Valorisation of a lignin-rich residue via catalytic pyrolysis over ZrO2/ZSM-5 technical catalyst

Abstract

The thermochemical valorisation of a lignin-rich residue has been investigated by thermal and catalytic pyrolysis. The catalyst, based on nanocrystalline ZSM-5, has been modified with ZrO2 and agglomerated with attapulgite (ZrO2/n-ZSM-5-ATP). Firstly, the effect of the temperature in thermal pyrolysis has been explored, establishing 600 °C as the optimal temperature to thermally decompose the lignin-rich feedstock, yielding 53.7 wt% of bio-oil* (water-free bio-oil). In contrast, the incorporation of the technical catalyst using an ex-situ reactor, as well as the increase in the catalyst/lignin ratio, strongly affected the mass and energy yields of products. Thus, a significant decrease of the bio-oil* yield was observed, although its composition was significantly improved, with a reduction of the oxygen content from 30 to 10 wt%. Comparing the parent zeolite with the technical catalyst, the latter afforded a bio-oil* production with lower oxygen content, a higher share of aromatics and lower concentration of heavy species (non-detected by GC–MS). In particular, the technical catalyst allows increasing the concentration in bio-oil* of GC–MS detected compounds, which are the most valuable for commercial applications, by a factor of 2.5 regarding the thermal test. Interestingly, these remarkable results are obtained despite working under mild catalytic conditions (450 °C, catalyst/lignin = 0.2 g/g).