Characterization and catalytic performance of CeO_2-Co/SiO_2 catalyst for Fischer-Tropsch synthesis using nitrogen-diluted synthesis gas over a laboratory scale fixed-bed reactor

The surface species of CO hydrogenation on CeO2-Co/SiO2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H2O and CO2 was the competitive reaction for the surface oxygen species, CH4 was produced via the hydrogenation of carbon species step by step, and C2 products were formed by the polymerization of surface-active carbon species （-CH2-）. Hydrogen assisted the dissociation of CO. The hydrogenation of surface carbon species was the rate-limiting step in the hydrogenation of CO over CeO2-Co/SiO2 catalyst. The investigation of total pressure, gas hourly space velocity （GHSV）, and product distribution using nitrogen-rich synthesis gas as feedstock over a laboratory scale fixed-bed reactor indicated that total pressure and GHSV had a significant effect on the catalytic performance of CeO2-Co/SiO2 catalyst. The removal of heat and control of the reaction temperature were extremely critical steps, which required lower GHSV and appropriate CO conversion to avoid the deactivation of the catalyst. The feedstock of nitrogen-rich synthesis gas was favorable to increase the conversion of CO, but there was a shift of product distribution toward the light hydrocarbon. The nitrogen-rich synthesis gas was feasible for F-T synthesis for the utilization of remote natural gas.

Effects of pretreatment and reduction on the Co/Al_2O_3 catalyst for CO hydrogenation

The purpose of this study was to investigate the effect of preadsorbed CO at different temperatures, calcination temperatures, the combined influence of reduction temperature and time, and pretreatment using hydrogen or syngas as reduction agents on the F-T synthesis （FTS） activity and selectivity of Co/Al2O3 catalyst. The reactivity of the carbon species at higher preadsorption temperature with H2 in TPSR decreased, whereas the carbon-containing species showed higher reactivity over Co/Al2O3 catalyst with low calcination temperature. This agreed well with the order of catalytic activity for F-T synthesis on this catalyst. The catalytic activity of the catalyst varied with reduction temperature and time remarkably. CODEX optimization gave an optimum reduction temperature of 756 K and reduction time of 6.2 h and estimated C5＋ yield perfectly. The pretreatment of Co/Al2O3 catalyst with different reduction agents （hydrogen or syngas） showed important influences on the catalytic performance. A high CO conversion and C5＋ yield were obtained on the catalyst reduced by hydrogen, whereas methane selectivity on the catalyst reduced by syngas was much higher than that on the catalyst reduced by hydrogen.

Influence of Molecular Sieve Supported Metal Oxides on the Desulfurization in Catalytic Cracking of Sulfur-containing Model Compounds and Hydrocarbons

Zn, La, Zr, Sn and Ti loaded molecular sieves were prepared by impregnation method. Conversions of benzothiophene and dibenzothiophene over the metal oxides modified ultra stable zeolite Y(USY), ZSM-5, β and MSU-2 molecular sieve catalysts were investigated by means of micro-activity test (MAT) experiments. The results showed that Zn and La loaded catalysts were better than the other metals, and ZSM-5 with lower SiO2/Al2O,3 mole ratio showed better results than those with higher SiO2/Al2O3 as far as desulfurization reaction is considered. A comparison of the desulfurization activities of the La/Zri-USY catalyst with USY catalyst indicated that the bimetal loaded USY catalyst gave good products selectivity when sulfur containing heavy oil was used as the feedstock. The sulfur content in gasoline fraction was decreased by 25%, and there was no loss in the Research Octane Number.

Synthesis of Dialkyl-substituted Terminal Olefin

Dialkyl-substituted terminal olefins were synthesized from the coupling reaction of a-olefins which were catalyzed by zirconocene dichloride/methylalumoxane （MAO） catalyst system under mild condition. High yield was gained and no other oligmer was detected. It was found that the ratio of AI/Zr is responsible for the selectivity of product.

Studies on the Polymerization of Styrene in the MCM-41 Phase

The polymerization of styrene in the media of MCM-41 is carried out by means of host-guest polymerization of styrene in MCM-41 mesoporous material with the aim to investigate the effects of interface and confinement of MCM-41 on host-guest interactions. Detailed physical properties of the mesoporous MCM-41 material containing polystyrene is characterized by XRD(X-ray diffraction), FT-IR(Fourier transform infrared), TGA(thermal gravimetric analysis), and nitrogen adsorption-desorption isotherms. We also find a great increase in the glass transition temperature of guest polystyrene influenced by the confined geometry of the host by differential scanning calorimetry(DSC).

