Determination of intrinsic kinetic of corncob char gasification with CO₂ and steam using multipore diffusion model

The intrinsic heterogeneous reactivity of biochar in CO2 and steam gasification plays an important role in thermochemical reactor design, adjusting operating conditions, and predicting the quality of biomass gasification products, especially when the combined valorization of syngas and biochar with important textural properties is required. In the present work, the intrinsic heterogeneous kinetics of CO2 and steam gasification of corn biochar is estimated by fitting a multimodal pore size distribution (PSD) with random capillary model evolution with respect to the experimental results by thermogravimetric analysis (TGA). As novelty the independence of the initial biochar textural properties was considered, using two samples with different initial pore size distributions (PSDs): A1 sample with an initial surface area of 54.09 m2/g and A2 sample with 22.14 m2/g. The experimental intraparticle gradient effect is considered by using samples with a particle size of 149 µm conventionally larger than those reported to guarantee chemical kinetic control at 60 µm. The apparent kinetics obtained by TGA revealed a difference of 70 kJ/mol for CO2 gasification and 30 kJ/mol for steam gasification in contrast to initial PSD change. The average activation energies and pre-exponential factor obtained by parametric fitting of the model with respect to the evolution of the conversion for CO2 gasification were E = 210.2 kJ/mol and A0 = 1.13*106 g/m2s, while steam revealed E = 136.64 kJ/mol and 7.1*102 g/m2s. Furthermore, the model reduced the activation energy differences with respect to different PSDs by 5 kJ/mol for CO2 and 18 kJ/mol for steam biochar gasification.