Enabling lower temperature pyrolysis with aqueous ionic liquid pretreatment as a sustainable approach to rice husk conversion to biofuels

Pyrolytic conversions of biomass-to-biofuels require relatively high temperatures concerning the low energy yield of resulting biofuels. This work uses aqueous [Bmim][OAc] for pretreatment to lower the peak pyrolysis temperature of rice husk. The mass yield of bio-oil from low temperature pyrolysis (335 °C) of pretreated rice husk was enhanced by 20.28%, and the energy yield of pyrolysis for bio-oil production increased by 17.65% with pretreatment. The bio-oils obtained from pretreated rice husk were enriched in desired components such as furfural, furanone and cyclopentenones, but reduced in alcohols, phenolic derivatives and phenylfuran versus the raw rice husk. The [Bmim][OAc] pretreatment expands the cellulose I lattice and contributes to the transformation of crystalline cellulose I to amorphous chains in rice husk. The β–O–4 arylether bond cleavage in lignin and the damage of original hydrogen bonds in cellulose and hemicellulose are responsible for lowering the pyrolysis temperature and average activation energy of pyrolysis. Up to 90% of [Bmim][OAc] was recovered using a 45.0 wt% K3PO4 solution and demonstrated similar effectiveness on a second batch of pretreatment. The results provide new insight into achieving higher energy conversion efficiency from lignocellulosic biomass pyrolysis with lower energy consumption for the sustainable development goals.