Petroleum Chemistry最新文献

Two series of zeolites, vis., the MEL and MFI types, with different Si/Al molar ratios were synthesized by a steam-assisted crystallization method, specifically dry gel conversion (DGC). Their physicochemical properties were characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray fluorescence analysis. The acidic properties were examined by IR spectroscopy of adsorbed pyridine and 2,6-di-tert-butylpyridine as well as by ammonia temperature-programmed desorption. The DGC-synthesized zeolites were distinguished by high crystallinity, small crystal size, and well-developed surface. All the samples exhibited high activity and deactivation resistance in the oligomerization of a butane–butylene fraction. A comparative assessment of the catalytic performance the MEL and MFI samples demonstrated that the structural difference between the MEL and MFI types barely affects their deactivation resistance. Therefore, MEL zeolite is a valid alternative to the MFI type in the development of oligomerization catalysts.

The paper describes the physicochemical characterization and catalytic testing of MFI zeolites with different SiO₂/Al₂O₃ ratios synthesized by steam-assisted crystallization (SAC) and modified with phosphorus (4 wt % loading). Their physicochemical properties were characterized by X-ray diffraction analysis, X-ray fluorescence analysis, scanning electron microscopy, low-temperature nitrogen adsorption, ammonia temperature-programmed desorption, and MAS NMR spectroscopy. Both the parent and P-modified MFI zeolites were then subjected to catalytic tests in cracking of n-dodecane. The yield of light olefins was enhanced only in two cases: when MFI zeolites with SiO₂/Al₂O₃ ratios of 30–70 were modified with 4 wt % phosphorus and when parent MFI zeolites with SiO₂/Al₂O₃ ratios of 100–220 were used. It was further found that, in terms of catalytic performance in the cracking of n-dodecane, the MFI zeolites synthesized by SAC were comparable to a commercially available MFI zeolite synthesized under hydrothermal conditions. Moreover, in contrast to the commercially available zeolite, phosphorus modification of the SAC-synthesized zeolite enhanced the yield of C₂–C₄ olefins.

This study investigates the chemical and phase compositions, acidic properties, and porous structure characteristics of an acidic support for a bifunctional catalyst. This catalyst was a high-crystallinity granulated hierarchical H-ZSM-5 molecular sieve promoted with 0.5 wt % Pt. The catalytic transformations of n-hexadecane and a diesel fuel were further investigated using this catalyst. The catalyst exhibited a higher activity in the hydrocracking of higher n-paraffins than a bifunctional catalyst that contained 20 wt % Al₂O₃ as a binder. Furthermore, at 220°C, 3 MPa, 2.0 h^–1, and H₂/feed = 800 m³/m³, a diesel fuel with a pour point of –68 °C was produced over the prepared catalyst with a yield of about 71–72 wt %.

The physicochemical properties of ZSM-5 zeolite samples modified with alkali metal cations (e.g., Li⁺, Na⁺, K⁺, and Cs⁺) were characterized. It was demonstrated that increasing the metal load led to a decrease in the textural properties of the zeolite such as specific surface area, total pore volume, and micropore volume; furthermore, it reduced the total concentration of acid sites by 23–25% (at 0.72 × 10^–2 mol % potassium or 0.38 × 10^–2 mol % cesium). In the cracking of n-dodecane, the modification of ZSM-5 with 2.34 × 10^–2 mol% cesium enhanced the yield of light olefins up to 40.1 wt %, which is comparable with the value achieved by a phosphorus-based ZSM-5 sample (40.3 wt %).

A procedure for regenerating the hydroconversion catalyst precursor was studied. The procedure involves separation of the catalyst concentrate from the hydrogenizate vacuum residue by filtration, heat treatment of the concentrate to obtain the ash residue, and leaching of compounds of Mo and other metals from the ash residue with aqueous ammonia and nitric acid. As shown by X-ray diffraction analysis, the ash residue after the oxidation of the catalyst concentrate contains both individual molybdenum oxide (MoO₃) and mixtures of double (NiMoO₄, V₂MoO₈, NiV₂O₆, Na_0.76V₆O₁₅) and triple (Fe₄V₂Mo₃O₂₀) oxides in the form of alloys. An efficient procedure is the pretreatment of the ash residue with 65% HNO₃, followed by the treatment of the resulting suspension with a mixture containing 10% NH₄OH and 5% (NH₄)₂CO₃. In so doing, up to 88–90% of Мо compounds are extracted into the resulting catalyst precursor solution.

