Prediction of Thermodynamic Properties of LevulinicAcid via Molecular Simulation Techniques

摘要

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–isobaricensemble and by comparing our simulation results with the correspondingdata from experiments reported in the literature. We have performedgrand-canonical transition-matrix Monte Carlo simulations in the temperaturerange from 580 to 690 K to estimate the vapor–liquid coexistencecurves in the temperature–density plane and the Clapeyron plots.From this data, the critical point (TC = 755 K, ρC = 285.4 kg/m³, and PC = 30.57 bar) has been estimated, and thismay be used as input to the equations of state employed in processsimulation software for design of industrial separation processesincluding those for “biorefining”. As levulinic acidis a “ketoacid”, hydrogen bonding occurs, and the liquidphase structure has also been studied using radial distribution functions.