Kinematic Modeling of Mechanocatalytic Depolymerization of α‐Cellulose and Beechwood

Abstract

Mechanocatalytic depolymerization of lignocellulose presents a promising method for the solid-state transformation of acidified raw biomass into water-soluble products (WSPs). However, the mechanisms underlining the utilization of mechanical forces in the depolymerization are poorly understood. A kinematic model of the milling process is applied to assess the energy dose transferred to cellulose during its mechanocatalytic depolymerization under varied conditions (rotational speed, milling time, ball size, and substrate loading). The data set is compared to the apparent energy dose calculated from the kinematic model and reveals key features of the mechanocatalytic process. At low energy doses, a rapid rise in the WSP yield associated with the apparent energy dose is observed. However, at a higher energy dose obtained by extended milling duration or high milling speeds, the formation of a substrate cake layer on the mill vials appear to buffer the mechanical forces, preventing full cellulose conversion into WSPs. By contrast, for beechwood, there exists a good linear dependence between the WSP yield and the energy dose provided to the substrate over the entire range of WSP yields. As the formation of a substrate cake in depolymerization of beechwood is less severe than that for the cellulose experiments, the current results verify the hypothesis regarding the negative effect of a substrate layer formed on the mill vials upon the depolymerization process. Overall, the current findings provide valuable insight into relationships between the energy dose and the extent of cellulose depolymerization effected by the mechanocatalytic process.

The Impact of Salts Formed by the Neutralisation of (Ligno)Cellulose Hydrolysates on the Hydrogenation of Sugars

“…Considering that only strong acids (HCl, H 2 SO 4 , HNO 3 ) are suitable as catalysts for the mechanocatalytic depolymerisation of lignocellulosic raw materials and that NaOH, NH 4 OH and KOH constitute plausible choices for the work‐up of sugars streams for the heterogeneously catalysed downstream processing, the effect of NaCl, NH 4 Cl, KCl, Na 2 SO 4 , (NH 4 ) 2 SO 4 , K 2 SO 4 , NaNO 3 , NH 4 NO 3 or KNO 3 upon the catalytic performance of Ru/C in recycling experiments was assessed. Additionally, reactions were performed in the absence of salts, but in the presence of mineral acids (18 mmol L −1 HCl, H 2 SO 4 or HNO 3 ).…”

“…The difficulties created by the strong adsorption of furfural and HMF on Ru surface has been recognised in the recent literature of hydrodeoxygenation of pyrolysis oils . Considering that furfurals will invariably be formed in the acid‐catalysed saccharification of lignocellulose, we chose to test activated carbon in the purification of the hydrolysates. From aqueous solutions, to remove 95 % of both HMF and furfural at an initial concentration of 10 mmol L −1 , it suffices to stir the solution in the presence of activated carbon (57 mg) for 10 min.…”

“…After 30 min stirring, the solvent was removed under reduced pressure. The obtained acid‐impregnated solid substrate (1.00 g) and 5 milling balls (stainless steel, 5 mm diameter) were filled into a planetary ball mill (Fritsch Pulverisette 7) at 800 rpm for 2 h, with 10 min break after 30 min milling intervals resulting in water‐soluble oligosaccharides (WSO), or water‐soluble products from beechwood, as reported elsewhere …”

Mechanochemie gasförmiger Reaktanten

“…[19] Als ein Ergebnis des schnellen und effizienten mechanischen Mischens bietet die Aktivierung durch Kugelmahlen zusätzliche Vorteile,w ie die Mçglichkeit eine der grçßten Herausforderungender chemischen Synthese zu überwinden:d ie Unlçslichkeit von Reagenzien im Reaktionsmedium. Dann wird der Mahlbecher entweder rotiert oder geschüttelt, um den Inhalt einem kontinuierlichen, mechanischen Einschlag oder durch die Kugeln ausgeübten tangentialen Kräften zu unterziehen (Abbildung 1).…”

“…Daher stand ein Verständnis und die Kontrolle der thermischen Aktivierung durch Kugelmahlen im Fokus der jüngsten Arbeiten auf diesem Gebiet. [19]. [ Abbildung 1.…”