Effects of dry and wet torrefaction pretreatment on microalgae pyrolysis analyzed by TG-FTIR and double-shot Py-GC/MS

TG-FTIR and double-shot Py-GC/MS were executed to investigate the effects of torrefaction pretreatment on microalga (Chlorella vulgaris ESP-31) pyrolysis. TG-FTIR was performed to analyze the pyrolysis and combustion gas of raw and wet torrefied microalgae, whereas double-shot Py-GC/MS was applied to investigate the product distributions of single and two-stage thermal degradation of the microalgae. From the result, wet torrefaction successfully eliminated the release of CO in the pyrolysis gas. The highest generation of C–H during pyrolysis was achieved by the microalgae pretreated with dilute sulfuric acid. In the combustion gas, the intensity of O–H absorption band was removed in the first stage after wet torrefaction. The Py-GC/MS analysis revealed that the fatty acids (48.22%) were the dominant component in the bio-oil derived from the microalgae pretreated by the dilute sulfuric acid in wet torrefaction. Meanwhile, the productivity of carbohydrate-derived products (anhydrous sugars) decreased from 18.58 to 0.39% in the pyrolytic bio-oil after the wet torrefaction pretreatment. In contrast, carbohydrate- and lipid-derived products were decreased in the bio-oil after the dry torrefaction pretreatment. Similarly, microwave-assisted wet torrefaction in sulfuric acid is an effective pretreatment technique to produce high-quality pyrolytic bio-oil for biofuel production.