Effect of torrefaction pretreatment on pyrolysis of microalgae

Microalgae biomass is a promising third-generation raw material for the production of biofuels and other valuable products. The greatest advantages of microalgae over current energy crops are that they have faster growth rates and do not compete with food production. This study aimed to investigate the effect of torrefaction pretreatment on the pyrolysis product yields of Spirulina Platensis microalgae. For this purpose, microalgae were first torrefacted at three different temperatures (220, 260, and 300 oC) and for a 1-hour treatment time. Then, torrefied microalgae samples and untreated microalgae were subjected to pyrolysis at three different temperatures (400, 500, and 600 oC) and for a 1-hour treatment time. Proximate and ultimate analyses and Fourier Transform Infrared Spectrophotometer (FTIR) analyses were performed to characterize the carbonized solid samples obtained from the torrefacted microalgae and the untreated microalgae, as well as the untreated microalgae and microalgae. Thermal Gravimetric Analysis (TGA) was also performed to reveal the combustion behavior of the torrefied microalgae obtained at different temperatures. In the torrefaction process of Spirulina Platensis, it was determined that solid product yield decreased as temperature increased, while liquid product yield increased concurrently. Proximate analysis results of torrefied microalgae (solid product) obtained from the torrefaction process showed that the fixed carbon content increased with torrefaction intensity, while volatile matter and ash amounts decreased with torrefaction temperature. The higher heating value of torrefied microalgae increased with torrefaction temperature, while ignition temperatures were higher than those of untreated microalgae. Pyrolysis results of untreated microalgae and torrefied microalgae obtained at different temperatures showed that torrefaction pretreatment was effective on solid product yield (carbonized solid product). The higher heating value of the carbonized solid samples obtained from the pyrolysis of torrefaction microalgae were determined to be lower than those of the torrefied microalgae samples.