دوماهنامه مهندسی شیمی ایران
پیاپی 128 (امرداد و شهریور 1402)

In this study, three composite adsorbents with different percentages zeolite ZSM-5 and silica aerogel, were synthesized. The adsorbents were characterized by FESEM, XRD, FTIR, BET-BJH, and zeta potential. By comparing the performance of the zeolite ZSM-5 (25)/silica aerogel (75) adsorbent as an optimal adsorbent and other inexpensive adsorbents, it was observed that the adsorbent studied in this experiment has good adsorption efficiency. The saturated adsorption capacity reached 476.2 mg/g for Pb+2. To obtain the best isotherm and kinetic model, error functions and regression coefficients, especially the Chi-square test (χ2) and sum square error (SSE), were used. The findings fit well with Temkin isotherm models, according to the adsorption isotherm investigations. The kinetic data for the pseudo-second-order kinetic model exhibited a high correlation coefficient and a low error function. The activation energies for lead were and 11.31 kJ/mol, respectively. These values indicate that physical adsorption has occurred. The Com3 absorbent was separated from the wastewater and reused after recovery. This feature caused the adsorbent to have a strong adsorption ability, so the adsorption process was performed in five cycles. FTIR and EDX analyses were performed to confirm the adsorption of heavy metals by the adsorbent. The results show that the zeolite ZSM-5/silica aerogel composite is a suitable adsorbent for the removal of various toxins(such as heavy metals) in aqueous systems that contain an adsorbate. As a result, the new zeolite ZSM-5/silica aerogel composite may be used on a larger scale as a material to absorb a variety of contaminants.

Silica aerogels are nanoporous materials with an open-pore structure and interesting properties such as low density, high porosity, low thermal conductivity, high specific surface area, low refractive index and high optical transmission. These unique properties provide enormous potential for a variety of applications such as insulators, catalysts, optics, adsorbents and drug delivery systems. A common method for preparing silica aerogels is the sol-gel process, followed by supercritical drying/ ambient pressure drying. Better understanding of mutually dependent processing parameters and their adjustment such as type of precursor, molar ratio of components, pH of silica solution, aging and washing time, solvent exchange process and surface modification can produce good quality aerogels depending on their application. In the present study, a review on the preparation of silica aerogels using sodium silicate, the mechanism of gel formation and the effect of process parameters on the structure and their properties are presented. Finally, the most important applications of silica aerogel in engineering sciences and recent developments in this field are mentioned.

Low-density polyethylene is a subset of polyethylene that is mainly used in the plastics industry. These polymers are formed at high pressures and temperatures using a radical reaction. The fouling phenomenon is the result of the thermodynamic phase separation of polymer and ethylene. This phase separation occurs in the wall area (wall close to the cooling flow) of the tubular reactor, which reduces heat transfer to the reactor jacket, reducing production and in critical cases dangerous decomposition of ethylene. The purpose of this study is to simulate the phenomenon of fouling and its effects on the temperature and pressure of the reactor based on the heat transfer problems. The solved mathematical model is formed based on heat transfer equations to solve the computational fluid dynamics equations which are used to calculate the phase equilibrium data for pressure and temperature: The obtained results show that by increasing the thickness of the fouling, the heat transfer rate decreases. The operating model was used based on thelow-density polyethylene with a grade of 2420H. Based on the model, it was found that with increasing the thickness of fouling from 0.1 to 1.2 mm, the outlet temperature of the reactor increases, but does not have a significant effect on the pressure drop inside the reactor: Moreover,10 °C increase in reaction temperature caused the volume percentage of the second phase (fouling) is reduced from 0.1833 to 0.1818 mm.

Microalgae biomass is considered as a sustainable feed for the production of high value compounds such as enzymatic and non-enzymatic antioxidants that are widely used in food, pharmaceutical, textile, leather as well as in the chemical industry. Increasing the yield of microalgae, achieving optimal culture conditions, optimal storage of antioxidant molecules after processing and downstream processing with energy saving are among the main obstacles to the production of antioxidants. Today, antioxidant compounds produced by microalgae as a result of stressful conditions, as important products in the field of human health, have received commercial attention. Oxidative stress due to acidity, metals, UV and temperature can cause the production of antioxidants in many different species of microalgae such as Dunaliella algae. Dunaliella algae cultivation has several advantages, including high growth rate, low production cost, as well as the ability to grow in stressful conditions such as high salt concentrations, high light intensity, and nitrogen restriction. This article provides an overview of the production of antioxidants in the Dunaliella microalgae cellular metabolism, the activity of antioxidant enzymes (POD, SOD, CAT) and strategies to increase antioxidant accumulation in microalgae.

