An Al2O3-TiB2 nanocomposite was successfully synthesized by the high energy ball milling of Al, B2O3 and TiO2. The structures of the powdered particles formed at different milling times were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thermodynamic calculations showed that the composite formed in two steps via highly exothermic mechanically induced self-sustaining reactions (MSRs). The composite started to form at milling times of 9–10 h but the reaction was not complete. The remaining starting materials were consumed by increasing the milling time to 15 h. The XRD patterns of the annealed powders showed that aluminum borate is one of the intermediate products and that it is consumed at higher temperatures. Heat treatment of the 6-h milled sample at 1100°C led to a complete formation of the composite. Increasing the milling time to 15 h led to a refining of the crystallite sizes. A nanocomposite powder with a mean crystallite size of 35–40 nm was obtained after milling for 15 h.
Magnesium hydroxide is an important chemical, and is usually obtained from seawater or brine via precipitation process. The particle size distribution of magnesium hydroxide has great effects on the subsequent filtration and drying processes. In this paper, micron-sized magnesium hydroxide with high purity, large particle size and low water content in filter cake was synthesized via simple wet precipitation in a mixed suspension mixed product removal (MSMPR) crystallizer. The effects of reactant concentration, residence time and impurities on the properties of magnesium hydroxide were investigated by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Malvern laser particle size analyzer. The results show that NaOH concentration and residence time have great effects on the water content and particle size of Mg(OH)2. The spherical Mg(OH)2 with uniform diameter of about 30 μm was obtained with purity higher than 99% and water content less than 31%. Furthermore, the crystallization kinetics based on the population balance theory was studied to provide the theoretical data for industrial enlargement, and the simulation coefficients (
Coker gas oil (CGO) is a poor-quality feedstock for fluidized bed catalytic cracking (FCC) or hydrocracking. The pretreatment of CGO, especially hydrotreating, can significantly improve the product quality and protect the catalyst. In this work, we studied the hydrodesulfurization (HDS) of CGO in a slurry reactor. All the experiments were carried out in an autoclave using a NiMo/Al2O3 catalyst at reaction temperature 340°C–400°C, pressure 6–10 MPa, and stirring speed 800 r·min-1, with hydrogen-to-oil ratio in the range of 500–1500. The effects of the operating parameters on the desulfurization ratio were investigated and discussed. A macro reaction kinetic model was established for the HDS of CGO in the slurry reactor.
A gliding arc discharge (GRD) reactor was used to decompose ethanol into primarily H2 and CO with small amounts of CH4, C2H2, C2H4, and C2H6. The ethanol concentration, electrode gap, input voltage and Ar flow rate all affected the conversion of ethanol with results ranging from 40.7% to 58.0%. Interestingly, for all experimental conditions the SH2/SCO selectivity ratio was quite stable at around 1.03. The mechanism for the decomposition of ethanol is also described.
The novel composite separators composed of polysulfone and zirconia were prepared by phase inversion precipitation technique. This technique allows pre-evaporation time and extraction temperature to be varied in order to obtain optimal performances of the separators. In order to evaluate practical applicability of those composite separators, a small-scale electrolysis experimental apparatus was used to investigate the changes of cell voltage, gas purity and separator stability. The results revealed a decreased cell voltage compared to the conventional asbestos separators, and the gas purity and separator stability met the requirements for industrial use.
Spherical particles of
A high-performance Ni/ZnO adsorbent was prepared by homogeneous precipitation using urea hydrolysis and characterized by N2 adsorption-desorption, X-ray diffraction (XRD), and scanning electron microscope (SEM). The adsorbent was applied to the deep desulfurization of gasoline and showed a high breakthrough sulfur capacity and a remarkably high volume hourly space velocity. The effects of coexisting olefins in gasoline as well as adsorptive conditions on the adsorptive performance were examined. It was found that olefins in gasoline had a slightly inhibiting effect on the desulfurization performance of the adsorbent. The optimum conditions were 673 K, 1.0 Mpa with a volume hourly space velocity of 60 h-1. Under the optimum conditions, ultralow sulfur gasoline could be produced and the breakthrough sulfur capacity of the adsorbent was 360 mg-s/g-sorb for the model gasoline.
The biosorption properties of dead sulfate reducing bacteria (SRB) for the removal of Cu(II) and Fe(III) from aqueous solutions was studied. The effects of the biosorbent concentration, the initial pH value and the temperature on the biosorption of Cu(II) and Fe(III) by the SRB were investigated. FTIR analysis verified that the hydroxyl, carbonyl and amine functional groups of the SRB biosorbent were involved in the biosorption process. For both Cu(II) and Fe(III), an increase in the SRB biosorbent concentration resulted in an increase in the removal percentage but a decrease in the amount of specific metal biosorption. The maximum specific metal biosorption was 93.25 mg?g–1 at pH 4.5 for Cu(II) and 88.29 mg?g–1 at pH 3.5 for Fe(III). The temperature did not have a significant effect on biosorption. In a binary metal system, the specific biosorption capacity for the target metal decreased when another metal ion was added. For both the single metal and binary metal systems, the biosorption of Cu(II) and Fe(III) onto a SRB biosorbent was better represented by a Langmuir model than by a Freundlich model.
