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

Abstract

This study investigated the use of fractional condensation, following the fast pyrolysis of three different ashrich 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.

Phase Equilibria Aided Optimization of Levoglucosan Extraction during Condensation of Fast Pyrolysis Bio-Oils

“…It also aids in ascertaining key unexplained phenomena that are usually associated with such processes. These have been successfully revealed in previous studies, , when the modified UNIFAC Dortmund (UNIFAC-DMD) was used to predict the yields and composition of FPBOs, detailing how crucial modeling such processes can be. In view of this, extending this to the extraction of LG from FPBOs tends to be stimulating.…”

“…Preparation of these biomass feedstocks prior to their pyrolysis conversion followed the same procedure elucidated elsewhere. 27 2.2. Bench-Scale Solvent Extraction of LG.…”

“…For most industrial-scale processes, condensation of the AC is avoided and instead, the vapors are combusted along with noncondensable pyrolytic gases and char to supply heat to the process. Alternatives are, however, currently being developed to valorize the AC as gasifier feed after mixing with char , and as a carbon source for microbial cultivation and anaerobic digestion, ,− although this is still not yet fully economical owing to the difficulties in dealing with inhibitory compounds such as phenols that are also retained in the AC. With the high solubility of LG in water, using the AC (containing about 85 wt % water) as an alternative solvent to freshwater in extracting LG could be promising toward realizing a sustainable biorefinery concept.…”

“…It is primarily made up of about 85 wt % water and traces of organic compounds such as carboxylic acids, ketones, phenols, and furans. 27 Owing to its low organic content and calorific value, it has seen only limited applications as compared to the ORC and, in most situations, it is discarded following costly treatment methods to remove organics. For most industrialscale processes, condensation of the AC is avoided and instead, the vapors are combusted along with noncondensable pyrolytic gases and char to supply heat to the process.…”

Modeling of Liquid–Vapor Phase Equilibria of Pyrolysis Bio-oils: A Review

“…Approaches like sequential condensation, − cold traps, and manipulation of the sweeping gas flow rate within the condensation vessels , permit the production of multiple bio-oil fractions and the tuning of their compositions and characteristics for different valorization pathways . Sequential condensation specifically frequently produces water-rich fractions at low temperatures, which have found increasing interest as fermentation substrate − or viscosity control to facilitate heavier bio-oil fraction pumpability . Beyond improved condensation design, various techniques are gaining traction for bio-oil valorization, including distillation, ,− liquid–liquid extraction, − membrane separation, − molecular distillation, and the environmentally friendly cold-water fractionation .…”