Demetallization Mechanism Of Vanadium Porphyrin And Nickel Porphyrin In Microwave Field

In the process of petroleum processing,nickel and vanadium mainly exist in porphyrin compounds,which are not easy to remove and can cause catalyst deactivatio n.Therefore,improving the removal efficiency of nickel and vanadium has great significance for improving petroleum processing technology and environme nta l protection.Compared with the traditional heating process for removing heavy metals from petroleum,the removal rate of nickel and vanadium can be greatly improved by introducing microwave radiation.However,the de-metallization mechanism of nickel porphyrins and vanadium porphyrins in microwave field is still unclear.Quantum chemical calculation method can explore the relationship between the structural characteristics of metal oporphyrins and their reactive sites at the molecular level,to further study the mechanism of microwave irradiation on promoting the de-metalliza t io n effect.The molecular structures of C₂₈-ETIO porphyrin,C₂₈-?ETIO-Ni?nickel porphyrin and C₂₈-?ETIO-VO?vanadium porphyrin were optimized and calculated by DFT/GGA/BLYP method.The corresponding structural parameters,dipole moments,molecular orbits,atomic charge and electronic vibration spectra were obtained.In order to explore the non-thermal and thermal effects of microwave irradiation on the de-metal ization reaction,the effects of electric field intensity and direction on the structure characteristics of the model compounds were studied.Furthermore,the structure characteristics and orbital energy of the model compounds were calculated by first-principles molecular dynamics.The results showed that metal atoms in metal oporphyrins are easily attacked by electrophilic reagents and acid demetallizers,among which vanadium porphyrins have the highest reactivity.The electric field intensity and direction have different effects on nickel porphyrin and vanadium porphyrin.Applying electric field which is parallel to the plane of porphyrin ring?x-axis direction?can greatly increase the activity of pyrrole ring and R-base on one side.Applying vertical electric field?z-axis direction?is beneficial to the occurrence of demillonization reaction.With the increase of vertical electric field,the length of Metal-N bond in metal oporphyrins increases first and then decreases.This is because when the vertical electric field of metal oporphyrins increases to 0.025 a.u.,the distorted mode of porphyrin rings changes from dome to saddle,and the distribution of HOMO and LUMO changes accordingly.This phenomenon can be used to explain the optimal power of microwave de-metallization in experiments.In particular,the distorted mode of vanadium porphyrin in E_-z electric field does not change with the increase of electric field intensity.Metal-N bond length increases with the increase of electric field intensity.In the dynamics simulation,the increase of temperature will also enhance the molecular reactivity.In conclusion,both the effects of electric field and the effects of heating the system can improve the structural instability and reactivity of metal oporphyrins.In other words,the non-thermal and thermal effects of microwave can both help to enhance the demetallization effect of metal oporphyrins.