Thermodynamic model of fast pyrolysis bio-oil advanced distillation curves

Abstract

Fast pyrolysis bio-oil (FPBO) is a complex organic liquid with over 1000 organic compounds. Therefore, little research exists on the prediction and modelling of liquid physicochemical properties and vapour-liquid phase behaviour. A thermodynamic model of the FPBO vapour-liquid equilibrium (VLE) in distillation will improve the understanding of bulk and FPBO fraction properties, and therefore, aid in the enhancement of FPBO for desired applications, such as condensation of pyrolysis vapours, fractionation, and evaporation during combustion. FPBO produced at 450 °C from softwood sawmill residues at a feed rate of 4 kg/h (~20 s residence time) in a pilot-scale auger reactor was distilled in an advanced distillation curve (ADC) apparatus at atmospheric pressure and at a vacuum of 5 kPa (abs). The ADC equipment allows for the data collection of true thermodynamic state points, including vapour phase composition data. UNIQUAC was the selected equation of states (EoS) to model FPBO distillation VLEs in a 20–flash series in VMGSim™. A surrogate mixture of water, 3,4,4′-biphenoltriol (pyrolytic lignin), inert solids, and multiple organic components was used to model and predict the VLE and consequently bulk physicochemical properties. It was found that GC-FID composition data (in area%), water content (Karl Fisher titration), distillation residue, and solid content were sufficient to inform the model (surrogate composition). This work improved the understanding of FPBO phase behaviour, composition, and bulk properties. The method allows for the identification of target components and fractions to enhance FPBO quality for desired applications.