Considering the need for excessive consumption of hydrocarbon resources and gas fuel supply in the cold seasons of the year, it has been suggested to use the drained oil and gas reservoirs and underground water aquifers to be used as natural gas storage reservoirs. Among the influential factors in natural gas storage are the reactions between fluid-fluid and fluid-rock, which is the most important of these wettability factors. Knowing these factors in the gas storage process will lead to better control and storage of natural gases in geological structures. Underground water aquifers are one of the structures with favorable conditions for natural gas storage which by wettability alteration to gas wetness in these, can be increased the natural gas storage capacity. For this purpose, this study has investigated the laboratory works done on the distribution and behavior of fluid in the samples of carbonate and sandstone in order to wettability alteration to gas wetness for the purposes of underground gas storage.

Fouling in heat exchangers is main causes of energy losses in oil and gas refineries. One way to reduce this energy loss in these refineries is to predict fouling resistance. In this paper, the fouling resistance rate is first estimated using the Buckingham's dimensionless groups. The resistance rate is then validated with the experimental data derived from the literature. The results show the relative error of 26.79% with the experimental data, which is rather low and acceptable as compared by those reported in the literature ranged from 40-59%. In general, by estimating the fouling resistance rate, the fouling threshold curve can be plotted and the position of the exchangers relative to it can be checked. The position of the exchangers would allow to reduce the amount of fouling and to stay in non-fouling area with the proper justifications of the operating conditions. The curve is also used to estimate the deposition resistance in the unstable state with the asymptotic model. This model has also been validated with the experimental data from the Australian light oil and Tehran refinery data. It is worthy to mention that the prediction of fouling instability has been less considered in the literature, although with this estimate it is possible to have a better and more regular cleaning program for exchangers and to reduce the problems caused by deposition in exchangers leading to lower operational costs.

One of the newest methods of waste management is benefiting from thermal plasma technology in gasification. Plasma gasification is a complicated process that requires much research. Plasma technology, meanwhile, can meet the energy and waste management needs of several communities, but the experimental study is not always feasible. In this study, an Aspen Plus model based on Gibbs free energy minimization is created in order to assess municipal waste and biomass as feedstocks. After validating the model, important parameters were examined which showed that increasing the amount of municipal waste in the feed can help improve the quality of syngas as the product of this process. The best steam to waste ratio for generating the highest amount of hydrogen production was obtained 2. It was also observed that the effect of steam-to-waste ratio on hydrogen production decreases with the increase of temperature above 800 degrees Celsius, and the increase of temperature in low steam-to-waste ratios has a greater effect on the amount of hydrogen production.

The process of photocatalytic reduction of carbon dioxide converts clean solar energy to value-added materials, while reduces the carbon dioxide greenhouse gas. TiO2 is the most widely used semiconductor in this process. However, its large bandgap energy and high rate of electron-hole pair recombination needs to be modified. In this review article, ways to modify TiO2, such as combining with semiconductors and doping metallic and non-metallic elements, as well as the structural features and performance of modified TiO2 photocatalysts with a special focus on charge transfer behavior have been investigated. Various types of photoreactors, including fixed bed, membrane, slurry, etc., have been investigated. Doping with metal and non-metal increases the yield of the product up to 207 times. TiO2 modified by doping with precious metals have high performance. Doping cheaper materials such as g-C3N4 can be employed to achieve similar performance. Moreover, the efficiency of monolith reactors is 23 and 14 times higher than slurry and fixed bed reactors, respectively.

In this study, ion-exchanged copper oxide-clinoptilolite photocatalysts with different weight percentages of copper oxide (from zero to 100%) were synthesized and investigated for the photocatalytic removal of tetracycline from wastewater. Characterization of samples photocatalysts by XRD, FESEM, EDX, UV-Vis DRS and BET/BJH analyzes showed that copper oxide was in the form of Cu2O in all samples and the addition of clinoptilolite decreased the size of copper oxide crystals from 50 to 37. Also, with increasing the amount of clinoptilolite, the degree of agglomoration of copper oxide decreases. While increasing the amount of clinoptilolite in the samples reduces the amount of light absorption, the bandgap energy becomes slightly larger, which reduces the possibility of recombination of charge carriers. The sample contains 50% by weight of copper oxide with a specific surface area of 116 m2/g has a suitable pore size for the entry and exit of tetracycline. This sample showed the highest amount of tetracycline photocatalytic removal (90.76%) in the initial concentration of tetracycline at 30 ppm, the amount of photocatalyst at 1 g/l and pH=7.