Levulinic aldehyde acetal

All resins initially adsorbed furan aldehydes and phenols (Fig. 1). In some cases, a subsequent release of adsorbed furan aldehydes and phenols was observed, resulting in concentrations slightly over the concentrations in untreated hydrolysate (Fig. 1). Levulinic, acetic, and formic acid initially adsorbed well to all resins. The trapped levulinic and acetic acid were released before formic acid. 

Besides converting wet biomass into hydrochar, the HTC process is also capable of coproducing chemicals, which include phenolic compounds, 2,5-HMF, and aldehydes (acetic, lactic, propenoic, levulinic, and formic acids) that can potentially be used in biorefineries (Axelsson et al., 2012 Hoekman et al., 2012 Oladeji et al., 2015). The formation and concentration of these chemicals can be controlled by adjusting the HTC process conditions (Libra et al., 2011 Xiao et al., 2012), such as temperature, pressure, and residence time. Therefore the HTC process could be a useful part of biological and thermochemical biorefineries, processing wet residues, and coproducing chemicals and hydrochar. 

The breakdown of furan aldehydes leads to the formation of formic and levulinic acid. Moreover, acetic acid is formed during the degradation of hemicellulose. Partial breakdown of lignin can generate a variety of phenolic compounds (23), which also inhibit S. cerevisiae (14,15). In contrast to furan aldehydes and aliphatic acids, the toxic effect of specific phenolic compounds is highly variable (15). Different raw materials and different approaches to prepare lignocellulose hydrolysates will result in different concentrations of the fermentation inhibitors (16,17). 

Isopropyl hexanoate Isopropyl isobutyrate Isopropyl isovalerate Isopropyl myristate p-Isopropylphenylacetaldehyde Isopropyl phenylacetate 3-(p-lsopropylphenyl) propionaldehyde Isopropyl propionate Isopropyl tiglate Isopulegol Isopulegone Isopulegyl acetate Isoquinoline Isosafrole Isovaleraldehyde Isovaleric acid cis-Jasmone Laurie aldehyde Lauryl acetate Lauryl alcohol Lepidine Levulinic acid d-Limonene dl-Limonene l-Limonene... 

The first step, ring opening, is a characteristic reaction of furan derivatives. The final step is an intermolecular oxidation-reduction reaction. Evidence for this mechanism (71) is given by the isolation under similar conditions of the acetal derivative of the intermediate five-carbon keto aldehyde, and by the high yield of levulinic acid produced from it by the action of acids. Yields as high as 80 % of levulinic acid have been obtained from 5-hy-droxymethylfurfural. Furthermore, radioactive formic acid is derived by this reaction from D-glucose-l-C whereas the accompanying levulinic acid is devoid of activity (7 ). 

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