## Materials & Methods
### Pyrolysis Unit  
Experiments were performed in the 1 kg h\({}^{-1}\) fluidized bed (sand) pyrolysis unit (as described in [29]) at the SPT group premises at the University of Twente (NL). Fluidized bed reactors (FBR) are among the most used pyrolysis reactors at the experimental level. Their technology is based on the combination of convection and conduction heat transfer phenomena to effectively convey the heat from the hot sand to the biomass [46]. This kind of reactor can obtain high bio-oil yields: given their poor thermal conductivity, the biomass particle size must be very small in order to reach the desired gas-solid heat transfer. The volatile mixing of sand with biomass particles leads to high heat and mass transfer coefficients, a favorable condition for fast pyrolysis. FBR can be well scaled up or down to meet different experimental requirements, and, in particular, the process temperature can be conveniently controlled, while catalysts can be introduced in the form of sand. Nevertheless, when considering industrial-scale applications of FBR, the process design and management might present some hurdles like the high volumes of carrier gas leading to considerable sand attrition problems and energy efficiency losses [47]. Building on a theoretical background [48], it has been possible to calculate all the functional parameters to achieve steady-state bed fluidization and to reach fast pyrolysis reactions and products. In our case, the bed was indirectly heated by being placed in an electric furnace in which two heating zones could be controlled independently. The main operating conditions and parameters of the process are listed in Table 1.  
The pre-existing layout was specifically modified to meet the required characteristic for the proposed experimental campaign. A simplified scheme of the pilot unit is presented in Figure 1.  
During operation, a Nitrogen flow was fed to the biomass hopper, creating a slight overpressure, which prevented vapors and gases leaving the fluidized bed pyrolysis reactor from flowing back to the hopper via the double screw feeding system. Sand was continuously fed to control the char holdup and to keep constant the bed height in the reactor. It is important to control and to know the char holdup as it catalyzes the cracking of pyrolysis vapors leading to a lower oil yield and influences fluidization behavior. A mass flow controller was used to set the feed rate of the fluidization flow, keeping a constant sand-to-biomass ratio roughly at around 1.5. Details of the condensation trail are described in the next section. The vapor/gas stream leaving the reactor results in containing sand fines and a fraction of the produced char. All the sand and most of the char particles were collected in a knockout vessel. A downstream series of three cyclones, equipped with collection vessels, to remove almost all residual char particles. The gaseous stream leaving the condensing section was mainly composed of non-condensable gases and a mixture of aerosols, which were collected in a tubular cotton gas filter (10 \(\upmu\)m). Finally, a dry gas meter was used to measure the gas flow before the main ventilation system. The custom bubbling fluidized bed reactor (BFBR) allows rapid heating of the biomass particles by mixing them in a stream of moving sand particles at high temperatures. The volatile mixing of sand with biomass particles leads to high heat and mass transfer coefficients. The sand bed is indirectly heated by being placed in an electric furnace in which two heating zones can be controlled independently.