Study On Catalytic Cracking Of Tar In Biomass Energy Utilization Process

Biomass is the fourth largest energy source following coal,oil and natural gas.However,the tar produced in the biomass utilization process may cause the operational troubles for its toxicity and corrosivity.It is necessary to find an economical and effective way to remove the tar during the biomass utilization process and improve the energy efficiency.The char based catalysts with wide source and simple preparation were adopted to catalytic cracking the biomass tar and the cracking mechanism of whichhas been studied in this thesis.The cyclohexane,n-heptane,toluene,thiophene and pyridine were selected as the model compounds of the biomass tar,while the coal char was selected as the catalyst support to prepare the char-based catalysts with different surface area and impregnated different metal.The change of the tar components for catalysis of char-based catalyst and the catalyst life was tested in the fixed bed reactor.The catalysts were characterized with X-ray diffraction?XRD?,N₂ isothermal adsorption-desorption?BET,BJH?,scanning electron microscopy spectroscopy?SEM-EDS?,and the products were analyzed by infrared spectroscopy?IR?,gas chromatography,gas chromatography-mass spectrometry?GC-MS?and other methods.The activated char catalysts?AC-X?were prepared by steam activation with abundant pores and high surface area.The amount of the alkali metal on the activated char surface was increased,but the crystallite structure changed little.Activated char has a great influence on the catalytic cracking effect of model compounds.The yield of H2 and CH4was increased by 138%and 24%respectively,and the liquid yield was reduced by 3.59%when the cyclohexane was catalytic cracked over 5g AC-15 catalyst,at 600?.The yield of H2 and CH4 reached 213.39mL/g and 23.05mL/g,respectively and the catalytic activity was still stable at 240min when the n-heptane was catalytic cracked under the same conditions.The catalytic cracking effect on the five model compounds was very different over the Fe-char and Ni-char catalyst prepared by impregnation method.The cracking effect on n-heptane over Ni-char catalyst is the best,while the cracking effect on cyclohexane over Fe-char catalyst is better.The catalytic activity of Ni-char catalyst is higher than that of Fe-char and char catalysts on the whole,but it is also deactived easily by coke deposition.The Ni-char catalyst has a certain industrial application value for its raw material obtained easily,prepared process simply and the higih catalytic activity.The products obtained from catalytic cracking different model compounds over different catalysts were analysied by GC-MS and IR.And the results showed that the contents of the model compounds n-heptane,cyclohexane,toluene,thiophene and pyridine were all decreased.Small molecule olefins were obtained when the lkanes were catalytic cracked over AC-15 and Ni-char catalysts.The hydrogenation and ring opening reactions usually occured when the alkanes and aromatics were cracked over AC-15 catalyst,while the ring-opening and reforming reactions mainly happened when the alkanes and aromatics were catalytic cracked over Ni-char catalyst.