## 3 Results and Discussion
### Effect of Organic Solvent for Furfural Production and Extraction  
Three kinds of organic solvents, THF, toluene, and DMSO, were evaluated to understand the effects of organic solvents on furfural production and extraction. Toluene is considered an effective solvent for furfural extraction [33], whereby it does not require additional salt for phase separation because of its immiscibility with water. DMSO has been used to improve the selectivity of 5-HMF from glucose by increasing the fructofuranose isomer and stabilizing 5-HMF by hydrogen bonding [34]. Under a similar mechanism, it was anticipated that DMSO could also improve furfural yield from xylose. Reaction conditions were set to the optimal values predicted from analysis of variance (ANOVA); this was a reaction temperature of 170 \({}^{\circ}\)C, reaction time of 120 min, xylose concentration of 10 g/L of, and the use of a 4% of sulfuric acid solution.  
Table 4 shows the furfural yield from the xylose standard solution depending on the organic solvent. THF had the highest furfural yield from the xylose standard, while DMSO had the lowest among the three solvents. It was assumed that DMSO may not effectively protect the generated furfural from acid or water as furfural has no hydroxyl group compared with 5-HMF. In addition, DMSO has a reduced interaction with furfural compared to the other organic solvents such as toluene or THF, as its polarity is higher than that of furfural. THF had a higher furfural yield than toluene, even though the polarity of toluene was close to furfural. To explain this phenomenon, the partition coefficient of furfural in THF/water and toluene/water was calculated by dividing furfural  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Source** & **Sum of Squares** & **DF** & **Mean Square** & _F-Value_ & _p-Value_ & **Coefficient** \\ \hline Model & 10,697.21 & 9 & 1188.58 & 14.13 & 0.0010 & 67.77 \\ X\({}_{1}\) & 4722.88 & 1 & 4722.88 & 56.14 & 0.0001 & 18.60 \\ X\({}_{2}\) & 2136.23 & 1 & 2136.23 & 25.39 & 0.0015 & 12.51 \\ X\({}_{3}\) & 0.00 & 1 & 0.00 & 0.00 & 0.9963 & 0.01 \\ X\({}_{1}\)X\({}_{2}\) & 955.35 & 1 & 955.35 & 11.36 & 0.0119 & \(-\)10.93 \\ X\({}_{1}\)X\({}_{3}\) & 21.51 & 1 & 21.51 & 0.26 & 0.6287 & \(-\)1.64 \\ X\({}_{1}\)X\({}_{3}\) & 6.48 & 1 & 6.48 & 0.08 & 0.7894 & 0.90 \\ X\({}_{1}^{\mathrm{+}}\) & 1646.23 & 1 & 1646.23 & 19.57 & 0.0031 & \(-\)12.08 \\ X\({}_{2}^{\mathrm{+}}\) & 1513.50 & 1 & 1513.50 & 17.99 & 0.0038 & \(-\)11.59 \\ X\({}_{3}^{\mathrm{+}}\) & 0.67 & 1 & 0.67 & 0.01 & 0.9314 & 0.24 \\ Residual & 588.94 & 7 & 84.13 & & & \\ Lack of fit & 588.89 & 5 & 117.78 & 4825.36 & 0.0002 & \\ Pure error & 0.05 & 2 & 0.02 & & & \\ Corrected total & 11,286.15 & 16 & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Analysis of variance (ANOVA) for furfural yield in dehydration xylose model compound and coefficients for quadratic equation.  
concentration in the organic solvent by the concentration of furfural in aqueous water (Table 4) to compare the solubility of furfural in a two-liquid mixture (water and organic solvent). To calculate the partition coefficient of furfural to THF/water, NaCl was added to separate THF from the water phase (salting out). THF had a higher partition coefficient than toluene, indicating that the former was more effective in extracting furfural than toluene, and yielding higher amounts of furfural.