(582k) Thermodynamic and Kinetic Analysis of ?-Valerolactone Ring Opening in Multiphase Reactors

 

Author: Xinlei Huang, Zijian Wang, and Jesse Q. Bond

 

Lignocellulosic biomass is an alternative source of industrial carbon. In general, biomass upgrading is predicated upon intermediate formation of functional platform molecules, which can be converted as desired into a range of commodity products. γ-valerolactone (GVL) is an example of one such platform as it provides a spectrum of interesting opportunities for the production of gasoline, jet, and diesel fuels; polymer precursors; and commodity and specialty chemicals. Of interest here is the acid-catalyzed ring opening of GVL to form pentenoic acid (PEA) isomers, which are a family of bifunctional alkene-acids that are of potential interest in the production of nylon.

GVL ring opening is kinetically facile, and it occurs readily in the gas phase over solid acids; however, thermodynamic limitations and secondary reactions make it generally difficult to recover pentenoic acids in good yield. Although GVL ring opening is entropically favorable, it is substantially endothermic, such that PEA yields are equilibrium limited below ≈ 20% at low temperatures. Raising operating temperatures will theoretically address this issue; unfortunately, increasing temperatures to the point where ring opening becomes thermodynamically favorable also makes undesired secondary reactions kinetically accessible. In particular, PEA isomers will undergo decarboxylation over solid acids, irreversibly forming butenes and carbon dioxide. Thus, there exists no gas-phase operating window where PEA isomers can be prepared in good single pass yield.

Instead, we propose that homogeneous mineral acids can be used in biphasic (aqueous-organic) reactors to navigate thermodynamic and kinetic constraints and deliver high PEA yields. Doing so rationally requires a detailed understanding of kinetic and thermodynamic aspects of ring opening in solution. Furthermore, it requires an understanding of how GVL, protons, and PEA isomers partition between water and various organic phases. This poster focuses on recent progress in understanding both reaction kinetics and thermochemistry of ring opening in condensed media and discusses the complex solution thermodynamics that are important in dictating the effectiveness of biphasic reactors.

Key Words: GVL ring opening, solution thermodynamics, liquid-phase kinetics