Reaction mechanism of syngas produced via pyrolysis of enteromorpha polysaccharides

Abstract

The mechanism of gas-phase products from pyrolysis of polysaccharides from Enteromorpha prolifera (PE) is researched. The sulfated polysaccharides are the most important polysaccharides in Enteromorpha prolifera. The molecular dynamics (MD) method is used to simulate the pyrolysis process of sulfated polysaccharides of Enteromorpha prolifera. Combined with the results of the pyrolysis simulations and density functional theory (DFT), rhamnose, glucuronic acid, glucose, and xylose are used as model compounds to estimate and calculate the reaction paths of hydrogen and carbon monoxide. In addition, fixed-bed pyrolysis experiments are performed with the above four monomers. The pyrolysis simulation results show that the pyrolysis process of sulfated polysaccharides is approximately divided into three stages: low-temperature, medium-temperature, and high-temperature stages. Gas-phase products are mainly produced in the high-temperature stage, and the main components of syngas are hydrogen, methane, and carbon monoxide. The simulation and experimental results show that pyrolysis of xylose is the most likely to generate hydrogen, followed by glucose, rhamnose, and glucuronic acid. The process of producing carbon monoxide from monomers goes through reactions such as dehydration, isomerization, C-C bond breakage, and decarbonylation. Moreover, the results of fixed-bed experiments indicate that when the four monomers are pyrolyzed individually, the highest proportions of hydrogen, carbon monoxide, and methane in the gas-phase products are obtained from the pyrolysis of xylose, glucuronic acid, and rhamnose. When the four monomers are mixed and then pyrolyzed, the proportion of hydrogen and carbon monoxide in the obtained gas-phase products decreases, and the proportion of carbon dioxide increases.