Modified Koufopanos' Mechanism in the Kinetics of in-situ Catalytic Pyrolysis of Co-pelletized Rice Husks and Ash

Abstract

Using rice husk ash as a cheap in-situ catalyst under certain pyrolysis operating conditions can affect the yield of rice husk pyrolysis products. The two-stage semi-global kinetic models were often used to predict these yields. This research aims to study the effect of rice husk ash catalyst addition, heating rate, and pyrolysis temperature on the kinetics and yield of rice husk pellet pyrolysis products. A modified kinetic model of the Koufopanos mechanism was proposed to predict the product's yield. The apparent pyrolysis kinetics were analyzed with the assistance of a self-designed macro-thermogravimetric analysis apparatus. The co-pelletized rice husk and ash were heated from 303 to 873 – 1173 K at 5, 10, and 40 K/min heating rates in a N₂ environment. Gas was collected and analyzed with gas chromatography equipped with a thermal conductivity detector at several temperature intervals during pyrolysis. It was found that the yield of the pyrolysis products can be described well by the proposed kinetic model. Adding a rice husk ash catalyst at 10 K/min reduced the activation energy of the primary gas and tar formation. It also enhanced the secondary pyrolysis reactions to form gas, which occurs more significantly at higher temperatures and heating rates. At low heating rates, heterogeneous secondary reactions tended to convert the primary tar into secondary gas. However, secondary reactions converted the primary tar into secondary tar at higher heating rates. On the other hand, increasing the pyrolysis temperature increased the gas yield and reduced the yield of tar and char.