Generation of highly amenable cellulose-I\u03b2 via selective delignification of rice straw using a reusable cyclic ether-assisted deep eutectic solvent system

Chiranjeevi Thulluri,Harshad Ravindra Velankar,Ravi Balasubramaniam

doi:10.1038/s41598-020-80719-x

Chiranjeevi Thulluri, Harshad Ravindra Velankar + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-80719-x

Copy DOI

Abstract

Cellulolytic enzymes can readily access the cellulosic component of lignocellulosic biomass after the removal of lignin during biomass pretreatment. The enzymatic hydrolysis of cellulose is necessary for generating monomeric sugars, which are then fermented into ethanol. In our study, a combination of a deep eutectic (DE) mixture (of 2-aminoethanol and tetra-n-butyl ammonium bromide) and a cyclic ether (tetrahydrofuran) was used for selective delignification of rice straw (RS) under mild conditions (100 °C). Pretreatment with DE-THF solvent system caused ~ 46% delignification whereas cellulose (~ 91%) and hemicellulose (~ 67%) recoveries remained higher. The new solvent system could be reused upto 10 subsequent cycles with the same effectivity. Interestingly, the DE-THF pretreated cellulose showed remarkable enzymatic hydrolysability, despite an increase in its crystallinity to 72.3%. Contrary to conventional pretreatments, we report for the first time that the enzymatic hydrolysis of pretreated cellulose is enhanced by the removal of lignin during DE-THF pretreatment, notwithstanding an increase in its crystallinity. The current study paves way for the development of newer strategies for biomass depolymerization with DES based solvents.

Highlights

Cellulolytic enzymes can readily access the cellulosic component of lignocellulosic biomass after the removal of lignin during biomass pretreatment
Microscopic observations of deep eutectic (DE)-THF treated and untreated samples matched with the results of compositional analysis which indicated that the pretreated rice straw samples had lower lignin content (~ 46%) and increased glucan content (~ 36%) over 10 solvent recycles (Table 1)
A newly developed solvent system comprising of deep eutectic solvents (DESs) and THF was successfully employed to carry out the selective delignification of rice straw for upto 10 recycles under milder pretreatment conditions

Summary

Introduction

Cellulolytic enzymes can readily access the cellulosic component of lignocellulosic biomass after the removal of lignin during biomass pretreatment. Microscopic observations of DE-THF treated and untreated samples matched with the results of compositional analysis which indicated that the pretreated rice straw samples had lower lignin content (~ 46%) and increased glucan content (~ 36%) over 10 solvent recycles (Table 1). We found that the O/C ratio of pretreated rice straw (1.26) was three times higher than the untreated biomass samples (0.42), due to reduced O and increased C contents possibly due to the selective removal of lignin.

Results

Conclusion