The production of 5-hydroxymethylfurfural (HMF) from
cellulose
is a crucial step in the production of high-value chemicals and fuels
from renewable cellulosic biomass. In this study, the influences of
the H2O/organic solvent ratio, the type of organic solvents,
the addition of NaCl, and the type and concentration of catalysts
on the catalytic conversion of cellulose into HMF in biphasic systems
were comprehensively studied, and the highest HMF yield of 45.7% was
obtained from cellulose in the H2O–tetrahydrofuran
(THF) biphasic system with Al2(SO4)3 as the catalyst. Further investigation reveals that the excellent
performance of the H2O–THF–Al2(SO4)3 reaction system was ascribed to the
high V
org/V
aque (60/1), high C[Al2(SO4)3]aque (0.38 g/mL), and low C[Al2(SO4)3]org (10–4 g/mL) of the reaction system.
Moreover, the byproduct formed during the conversion of cellulose
in the H2O–THF–Al2(SO4)3 reaction system was characterized by liquid chromatography–mass
spectrometry (LC–MS) and LC–MS2 to detect
considerable initial polymers. One plausible mechanism of glucose
conversion in the H2O–THF biphasic system was proposed
based on the detected compounds.
To reveal the hydrothermal conversion
routes of the biomass-derived
furanic compounds, the soluble products formed during the hydrothermal
conversion of 5-hydroxymethylfurfural (HMF), furfural, and furfuryl
alcohol were analyzed by liquid chromatography–mass spectrometry
(LC–MS) and LC–MS/MS. Multiple carbocyclic compounds
containing hydroxy group and carbonyl group were detected, with a
molecular mass in the range of 154–272 Da and carbon chain
of the length 8–15. The formation of these soluble carbocyclic
compounds was proposed to involve hydrolytic ring-opening of the furanic
ring, intermolecular aldol condensation, intramolecular aldol condensation,
and C–C cleavage reaction. The C–C cleavage reaction
was proposed to occur on the dicarbonyl structure of the formed primary
polymers.
aqueous phase under the reaction temperature, jointly leading to high V org /V aque , high C[Al 2 (SO 4 ) 3 ] aque and low C[Al 2 (SO 4 ) 3 ] org in the biphasic system. All of these results yield the excellent performance of these biphasic systems in the conversion of cellulose into HMF. The addition of CHX into the biphasic system can decrease the solubility of Al 2 (SO 4 ) 3 in the organic phase, thus improving the stability of HMF in the reaction system. The influences of catalyst usage, reaction temperature and time, and cellulose/ solvent ratio were all explored, and a high HMF yield of 71.2% was obtained in the H 2 O-THF-CHX biphasic system with an H 2 O/THF/CHX volume ratio of 3/16/3 under optimized conditions.
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