The Fundamental Research Of Preparing Liquid Fuel Based On Microwave Pyrolysis Of Biomass

Biomass is an important renewable resources and its conversion to high qulity liquid fuels based on pyrolysis technology is of great significance to relax energy tension and environmental pollution of our country and to realize sustainable development of national economy.The thermal characteristics of several types of biomass were investigated by utilizing thermal analyzer.The study indicates that the pyrolysis temperature for the three land biomass species(pine wood,cotton stalk and fir wood) changes inversely with the yield of the ash from the biomass.The catalytic effects of the six inorganic compounds(NaOH,Na₂CO₃,Na₂SiO₃,NaCl,TiO₂ and HZSM-5) on pyrolysis of the three land biomass species vary regularly to some extent with the acidity or basicity of these compounds.The thermal stability of the six seaweeds are much lower than that of the three land plants. The one-step reaction models for pyrolysis of all the studied biomass species have been established and a three compoment-parallel-independent reaction model for pyrolysis of lignocellulusic biomass has also been proposed.A bench scale microwave pyrolysis installation has been set up, the frequency employed is 2450MHz and the power capacity can be adjusted from zero to 4kW proportionally. A serial three phase U-shaped tube train immersed in the ice-water mixture bath is used for cooling and collecting the condensable components. SiC is used as microwave absorber when the sawdust is to be pyrolyzed and it is not used when the wood blocks are the feedstock. This installation is used for pyrolysis of the sawdust of the three land plants at ca. 470℃and the emphasis is put on the catalytic effects of the eight inorganic additives on the microwave pyrolysis.The oil yield is between 10-30% and ca. 30% water exists in the liquid products. All of the eight additives have increased yields of solid products greatly and decreased yields of gaseous products more or less. Yields of liquid products are subjected to no dramatic change except NaCl, H₃PO₄ and Fe₂(SO₄)₃ have increased the liquid yields moderately.The gases produced from pyrolysis consist mainly of H₂, CH₄, CO and CO₂. All of the eight additives have made these gases evolve earlier, among which the four sodium additives have the most marked effect, which can make the gases evolve 4-6min earlier. Most additives have made the molar fraction of H₂, CH₄ and CO increase and those of CO₂ decrease.More light components, among which acetol takes priority, appear in the liquid products from microwave pyrolysis compared with Py-GC-MS analysis and fast pyrolysis in the conduit-spouting fluidized reactor. The acetol formation can be further enhanced up to a relative concentration of 50% by alkaline catalysts NaOH, Na₂O₃ etc, whereas furfural and 4-methyl guaiacol or (z)-2-butene-1,4-diol can be selectively formed with a total relative concentration of the two components up to 80% when H₃PO₄ or Fe₂(SO₄)₃ is used as the catalyst. Meanwhile, the study indicates that the semicoke from microwave pyrolsysis has good gasification reactivity.The reactivity and gasification kinetics of the semicoke from pine wood by microwave pyrolysis have been investigated by utilizing thermal analyzer. The results show that strong bases NaOH and Na₂CO₃ have greatly increased the reactivity of the semicoke and complete gasification time is very short. Neutral salts NaCl and Fe₂(SO₄)₃ have also increased the reactivity of the semicoke considerably. The reactivity of the semicoke in the low conversion range mainly depends on the microstructure of itself, whereas that rising quickly in the high conversion range can be ascribed to the prompt concentration rise of the minerals. The reactivity of the semicoke from microwave pyrolysis is higher than that from conventional pyrolysis and this can be due to the more open hole and higher specific surface area of the former formed by devolatilization from inner part to external part. It is found that the gasification process is controlled by external diffusion through applying non-reacted shrinkage reaction core model.Finally, an integrated technology route for preparing high quality liquid fuel has been proposed through fully utilizing the liquid products with unique composition and distribution, hydrogen rich gases and active semicoke obtained by microwave pyrolysis, combining the traditional technological route for indirect liquefaction of coal and the latest thoughtway for synthesis of liquid alkanes from biomass-derived feedstock. Figure [74] table [26] reference [126]...