Deuk Ki Lee

Hydrotreatment of an atmospheric residual oil over the dispersed cobalt and molybdenum catalysts in a carbon expanded-bed reactor

Atmospheric residual oil hydroprocessing over a dispersed catalyst of cobalt and molybdenum was conducted in continuous mode under 6.9 MPa of H2 using an expanded-bed reactor which was loaded with an appropriate amount of activated carbon granules. As dispersed catalyst precursors, oil-soluble cobalt naphthenate and molybdenum naphthenate were used. Throughout this work, the optimum catalyst composition showing the maximum hydrodesulfurization (HDS) activity was determined, and the possibility of in situ development of a carbon-supported catalyst by the deposition of the oil-dispersed catalysts on the reactor-loaded carbon granules during the reaction was also examined. The co-dispersed CoMo catalyst system showed highly selective promotion effects on the hydrotreatment reactions such as HDS, hydrodemetallization and asphaltene conversion. The maximum activity promotion for such hydrotreatment reactions occurred at a Co/(Co + Mo) atomic ratio of 0.3. However, the conversion of heavier to lighter oil fractions, i.e. hydrocracking activity, was highest over Mo alone and decreased with increasing Co content. The expanded-bed reactor was successfully applied to this hydrotreatment system. The reactor-loaded activated carbon played the role of dispersed catalyst immobilizer, contributing to the catalytic reaction performance.

Effects of transition metal addition to CoMo/ γ-Al2O3 catalyst on the hydrotreating reactions of atmospheric residual oil

Abstract The effects of transition metal addition to a commercial CoMo/ γ-Al2O3 catalyst on the hydrotreatment of atmospheric residual oil were investigated using a continuous flow fixed bed reactor operated at 420°C and 6.9 MPa. Nickel, ruthenium and tungsten were used as an additive to the catalyst. Catalyst performances were evaluated in terms of activities and initial deactivation rates in sulfur removal, conversion of heavier to lighter oil fractions, and removal of asphaltenes. Among the metal additive-modified CoMo/ γ-Al2O3 catalysts, NiCoMo/ γ-Al2O3 and WCoMo/ γ-Al2O3 showed a more improved reaction performance than commercial CoMo/ γ-Al2O3 whereas RuCoMo/ γ-Al2O3, did not. The performance improvements observed after addition of nickel or tungsten were thought to be mainly a result of the promotion effect on the catalytic activity in hydrodesulfurization. Significant improvements of catalyst performance were obtained by the addition of a small amount of tungsten (0.5 wt.-%). Tungsten was considered to be promising as a secondary promoter of CoMo/ γ-Al2O3.

Modification of the alumina‐supported Mo‐based hydrodesulfurization catalysts by tungsten

The incorporation effect of tungsten as an activity‐promotional modifier into the Ni‐promoted Mo/γ‐Al2O3 catalyst was studied. Series of W‐incorporated catalysts with different content of tungsten were prepared by changing the impregnation order of nickel and tungsten onto a base Mo/γ‐Al2O3. Catalytic activities were measured from the atmospheric reactions of thiophene hydrodesulfurization (HDS) and ethylene hydrogenation (HYD). The HDS and HYD activities of the WMo/γ‐Al2O3 catalysts (WM series) initially increased and subsequently decreased with increasing content of tungsten as compared with those of their base Mo/γ‐Al2O3. The maximal activity promotion occurred at the W/(W + Mo) atomic ratio 0.025. For the Ni‐promoted Mo/γ‐Al2O3 catalysts, the effect of W incorporation was greatly dependent on the impregnation order of tungsten. The catalysts prepared by impregnating Ni onto the WMo/γ‐Al2O3 catalysts showed the same trend of activity promotion as for the WM series, while those by impregnating W onto a NiMo/γ‐Al2O3 catalyst resulted in lower activities than their base NiMo/γ‐Al2O3 catalyst. To characterize the catalysts, temperature‐programmed reduction and low‐temperature oxygen chemisorption were conducted. The effects of W incorporation on the NiMo‐based catalysts were discussed in reference to those on the CoMo‐based catalysts.

