Bio-BTX production from the shape selective catalytic fast pyrolysis of lignin using different zeolite catalysts: Relevance between the chemical structure and the yield of bio-BTX

As the most abundant aromatic bio-polymer in nature, lignin can be converted into bio-BTX via the shape selective catalytic fast pyrolysis process (SS-CFP). In this work, three types of MWL were isolated from softwood (Chinese fir), hardwood (poplar), and herbaceous biomass (corn stover), namely CF-MML, P-MWL, and CS-MWL. The chemical structural of lignin was analyzed by gel permeation chromatography (GPC), 2D-HSQC-NMR, and 31P NMR. Five types of the parent zeolites (HZSM-5 (25), HZSM-5 (85), Al-MCM-41, HY, and USY) and the Zn modified HZSM-5 (25) with different loading amounts (1% to 4%) were screened. Results showed that CF-MWL had the highest carbon content (59.90%). P-MWL had highest content of β-O-4 linkage (53.90%) and Mw (2778 g/mol). Among the five parent zeolites, HZSM-5 (25) was the most effective catalyst to produce bio-BTX with the highest selective yield of 56.56% at the optimal operation parameters. As a bi-functional catalyst, the incorporation of Zn on zeolite promoted the formation of BTX, where metal promoted the reaction rates of de‑oxygenation reaction and aromatization reaction, while the HZSM-5 remains the ability of shape selectivity. The maximum selective yields of BTX were 65.02% (CF-MWL) > 63.77% (CS-MWL) > 63.41% (P-MWL) when the Zn loading amount was 2%.