Densification of biorefinery schemes by H-transfer with Raney Ni and 2-propanol: A case study of a potential avenue for valorization of alkyl levulinates to alkyl γ-hydroxypentanoates and γ-valerolactone

Alkyl gamma-hydroxypentanoates and gamma-valerolactone are promising platform chemicals that can be produced from alkyl levulinates in the lignocellulosic biorefinery. Accordingly, this report aims to provide in-depth insight into the molecular aspects involved in the conversion of alkyl levulinates by H-transfer catalyzed by Raney Ni and using 2-propanol as an H-donor and solvent. We demonstrate this methodology as a highly flexible approach in regard to the high degree of control over the product selectivity. In fact, up to 90% yield of alkyl gamma-hydroxypentanoates is obtained at temperatures as low as 298 K. In turn, 94% yield of gamma-valerolactone is achieved at 393 K. In order to shed light on the fundamental aspects of this chemical route, we address: (1) the energetics of the transfer vs. conventional hydrogenation of methyl levulinate, (2) the thermal stability of methyl gamma-hydroxypentanoate in the absence and in the presence of solid catalyst, and (3) the stability of Raney Ni in the conversion of several alkyl levulinates. Lastly, a process concept based on the current results is also proposed. This concept provides a comprehensive overview of the practical possibilities of this process as part of the lignocellulose-based biorefineries. (c) 2013 Elsevier B.V. All rights reserved.