Catalytic Pyrolysis Of Chlorella Vulgaris To BIO-OIL

Fast pyrolysis is a promising technique to convert biomass into a liquid product known as bio-oil. Now raw materials are mainly focused on the maize straw, rice straw, wood and so on, which is restricted to development of biomass energy. Marine microalgaes have high output and a strong ability to adapt. Furthermore, they do not occupy cultivated land. Therefore, marine microalgaes are becoming an active research field in biomass energy. A series of investigations on the catalytic pyrolysis of chlorella vulgaris to obtain bio-oil were carried out in this paper.Thermogravimetric analyzer (TGA) and infrared analyzer were used to examine the pyrolysis characteristics of chlorella vulgaris. The results showed that the pyrolysis process of chlorella vulgaris consisted of the dehydration, fast pyrolysis and slow weight-loss, and the main pyrolysis temperature ranged from160to600℃. When pyrolysis temperature was below200℃, it chiefly carried on the evaporation of free water. At450℃, the majority of carbohydrates, lipid and protein started a series of pyrolysis reactions. The releasing amount of CO2, CO reached a peak with the acetal bond and peptide bond breaking. The pyrolysis of carbohydrates and protein almost ended, while some organic components emissed at600℃. At700℃, the pyrolysis of chlorella vulgaris completely ended.In a bench tube furnace pyrolysis device, the direct pyrolysis and catalytic pyrolysis experiments of chlorella vulgaris were performed, studying the effects of various catalysts on pyrolysis process of chlorella vulgaris. The yield of bio-oil from direct pyrolysis was low, and its quality was poor. Moreover, the bio-oil was composed of many acids and nitrogenous compounds, while hydrocarbons in the bio-oil were a few. By adding HZSM-5zeolites (Si/Al=38,50), moisture content of bio-oil decreased and its calorific value increased. Furthermore, the amount of hydrocarbons increased, and the amount of acids significantly reduced. By adding HY zeolite, the yield of bio-oil decreased, while its moisture content increased and its calorific value decreased. In addition, bio-oil contained abundant polycyclic aromatic hydrocarbons and nitrogenous compounds, especially naphthalene.To increase the product yields and improve the quality of bio-oil, the influence of pyrolytic parameters on the pyrolysis characteristics of chlorella vulgaris was studied. Pyrolysis temperature and catalyst mass fraction had important effects on the product yields and quality of bio-oil. Secondary cracking reactions of bio-oil were more severe with the increase of pyrolysis temperature. When catalyst mass was insufficient, it can not provide sufficient acidic sites to catalytic reactions. When catalyst mass was excess, side catalytic reactions occured easily. Heating rate and gas flow rate also had a profound effect on the pyrolysis of chlorella vulgaris. The higher heating rate was, the less aqueous phase product was and the greater yield of bio-oil was. The optimal pyrolytic conditions were as follows:pyrolysis temperature,600℃; heating rate,22.5℃/min; gas flow rate,0.2L/min; catalyst mass fraction,20%. Under the optimal pyrolytic conditions, it led to a remarkable increase of hydrocarbons and alcohols in bio-oil and a decrease of acids. In addition, oxygenated compounds such as ketones and aldehydes in direct pyrolysis experiment carried on polymerization and catalytic deoxidation with the role of HZSM-5/50zeolite.Finally, the article studied the effects of M/HZSM-5(M=Fe, Zn, Ni, Mo and Co) on the catalytic pyrolysis of chlorella vulgaris. The presence of Fe, Ni, Mo and Co caused a decrease of the bio-oil and its calorific value. The use of Ni/HZSM-5zeolite led to an increase of gaseous product and a decrease of aqueous phase product. The use of M/HZSM-5(M=Fe, Zn, Mo and Co) zeolites contributed to increase the yield of aqueous phase product. In addition, the presence of Fe, Zn and Ni caused a marked decrease of acids and an increase of hydrocarbons. Other two kinds of metal components (Mo and Co) were not conducive to deoxygenation reactions, and this led to an increase of acids.