Abstract
BackgroundThe biorefinery based on an effective and economical process is to fractionate the three primary constituents (cellulose, hemicelluloses, and lignin) from lignocellulosic biomass, in which the constituents can be respectively converted into high-value-added products. In this study, a successive treatment with dilute acid (0.25–1.0 % aqueous H2SO4, 100–150 °C, 0.5–3.0 h) and alkali (1.5 % aqueous NaOH, 80 °C, 3 h) was performed to produce xylooligosaccharides (XOS), high-purity lignin, and cellulose-rich substrates to produce glucose for ethanol production from rice straw (RS).ResultsDuring the dilute acid pretreatment, the maximum production of XOS (12.8 g XOS/100 g RS) with a relatively low level of byproducts was achieved at a relatively low temperature (130 °C) and a low H2SO4 concentration (0.5 %) for a reaction time of 2.0 h. During the alkali post-treatment, 14.2 g lignin with a higher purity of 99.2 % and 30.3 g glucose with a higher conversion rate by enzymatic hydrolysis were obtained from the successively treated substrates with 100 g RS as starting material. As the pretreatment temperature, H2SO4 concentration, or time increased, more β-O-4 linkages in lignins were cleaved, which resulted in an increase of phenolic OH groups in lignin macromolecules. The signal intensities of G2 and G6 in HSQC spectra gradually reduced and vanished, indicating that a condensation reaction probably occurred at C-2 and C-6 of guaiacyl with the side chains of other lignin.ConclusionsThe present study demonstrated that the successive treatments with dilute acid and alkali had a synergetic effect on the fractionation of the three main constituents in RS. It is believed that the results obtained will enhance the availability of the combined techniques in the lignocellulosic biorefinery for the application of the main components, cellulose, hemicelluloses, and lignin as biochemical and biofuels.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0632-9) contains supplementary material, which is available to authorized users.
Highlights
IntroductionThe biorefinery based on an effective and economical process is to fractionate the three primary constituents (cellulose, hemicelluloses, and lignin) from lignocellulosic biomass, in which the constituents can be respectively converted into high-value-added products
The biorefinery based on an effective and economical process is to fractionate the three primary constituents from lignocellulosic biomass, in which the constituents can be respectively converted into high-value-added products
The solid yields decreased from 76.54 to 56.15/100 g rice straw (RS) as the pretreatment temperature, H2SO4 concentration, or time increased. This is mainly due to the degradation of hemicelluloses, which was further confirmed by the chemical constituents and Fourier transform infrared (FT-IR) spectral analysis of the dilute acid pretreated substrates (Table 2; Additional file 1: Figure S1)
Summary
The biorefinery based on an effective and economical process is to fractionate the three primary constituents (cellulose, hemicelluloses, and lignin) from lignocellulosic biomass, in which the constituents can be respectively converted into high-value-added products. A significant type of biomass burning is a common way to eliminate waste after harvesting in China, such as in Shandong and Hebei Provinces, which is an important source of greenhouse gases and particulate pollutants in the atmosphere and has a remarkable effect on global atmospheric chemistry and global warming [1, 2] To avoid this pollution, many new schemes, including papermaking and bioethanol production are developed for the application of straw [3, 4]. Alkali treatment is a very effective method to separate lignin, especially from the pretreated biomass It can further disrupt the cell wall by partially dissolving lignin and obtain cellulose-rich residues [16]. Celluloserich residues can be further converted to glucose with high yields by enzymatic hydrolysis, which provides a high efficient way for bioethanol production
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