Effects of Low Temperature Hydrothermal Pretreatment on N Distribution and Pyrolysis Characteristics of Chlorella pyrenoidosa Residue with High Protein Content

The hydrothermal degradation characteristics of high-protein chlorella in low-temperature hydrothermal pretreatment were studied by hydrothermal kettle. The product yield, elemental composition, energy recovery and key elements C and N of 125-200 °C were investigated. The results show that a large amount of C and N elements are enriched in the aqueous phase, and increasing the temperature (>175 °C) is beneficial to the deamination reaction and thus the relative content of NH3 in the aqueous phase. As the pretreatment temperature increases, the distribution of N in the oil phase product increases gradually and increases rapidly after 175 °C; the solid phase yield and energy recovery rate gradually decrease, but at the same time, its N/C and O/C also decrease, indicating Hydrothermal pretreatment is a upgrading process. The functional group structure and thermal degradation characteristics of the raw materials and algae residue were analyzed by FT-IR, XPS, TG-FTIR-MS and Py-GC-MS. The results show that the hydrothermal pretreatment process changes the relative content of different functional groups of C and N. Compared with the raw materials, the relative content of CC in algae residue increases, while the relative content of C-N and C-O decreases. In addition to protein-N and Quaternary amine-N, a small amount of pyridine-N appeared in the algal residue after pretreatment. The content and structural changes of the functional components of the solid algae residue reduce the release of NH3 and HCN in the thermogravimetric process and the content of the N-containing heterocyclic compound in the rapid pyrolysis product.