## 4 Conclusions  
The current study confirms that fractional condensation applied to fast pyrolysis vapors of lignocellulosic biomass is a promising and feasible approach to concentrate classes of compounds, aiming at controlling the quality of bio-oil fractions. Bio-oil yields in the quenching columns were observed to slightly vary with the condensing temperature. The identified trend confirms to be linked to the temperature decrease, resulting in higher yields at lower temperatures of condensation as the dew points of chemical compounds and the flash condensation theory can well unfold. From a qualitative point of view, a slight difference can be noticed in the evolution of products collected in the first and second condenser as the temperature of the first was decreased, while differences in viscosity became a relevant issue preventing the operator from easy removal of the condensed compounds at each step of the investigated temperature range (100-170 \({}^{\circ}\)C). With the increase in the condensation temperature, a significant concentration of heavy compounds was detected in the first fraction (e.g., levoglucosan concentration presents an almost threefold increase from 4 to 13 wt.%). The second scrubber concentrated mainly on mid and light organic compounds for all the tested conditions (phenols, cyclopentenones, and some furans). What is important to emphasize from a qualitative point of view is the reduction in the acidity of the bio-oil with the rise in temperatures, ranging from 6 wt.% at 100 \({}^{\circ}\)C to 1.24 wt.% at 170 \({}^{\circ}\)C, as well as the low water content, around 7% for all the experiments due to the high condensation temperature of the second scrubber (i.e., 70 \({}^{\circ}\)C). The second cut visually appeared as single-phase liquid: no phase separation occurred at the time of extraction nor after several months of storage. The removal of light organic polar compounds and water improved the stability of the bio-oils. The reported low acidity values of the central fraction are known as important features for good bio-oil aging properties. Therefore, improved bio-oil quality was experimentally achieved, thus resulting in a potentially reduced energy demand in the downstream upgrading processes (i.e., lower hydrogen demand for the next hydrotreatment steps) for alternative fuel production. Average mass balance figures for all the experiments resulted in 12.7% of produced char, 62.9% of bio-oil, and 15.4% of non-condensable gases, accounting for an overall mass balance closure of 92% of the initial feedstock. Although 10% of the chemical energy of the feedstock was lost as heat losses and thermal power transferred to the cooling fluids, a considerable energy concentration effect was obtained by combining fast pyrolysis with fractional condensation: the bio-oils collected in the first and second condensers constitute 43% of the chemical energy of the biomass input, while the energy retained in the aqueous phase (13.7%) indicates the presence of soluble organics in the aqueous fraction. The energy content of the collected fractions was observed to remain rather constant over the temperature variations of the first scrubber, presenting a significantly high heating value (HHV) of \(\simeq\)21.5 MJ kg\({}^{-1}\) for the target fraction. A good trade-off between energy efficiency and product quality could result in setting the first spray column temperature at about 130 \({}^{\circ}\)C.  
In conclusion, the overall energy assessment of the process supported by the qualitative analyses of the products resulted in a better understanding of the overall performance and product characteristics from fractional condensation: good quality bio-crude for fuel applications has been produced, while at the same time process energy requirements have been evaluated assessing the self-sufficiency of the conversion process. Therefore, the investigated condensation solutions offer a high potential in a modern biorefinery integration, including the combined production of bio-derived fuels and chemicals.