Sharif Digital Repository

An acid treatment of the cordierite monolith followed by coating of the CNT onto it by means of catalytic decomposition of methane was performed. The resulting material utilized as the support for the CoMo catalyst. The characterization outcomes showed that the CNTs were distributed uniformly on the surface of the monolith leading to a high BET surface area and relatively good adhered mesoporous layer of CNTs. Moreover, the catalytic activity of the resulting catalysts determined in an HDS reaction of naphtha. It was concluded that the activity of the CoMo catalyst over the CNT coated monolithic support (FACNT) was higher than that of the CoMo deposited onto the acid-treated monolith and... 

In this work, cristobalite crystallization and its effects on mechanical and chemical behaviour of injection moulded silica-based ceramic cores were investigated. In order to simulate casting process condition, the sintered samples at 1220 °C were also heated up to 1430 °C. Flexural strength test was carried out on both sintered and heat treated samples. Chemical resistance of the cores was evaluated by leaching the samples inside 43. wt% KOH solution at its boiling point. Phase evolution and microstructure were investigated by thermal analyses (DTA and DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM). Results showed that cristobalite was... 

The effects of SiO 2 and K 2O were investigated on the glass forming ability (GFA) and structural characteristics of CaOTiO 2P 2O 5 system. Differential thermal analyzer (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and 31P magic angle spinning NMR methods were applied for characterizations of the system. Unwanted crystallization in the initial three components base glass composition was observed by adding SiO 2 and crystalline phases such as TiP 2O 7, rutile (TiO 2) and cristobalite (SiO 2) were formed in it. The results showed that K 2O prevents crystallization of glasses and promotes the formation of glass. FT-IR and X-ray diffraction showed that the addition... 

In this paper, the effects of two methods of iridium impregnation into HZSM-5 on catalyst stability, selectivity for propylene and byproducts in the conversion of methanol to propylene (MTP) were investigated in a continuous flow isotherm fixed-bed reactor. XRD, BET surface area, NH 3-TPD and ICP-AES analytical techniques were applied to define the physical and chemical characteristics of zeolites. The reaction was conducted at 480°C and 1 bar with WHSV = 1 h -1, and with an equal weight percent of methanol and water in the feed. The results revealed that iridium impregnation into HZSM-5 powder led to enhanced propylene selectivity (8%) and catalyst stability while iridium impregnation into... 

Petroleum monoaromatics including benzene, toluene, ethylbenzene, and xylenes (BTEX) are among the notorious volatile organic compounds that contaminate water and soil. In this study, a surfactant- modified natural zeolite and its relevant granulated nanozeolites were evaluated as potential adsorbents for removal of petroleum monoaromatics from aqueous solutions. All experiments performed in batch mode at constant temperature of 20°C and pH of 6.8 for 48 h. The results revealed that the amount of BTEX uptake on granulated zeolites nanoparticles were remarkably higher than the parent micron size natural zeolite (in the order of four times). The isotherms data were analyzed using five models... 

Inclusion of nano-clays into hydrogels is an efficient approach to produce nanocomposite hydrogels. The introduction of nano-clay into hydrogels causes an increase in water absorbency. In the present work, Nanocomposite hydro-gels based on kappa-carrageenan were synthesized using sodium montmorillonite as nano-clay. Acrylamide and meth-ylenebisacrylamide were used as monomer and crosslinker, respectively. The structure of nanocomposite hydrogels was investigated by XRD and SEM techniques. Swelling behavior of nanocomposite hydrogels was studied by varying clay and carrageenan contents as well as methylenebisacrylamide concentration. An optimum swelling capacity was achieved at 12% of sodium... 

The separation of xylene isomers is an important application in separation processes that is based on their adsorption properties on different adsorbents. In this work, the Price and Danner method was employed with a neural network to investigate the adsorption behavior of binary systems of p-xylene/m-xylene, p-diethyl benzene/m-xylene, and p-diethyl benzene/p-xylene and the ternary system of p-diethyl benzene/m-xylene/p-xylene at 130 and 175°C. The Redlich-Kister, Wilson, and NRTL models were used to determine the activity coefficients in the adsorbed phase. Comparison with experimental data from the literature indicated that the proposed thermodynamic model would best determine surface... 

Depending on the type of dopant metal, many kinds of zircon based pigments are produced and blue vanadium pigment is the most important one of them. In this study, blue zircon ceramic pigments were synthesized from intermediate product, resulting from decomposition of zircon sand with NaOH. In this regard, various amounts of sulfuric acid, water, NH4VO3 as colorant, NaF as mineralizer and extra quartz were added to the prepared Na 2ZrSiO5. Role of quartz was to omit the repercussions of presence of free zirconia in the composition. The main objective of this work is to assess various reactions at different temperatures during blue pigment synthesis. Phase analysis was done by X ray... 

The objective of this study was to evaluate the effects of P 2O5 particle size distribution on the crystalline phases and microstructure of lithium disilicate glass-ceramics derived from the TiO2-ZrO2-Li2O-CaO-Al2O 3-SiO2 system for dentistry applications. The samples were made via fusion and casting procedure. Crystallisation as well as the morphology and microstructure of the samples were investigated using X-ray diffraction, differential scanning calorimetric and scanning electron microscopy. The results showed that the crystallisation of the samples occurred in the range of 500-650°C. The main crystalline phase was lithium disilicate (Li2Si2O5) along with Lithium metasilicate (Li2SiO3),... 

In the present research, proton exchange membranes based on partially sulfonated poly (ether sulfone) (S-PES) with various degrees of sulfonation were synthesized. It was found that the increasing of sulfonation degree up to 40% results in the enhancement of water uptake, ion exchange capacity and proton conductivity properties of the prepared membranes to 28.1%, 1.59 meq g -1, and 0.145 S cm -1, respectively. Afterwards, nanocomposite membranes based on S-PES (at the predetermined optimum sulfonation degree) containing various loading weights of organically treated montmorillonite (OMMT) were prepared via the solution intercalation technique. X-ray diffraction patterns revealed the... 

