Catalytic pyrolysis of duckweed with phosphoric acid: Products yield and composition

The excessive presence of duckweed has led to the deterioration of water quality, which requires an efficient method for its high-value conversion. Therefore, catalytic pyrolysis of duckweed was conducted to elucidate the effects of H3PO4 impregnation on the yield and composition of the gaseous, liquid and solid products. The results showed that after H3PO4 impregnation, the solid and gas yields increased by up to 43.67 % and 51.78 %, respectively, compared to the case without H3PO4. Both the yields and fraction of H2 increased remarkably, after H3PO4 impregnation, resulting in an increase of H2/CO ratio. At low temperature of 400–500 °C, H3PO4 impregnation effectively reduced the oxygenated compounds and facilitated the formation of N-containing compounds. With increasing temperature, the phosphoric acid promoted the aromatization of aliphatic hydrocarbons to form aromatic hydrocarbons and enhanced the production of phenols. Additionally, the introduction of H3PO4 increased the carbon retention in solid char by 9.9–19.3 % probably due to the formation of relatively stable phosphate esters via crosslink reactions with the saccharides in duckweed. The optimal temperature and H3PO4 impregnation ratio were recommended considering the yield and composition of the products, as well as the energy consumption during pyrolysis.