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521.
In this study, the effect of mechanical activation was evaluated on the leaching efficiency of copper sulphidic concentrate in 0.5 M sulphuric acid medium. The mechanical activation of samples was performed by a high energy planetary ball mill under the atmospheric conditions. The results showed that there was an optimum time of MA, about 6 h, in which the leaching efficiency reaches its maximum value (42% for 7 h of leaching). The improvement of leaching efficiency due to mechanical activation can be attributed to the significant decrease of the size of particles and the intense structural disordering of particles.  相似文献   
522.
Nanocrystalline calcium aluminate (CaO.2Al2O3) was prepared by a simple co-precipitation method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG-PPG-PEG, MW:5800) as surfactant and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N2 adsorption (BET), Temperature programmed reduction and oxidation (TPR-TPO) and Scanning electron microscopy (SEM) techniques. The results showed that the prepared support has a high potential as support for nickel catalysts in methane reforming with carbon dioxide. The results showed high catalytic activity and stability for the prepared catalysts. Among the prepared catalysts 15% Ni/CaO.2Al2O3 was the most active catalyst and showed the highest affinity for carbon formation. In addition, 7% Ni/CaO.2Al2O3 possessed high catalytic stability during 50 h time on stream. The TPO analysis revealed that increasing in nickel content increased the amount of deposited carbon over the spent catalysts. SEM results detected only whisker type of carbon for all spent catalysts.  相似文献   
523.
In this paper, a series of mesoporous supported nickel based catalysts on nanocrystalline alumina carrier promoted with various metals (Fe, CO, Zr, La and Cu) were prepared and employed in carbon dioxide methanation reaction. The samples were characterized by XRD, BET, TPR and SEM techniques. The BET results showed that the incorporation of promoters into nickel based catalysts decreased the surface area. The results showed that among the prepared catalysts, 30 wt.%Ni-5 wt.%La/Al2O3 and 30 wt.%Ni-5 wt.%Fe/Al2O3 possessed the highest surface area and the largest pore volume, respectively. Likewise, there was a slight decrease in the pore volume and the average pore diameters of the promoted samples. The TPR results depicted that the incorporation of the promoters enhanced the reducibility of the catalysts and shifted the reduction of NiO species to a lower reduction temperature. The CO2 conversions of all promoted catalysts except Cu-promoted sample were higher peculiarly at low temperatures compared to those attained for the unpromoted catalyst. 30 wt.%Ni-5 wt.%Fe/Al2O3 catalyst exhibited the best catalytic performance (70.63% CO2 conversion and 98.87% CH4 selectivity at 350 °C), high stability and desirable resistance against sintering.  相似文献   
524.
Prominent equipment with a very high demand for fuels in refineries is the fired preheater of crude oil. There are two main reasons to investigate the energy usage of such fired heaters. First, this is essential to the economic value of the refinery process unit and second, this is located at the beginning of the process line, which causes inefficient performance or damage in downstream equipment if it is not tuned properly. This paper concentrates on the thermal modeling of a fired heater of crude oil to evaluate the effect of influential parameters on fuel consumption. As the number of variables is markedly high, and considering the complexity of thermal modeling, all equations in a code yield predefined heater efficiency. Results from the model show that the increase in heater size yields a decrease in efficiency. It was also found that with a constant dimension of the fired heater, change in the number of pipes is much less influential rather than more inexpensive ideas like increasing speed of the burning gas on reduction of the fuel consumption. In other words, it was found that a distance of 500–650 mm from the center to the center distance of the pipes is the optimal distance to reduce fuel consumption.  相似文献   
525.
In this study methane autothermal reforming (ATR) was investigated over Ni/Al2O3 and Ni/Al2O3–CeO2 catalysts. The catalyst carriers were prepared through a facile one-step method, which produced mesoporous nanocrystalline carriers for Ni catalysts. The samples were characterized by XRD, TPR, BET, TPO and SEM characterization techniques and the catalytic activity and stability were also studied at different conditions (GHSV and feed ratio) in methane ATR. It was found that the nickel catalyst supported on 3 wt.% Ce–Al2O3 exhibited higher activity compared to the catalysts supported on the Al2O3 and promoted Al2O3 with 1 and 6 wt.% Ce. The results also showed that the nickel catalyst supported on 3 wt.% Ce–Al2O3 possessed the highest resistance against carbon deposition in ATR reaction.  相似文献   
526.
In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al2O3 catalysts with various Co loadings, and the prepared catalysts were used in CO2 methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al2O3 sample with a specific surface area of 129.96 m2/g possessed the highest catalytic performance in CO2 methanation (76.2% CO2 conversion and 96.39% CH4 selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.  相似文献   
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