Mechanism research on catalytic pyrolysis of sulfated polysaccharide using ZSM-5 catalysts by Py-GC/MS and density functional theory studies

The mechanisms of primary product formation on catalytic pyrolysis of seaweed sulfated polysaccharide with ZSM-5 were examined in detail by using Py-GC/MS analysis and subsequent density functional theory. Results showed that furfurals were the main product (50.3%) in bio-oil during the catalytic pyrolysis of sulfated polysaccharides. Furfural (9.1%), 5-(Hydroxymethyl)-2(5 H)-furanone (3.1%) and acetone (3.2%) were defined as typical products of Glucuronic acid unit. 5-methyl furfural (41.2%), 5-methyl-2(3 H)-Furanone (0.5%) and 5-methyl furan (5.4%) can be converted from rhamnose unit. The subsequent density functional theory calculation indicated that the catalytic pyrolysis of sulfated polysaccharides by ZSM-5 catalyst could boost the pyrolysis and upgrade the bio-oil quality since the promotion of hydrodeoxygenation on catalytic reactions and ZSM-5 could promote the formation of 5-methyl furfural. The hydrogen bonding and van der Waals force interactions improved the pyrolysis pathways and decreased the energy barrier, which promoted the pyrolysis. This study confirmed that ZSM-5 had a catalytic influence on pyrolysis of sulfated polysaccharides through theoretical and experimental analysis, which is helpful to understand the formation mechanism of seaweed catalytic pyrolysis products.