K2CO3- and K2CO3/porous SiO2-doped steam activated extruded carbons based on multi-component biochar composite: Preparation, characterization and kinetic gasification behavior

Abstract

In this work, the preparation and characterization of new steam-activated K2CO3/porous SiO2-doped extruded activated carbons based on multi-component biochar composite with different gasification levels are described and compared with K2CO3-doped extruded activated carbons. The steam activation was performed in a rotary kiln quartz tube reactor in batch mode (Froude number: 1.59 × 10–3, volumetric filling degree < 6%) at an activation temperature of 880 °C. The prepared activated carbons were characterized by chemical analyses, X-ray fluorescence spectroscopy (XRF), BET-surface area and porosity measurements. The gasification of the K2CO3-doped carbons follows a zero-order kinetic with a reaction rate constant of k0 = 5.25 × 10–3 min–1 and a half-value time of τ0.5 = 95.2 min indicating that the K2CO3 catalyst maintains the catalytic activity during steam activation up to a carbon conversion of XC = 68%. The co-gasification of the K2CO3/porous SiO2-doped carbons can preferably be described by applying the shrinking unreacted grain model (SUGM) for spherical particles. A reaction rate constant of kSUGM,s = 4.75 × 10–3 min–1 with τ0.5 = 130.3 min is calculated for the chemical reactivity of the rate limiting step. The high catalytic activity of the K2CO3 catalyst was reduced here by forming a K2O × SiO2 species. An oxygen transfer via a catalytic active potassium intercalate by forming a oxygenated C(O) intermediate is proposed to describe the reaction mechanism of the gasification process in the presence of a stable and non-stable catalyst.