Pyrolytic conversion of construction, renovation, and demolition (CRD) wood wastes in Québec to biochar: Production, characterization, and identifying relevant stability indices for carbon sequestration

Management of heterogeneous construction, renovation, and demolition (CRD) wood residues in Québec brings into light, a widespread topic under discussion related to their current disposal methods in landfills, that may lead to environmental concerns. With rising forfeitures from a legal standpoint, alternative treatment methods for CRD wood wastes are being explored. Thermochemical biomass conversion techniques can be employed to depolymerize low-quality end-of-life CRD wood and valorize it to bio-based products. Biochar, a carbonaceous material obtained through heat treatment of wood under the absence of oxygen via slow pyrolysis, can be tailored for specific end-use applications in hard-to-abate industrial sectors pertinent to energy, composite materials, and environmental amendments. However, there is a scarcity of comprehensively understanding CRD wood pyrolysis and projecting the biochar product's stability due to a lack of relevant studies and frequent inconsistencies amidst currently available methods. Nevertheless, in the present study, CRD wood is pyrolyzed in a horizontal tube furnace of two scales under laboratory conditions. Temperatures ranging from 300 to 800 °C, biomass residence time (BRT) of 30-120 min, heating rates of 20-55 °C/min, and mass of feedstock between 100 and 500 g were the operational conditions chosen for experimentation. Evaluation of biochar stability was carried out by the proximate and ultimate analysis, Van-Krevelen plots, TGA/DTG profile, R50 recalcitrance, SEM-EDX, and Raman I_D/I_G methods. Data analysis indicated that carbon content (89-90 %), FC (70-74 %), TSF (73-75 %), R50 (0.64-0.65), and I_D/I_G (0.972) increased with an increase in BRT (120 min) and pyrolysis temperature (800 °C) rendering its utilization in metallurgical applications as a reductant. A surface area of 220-270 m²/g was also detected for these biochar at 800 °C recommending its implementation for adsorption applications. Biochar's cation exchange capacity (CEC), pH, and hydrophobicity also increased at high temperatures nurturing the ability to be used for soil pH adjustment as part of remediation activities. SEM-EDX proved that ash content predominantly harboring alkaline and alkaline earth metals (AAEM) like Ca and K also increased but to a certain point from where their devolatilization is implicit, thereby concentrating stable carbon. As for functionalities in biochar, they decreased from 500 to 800 °C verifying the rejection of oxychemicals groups. Noticeable striations associated to C-H/C-O/C=O vibration, stretching, and bending from FTIR spectral bands were linked to terminal dehydrogenation, condensation, and aromatization reactions highlighting the development of CC and CC linkages commonly assigned to aromatics. Evident from low Van-Krevelen H/C (0.51-0.09) and O/C (0.08-0.02) indices, it can be extrapolated that high-temperature biochars in PR:1 and PR:2 possess a high permeance that could bolster its utilization in carbon sequestration/draw-down and other CDR applications.