Том 10, № 3 (2018)

The effect of diffusion limitations on the Fischer–Tropsch synthesis of long-chain hydrocarbons on a cobalt–alumina–silica gel catalyst are analyzed at pressures of 1.5 and 2.0 MPa, depending on the particle size distribution (0.4–6.0 mm), gas hourly space velocity (100–1000 h⁻¹), and composition of the synthesis gas (H₂ : CO = 1, 2, and 5). It is shown that mass limitations increase the selectivity and productivity of C₃₅₊ hydrocarbons (waxes) and the probability of hydrocarbon chain growth. The effect of intradiffusion limitations is estimated at different compositions of the synthesis gas from changes in the apparent energy of activation in the temperature range of 179–225°С. In the high-temperature region, the apparent energy of activation falls from 97.1 to 67.0–82.9 kJ/mol as the H₂/CO ratio rises from 1 to 5.

In view of the worsening quality of crude oil, the use of unconventional petroleum feedstocks (heavy oils, bitumens, residues, etc.) in processing is becoming increasingly important. The processing of heavy oil feedstocks (HOF) requires the development of new effective techniques that will lead to an increase in the yield of light fractions, suppression of coke formation, and saturation of liquid products with hydrogen. At the same time, the capital and operating costs of the process should be minimized because the cost of production and transportation for HOF is several times higher than for light and middle oils. The present review summarizes the results of studies of the catalytic steam cracking of HOF—a potential alternative to conventional HOF upgrading based on carbon rejection (thermal cracking, visbreaking, catalytic cracking) or hydrogen addition (hydrocracking). The main differences of this process from HOF upgrading with water (aqueous pyrolysis in sub- or supercritical water), the peculiarities of the catalytic steam cracking depending on the process conditions and the type of catalyst, and possible mechanisms of water participation in the process were discussed.

More than 70% of the world’s reserves of hydrocarbons is in the form of heavy petroleum feedstocks. Increasing the efficiency and depth of processing of such feedstocks is an important problem of petroleum refining. Cobalt powders and their catalysts prepared in a single stage are tested for the first time in the cracking process at the Novokuibyshevsk petroleum refinery. The composition and properties of the samples are studied via X-ray phase analysis, scanning electron microscopy, and temperature-programmed reduction. Surfaces of cobalt contains oxygen in Co₃O₄ and CoO inside layers, while mechanoactivation redistributes some of these oxides and alters the composition of products of tar cracking. Cobalt has more catalytic activity in the cracking of tar after mechanoactivation than the original powder. The yield of light fractions is 70% with mechanically activated cobalt, 10 wt % higher than without mechanoactivation, and 25% higher than with no cobalt powders.

The modification effect of NiCu–SiO₂ catalysts by molybdenum on their activity and selectivity in the hydrogenation of furfural—a product of the acid hydrolysis of hemicellulose biomass—was studied. The original NiCu catalyst was synthesized by the sol–gel method and stabilized with 10 wt % SiO₂ by impregnating the calcined sol–gel with an appropriate amount of ethyl silicate. Molybdenum was introduced by impregnation of the original catalyst with an aqueous solution of ammonium molybdate. The selective hydrogenation of furfural was carried out in a batch reactor at temperatures of 100–200°C and a hydrogen pressure of 6 MPa. It was shown that an increase in the process temperature in the presence of the molybdenum-containing catalyst increases the yield of 2-methylfuran and products of complete hydrogenation. At low process temperatures a small amount of 2-methylfuran is formed; the main products are furfuryl and tetrahydrofurfuryl alcohols. The modified NiCuMo–SiO₂ catalysts exhibit higher activity in hydrogenation of furfural and greater 2-methylfuran selectivity than the respective parameters of NiCu systems, due apparently to the formation of NiMo(Cu) solid solutions, and the formation of Mo^x+ on the catalyst surface.

The properties of iron subgroup metals (Fe, Co, Ni) on a mesoporous carbon Sibunite support during the formation of carbon in the catalytic pyrolysis of high-molecular alkanes (hexane, undecane, and hexadecane) were studied. In the case of the NiO/Sibunite catalyst, the rate of carbon formation at temperatures of 500–600^оС decreased in the series hexane > undecane > hexadecane. Carbon is deposited in the form of carbon nanofibers. The activity series of reduced catalysts in carbon formation was determined: 10%NiО/Sibunite > 10%CoО/Sibunite > 10%Fe₂О₃/Sibunite. The morphology of carbon that formed on the 10%CoО/Sibunite catalyst depends on the particle size of the active component: multiwalled carbon nanotubes (MCNTs) grow on particles of 10–30 nm, and carbon nanofibers grow on particles larger than 30 nm. The X-ray diffraction studies of Fe₂O₃/Sibunite after the reaction showed that the active component can be in the form of metal or iron carbide, the fraction of each phase in the catalyst depending on the particle size of the active phase. For particles of 10–30 nm, iron is in the form of metal, for larger particles, it is in the form of carbide. It was concluded that iron carbide particles are responsible for the formation of carbon nanofibers, and iron particles are responsible for the formation of MCNTs.

A new Ru-containing catalyst based on Fe₃O₄–SiO₂ particles that exhibit magnetic properties is proposed for the hydrogenolysis of cellulose to glycols and the hydrolytic hydrogenation of inulin to mannitol. The effect of process parameters on the selectivity toward the main products is studied. Under optimum conditions of cellulose hydrogenolysis, the total glycol selectivity is ≈40% (ethylene glycol, 19.1%; propylene glycol, 20.9%) at 100% cellulose conversion. In the hydrolytic hydrogenation of inulin, the maximum mannitol selectivity is 44.3% at a 100% conversion of the feed polysaccharide. The proposed catalyst is stable under hydrothermal process conditions, and can be easily separated from the reaction mass using an external magnetic field.