Abstract:Levulinate ester has been identified as a promising renewable fuel additive and platform chemical. Here, the use of a wide range of common metal salts as acid catalysts for catalytic upgrading of biomass-derived furfuryl alcohol to butyl levulinate was explored by conventional heating. Both alkali and alkaline earth metal chlorides did not lead effectively to the conversion of furfuryl alcohol, while several transition metal chlorides (CrCl 3 , FeCl 3 , and CuCl 2 ) and AlCl 3 exhibited catalytic activity for the synthesis of butyl levulinate. For their sulfates (Cr(III), Fe(III), Cu(II), and Al(III)), the catalytic activity was low. The reaction performance was correlated with the Brønsted acidity of the reaction system derived from the hydrolysis/alcoholysis of cations, but was more dependent on the Lewis acidity from the metal salts. Among these investigated metal salts, CuCl 2 was found to be uniquely effective, leading to the conversion of furfuryl alcohol to butyl levulinate with an optimized yield of 95%. Moreover, CuCl 2 could be recovered efficiently from the resulting reaction mixture and remained with almost unchanged catalytic activity in multiple recycling runs.
Abstract:The use of common metal salts as catalysts for 5-ethoxymethylfurfural (EMF) synthesis from carbohydrate transformation was performed. Initial screening suggested AlCl 3 as an efficient catalyst for EMF synthesis (45.0%) from fructose at 140 • C. Interestingly, CuSO 4 and Fe 2 (SO 4 ) 3 were found to yield comparable EMF at lower temperature of 110 to 120 • C, and high yields of ethyl levulinate (65.4-71.8%) were obtained at 150 • C. However, these sulfate salts were inactive in EMF synthesis from glucose and the major product was ethyl glucoside with around 80% yield, whereas EMF of 15.2% yield could be produced from glucose using CrCl 3 . The conversion of sucrose followed the accumulation of the reaction pathways of fructose and glucose, and a moderate yield of EMF could be achieved.
To enhance the yield of alkyl levulinates, a mixed-acid catalyst system consisting of CrCl3 and H3PO4 was investigated for the transformation of furfuryl alcohol (FA). The CrCl3−H3PO4 system exhibited a positive synergistic catalytic activity for the synthesis of alkyl levulinates, which was especially obvious for n-butyl levulinate (BL) synthesis. The strongest synergic effect of mixed-acid system for BL production was achieved at the CrCl3 molar ratio of 0.3 (based on total moles of CrCl3 and H3PO4). Furthermore, the mixed-acid systems consisting of Cr-salts combined with H3PO4 and its salts in catalyzing FA conversion to BL were evaluated, and the evolution process of FA to produce BL was explored in the presence of CrCl3−H3PO4, sole CrCl3, and sole H3PO4. A possible synergistic catalytic pathway of CrCl3 combined with H3PO4 was proposed. Finally, the key process variables were examined. Under optimal conditions, a high BL yield of 95% was achieved from 99% FA conversion catalyzed by the synergy of CrCl3 and H3PO4.
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