Lignocellulose conversion for biofuel: a new pretreatment greatly improves downstream biocatalytic hydrolysis of various lignocellulosic materials

Abstract

Background: Lignocellulosic biomass is an attractive renewable resource for future liquid transport fuel. Efficient and cost-effective production of bioethanol from lignocellulosic biomass depends on the development of a suitable pretreatment system. The aim of this study is to investigate a new pretreatment method that is highly efficient and effective for downstream biocatalytic hydrolysis of various lignocellulosic biomass materials, which can accelerate bioethanol commercialization.

Results: The optimal conditions for the hydrogen peroxide-acetic acid (HPAC) pretreatment were 80 °C, 2 h, and an equal volume mixture of H2O2 and CH3COOH. Compared to organo-solvent pretreatment under the same conditions, the HPAC pretreatment was more effective at increasing enzymatic digestibility. After HPAC treatment, the composition of the recovered solid was 74.0 % cellulose, 20.0 % hemicelluloses, and 0.9 % lignin. Notably, 97.2 % of the lignin was removed with HPAC pretreatment. Fermentation of the hydrolyzates by S. cerevisiae resulted in 412 mL ethanol kg(-1) of biomass after 24 h, which was equivalent to 85.0 % of the maximum theoretical yield (based on the amount of glucose in the raw material).

Conclusion: The newly developed HPAC pretreatment was highly effective for removing lignin from lignocellulosic cell walls, resulting in enhanced enzymatic accessibility of the substrate and more efficient cellulose hydrolysis. This pretreatment produced less amounts of fermentative inhibitory compounds. In addition, HPAC pretreatment enables year-round operations, maximizing utilization of lignocellulosic biomass from various plant sources.

Keywords: Bioethanol; Energy efficiency; Lignocellulosic biomass; Pretreatment.

Fig. 1

A proposed conceptual model for the mechanism of enhanced enzymatic saccharification of lignocellulosic biomass by delignification using the hydrogen peroxide (H₂O₂)-acetic acid (CH₃COOH) (HPAC) pretreatment

Fig. 2

a Effect of different volume ratios of hydrogen peroxide/acetic acid. (Conditions: temperature, 80 °C; time, 2 h) b Effects of temperature on relative conversion to sugars. (Substrate: pine wood, Conditions: volume ratio of hydrogen peroxide/acetic acid, 5:5; time, 2 h) c Solid recovery after the HPAC pretreatment

Fig. 3

a Effects of different organo-solvent pretreatments on enzymatic hydrolysis of pine wood. (A acetic acid, H hydrogen peroxide, PAC peracetic acid). b Influence of different pretreatment methods on sugar yields (RS rice straw, PW pine wood, OW oak wood)

Fig. 4

Solid ¹³C-NMR spectra for pretreated and untreated pine wood

Fig. 5

a Conversion rate of glucose to ethanol and the concentrations of sugars and ethanol. b Time course of sugar utilization and ethanol production by Saccharomyces cerevisiae from hydrolyzate using an enzyme mixture containing cellulase (10 FPU/g DM) and xylanase (20 IU/g DM) after the HPAC pretreatment. Note: a 0 h, b 0.5 h, c 1.0 h, d 1.5 h, e 2.0 h, and f 2.5 h of HPAC pretreatment time

Fig. 6

Material balances for 1 kg of HPAC-pretreated lignocellulosic biomass materials extrapolated from the results of 10.0-g-dry weight scale experiments