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 (CrCl3, FeCl3, and CuCl2) and AlCl3 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, CuCl2 was found to be uniquely effective, leading to the conversion of furfuryl alcohol to butyl levulinate with an optimized yield of 95%. Moreover, CuCl2 could be recovered efficiently from the resulting reaction mixture and remained with almost unchanged catalytic activity in multiple recycling runs.
Highlights
Given the gradual depletion of fossil fuel resources and rising environmental concerns, increasing effort has been devoted to the development of alternative fuels and chemicals from abundant and renewable biomass resources [1,2,3,4]
The effect of a wide range of various metal chlorides on the catalytic transformation of furfuryl alcohol to butyl levulinate in n-butanol was screened at 110 ◦ C after 60 min reaction time using a 0.3 mol/L furfuryl alcohol solution and a 0.02 mol/L solution of metal chloride as the catalyst
It can be seen that all alkali and alkaline earth metal chlorides did not lead effectively to the conversion of furfuryl alcohol, and there was no obvious difference with the blank
Summary
Given the gradual depletion of fossil fuel resources and rising environmental concerns, increasing effort has been devoted to the development of alternative fuels and chemicals from abundant and renewable biomass resources [1,2,3,4]. Acidic ionic liquids were found to be efficient and reusable catalysts for the alcoholysis of furfuryl alcohol to levulinate esters [6,25]. Al2 (SO4 ) was highly active in the catalytic synthesis of methyl levulinate from carbohydrates in methanol, giving a 64% yield of methyl levulinate from glucose [28] These metal salts are earth-abundant and commercially available, providing inexpensive and environmentally benign catalyst sources for biomass conversion. The use of a wide range of metal salts as acid catalysts for the alcoholysis of furfuryl alcohol to butyl levulinate with conventional heating was evaluated. In the case of their corresponding sulfates, the catalytic activity dropped markedly Among these investigated metal salts, CuCl2 emerged as a preferred catalyst supplier with unique selectivity for the synthesis of butyl levulinate. The reusability of the CuCl2 catalyst was performed to demonstrate the versatility of the catalytic strategy
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