Selective Oxidation of Light Hydrocarbons Using Lattice Oxygen Instead of Molecular Oxygen

In this paper, selective oxidation of n-butane to maleic anhydride (MA) and partial oxidation of methane to synthesis gas with lattice oxygen instead of molecular oxygen are investigated. For the oxidation of butane to MA in the absence of molecular oxygen, the Ce-Fe promoted VPO catalyst has more available lattice oxygen and provides higher conversion and selectivity than that of the unpromoted one. It is supposed that the introduction of Ce-Fe complex oxides improves redox performance of VPO catalyst and increases the activity of lattice oxygen. For partial oxidation of methane to synthesis gas over LaFeO3 and La0.8Sr0.2FeO3 oxides, the reaction with flow switched between 11% O2-Ar and 11% CH4-He at 900℃ was carried out. The results show that methane can be oxidized to CO and H2 with selectivity over 93% by the lattice oxygen of the catalyst in an appropriate reaction condition, while the lost lattice oxygen can be supplemented by air re-oxidation. It is viable for the lattice oxygen of the LaFeO3 and La0.8Sr0.2FeO3 catalyst instead of molecular oxygen to react with methane to synthesis gas in the redox mode.

Comparison of LaFeO_3,La_(0.8)Sr_(0.2)FeO_3,and La_(0.8)Sr_(0.2)Fe_(0.9)CO_(0.1)O_3 perovskite oxides as oxygen carrier for partial oxidation of methane

Comparison of LaFeO3, La0.8Sr0.2FeO3, and La0.8Sr0.2Fe0.9CO0.1O3 perovskite oxides as oxygen carrier for partial oxidation of methane in the absence of gaseous oxygen was investigated by continuous flow reaction and sequential redox reaction, Methane was oxidized to syngas with high selectivity by oxygen species of perovskite oxides in the absence of gaseous oxygen. The sequential redox reaction revealed that the structural stability and continuous oxygen supply in redox reaction decreased over La0.8Sr0.2Fe0.9Co0. 1O3 oxide, while LaFeO3 and La0.8Sr0.2FeO3 exhibited excellent structural stability and continuous oxygen supply.

Effect of calcination temperature and reaction conditions on methane partial oxidation using lanthanum-based perovskite as oxygen donor

We investigated the effect of calcination temperature, reaction temperature, and different amounts of replenished lattice oxygen on the partial oxidation of methane （POM） to synthesis gas using perovskite-type LaFeO3 oxide as oxygen donor instead of gaseous oxygen, which was prepared by the sol-gel method, and the oxides were characterized by XRD, TG/DTA, and BET. The results indicated that the particle size increased with the calcination temperature increasing, while BET and CH4 conversion declined with the calcination temperature increasing using LaFeO3 oxide as oxygen donor in the absence of gaseous oxygen. CO selectivity remained at a high level such as above 92%, and increased slightly as the calcination temperature increased. Exposure of LaFeO3 oxides to methane atmosphere enhanced the oxygen migration of in the bulk with time online owing to the loss of lattice oxygen and reduction of the oxidative stated Fe ion simultaneously, The high reaction temperature was favorable to the migration of oxygen species from the bulk toward the surface for the synthesis gas production with high CO selectivity. The product distribution and evolution for POM by sequential redox reaction was determined by amounts of replenished lattice oxygen with gaseous oxygen. The optimal process should decline the total oxidation of methane, and increase the selectivity of partial oxidation of methane.

Numerical study on soot removal in partial oxidation of methane to syngas reactors

The serious carbon deposition existing in catalytic partial oxidation of methane(CPOM) to syngas process is one of the key problems that impede its industrialization. In this study, 3-dimensional unsteady numerical simulations of the soot formation and oxidation in oxidation section in a heat coupling reactor were carried out by computational fluid dynamics(CFD) approach incorporating the Moss-Brookes model for soot formation. The model has been validated and proven to be in good agreement with experiment results. Effects of nozzle type,nozzle convergence angle, channel spacing, number of channels, radius/height ratio, oxygen/carbon ratio, preheat temperature and additional introduction of steam on the soot formation were simulated. Results show that the soot formation in oxidation section of the heat coupling reactor depends on both nozzle structures and operation conditions, and the soot concentration can be greatly reduced by optimization with the maximum mass fraction of soot inside the oxidation reactor from 2.28% to 0.0501%, and so that the soot mass fraction at the exit reduces from0.74% to 0.03%.

Catalytic Partial Oxidation of Methane with Air to Syngas in a Pilot-Plant-Scale Spouted Bed Reactor

On the basis of hydrodynamic and scaling-up studies, a pilot-plant-scale thermal spouted bed reactor (50 mm in ID and 1500 mm in height) was designed and fabricated by scaling-down cold simulators. It was tested for making syngas via catalytic partial oxidation (CPO) of methane by air. The effects of various operating conditions such as operating pressure and temperature, feed composition, and gas flowrate etc. on the CPO process were investigated. CH4 conversion of 92.2% and selectivity of 92.3% and 83.3% to CO and H2, respectively, were achieved at the pressure of 2.1 MPa. It was found that when the spouted bed reactor was operated within the stable spouting flow regime, the temperature profiles along the bed axis were much more uniform than those operated within the fixed-bed regime. The CH4 conversion and syngas selectivity were found to be close to thermodynamic equilibrium limits. The results of the present investigation showed that spouted bed could be considered as a potential type of chemical reactor for the CPO process of methane.

