## 3 Results and Discussion
### Characterization of the RL
#### 3.2.2 Elemental Analysis of the RL  
The KL feedstock, untreated RL sample, and RL sample obtained from the DES treatment of KL at varying temperatures, times, and DES-to-lignin ratios were subjected to elemental analysis, and the obtained results are summarized in Table 1. Notably, the KL feedstock exhibited higher levels of O, N, and S compared to the untreated RL sample obtained from KL. For instance, the O, N, and S contents of KL were 32.26%, 1.02%, and 1.22%, respectively. Following KL depolymerization at 190 \({}^{\circ}\)C for 8 h in ethanol, these values decreased to 32.10%, 0.61%, and 1.13%, respectively, in the RL, resulting in a relatively high HHV of 24.82 MJ kg\({}^{-1}\). Following DES treatment under the same reaction conditions, the O, N, and S content further decreased, while the C and H contents increased, leading to an increase in the HHV to 26.44 MJ kg\({}^{-1}\). These findings indicate that the DES effectively catalyzes hydrogenation, hydrodesulfurization, and deoxygenation during lignin depolymerization in ethanol. The elevated levels of O and N in the raw KL impact its energy density, chemical reactivity, material properties, and stability. In particular, high O levels can lower energy density and increase the likelihood of harmful emissions during  
Figure 4: FT-IR spectra of the raw KL (**a**), RL sample after DES treatment at 190 \({}^{\circ}\)C for 8 h (**b**), and RL sample without DES treatment at 190 \({}^{\circ}\)C for 8 h (**c**) in ethanol. combustion, while higher N contents can lead to the formation of nitrogen oxides (NOxs). In contrast, the RL samples with reduced O and N levels demonstrate improved energy values, low environmental impact, enhanced stability, and improved material properties, rendering them favorable for various applications. Figure 6A illustrates the O/C and H/C ratios of the KL feedstock, untreated RL sample, and RL sample obtained from DES treatments, while the corresponding S/C and H/C ratios are depicted in Figure 6B. Notably, the O/C and H/C ratios of the KL and RL samples exhibit considerable variations. Initially, KL exhibited O/C and H/C ratios of 0.016 and 0.094, respectively. After depolymerization at 190 \({}^{\circ}\)C for 8 h, the O/C ratio of the untreated RL sample slightly decreased to 0.015, while its H/C ratio increased to 0.095. Following DES treatment, the O/C ratio further decreased to 0.014, while the H/C ratio increased to 0.099, suggesting that the DES enhances the hydrogenation of unsaturated bonds in lignin and its  
Figure 5: FT-IR spectra of the RL sample at different reaction temperatures (**A**) and times (**B**). In (**A**) raw KL (a) and RL sample obtained after DES treatment in ethanol at 110 (b), 170 (c), 190 (d), and 210 \({}^{\circ}\)C (e) for 8 h. In (**B**) raw KL (a) and RL sample obtained after DES treatment in ethanol at 190 \({}^{\circ}\)C for 4 (b), 8 (c), and 10 h (d). depolymerized products. Furthermore, the S/C ratio of KL was 0.020, which decreased to 0.011 for the RL sample obtained from the DES treatment. These results imply that the DES facilitates the hydrogenolysis of lignin into various monomeric products, followed by their hydrogenation and deoxygenation, yielding saturated phenolic monomers.