Torrefaction of Leucaena Leucocephala under isothermal conditions using the Coats-Redfern method: kinetics and surface morphological analysis

The effects of temperature and holding times on the torrefaction of Leucaena Leucocephala (Leucaena) were elucidated via a novel isothermal decomposition approach. The torrefaction was performed in a fixed-bed reactor at temperature ranged from 200 to 300 degrees C for 20, 40 and 60 min. The effects of both torrefaction temperature and holding time were studied quantitatively and qualitatively by evaluating the distribution product yields and surface morphological changes. Quantitatively, the mass yield decreased with increasing temperature for all tested holding times, while the liquid and gas yields increased steadily due to the release of volatiles from the biomass decomposition. Qualitatively, significant morphological changes on Leucaena due to torrefaction were evidently captured via SEM imaging analysis. For torrefaction temperatures from 200 to 260 degrees C, the raw and torrefied Leucaena showed that pore evolution process had become evident. However, for torrefaction temperatures from 280 to 300 degrees C, the torrefied Leucaena revealed that the internal structure of torrefied Leucaena underwent pore development process. The pore development was noticeably observed for all temperatures. The values of activation energy (E-a) and pre-exponential factor (ln A) for the torrefaction were calculated based on the Coats-Redfern method for first order reaction. The values of E-a and ln A for 20, 40 and 60 min were found to be 39.75, 40.10 and 42.31 kJ/mol, and 3.92, 4.14 and 4.67. As a conclusion, the torrefaction of Leucaena from 200 to 300 degrees C for 20 min holding time is more reactive as compared to that at higher holding time.