Accepted Manuscript Responsive Behavior of Regenerated Cellulose in Hydrolysis under Microwave Radiation Jinping Ni, Haining Na, Zhen She, Jinggang Wang, Wenwen Xue, Jin Zhu PII: DOI: Reference:
S0960-8524(14)00725-1 http://dx.doi.org/10.1016/j.biortech.2014.05.066 BITE 13474
To appear in:
Received Date: Revised Date: Accepted Date:
28 March 2014 19 May 2014 20 May 2014
Please cite this article as: Ni, J., Na, H., She, Z., Wang, J., Xue, W., Zhu, J., Responsive Behavior of Regenerated Cellulose in Hydrolysis under Microwave Radiation, Bioresource Technology (2014), doi: http://dx.doi.org/ 10.1016/j.biortech.2014.05.066
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Responsive Behavior of Regenerated Cellulose in Hydrolysis under Microwave Radiation Jinping Ni, Haining Na, Zhen She, Jinggang Wang, Wenwen Xue, Jin Zhu* Ningbo Key Laboratory of Polymer Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, China Corresponding to Dr. Jin Zhu; Email: [email protected]
. Tel: 86-574-86685283, Fax: +86-574-86685186
Abstract: This work studied the responsive behavior of regenerated cellulose (RC) in hydrolysis under microwave radiation. Four types of RC with different crystallinity (Cr) and degree of polymerization (DP) are produced to evaluate the reactivity of RC by step-by-step hydrolysis. Results show Cr is the key factor to affect the reactivity of RCs. With hydrolysis of amorphous region and the formation of recrystallization, the Cr of RC reaches a high value and thus weakens the reactivity. As a result, the increment of cellulose conversion and sugar yield gradually reduces. Decrease of the DP of RC is helpful to increase the speed at the onset of hydrolysis and produce high sugar yield. But, there is no direct influence with the reactivity of RC to prolong the time of pretreatment. This research provides an accurate understanding to guide the RC preparation for sugar formation with relative high efficiency under mild reaction conditions. Keywords: Regenerated cellulose, Responsive behavior, Recrystallization
Introduction The research on exploring renewable and green feedstock to replace fossil resource has been promoted strongly due to the fossil resource depletion and the awareness of environment crisis (Chheda et al., 2007; Huber and Corma, 2007). Glucose as a promising green feedstock was emphasized by researches during past decades because of its feasibility to convert to food, chemicals, and fuel by the simple biological and/or chemical processes (Huber et al., 2005; Zhao et al., 2007; Lin and Tanaka, 2006). Therefore, hydrolysis of cellulose (which is the most abundant and sustainable biomass resource on the earth) to produce the nonfood-competing glucose, is recognized as one of the most important research directions. However, effective disruption of the recalcitrant crystalline structure of cellulose in hydrolysis is a great challenge. Because abundant hydrogen bonds exist between the molecular chains, the structure of cellulose is very stable and difficult to be hydrolyzed (Himmel et al., 2007; Jarvis, 2003). Strong acid (Tsubaki et al., 2013; Amarasekara et al., 2012), strong base (Bobleter, 1994), and high temperature (Zhao et al., 2009) had ever been chosen to break the recalcitrant crystalline structure of cellulose, but these severe conditions are inevitable to initiate the unexpected side reaction of glucose during hydrolysis. With the aim to improve the reactivity of cellulose in hydrolysis under mild conditions and thus reduce the side reaction of glucose, the pretreatment to disrupt the crystalline structure is considered to be included in the process of hydrolysis. Under this consideration, many pretreatment methods consisting of dissolution (Harmer et al., 2009; Tadesse and Luque, 2011;
Kuo and Lee, 2009a), ball milling (Zhao et al., 2006; Peng et al., 2013), plasma (Benoit et al., 2011), and ultrasound (Zhang et al., 2013) were respectively tried in scientific researches. But, together with alteration of crystalline structure, the degree of polymerization of cellulose is also decreased during pretreatment. This phenomenon results in the difficulty to accurately understand the relation between the effect of pretreatment and the reactivity of cellulose in hydrolysis. It usually makes us not to find the most suitable pretreatment method to control the process of cellulose hydrolysis. The improvement of the yield and selectivity of glucose from cellulose hydrolysis was not always satisfied (Zhao et al., 2006; Kim et al., 2010). In our previous study, we established a two-step hydrolysis of cellulose to produce glucose under mild reaction conditions (Ni et al., 2013). During the first step, the microcrystalline cellulose is pre-treated to form regenerated cellulose (RC). And then, the RC is further hydrolyzed to sugar. Followed by this methodology, the yield and selectivity of sugar can be obviously improved under relative mild conditions. During this two-step process, the similar issue concerning with inaccurately understanding to guide the RC preparation for sugar formation also hinders us to choose the much mild reaction conditions in hydrolysis for high efficiency. It’s imperative for us to carry out the detailed research to elucidate the reactivity of RC in hydrolysis. In this study, we focus on the responsive behavior of RC in step-by-step hydrolysis. By controlling the conditions of pretreatment and regeneration, the reactivity of RC in hydrolysis is discussed in detail. The key structural factor of RCs to response with hydrolysis under mild condition is presented.
2. Experimental Methods 2.1 Chemicals The original cellulose (OC) from Jiangsu Longhao new materials company refers to the microcrystalline cellulose (cellulose amount over 97 %), which is vacuum dried at 100 °C for 6 h before use. D-(+)-glucose (the reference material for HPLC, GR grade, >99.5%) and hydrates of H3PW12O40 are supplied by Aladdin Reagent. All the solvents are in chemical grade and use without purification. 2.2 Preparation of regenerated celluloses 20.0 g OC was firstly mixed with 200 mL 85 % H3PO4 for 1 h and then pre-treated at 50 °C for 1 h to form a viscous cellulose solution. Three types of regenerated cellulose (RC) marked as RC11, RC12 and RC13 were respectively obtained from this solution by controlling regeneration conditions. Ice-cold ethanol was added into the solution with vigorous stirring to produce white cloudy precipitate RC11. RC12 was obtained by adding 600 mL water into the solution under constant agitation at 100 rpm for 1 h. The cellulose solution was also added drop by drop into 2 L water under constant stirring at 100 rpm to produce RC13. RC4 was prepared by prolonging the reaction time of pre-treatment to 4 h at 50 °C, and then followed by adding 600 mL ice-cold ethanol with vigorous stirring. All the RCs was filtered and washed with water for three times. Saturated Na2CO3 solution was used to neutralize residual H3PO4. Then the RCs were washed again by water to remove the salts. Finally, the RCs was suspended in ethanol and filtered to remove the residual water. After vacuum dried at 50 °C for 24 h, all the precipitate was grounded into powders