Application of catalysts for obtaining 1,6-anhydrosaccharides from cellulose and wood by fast pyrolysis

The present work is devoted to the estimation of the effect of phosphoric acid and Fe³⁺ ions on the 1,6-anhydrosaccharides levoglucosan (LG) and levoglucosenone (LGone) contents in volatile products obtained from wood and microcrystalline cellulose by analytical pyrolysis. It was shown that the LG and LGone contents can be influenced by the pre-treatment. Iron was introduced into the biomass either by soaking in iron(III) sulfate solution alone or in the presence of ammonium, a treatment, in the course of which iron oxihydroxide is formed. It was demonstrated that a previous decationization of wood plays an important role for the subsequent results of Fe³⁺ ion treatment.The 1,6-anhydrosaccharides content in volatile products and the ratio of LG/LGone is governed by the phosphoric acid concentration. The same is true for cellulose soaked by iron sulfate: at higher concentration, the LGone content increases and the LG/LGone ratio decreases. The mechanism of the action of iron ions depends on the iron species formed upon the cellulose-containing raw materials pre-treatment procedures with iron sulfate. Upon pyrolysis, the adsorbed iron sulfate increases the amount of both LG and LGone in volatile products through the acidic catalysis mechanism owing to sulfate anions activity. The pre-treatment by the ion-exchange method could be considered as an efficient technique for obtaining the biooil containing levoglucosan in high content: 44.8% from cellulose and 27.3% from wood. The results are interpreted based on the quantitative evaluation of the pyrograms and the ESR spectra of the treated wood.