Pyrolysis of microalgae biomass over carbonate catalysts

Microalgae are seen as potential biomass to be used in a biorefinery concept. Several technologies can be used to convert microalgal biomass, but pyrolysis is viewed as a unique pathway to obtain valuable chemicals distributed in three phases: liquid (bio-oil), gas (bio-gas) and solid (bio-char). The liquid phase, bio-oil, usually presents higher heating value than raw biomass, but acidity and oxygen content are major drawbacks.In situcatalyzed pyrolysis can help to decrease the oxygen content and acidity of pyrolytic bio-oils.Chlorella vulgarisandScenedesmus obliquuswere pyrolyzed in a fixed-bed reactor using commercial carbonate catalysts (Li2CO3, Na2CO3, K2CO3, MgCO3, SrCO(3)and MnCO3). The catalysis pyrolysis temperature (375 degrees C) was selected from thermal degradation profiles obtained using thermogravimetry under nitrogen flow and corresponds to the maximum degradation rate for both microalgae. In spite of similar volatile and fixed carbon contents, microalgae performed differentially during pyrolysis mainly due to the different contents of carbohydrates, oils and proteins.Chlorella vulgarisandScenedesmus obliquusshowed bio-oil yield in the range 26-38 and 28-50 wt%, respectively. Only sodium carbonate was able to decrease the bio-char yield, confirming that carbonate catalysts prompt simultaneously gasification and carbonization reactions. Fourier transform infrared spectra of produced bio-oils showed a net decrease of acidity, associated with carbonyl species when carbonate catalysts were used. Bio-char morphology, for both microalgae, showed evidence of melting and resolidification of cell structures, which might be due to the lower melting points of the pyrolysis products obtained from proteins and lipids. (c) 2020 Society of Chemical Industry