Abstract
Four novel choline carboxylate aqueous solution systems were developed by mixing H2O with choline nicotinate [Ch][Na], choline ferulate [Ch][Fa], choline vanillate [Ch][Va] and choline syringate [Ch][Sa]. The solubility of lignin in the four solvents was determined at 25 °C. The influence of the molar ratio of H2O to [Ch][Na] ([Ch][Fa], [Ch][Va] and [Ch][Sa]) and the anionic structure on lignin solubility were systematically investigated. It was found that, the anionic structure and H2O content significantly affected lignin dissolution. Interestingly, H2O/[Ch][Na] and H2O/[Ch][Fa] solvents show efficient capacity for lignin dissolution even at room temperatures. The dissolution of lignin in H2O/[Ch][Na] and H2O/[Ch][Fa] solvents is mainly ascribed to the interaction of lignin with the alkyl chain in the anion and cation dissociated from [Ch][Na]([Ch][Fa]) by H2O. In addition, the recycling of the lignin solvent was examined, and the structure and thermostability of the lignin regenerated from the solvent were also estimated.
Highlights
With the rapid depletion of fossil resources, the production of chemicals and materials from renewable lignocellulosic biomass in place of fossil resources is attracting much attention [1]
Alfa Aesar (Haverhill, MA, USA); nicotinic acid (98.0%), ferulic acid (99.0%), vanillic acid (98.0%), and syringic acid (98.0%) were purchased from Aladdin Industrial Corporation (Shanghai, China); deuterated DMSO (DMSO-d6 ) used for nuclear magnetic resonance (NMR) spectra examination was purchased from Qingdao Weibo Tenglong Technol
It can be seen that the melting temperatures Tm or glass transition temperatures Tg range from −7 ◦ C to 103 ◦ C. This indicates that, for the choline carboxylates with the same [Ch]+ cation, Tm /Tg considerably depends on anionic structure
Summary
With the rapid depletion of fossil resources, the production of chemicals and materials from renewable lignocellulosic biomass in place of fossil resources is attracting much attention [1]. The ILs are usually expensive, very viscous or toxic and the bio-derived ILs exhibit poor dissolution capacity for lignin. In this context, some IL–water solutions were developed as lignin solvents. Binary solvent systems consisting of γ-valerolactone + water (dimethyl sulfoxide, N,N-dimethylformamide or ILs) have been reported to efficiently dissolve various types of lignin [25]. Xu et al developed 13 novel kinds of choline carboxylate/H2 O solvents for lignin [28]. [Ch][Fa], [Ch][Va] and [Ch][Sa] is based on the fact that choline cation is biodegradable [29], and the paired anions [Na]− , [Fa]− , [Va]− and [Sa]− are derived from nicotinic acid, ferulic acid, vanillic acid and syringic acid, respectively. Nicotinic acid is vitamin B3, and ferulic acid, vanillic acid and syringic acid are often used as medicine, spice and food additives
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