Sharif Digital Repository

In this study equilibrium condition of pure hydrogen hydrates is determined with Lee-Holder model. Two hydrogen molecules and four hydrogen molecules encaged in the small and large cavities respectively. Langmuir constant of hydrogen is calculated with the Exp-6 potential. Lee et al. reported parameter of this model by integrating ab initio calculation with classical statistical thermodynamics. This model reasonably predicts dissociation pressures of hydrogen hydrates.Calculated reference parameters are used in modeling of binary hydrogen hydrates. Lattice distortion model is used for modeling of binary hydrogen hydrates with tetrahydrofuran (THF) as a promoter. Cavity radius and parameters... 

Due to the wide application of Mass Concrete in the body and the foundation of dams, foundations of tall buildings, industrial machinery, and power plants, foundation and piers of bridges, etc.,it is necessary to devise methods in order to prevent the adverse effects of the high volume of such concretes. Since the major negative outcome of high volume is the decrease of the strength of concrete, which in turn is the direct consequence of the cracks resulted from high increase in the temperature within the volume of the concrete as a result of Hydration process and the produced heat which remains inside the bulk of concrete, any solution should involve some form of transferring the heat to... 

The most important raw material for production of titanium dioxide is titanium that used in Aerospace, Plastic, Pigment and Pharmacy industries. Due to the presence of titanium minerals in Iran, reduce imports of titanium dioxide is one of the goals of the Ministry of Industries and Mines to achieve self-sufficiency in the production of TiO2.One of the very rich sources of titanium is alluvial sands in northern of Iran. In this study the TiO2 high grade pigment production from these sources has been investigated. Titanium-bearing sands with 9.5% TiO2 are used to produce high grade TiO2 pigment. After magnetic separation stage and reach a purity of 16.2% TiO2, upgrading slag step is not... 

Pavement preventive maintenance methods such as slurry seals are cost-effective treatments that enhance pavement longevity. Incorporation of recycled materials such as reclaimed asphalt pavement (RAP) into asphalt pavements helps further reduce costs and energy consumption. Because the use of emulsions and pavement preventive methods is uncommon in Iran, there is little experience with the technology in this area. The present study designed and developed slurry seal and emulsion test devices at Sharif University lab to study the feasibility of incorporation of RAP into slurry seal mixtures while respecting the limits specified by the ISSA and ASTM. Two slurry seal mixtures in which cement... 

Concrete is the most used man-made material on earth, albeit is responsible for the ten percent of the carbon dioxide gas emitted by human to atmosphere. Also the most important constituent of concrete, hydrated cement, has a sophisticated structure yet its precipitation, composition, mechanical properties and morphology has been the subject of dispute among cement researchers. On the other hand, according to the increasing focus on sustainable development, design of optimum materials has become important. Several models have been proposed for the structure of cement hydrate while every model has its own advantages and disadvantages. Recently, a combinatorial model at atomic scale has been... 

Gas hydrate is a nonstoichiometric structure that has been produced from water and gas in appropriate thermal and pressure conditions. There has been a long time that scientists work on predicting hydrate production condition. Predicting the hydrate behavior for pure substances is easier than mixtures; because there are some behaviors of mixtures that we do not know their reasons yet. In this thesis, there has been tried to give a model to describe hydrate reactions to temperature and pressure changes besides predicting the hydrate type and the cage occupancy. Since the hydrate behavior is nonstoichiometric, it is useful to know the cage occupancy to predict the amount of hydrate... 

Magnesia-Doloma refractories has advantages such as stability in alkaline environments, clean steel production, resistance to acid slag, good cement kiln coating flexibility, low production cost. It also has some weaknesses such as low resistance to thermal shock and quick hydration. In the present study using Birjand Mines Magnesite powders and Dolomites from Zefreh, Esfahan, Magnesia-Doloma clinkers were pressed under the pressure 90 MP and prepared at 1650⁰C in furnace under air atmosphere. The effect of adding 0, 2, 4, 6, and 8% of the Microparticles and Nanoparticles of α-Alumina on microstructure, physical properties, hydration resistance and Thermal shock resistance was studied. Phase... 

