## 3 Results and Discussion
### Mass Balance and Yield Calculations  
The experimental campaign produced 11 samples of bio- oils (divided among the first, second, and aqueous phase fractions) and as many measurements on the non-condensable gases. Differently, char maintained uniform properties for all runs since it was not affected by any upstream variation from the bio-oil condensing apparatus. The mass balance closure of the experiments was always between 88% and 95%, with an overall average of 92%. Product yields have been determined on an as-received basis. The overall liquid yields were obtained approximatively equal either for the ESP setup or the quenching columns systems. The average figures are in good agreement with those shown in the literature [4] and can be summarized as follows: 12.7% of produced char, 62.9% of bio-oil, and 15.4% of non-condensable gases. The average mass balance closure was calculated at approximately 92% of the initial feedstock, and results are reported in the Sankey diagram given in Figure 7.  
Hereafter, Table 8 shows the bio-oil yield and distribution among the condensers as a function of the temperature in the first step. Initially, the ESP setup was operated for several trials keeping the condensing temperature fixed (T\({}_{\text{cond}}\) = 70 \({}^{\circ}\)C) in order to evaluate procedures and results in reproducibility. The results have shown good replicability. Figure 7: Average mass balance (Nitrogen-free). When operating the first condenser at 100 \({}^{\circ}\)C, more than 27 wt.% of the produced liquids condensed at this stage, while at temperatures of 130 \({}^{\circ}\)C and 170 \({}^{\circ}\)C, this amount roughly accounted for 23 wt.%. The first condensation temperature was varied over a span ranging from 170 \({}^{\circ}\)C to 100 \({}^{\circ}\)C, resulting in a trend of the increasing amount of collected liquids in the first column as the operating temperature decreased. At higher temperatures, liquid yields were slightly lower for the collection of sugars and lignin-derived oligomers in the heavy fraction. At the same time, the variation of first stage temperature influenced the bio-oil yield in the second condenser. This led to an increased mass yield of the second scrubber as the temperature of the first condenser was augmented, reaching a maximum value of 21 wt.%. Yields of the last two liquid collectors (i.e., including the gas filter) have shown to settle around a constant value (of 45 wt.% and 11 wt.% respectively) as the temperature never varied during the experimental campaign. Tests with ESP setup reported the condensation of the largest fraction of bio-oil in the first step, including a high percentage of acidic compounds (up to 40 wt.% of the total amount of detected acids), which are an unwanted feature in terms of bio-fuel aging and storage properties [65]. In the aqueous fraction, a high content of acids and a tiny percentage of furnics were identified as well; different analytical approaches could allegedly detect more light organics. Figure 8: Mass distribution of bio-oil, Spray Condensers setup. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Oil Fraction** & \begin{tabular}{c} **Average Yield, Y** \\ **(kg/kg\({}_{\text{oil}}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Std. Dev, \(\sigma_{\gamma}\)** \\ **(kg/kg\({}_{\text{oil}}\))** \\ \end{tabular} &
\begin{tabular}{c} **Relative Spread,** \\ **\(\sigma_{\gamma}\)/Y \(\times\) 100\%** \\ \end{tabular} \\ \hline
**ESP** & 55.57 & 5.9 \(\times\) 10\({}^{-3}\) & 1.1 \(\times\) 10\({}^{-2}\) \\
**Intensive cooler** & 43.45 & 7.9 \(\times\) 10\({}^{-3}\) & 1.8 \(\times\) 10\({}^{-2}\) \\
**Gas filter** & 0.99 & 1.4 \(\times\) 10\({}^{-3}\) & 1.5 \(\times\) 10\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Reproducibility of three identical experiments, with respect to the reactor conditions (Treactor = 500 \({}^{\circ}\)C, reactor = 0.6–1.1 s, hot = 0.6–1.1 s, fw, biomass = 10–12%).