Pretreatment of microcrystalline cellulose by ultrasounds: effect of particle size in the heterogeneously-catalyzed hydrolysis of cellulose to glucose
Résumé
In this paper, we show that ultrasound technology is a powerful tool for enhancing the reactivity of microcrystalline cellulose (MCC) in the presence of a solid acid catalyst. The effects of sonication on the MCC structure were studied using different characterization methods. In particular we found that pretreatment of cellulose by ultrasounds resulted in a drastic decrease of MCC particle size (<0.4 μm), leading to a better interaction with solid catalyst surfaces. As a result, the subsequent hydrolysis of sonicated MCC over a recyclable sulfonated carbon solid catalyst was found to be highly selective in producing water-soluble reducing sugars. Using such a pretreatment, glucose was produced with similar yields (up to 42%) to those obtained using conventional pretreatment methods such as ball-milling or ionic liquids, thus showing the efficiency of such a method. From the viewpoint of green chemistry, the pretreatment by ultrasound has noticeable advantages such as (1) the use of water as a unique solvent, (2) short reaction time (<3 h), (3) no need of external source of heating (ensured by dissipated energy from sonication) and (4) no polluting effluent involved or produced.