Hydrogenation of Levulinic Acid to γ-Valerolactone via Green Microwave-Assisted Reactions Either in Continuous Flow or Solvent-Free Batch Processes

In the search for a more sustainable future, the biorefinery approach can help by replacing fossil feedstocks with renewable sources. When biorefineries meet circular economy, the production of new platform chemicals from residual lignocellulosic biomasses becomes the joint goal. In this frame, the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) has gained increasing interest, with the aim of producing intermediates for the chemical industry. Enabling technologies, particularly microwaves, have proven to be an efficient tool for process intensification, as they can reduce the reaction time and the formation of byproducts. In this work, MW-assisted processes with heterogeneous Ru-based catalysts were exploited for the reduction of LA both with H2 and 2-PrOH as reductants. Different metal loadings and supports were considered, such as a commercial active carbon (Ru/AC) and titania (Ru/TiO2). Among the different hydrogen sources, molecular hydrogen led to milder reaction conditions, enabling the complete flash conversion of LA in only 2 min without any solvent. In terms of catalytic activity, AC showed slightly better performances as support. In addition, flow MW-assisted processes were tested using a multiphase reactor, reaching complete conversion in only 8 min in an open loop system for both the tested catalysts. Performance enhancement and material reuse support the suitability of flow approach, paving the way for a sustainable and scalable process.