Abstract
Hydroxymethylation of 2-furaldehyde (furfural) toward 5-hydroxymethyl-2-furaldehyde (HMF) was examined in this work among various zeolites with an aqueous formaldehyde as a reagent in a batch and a flow reactor system. It was found that the zeolite beta gave high activity and good reusability with calcination treatment before each run for the target reaction in the batch system. The unique stability of the HMF yield in the liquid-flow system was also observed only in the case of zeolite beta. The effect of the SiO2/Al2O3 ratio in the zeolite beta suggested that hydrophobicity would be an important factor in faster hydroxymethylation with an aqueous formaldehyde reagent. The highest turnover frequency (TOF) for HMF production was found to be 2.4 h−1 in the case of zeolite beta with SiO2/Al2O3 = 440 in the batch reactor system. An approximately 30% yield for HMF was achieved under optimum conditions for zeolite beta catalysts.
Highlights
Catalytic biomass transformations towards highly value-added chemicals and materials have been an attractive research area in recent decades in relation to constructing a green and sustainable future society [1,2,3,4,5,6]
To resolve this weakness of furfural, we have recently examined the direct hydroxymethylation of furfural and its derivatives (C5) with an aqueous formaldehyde reagent to produce the corresponding
Four types of typical zeolites and normal SiO2 -Al2 O3 were tentatively compared with regard to their reactivity for the hydroxymethylation of furfural towards HMF in a batch reactor system and a flow reactor system
Summary
Catalytic biomass transformations towards highly value-added chemicals and materials have been an attractive research area in recent decades in relation to constructing a green and sustainable future society [1,2,3,4,5,6]. 5-hydroxymethyl-2-furaldehyde (HMF) is the most important furaldehyde: it possesses two functionalities of formyl and hydroxyl groups on a furan ring at the second and fifth positions and this character enables various successive transformations to afford 2,5-furandicarboxylic acid [7,8], 2,5-diformylfuran [9,10], 2,5-bis(hydroxymethyl)furan (BHMF) [11,12], 2,5-dimethylfuran [13,14,15], 5-hydroxymethylfurfurylamine (HMFA) [16], 1,6-hexanediol [17], levulinic acid [18,19], aldol-adducts [20], and so on [21,22,23]. The structural character of furfural, a formyl group linked on a furan ring at the second position, decreases its potential as a starting material in comparison with HMF
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