Modification by SiO2 of Alumina Support for Light Alkane Dehydrogenation Catalysts

Due to the continuously rising demand for C3–C5 olefins it is important to improve the performance of catalysts for dehydrogenation of light alkanes. In this work the effect of modification by SiO2 on the properties of the alumina support and the chromia-alumina catalyst was studied. SiO2 was introduced by impregnation of the support with a silica sol. To characterize the supports and the catalysts the following techniques were used: low-temperature nitrogen adsorption; IR-spectroscopy; magic angle spinning 29Si nuclear magnetic resonance; temperature programmed desorption and reduction; UV-Vis-, Raman- and electron paramagnetic resonance (EPR)-spectroscopy. It was shown that the modifier in amounts of 2.5–7.5 wt % distributed on the support surface in the form of SiOx-islands diminishes the interaction between the alumina support and the chromate ions (precursor of the active component). As a result, polychromates are the compounds predominantly stabilized on the surface of the modified support; under thermal activation of the catalyst and are reduced to the amorphous Cr2O3. This in turn leads to an increase in the activity of the catalyst in the dehydrogenation of isobutane

CFD-Simulation of Isobutane Dehydrogenation for a Fluidized Bed Reactor

In the present study, a mathematical model of the isobutane dehydrogenation process for a laboratory reactor with a diameter of 2.8 cm and a height of 70 cm was created using CFD methods. A two-fluid model was selected as a model for the fluidization simulation, when the gas and solid granular phases were considered as continuous. The model of chemical kinetics considers three reactions that make the main contribution to the products mass fraction at the reactor outlet: the reaction of catalytic dehydrogenation of isobutane to isobutylene, the reaction of thermal cracking of isobutylene with the formation of methane and propylene, and the reaction of catalytic hydrogenation of propylene. The model was verified in a series of experimental studies. Experimental studies and numerical simulations were carried out for the process parameters: gas velocity 0.008, 0.012 and 0.016 m/s, gas temperature 550, 575, 600 and 625 °C, and catalyst mass 75, 100 and 125 g. The optimal process temperature was 575 °C, where the yield of isobutylene averaged 47.6% of the mass. As the temperature decreased, the yield of isobutylene decreased to 40.1% by weight on average. With an increase in temperature, the yield of isobutylene increased to 52.8% by weight on average, and the total yield of products of side reactions increased to 20% by weight on average. Changes in the gas velocity and catalyst mass had an insignificant effect on the values of the yield of isobutylene, but significantly affected the values of the yield of the by-products

CFD-Simulation of Isobutane Dehydrogenation for a Fluidized Bed Reactor

In the present study, a mathematical model of the isobutane dehydrogenation process for a laboratory reactor with a diameter of 2.8 cm and a height of 70 cm was created using CFD methods. A two-fluid model was selected as a model for the fluidization simulation, when the gas and solid granular phases were considered as continuous. The model of chemical kinetics considers three reactions that make the main contribution to the products mass fraction at the reactor outlet: the reaction of catalytic dehydrogenation of isobutane to isobutylene, the reaction of thermal cracking of isobutylene with the formation of methane and propylene, and the reaction of catalytic hydrogenation of propylene. The model was verified in a series of experimental studies. Experimental studies and numerical simulations were carried out for the process parameters: gas velocity 0.008, 0.012 and 0.016 m/s, gas temperature 550, 575, 600 and 625 °C, and catalyst mass 75, 100 and 125 g. The optimal process temperature was 575 °C, where the yield of isobutylene averaged 47.6% of the mass. As the temperature decreased, the yield of isobutylene decreased to 40.1% by weight on average. With an increase in temperature, the yield of isobutylene increased to 52.8% by weight on average, and the total yield of products of side reactions increased to 20% by weight on average. Changes in the gas velocity and catalyst mass had an insignificant effect on the values of the yield of isobutylene, but significantly affected the values of the yield of the by-products

Formation of Phases and Porous System in the Product of Hydrothermal Treatment of χ-Al2O3

The presence of χ-Al2O3 resulting from thermal decomposition gibbsite as part of alumina catalysts is unfavorable because of its acid characteristics. One of the available techniques of χ-Al2O3 removal is crystallization under hydrothermal conditions into boehmite, which is a main precursor of active γ-Al2O3. The influence of products of the hydrothermal treatment of χ-Al2O3 obtaining in result of thermal decomposition gibbsite under T = 150–200 °C, P = 0.5–1.5 MPa and pH = 4.0–9.2 were studied. The hydrothermal treatment products in these conditions are gibbsite and boehmite phases which are formed coincidently by parallel ways. In the alkaline medium at pH = 8.0–9.2 three-dimensional parallelepiped boehmite crystals with the edge length > 200 nm are formed, at pH = 4.0 two-dimensional rhombic-shaped plates with thickness 20–100 nm and with the edge length ~ 80–500 nm are formed. Crystallization of coarse boehmite particles promotes the formation of large and closed mesoporous

