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

The intricate composition of pyrolysis bio-oil necessitates
the
development of reliable phase equilibrium models, with a specific
focus on liquid–vapor equilibrium pertinent to both condensation
design and distillation, especially when utilizing nonwood feedstocks.
Four key challenges intrinsic to pyrolysis bio-oil are scrutinized:
the selection of an appropriate phase equilibrium model, formulation
of a suitable surrogate mixture, representation of the elusive high-molecular-weight
residue fraction, and the estimation of absent thermophysical properties.
Despite a discernible inclination toward activity coefficient models,
the literature reveals a diverse array of phase equilibrium models,
pointing to the indispensability of considering a nonideal liquid
phase and raising concerns about the reliability of certain models
in the absence of comprehensive experimental data. The judicious choice
of a surrogate mixture emerges as pivotal, given the prevalence of
unknown components and the dearth of precise compound-specific data,
foreseeing a future where diverse surrogate mixtures coexist. Existing
surrogate mixtures are reviewed and recommendations given to guide
effective design of such mixtures. The absence of thermophysical properties
for pyrolysis bio-oil compounds prompts the use of estimation methods,
introducing a challenge in achieving comparable reliability to experimental
values. Quantitative comparison of estimation performance shows no
distinct trend favoring a singular estimation method, a composite
of approaches is suggested to enhance overall model precision. To
propel the field forward, a critical need is identified for augmented
availability of reliable experimental phase equilibrium data for both
pyrolysis bio-oil and its constituent compounds, coupled with their
thermophysical properties, to establish a robust foundation for the
widespread and efficient application of pyrolysis bio-oil across diverse
industries.