###### Abstract
One possible solution to achieve selective bio-oil fractions consists in taking advantage of the specific temperatures at which the various organic groups go through the condensation step. Two main different approaches are reported in the literature, the first one is fractional distillation which operates on the final liquid products obtained from pyrolysis, while the other approach is the fractional condensation of hot pyrolysis vapors. The latter has the main advantage of minimizing the thermal energy demand compared to distillation, acting directly on a hot vapor stream [9]. Distillation instead fractionates bio-oil components according to their different volatilities. Nevertheless, fast pyrolysis bio-oils have a thermally unstable behavior due to the high reactivity of organic molecules even at low temperatures (\(<\)100 \({}^{\circ}\)C), resulting in low yields [10]. This behavior contrasts with conventional petroleum-derived fuels, namely diesel and kerosene, which have an up to 90 wt.% distillation yield between 220-300 \({}^{\circ}\)C and 190-240 \({}^{\circ}\)C, respectively [11]. Literature, such as [8], confirms that under atmospheric pressure, bio-oil starts boiling below 100 \({}^{\circ}\)C, and the distillation process leaves up to 35-50 wt.% of the initial material as a residue. Other distillation techniques for bio-oil applications, such as vacuum and flash distillation, have been extensively used and well described in the literature [12; 13; 14]: however, technical difficulties in distilling raw FPBO still have to be effectively tackled [15; 16; 17]. Traditionally, bio-oil cannot be easily distilled because of its high content of reactive oxygenates that give rise to polymerization and condensation reactions [18]. Described results for direct distillation of bio-oil are not deemed satisfactory, mainly due to the formation of high residue yields as a result of pyrolytic lignin deposition [19]. Moreover, it is widely known that bio-oils produced from pyrolysis of solid woody biomass show poor thermal stability and aging-related properties that could hinder their path to large-scale applications. Several techniques have been investigated to improve the properties of FPBO, for instance, through the addition of methanol or other alcohols in different proportions to lower the viscosity and delay the aging rate during storage [20; 21; 22]. Understanding the bio-oil physical and chemical aging mechanisms is still nowadays a key step toward the design of more efficient production and upgrading processes [23]. Besides that, all bio-oil separation approaches must prove to be economically and environmentally feasible to ensure that the value of the targeted products exceeds the recovery cost [24]. This implies that the energy demand for recovering a bio-derived fuel should remain a modest fraction of the heating value of the final product itself. Since the distillation of fast pyrolysis bio-oils might not be attractive for the above-mentioned reasons, fractional condensation of bio-oil vapors has been constantly investigated as an effective solution to separate major bio-oil constituents [25; 26; 27]. Following this approach, the product stream from the fast pyrolysis reactor is generally cooled down and condensed through a series of condensers kept at different temperatures to allow the collection of the different liquid fractions based on their dew point [28]: condensers temperatures are varied with the aim of reducing the water content of pyrolysis oil [29; 30]. A higher condenser temperature could be beneficial to the bio-oil quality; however, the application of a higher condensing temperature could result in a loss of lighter organics. Due to the complex nature of pyrolysis volatiles, researchers generally used a combination of multiple condensation steps to allow for the complete recovery of the liquids by separation from non-condensable gases. Among these technologies, cooling and precipitator systems are some of the most frequently adopted solutions.