The conversion of methanol to dimethyl ether was carried out over various commercial mordenite and ion-exchanged catalysts to evaluate the catalytic performance of mordenite catalysts with different pore structures and acidities. These catalysts were compared for their catalytic properties in a fixed-bed reactor at 1 atm, 573 K and LHSV of 2.84 h− 1. The catalysts were characterized by BET, ICP, NH3-TPD, XRD, TGA and FT-IR techniques. The ion-exchanged mordenite showed higher activity, selectivity and good stability in dehydration of methanol due to the addition of medium acid sites. Also, the effect of water on catalyst deactivation was investigated over two selected catalysts in order to develop a suitable catalyst for synthesis of dimethyl ether. It was found that the H-mordenite catalyst supplied by Süd-chemie Co., (MCDH-1) was more active and less deactivated than another one in a feed containing 20 wt.% water. 相似文献
Hydrodesulfurization (HDS) of dibenzothiophene in a batch reactor was performed at 5.5 MPa and 320 °C on CoMoS/Al2O3‐TiO2 using trans‐1,2‐cyclohexanediamine‐N,N,N′,N′‐tetraacetic acid (CYDTA) as a complexing agent for the preparation method. The effects of titania, concentration of CYDTA, and preparation procedure were investigated by using X‐ray diffraction, BET, Fourier transform infrared spectroscopy, and temperature‐programmed desorption of ammonia experiments. The catalyst prepared by impregnation with γ‐alumina and titanium isopropoxide as raw materials and a CYDTA/Co mole ratio of 1.2 provided an HDS activity (on a pseudo‐first‐order kinetic constant basis) value ~3.8 times higher compared to that of a CoMo/Al2O3 catalyst. 相似文献
Analytical methods including ultra-performance liquid chromatography (UPLC) and high-performance liquid chromatography (HPLC) with photodiode array (PDA) detector were developed for the analysis of caffeoylquinic acid derivatives in seeds, leaves and roots of Arctium lappa L. Separation was performed on C18 column utilising 5% (v/v) acetic acid in water and acetonitrile at 330 nm. Both methodologies were validated in terms of linearity, precision, and recovery. The results showed that the major advantages of UPLC, over HPLC were the fast analysis, narrow peaks, high sensitivity, and reduction of solvent consumption. Subsequently the methods were applied for the identification and quantification of chlorogenic acid (5-CQA) and 1,5-dicaffeoylquinic acid (1,5-DCQA) as main compounds in samples. The total phenolic content of samples ranged from 3.93 to 14.13 g of 5-CQA equivalent/100 g dry weight (DW). There was a significant variability from 89 to 571 mg/100 g for 5-CQA and 48 to 486 mg/100 g for 1,5-DCQA in dry material. 相似文献
Efficient use of solar radiation needs detailed knowledge of its spatial and temporal variations. Such information can be achieved using interpolating measured irradiance by ground stations. But more reliable results can be obtained by processing geostationary satellite images. Heliosat is an algorithm which has been developed to estimate global horizontal irradiance at ground level from images taken in the visible band by the Meteosat satellites.The aim of this study was to evaluate the Heliosat-II model by using daily global solar irradiation data measured at the four radiometric stations in Iran as well as Meteosat-5 images which are recorded by a spacecraft over 63°E. Mean RMSD% and MBD% for all stations were 11.7% and 1.9%, respectively. The mean values of intercept, slope and correlation coefficient were 0.82 (kWh m−2), 1.05 and 0.93, respectively. Seasonally, the maximum RMSD occurs in autumn (22.1%) and the minimum is experienced in spring (8.4%). This accuracy is a great achievement for producing a high quality solar radiation atlas in a country such as Iran with very sparse radiometric network and frequently unreliable measured irradiation data. 相似文献
The thermal wave and the Pennes bioheat transfer models are solved analytically by employing the Laplace transform method for small and large values of reflection power (albedo) during laser irradiation. Most of the previous studies have been based on the infinite heat diffusion velocity, but non-Fourier thermal behavior has been observed experimentally in biological tissue. At low initial albedo values, the temperature in the skin depth that directly results from conduction heat transfer process is caused by the lengthy thermal relaxation time in skin tissue. This condition generates a big difference between the thermal wave and Pennes results at the beginning of the heating process. This difference increases under short-time heating condition and high heat flux. However, with high initial albedo, the temperature distribution in the skin depth becomes negligible because of the skin absorption of laser beams. The non-Fourier effect should be considered during laser heating with low albedo, because errors in the predicted temperature values may occur.
During the milling process, self-excited vibration or chatter adversely affects tool life, surface quality and productivity rate. In this paper, nonlinear cutting forces of milling process are considered as a function of chip thickness with a complete third order polynomial (instead of the common linear dependency). An optimal control strategy is developed for chatter suppression of the system described through nonlinear delay differential equations. Counterbalance forces exerted by actuators in x and y directions are the control inputs. For optimal control problem, an appropriate performance index is defined such that the regenerative chatter is suppressed while control efforts are minimized. Optimal control law is determined based on variation of extremals algorithm. Results show that under unstable machining conditions, regenerative chatter is suppressed effectively after applying the optimal control strategy. In addition, optimal controller guarantees robust performance of the process in the presence of model parametric uncertainties. 相似文献
Absorption and emission spectra of three hetarylazoquinoline compounds with different substituents were examined in liquids and liquid crystalline solvents for the first time. The spectral features of the hetarylazoquinoline dyes were explained according to azo/hydrazone tautomerism in conjunction with the solvatochromic characteristic of the preferred tautomer. The nature and extent of solute-solvent interactions were described using Kamlet-Taft and Katritzky multiparameter polarity scales. It was observed that solvatochromic azo/hydrazone tautomerism depend on multiple solute-solvent interactions, in particular on specific interactions and the solvent ability to transport the hydrogen atom through the media. In addition, it was concluded that anisotropic hosts prevent shift of the tautomeric equilibrium toward the hydrazone form. 相似文献
In this work mesoporous nanocrystalline γ-Al2O3 has been synthesized by a three step (hydrolysis, condensation and hydrothermal treatment) sol–gel procedure in nitric acid
medium with cationic surfactant (hexadecyltrimethyl ammonium bromide) as template. The prepared sample was employed as a carrier
for the n-dodecane dehydrogenation catalyst. The synthesized samples were characterized by X-ray diffraction (XRD), N2 adsorption (BET), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric (TG)
and temperature programmed reduction (TPR) techniques. The nitrogen adsorption analysis showed that the samples possessed
mesoporous structure with high specific surface areas larger than 370 m2 g−1 and pore volumes larger than 1.5 cm3 g−1. The prepared samples also showed a high thermal stability up to 750 °C which is important for carrier of heterogeneous catalysts.
The results of catalyst testing in the dehydrogenation reaction of n-dodecane confirmed that the synthesized support has a
good potential to function as a carrier for n-dodecane dehydrogenation catalysts. 相似文献