###### Abstract  
Fast pyrolysis of biomass is a well-known opportunity for sustainable alternative fuel production for transport and energy. However, bio-oils from biomass pyrolysis are viscous, acidic bio-crudes that need further steps of upgrading before being used either as fuels or chemicals. A process that is complementary to bio-oil hydrotreatment or co-processing consists of optimizing and tuning the upstream condensation steps of fast pyrolysis to separate and concentrate selected classes of compounds. This can be implemented by varying the condensation temperatures in a multi-step condensation unit. In this study, fractional condensation of fast pyrolysis vapors from pinewood has been applied to a bubbling fluidized bed reactor of 1 kg h\({}^{-1}\) feed. The reactor was operated at 500 \({}^{\circ}\)C [1] and connected to a downstream interchangeable condensation unit. Tests were performed using two different condensing layouts: (1) a series of two spray condensers and a tube-in-tube water-jacketed condenser, referred to as an intensive cooler; (2) an electrostatic precipitator and the intensive cooler. Using the first configuration, which is the focus of this study, high boiling point compounds--such as sugars and lignin-derived oligomers--were condensed at higher temperatures in the first stage (100-170 \({}^{\circ}\)C), while water-soluble lighter compounds and most of the water was condensed at lower temperatures and thus largely removed from the bio-oil. In the first two condensing stages, the bio-oil water content remained below 7% in mass (and therefore, the oil's high calorific content reached 22 MJ kg\({}^{-1}\)) while achieving about 43% liquid yield, compared to 55% from the single-step condensation runs. Results were finally elaborated to perform a preliminary energy assessment of the whole system toward the potential upscaling of this fractional condensation approach. The proposed layout showed a significant potential for the upstream condensation step, simplifying the downstream upgrading stages for alternative fuel production from fast pyrolysis bio-oil. biomass; biofuels; fast pyrolysis; fractional condensation; bio-oil; phase separation; alternative fuels +
Footnote †: journal: _Sciences_  
0000-0001-6600-0000-0001-6600-00001  
over the globe. Among the conversion routes already available at a commercial scale, including both biological and thermochemical processes, fast pyrolysis of lignocellulosic feedstock is a market-ready conversion pathway with a high Technology Readiness Level (TRL) for rapid growth at the European Union (EU) level [1]. The main product, called Fast Pyrolysis Bio-Oil (FPBO), is a bio-crude that can be further converted to fuels or valuable bio-based chemicals production [2]. The conversion process involves the generation of condensable hot organic vapors consisting of fragments of cellulose, hemicellulose, and lignin polymers, obtained through rapid heating of biomass in an inert atmosphere, followed by fast quenching or cooling [3]. Pure FPBO is not suitable for direct use as a transportation fuel in existing systems due to its chemical and physical properties, such as its high-water content, instability, acidity, and high oxygen content [4]. Upgrading is, therefore, necessary to improve FPBO quality to meet end-use requirements, up to hydrocarbon fuels (i.e., hydro or catalytic deoxygenation [5]). Alternatively, FPBO can be fed with crude oil streams in existing refineries as co-processed material for the production of liquid hydrocarbon fuels [6; 7]. In addition, bio- oils can also be used as feedstock for bio-based chemicals to substitute specific petroleum-derived molecules with organic-derived chemicals (e.g., phenols) [8]. Developing an effective separation method to extract specific components could be a potential route to improve the bio-oil quality prior to further upgrading (e.g., by removing acidic components and water) and/or extracting valuable organic chemicals for various application.