Three-phase Trickle-bed Reactor Research Articles

Three-phase trickle-bed reactor model for industrial hydrotreating processes: CFD and experimental verification

Catalytic hydrotreating (HDT) is a process used to remove impurities from refinery streams, reacting a given feed with hydrogen at high temperature and pressure in a trickle-bed reactor. In order to optimize the operation of such reactors, one needs information about the detailed performance of the reactor. However, mathematical models of such reactors have not received due attention in last decades. Therefore, this work aimed at revisiting a plug flow HDT model to predict the performance of industrial diesel hydrotreating reactor, which considers most of the HDT reactions, gas-liquid and liquid-solid mass transfer, as well as the influence of catalyst deactivation and quenches injection on model predictions. A fourteen pseudo-component reactional network was proposed and successfully used. Computational fluid dynamics (CFD) predictions verified the plug flow behavior of the industrial HDT reactor. Both the CFD and plug flow models were verified using real process plant data, inspecting residual sulfur content and temperature profiles, with maximum relative error of 14%. Pressure and species concentration profiles as well as the effect of inlet pressure and temperature on final sulfur content were predicted and discussed. Catalyst deactivation is an important factor for accurate prediction of industrial HDT over time of campaign.

Kinetic parameter estimation and simulation of trickle-bed reactor for hydrodesulfurization of whole fraction low-temperature coal tar

With whole-fraction low temperature coal tar (LTCT) as raw material, which boiling point range is 209–514 °C. This paper conducts hydrotreatment (HDT) test for 1176 h on trickle-bed reactor (TBR) with commercial NiMo/Al2O3-SiO2 catalyst. The reaction conditions are as follows: reaction temperature 613–653 K, reaction pressure 10–14 MPa, liquid hourly space velocity (LHSV) 0.2–0.4 h−1, and hydrogen-to-oil volume ratio 1000:1. Considering the short life of coal tar HDT catalyst, a kinetic model of whole-fraction LTCT hydrodesulfurization (HDS) including running time (t1) and catalyst half-life (tc) was established. The kinetic parameter estimation was conducted according to the experimental data, and the results are as follows: activation energy 94965 J/mol, reaction order 1.5, and the relative error of the model is less than 5%.Based on the premise of steady state operation, the HDS reaction happened in the three-phase trickle-bed reactor was simulated by combining the mass transfer, reaction kinetics model and physical property data of LTCT. The results show that the experimental and simulated values of sulphur content at the exit of the reactor are within the error range of 5%. By simulating the whole-fraction LTCT HDS reactor, the pattern of changes in the concentrations of hydrogen sulfide, hydrogen and sulfur in gas, liquid and solid phases according to the length of the reactor were obtained. Based on this, this paper discusses on the impacts of each process parameter and hydrogen sulfide partial pressure on LTCT HDS, and works out the reaction characteristics of whole-fraction LTCT HDS different from crude oil fraction. Finally, this paper analyzes the influence of different process conditions on internal gradients of catalyst, and concludes the influence of each parameter on effectiveness factor of particle. The increase of temperature, decrease of pressure or increase of LHSV can all cause the decrease of effectiveness factor, wherein the temperature has the most significant effect on the effectiveness factor, followed by LHSV, and pressure has the weakest effect. These findings contribute to a more in-depth understanding of the features and rules of LTCT HDS, and can also give us some guidance for industrial reactor simulation.

Catalytic wet air oxidation of bisphenol A model solution in a trickle-bed reactor over titanate nanotube-based catalysts

Titanate nanotube-based catalysts were prepared via alkaline hydrothermal synthesis route followed by heat-treatment at different temperatures, ranging from 300 to 700°C. The resulting metal-free solids were then applied as a catalyst in a three-phase trickle-bed reactor, where catalytic wet air oxidation (CWAO) reactions of model aqueous bisphenol A (BPA) solution were performed. Mainly, the CWAO experiments were conducted at 200°C with oxygen partial pressure of 10bar over 300mg of a catalyst. It was observed in the given range of operating conditions that BPA undergoes both non-catalytic as well as catalytic oxidation routes, while the latter is far more pronounced. At 210°C and in the presence of 0.5g of titanate nanotube-based catalyst, which was annealed at 600°C, complete BPA removal was obtained. From TOC point of view, approximately 70% conversion was achieved indicating the persistence of refractory intermediates of lower carboxylic acids. The cross-section of results derived from various analytical techniques, which were used to identify surface, textural and morphological properties, revealed that balanced physicochemical properties are required to achieve meaningful extent of BPA removal. During 2–4 day time on stream, no catalyst deactivation occurred that could be attributed to the dissolution of active powders, or to the carbonaceous deposits accumulated on the catalyst surface. Therefore, these nanotubular materials can be regarded as innocuous and efficient long-term catalysts for oxidation of hazardous organic compounds (such as BPA) in the CWAO process.

