Study On The Structure Characteristics Of Porphyrins In Two Crude Oil And Impact On Residue Catalytic Cracking Process

Improving the degree of light-end products of heavy oil is an urgent task on higher utilization and clean transformation of oil resources. Through separation and purification of porphyrins and non-porphyrin metal in heavy oil, meanwhile recognition the type, distribution, molecular weight, molecular structure characteristics of porphyrin compounds at the molecular level, could enrich the scientific understanding of porphyrin compounds, which has an important meaning for improving the level of applied basic theory on FCC process and technology integration.The method on separation and enrichment of metal porphyrins has been studied. The Venezuela 380 crude oil and Yichang tube-transporting oil residue were used as research object. And the methods of solvent extraction and column chromatography separation were employed to separate the different metall porphyrins. The results showed that, acetonitrile was the most suitable extraction solvent both for the Venezuela 380 crude oil and Yichang tube-transporting oil residue in the solvent extraction process. In the process of Column chromatography separation, the the solvent ratio and dosage for different metal porphyrins were determined. After enrichment, the concentration of nickel and vanadium porphyrins were raised 33 and 77 times respectively in Venezuela 380 crude oil, and also 92 and 108 times respectively in Yichang tube-transporting oil residue.The method of ultraviolet-visible spectrum (UV-Vis) and mass spectrometry (MS) were employed on structure characterization of the different porphyrins in both Venezuela 380 crude oil and Yichang tube-transporting oil residue. The results indicate that the contents of ETIO and DPEP homologues in vanadium porphyrins of Venezuela crude oil are 80.7% and 19.3%, respectively. Furthermore, the C28-ETIO shows the largest abundance in the ETIO homologues while the C31-DPEP has the largest abundance in DPEP. The contents of ETIO and DPEP homologues in vanadium porphyrins of Yichang tube-transporting oil residua are 82.1% and 17.9%, respectively. Furthermore, the C34-ETIO shows the largest abundance. Meanwhile the contents of ETIO and DPEP homologues in nickel porphyrins of Yichang tube-transporting oil residua are 83.4% and 16.6%, respectively. Furthermore, the C35-ETIO shows the largest abundance.On the basis of above, the typical metal porphyrins in two heavy oils were simulated in molecular level with the method of quantum chemistry calculation based on the density functional theory. Through the simulation and optimization of space molecular structure, the information such as key parameters, dipole moment and electronic absorption spectrum were received. The results of the key parameters and dipole moment had showed that the polarity of nickel porphyrins is less than the vanadium porphyrins. Meanwhile, DPEP porphyrins' molecular polarity was slightly bigger than ETIO porphyrins'. The porphyrins'characteristic absorption peaks of Soret and Q absorption band were calculated. The order of different porphyrins'stability from strong to the weak was C35-(ETIO-Ni)> C35-(DPEP-Ni)> C28-(ETIO-VO)>C34-(ETIO-VO)>C31-(DPEP-VO)。There was a large part of the metal compounds existed as non-porphyrins in heavy oil, the method of its separation was studied. Venezuela 380 oil was employed as the research object, and two steps extraction which firly with solvent of acetonitrile and secondly DMF was used to isolated the metal non-porphyrin compounds. The analysis results showed that metal non-porphyrin compounds in Venezuelan 380 crude oil was metal complex with lower molecular weight and four coordination based structure. Some of the spatial structure parameters such as bond length and dihedral angle of metal non-porphyrin compounds were calculated by using quantum chemical calculation method. Compared with metal porphyrins, metal non-porphyrin compounds in Venezuela 380 crude oil had lower coplanarity and weaker conjugation.Finally, the impacting of metal porphyrins in Venezuela crude oil and Yichang tube-transporting oil residua on the product distribution and catalyst properties of catalytic cracking process was inspected.The results showed that in the conditions that catalysts used in each experiment was fresh, the trend of the product's yield changed with the vanadium porphyrins content was much flatter, which means that nickel porphyrins had greater impaction on the reaction selectivity; Through the results of the catalyst recycling experiment, nickel porphyrin had smaller destructive effect on the catalytic activity. The process of metal removing from metalloporphyrins was speculated, which was:firstly, metal porphyrin had a reversible hydrogenation in one of its outer ring, which generated metal porphine; secondly, metal porphine are further decomposed, generating metal and free porphine. In the process of catalyst cracking, vanadium porphyrins were much easier to had a demetallation. Metal had a oxidation reaction in catalyst regeneration process, generated NiO and V2O5. NiO prevented the contaction of fuel oil and the catalytic activity center, whereas V2O5 had a reaction with the active center of zeolite which resulted the permanent deactivation of the catalyst.