Avaliação cinética da síntese de carbeto de tungstênio (WC) via reação gás-sólido entre paratungstato de amônio (APT) e a mistura gasosa CH4-H2 em reator de leito fixo

Abstract

The application of tungsten carbide (WC) stands out in the mechanical, chemical and aerospace industries for presenting a unique combination of properties, such as high hardness, high melting point, high wear resistance, great chemical and thermal stability. Traditionally, its production occurs via a carburization reaction between a tungsten source and a carbon source at high temperatures (1400°C and 1800°C) and long reaction time. Several WC synthesis methods have been investigated in order to obtain powders with high purity and high surface area, and to optimize processing. The Department of Chemical Engineering at UFRN (DEQ) developed a synthesis route via gas-solid reaction between ammonium paratungstate (APT) and the CH4-H2 mixture capable of producing pure tungsten carbide after one hour of reaction at a temperature of 850 °C in a fixed bed reactor. Various processing conditions were studied, but kinetic data analysis was not performed. This type of analysis is a fundamental step in evaluating the feasibility of implementing the synthesis process on a large scale. Thus, the present work aims to carry out a kinetic evaluation of the WC synthesis developed by DEQ from methane conversion data available in the literature. The synthesis data were obtained using the "Digitalize" tool of the Origin® software, and modeled to verify which kinetic model best fits the reaction: the Power Law Model (first order reaction) or the Avrami Model. The results indicate that the 1st order model fits the analyzed experimental data (R2 > 0.90). Kinetic constant of k= 0.0017 min-1 with R² = 0.935 was determined for synthesis reactions at T=850°C, Q=17L/h and 1 hour of isotherm.