(427g) Prediction of Thermodynamic Properties, Structure and Vapour-Liquid Coexistence Properties of Levulinic Acid Using Monte Carlo Simulations

Second generation biofuels are a complex mixture of organic compounds which 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 by-products. [1] For oxygen-containing compounds which decompose at elevated temperatures and pressures, determining the vapour-liquid equilibria (VLE) data at high temperatures via the experimental route may be challenging. The experimental data for this compound is limited to a temperature range of 375 K to 519 K (normal boiling point) where the vapour pressures are relatively low. [2] From group contribution methods, the critical point is estimated to be at 716.8 K, 39.4 bar and 331.7 cm³/kmol . The molecular simulation approach is a cost-effective tool to obtain the necessary data (including the critical properties) while also allowing us to understand the microscopic origins of macroscopic observable properties. We have employed the transferrable potential for phase equilibria – united atom (TraPPE – UA) force field [3] to describe the interactions in this system with the parameters for a torsional interaction which is not reported in literature (levulinic acid is a ketoacid) being determined by us from density functional theory calculations. We have verified our parameterization via density computations in the isothermal isobaric ensemble and comparing our simulation results with that from experiments (within 5%) reported in the literature.[4] We have performed grand-canonical transition matrix Monte Carlo simulations in the temperature range from 375 K to 650 K to estimate the vapour –liquid coexistence curves in the temperature – density plane and the Clausisus-Clapeyron plots. From this data, the critical point can be estimated to be used as input to the equations of state employed in process simulation software for design of industrial separation processes including those for ‘bio-refining’. As levulinic acid is a ‘ketoacid’ , hydrogen bonding occurs and the liquid phase structure has also been studied using radial distribution functions.

References

[1] Zhou, et al. Chem. Soc. Rev., 2011, 40, 5588–5617

[2] NIST Chemistry Webbook, NIST Standard Reference Database Number 69, Eds. P.J. Linstrom and W.G. Mallard, National Institute of Standards and Technology, Gaithersburg MD, 20899

[3] Eggimann, et al. Molec. Simul. 2014, 40, 101-105

[4] Guerro, et al. Energy Fuels, 2011, 25, 3009 - 3013