Slow pyrolysis of xylan as pentose model compound for hardwood hemicellulose: A study of the catalytic effect of Na ions

About the Influence of Doping Approach on the Alkali Metal Catalyzed Slow Pyrolysis of Xylan

“…Experiments on beechwood xylan under slow pyrolysis conditions confirmed the role of AAEMs in favouring both char and gas productions but highlighted that dehydration reactions are depressed, while reactions leading to the formation of light oxygenates via ring scission are preferred [20]. Moreover, recent works on xylan doped through a cationic exchange approach with controlled quantities of potassium or sodium ions after a complete demineralization [21,22] indicated that both K + and Na + favoured ring opening, rearrangement, and rehydration reactions leading to the production of lowmolecular-weight compounds [21,22]. e same authors highlighted, indeed, that the production of CO 2 is enhanced to a larger extent and its production in presence of metal ions is shifted at lower temperature confirming that the effect of alkali ions on ring scission reactions becomes more relevant with the increase in the ion concentration [21,22].…”

“…Xylan-based samples were pyrolysed at 7 K/min up to 973 K in a lab-scale reactor described in detail elsewhere [8,16,17,[20][21][22].…”

“…A wide literature is available on the effect of AAEMs on the pyrolysis of biomasses and cellulose [10][11][12][13][14][15][16][17], whereas only few works reported about the effect of metals on hemicellulose pyrolysis [18][19][20][21][22]. Inherent alkali and alkaline earth metallic (AAEM) species are known to affect both the temperature and the mechanism of biomass thermal decomposition [23][24][25].…”

“…Moreover, recent works on xylan doped through a cationic exchange approach with controlled quantities of potassium or sodium ions after a complete demineralization [21,22] indicated that both K + and Na + favoured ring opening, rearrangement, and rehydration reactions leading to the production of lowmolecular-weight compounds [21,22]. e same authors highlighted, indeed, that the production of CO 2 is enhanced to a larger extent and its production in presence of metal ions is shifted at lower temperature confirming that the effect of alkali ions on ring scission reactions becomes more relevant with the increase in the ion concentration [21,22]. e comprehension of the effects of minerals on xylan pyrolysis is also complicated by the presence in the xylan structure of carboxylic acids such as 4-O-MeGlcA, whose form (uronate vs. uronic acid form) alters the thermal behaviour of the polysaccharide [32].…”

“…is approach is based on a weak interaction between AAEMs and the feedstock and it works quite well with biomasses, lignin, and neutral polysaccharides as cellulose [10][11][12][13][14][15][16][17]. e results are not so obvious for polysaccharides bearing acidic functionalities as xylan, considered as representative of hemicellulose, since a tight interaction between AAEMs and the acidic moieties in the polysaccharides (uronates in the case of xylan) seems required [21,22,32].…”