Basic Study On Selective Preparation Of Aromatic Hydrocarbons By Fast Catalytic Pyrolysis Of Biomass Under Hydrogen Supply

Lignocellulosic biomass has abundant resources,as the only renewable carbon source,biomass has unique advantages in replacing existing fossil energy sources.But because of its complex structure,it has not been efficiently used for energy,the advent of fast pyrolysis technology makes the use these biomass for energy full of prospects.Zeolite catalysts can directly convert biomass into aromatic products in one step.Such aromatic compounds can be used in the existing chemical synthesis or have a wide range of uses such as fuel additives.Among many zeolite catalysts,the HZSM-5 stands out due to its strong acidity and suitable pore structure and has been widely studied for its excellent selectivity to aromatic products.However,the rapid deactivation during catalytic pyrolysis biomass and the high proportion of PAHs with strong toxicity in the product limited the application of this conversion method.For this purpose,the main factors affecting the catalysis were studied separately.On the one hand,the catalyst was impregnated with metal,and on the other hand,an additional solid hydrogen donor was introduced into the biomass to increase the hydrogen-to-carbon ratio of the feed.The role of calcium formate in HZSM-5 catalytic pyrolysis of pine and aromatic product distribution of bimetal-modified HZSM-5 under the hydrogen supply of calcium formate were studied in order to achieve higher MAHs yield and more stable catalytic activity.1.Selective production of monocyclic aromatic hydrocarbons from ex-situ catalytic fast pyrolysis of pine over HZSM-5 catalyst with calcium formate as a hydrogen sourceThe introduction of calcium formate as a hydrogen donor to the ex-situ catalytic fast pyrolysis of pine in lab-scale experiments selectively increased the yield of MAHs while inhibited the formation of harmful PAHs.The optimal ratio of calcium formate:pine was 1:2 in lab-scale fixed bed,which achieved the highest yield of aromatic hydrocarbons at 650℃.The maximum yield of MAHs was 9.45 wt%(7.80 wt%in control experiments)respectively,and that of PAHs was 1.14 wt%respectively(1.70 wt%in control experiments).As the main solid product of calcium formate,the calcium carbonate inhibited the amount of pyrolytic vapors of pine,reducing the amount of oxygenates that would bind to the active sites of HZSM-5.But the overall effect of calcium formate increased the formation of aromatic hydrocarbons due to its release of hydrogen.The in-situ hydrogen source from calcium formate together with pyrolytic vapors from pine then were converted over HZSM-5 catalyst followed the hydrocarbon pool mechanism and phenolic pool mechanism.The improved H/Ceff of feedstock by calcium formate maintained the activity of each pool,leading to the promotion of MAHs formation and a decrease in PAHs yield.As a result,the coke that formed from PAHs were reduce,suggesting less carbon deposition on the catalyst surface and a longer catalyst life.The catalyst stability test also indicated that calcium formate as the hydrogen donor enhanced the anti-deactivation ability of the catalyst.2.Selective production of monocyclic aromatic hydrocarbons from ex-situ catalytic fast pyrolysis of pine over 1Mo0.5Mg/HZSM-5 catalyst with calcium formate as a hydrogen sourceAfter adding calcium formate as hydrogen supply donor,the hydrogen-carbon ratio of the biomass was improved,and the yield and distribution of aromatics are improved and optimized.This chapter continued to optimize the catalysts in the catalytic system on this basis,in order to achieve better hydrogen supply effect and monocyclic aromatic hydrocarbon yield.The HZSM-5 catalyst was modified with a bimetal,and then Mo,Mg,Zn,and Ga were supported on the HZSM-5 in a combined form using impregnation method.The effects of different bimetal modification,catalytic pyrolysis temperature,amount of catalyst and calcium formate on the yield and distribution of aromatic products were studied.the ex-situ catalytic fast pyrolysis of pine in Py-GC/MS and lab-scale experiments selectively increased the yield of MAHs while inhibited the formation of harmful PAHs.The optimal ratio of calcium formate:pine was 3:1 in Py-GC/MS,and 1:2 in lab-scale fixed bed,which both achieved the highest yield of aromatic hydrocarbons at 650℃.The maximum yield of MAHs was 12.79 wt%and 9.67 wt%(10.65 wt%and 9.45 wt%in control experiments)respectively,and that of PAHs was 1.09 wt%and 1.03 wt%respectively(2.06 wt%and 1.14 wt%in control experiments).The distribution of aromatic products has changed significantly.Benzene has become the main product of monocyclic aromatic hydrocarbons.The content of xylene has been greatly reduced,and the content of unsubstituted monocyclic aromatic hydrocarbons has been greatly increased.