Mechanism of Hydrodenitrogenation on Phosphides and Sulfides

The mechanism of hydrodenitrogenation (HDN) of 2-methylpiperidine was studied over a silica-supported nickel phosphide catalyst (Ni2P/SiO2, Ni/P = 1/2) and a commercial Ni-Mo-S/Al2O3 catalyst in a three-phase trickle-bed reactor operated at 3.1 MPa and 450-600 K. Analysis of the product distribution as a function of contact time indicated that the reaction proceeded in both cases predominantly by a substitution mechanism, with a smaller contribution of an elimination mechanism. Fourier transform infrared spectroscopy (FTIR) of the 2-methylpiperidine indicated that at reaction conditions a piperidinium ion intermediate was formed on both the sulfide and the phosphide. It is concluded that the mechanism of HDN on nickel phosphide is very similar to that on sulfides. The mechanism on the nickel phosphide was also probed by comparing the reactivity of piperidine and several of its derivatives in the presence of 3000 ppm S. The relative elimination rates depended on the structure of the molecules, and followed the sequence: 4-methylpiperidine approximately piperidine > 3-methylpiperidine > 2,6-dimethylpiperidine > 2-methylpiperidine. [Chemical structure: see text] This order of reactivity was not dependent on the number of alpha-H or beta-H atoms in the molecules, ruling out their reaction through a single, simple mechanism. It is likely that the unhindered piperidine molecules reacted by an S(N)2 substitution process and the more hindered 2,6-dimethylpiperidine reacted by an E2 elimination process.

Effect of Phosphorus Content in Nickel Phosphide Catalysts Studied by XAFS and Other Techniques

A series of novel, high-activity supported nickel phosphide hydroprocessing catalysts (Ni 2P/SiO 2) was synthesized by means of temperature-programmed reduction (TPR), and the effect of phosphorus content on hydroprocessing performance and catalyst structure was studied. The catalysts were characterized by BET surface area determinations, CO uptake titrations, X-ray diffraction (XRD) analysis, elemental analysis, and extended X-ray absorption fine structure (EXAFS) measurements. The activity of the catalysts was studied in a three-phase trickle-bed reactor operated at 3.1 MPa and 643 K in the hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) of a model liquid feed containing 2000 ppm nitrogen (quinoline), 3681 ppm sulfur (dibenzothiophene), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The samples were prepared with initial Ni/P ratios of 2/1, 1/1, 1/1.8, 1/2, 1/2.2, and 1/3, but the samples with excess P lost some of their P content during reduction and the main phase obtained was Ni 2P. Activity and stability of the catalysts were affected profoundly by the phosphorus content, both reaching a maximum with an initial Ni/P ratio of about 1/2 (actual Ni/P=1/0.57 after reaction). At this optimal P content, the activity was excellent, with steady state HDS conversion of 100% and HDN conversion of 81%, which were much higher than that of a commercial Ni–Mo–S/Al 2O 3 catalyst with corresponding HDN conversion of 76% and HDN conversion of 38%. The stability of the optimal composition was also high, with no deactivation observed over 90 h in HDS and only a slight deactivation in HDN. EXAFS analysis of the catalysts indicated the formation of a Ni 2P phase for the sample with an initial Ni/P ratio of 1/2, which was retained after reaction. At lower P content some Ni metal and Ni 12P 5 was obtained, and at higher P content, the Ni 2P active phase was blocked by excess P. The activity results indicate that on these novel catalysts, the HDN reactions are structure sensitive while the HDS reactions are structure insensitive.

Synthesis, Characterization, and Hydrotreating Activity of Several Iron Group Transition Metal Phosphides

