Abstract
Alkyl levulinates (ALs) represent outstanding bio-fuels and strategic bio-products within the context of the marketing of levulinic acid derivatives. However, their synthesis by acid-catalyzed esterification of pure levulinic acid, or by acid-catalyzed alcoholysis of furfuryl alcohol, although relatively simple, is still economically disadvantageous, due to the high costs of the pure precursors. The direct one-pot alcoholysis of model C6 carbohydrates and raw biomass represents an alternative approach for the one-step synthesis of ALs. In order to promote the market for these bio-products and, concurrently, the immediate development of new applications, it is necessary to speed up the intensification of their production processes, and this important achievement is onlypossible by using low-cost or, even better, waste biomasses, as starting feedstocks. This review provides an overview of the most recent and promising advances on the one-pot production of ALs from model C6 carbohydrates and real biomasses, in the presence of homogeneous or heterogeneous acid catalysts. The use of model C6 carbohydrates allows for the identification of the best obtainable ALs yields, resulting in being strategic for the development of new smart catalysts, whose chemical properties must be properly tuned, taking into account the involved reaction mechanism. On the other hand, the transition to the real biomass now represents a necessary choice for allowing the next ALs production on a larger scale. The improvement of the available synthetic strategies, the use of raw materials and the development of new applications for ALs will contribute to develop more intensified, greener, and sustainable processes.
Highlights
Levulinic acid (4-oxopentanoic acid, gamma ketovaleric acid or 3-acetylpropionic acid) is a linear C5-alkyl carbon chain, which is considered to be one of the top 12 most promising chemicals derived from biomass [1,2,3,4]
In order to enhance their production on a larger industrial scale, it is necessary to start directly from cheap precursors, such as C6 carbohydrates and, even better, lignocellulosic or waste biomasses, rather than from more expensive and pure levulinic acid
This review has been focused on the use of model C6 carbohydrates and real biomasses in the direct alcoholysis to give different levulinates, dealing with the most interesting and recent advances in catalysis
Summary
Levulinic acid (4-oxopentanoic acid, gamma ketovaleric acid or 3-acetylpropionic acid) is a linear C5-alkyl carbon chain, which is considered to be one of the top 12 most promising chemicals derived from biomass [1,2,3,4]. The choice of this class of levulinic acid derivatives as starting feedstock for further up-grade is very attractive, due to the moderate reactivity of the carboxylate group, leading to remarkable advantages for the selectivity towards the final product(s) of interest. Up to now, the market attention has mainly been focused on ethyl levulinate (EL) production, which is a valuable fuel-additive and a potential biomass-derived platform molecule [15], having a global market size of $ 10.5 Million in 2019, favorably increasing up to about $ 11.8 Million by 2022, with an estimated growth rate of 3.6% [16] In this context, other independent economic evaluations have confirmed a promising economic outlook for the EL production [17], but only if low-cost or, even better, waste biomasses, will be used as starting feedstocks [2]
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