Abstract
Cellulose is the single largest component of lignocellulosic biomass and is an attractive feedstock for a wide variety of renewable platform chemicals and biofuels, providing an alternative to petrochemicals and petrofuels. This potential is currently limited by the existing methods of transforming this poorly soluble polymer into useful chemical building blocks, such as 5-hydroxymethylfurfural (HMF). Ionic liquids have been used successfully to separate cellulose from the other components of lignocellulosic biomass and so the use of the same medium for the challenging transformation of cellulose into HMF would be highly attractive for the development of the biorefinery concept. In this report, ionic liquids based on 1-butyl-3-methylimidazolium cations [C4C1im]+ with Lewis basic (X = Cl−) and Brønsted acidic (X = HSO4−) anions were used to investigate the direct catalytic transformation of cellulose to HMF. Variables probed included the composition of the ionic liquid medium, the metal catalyst, and the reaction conditions (temperature, substrate concentration). Lowering the cellulose loading and optimising the temperature achieved a 58% HMF yield after only one hour at 150 °C using a 7 mol % loading of the CrCl3 catalyst. This compares favourably with current literature procedures requiring much longer reactions times or approaches that are difficult to scale such as microwave irradiation.
Highlights
The biorefinery concept requires routes that are efficient in terms of both materials and energy for the conversion of biomass to useful platform chemicals [1,2]
Our previous study on monosaccharides achieved a yield of 96% HMF from fructose and 90%
In order to probe this, mixtures of ionic liquids were tested for the conversion of cellulose to HMF but very poor (5%) HMF yields were detected (Table 1, Entry 7). These results suggested that the presence of [C4 C1 im][HSO4 ] lowers the conversion of cellulose to HMF, and strongly suggests that the [HSO4 ]− anion inhibits the glucose–fructose interconversion, as was already verified in our previous research on lowers the conversion of cellulose to HMF, and strongly suggests that the [HSO4]− anion glucose to HMF
Summary
The biorefinery concept requires routes that are efficient in terms of both materials and energy for the conversion of biomass to useful platform chemicals [1,2]. The processing of lignocellulosics requires energetically demanding pretreatment routes to separate lignin from cellulose [3], and subsequent cellulosic sugar and biofuel production relies on slow biocatalytic transformations (enzymatic saccharification and microbial fermentation) [4]. Cellulose and hemicellulose make up the largest part of lignocellulosic biomass and account for. Many recent papers have reviewed the use of ionic liquids for accessing the cellulose in lignocellulosic biomass; these articles focus mainly on the advantages of ionic liquids in the isolation of cellulose compared with traditional methods [6,7,8,9,10,11,12]. It has been shown that ionic liquids can decrystallise the cellulose portion of biomass and disrupt linkages
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