Recent advancements in the ionic liquid mediated lignin valorization for the production of renewable materials and value-added chemicals

Lignin is the most abundant aromatic polymer available on earth and is a recalcitrant by-product in the lignocellulose biomass-based industry. In recent times even though about 1 g of lignin is released per liter of bioethanol produced, the lignin valorization rates are relatively low and challenging, as it has an irregular complex structure and requires high-level conversion techniques. Most of the lignin conversion methods deliver toxic by-products or have a lower product yield due to mild lignin solubilization. Recently, Ionic liquids (ILs), which are greener and recyclable solvents, have attributed excellent solvation properties towards lignin, while simultaneously helping in its valorization. In this review, we have discussed the potential of ILs-mediated lignin valorization to produce different end commodities like hydrogels, flavours, and alkanes. This article emphasizes on the various ILs utilized, their effects on lignin, and the advanced strategies available for conversion. The valorization rate is improved by the addition of chemical or biological catalysts i.e., lignin-degrading enzymes (LDEs). Nevertheless, the biocatalyst is influenced in the system, so the effect of LDEs during ILs mediated lignin bioconversion and the available strategies to improve LDEs effectiveness have also been depicted. Also, the economic viability and the futuristic demands like developing innovative process design, engineering tolerant LDEs, and designing biocompatible ILs that will facilitate the commerciality of ILs-mediated lignin valorization have been discussed. Overall, a comprehensive insight has been established that highlights the technological advancements in the ILs-based valorization that can avail in the sustainable production of renewable commodities utilizing lignin in near future.