Behaviors and non-isothermal kinetics of Chlorella pyrenoidosa fodder pyrolysis by a modified kinetic compensation effects and a parallel two-step reaction model

The TG-FTIR and Py-GC/MS techniques are applied to investigate the behaviors and kinetics of the Chlorella pyrenoidosa fodder (CPF) pyrolysis under slow and fast heating, respectively. TG-FTIR results reveal that the CPF pyrolysis mainly occurs in temperature range of 150-600 degrees C, where 432 degrees C is responsible for the fastest releases of bio-oil and gases. The NH3 and nitrogenous organic compounds derived from protein decomposition generate over the entire pyrolytic temperature range. According to the Py-GC/MS, the bio-oil has maximum contents of C11-C22 (similar to 66.5 wt%) and C4-C10 (similar to 99.2%) compounds at 600 degrees C and 800 degrees C, respectively. Higher pyrolytic temperature is appropriate for bio-oil conversion to gasoline energy potential. Temperature increasing can convert the C11-C22 into C4-C10, attributing to cracking the long carbon chain to a shorter length. The Vyazovkin method and a modified kinetic compensation effects (KCE) model are adopted in model-free procedure to investigate the single-step pyrolysis of CPF. Kinetic results showed that the CPF pyrolysis has an average activation energy of 181.7 kJ/mol. But the activation energy varies greatly with conversion rate from 128 kJ/mol to 438 kJ/mol attributing to mechanism changes. The modified KCE model, which enabled activation energy fluctuations, could optimize the single-step pyrolysis of CPF with reaction order of n=7.8. A parallel two-step reaction (PTSR) model which assumes the pseudo protein and carbohydrate decompose independently in two-step reaction was developed to depict the multi-step pyrolysis of CPF. This PTSR model could fit the experiments well with very low relative deviation. The activation energies of pseudo protein and carbohydrate were 94.22 kJ/mol and 154.85 kJ/mol in the first-step reaction and 109.37 kJ/mol and 142.84 kJ/mol in the first and second step reaction, respectively. The lipid pyrolysis follows a single-step reaction with activation energy of 156.83 kJ/mol.