Efficient production of glucose by microwave-assisted acid hydrolysis of cellulose hydrogel
Graphical abstract
The hydrolysis of cellulose hydrogel is greatly improved compared with cellulose powder.
Introduction
Cellulose, the most common natural organic polymer, is considered as an almost inexhaustible source of raw material for the increasing demand for environment friendly and biocompatible products. Conversion of cellulose is of vital importance in the biofuel industry. Over the past years, much work has focused on developing effective technologies for acid hydrolysis of cellulose to glucose (Huang and Fu, 2013, vom Stein et al., 2010, Zhang and Lynd, 2004). A variety of pretreatment methods also have been developed to its activation prior to catalytic hydrolysis, mainly including physical pretreatment such as ball-milling (Zhao et al., 2006), non-thermal atmospheric plasma (Benoit et al., 2011), solvent pretreatment such as ionic liquids (Qu et al., 2014), dilute acids (Chimentao et al., 2014) and concentrated acids (Ni et al., 2013). But clearly, it is desirable to develop a simple, green, and low-cost route to treat cellulose and perform the catalytic conversion in a more rational way.
The degradation of cellulose aggregations is step-by-step from the surface to inner, resulting in a slow depolymerization rate. Solving of cellulose will be helpful to the hydrolysis as the cellulose chains are free approached in these forms. It is well-known that cellulose is difficult to be dissolved in the common solvent for the existence of crystalline structure of complex hydrogen-bonding network. Recently, a new class of cellulose solvent has been developed, namely, aqueous solutions of NaOH or LiOH and urea used at low temperatures (Cai and Zhang, 2005). Under optimized conditions, these solutions can readily dissolve even highly crystalline cellulose; and the regeneration of cellulose from the solvents gives highly transparent cellulose hydrogels (Chang et al., 2010). Usually, hydrogels are chemically or physically crosslinked structures composed of hydrophilic polymers in a three dimensional network. The hydrolysis of cellulose hydrogel in the presence of a catalyst could be enhanced due to the exposure of more reaction sites and much easier diffusion of the catalyst into the cellulose molecular. Thus, it provides a chance to obtain high-value chemicals from the material. However, the acid hydrolysis of cellulose in its hydrogel form has scarce reports until now. The present work is aimed at investigating the hydrolysis of cellulose hydrogel to glucose with diluted sulfate acid as the catalyst. As microwave heating presents a potentially fast, efficient, and selective method for the thermal treatment of biomass in the last decade, the hydrolysis reaction was performed in a microwave accelerated reaction system.
Section snippets
Materials
α-Cellulose with an average particle size of 50 μm, levulinic acid (LA), 5-hydroxymethyl-2-furaldehyde (HMF) and furfural were supplied by Aladdin Reagent. Microcrystalline cellulose, H2SO4, NaOH, ethanol, Na2CO3, potassium ferricyanide and filter paper were purchased from Sinopharm Chemical Reagent. Glucose assay kits were obtained from Changchun Huili Biotech. Co., Ltd. Absorbent cotton was purchased from Shanghai Dai Di Medical Instrument Co., Ltd. and used as cotton fiber. Ramie fiber was
Characterization of RCH
The X-ray diffraction patterns were shown in Fig. S1. The spectrum for α-cellulose showed the characteristic sharp peaks of cellulose I at 14.8°, 16.3°, 22.6° and 34.5° (Ni et al., 2014). In contrast, RCH showed two broad peaks at around 29° and 41°, which was apparently resulted from scattering by liquid water. In addition, another very weak peak at 20° could be observed, indicating the presence of crystallization of cellulose II (Ni et al., 2014). Furthermore, the crystallinity (Cr) was
Conclusions
In conclusion, a simple and effective route for the high yield production of glucose from cellulose was developed. This process uses a combination step of the dissolution of cellulose in aqueous NaOH/urea solution and regeneration with water, followed by an acid hydrolysis producing sugars under microwave irradiation. The pretreatment method exhibits an important way to reduce the reaction difficulty for cellulose hydrolysis as the chains are free approached in the form of hydrogel. Ozone
Acknowledgements
This work was financially supported by the National Science Foundation of China (Grant No. 21304072).
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