A Novel Technology for Synthesizing Pentasil Zeolites Based on Solid-Solid Mass Transformation Mechanism

A novel technology of preparing zeolites based on solid-solid mass transformation mechanism is developed for the first time. By employing this technology, three different types of highly crystallized pentasil zeolites, ZSM-35 (FER-type), Silicalite-1(MFI-type) and Mordenite(MOR-type), are successfully synthesized in the solid system. In terms of commercial production, the technology-could simplify synthesis procedure and make the continuous production of zeolites possible, so as to improve the productivity. Additionally, it is environmentally friendly because the crystallization occurs in solid phase where there exists no pollution caused by waste liquid. Therefore, this technique provides us with a new industrial process for the clean and continuous production of zeolites. The characteristics in synthesis chemistry and the crystallization mechanism involved in the technology are also discussed.

Synthesis gas production using oxygen storage materials as oxygen carrier over circulating fluidized bed

A novel process for synthesis gas production over Circulating Fluidized Bed （CFB） using oxygen storage materials as oxygen carder was reported. First, oxygen in the air was chemically fixed and converted to lattice oxygen of oxygen storage materials over regenerator, and then methane was selectively oxidized to synthesis gas with lattice oxygen of oxygen storage materials over riser reactor. The results from simulation reaction of CFB by sequential redox reaction on a fixed bed reactor using lanthanum-based perovskite LaFeO3 and La0.8Sr0.2Fe0.9CO0.1O3 oxides prepared by sol-gel, suggested that the depleted oxygen species could be regenerated, and methane could be oxidized to synthesis gas by lattice oxygen with high selectivity. The partial oxidation of methane to synthesis gas over CFB using lattice oxygen of the oxygen storage materials instead of gaseous oxygen should be possibly applicable.

A scenario-based clean diesel production strategy for China National Petroleum Corporation

Facing increasingly strict environmental regulations on transportation fuels, China National Petroleum Corporation （CNPC）, the second largest supplier of petroleum products in China, needs to upgrade its transportation fuels. Using the scenario-based analysis method, this paper analyzes how the output and emission related properties, including cetane number, and sulfur and aromatics contents of diesel produced by CNPC, will vary with changes in the configuration of diesel production units in the next 5-10 years. The results showed that, to upgrade its diesel, CNPC needs to adjust its diesel pool by decreasing the share of fluid catalytic cracking （FCC） diesel and increasing the shares of hydrocracking （HDC） and hydrotreating （HDT） diesel. Furthermore, to produce ultra-low-sulfur diesel, straight-run diesel as well as poor diesel blendstocks such as FCC diesel and coker diesel should be hydrotreated before being blended into finished diesel. Developing highly efficient HDC and HDT catalysts and corresponding processes is the key to CNPC economically producing more and cleaner diesel.

H_2-induced CO adsorption and dissociation over Co/Al_2O_3 catalyst

The activation of adsorbed CO is an important step in CO hydrogenation. The results from TPSR of pre-adsorbed CO with H2 and syngas suggested that the presence of H2 increased the amount of CO adsorption and accelerated CO dissociation. The H2 was adsorbed first, and activated to form H＊ over metal sites, then reacted with carbonaceous species. The oxygen species for CO2 formation in the presence of hydrogen was mostly OH^＊, which reacted with adsorbed CO subsequently via CO^＊＋OH^＊ → CO2^＊＋H^＊; however, the direct CO dissociation was not excluded in CO hydrogenation. The dissociation of C-O bond in the presence of H2 proceeded by a concerted mechanism, which assisted the Boudourd reaction of adsorbed CO on the surface via CO^＊＋2H^＊ → CH^＊＋OH^＊. The formation of the surface species （CH） from adsorbed CO proceeded as indicated with the participation of surface hydrogen, was favored in the initial step of the Fischer-Tropsch synthesis.

Numerical study of liquid coverage in a gas-liquid-solid packed bed

In this work, computational fluid dynamics （CFD） simulations using the volume-of-fluid （VOF） model were employed to investigate the effects of liquid properties, liquid and gas flow rates, and wettability of particles on liquid maldistribution at the microscopic level in a fixed bed reactor. The simulation results show that the number of wetted particles decreases with increasing gas velocity, consequently leading to lower liquid-solid contact areas. The radial liquid distribution is greatly enhanced by increasing the liquid flow rate, whereas the time for the liquid to pass through the whole bed is decreased, as expected. Based on simulation results, it was found that the liquid-solid contact area can be increased by using liquids of high viscosities and more wettable particles. However, the flow-through time increases with increasing liquid viscosity. An increase in the gas density showed a minimal impact on the liquid flow- through time, and the liquid density does not impact the radial liquid distribution or the liquid flow time within a range of liquid densities typically encountered in the petrochemical industry.

Application of gamma-ray attenuation technology in density measurement of a slurry reactor

Axial density profile of the gas-liquid-solid mixture in a slurry bubble column was measured by gamma-ray attenuation technology.Several measures for improving measurement precision were presented based on the discussion on attenuation law.It was found that the response frequency and the ray intensity should be as high as possible to improve the measurement precision.The mass absorption coefficient depended on not the object’s thickness but the location where the object was placed between the ray source and the detector.The results showed that the density in the column decreases with the increase of column height,which indicates that the measurement by gamma-ray attenuation is reasonable.