Application of the distributed activation energy model to the kinetic study of pyrolysis of Nannochloropsis oculata

Pyrolysis of algae is a promising route to produce high quality bio-oil and renewable chemicals. Owing to its complex structural composition, multiple pseudo-components are required to describe its thermal decomposition in a wide temperature range and evaluate the reaction kinetics. In this study, the pyrolysis behavior of the microalga, Nannochloropsis oculata (N. oculata), was studied by means of a thermogravimetric analyzer at various heating rates. A four-parallel-reaction scheme characterizing the pyrolysis of carbohydrate, protein, lipid and the secondary decomposition of char was employed to model thermal degradation using distributed activation energy model (DAEM). The average and standard deviation of activation energy, pre-exponential factor, and composition of the model components for pyrolysis of N. oculata were estimated. The model mass loss and differential mass loss profiles matched well with the experimental data at different heating rates. Based on the model predictions, the decomposition of proteins, carbohydrates, lipids and char occurred in the temperature regimes of 200-450 degrees C, 200-300 degrees C, 400-500 degrees C, and 750-900 degrees C, respectively. To gain valuable insights on the pyrolysate composition at various temperature regimes, analytical pyrolysis-gas chromatography/mass spectrometry experiments were performed. Indole and phenol, aliphatic and aromatic hydrocarbons, and long chain oxygenates were observed as the major pyrolysates in the temperature regimes of 30-350 degrees C, 350-600 degrees C and 600-1000 degrees C, respectively.