Theoretical study of the structure and properties of Ni/V porphyrins under microwave electric field: A DFT study

摘要

Petroporphyrins with nickel (Ni) and vanadium (V) metals in crude oil are harmful to the catalysts of fluid catalytic cracking (FCC) and residue hydrocracking (RHC) as well as their processes. However, the presence of Ni/V as porphyrins makes them extremely difficult to remove. Recently, microwave method has attracted particular interests for high demetallization efficiency of Ni and V compounds from crude oils. In order to achieve better performance, it is indispensable to understand the theory and mechanism of microwave demetallization. The structure and electronic properties of Ni/V porphyrins were hereby studied via the density functional theory with BLYP functional. External electric fields of different directions and intensities were applied in the simulation. The calculation results demonstrated that the activity of pyrrole ring and -CH3 group can be greatly improved by applying parallel electric field (E-x or E-x), whilst the vertical electric field (E-x or E-x) mainly enhanced the activity of metal atoms. It was also found that the deformation mode of the porphyrin ring changed from dome to saddle style when the vertical electric field was larger than 0.025 a.u, meanwhile, the length of Metal-N bond decreased accordingly. This deformation regularity of the spatial structure innovatively explained the existence of an optimum microwave power in experiments.