Second-generation
biofuels are a complex mixture of organic compounds
that can be further processed to hydrocarbon fuels and other valuable
chemicals. One such chemical is levulinic acid (IUPAC name: 4-oxo
pentanoic acid), which is a highly versatile ketoacid obtained from
cellulose present in agricultural byproducts. For oxygen-containing
compounds that decompose at elevated temperatures and pressures, determining
the vapor–liquid equilibria data at high temperatures via the
experimental route may be challenging. The molecular simulation approach
is a cost-effective tool to obtain the necessary data while also allowing
us to understand the microscopic origins of macroscopic observable
properties. We have employed the transferable potential for phase
equilibria-united atom force field to describe the interactions in
this system with the parameters for a torsional interaction that are
not reported in the literature (levulinic acid is a ketoacid) being
determined from density functional theory calculations. We have verified
our parameterization via density computations in the isothermal–isobaric
ensemble and by comparing our simulation results with the corresponding
data from experiments reported in the literature. We have performed
grand-canonical transition-matrix Monte Carlo simulations in the temperature
range from 580 to 690 K to estimate the vapor–liquid coexistence
curves in the temperature–density plane and the Clapeyron plots.
From this data, the critical point (
T
C
= 755 K, ρ
C
= 285.4 kg/m
3
, and
P
C
= 30.57 bar) has been estimated, and this
may be used as input to the equations of state employed in process
simulation software for design of industrial separation processes
including those for “biorefining”. As levulinic acid
is a “ketoacid”, hydrogen bonding occurs, and the liquid
phase structure has also been studied using radial distribution functions.
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