Recent advances for sustainable production of levulinic acid in ionic liquids from biomass: Current scenario, opportunities and challenges
Abstract Levulinic acid (LA) is a unique potential building block chemical which has attracted significant attention of researchers globally due to its potential utility to synthesize a variety of commercially important value added energy compounds. Conversely, efficient production of LA from lignocellulosic biomass is limited by some challenges that relate to the use of a proper solvent-catalytic system and reaction processing parameters. The existing literature shows that, reaction processing parameters and ionic liquid (IL) properties are key aspects which essentially determine the yield of LA and formation of side-products (formic acid and humin). In IL media, an improved LA yield can be achieved by maintaining appropriate optimal reaction conditions. Moreover, direct synthesis of LA from biomass in IL is at the development phase, where further research efforts are needed to improve process efficiency for sustainable synthesis of LA. In view of this, the present review serves to highlight the ongoing research related to (i) use of IL as unique solvent-catalytic system for direct synthesis of LA, (ii) influence of each reaction processing parameter and IL properties on LA yield (iii) mechanism of direct LA synthesis in IL media (iv) global market scenario, (vi) downstream processing for effective LA separation as well as IL recycling and (vi) sustainable applications of by-products in LA formation. This article also outlines future opportunities and challenges for construction of a successful model biorefinery for LA synthesis in IL media.