Liquid-phase oxidation of dearomatized oil distillate from a mixture of Azerbaijan crudes in the presence of homogeneous catalysts based on Mn(II), Cr(III), and Со(II) bromobenzoates was studied. These catalysts allow preparation of synthetic petroleum acids and hydroxy acids in high yield (>40 wt %). The influence of the kind of the catalyst on the composition of the oxidation products was examined. Manganese(II) bromobenzoate showed the highest catalytic activity. We have determined for it the optimum process conditions at the feed rate of 300 L/(kg h) and atmospheric pressure: oxidation time 5 h; catalyst concentration 1 wt %; 140°С. The total yield of petroleum acids under these conditions was 46%.

The catalytic activity of suspensions of cobalt-promoted molybdenum disulfide particles in hydroconversion of the petroleum vacuum residue was studied. Catalyst particle suspensions were prepared from inverse emulsions of aqueous solutions of the precursors (ammonium paramolybdate, cobalt nitrate or acetate) directly in the feed (in situ). Two procedures were used for preparing the promoted catalyst: consecutive or simultaneous addition of the precursors to the dispersion medium. The toluene-insoluble particles (TIPs) containing the spent catalyst had the size from 380 to 410 nm and contained the MoS₂, МоО₃, and Co₉S₈ crystalline phases. The cobalt-promoted dispersed catalyst exhibits the maximal activity in hydrodesulfurization and hydrogenation at the cobalt content of 33 at. %. The effect observed is due to the formation of a variable-composition Мо–Со–S phase, which cannot be identified by X-ray diffraction, on the surface of MoS₂ particles. A further increase in the promoter concentration leads to blocking of the MoS₂ particle surface with Co₉S₈ crystals, which, in turn, leads to a decrease in the catalyst activity in hydrodesulfurization and hydrogenation of high-molecular-mass feed components, to an increase in coking, and to a decrease in the fraction of paraffin–naphthene hydrocarbons in the hydrogenation product.

New oil sorbents, superhydrophobic aerogels of reduced graphene oxide (rGO) and polytetrafluoroethylene (PTFE), were developed. The rGO/PTFE aerogels of 2 : 3, 1 : 1, and 3 : 2 compositions were prepared as granules and blocks with contact angles larger than 160°. The rGO/PTFE (2 : 3) granules and the block of the same composition exhibit the highest sorption capacity for crude oil: 26 and 58.5 g/g, respectively. A procedure was suggested for utilization of the oil-loaded aerogels by distillation of low-boiling fractions and pressing of the aerogel to obtain a hydrophobic additive to asphalt concrete mixtures.

Using various solvents (dioxane, n-butanol, isopropanol, ethanol, acetonitrile, dimethyl sulfoxide), the cogelation of methyltrimethoxysilane and tetraethoxysilane in a molar ratio of 1 : 1 was carried out. The resulting gels were dried in supercritical carbon dioxide to obtain SiO₂ aerogels, which possessed specific surface areas of 1000–1500 m²/g, apparent densities of 0.055–0.095 g/cm³, and porosities of 95–99%. Comparative analysis of the properties of the aerogels revealed that the type of the solvent used during the sol-gel synthesis significantly impacted the textural characteristics of the materials. Specifically, the use of highly polar solvents (acetonitrile and dimethyl sulfoxide) resulted in materials with high specific pore volumes (17–18 cm³/g), whereas low-polar solvents (dioxane) yielded materials with lower specific pore volumes (less than 12 cm³/g). The adsorption capacity of the obtained aerogels with respect to heavy oil was determined to be 6–14 g/g. The impact of the dielectric constant and Hansen solubility parameters of the solvent on the properties of SiO₂-based aerogels are discussed.

Ten osmium complexes containing polypyridine and cyclometalated ligands have been studied as catalysts for the oxidation of alkanes. The complexes effectively catalyze the oxygenation of alkanes (cyclohexane, n-heptane, methylcyclohexane, hydrogen peroxide in acetonitrile solution in air at 60°C in the presence of silver salts as the co-catalysts. Alkanes are oxidized mainly to alkyl hydroperoxides, which are easily reduced by PPh₃ to the corresponding alcohols. The oxygenation of cyclohexane catalyzed by osmium complexes used at a low concentration (2.5 × 10^–4 M) gave the maximum yield of oxidation products of 35% in the case of complex (ttpy)₂OsCl₃ (ttpy = 4′-(p-tolyl)-2,2′:6′,2′′-terpyridine). The measurement of regio- and bond selectivity parameters for the oxidation of linear and branched alkanes, kinetic analysis of the dependence of the initial rate of cyclohexane oxidation on concentration alkane and analysis of the competitive oxidation of cyclohexane and n-hexane indicates that oxidation induces the interaction of the osmyl-oxo complex with the substrate. The structure of a new cyclometalated complex [(η⁶-cymene)Os(bq)(MeCN)](PF₆) (bqH = 7,8-benzoquinoline) was determined by SC-XRA.