Microwave-assisted catalyst-free hydrolysis of fibrous cellulose for deriving sugars and biochemicals

Songshan Jiang,Helen Daly,Huan Xiang,Huiping Zhang,Ying Yan,Xiaolei Fan,Christopher Hardacre

doi:10.1007/s11705-019-1804-5

Abstract

Microwave (MW) assisted catalyst-free hydrolysis of fibrous cellulose (FC, cellulolysis) at 200°C promoted a cellulose conversion of ca. 37.2% and quantitative production of valuable C5/C6 sugars (e.g., glucose) and the according platform biochemicals (e.g., 5-hydroxymethylfurfural), corresponding to an overall selectivity of 96.5%. Conversely, conventional hydrothermal cellulolysis under similar conditions was not effective, even after 24 h, carbonising the FC. Based on the systematic study of MW-assisted cellulolysis, the specific interaction between water molecules and macroscopic FC under the MW irradiation was proposed, accounting for the interpretation of the experimental observation. The kinetic energy of water molecules under the MW irradiation facilitated the C–C (in the non-hindered surface–CH2OH groups) and C–O–C bond breaking (inside the cellulose cavities) in FC, producing primary cellulolysis products of xylose, glucose and cellobiose.

Highlights

The future depletion of fossil carbon reserves/resources and global warming has meant that biomass valorisation is required as a sustainable and green route for producing C5/C6 sugars, platform chemicals and fuels
A standard procedure of the cellulolysis experiment is described as: (i) fibrous cellulose (FC) suspended in water was prepared by stirring FC (300 mg) with the deionised water (10 mL) in the Pyrex vial (2 min); (ii) the vial containing the suspension was transferred to the MW reactor for treatment; (iii) the hydrolysed products was centrifuged at 4400 r/min to separate the solid residual from the liquid fraction
The softening temperature of FC in pure water was determined as 200°C, evidenced by the sudden conversion of FC to glucose

Summary

Introduction

The future depletion of fossil carbon reserves/resources and global warming has meant that biomass valorisation is required as a sustainable and green route for producing C5/C6 sugars, platform chemicals and fuels. Cellulose can be obtained from biomass such as grasses, wood and other agriculture residuals and can be converted to sugar. The corrosive nature of acids, as well as the associated separation issues (e.g., the liquid-phase separation of mineral acids from the soluble products and the solid-phase separation of solid catalysts from the cellulose residuals), hinder their operations at scales [8,9]. Enzymatic hydrolysis is highly selective to glucose in reducing sugar (above 83%) [10], the long reaction time (e.g., 72 h), highly diluted system and separation issues make it impractical for biomass valorisation [2,11,12]. Especially under catalyst-free conditions, microwave irradiation was found favourable to promote the transformation of cellulose to C6 molecules with high selectivities [13]

Methods

Results

Conclusion