Polydisperse Size Distribution of Monomers and Aggregates of Sulfur-Containing Compounds in Petroleum Residue Fractions

Dimension of sulfur-containing compounds in a residue is crucial to hydrodesulfurization catalyst design. Size distributions of sulfur compounds in fractions of Venezuela atmospheric residue were determined from the bulk-phase diffusion coefficients, which were measured at 298 K by a diaphragm cell by using 200 nm polycarbonate membranes. Sulfur compounds in all fractions show obvious size polydispersity. The size of four narrow SFEF (supercritical fluid extraction and fraction) fractions varies slightly with the concentrations of 1 g/L to 40 g/L. However, maltenes and asphaltenes from the end-cut showed significant variation in size over concentrations of 0.1 g/L to 40 g/L, which indicates a coexistence of various monomers and aggregates. The monomers are dominated in maltenes, whereas aggregates dominated in asphaltenes. The hydrodynamic diameter of sulfur-containing monomers of four SFEF fractions ranges from 0.74 to 1.45 nm at a concentration of 1 g/L. The size of maltene monomers spans a range of 1.87 to 2.29 nm at 0.1 g/L and presents a more significant polydispersity than SFEF fractions. The size variation of the SFEF fractions and maltenes to yields demonstrates a continuous distribution in size for the petroleum residue. However, asphaltene aggregates cover the span of diameters from about 4.29 to 5.54 nm at a concentration of 0.1 g/L, and the values are larger than those of 1–3 nm found in most literature for asphaltene molecules. The average diameters of asphaltene fractions decreased to 4.02 and 3.95 nm at concentrations of 0.05 g/L and 0.03 g/L, respectively. It reveals that aggregation of asphaltene molecules can occur at concentration lower than 0.1 g/L and a state of coexistence of asphaltene monomers and aggregates at 0.05 to 0.1 g/L

Restrictive Diffusion in the Hydrodesulfurization over Ni-MoS₂/Al₂O₃ with Different Crystal Forms

Al₂O₃ materials with different crystal forms were synthesized via the hydrothermal synthesis method using the low-cost raw material, and then the corresponding NiMo/Al₂O₃ catalysts were prepared by using Al₂O₃ materials with different crystal forms as the supports. The restrictive diffusion effects on the hydrodesulfurization reaction of different reactants with different molecular sizes over the NiMo/Al₂O₃ catalysts with different crystal forms were investigated systematically for the first time. NiMo/δ-Al₂O₃ exhibited the highest values of the effective factor (η) and effective diffusion coefficient (<i>D</i>_e), which could be ascribed to its proper pore diameter and relatively concentrated pore diameter distribution. The hindered magnitudes of diffusion decrease in the order of NiMo/δ-30 (2.23) < NiMo/θ-30 (2.83) < NiMo/γ-30 (3.42), indicating that the restrictive diffusion effect of NiMo/δ-30 catalyst was weaker than those of the other two catalysts

Optimal Synthesis of Hierarchical Porous Composite ZSM-5/SBA-16 for Ultradeep Hydrodesulfurization of Dibenzothiophene and 4,6-Dimethyldibenzothiophene. Part 2: The Influence of Aging Temperature on the Properties of NiMo Catalysts

ZSM-5/SBA-16 (ZS) supports were prepared using the two-step hydrothermal crystallization method. The effect of the aging temperature on the structural properties of the series ZS supports was studied. The prepared samples were analyzed by X-ray diffraction, scanning electron microscopy, N₂ physisorption, ²⁷Al magic angle spinning nuclear magnetic resonance, H₂ temperature-programmed reduction, Raman, X-ray photoelectron spectroscopy, pyridine–Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy. The hydrodesulfurization performances of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) were examined at <i>T</i> = 340 °C and <i>P</i>_H₂ = 4 MPa. The NiMo/ZS-45 catalyst synthesized at the aging temperature of 45 °C exhibited the best catalytic activities of DBT and 4,6-DMDBT, which were attributed to its regular shape, well-organized pore structure, high sulfidation degree, and a compromise between the acidity and metal–support interaction (MSI, Mo–O–Si). Moreover, the possible DBT and 4,6-DMDBT HDS reaction networks over NiMo/ZS-45 were proposed

Hierarchical ZSM‑5 Zeolites with Tunable Sizes of Building Blocks for Efficient Catalytic Cracking of <i>i</i>‑Butane

