UTiLIsATION OF A BASIC K-GRAFTED USY ZEOLITE IN catalytic pyrolysis OF Wheat straw TO PRODUCE VALUABLE OXYGENATED COMPOUNDS

Abstract The catalytic properties of K-grafted USY zeolite in fast pyrolysis of acid-washed wheat straw have been investigated using the parent USY sample as a reference. Potassium was incorporated into the zeolite by replacing H+ protons from framework hydroxyl groups with K+ cations. CO2-TPD confirmed the presence of basic sites, with mainly weak-mild strength, in the resulting material. Catalytic tests were performed in a down-flow fixed bed reactor with two furnaces. The thermal zone operated at 550 °C, whereas the temperature of the catalytic bed was varied from 400 to 500 °C. The catalysts were tested at two different catalyst to biomass ratios (C/B = 0.2 and 0.6). The K-USY sample was quite more active in bio-oil* (bio-oil in a water-free basis) conversion and upgrading than the parent zeolite, as denoted by the increased production of gases and the lower oxygen content of the organic liquid phase, although it also suffered higher coke deposition. Sharp changes were observed in the bio-oil* composition when using the K-USY catalyst. In particular, the presence in this material of a high population of weak-mild basic sites favoured the conversion of lignin oligomers and the occurrence of ketone-forming reactions from holocellulose. As a result, phenols and ketones were the main components (with an overall concentration up to 31.5 wt.%) in the bio-oil* obtained over K-USY, which is an interesting result due to their potential use for the preparation of fine chemicals with high-added value.