PRELIMINARY STUDY ON THE INFLUENCE OF PYROLYSIS PROCESS CONDITIONS ON THE TEXTURAL PROPERTIES OF ACTIVATED CARBONS FROM WHEAT STRAW-DERIVED BIOCHARS

摘要

It is widely known that biochar can be used in a wide range of applications including -but not limited to- soil amendment, energy production, adsorption and catalysis . For the last two final uses, however, the pristine biochar produced through pyrolysis processes does not have an appropriate porosity development. In fact, the porosity of biochar is mainly due to narrow micropores . Therefore, an activation process is needed to develop a more hierarchical porous structure in order to facilitate the diffusion path of the corresponding adsorbates and/or reactants. To date, there is almost no research on how the pyrolysis process conditions, at which the biochar precursors are produced, can affect the porosity of the subsequent activated biochars. The aim of this work is to evaluate how the slow pyrolysis process conditions adopted for the production of biochars from wheat straw pellets can affect the textural properties of the final activated carbons, which are obtained via physical activation with CO_2 at 800 °C of the raw biochars. For this purpose, the following operating parameters were selected: the absolute pressure (from 0.2 to 0.9 MPa), the pyrolysis peak temperature (from 400 to 550 °C), and the type of gas atmosphere during pyrolysis (pure N2 or a binary mixture of CO_2 and N_2 60:40 v/v). Not only the main effect of these parameters individually but also the possible effects derived from the interactions between them have been considered. To this aim, an unreplicated 2-level factorial design has been adopted to objectively analyze the influence of these parameters on the response variables (i.e., the BET specific surface area, pore volumes, and pore size distribution of the physically activated biochars).