Dissolution of Eucalyptus Powder with Alkaline Ionic Liquid [Mmim]DMP under Microwave Conditions

Abstract

An orthogonal design was used to study three factors-melting temperature, time, and solid-liquid ratio-and how they affected the dissolution rate of eucalyptus powder. The optimum solution conditions were 170 °C, 20 min, and a solid-liquid ratio of 1:25. Composition analysis of the residue indicated that, in the dissolving process, acidinsoluble lignin was converted into acid-soluble lignin, and a part of the lignin was degraded or modified. After dissolution, the crystalline structure of cellulose deteriorated, the relative crystallinity decreased, and the crystal form changed from type I into amorphous. Wood powder degradation occurred during dissolution, and a higher dissolution rate led to greater degradation. In a low-temperature environment below 225 °C, the residue thermal stability decreased slightly with increasing dissolution rates, but it greatly improved in a high-temperature environment of 225 to 600 °C. Keywords INTRODUCTIONLignocellulose is the most abundant renewable resource on the planet. Its main components of cellulose, hemicellulose, and lignin are important chemical raw materials (Zhang 2008;King et al. 2009;Kuo and Lee 2009;Zhang et al. 2009). However, due to the complex structure of lignocellulosic cell wall, its components are difficult to separate, which is a great obstacle in using lignocellulose (Chen and Kuo 2010). Traditional separation methods are cooking with inorganic acid or alkali and extraction with organic solvents. These methods not only change lignocellulosic structure but also have the problems of high cost and serious pollution. Ionic liquids are green solvents with low vapor pressure, adjustable nature, good solubility, and high thermal stability (Rehman and Zeng 2012;Lozano et al. 2014;Findrik et al. 2016), and they have broad application prospects in the dissolution and separation of lignocellulose (Cole et al. 2002;Fang et al. 2006;Ren et al. 2013).Previous literature includes studies of the dissolution of a single component with ionic liquids. Some alkyl-substituted imidazolium ionic liquids effectively dissolve cellulose (Swatloski et al. 2002) (Pu et al. 2007). However, because of the complicated structure of lignocellulose, the dissolution rate of whole components with ionic liquids is not high. In a study on the dissolution of Masson pine, PEER-REVIEWED ARTICLE bioresources.com Chen et al. (2016). "Dissolving eucalyptus in ionic liquid," BioResources 11(4), 9710-9722. 9711 poplar, eucalyptus, and oak in the [C4mim]Cl/DMSO solvent system, non-pretreated lignocellulose heated to 100 °C for 24 h could be partially dissolved (Fort et al. 2007). The low dissolution rate of all components is an urgent problem hindering the use of biomass resources.To promote the application of ionic liquids in biomass materials and improve the dissolution rate of whole components, the present work involves an orthogonal design for the lignocellulosic dissolution factors of melting temperature, time, and solid-liquid ratio under microwave conditions, and the optimized solution scheme w...

A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids

“…Other process parameters such as stirring speed, solid/liquid ratio, wood and cellulose particle and molecular size [60,95,96], the use of microwave heating [97,98], and ultrasonication [99] are also important and have been thoroughly explored in the literature. It has also been observed that wood dissolution is affected by environmental conditions.…”

Preparation and structural characterization of lignin micro/nano-particles with ionic liquid treatment by self-assembly

“…More importantly, ionic liquids also have amphipathic properties which allows easy precipitation of dissolved lignin to form lignin micro/nano-particles by adding acid water (Acid deionized water). In this paper, 1,3-dimethyl-imidazolium dimethyl phosphate ([Mmim][DMP]), which is known to have a good lignin solubility according to the researches by our team [10,11] , was employed to develop a rapid and complete alkali lignin dissolution method with low temperature and characterize the regenerated lignin micro/nano-particles by Fourier transform infrared spectroscopy (FT-IR), the elemental analysis, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), 2D heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy. Furthermore characterization of regenerated lignin micro/nano-particles morphology was observed by scanning electron microscopy (SEM) and polarized light microscopy (PLM).…”