Author ORCID Identifier

https://orcid.org/0000-0002-7613-4262

Date Available

1-3-2025

Year of Publication

2024

Degree Name

Doctor of Engineering (DEng)

Document Type

Doctoral Dissertation

College

Agriculture; Engineering

Department/School/Program

Biosystems and Agricultural Engineering

First Advisor

Dr. Jian Shi

Abstract

The development of green solvents is a pivotal endeavor in achieving the goals of green chemistry. Ionic liquids (ILs) and deep eutectic solvents (DESs) have emerged as promising green alternatives to conventional organic solvents due to their low toxicity, potential biodegradability, low volatility, and high tunability. Compared to ILs, DESs have attracted more attention recently as they are easier and less expensive to produce. Hydrophobic DESs (HDESs), a new generation of DESs introduced in 2015, have gained considerable interest for their ability to overcome the instability issues of traditional DESs when exposed to water. This advancement extensively broadens the application scope of DESs. This research aims to develop HDESs based on lignin derivatives as well as their application in various fields, contributing to more sustainable processes. Firstly, a class of novel hydrophobic DESs was developed by screening potential combinations of lignin derivatives. The lignin derived DESs presented lower viscosity (16-40 mPa·s) as compared to many hydrophilic DESs and ILs. They also showed tolerance to the temperature as low as -75 ℃. Moreover, the formation of hydrogen bonds between the components of the prepared DESs was investigated by molecular dynamics (MD) simulations and validated by FTIR. In the end, five lignin-derived HDESs made from menthol, thymol, and 2,6-dimethoxyphenol were considered promising green solvents due to their environmentally friendly constituents. Secondly, the application of the developed lignin-based HDES for the removal of nanoplastics (NPs) was investigated. As the emerging contaminations in aqueous systems, micro- and nano-plastics (MNPs) have been widely found to exist in the environment and even in organisms, which potentially threatens the ecosystems and human health. However, the studies evaluating the removal of these particles, especially the nano-sized particles, are limited. Herein, this work investigated the extraction of polystyrene and polyethylene terephthalate nanoparticles from water using lignin-based HDESs. The removal efficiency was calculated via the pyrolysis-gas chromatography−mass spectrometry, with the highest removal efficiency exceeding 95%. Various techniques including Fourier-transform infrared analysis, contact angle measurements, MD simulations, kinetics, and isotherm studies were also evaluated to gain insights into the removal process. Thirdly, the lignin derived HDESs were used in a facile one-pot fractionation of biomass components. High removal rates of hemicellulose (62-80%) and lignin (42-61%) were achieved for both wheat straw and poplar wood after pretreatment. The treated substrates also offered 4-11 times higher glucose yields than the raw materials during the enzymatic hydrolysis. Compared to the pretreatment process using conventional DESs, the use of lignin-based HDESs offers benefits such as fewer processes, simplified recovery of solvents and products, and decreased energy costs, which contribute to intensified biomass fractionation. Lastly, the use of lignin based HDESs as a replacement for the toxic N, N-dimethylformamide (DMP) in the manufacturing of lignin derived silicon-carbon (Si/C) anode material for lithium-ion batteries was investigated. The effects of the lignin sources and the solvents were examined. The mechanisms underlying the performance differences in the obtained Si/C composites were studied by various analytical methods to provide insights for the future development of the process.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.08

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Available for download on Friday, January 03, 2025

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