Effect of process conditions on the surface properties of biomass chars produced by means of pyrolysis and CO 2 gasification

Abstract

Biomass char is defined as the carbonaceous by-product of biomass pyrolysis or gasification and is an undesired by-product that is disposed as a waste, usually at a very high cost. Chars have interesting characteristics like high carbon content and high porosity. These characteristics can make attractive the utilization of biomass char for alternative and innovative applications, e.g. as precursors for activated carbons or as filtering mediums. In this framework, this present work focuses the attention on the surface properties of char which is a key parameter for the evaluation of its applicability in adsorption applications. The combination of three main variables has been considered: the carrier gas (nitrogen or carbon dioxide), the temperature (set at 500°C, 700°C and 900°C) and the initial heating rate (10°C min⁻¹, 30°C min⁻¹ or 50°C min⁻¹). Maximum heating values are observed at 700°C for the case of inert atmosphere (pyrolysis) and the values reduce slightly for the case of CO₂ gasification. On the contrary, CO₂ gasification has a positive effect on the porosity of the biomass chars. This present research has the scope to provide a first insight on the effect of operating conditions on the optimal char characteristics for the utilization of biomass char as a cheap alternative for filters and adsorbents. An interesting future potential transition of existing biomass CHP facilities would be the evolution into biorefineries, in accordance with the new mandates about Circular Economy.