactivation Niobium carbide a b s t r a c t The gas phase kinetic study referent the carburization of NbO 2 to NbC is presented in this paper. The reaction took place in a rotating cylinder reactor, with rotation velocity (r) of 5 rpm, at temperatures of 1148, 1173 and 1223 K, gas phase flow of 4.033 × 10 -6 m 3 /s and Nb 2 O 5 initial mass of 0.004 kg. The reaction mechanism is represented by the reduction of Nb 2 O 5 into NbO 2 (first reaction), followed by the carburization of NbO 2 into NbC (second reaction). In this work the kinetic model of gas phase was carried out for the second reaction which is represented by two steps: the first regards the consumption of CH 4 and second, the deactivation of NbO 2 . From chromatographic analysis of the gas products at the reactor outlet, the molar consumption of CH 4 with reaction time was determined. The results showed the kinetic behavior in the first step represented by a pseudo-first-order model and in the second step by first-order deactivation models. In the present study, it was determined the kinetic constant (k), the activation energy (E) of the first and second steps, the velocity constant for deactivation k ′ and the decline constant k d that expresses the deactivation factor of NbO 2 . Statistical parameters showed satisfactory agreement between the experimental data and those predicted by the model. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The kinetic study for the formation of NbC through a gas–solid reaction obtained significant contributions from other inves- tigations that presented stoichiometric equation models and determined the kinetic constant and activation energy for the first step reduction reaction of Nb 2 O 5 to NbO 2 , Teixeira da Silva et al. [1]. Although final products of a balanced reaction are determined only by temperature, pressure, and the chemical species present, the mechanism and reaction rates depend on a large number of variables such as solid particle size, diffusion rates, gas concentra- tion, porosity and impurity. The reaction rate equations are grouped under different mecha- nisms and can be represented by the expression: F (x) = k × t where k = k o × e (-E/(Rg×T)) , where k o is the Arrhenius pre-exponential fac- tor, k (s -1 ) is the reaction rate constant, E (kJ/mol) is the activation energy, R g is the universal gas constant, and T(K) is the temperature. The activation energy values reported for carburization reac- tions are in general between 200 and 800 kJ/mol, which indicates high temperature sensitivity. Reduction/carburization processes ∗ Corresponding author. Tel.: +55 84 9981 2989. E-mail address: joao@eq.ufrn.br (J.F. de Sousa). involving highly endothermic gas–solid reactions favor contact effi- ciency under isothermal conditions as well as the removal of CO as a co-product, Weimer and Alan [2]. High-temperature rotating oven applications for the reduction and carburization of metallic oxides have been reported only in small scale operations, focused merely on theoretical aspects such as heat transfer or material transport. A considerable number of patents have been published, but most of the applications are still in development. This article presents the gas phase kinetic study results of the gas–solid reaction of Nb 2 O 5 to NbC in a rotating cylinder reactor with respect to first (consumption of methane) and second steps (deactivation) of carburization reaction of NbO 2 to NbC (isothermal region) estimating the kinetic constant (k), activation energy (E) the velocity constant for deactivation k d and the decline constant that expresses the deactivation factor of NbO 2 . Niobium carbide was prepared by carbothermic reduction, Fontes et al.[3], starting from commercial niobium pentoxide powders. The results showed that the rotational effect of the rotat- ing cylinder reactor reduced substantially the total reaction time of carbothermic reduction of NbO 2 to NbC, and influenced sig- nificantly the conversion. The solid conversion remained above 74%. The NbC was produced from commercial niobium pentoxide, using a similar procedure adopted by Kim et al. [4]. Preliminary 1385-8947/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2012.01.034