Catalytic valorisation of the effluents generated during the defibrillation process of cellulose from almond hulls: A holistic zero-waste biorefinery approach

5 figures, 7 tables.-- Supplementary information available.
The acid-free hydrothermal microwave–assisted selective scissoring (Hymass concept) of cellulosic substrates is gaining keen interest in the field of materials science. Besides, implementing catalytic methodologies to upgrade side streams produced during this process could contribute to better, holistic utilisation of the starting feedstock. This work depicts a zero-waste biorefinery concept based on cellulose defibrillation from almond hulls using various hydrotreatment technologies (hydrogenation and hydrodeoxygenation) for downstream processing on a ruthenium catalyst. Therein, the hemicellulose separated from the biomass preconditioning step was converted into sugar alcohols and/or marketable polyols with a relatively high yield (47.4%) by hydrolytic hydrogenation (437 K, 3h, 5.0 MPa H2). Meanwhile, a family of bioactive compounds (3-hydroxypyridines) could be directly extracted from the hydrolysate stream derived from microwave digestion, along with an energy carrier that was chemically stabilised (503 K, 60 min, 4.0 MPa H2) to obtain fuel additives (diethyl succinic acid, DES) and/or fuel intermediates.
The authors are grateful for the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO, Project ENE2017-83854-R) and the I+D+i project PID2020-115053RB-I00, funded by MCIN/AEI/10.13039/501100011033. J.R. is grateful to the Spanish Ministry of Science, Innovation and Universities for the Juan de la Cierva Incorporación (JdC-I) fellowship (Grant Number: IJC2018-037110-I) awarded.