Homogenous hydrolysis of cellulose to glucose in an inorganic ionic liquid catalyzed by zeolites

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ORIGINAL RESEARCH

Homogenous hydrolysis of cellulose to glucose in an inorganic ionic liquid catalyzed by zeolites Tao Wu . Ning Li . Xuejun Pan

. Sheng-Li Chen

Received: 15 May 2020 / Accepted: 20 August 2020 Ó Springer Nature B.V. 2020

Abstract Zeolites (ZSM-5 and Beta) with different SiO2/Al2O3 ratios were synthesized as solid acids for hydrolyzing cellulose in an inorganic ionic liquid system (lithium bromide trihydrate solution, LBTH) under mild conditions. The results indicated that the texture properties of zeolite had little effect on catalytic activity, while acidity of zeolite was crucial to the cellulose hydrolysis. In the LBTH system, H-form zeolites released H? into the solution from their acid sites via ion-exchange with Li?, which hydrolyzed the cellulose already dissolved. This

unique homogeneous hydrolysis mechanism was the primary reason for the excellent performance of the zeolites in catalyzing cellulose hydrolysis in the LBTH system. It was found cellulose could be completely hydrolyzed to glucose and oligoglucan by 2% (w/w on cellulose) zeolite at 140 °C within 3 h with a single-pass glucose yield 61%. The zeolites could be recovered with 50% initial catalytic activity after regeneration and reused with stable catalytic activity.

Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03411-3) contains supplementary material, which is available to authorized users. T. Wu  N. Li  X. Pan (&) Department of Biological Systems Engineering, University of Wisconsin-Madison, 460 Henry Mall, Madison, WI 53706, USA e-mail: [email protected] T. Wu  S.-L. Chen State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of PetroleumBeijing, Beijing 102249, People’s Republic of China

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Cellulose

Graphic abstract

Keywords Solid acid  Cellulose dissolution  Molten salt hydrate  Hydrolysis mechanism  Lithium bromide

Introduction As the most abundant natural polymer, cellulose has been consensually considered as a renewable resource to replace fossil for sustainable production of chemicals and fuels (Huang et al. 2019). Effective hydrolysis of cellulose to glucose is a key step for the conversion of lignocellulosic biomass to liquid fuels and value-added chemicals via so-called sugar platform (Jiang et al. 2019; Mu et al. 2019). Mineral acids, such as H2SO4 and HCl, are the most common catalysts for hydrolyzing cellulose to glucose (Rinaldi and Schuth 2010). Although they are effective, the mineral acids have issues related to equipment erosion, poor selectivity, and acid recovery. Enzyme (cellulase) is a selective catalyst which works effectively at moderate temperature (Hammerer et al. 2018). However, the cellulase suffers from high price, slow reaction, and poor reusability. Solid acids have attracted more attention in recent years for cellulose hydrolysis (Huang and Fu 2013; Shrotri et al. 2018),

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because of their easy separation, good recyclability, and c