Studies in the hydrolysis of cellulose using cellulase in imidazolium based ionic liquid
Ionic liquids are the modern day revelations as a green solvent. These solvents have found many applications in biofuel strategy. The cellulose pretreatment using ionic liquid is currently being studied for future biofuels from lignocellulosic biomass. The strategy involves the dissolution of cellulose in these solvents, followed by precipitation by an anti-solvent like water or acetone, leading to the formation of amorphous cellulose which is easy to hydrolyze by biocatalytic methods. Further studies had been conducted in the inhibitory effect of ionic liquid traces present in pretreated cellulose, on the biocatalytic hydrolysis by cellulase. Apart from this, biocatalytic hydrolysis had been studied in binary aqueous-ionic liquid solution for a one-pot process for simultaneous pretreatment & hydrolysis. These process involved the study of biocatalytic hydrolysis in imidazolium based ionic liquids namely, [EMIM]OAc & [BMIM]Cl, as hydrophilic solvents. These solvents have anions with predominantly strong hydrogen bond acceptor capacity. The study reveals the deactivation of the enzyme in presence of these ionic liquids. Thus in an effort to increase the hydrolysis efficiency of the enzyme without loosing the hydrogen bond acceptor capacity of the IL, was essentially required. Thus in the present study, we have investigated one-pot biocatalytic hydrolysis of cellulose in IL with variable alkyl chain length of the cation leading to hydrophobic environment around the biocatalyst. The ILs used in the present study are [BMIM]Cl, [HMIM]Cl & [OMIM]Cl. The biocatalysis was studied in both homogenous as well as heterogeneous conditions. In homogenous conditions dissolution of cellulose was maintained throughout the reaction period. The homogenous biocatalysis was studied with or without the presence of surfactants. The results indicate that [HMIM]Cl is a promising solvent for cellulase catalyzed hydrolysis of cellulose in both homogenous & heterogeneous condition, resulting in more than 70% hydrolysis in presence of non-ionic surfactant PEG-1500 and in the binary mixture of 40% w/w [HMIM]Cl in citrate buffer, respectively.