In this article, preparation of polypropylene/clay nanocomposites (PPCNC) via in situ polymerization is investigated. MgCl2/montmorillonite bisupported Ziegler-Natta catalyst was used to prepare PPCNC samples. Montmorillonite (MMT) was used as an inert support and reinforcement agent. The nanostructure of the composites was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Obtained results showed that silica layers of the MMT in these PPCNC were intercalated, partially exfoliated, and uniformly dispersed in the polypropylene matrix. Thermogravimetric analysis showed good thermal stability for the prepared PPCNC. Differential... 

The deactivation of solid acid catalysts in liquid phase alkylation of isobutane with 2-butene was investigated. Since under liquid phase conditions the alkylation reaction is severely diffusion limited, effects of diffusion on the rate of reaction and deactivation pathways were considered. In the present work, an attempt has been made to implement more appropriate assumptions in order to properly model catalyst deactivation in a mixed reactor. Accordingly, spatial variation of diffusivity in the pores of the catalyst was considered as a function of time on stream. The effect of the pore mouth plugging was also investigated and it was found that this phenomenon had a pronounced effect on the... 

This paper deals with simulation of transport phenomena in micro and nano pores. The number of cavities and the cavity radius were estimated by using Henry's law for adsorption of Argon onto ZSM-5 and NaX zeolites. This work showed both of zeolites have pores with average size less than 1 nm. Then with using micro- nano channel assumption instead of micro-nano pores, gas flow and heat transfer were investigated. Subsonic nonideal gas flow and heat transfer for different Knudsen number are investigated numerically using the Direct Simulation Monte Carlo method modified with a consistent Boltzamnn algorithm. The collision rate is also modified based on the Enskog theory for dense gas. It is... 

The objective of the present work is development of joint approximate diagonalization of eigenmatrices (JADE) as a member of independent component analysis (ICA) family, for the analysis of gas chromatography-mass spectrometry (GC–MS) and comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC–MS) data to address incomplete separation problem occurred during the analysis of complex sample matrices. In this regard, simulated GC–MS and GC × GC–MS data sets with different number of components, different degree of overlap and noise were evaluated. In the case of simultaneous analysis of multiple samples, column-wise augmentation for GC–MS and column-wise super-augmentation... 

High silicon fly ash (HSFA) utilized as a source of silicon in synthesizing of Na-A, -X and -Y zeolites through alkali fusion followed by hydrothermal treatment at 100 °C for 12 h. Various types of zeolites with different degrees of purity were prepared by changing Si/Al ratio of the reaction mixture from 1.6 to 3.0. In addition, exact boundaries of this ratio for synthesis of each zeolite type were determined. Furthermore, the effect of NaOH amount utilized in alkaline fusion step on crystalinity of samples investigated. The synthesized zeolites were characterized using various techniques including; XRD, TGA, FTIR, SEM and BET. The ion-exchange behaviors of zeolitic samples tested with... 

Hydroxyapatite (HAp) nanostrips were rapidly obtained during a mild microwave heating method. Applying microwave irradiation to Ca(NO3)2·4H2O/CTAB/Na2HPO4 precursor solution, the HAp precipitation process was occurred directly and without common crystallographic transformations including dissolution and slow recrystallization. The cationic surfactant CTAB was used as a soft template to modify nucleation and growth process. TEM investigations showed that the fabricated nanostrips had a width and length of about 10 and 55 nm, respectively. The X-ray diffraction pattern revealed that the fabricated well-crystallized and high purity hydroxyapatite nanostrips had a pattern similar to the bone... 

The use of a draft tube fluidized bed bioreactor (DTFBB) has been successfully demonstrated for the bioleaching of a chalcopyrite concentrate (Mousavi, et. al., 2005). In the present paper this technique was used for the bioleaching of zinc from a sphalerite bearing low-grade ore. A strain of the thermophilic bacterium, Sulfobacillus, has been isolated from the Kooshk lead and zinc mine near the city of Yazd (Iran) and is tested at temperatures 47 °C-72 °C. This is compared to leaching with a strain of the mesophile Acidithiobacillus ferrooxidans, which has been adapted to the high levels of zinc and the presence of the low-grade ore, and which was tested at temperatures 18 °C-42 °C. The... 

Chip-based micro fluidic separation systems often use serpentine channels to attain long separation lengths in a compact area. Such designs suffer from the dispersion, mostly 'racetrack' effect, due to the bends in the micro channels. The main goal of this paper is obtaining a model which has minimal racetrack in a serpentine geometry. A numerical analysis leads us to an optimized model which is different from previous attempts in this field. Our model uses modified turn radii, optimal length between bends with a constant zeta-potential boundary condition and a constant width through micro channel turns. It is shown that traveling fluid in this geometry has minimal dispersion as well as... 

Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler-Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl4 and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nano- structure of composites was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay... 

Synthesis of dimethyl ether (DME) via methanol dehydration were investigated over various catalysts, and via direct CO hydrogenation over hybrid catalysts composed of Al-modified H-Mordenite zeolite and Cu/ZnO/ZrO 2. H-Mordenite zeolite exhibited the highest activity in dehydration of methanol. However, its selectivity toward dimethyl ether was rather low. For this reason, the H-Mordenite was modified. Modification of zeolites was performed by wet impregnation method and considered catalysts were characterized by AAS, XRD and NH3-TPD analyses. Results of catalytic tests indicated that H-Mordenite modified with 8 wt% aluminum oxide was the best catalyst for synthesis of dimethyl ether from...