Magnesia–Doloma refractories are considered as a mixed product of alkali products i.e. sintered (fused) magnesia and doloma in which 50-80 wt% magnesia is contained. These refractories enjoy some advantages such as high slag resistance corrosion, high-temperature performance, potential for production of pure molten iron and low cost due to abundance of magnesia and doloma resources in access. However, there exist some problems with these refractories that render them unsuitable for some applications. Among these cases, poor resistance of hydration can be cited that may constrain the amount of this refractory in various industrial applications. In the present work, the addition effect of... 

According to the importance of conversion and transmission of energy, and introduction of hydrate formation process as an alternative method, in this study, the nano-graphene oxide is used to increase the rate if methane gas hydrates formation. The experiments were performed at different concentrations of 30 to 70 ppm and the results were compared with pure water. The effect of temperature and pressure on hydrate formation at temperatures of 1 and 2˚C and pressures of 48 and 53 bar were studied. And it was found that nano-graphene oxide can be used to accelerate the methane hydrates formation. The effect of ultrasonic on methane hydrate formation has been studied that it was found that the... 

In this study two approaches were applied to predict the hydrate dissociation pressure of natural gas in the presence of aqueous water. One approach applied van der Waals and Platteeuw solid solution theory & PR EOS the other applied a feed forward multi layers artificial neural network (ANN) with 19 input variables (temperature, existence of hydrocarbon liquid and ice phase, gas phase composition, inhibitor composition in aqueous phase), and one hidden layer with 17 neurons. In comparison of both methods it was concluded that, in temperature above 12℃ , ANN is more accurate than thermodynamic model, but in lower temperature thermodynamic model is comparable with ANN. The trained network... 

In this study thermodynamics and kinetics effects of two ionic liquids (ILs) on the formation and dissociation of methane and carbon dioxide hydrates were investigated. The ILs used in this study are 1-butyle-3-metylimidazolium tetrafluoroborate, [Bmim][BF4], and 1-butyle-3-metylimidazolium methyl sulfate, [Bmim][MS]. At the first step of experimental section, the tetrahydrofuran (THF) was used in atmospheric pressure. The structure of THF hydrate is similar to natural gas hydrate; therefore it is used as a model for studying the properties and investigation of inhibitors effects on gas hydrates. In order to consider the effects of foregoing ILs on the formation and dissociation of gas... 

Formation of gas hydrates is a challenge in the oil and gas industry. Gas hydrate formation can be prevented by several methods. One of these methods is to utilize of inhibitor components. The gas hydrate inhibitors can affect hydrate formation from two aspects, i.e., thermodynamic or kinetic. In this work, thermodynamic and kinetic effects of [Emim][BF4] ionic liquid on growth and dissociation of methane hydrate crystal were investigated using molecular dynamics simulation. Molecular dynamics simulation is powerful tool to investigate the thermophysical, structural, and dynamic properties of methane hydrate and the formation, dissociation, and inhibition mechanisms at the molecular scale.... 

Gas hydrates are ice-like clathrate compounds. Methane, carbon dioxie and natural gas compounds can form gas hydrate and plug pipelines, in order to preventing of gas hydrate formation, inhibitors like electrolytes are added to the natural gas pipelines. In this work a model proposed to predict the hydrate formation conditions in presence of some inhibitors such as NaCl, KCl, NaBr, KBr, [BMIM][BF4] and [BMIM][Br]. So a new equation of state that can be applied to both electrolyte and associating solutions called GV-SAFT-MSA is developed. Two dialkylimidazolium ionic liquids [BMIM][BF4] and [BMIM][MS] have been investigated for their potential application as novel gas hydrate inhibitors. The... 

