Combining hot-compressed water and ball milling pretreatments to improve the efficiency of the enzymatic hydrolysis of eucalyptus

Hiroyuki Inoue,Tsuyoshi Sakaki,Shinichi Yano,Shigeki Sawayama,Takashi Endo

doi:10.1186/1754-6834-1-2

Abstract

BackgroundLignocellulosic biomass such as wood is an attractive material for fuel ethanol production. Pretreatment technologies that increase the digestibility of cellulose and hemicellulose in the lignocellulosic biomass have a major influence on the cost of the subsequent enzymatic hydrolysis and ethanol fermentation processes. Pretreatments without chemicals such as acids, bases or organic solvents are less effective for an enzymatic hydrolysis process than those with chemicals, but they have a less negative effect on the environment.ResultsThe enzymatic digestibility of eucalyptus was examined following a combined pretreatment without chemicals comprising a ball milling (BM) and hot-compressed water (HCW) treatment. The BM treatment simultaneously improved the digestibility of both glucan and xylan, and was effective in lowering the enzyme loading compared with the HCW treatment. The combination of HCW and BM treatment reduced the BM time. The eucalyptus treated with HCW (160°C, 30 minutes) followed by BM (20 minutes) had an approximately 70% yield of total sugar with a cellulase loading of 4 FPU/g substrate. This yield was comparable to the yields from samples treated with HCW (200°C, 30 minutes) or BM (40 minutes) hydrolyzed with 40 FPU/g substrate.ConclusionThe HCW treatment is useful in improving the milling efficiency. The combined HCW-BM treatment can save energy and enzyme loading.

Highlights

Lignocellulosic biomass such as wood is an attractive material for fuel ethanol production
The crystallinity index (CrI) of eucalyptus pretreated using a planetary ball milling (BM) decreased to 7.6% with 20 minutes of milling (Table 1), indicating that cellulose microfibrils in the wood cell wall were disrupted
Our results suggest that the effect of BM treatment on the enzymatic digestibility is closely related to the mechanochemical breakdown of an ultrastructure such as the cellulose-hemicellulose-lignin network that occurs following the disruption of cellulose microfibrils

Summary

Introduction

Lignocellulosic biomass such as wood is an attractive material for fuel ethanol production. Pretreatments without chemicals such as acids, bases or organic solvents are less effective for an enzymatic hydrolysis process than those with chemicals, but they have a less negative effect on the environment Lignocellulosic biomass, such as wood and agricultural residues, is an attractive material for fuel ethanol production because it contains large amounts of potentially fermentable sugars in the form of cellulose and hemicellulose. The removal of hemicellulose and lignin from lignocellulosic biomass by adding inexpensive chemicals such as acids, bases or organic solvents is known to have a significant effect on enzymatic hydrolysis [2,5,6,7] These chemicals may require corrosion-resistant reactors and must be neutralized or recycled to reduce their negative impacts on the environment as well as on subsequent processes (for example, fermentation)

Methods

Results

Conclusion