RESUMEN
Heavy fractions (e.g., asphaltene and resin) can easily be subjected to physical aggregation and chemical coking reaction through molecular force in the process of lightweight processing and use of coal tar (CT), such that the normal processing and use can be affected. In this study, hydrogenation experiments were performed by regulating the catalyst to oil ratio (COR), while the heavy fractions of the hydrogenated products were extracted based on a novel separation method (e.g., the resin with a poor separation effect and rare existing research). The samples were analyzed through Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. On that basis, the composition and structure characteristics of heavy fractions and the law of hydrogenation conversion were investigated. As indicated by the results, with the rise of the COR, the saturates, aromatics, resins, and asphaltenes (SARA) contents indicated the law of increasing the content of saturate, decreasing the content of other fractions, as well as sharply decreasing the content of asphaltene. Moreover, with the increase of the reaction condition, the relative molecular weight, the content of the hydrogen bonded functional groups and C-O groups, the carbon skeleton properties, the number of aromatic rings, and the stacking structure parameters were progressively reduced. In comparison with resin, asphaltene was characterized by large aromaticity and more aromatic rings, short and less alkyl side chains, as well as more complex heteroatoms on the surface of the heavy fractions. The results achieved in this study are expected to lay a solid basis for the relevant theoretical research and facilitate the industrial use process of CT processing.
RESUMEN
Defect engineering plays an important role in improving the performance of catalysts. To clarify the roles of Co and P vacancies in CoP for water splitting, a theoretical study based on density functional theory was carried out in this paper. The geometric and electronic structures, activity and stability of the CoP (101)B surface, CoP (101)B with the Co vacancy (Covac) and the P vacancy (Pvac) are investigated. The results indicate that the CoP (101)B surface with Pvac and Covac can enhance the electron transfer to the surface. The Pvac will upward shift the Co d-band center near the vacancy site, which promotes the adsorption of H on the Co atom. As a result, the bridge Co-Co sites near the vacancy become the active sites for the hydrogen evolution reaction (HER) (ΔGH* = 0.01 eV). The loss of the Co atom also results in an upward shift of its d-band center, which will enhance the H adsorption on the adjacent Co sites. The unevenly distributed electrons due to the presence of vacancies on the surface cause spontaneous dissociation of H2O molecules. Furthermore, the thermodynamic analysis and surface energy find that the CoP (101)B and (101)B facets with Covac and Pvac present good stability. The current work has shed light onto the mechanism of water splitting on the surface of phosphide with vacancies. Our study suggests that engineering vacancies on CoP is a feasible route to improve its catalytic activity.
RESUMEN
At present, a few chemicals can be separated after further processing of high-temperature coal tar (HTCT) distillates, which have a lower utilization. However, hydrogenation to produce clean fuel oil has not been widely reported in literature. Thus, due to the use of new feedstocks and the implementation of more severe environmental legislations, deep hydrodesulfurization (HDS) of HTCT will face formidable challenges. A series of HDS experiments were performed in a continuous isothermal trickle bed reactor in which the reactor temperature was varied from 648 to 678 K, the pressure from 12 to 16 MPa, and the liquid hourly space velocity (LHSV) from 0.25 to 0.35 h-1, and hydrogen-to-oil ratio kept constant at 2000 L/L. Based on the experimental data, possible reaction pathways of HDS reaction were investigated, and a modified Langmuir-Hinshelwood (LH) HTCT desulfurization kinetic model was established. gPROMS software was used to obtain optimal kinetic parameters that are as follows: EA = 26,842, K 0 = 93,958, α = -1.14, n = 1.65, and m = 0.86. The model can well reproduce various working conditions and has better prediction accuracy. Some characteristics of HTCT HDS reactions were discovered; the reaction order (n) of HTCT HDS is slightly higher than that of crude oil and medium/low-temperature coal tar (M/LTCT), but the activation energy (EA) is relatively smaller. The established reactor model was used to predict the changes of the concentration of hydrogen, hydrogen sulfide, and sulfur compounds in the gas, liquid, and solid phases along the length of the reactor, respectively. The model was also used to predict the effects of pressure, temperature, and LHSV on the conversion rate of sulfur and catalyst effectiveness factors. The results showed that the LHSV has a greater impact on the conversion rate, and the pressure and temperature are less pronounced at high-severity operating conditions; the effectiveness factor is significantly smaller than that of other HDS processes, temperature has a greater effect on the effectiveness factor, followed by pressure and LHSV. The conclusion can provide a basis for further understanding the HTCT hydrotreating process.