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

Abstract

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 H 2 and 2-PrOH as reductants. Different metal loadings and supports were considered, such as a commercial active carbon (Ru/AC) and titania (Ru/TiO 2 ). 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.

Comparative Study of Batch and Continuous Flow Reactors in Selective Hydrogenation of Functional Groups in Organic Compounds: What Is More Effective?

“…G. Grillo et al [ 60 ] investigated hydrogenation of levulinic acid to GVL under microwave (MW) irradiation in batch or continuous flow processes over Ru/AC and Ru/TiO 2 catalysts. It was suggested [ 60 ] that using microwave irradiation can improve conversion of levulinic acid in a shorter time.…”

Process intensification in continuous flow organic synthesis with enabling and hybrid technologies

“…The use of MW irradiation and flow conditions produced a dramatic rate enhancement in comparison to conventional heating, with a 1,900-fold increase for the congested phenol to give trimethoxybenzene. Cravotto and co-workers have documented the effectiveness of FlowSynth and have described MW-assisted γ-valerolactone production through levulinic acid hydrogenation in continuous flow mode over heterogeneous palladium (Tabasso et al, 2016), and, more recently, ruthenium catalyst (Ru/AC Ru/TiO 2 ) (Grillo et al, 2021). A novel protocol for continuous MW-assisted alkyne semi-hydrogenation under heterogeneous catalysis was reported in 2018 (Calcio Gaudino et al, 2018).…”

Supported rhenium catalysts for the hydrogenation of levulinic acid derivatives: limits and potential

“…8 In literature, most works deal with the conversion of LA and its ester towards g-valerolactone (GVL) because LA is the most easily obtainable compound, either by hydrogenation with H 2 or by catalytic H-transfer hydrogenation with light, biobased alcohols, in both liquid-and gas-phase continuous ow reactors. [9][10][11][12][13][14][15][16] The most recent advances in literature, however, have also led to different consecutive reduction products. 17 For instance, 2-methyltetrahydrofuran (2-MTHF) was proposed as an efficient fuel additive for gasoline formulations and as an eco-friendly solvent alternative to THF.…”

“…8 In literature, most works deal with the conversion of LA and its ester towards γ-valerolactone (GVL) because LA is the most easily obtainable compound, either by hydrogenation with H 2 or by catalytic H-transfer hydrogenation with light, bio-based alcohols, in both liquid- and gas-phase continuous flow reactors. 9–16…”