Quantification and redox property of the oxygen-bridged Cu2+ dimers as the active sites for the NO decomposition over Cu-ZSM-5 catalysts

For a range of Cu-ZSM-5 catalysts with different Cu-exchange levels on the two kinds of ZSM-5 with different Si/A1 ratios, temperature programmed reduction using CO (CO-TPR) followed by H2 (H2-TPR), and temperature programmed desorption of oxygen (O2-TPD) were conducted using an online mass spectrometer to characterize and quantify the copper species on the catalysts in the calcined state. Copper species on the ZSM-5 were quantitatively characterized as Cu2+, (Cu-O-Cu)2+ and CuO after calcination in oxygen environment. The N2 formation activities of the catalysts in the decomposition of NO were well correlated with the quantified catalytic amounts of the Cu2+ ions involved in the Cu-dimers, (Cu-O-Cu)2+. The mol fraction of the Cu ions present as the Cu-dimers increased at the sacrifice of the isolated Cu2+ with increasing Cu ion exchange level, suggesting that the species could be formed between the two Cu2+ in close proximity. Oxygen that could be thermally desorbed from the oxidized catalysts in the O2-TPD was responsible for the reduction of the Cu-dimers. It was concluded that the decomposition of NO over Cu-ZSM-5 catalyst proceeded by the redox of (Cu-O-Cu)2+, as active centers. With the temperature programmed surface reaction using N2O or NO over an oxidized catalyst sample as well as the O2-TPD, it was possible to estimate the change of the oxidation state of the Cu ions engaged in the Cu-dimers.

Development of the Al2O3-supported NaNO3-Na2Mg(CO3)2 sorbent for CO2 capture with facilitated sorption kinetics at intermediate temperatures

For the development of a dry solid sorbent having quite fast CO2 sorption kinetics in an intermediate temperature range of 245–300 °C to be applicable to a riser-type fluidized bed carbonator, samples of Al2O3-supported MgCO3 (1.2 mmol/g) promoted with different molar amounts of Na2CO3 (1.2, 1.8 mmol/g) and/or NaNO3 (0.6 mmol/g) were prepared by incipient wetness pore volume impregnation. For a reference, an unsupported bulk phase sorbent of NaNO3-Na2Mg(CO3)2 was also prepared. From the sorption reaction using a gas mixture containing CO2 by 2.5–10% at 1 bar for the sorbents after their activation to MgO, Al2O3-supported sorbents were featured by their rapid carbonation kinetics in contrast to the unsupported sorbent showing a quite slow carbonation behavior. The addition of Na2CO3 to the MgCO3/Al2O3 sorbent made MgO species more reactive for the carbonation, bringing about a markedly enhanced kinetic rate and conversion, as compared with the unpromoted MgCO3/Al2O3 sorbent having a small negligible reactivity. The addition of NaNO3 to MgCO3/Al2O3 or to Na2CO3-MgCO3/Al2O3 induced the same promotional effects, but to a lesser magnitude, as observed for the Na2CO3 addition. It was also characteristic for all these MgCO3-based sorbents that initial carbonation conversions with time appeared as sigmoid curves. For the Al2O3-supported sorbent comprised of NaNO3, Na2CO3, and MgCO3 by 0.6, 1.8, and 1.2 mmols, respectively, per gram sorbent, showing the best kinetic performance, a kinetic equation capable of reflecting such sigmoid conversion behavior was established, and its applicability to a riser carbonator was examined throughout a simple model calculation based on the kinetics obtained.

Ru-Promoted CrO x /Al2O3 Catalyst for the Low-Temperature Oxidative Decomposition of Trichloroethylene in Air

A series of Ru-promoted CrOx/Al2O3 as catalysts for the low-temperature oxidative decomposition of trichloroethylene (TCE) were characterized and evaluated in comparison with an unpromoted CrOx/Al2O3 catalyst. Catalyst characterization was conducted by surface area measurement, X-ray diffraction and X-ray photoelectron spectroscopy. Catalyst performance in the TCE decomposition reaction was evaluated with respect to the initial catalytic activity, the rate of catalyst deactivation, and the product concentrations of CO and Cl2 under dry or wet air conditions. The presence of a small amount of Ru, as much as 0.4 wt% in a CrOx/Al2O3 catalyst, brought about several beneficial effects on the catalytic reaction performance. As compared with the unpromoted CrOx/Al2O3, this Ru-promoted CrOx/Al2O3 catalyst showed enhanced catalytic activity (249 versus 264 °C in terms of temperature at which 50% of TCE conversion occurred), a reduced concentration of CO (180 versus 325 ppm) in the product, and a decreased propensity to deactivation. Performance improvements of the Ru-promoted CrOx/Al2O3 catalyst were thought to originate from its enhanced oxidation activity due to the coexisting highly-dispersed Ru oxides rendering less active Cr(III) to more active Cr(VI), and facilitating the process of supplying activated oxygen for the reaction system.

