The deterioration of bio-oil and catalyst during the catalytic upgrading of biomass pyrolysis volatiles

Abstract

ABSTRACT The tin (Sn)-modified HZSM-5 was employed to upgrade biomass pyrolysis volatiles to prepare bio-oil, and the deterioration of bio-oil and catalyst was focused. A new parameter indicating the physicochemical properties was defined as the comprehensive fuel-grade index (CFI). The catalyst initially demonstrated the better performance to transform oxygen-containing organics to hydrocarbons; consequently, the bio-oil had a higher CFI value. The fresh catalyst produced 33.43% of bio-oil with the higher hydrocarbon content of 41.60%, and the proportions of monocyclic aromatic hydrocarbons (MAHs) and light aliphatic hydrocarbons (LAHs) reached 74.59% and 20.02%, respectively. However, with the extension of catalyst using-time, the obvious decrease of hydrocarbons caused the significant decrease of CFI. Furthermore, the cracking and reforming diffusion performance supported by the acid and textural properties of the catalyst deteriorated severely, which contributed to the proportion increase of polycyclic aromatic hydrocarbons (PAHs). The decrease of the acid and textural properties were attributed to the coke generated and deposited into the pores and on the surface of the catalyst. The deposited cokes could be divided into two types including semihydrogenated coke and carbonaceous coke, and the former was the main one. The carbonaceous coke was formed in the initial stage of catalytic reaction, gradually inducing more precursors to cover active sites and block pores, and then generated more semihydrogenated coke, eventually causing the catalyst performance deterioration. This study provided an insight for improving sustainability in terms of understanding process deterioration.