Towards the Production of High Added-Value Products from the Pyrolysis and Steam Pyro-Gasification of Five Biomass-Based Building Insulation Materials at End-of-Life

Pyrolysis and gasification are two promising thermochemical conversion processes to transform biomass feedstocks into valuable fuels. Pyrolysis leads to the generation of biochar, tar (or bio-oil), and permanent gas while gasification produces mainly a syngas. This study explores the slow pyrolysis (550 °C) and steam pyro-gasification (850 °C), in a semi-rotating reactor, of five biomass-based insulation materials namely: cellulose wadding (CW) and panels consisting of textile, hemp, wood, and mixed fibers, after their characterization. Subsequently, the properties of the gaseous, solid and liquid products were investigated and their potential application was proposed. The pyrolysis bio-oils derived from hemp, mixed and wood fibers have low energy content (18.6–20.94 MJ/kg), high oxygen content (43.45–47.99 wt.%) and high viscosity (149–494 mPa.s), requiring further upgrading to transportation fuels. Biochars showed a high carbon content (65–85 wt.%), high heating value (20–32 MJ/kg) and a low specific surface area (0–18 m2/g), making them suitable for use as solid fuels. The only exception was textile biochar which revealed the highest surface area of 375 m2/g and a microporous structure (66%), hence its use as an adsorbent was recommended. The steam pyro-gasification generated hydrogen-rich syngas (around 50 mol.% H2) with medium calorific value (13–18 MJ/Nm3). The CW syngas presented a H2/CO ratio of 2.8, which favors its valorization via Fischer–Tropsch processes (diesel fuels). Boron was concentrated in CW pyro-gasification ash. Consequently, pyrolysis was favored for textile panels for microporous biochar formation and hemp/wood/mixed panels for bio-oil production; while gasification was privileged to CW for syngas production and boron recovery.