Mechanism research on the pyrolysis of seaweed polysaccharides by Py-GC/MS and subsequent density functional theory studies

- Sulfated polysaccharide was selected as a model compound of seaweed polysaccharide.
- The main products of the sulfated polysaccharide pyrolysis are P6 and P10 detected by experiments.
- The predicted main products are COx, SOx, P6, P10, which agrees with related experimental results.

In order to understand the pyrolysis mechanism of seaweed polysaccharide, the sulfated polysaccharide was selected as the model compound in pyrolysis process and was theoretically investigated by employing density functional theory method B3LYP with the 6-31G+ (d, p) basis set. The pyrolysis gas chromatography mass spectrometry (Py-GC/MS) results indicate that the main products comprised furan and its derivatives, and the peak area percentage is 56%, among which the 5-methyl furfural (P6) is a major product that takes up more than 39.97%. Seven potential pathways were proposed to interpret the pyrolysis mechanism. The standard kinetic and thermodynamic parameters for all reaction pathways were obtained by DFT calculations. Based on both theoretical calculations and related experimental facts, the predicted main products are CO, CO2, SO3, furfural (P6) and 5- methyl furfural (P10), which are in good accordance with related experimental results. The proposed mechanism of reaction pathways for sulfated polysaccharide pyrolysis provides insight into the pyrolysis behavior of seaweed polysaccharide.