In this work, the removal of SO2 from gas mixture with air and SO2 by ammonium bicarbonate aqueous solution as absorbent was investigated experimentally in a bubble column reactor. The effects of the concentration of ammonium bicarbonate, the SO2 inlet concentration of gas phase and the gas flow rate on the removal rate of SO2 were studied. The results showed that the higher the SO2 inlet concentration and the gas flow rate, the shorter the lasting time of SO2 completely removed in gas outlet, and then the faster the decrease in the removal rate of SO2. The lasting time of SO2 completely removed in gas outlet increased with increasing ammonium bicarbonate concentration. During the process of SO2 absorption, there was a critical pH of solution. When the solution pH was less than the critical pH, it would sharply fall, resulting in a rapid decrease of the SO2 removal rate. A theoretical model for predicting the SO2 removal rate has been developed by taking the chemical enhancement and the sulfite concentration in the liquid phase into account simultaneously.
The TiO2 hollow nanospheres with diameters of about 230 nm were prepared by a simple and controllable route based on hydrolysis of Ti(OBu)4 on the surfaces of the Cu2O solid nanospheres followed by inward etching of the Cu2O nanospheres. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The further post-heat treatment led to the high crystallization of the TiO2 hollow nanospheres. The photocatalytic performances of these samples were evaluated for the photodegradation of rhodamine B (RhB) under UV-light irradiation. The as-prepared TiO2 hollow nanospheres showed higher photocatalytic activity than the CuO and the CuO/TiO2 hollow nanospheres. Effects of temperature and time for post-heat treatment of TiO2 as well as initial RhB concentrations on the RhB photodegradation have also been studied. The results show that the TiO2 hollow nanospheres have the good reusability as photocatalysts and are promising in waste water treatment.
TS-1/SiO2 catalyst for the epoxidation of propylene with hydrogen peroxide in a fixed-bed reactor has been investigated. The catalyst activity decreases gradually with the online reaction time, but the selectivity of propylene epoxide is kept at about 93%. The fresh, deactivated and regenerated catalysts were characterized with X-ray diffraction, Fourier transform infrared spectroscopy, ultra-violet-visible diffuse reflectance, Brunner-Emmett-Teller method and thermogravimetric analysis, and the deactivated catalyst was regenerated with H2O2/methanol solution. Compared with the fresh catalyst, both the framework structure and the content of titanium in the framework of the deactivated and regenerated TS-1/SiO2 catalysts were not changed. The major reason of the catalyst deactivation was the blockage of the channels of the catalyst by bulky organic by-products, which covered the active centers of titanium in TS-1. The deposited materials on the deactivated TS-1/SiO2 catalyst could be removed by treatment with hydrogen peroxide/methanol solution or pure methanol; the higher the treatment temperature and the higher the concentration of H2O2 in methanol, the higher the extent of the regeneration. The regeneration treatment did not influence the product selectivity in the propylene epoxidation.
The decomposition mechanism of ammonium sulfate catalyzed by ferric oxide was investigated in this paper. The decomposition kinetics parameters were determined via a global optimization of the Kissinger iterative method using the non-isothermal thermogravimetric analysis data. The products and intermediates were synchronously characterized by X-ray diffraction and mass spectrometry. The obtained results indicate that the decomposition process of ammonium sulfate catalyzed by ferric oxide can be divided into four stages of which the activation energies are 123.64, 126.58, 178.77 and 216.99 kJ·mol-1 respectively. The decomposition mechanisms at the first and the fourth stage both belong to Mample power theorem, the second stage belongs to Avrami-Erofeev equation and the third belongs to contracting sphere (volume) equation. The corresponding pre-exponential factors (
Macroreticular ion exchange resin catalysts were prepared by suspension polymerization, and then modified by alkylmercaptoamines. The modified catalysts were characterized by N2 adsorption/desorption measurements, scanning electron microscopy and differential scanning calorimetry. Key factors such as the mercaptan content, the degree of crosslinking and the structures of the promoters were investigated for the synthesis of Bisphenol A (BPA). At optimal conditions, the macroreticular ion exchange resin catalysts modified by alkylmercaptoamines showed high catalytic activity and selectivity for BPA synthesis.
A facile method for the carbonylative cyclization of
Zeolites have been regarded as one of the most important catalysts in petrochemical industry due to their excellent catalytic performance. However, the sole micropores in zeolites severely limit their applications in oil refining and natural gas conversion. To solve the problem, mesoporous zeolites have been prepared by introducing mesopores into the zeolite crystals in recent years, and thus have the advantages of both mesostructured materials (fast diffusion and accessible for bulky molecules) and microporous zeolite crystals (strong acidity and high hydrothermal stability). In this review, after giving a brief introduction to preparation, structure, and characterization of mesoporous zeolites, we systematically summarize catalytic applications of these mesoporous zeolites as efficient catalysts in oil refining and natural gas conversion including catalytic cracking of heavy oil, alkylation, isomerization, hydrogenation, hydrodesulfurization, methane dehydroaromatization, methanol dehydration to dimethyl ether, methanol to olefins, and methanol to hydrocarbons.