Agenda de l'ENS de Lyon

Second generation biomass is mainly composed of saccharides building units that are a valuable renewable feedstock to produce high added-value chemicals. In order to obtain separate streams of each sugar (xylose, glucose, ...), the incorporation of a separation step is necessary in a biorefinery after lignocellulose fractionation. This work aims at studying the separation of lignocellulosic monosaccharides molecules (mainly glucose and xylose) by adsorption, using zeolites and understanding the mechanisms responsible for this separation. Faujasite-type zeolites NaX (Si/Al = 1.2) and NaY (Si/Al = 2.6) were exchanged with K⁺, Ca²⁺, Sr²⁺, and Ba²⁺ and the adsorbents were characterized. Breakthrough experiments with a binary feed solution of glucose and xylose showed that the nature of the counterion and the Si/Al ratio have a large influence on the selectivity. BaX and BaY are good candidates for the separation where BaX is selective to xylose and BaY to glucose. The temperature did not impact the monocomponent adsorption isotherms. The addition of ethanol to the feed mixture (0 to 50 % wt) increased the adsorbed quantities of both sugars in BaX and BaY. The presence of ethanol in the feed changed the selectivities obtained from aqueous solutions. Density Functional Theory (DFT) calculations were performed on periodic systems (code VASP) of zeolites models exchanged with the same cations used in the experimental conditions. Several adsorption modes of glucose and xylose were characterized.