Molecular Oxygen-Promoted Synthesis of Methyl Levulinate from 5-Hydroxymethylfurfural

Abstract

Methyl levulinate (ML) is a biobased platform molecule, which has versatile applications in fine chemical synthesis and food additives. However, during the ML production, one of the main barriers is that humins are usually cogenerated, which leads to poor reaction efficiency and catalyst deactivation. The following findings are herein reported for the first time: in a catalytic system with H-beta25, molecular oxygen could act as both a humins cleaner and a reaction accelerator for the synthesis of value-added ML from 5-hydroxymethylfurfural (HMF) or furfuryl alcohol (FA). The reaction efficiency and the catalyst reusability were significantly improved in the presence of oxygen. Besides, the effects of different reaction parameters as well as catalysts have been investigated. The mechanism of ML formation from HMF in the presence of O 2 and the role of O 2 in humins removal were also proposed.

Production of levulinic acid and alkyl levulinates: a process insight

“…Also in this case, a dedicated sustainability assessment should be carried out to quantify the comparison among the routes. However, less explored than furan and cellulose as feedstock for the synthesis of levulinates, 125 solvolysis of HMF has been tested with various acid-catalysts, mainly heterogeneous (Table 4), such as zeolites, 128,129 zirconia, sulfated zirconia, mesoporous silica, 129 heteropolyacid, 126 ion exchange resins, 130 and ionic liquids. 131 Even though in the presence of a complete HMF conversion, literature experiment data measure low yields of levulinic esters and acid (low intensified process).…”

“…Neves and her group 135 considered that due to a higher efficient theoretical carbon atom for the FA-to-alkyl levulinate system than for the HMF-to-alkyl levulinate, and lower production of by-products. 125 Humins are also inevitably produced from the degradation of HMF and furfural in an acidic environment, leading to limitations on the catalytic activity and efficiency of downstream processes 128,136 (negative effect on "Reduce Derivatives"). In addition to the use of special solvents to ensure its complete solubilization and prevent fouling and deactivation of the catalyst 137 (negative effect on "Safer Solvents and Auxiliaries"), oxygen has been tested as a possible suppressor of the formation of humins and promoter of the selectivity to desired products (positive effect on "Catalysis").…”

“…Wang and his group studied the production of methyl levulinate from HMF, catalyzed by zeolite, in the presence of oxygen; it resulted in a phenomenon of humins removal via oxidative species formed at high temperatures (up to 150 °C), compared to nitrogen in the same conditions. 128 Furthermore, the employment of inefficient technologies might lead to hotspots or/and non-uniformity of reacting temperature, facilitating the formation of by-products, with effects on "Inherently Safer Chemistry for Accident Prevention". Microwave-assisted heating has several advantages in rapid and homogeneous heating, reduced time-contact and higher product yield, 138 being promising from "Inherently Safer Chemistry for Accident Prevention" point of view.…”

“…140,142,148,149 The production of humins is one of the significant limitations in the conversion to LEs by furfural and HMF, leading to the loss of substrate, catalyst fouling, deactivation and problematic separation post-treatments. 128 Furfural can be converted into levulinic acid and esters via multiple steps (Fig. 6), involving the partial hydrogenation of furfural to furfuryl alcohol in gas or liquid phase and following by the acid-catalyzed conversion of furfuryl alcohol into levulinic acid or ester in the liquid phase, respectively aqueous or alcoholic.…”

Engineering Bacillus Subtilis for the production of High Fructose Syrup: Opportunities and Prospects

“…HMF is produced by dehydration of fructose and induced by acid or metal catalyst [61]. Besides, HFS can be used as raw material for valuable biobased fine chemicals such as biofuels, green solvents, and lubricants, plastics [64].…”