## 4 Conclusions  
This study aimed to optimize furfural production from pentose in the dilute acid hydrolysate of _Quercus monoglica_. The main component of the acid hydrolysate was XMG, which was dominated by xylose. The optimization of furfural production was conducted using RSM with a xylose standard solution and an extracting solvent THF, to enhance furfural yield. The optimal conditions included a reaction temperature of 170 \({}^{\circ}\)C at a reaction time of 120 min with a xylose concentration of 10 g/L; the predicted furfural yield  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{8}{c}{**Concentration (g/L)**} \\ \cline{2-7}  & **Furfural** & **Glucose** & **XMG** & **Arabinese** & **Formic Acid** & **Acctic Acid** & **Acidic Lightin** \\ \hline Before separation & 3.08 \(\pm\) 0.11 & 0.09 \(\pm\) 0.02 & 0.22 \(\pm\) 0.03 & 0.05 \(\pm\) 0.02 & 0.49 \(\pm\) 0.02 & 1.22 \(\pm\) 0.03 & 0.84 \(\pm\) 0.02 \\ Organic phase & 4.84 \(\pm\) 0.10 & 0.00 \(\pm\) 0.00 & 0.09 \(\pm\) 0.00 & 0.00 \(\pm\) 0.00 & 0.63 \(\pm\) 0.02 & 1.61 \(\pm\) 0.04 & 1.24 \(\pm\) 0.00 \\ Aqueous phase & 0.58 \(\pm\) 0.05 & 0.25 \(\pm\) 0.05 & 0.29 \(\pm\) 0.05 & 0.05 \(\pm\) 0.00 & 0.21 \(\pm\) 0.00 & 0.55 \(\pm\) 0.03 & 0.21 \(\pm\) 0.00 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Concentration of chemicals in furfural produced liquor prior to and after phase separation (organic phase, aqueous phase) through the addition of NaCl.  
Figure 2: Extraction rate of products in furfural generated hydrolysate by extracting solvent (THF).  
was 75.1% under these conditions. An experimental furfural yield of 72.39% was obtained under the optimal experimental conditions, similar to the predicted yield. Extracted solvents such as THF, toluene, and DMSO were evaluated to understand the effect of the solvent on furfural yield. THF achieved the highest furfural yield, while DMSO had the lowest yield. Based on this result, furfural was produced from dilute acid hydrolysate under optimized reaction conditions using THF as the extracting solvent. A furfural yield of 68.20% was obtained based on pentose in the hydrolysate, similar to that of the xylose standard solution (72.39%). Following phase separation through the addition of NaCl, 86.03% of the furfural produced was in the organic phase. The THF, and two additional extractions using fresh THF enhanced the furfural extraction rate to 94.63%.  
Conceptualization, J.-H.K. and B.K.; methodology, S.-M.C. and J.-H.K.; formal analysis, J.-H.K. and J.-H.C.; investigation, J.-H.K.; resources, H.J. and S.M.L.; data curation, J.-H.K. and J.-H.C.; writing-original draft preparation, J.-H.K.; writing-review and editing, J.-H.K.; visualization, J.-H.K.; supervision, I.-G.C. and B.K.; project administration, B.K. All authors have read and agreed to the published version of the manuscript.  
This study was carried out with the support of the R & D program for Forest Science Technology (Project No. 2020226C10-2022-AC01) provided by the Korea Forest Service (Korea Forestry Promotion Institute) and the Research Program (FP0900-2019-01) of the National Institute of Forest Science (NIFoS) (Seoul, Republic of Korea).  
Not applicable.  
The authors declare no conflict of interest.