Gas hydrates are ice-like clathrate compounds. Methane and carbon dioxide can form gas hydrate and plug pipelines, in order to preventing of gas hydrate formation, inhibitors like salts and alcohols are added to the natural gas pipelines. In this work a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate formation conditions for carbon dioxide and methane in the presence of aqueous ionic liquid solutions. The statistical model of Van der Waals and Platteeuw mixed with Holder model is employed for hydrate phase. An equation of state applicable to the systems containing electrolyte developed by coupling the statistical associating fluid theory... 

The formation of gas hydrates in oil and gas industries has been the subject of long-standing problems. For example, the hydrate formation may occur and block gas pipelines which can lead to safety hazards. All of these will result in catastrophic economic losses and ecological risks. Therefore, various methods were developed to mitigate the formation of gas hydrate. In many cases, the hydrate inhibition by adding kinetic and thermodynamic inhibitors to the system is the only viable option. But recently using ionic liquids as novel hydrate inhibitors and the discovery of dual function thermo-kinetic inhibitors have been studied. In this project the performance of six imidazolium-based ionic... 

Hydrated lime has been used as an anti-stripping agent with acceptable performance. Numorous studies have been conducted to evaluate hydrated lime as an anti-stripping agent, however effect of hydrated lime on performance properties of asphalt mixture has not been fully addressed. In the present study, the effect of hydrated lime was investigated. In this study, three methods of adding hydrated lime were evaluated. These methods consist of a) adding dry hydrated lime to dry aggregates, b) adding hydrated lime to the binder to form mastic, and c) adding slurry lime to dry aggregates.
More uniform distribution of hydrated lime on aggregate surface in the slurry method improved performance... 

Increased environmental concerns and high oil prices have encouraged highway agencies to maximize the use of recycled materials like Reclaimed Asphalt Pavements (RAP) in pavement construction. However, utilization of RAP has limited to low percentage, generally less than 25%. This is due aged, stiffer, and less strain tolerant asphalt binder in RAP. As the RAP proportion increases, a large amount of the aged binder will be introduced into the mixture. The excessive stiffness of HMA mixture tends to lead to less workable mixture. Studies were conducted to examine the effect of Sasobit on the workablility of high RAP mixtures. The results indicated while the utilization of Sasobit had improved... 

Many researchers were interested in gas hydrates because of their especial properties. These researches divided in two fields, thermodynamic and kinetic. The studies on first field began since many years ago, and they provided suitable results. But the investigation of hydrate formation kinetic started for 30 years ago, approximately, and according to its features such as high complexity of crystallization process and severe dependency on system, yet the comprehensive and pervasive model was not presented. At this project, after the presentation and survey of diverse models, in order to kinetic modeling of available data, among different kinetic models a reaction model selected. Then primary... 

In this research, some inhibitors based on quaternary monoammonium salts and quaternary diammonium salts containing different anions were synthesized to prevent formation of methane gas hydrates, and they were characterized using 1H and 13C NMR spectra, IR spectroscopy, elemental analysis and mass spectrometry. Then, the synthesized compounds were used in an autoclave under 128 bar pressure under controlled isothermal conditions to determine retention time considering displacement amount of the gas hydrate temperature- pressure chart and also to determine subcooling of the samples using HW Hydrate software. According to the results T3, T4 and TBAHF compounds in their pure form, not only... 

Water plays an essential role in the daily lives of humans, plants, and animals. Due to the lack of safe water on the planet, in recent years there have been many challenges in the field of water treatment, which has made water desalination technology always one of the most advanced technologies. The most advanced technology in this field is the use of nanotechnology in water and wastewater treatment, especially the use of Membrane processes such as reverse osmosis. Unlike conventional reverse osmosis membranes, nanoporous membranes can ensure rapid water transfer during the displacement process. The purpose of this thesis is to introduce new monolayers that have an incredible performance in...