## Materials & Methods
### Condensation Units  
Two condensation configurations were considered (Figure 2). The first configuration was made by a thermally controlled ESP (Electrostatic Precipitator) as the main condensing system, followed by the intensive cooling stage meant to condense the very light vapors. The gaseous stream leaving the tubular reactor is condensed in a custom-made jacketed electrostatic precipitator tube with an internal diameter of 6.2 cm and 44 cm in length, operating a single electrode at 10 kV.  
Temperature is controlled via circulating pre-heated water inside the ESP outer cylinder. During the experimental campaign, the ESP has also been always kept at a temperature of 70 \({}^{\circ}\)C by circulating pre-heated tap water inside the outer cylinder. The produced oil is collected in a coated bottle directly connected and sealed at the bottom of the precipitator tube and then extracted and weighed at the end of every experiment. The second configuration is based on spray condensers. It is composed of a spray condensers train that allows the simultaneous control of three different condensing temperatures to divide different boiling fractions present into the hot vapors.  
First, two counter-current spray condensers were placed in series, which perform the direct-contact heat exchange that maximizes the liquid yields thanks to the simultaneous transfer of heat and mass. During the experiments, the temperature of the vapors leaving the condenser and the produced liquids were measured through thermocouples placed at the inlet and the outlet of each section.  
Figure 1: Layout of the pyrolysis unit connected to the fractional condensation train: (1) biomass storage hopper; (2) mechanical stirrer; (3) feeding stirrer; (4) cooling jacket; (5) sand storage hopper; (6) fluidized bed reactor; (7) overflow vessel; (8) cyclones; (9) spray condensers; (10) intensive cooler. Adapted from [29].  
The residence time of the produced liquids in the collector underneath the condenser (at the condenser's temperature) was approximately 0.5-1 h. The pressure in the condensers was monitored during all the experiments and was always 1.1 \(\pm\) 0.01 bar.  
Bio-Oil Collection Methods--Spray Condensers  
A closed-loop spray hydrocarbon quench system was incorporated into the fast pyrolysis pilot-scale facility in order to operate the direct-contact condensation system. The selected coolant fluid for this solution was a paraffin oil (Shell Ondina 919), composed of C 20 isoparaffinic hydrocarbons boiling between 280 and 300 \({}^{\circ}\)C. It was selected because of its low vapor pressure, thermal stability, and (alleged) immiscibility with bio-oil; its main properties are presented in Table 2.  
After condensation, bio-oils samples were removed from the bottom of the condenser. Subsequently, the mixture of paraffin oil and bio-oil was poured into a funnel and separated via gravitational phase separation thanks to the different density properties of the two liquids (Bio-oil = 1.2 kg dm\({}^{-1}\), Shell Ondina 919 = 0.856 kg dm\({}^{-1}\)).  
Fast pyrolysis bio-oils and isoparaffins are immiscible, as they cannot form a homogeneous liquid. Nevertheless, according to some recent studies [41], contact between the two fluids results in a mass transfer, which is negligible for most bio-oil components but should not be ignored in a few specific cases.  
Figure 2: Fast Pyrolysis experimental setup: (**a**) ESP configuration, (**b**) Spray condensers route, (**c**) Pilot unit overview.  
Concentrations of some compounds identified as being leached out of bio-oil into the quenching fluid have been estimated to be in the range of 0.01-0.1% (by mass). Although these figures could represent a significant issue in certain cases, it was reasonable to consider these effects as negligible in the present work.