جستجوی مقالات مرتبط با کلیدواژه "زئولیت a" در نشریات گروه "شیمی"

The aim of this study was investigation the efficiency of the vanadium/Y zeolite shaped catalysts in the combined oxidative-adsorptive desulfurization of model fuel containing 1000 ppm dibenzothiophene (DBT) in a continuous fixed bed reactor. The shaping process was performed by extrusion method using 50 wt.% of boehmite as a binder. Vanadium was impregnated before shaping (VZB(50)) and after shaping (V/ZB(50)). The synthesized catalysts were characterized using different analysis. The obtained results indicated that specific surface area and pore volume of the zeolite decreased after shaping. However the use of boehmite as a binder significantly increased the meso-pore volume. The initial activity of VZB(50) catalyst in the DBT removal was higher than that of V/ZB(50) due to its higher surface area, meso-pore volume and higher acidity. But V/ZB(50) was almost stable during 5 h of reaction, because of more uniform dispersion of vanadium over the support. While vanadium of VZB(50) was leached leading to deactivation. Comparison of the efficiency of catalysts with different geometric shapes also showed the use of extrudes with non-cylindrical cross-section is a good suggestion providing more surface area per unit volume. 82% DBT removal was obtained under mild reaction conditions employed in the combined oxidative-adsorptive desulfurization.

Adsorption capacity and selectivity are two major challenges that adsorption desulfurization faces. One way to overcome these challenges is to use mesoporous zeolites. In this study, the effects of mesoporosity on the adsorption desulfurization performance with NaY zeolite adsorbent were investigated. In order to optimize the parameters, the desilication operation was performed with a mixture of sodium hydroxide (NaOH) and tetrapropylammonium hydroxide (TPAOH) solution at room temperature with ratios of R=  = 0, 0.25, 0.5, 0.75. The adsorbents were characterized by XRD, BET, FE-SEM and FT-IR. The results showed that ATY (0.5)-0.25R adsorbent has the highest mesopore surface with the value of 54.03 m2/g. Meanwhile, the adsorption desulfurization performance in a batch reactor was tested using different model fuels containing the sulfur compounds thiophene and dibenzothiophene. The results showed that different ratios of NaOH/TPAOH solution play an important role in the adsorption of sulfur compounds. In addition, Cu metal ion was impregnated on the parent zeolite and ATY (0.5M)-0.25R adsorbents in order to increase the adsorption capacity. It has been shown that the adsorption capacity of the adsorbents increases with ion exchanging of Cu metal ion, so that the Cu-0.25R adsorbent has the highest adsorption capacity of the sulfur compounds thiophene and dibenzothiophene with the values ​​of 18.28 and 21.83 mg S/g, respectively. In this regard, the effect of temperature on the Cu-0.25R adsorbent on the adsorption of thiophene has been investigated. It has been shown that, the adsorption of thiophene has increased with increasing temperature and has reached its maximum at 50 ° C. Thermodynamic studies showed that the adsorption process is endothermic. The kinetic models of adsorption of sulfur compounds followed the pseudo – second – order equation. The adsorption isotherm was well matched to the Langmuir isotherm equation and its maximum adsorption capacity for thiophene and dibenzothiophene sulfur compounds was 18.38 and 23.43 mg/g, respectively.

This paper aims to study the modified zeolite Y using different dealumination methods and the effect of each of these methods on the structural framework of zeolite. The dealumination is performed by EDTA solution (acidic form), ammonium chloride (NH4Cl), and hydrochloric acid (HCl) solution. To investigate the effect of the dealumination process on the stability of the structures modified samples are studied using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersion X-ray (EDX). By comparing the three methods, it can be concluded that EDTA is the most suitable method because it is not only preserved the structure but also removed the extra-framework aluminum and increases the Si/Al ratio. In addition, in the hydrochloric acid treatment, the extra-framework aluminum is also removed, but in the calcination process (NH4Cl), the extra-framework aluminum is still present, and therefore, the Si/Al ratio is lower than the previous two methods.