A series of iron, cobalt, and nickel metal phosphides of chemical formula Fe2P, CoP, and Ni2P with specific surface areas of around 3 m2 g−1 were synthesized by means of temperature-programmed reduction (TPR) of the corresponding phosphates. These phosphides were also successfully prepared in dispersed form on a silica support (90 m2 g−1) for use as catalysts. The phase purity of these materials was established by X-ray diffraction (XRD), and surface properties were determined by N2 BET specific surface area (Sg) measurements and CO uptake determinations. The activity of the silica-supported catalysts in hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) was evaluated in a three-phase trickle-bed reactor using a model liquid feed containing 2000 ppm nitrogen as quinoline, 3000 ppm sulfur as dibenzothiophene, 500 ppm oxygen as benzofuran, 20 wt% aromatics as tetralin, and balance aliphatics as tetradecane. The reactivity study showed that the HDS activity sequence for the three samples was Ni2P/SiO2>CoP/SiO2>Fe2P/SiO2, while the HDN activity followed the sequence CoP/SiO2>Ni2P/SiO2>Fe2P/SiO2. Compared with a commercial Ni–Mo–S/γ-Al2O3 catalyst, Ni2P/SiO2 had a higher HDS activity (90 vs 76%), but a lower HDN activity (14 vs 38%), based on equal sites loaded in the reactor. The sites were determined by CO chemisorption for the phosphide and low-temperature O2 chemisorption for the sulfide. XRD and X-ray photoelectron spectroscopy characterizations of the spent catalysts indicated that the Ni2P/SiO2 catalyst was tolerant of sulfur.

Transition Metal Bimetallic Oxycarbides: Synthesis, Characterization, and Activity Studies

A new family of bimetallic oxycarbide compounds MI–MII–O–C (MI=Mo, W; MII=V, Nb, Cr, Fe, Co, Ni) has been synthesized by carburizing bimetallic oxide precursors using a temperature-programmed method. The oxide precursors are prepared by conventional solid-state reaction between two appropriate monometallic oxides. The synthesis involves passing a 20 mol% CH4 in H2 mixture over the oxide precursors while raising the temperature at a linear rate of 8.3×10−2 K s−1 (5 K/min) to a final temperature (Tmax) which is held for a period of time (thold). The synthesis, chemisorption properties, and reactivation of the materials indicate that the compounds can be divided into two groups of different reducibility (high and low). Their surface activity and surface area are evaluated based on CO chemisorption and N2 physisorption measurements. It is found that the CO number density correlates with the reducibility of the compounds.The catalysts were evaluated for hydroprocessing in a three-phase trickle-bed reactor operated at 3.1 MPa and 643 K. The feed was a model liquid mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The bimetallic oxycarbides had moderate activity for HDN of quinoline, with Nb–Mo–O–C showing higher HDN than a commercial sulfided Ni–Mo/Al2O3 catalyst tested at the same conditions. X-ray diffraction of the spent catalysts indicated that the oxycarbides of the early transition metals were tolerant of sulfur, while those involving the late transition metals showed bulk sulfide phases.

Mass Transfer Limited Wet Oxidation in Trickle-Bed Reactor

Catalytic activity of CuO-supported catalyst in phenol oxidation, and the influence of reaction conditions, viz. temperature (125-170 °C), oxygen partial pressure (1-7 MPa) and liquid feed (30-760 ml h-1), in the continuous operation using 17.9 mm i.d. trickle-bed reactor is presented. The hydrodynamic impact on the three-phase trickle-bed reactor performance in an environmental application of catalytic wet oxidation was also investigated. The results of trickle-bed operation were strongly influenced by wetting efficiency. An insufficient catalyst wetting can be to compensated by filling the catalyst bed voids by fine glass spheres. In the case of the gas transfer limited reaction, a better wetting of the catalyst can lead to worse reactor performance due to lower reaction rates.

New Catalysts for Hydroprocessing: Bimetallic Oxynitrides: II. Reactivity Studies

Bimetallic oxynitrides of the typeMIMIIOxNywere used as catalysts in hydrotreating reactions at 3.1 MPa and 643 K. The catalysts were prepared by nitriding bimetallic oxide precursors, where MoO3or WO3was one of the components, as described in the companion paper. The reactions were studied in a three-phase trickle-bed reactor operated at 3.1 MPa and 643 K. The feed was a model liquid mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The activities of the bimetallic nitrides were compared to a commercial sulfided Ni–Mo/Al2O3catalyst tested at the same conditions. The bimetallic oxynitrides were active for HDN of quinoline with V–Mo–O–N showing higher HDN activity than the commercial sulfided Ni–Mo–S/Al2O3catalyst. The HDS activity of the bimetallic oxynitrides ranged from 9 to 37% with Co–Mo–O–N showing the highest HDS activity among the oxynitrides tested. X-ray diffraction analysis of the spent catalysts indicated that the oxynitrides consisting of early transition metals (Group 4–Group 6) were tolerant of sulfur, while catalysts involving metals of Group 7 and Group 8 showed bulk sulfide phases. X-ray photoelectron spectroscopic analysis of the catalysts before and after the reaction indicated the incorporation of sulfur on the surface of the catalysts after prolonged exposure to the reactants.