Thermodynamic features of the Cu-ZSM-5 catalyzed NO decomposition reaction

Over a Cu-ZSM-5 catalyst with a quantified amount of the active Cu2+-dimers (Cu2+-O2--Cu2+), the kinetics of the catalytic NO decomposition to N2 and O2 was derived on the basis of the proposed reaction mechanism, and such thermodynamic data as adsorption enthalpies of NO and O2 onto the Cu ion dimer sites were evaluated. It was revealed that the enthalpy of the adsorption of NO (δH=-34.1 kcal/mol) onto a reduced Cu+-dimer, as the initiating step of NO decomposition catalysis, was higher than that (δH=-27.8 kcal/mol) onto an oxidized Cu2+-dimer, or that (δH=-27.4 kcal/mol) of the dissociative adsorption of O2 onto the two reduced Cu+-dimers in neighbor. The strong inhibition effect of gas phase oxygen on the kinetic rate of NO decomposition at 400–600 ‡C could be explained by the thermodynamic predominance of the oxidized Cu2+-dimers against the active reduced Cu+-dimers on the catalyst even at high temperature and under the low partial pressure of oxygen. It was also found that the maximum catalytic activity at temperatures around 500 ‡C, which was commonly observed in the Cu-ZSM-5 catalyzed NO decomposition reaction, was attributed to the relatively large enthalpy of NO adsorption onto the reduced Cu+-dimers as compared to that of the reaction activation energy (=19.5 kcal/mol), resulting in less favored NO adsorption at the higher temperatures than 500 ‡C.

First-stage direct liquefaction of a subbituminous coal with oil-soluble metal naphthenates as dispersed catalyst precursors

Abstract The activities of catalysts produced from Mo, Co and Fe naphthenate oil-soluble precursors were investigated and the particle size and crystalline phase of each metal sulfide from each metal precursor were determined by SEM-EDX, TEM and XRD. Also, the synergistic effect between Fe and Co or between Fe and Mo in the hydroliquefaction of Usibelli (Alaska) subbituminous coal was investigated. In catalytic liquefaction experiments, excess elemental sulfur (three times the stoichiometrically required amount to convert the metal to the respective sulfide form: FeS 2 , Co 9 S 8 and MoS 2 ) was added to produce highly dispersed metal sulfide catalysts in situ . Parametric continuous unit tests were carried out to verify the reproducibility of the batch microautoclave results and to gather enough sample for further quantitative analyses of the coal liquid products (distillate yields and H/C atomic ratio). The hydrogen pressure drop or relative hydrogen consumption followed the order Mo > Co > Fe. This trend gave good linear correlations with coal liquefaction yields (coal conversion and oil yield). It was confirmed that the addition of Co or Mo as a promoter to Fe as a primary component gave a synergistic effect on both coal liquefaction yields (coal conversion, oil yield and distillate) and H/C ratio of the liquid products.

Kinetic modeling and dynamic simulation for the catalytic wet air oxidation of aqueous ammonia to molecular nitrogen

A kinetic model for the catalytic wet air oxidation of aqueous ammonia over Ru/TiO2 catalyst was developed considering the consecutive reaction steps as follows: (i) formation of active oxygen sites O* by the dissociative adsorption of aqueous O2 on the catalyst, (ii) oxidation of aqueous NH3 by the reaction with three O* sites to produce HNO2, (iii) aqueous phase dissociation of HNO2 into H+ and NO2−, (iv) formation of NH4+ by the association of NH3 with the HNO2-dissociated H+, (v) formation of N2 by the aqueous phase reaction between NO2− and NH4+, (vi) formation of NO3 by the reaction of NO2− with an O* site. For each reaction step, a rate equation was derived and its kinetic parameters were optimized by experimental data fitting. Activation energies for the reactions (ii), (v), and (vi) were 123.1, 76.7, and 54.5 kJ/mol, respectively, suggesting that the oxidation reaction of aqueous NH3 to HNO2 was a ratedetermining step. From the simulation using the kinetic parameters determined, the initial pH adjustment of the ammonia solution proved to be critical for determining the oxidation product selectivity between desirable N2 and undesirable NO3− as well as the degree of oxidation conversion of ammonia.

Simulation for Possible Coke-Free Operation of a Packed Catalyst Bed Reactor in the Steam-CO 2 Reforming of Natural Gas

A tubular packed bed reactor for the steam-CO2 combined reforming of natural gas to produce the synthesis gas of a target H2/CO ratio 2.0 was simulated. The effects of the reactor dimension, the feed gas composition, and the gas feeding temperature upon the possibility of coke formation across the catalyst bed were investigated. For this purpose, 2-dimensional heterogeneous reactor model was used to determine the local gas concentrations and temperatures over the catalyst bed. The thermodynamic potential distribution of coke formation was determined by comparing the extent of reaction with the equilibrium constant given by the reaction, CH4+2CO ⇔3C+2H2O. The simulation showed that catalysts packed in the central region nearer the entrance of the reactor were more prone to coking because of the regional characteristics of lower temperature, lower concentration of H2O, and higher concentration of CO. With the higher feeding temperature, the feed gas composition of the increased H2O and correspondingly decreased CO2, or the decrease in the reactor diameter, the volume fraction of the catalyst bed subsequent to coking could be diminished. Throughout the simulation, reactor dimension and reaction condition for coking-free operation were suggested.