Galvanic replacement reactions are a special method for the synthesis of multi-nucleus nanoparticles of various metals within the bed of clinoptilolite. In this method, first, zinc metal cation (Zn +2) after replacing on the clinoptilolite bed was reduced to zinc metal nanoparticles using sodium borohydride salt. Then, the iron (Fe +2) and copper (Cu +2) salts with zinc metal nanoparticles were located on the clinoptilolite bed participate in the oxidation and reduction reactions by citing the potential of various cations in the electrochemical series. The result of these reactions is the formation of deposits of iron and copper nanoparticles on zinc nanoparticles. The selection of appropriate concentrations of cations and determination of the cause of stopping the growth of nanoparticles in each step was carried out by determining appropriate concentrations. XRD, FT-IR, TEM and SEM techniques were used to prove the various stages of work. The effect of the presence and absence of clinoptilolite on increasing the antimicrobial properties of zinc/ iron/ copper three-nucleus nanocomposites and also stability in aquatic environments using bacterial E-coli and Pasteurella specimens have been investigated.

In this work, natural clinoptilolite nanaostructures were prepared from natural zeolite and used to remove Cu2 cation from polluted water. In the first section the natural clinoptilolite particles were converted to nanostructures using a ball mill. The natural clinoptilolite and prepared nanostructures samples were characterized by SEM, XRD, and BET. The SEM images approved the development of clinoptilolite nanostructures. The result obtained from BET analysis indicated the increase pore volume of clinoptilolite nanostructures related to the clinoptilolite microparticles. In the second part of this work, the nanostructures were used as adsorbent for removal of Cu2 cation from polluted water. Effect of initial pH of solution, adsorbent dosage and contact time on the Cu2 removal efficiency was investigated, where the 6, 1.2 g/L and 6 were determined as optimum conditions, respectively. Isotherm and kinetics of the adsorption process were analyzed. The equilibrium data were fitted well to the Langmuir isotherm model and pseudo-second-order kinetic model.

In this research, the composite of TiO2/Zeolite as a cheap and effective photocatalyst was prepared for the removal of methyl orange dye in water solution. At first, TiO2 solution was successfully synthesized and then combined with appropriate amount of Clinopatilolite zeolite. The prepared samples were calcined at different temperatures. The synthesized photocatalysts were characterized by, X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and Fourier transform infrared (FTIR). The effect of the calcination temperatures and the amount of zeolite in composite of the as-synthesized photocatalysts on crystal structure, morphology and photocatalytic degradation of methyl orange dye solution were studied. The results of the experiments showed that combining of zeolite with TiO2 induced the enhancement of photocatalytic activity and optimal zeolite content was obtained about 0.1 g (0.33 wt.% ). Also calcination temperature has a great influence on the photocatalytic activity of the synthesized samples. The optimal calcination temperature was obtained 300⁰C. The composite of TiO2/Zeolite powders obtained from the optimum condition showed uniform spherical shape, anatase crystalline structure and few agglomerates. The methyl orange was removed more than 96% within 60 min of the process with optimum calcinations temperature and zeolite content.

Separation is usually one of the costly stages in chemical and petrochemical industries. Pressure Swing Adsorption (PSA) is an important unit for gas separation and purification. In order to develop the PSA technology, a pilot plant including four beds each with 1 meter length and 3.5 centimeter diameter was designed and built in Tarbiat Modares University. This pilot includes vaccum pump, control systems and analysis systems to study the operational conditions of beds carefully. In order to test this pilot plant, separation of CO2 /N2 mixture using Zeolite 13X type and carbon molecular sieve was studied. In this study an 8 stage cycle including: repressurization with feed, adsorption, equalization to depressurization, blow down, purge in medium pressure, equalization to pressurization, evacuation and preloading was used. The test have been done in pressure range of 2.7 to 4.7 bar, cycle time of 400 to 640 seconds and 3 product flow rate (1, 2, 3 L/min). The effects of pressure, cycle time and product flow rate were studies, using 560 seconds for a cycle time at 3.7 bar, the maximum purity of 97.6% was obtained.