Isoconversional methods are commonly used to process the thermogravimetric analysis (TGA) data and to simultaneously obtain the effective activation energies for lignocellulosic biomass pyrolysis. However, the widely used isoconversional methods may lead to some systematic problems, for example, numerical instability for the Friedman method and significant errors in the kinetic parameters for the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. To avoid the above problems, a modified Friedman isoconversional method has been developed in this work to accurately determine effective activation energies for solid-state reactions, such as biomass pyrolysis reactions. Through processing theoretically simulated data of strongly varying activation energy, the modified method applying for narrow intervals of conversion degree was proven to be capable of calculating the conversion dependence of activation energy accurately and reducing the effect of data noise. The modified Friedman isoconversional method was employed to process the non-isothermal TGA data of wheat straw pyrolysis at heating rates of 2.5, 5, 10, and 20 K min–1 and the kinetic data of beech sawdust pyrolysis at 5, 10, and 20 K min–1 from the literature. The results showed that the effective activation energies for the pyrolysis of wheat straw and beech sawdust varied significantly with the degree of conversion (in the conversion range from 0.05 to 0.85, the effective activation energies for wheat straw pyrolysis varied from 154 to 379 kJ mol–1, while 155–316 kJ mol–1 was reported for beech sawdust pyrolysis).
Catalytic fast pyrolysis (CFP) has recently aroused great interest for the high potential in upgrading bio-oils as renewable energy. However, conventional catalysts often exert diffusion resistance to large intermediate oxygenates. In this study, Fe-modified hierarchical ZSM-5 prepared by alkali and Fe loading of 2, 4, 6, 8 wt% were characterized by the analysis of XRD, BET, TEM, and NH3-TPD. Catalytic pyrolysis of poplar sawdust via Fe-modified hierarchical ZSM-5 was conducted using Py-GC/MS and TG-FTIR. The results indicated that alkali treatment and Fe loading of the catalyst introduced a hierarchical and porous structure and improved its acidity, leading to high mono-aromatics and olefins selectivity. The hierarchical ZSM-5 with 4 wt% Fe loading exhibited superior performance with high selectivity towards mono-aromatics of 15.30%. TG-FTIR analysis shows the volatiles release characteristics and FTIR spectra were consistent with pyrolysis behavior. Kinetic analysis reveals Fe-modified hierarchical ZSM-5 lowers the apparent activation energy in CFP of poplar sawdust.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)