Catalytic Hydroconversion Of Shengli Lignite And Coal Model Compounds Over Pd-Ni/HZSM-5

Low aromaticity and high amount of oxygen-bridged bonds among aromatic structures units make it possible to obtain aromatic chemicals directly from lignite.In this paper,monometallic Pd/HZSM-5,Ni/HZSM-5 and bimetallic Pd-Ni/HZSM-5 were firstly prepared by impregnation method using Pd and Ni as active components,HZSM-5 as support.Catalysts were characterized through N₂ adsorption-desorption,XRD,XPS,TEM,SEM,H2-TPR and NH3-TPD.Then,diphenyl ether?DPE?and various model compounds containing C-O bonds were selected as substrates to evaluate the performances of catalysts under 1-20 bar hydrogen pressure in the temperature range of 120-220 oC.Shengli lignite?SL?was thermal dissolved using isomeric methanol/toluene mixed solvent in a 100 m L steel autoclave reactor affording soluble portions?SPs?and thermal dissolution residue?TDR?.Subsequently,the TDR was catalytic hydroconversion?CHC?at 300 oC over Pd-Ni/HZSM-5 catalyst,acquiring soluble species?CTSPs?and residue?CTDR?.Combined with the characterization of gas chromatography/mass spectrometer?GC/MS?,Fourier transform infrared?FTIR?spectrometer,solid-state 13 C NMR and thermogravimetric analyzer?TGA?,the composition and structural characteristics of SPs,CTSPs,SL,TDR and CTDR were characterized.N₂ adsorption-desorption and XRD characterization results of catalysts show that the pore characteristics and framework structure of HZSM-5 were remained after loading metals.XPS,TEM and H2-TPR analyses reveal the interactions between Pd and Ni in the bimetallic Pd-Ni/HZSM-5 catalyst.Electrons transferred from Pd to Ni,result in electron-rich Ni sites.Moreover,the addition of Pd promotes the dispersion of Ni and reduces the reduction temperature of Ni O.NH3-TPD analysis showes that the bimetallic Pd-Ni supported on HZSM-5 exhibited stronger acidity than those supported on Si O2 and g-Al2O3,which were mainly weak and medium acid sites.Compared with Pd/HZSM-5 and Ni/HZSM-5,Pd-Ni/HZSM-5 exhibited excellent activity and selectivity toward the conversion of DPE to alkane,and the Pd/Ni ratio of 1:10 was found to be optimal.Pd-Ni supported HZSM-5 exhibited higher catalytic activity than that supported Si O2 and Al2O3 due to its strong acidity.DPE conversion increased with the increases of reaction temperature,H2 pressure and holding time,and DPE is totally converted into cyclohexane at 220 oC under 2 MPa H2 within 2 h.Direct cleavage of C-O bond in DPE was achieved under low H2 pressure mainly affordingbenzene and phenol,while high H2 pressure was favorable for cleavage of C-O bond and hydrogenation of benzene rings in DPE.The Pd1-Ni10/HZSM-5 catalyst also showed high activity in hydrogenolysis of other model compounds containing various C-O bonds.The SPs yields increase with temperature increasing,and the SPs yield in methanol/toluene mixed solvent is 24.37% at 320 oC.The GC/MS dectectable compounds in SPs are mainly composed of aromatics and phenols.The yields of soluble species from CHC of TDR?27.7%?are higher than those from non-catalytic hydroconversion,suggesting that Pd1-Ni10/HZSM-5 catalyst show excellent activity in CHC of TDR.The soluble species from CHC of TDR are divided into two layers in nhexane.The upper layer are mainly composed of aromatics and a small amount of phenols,ethers and ketones,and the SPs in lower layer are mainly aromatics and a small number of alkanes and esters.It is suggested that the Pd1-Ni10/HZSM-5 catalyst can break the covalent bonds connected with aromatic rings in TDR and promote the release of aromatic chemicals.From solid-state 13 C NMR and TGA analyses of SL,TDR and CTDR,it was found that the aliphaticity index and weak Cal-O bond in TDR decreased while aromaticity index increased,and the aromaticity index and strong Cal-O bond in CTDR decreased while the aliphaticity index increased.These results indicate that thermal dissolution can break the weak bridge bonds in SL and destroy the aliphatic structures in the macromolecule skeleton,releasing some organic species,while CHC can break the strong covalent bonds in TDR and destroy the aromatic structures in the macromolecular framework,further promoting the release of organic species.This thesis contains 31 Figures,22 Tables,and 108 References.