Influence of CaO and HZSM-5 on oxygen migration in Chlorella vulgaris polysaccharide pyrolysis

Abstract

With polysaccharides of Chlorella pyrenoidosa as the raw material, the effects of CaO and HZSM-5 on the yield of bio-oil and the oxygen content in each phase in the pyrolysis of Chlorella vulgaris polysaccharides (CVP), which occurred in a tube furnace at 600 °C, were comprehensively investigated. The reaction path of deoxidation was also analyzed by TG, GC and GC–MS. The GC–MS analysis of liquids showed that liquids from the pyrolysis of chlorella polysaccharides included a range of light oxygenated compounds (e.g., furans, ketones and phenols), and the oxygen content of furan compounds decreased significantly with CaO and HZSM-5. Compared with the direct pyrolysis of polysaccharides (CVP), the catalytic pyrolysis contributed to the decrease in the oxygen content of organic components by 7.32% and 5.76%. The GC analysis showed that there was a remarkable downtrend in the release of oxygen-containing gas (CO and CO2), and the emission of CO2 decreased from 53.11% to 32.92%. The results of the thermogravimetric analysis indicated that the reaction paths of deoxidation in the pyrolysis process of polysaccharides (CVP) with CaO and HZSM-5 varied from those of the direct pyrolysis process: the catalytic pyrolysis with HZSM-5 promoted the conversion of carbohydrate from furans to aromatics over strong acid sites, which was consistent with previous studies; CaO not only acted as a catalyst but also participated in the reaction to change the reaction paths. All results and findings can help to further understand the thermochemical utilization of CPP for bio-oil. Keywords: Chlorella vulgaris polysaccharides, CaO, HZSM-5, Pyrolysis, Organic compounds, Deoxidation, Reaction paths