Hierarchical ZSM-5 zeolites have been receiving increasing attention from both fundamental research and industrial applications. From the chemical engineering viewpoint, the introduction of building block of ZSM-5 could give consideration to both external surface acidities and diffusion properties which are important in parallel sequence reaction for the final product distribution. In this work, hierarchical ZSM-5 with different sizes of building blocks were successfully prepared by tuning the water/silica ratio during the synthesis. With varying the size of building blocks, the diffusion property and external surface acidity were finely regulated, and it significantly influences the performances of ZSM-5 during catalytic cracking reaction. The catalyst with proper size of building blocks exhibited the optimized yield of olefins and lowest carbon deposition during 72 h reaction in catalytic cracking of <i>i</i>-butane. The strategy proposed herein could be helpful for the engineering design of hierarchical zeolites for industrially important catalytic reactions

Self-Assembly of Hierarchically Porous ZSM-5/SBA-16 with Different Morphologies and Its High Isomerization Performance for Hydrodesulfurization of Dibenzothiophene and 4,6-Dimethyldibenzothiophene

ZSM-5/SBA-16 (ZS) composite materials with different morphologies were synthesized successfully. The series supports were utilized to prepare NiMo/ZS for dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) reactions. Series ZS supports and NiMo/ZS were well characterized to investigate their structure–property relationship. The NiMo/ZS catalyst (NiMo/ZS-3) with uniform morphology and well-ordered pore channels showed the maximum <i>k</i>_HDS and TOF values of DBT and 4,6-DMDBT HDS. The <i>k</i>_HDS value (13.9 × 10^–4 mol g^–1 h^–1) of DBT over NiMo/ZS-3 was more than 2 times greater than that over the reference NiMo/ZS-M catalyst (5.5 × 10^–4 mol g^–1 h^–1), 3 times greater than that over the NiMo/SBA-16 catalyst (4.4 × 10^–4 mol g^–1 h^–1), and almost 4 times greater than that over the NiMo/ZSM-5 catalyst (3.5 × 10^–4 mol g^–1 h^–1). Furthermore, the <i>k</i>_HDS value (8.4 × 10^–4 mol g^–1 h^–1) of 4,6-DMDBT over NiMo/ZS-3 was more than 3 times greater than that over the reference NiMo/ZS-M catalyst (2.8 × 10^–4 mol g^–1 h^–1), more than 4 times greater than that over the NiMo/SBA-16 catalyst (1.7 × 10^–4 mol g^–1 h^–1), and almost 5 times greater than that over the NiMo/ZSM-5 catalyst (1.6 × 10^–4 mol g^–1 h^–1). The superior DBT and 4,6-DMDBT HDS performances were assigned to the uniform morphology, well-ordered pore channels, and high B/L ratio of the NiMo/ZS-3 catalyst and the suitable dispersion of the MoS₂ active phases. HYD was the preferential route for DBT HDS, while ISO was the preferential route for 4,6-DMDBT HDS because of the high B/L ratio of NiMo/ZS-3. Moreover, the DBT and 4,6-DMDBT HDS reaction networks of the series NiMo/ZS are presented

Hydro-upgrading Performance of Fluid Catalytic Cracking Diesel over Different Crystal Forms of Alumina-Supported CoMo Catalysts

A series of CoMo/Al₂O₃ catalysts was prepared using different crystal forms of alumina (including γ-Al₂O₃, δ-Al₂O₃, θ-Al₂O₃, and α-Al₂O₃) as supports for the hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of fluid catalytic cracking diesel. The physicochemical properties of the supports and the corresponding catalyst were analyzed by various characterization methods. The results showed that δ-Al₂O₃ possessed a moderate surface area, a concentrated pore size distribution, and less surface hydroxyl groups. The CoMo/δ-Al₂O₃ catalyst exhibited the highest HDS and HDN efficiencies, 98.4 and 96.1%, respectively. This could be attributed to its reduced metal–support interaction, moderate stacking morphology, and highest sulfidation degree of active phases. The HDS and HDN efficiencies of the catalysts followed the order of CoMo/α-Al₂O₃ (87.3 and 72.2%) < CoMo/γ-Al₂O₃ (94.8 and 87.9%) < CoMo/θ-Al₂O₃ (96.2 and 90.1%) < CoMo/δ-Al₂O₃ (98.4 and 96.1%)