Influence of the Obtaining Method on the Properties of Amorphous Aluminum Compounds

Amorphous aluminum compounds are formed during the synthesis of the γ-Al2O3 catalyst precursor. Amorphous compounds influence on the alumina catalyst variously due to different physicochemical properties, which depend on the method of their preparation. In this research, the comparative analysis of physicochemical properties of amorphous aluminum compounds that were obtained by the precipitation method, the thermal decomposition of aluminum nitrate, and alcoxide hydrolysis product were studied. It is the first time that a new method for calculating of quantitative phase composition of amorphous aluminum compounds using the X-ray powder diffraction, thermogravimetric and differential scanning calorimetry analysis, mass-spectrometry, and CHN-analysis was described. Properties of obtaining samples were studied using scanning electron microscopy, low-temperature nitrogen adsorption, and temperature programmed desorption of ammonium analyses. The methods of precipitation and thermal decomposition of aluminum nitrate allows for obtaining non-porous samples consisting of a mixture of amorphous phases (hydroxide and basic salt) that contain the metals impurities and have low acidity of the oxides obtained from them. The highly porous amorphous alumina formed by the thermal decomposition of the alcoxide hydrolysis product with the least amount of impurities and a high acidity of the surface was observed

Quantitative Analysis of Lewis Acid Centers of γ‑Alumina by Using EPR of the Adsorbed Anthraquinone as a Probe Molecule: Comparison with the Pyridine, Carbon Monoxide IR, and TPD of Ammonia

Quantitative electron paramagnetic resonance (EPR) measurements were done on the alumina oxide surface by using 9,10-anthraquinone probe (AQ) with the AQ amount in the range of (0.5–20) wt %. The nature of three paramagnetic centers observed simultaneously is ascribed to the strong, medium, and weak Al Lewis acid sites on the basis of combined EPR study/infrared (IR) spectroscopy of the adsorbed CO and pyridine/temperature-programmed desorption (TPD) of ammonia. It is shown how the optimal concentration of AQ probe molecule for the exhaustive quantitative examination of alumina surface can be determined directly from EPR. A possibility to characterize the surface distribution of Lewis acid centers by AQ molecules is discussed

Ex Situ Upgrading of Extra Heavy Oil: The Effect of Pore Shape of Co-Mo/γ-Al2O3 Catalysts

Co-Mo/γ-Al2O3 catalysts with different pore shapes were synthesized for the ex situ upgrading of extra heavy oils by hydrodesulfurization (HDS), hydrodemetallization (HDM), and hydrodeasphaltization (HDA). The catalysts were synthesized using aluminum oxides that were prepared by various methods. It was found that using the product obtained by the thermochemical activation of gibbsite leads to the formation of slit-shaped pores in aluminum oxide, while the application of the hydroxide deposition method by the precipitation of sodium aluminate and nitric acid gives cylindrical pores in aluminum oxide. Co-Mo catalysts synthesized using these two types of pores exhibit different catalytic activities. The catalyst synthesized on a carrier with cylindrical pores exhibited a higher catalytic activity in sulfur, heavy metals, and asphaltenes removal reactions that are synthesized on a carrier with slit-like pores. This is because the presence of cylindrical pores leads to a decrease in diffusion restrictions when removing large molecules of asphaltenes and sulfur-containing and metal-containing compounds

Ex Situ Upgrading of Extra Heavy Oil: The Effect of Pore Shape of Co-Mo/γ-Al₂O₃ Catalysts

Co-Mo/γ-Al2O3 catalysts with different pore shapes were synthesized for the ex situ upgrading of extra heavy oils by hydrodesulfurization (HDS), hydrodemetallization (HDM), and hydrodeasphaltization (HDA). The catalysts were synthesized using aluminum oxides that were prepared by various methods. It was found that using the product obtained by the thermochemical activation of gibbsite leads to the formation of slit-shaped pores in aluminum oxide, while the application of the hydroxide deposition method by the precipitation of sodium aluminate and nitric acid gives cylindrical pores in aluminum oxide. Co-Mo catalysts synthesized using these two types of pores exhibit different catalytic activities. The catalyst synthesized on a carrier with cylindrical pores exhibited a higher catalytic activity in sulfur, heavy metals, and asphaltenes removal reactions that are synthesized on a carrier with slit-like pores. This is because the presence of cylindrical pores leads to a decrease in diffusion restrictions when removing large molecules of asphaltenes and sulfur-containing and metal-containing compounds