Abstract
Biorefinery using lignocellulosic biomass is a promising alternative to petrochemical refineries.
All three major components of the biomass, including cellulose, hemicellulose, and lignin, have
high potential to produce bio-based fuels and platform chemicals. To achieve an effective
conversion of the biomass into fuels and chemicals, a pretreatment step breaking down the
recalcitrant biomass structure is essential. Traditional pretreatment techniques often require
intensive energy input, generate high vapor pressure, and cause equipment corrosion. Also, most
of them only focus on the utilization of the carbohydrate fraction of the biomass, resulting in
irreversible lignin structural modification that hinders lignin valorization. Therefore, advanced
pretreatment approaches facilitating total biomass utilization while being green and economically
feasible are highly desirable. Deep eutectic solvent (DES) synthesized with quaternary ammonium
salts like choline chloride (ChCl) as the hydrogen bond acceptor (HBA) and renewable compounds
as hydrogen bond donor (HBA) is appealing for biomass pretreatment. They are non-volatile,
thermally stable, highly tunable, and easy to prepare. Most DES pretreatments can be conducted
under relatively mild temperatures (less 160 ℃), leading to less lignin structural modification in
addition to high yields of fermentable sugar. Moreover, preparing DES with lignin-based phenolic
chemicals facilitates a sustainable biorefinery process. Since the solvent can be obtained from
fractionated lignin after pretreatment, it not only valorizes both lignin and carbohydrates but also
reduces the overall cost of the process.
In this dissertation, we report that lignin-based DES prepared with p-Hydroxybenzoic acid (PB),
a pendant group acylated to lignin of poplar and willow in nature, is promising to achieve a
sustainable biorefinery process. Chapter 1 overviews various pretreatment technologies developed
for biomass conversion. Chapter 2 reports the screening of lignin-based DESs, along with the
effect of temperature and time on PB-based DES pretreatment. Chapters 3 and 4 describe the
integrated process utilizing transgenic biomass rich in PB as the feedstock. PB-based DES
effectively broke down the biomass, and PB was selectively isolated from the fractionated lignin,
facilitating a sustainable biorefinery process. In chapter 5, the effect of lignin-based threecomponent DES on biomass pretreatment was studied to further exploit the potential of ligninbased DES solvent systems