The catalytic upgrading of sugar derivatives into valuable building blocks represents an extremely important challenge intrinsic to the attempts to establish a green economy. However, the significance of separation and purification are often relegated to a marginal role or overlooked completely despite this aspect being critical for potential scale up. It is well established that the synthesis of 5-hydroxymethylfurfural (HMF) from sugars in ionic liquid media is a valuable, sustainable and high-yielding chemical pathway, but product separation has always remained an unresolved issue. In this contribution, the separation of HMF and three of its derivatives, 2,5diformylfuran (DFF), 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA) from ionic liquids is analyzed. Various ionic liquids are screened in order to obtain an optimal separation process. The extraction of HMF is studied from the hydrophobic methyltrioctylammonium ionic liquids with water, obtaining a favorable partition coefficient for the aqueous phase. In contrast, its derivatives, DFF, FFCA and FDCA, can be easily separated by phase separation. DFF retains its sublimation attributes in the ionic liquid and can be readily separated in quantitative yields in high purity. This behavior is observed in ionic liquids but is not achievable in common organic solvents. FDCA and FFCA are separated by water addition and precipitation. It is found that less water is required for the precipitation of these compounds compared to dimethylsulfoxide (DMSO), which is a frequently employed reaction medium for their generation. The energy balance for regeneration of the ionic liquid after water addition is estimated using the enterprise ionic liquids database ILUAM. This study provides a set of solvent design guidelines for the selective synthesis, isolation and purification of these compounds in ionic liquids, aiding future reaction design.
Process simulations allow the evaluation of the emissions and selling price for the production of the key monomer FDCA based on different feedstocks and solvent systems, alongside considerations of safety and current process development.
The noncoordinating ionic liquid [bmim][OTf] (bmim=1‐butyl‐3‐methylimidazolium) is an effective and versatile solvent for the high‐yield dehydration of fructose to the platform chemical 5‐hydroxymethylfurfural (HMF) over short reaction times. In contrast to prior studies in which low yields were obtained for this transformation in ionic liquids (ILs) with noncoordinating anions, this contribution reveals that the water content is an essential parameter for an efficient reaction in ILs. Achieving the optimum amount of water can increase the yield dramatically by regulating the acidity of the catalyst and partially suppressing the side reaction caused by self‐condensation of HMF. Using acid catalysis in [bmim][OTf] with 3.5 % water content, yields above 80 % can be achieved at 100 °C in only 10 min, even at high (14 %) fructose loading. These results also suggest that [bmim][OTf] represents a superior medium for solvent extraction of HMF compared to halide‐based ILs, allowing the option of isolation or further valorization of the HMF formed.
The
study focused on the dual role of water as a cosolvent and
an antisolvent in the [HSO4]-based protic ionic liquid
biomass fractionation process using N,N,N-dimethylbutylammonium hydrogen sulfate, [DMBA][HSO4]. The effectiveness of biomass fractionation using [DMBA][HSO4] mixed with different concentrations of water of conventional
biorefinery feedstocks (Miscanthus and
pine softwood) and nonconventional low-cost lignocellulosic biomass
waste (treated timber and postconsumer waste wood) was investigated.
The pulp composition, lignin extraction, and enzymatic hydrolysis
of the cellulose pulp were analyzed after pretreatment at 170 °C
for 30 min. We showed that it is possible to reduce the ionic liquid
use in the process by increasing the water concentration as a cosolvent
while still maintaining the effective biomass deconstruction forMiscanthus and postconsumer waste wood. However,
softwood biomass showed higher resistance to fractionation at higher
water concentrations in the pretreatment medium. We also investigated
the impact of reducing the amount of water used as an antisolvent
for lignin precipitation in terms of lignin yields and properties.
The robust performance of the fractionation process at the optimized
antisolvent use was demonstrated using the challenging feedstock pine
softwood over six pretreatment cycles. Finally, we demonstrated the
significance of evaluating water use for the energy requirements of
the process, particularly in the ionic liquid regeneration step, achieving
a 65% energy reduction.
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