Study On Catalytic Conversion Of Biomass And Plastic Wastes For Upgraded Fuels And Regulation Of Deposited Coke Performance

Biomass has the disadvantages of high oxygen content and low hydrogen content,which result in the poor quality of liquid and gaseous products from biomass pyrolysis so that it could not be used as fuel.Thereby,we conducted experiments of co-pyrolysis and catalytic cracking/reforming of hydrogen-rich plastic waste and biomass to produce high-grade chemicals and fuels over transition metal based catalysts,and study the characteristics and yields of three-phase products,and finally reveal the synergistic effects of co-pyrolysis.Meanwhile,in order to overcome the adverse impact of coke deposition on the metal catalyst,the structural nature of the deposited coke were regulated by adjusting important process parameters and then transformed into high value-added carbon nanomaterials.The main contents are as follows:The co-pyrolysis and catalytic cracking of biomass/plastics blends was carried out over Ni/char catalyst to probe the effect of different feedstock blending ratios on the yield and concentration of three-phase products,as well as the nature of carbon depositions.The correlationship between coke deposition and gas products was studied for better understanding of co-pyrolysis process.The results showed that the gases yield at plastic ratio of 50%reached the maximum value of 70.4%compared to theoretical ones,showing the best synergistic effect.For higher plastic ratio of more than 50%,H₂ yield increased to 975 m L/g with increasing plastic ratio,while the coke yield remarkably increased from 3.8 to 46.5%.That was due to large amounts of hydrocarbon molecules condensed on the catalyst surface,subsequently dehydrogenated and polymerized to release H₂ and form deposited coke.In addition,the unique hollow structure of carbon nanotubes（CNTs）reduced the degree of pore blockage and metal encapsulation,and attenuated the deactivation of the catalyst.In order to improve the quality of syngas and regulate performance of CNTs,co-pyrolysis and catalytic cracking of biomass and plastic wastes using steam as gasifying agent were investigated.The results demonstrated that the addition of steam decreased the tar and carbon yields obviously,and increased the gas yield to 87.4%,due to steam reforming reaction with macromolecules and water-gas shift reaction.The H₂ yield was elevated to 490m L/g with the best synergy at plastic ratio of 50%.The yields of CH₄ and C_2-4 hydrocarbons decreased.Although the CNTs yield（88mg/g）after steam reforming was almost the same as that of no steam,the amorphous carbon was remarkably diminished due to amorphous carbon being more active than CNTs to interact with steam to form H₂ and CO,the quality and purity of carbon nanotubes were improved ultimately.An integrated process coupling catalytic co-pyrolysis of biomass/plastic wastes and in-line catalytic upgrading of uncondensable pyrolysis gas were conducted over ZSM-5 and Ni/γ-Al₂O₃ to simultaneously produce aromatics-rich bio-oil and carbon nanotubes.The influence of feedstocks blending ratio on the characteristics of bio-oil and CNTs were established.The possible reaction pathway of carbon deposition was also probed.The results showed that low plastic ratio of 25%in the feedstock siginificantly enhanced the selectivity of monoaromatics（benzene,toluene,and xylene）.The maximum yield（44.4%）of monoaromatics was obtained at plastic ratio of 75%,and naphthalene and its derivates decreased.CNTs were successfully synthesized on Ni based catalysts,with the yield increasing from 17 to 139 mg/g_cata after the addition of plastics.The growth pathway of ultrafine-diameter（3.9-8.5nm）CNTs for pure biomass was mainly through decarboxylation and decarbonylation of oxygen-containing compounds at ZSM-5 acid sites to generate CO,followed by disproportionation reaction on extremely fine nickel particles to generate CNTs.With addition of plastics to biomass,hydrocarbon gases as dominated carbon source were decomposed on catalyst for the growth of CNTs with diameter of～16 nm.Meanwhile,the low concentration of CO₂ inhibited dry reforming reaction with C₁-C₄ hydrocarbons and carbon deposition,reducing the etching degree of carbon tube.The cost-effective red mud（RM）as bauxite residue was investigated for catalytic conversion of plastic wastes into H₂-rich syngas and magnetic carbon nanocomposites.The influence of catalytic temperature（700-850°C）on the performance of syngas and carbon nanocomposites was discussed comprehensively.The carbon/RMs were initially applied to chromium（VI）removal in sewage.The results showed that the introduction of RM catalyst elevated gas yield from 23.8 to 60.3%as a rise of catalytic temperature,due to its high iron activity for scission of polymer chains.The H₂ yield and concentration reached maximum values of 644.8 m L/g and of 63 vol%at 850°C.When the temperature exceeded 750°C,large amount of homogeneous CNTs depositing on the RM surface that modified dispersion of iron sites and diminished nanoparticle size of iron.Simultaneously,gaseous and solid phases provided a reductive environment for iron oxides to transform to metallic iron.XRD and XPS results verified that higher temperature provided adequate carbon components surrounding iron species to form metallic iron.Carbon nanocomposite at temperature of 800°C（RM-800）delivered the best removal efficiency of 81.6%with maximum adsorption capacity of 193.8mg/g.The adsorption model and XPS analysis revealed that RM-800 had the synergistic effect of sufficient Fe⁰ exposure and CNTs growth that poromted chemical reduction and electrostatic attraction capacity.