The Study Of Algae Pyrolysis Bio-oil And Nitrogen Evolution Rule In Heavy-oil

Algae,as a new and clean alternative energy,has a promising application prospect.Pyrolysis is helpful to realize the efficient conversion of algae into biofuels.However,the high nitrogen content in algae results in a large quantity of nitrogen-containing compounds in its pyrolysis bio-oil,which also contains numerous heavy-oil components with complex and unstable properties.These two defects greatly reduce the quality of bio-oil,leading to the severe environmental and economic problems in the production,application and subsequent upgrading of bio-oil,which seriously restrict the promotion and application of algae pyrolysis bio-oils.This work focuses on exploring the composition characteristics of algae pyrolysis bio-oil and the formation and evolution path of nitrogen-containing compounds in the pyrolysis process,it is conducive realizing the efficient and valuable utilization of algae pyrolysis bio-oil.Three different algae,Nannochloropsis sp.（NS）,Spirulina platensis（SP）and Enteromorpha prolifera（EP）,were pyrolyzed at a heating rate of 10–25℃/s at 300℃–700℃ in a fixed-bed reactor.The pyrolysis bio-oil and its heavy-oil components were characterized by a gas chromatography-mass spectrometry（GC-MS）,a Fourier transform ion cyclotron resonance mass spectrometry（FT-ICR-MS）and a user-defined Matlab program.On this basis,the applicability and compatibility of GC-MS and FT-ICR-MS were investigated in the study of algal bio-oil components.Then,the effects of algae with different components and pyrolysis temperature on the bio-oil composition and nitrogen-containing compounds were discussed.Finally,the possible evolution path of nitrogen in the heavy-oil was obtained.The positive electrospray ionization had a better ionization effect on nitrogen-containing compounds in bio-oil,and methanol,as a solvent for algae pyrolysis bio-oil,matched both GC-MS and FT-ICR-MS devices.In terms of bio-oil study,the content of CHO component in GC-MS results was much higher than that of FT-ICR-MS,while the content of nitrogen-containing component（CHN+CHON）was much lower.It may be because the molecular weight of CHO components in bio-oil is relatively small,and the compounds with more nitrogen number tends to be less-volatile.In addition,GC-MS only analyzed a very small amount of sulfur compounds,while FT-ICR-MS results showed that the sulfur compounds content could exceed 20%,mainly S₁ and S₁O_1-2(S₁O_1-5)components.The two devices were complementary in the molecular weight and physicochemical properties of the bio-oil compounds,but these two results are difficult to be unified,which is an urgent problem to be solved.FT-ICR-MS results showed that there were a lot of heavy-oil components（molecular weight≥200 Da）in the bio-oil.As the temperature rises,these heavy-oil components gradually transformed to lighter components.SP and NS heavy-oils only contained small amounts of condensed aromatics（2.43%and 1.62%,respectively）at 700℃,while carbohydrates（0.25%–5.01%）only appeared in EP heavy-oils at 300℃–600℃.At 300℃–700℃,SP and NS heavy-oils were mainly composed of N_1-3 components with the content of more than 60%,mainly amides,nitriles and nitrogen-containing heterocyclic compounds（indole,quinoline,etc.）.EP heavy-oils mainly contained N₀ and N₄ compounds,the content of which can be up to 50%–68%.Nitrogen-containing compounds in heavy-oils underwent strong Maillard reaction and deoxygenation reactions at high temperatures,thereby becoming more aromatic and containing less oxygen.In general,when algae pyrolysis is used to produce high quality bio-oil and high value-added compounds,attention should be paid not only to the yield,but also to the characteristics of heavy-oil components and nitrogen-containing components.