Abstract
The depolymerization of cellulose to glucose is a challenging reaction and often constitutes a scientific obstacle in the synthesis of downstream bio-based products. Here, we show that cellulose can be selectively depolymerized to glucose by ultrasonic irradiation in water at a high frequency (525 kHz). The concept of this work is based on the generation of H˙ and ˙OH radicals, formed by homolytic dissociation of water inside the cavitation bubbles, which induce the cleavage of the glycosidic bonds. The transfer of radicals on the cellulose particle surfaces prevents the side degradation of released glucose into the bulk solution, allowing maintaining the selectivity to glucose close to 100%. This work is distinguished from previous technologies in that (i) no catalyst is needed, (ii) no external source of heating is required, and (iii) the complete depolymerization of cellulose is achieved in a selective fashion. The addition of specific radical scavengers coupled to different gaseous atmospheres and ˙OH radical dosimetry experiments suggested that H˙ radicals are more likely to be responsible for the depolymerisation of cellulose.
Highlights
The depolymerisation of cellulose[1] to glucose has become an important reaction paving the way to various biobased chemicals such as ethanol, furandicarboxylic acid, caprolactam, sorbitol, levulinic acid, g-valerolactone, among many others.[2]
Being able to selectively depolymerize cellulose with Hc and cOH radicals without side degradation of released glucose into the bulk solution is a challenging scienti c task, which is addressed in this study
We show here that high frequency ultrasound (HFUS) is an alternative technology capable of selectively depolymerizing cellulose to glucose
Summary
The exploration of alternative technologies capable of selectively depolymerizing cellulose to glucose with a high efficiency is still an open scienti c question.[9]. Inspired by our previous works on NTAP,[13] we conceived that these in situ produced radicals should theoretically induce the cleavage of the glycosidic bonds of cellulose.[16] Being able to selectively depolymerize cellulose with Hc and cOH radicals without side degradation of released glucose into the bulk solution is a challenging scienti c task, which is addressed in this study. The implosion of cavitation bubbles is very asymmetric and generates high-speed jets of liquid towards the surface, a good mean to concentrate radicals on a particle.[17] Applied to cellulose, this physical principle should be an efficient mean to control the reaction selectivity by concentrating radicals on the cellulose particle surfaces, preventing side reactions of released glucose into the bulk solution
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