# Deep Eutectic Solvent Pretreatment and Green Separation of Lignocellulose
## 3 Definition of Deep Eutectic Solvent Effects
For example, microwave and ultrasonic treatments provide distinct advantages over conventional conduction and convective heating methods [91; 92]. Microwave radiation can transfer heat more quickly and evenly through dipole rotation and ion conduction with lower energy loss, which greatly reduces the reaction/extraction time without compromising the ease of control [93]. In addition to directly interacting with polar molecules in DES, microwave energy can selectively heat polar portions of biomass. At the same time, it improves the interaction between DES and lignin, and microwave-induced molecular scale stirring and mixing increases the mass transfer rate, making lignin easier to extract and dissolve [94]. The special cavitation effect of ultrasound can change the structure andproperties of biomass during treatment [95]. For lignocellulosic, ultrasound treatment can destroy the outer structure of the lignin, separate out the hemicellulose and increase the accessibility of cellulose molecules [96]. Some studies have found that the yield of reducing sugar from biomass is increased by enzymatic hydrolysis or acid hydrolysis after ultrasonic pretreatment [97]. Pretreatment or assisted separation of lignocellulosic raw materials using chemical agents such as acids, bases, or alcohols has been shown to be an effective way to improve the separation efficiency. [PERSON] et al. [50] added 1 wt% hydroxeyethyl sulfonic acid to DES of ChCl/PEG 600 to construct an acid lignocellulosic separation system and isolated more than 83% lignin and almost all hemicellulose from sugarcane bagasse. This proved that acidic environment can significantly improve the separation effect of lignocellulosic [98]. [PERSON] et al. [6] achieved more than 97% and 87% removal rates of lignin and hemicellulose from poplar by KOH pretreatment. It was found that the BET (Brunauer-Emmett-Teller) surface area of the pretreated material increased and the contact angle between poplar and DES decreased, which increased the subsequent lignin removal rate [6]. Alkaline hydrogen peroxide pretreatment (AHP) has good performance in biomass deconstruction. It is beneficial to moderate the processing conditions of DES. The main mechanism of action is the dissociation of H\({}_{2}\)O\({}_{2}\) under alkaline conditions to produce highly reactive oxygen species (ROS), such as hyperhydroxylated anions (HOO-) and free radicals (HO-). ROS depolymerizes lignin by attacking the lignin side chain and reacts with the enone chromophore (such as the quinone structure) in lignin to increase the dissolution of lignin and reduce the polymerization of lignin [99]. [PERSON] et al. [16] used hydrogen peroxide to pretreat industrial xylose residue at 60 \({}^{\circ}\)C, removing more than 97% of lignin. This has greatly reduced the energy consumption in the separation process compared to similar raw materials without pretreatment. Mechanochemical pretreatment processes have been increasingly recognized as green methods for deconstructing lignocellulosic through mechanical forces such as shock, compression, shear, and friction [100]. Ball milling has been widely used in research and industry as a mechanical treatment to break and reduce sample particle size. In biomass pretreatment, ball milling can effectively deconstruct materials and increase the contact area between lignocellulosic components and DES, thus accelerating the separation rate [101]. This characteristic makes ball milling a method to simplify the separation conditions of lignocellulosic [102]. Impressively, [PERSON] et al. used DES to remove lignin from poplar wood during ball milling, achieving a removal rate of over 99% at room temperature [54]. Hydrothermal pretreatment is a straightforward and effective method that relies solely on the addition of water, making it widely used in the processing of lignocellulosic biomass [103]. Its simplicity offers an opportunity to reduce production costs [104].