Abstract
Biomass-derived levulinic acid (LA) is an excellent substrate to obtain high-value esters that can be used as second-generation biofuels and biofuel additives. The present study focuses on the identification and definition of the key parameters crucial for the development of chemically and environmentally efficient protocols operating in continuous-flow for the preparation of structurally diverse alkyl levulinates via the esterification of LA. We have focused on the use of solid acid catalysts consisting of sulfonated cation exchange resins and considered different aliphatic alcohols to prepare levulinates 3 and 11–17 regioselectively, and in good to high yields (50–92%). Direct correlations between several reaction parameters and catalyst activity have been investigated and discussed to set proper flow reactors that allow minimal waste production during the workup procedure, enabling Environmental factor (E-factor) values as low as ca. 0.3, full recoverability and reusability of the catalysts, and the production of levulinates up to ca. 5 gxh−1 scale.
Highlights
Levulinic acid (LA) has been recognized by the US Department of Energy as one of the top biomass-derived platform molecules, owing to its exceptional reactivity and to the fact that it can be produced at relatively low cost from lignocellulose waste [1,2,3].The catalytic upgrading of such a platform molecule into second-generation biofuels and biofuel additives is currently of great interest [4,5,6]
Fuel additives based on levulinic acid (LA) exhibit characteristics that make them appropriate for replacing current cold flow improvers in diesel
They may be employed as gasoline and diesel oxygenated additives, which help to achieve appropriate lubricity, flash point stability, and cleaner burning fuels
Summary
15® (A-15) and polystyrene-supported p-toluensulfonic acid (PS-pTsOH), both available in the market, as well as perfluorosulfonic polymer Aquivion® PFSA in the form of micronized pellets (Aquivion mP98) from Solvay Specialty Polymers S.p.A., which has not yet become commercially available It is well-known that the morphology of polymer-supported catalysts is a critical parameter from the point of view of their use under flow conditions [52]. Due to the smaller dimension of the pellets, the stirring of the reactants and the isolation of the product become easier under conventional batch conditions This form of Aquivion PFSA is expected to be more useful in view of our final set of a flow procedure [53]. Since in flow systems the substrate is forced into intimate contact with an excess of the catalyst [52], higher conversions were achieved (93–99%)
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