Using Fractional Condensation to Optimize Aqueous Pyrolysis Condensates for Downstream Microbial Conversion

This study investigated the use of fractional condensation, following the fast pyrolysis of three different ash-rich biomass feedstocks, to optimize the composition of aqueous pyrolysis condensates (ACs) for downstream microbial conversion. Optimum conditions were first predicted and established theoretically by means of vapor–liquid equilibrium flash calculations that employed the modified UNIFAC Dortmund (UNIFAC-DMD) model. Thereafter, theoretical models were experimentally validated on a 10 kg/h fast pyrolysis setup. Model predictions revealed that a temperature combination of 120 and 50 °C on the first and second staged condensers, respectively, returned optimum production of AC yield and substrates at the expense of inhibitors. Satisfactory agreement existed between most experimental data and model predictions, and the qualitative trend was mostly reproduced correctly. Some noteworthy deviations were, however, observed, most especially for inhibitory compounds, which were blamed on the limitation of the UNIFAC-DMD model in accurately predicting the phase behavior of organic compounds at such very low concentrations as well as the scarcity of precise vapor pressure data for some of these organic compounds. Nonetheless, the study demonstrated how valuable theoretical phase equilibrium models are in predicting the composition of fast pyrolysis bio-oils and how fractional condensation proves to be a key upstream pre-treatment for valorizing ACs.