دوماهنامه مهندسی شیمی ایران
پیاپی 125 (بهمن و اسفند 1401)

From 1990 to 2020, carbon dioxide emissions have dramatically increased (50%). It has already caused global warming and affected the environment and human health care. Moreover, carbon dioxide has dramatically increased up to 2 times in atmosphere since BCE, and the temperature of earth surface also raised 1°C from the past fifty years. Although novel technologies integrated carbon capture utilization and storage (CCUS) has been already proposed, there are still significant challenges such as cost, economic barriers, and uncertainties on environmental impacts. One promising way to mediate these issues is to utilization of carbonic anhydrase (CA) as enzyme in a eco-friendly manner without any secondary pollutants. In order to utilize CAs in carbon sequestration, high stable CAs on the extreme and harsh environment is essential. This review aims to present advanced developments in CA, efficient engineering strategies to improve the productivity and stability, immobilization techniques towards an industrial operating system. Recent challenges in industrial CAs application as well as its usage perspective in environmental protection have been also discussed.

The membrane electrode assembly (MEA) is a key unit of proton exchange membrane (PEM) fuel cells. The MEA materials, structures, components and fabrication technologies have strong effects on the corresponding fuel cell performance. In particular, the catalyst layers, where the electrochemical reactions take place, are the most important components. Over the past several decades, many efforts have been made to develop high performance PEM fuel cells. MEA performance with advanced catalyst layers has been significantly improved by employing different fabrication methods, changing the catalyst layer structures, and using different components. During PEM fuel cell performance optimization, how to evaluate catalyst layers and their corresponding MEAs becomes critical. The major purpose of such an evaluation is to understand the relationship between fuel cell performance and MEA component structures/compositions. Based on this understanding, catalyst layer/MEA optimization with respect to performance can be carried out in terms of materials used, component compositions, and fabrication parameters. Through optimizing the catalyst layers and MEAs, catalyst utilization can be improved, gas diffusion overpotential reduced, and membrane ohmic losses decreased, while water management inside the catalyst layers/MEAs can also be improved. Therefore, catalyst layer/MEA evaluation is a necessary step in fuel cell development. Accordingly, many electrochemical methods have been developed to evaluate the performance of the catalyst layer/MEA. In this review paper, the principles and methods of catalyst layer/MEA evaluation have been introduced, with some detailed analysis.

According to the importance of water vapor available in the natural gas, achieving a powerful absorbent looks quite necessary. In this study, for the first time, tetraethylene glycol (TREG) and its mixture with triethylene glycol (TEG) were used to remove water vapor from a wet air stream. Following this, to achieve a good vision about the performance of TREG, the results were compared with the pure TEG and the impact of gas flow rate was considered. Based on the obtained results, all absorbents applied in this work resulted in a better performance in lower gas flow rates. Further, although TEG was the best absorbent at low gas flow rates, TREG had the best performance in water vapor removal at high gas flow rates. Finally, in the best operational condition in this work, the use of TEG led to the reduction of water vapor from 90% to about 10% at 60 ml.min-1. However, applying TERG had a better result at 120 ml.min-1 and caused the water vapor to reduce from 90% to approximately 5%. High water vapor absorption in high flow rates indicates the high capability of TREG to employ in gas dehydration processes in industrial scales.

Fluidized beds are widely used in various processes such as mixing, catalytic and non-catalytic reactions, etc. In this article, the hydrodynamic characteristics of a gas-solid semi-cylindrical fluidized bed, which are affected by bubble properties including shape, size and rising velocity, are investigated for glass beads of 420 μm. For this purpose, a digital image analysis technique was employed to study the bubble behavior. The experiments were carried out in a semi-cylindrical fluidized bed with a diameter of 14 cm at ambient pressure and temperature. The static bed height was 21 cm (L/D=1.5) in all cases and the superficial gas velocity was varied in the range of 0.2 to 0.8 m/s. All properties of bubbles were investigated by increasing the superficial gas velocity and against the height of the bed. The results showed that aspect ratio, size and rising velocity of bubbles increase with increasing the superficial gas velocity. The size and rising velocity of bubbles, which were obtained experimentally, were found to be in good agreement with the values calculated by existing correlations with relative errors of 3.5% and 7 %, respectively. Moreover, all above mentioned properties of bubbles increase by increasing the height of the bed. The advantage of a semi-cylindrical bed over a cylindrical one is that through its flat surface, the phenomena inside the bed can be observed by a non-intrusive method. The results of these experiments can help to understand the complicated hydrodynamic behavior of fluidized beds.

Synthesis method and forming parameters influence the structural properties of granules. In this paper, oil drop was used to synthesize spherical γ-alumina granules. Orthogonal matrix was applied in the Taguchi experimental design to investigate the effect of calcination temperature, additive percentage (PVA %), and column length of oil drop on the granule structures; including specific surface area, pore diameter, and pore volume. XRD analysis confirmed the formation of γ-alumina phase in the synthesized granules. According to the ANOVA, column length had the most significant effect on the specific surface area (61.7%), and on the pore volume of granules (82.4%). Additive percentage had the most significant effect on the pore diameter of γ-alumina granules (92.8%). Maximum responses were achieved by tuning the additive percentage, column length, and calcination temperature at 0%, 45 cm, and 500 °C, respectively.

Formic acid has different applications in various industries because of its unique properties, therefore, the production of this acid (using plants as a reducing agent instead of chemicals and waves) is important. In this study, ZnO nanoparticles were synthesized using green method by plant of Amaranthus Retroflexus and irradiation assisted. Silver nanoparticles were also doped on zinc oxide nanoparticles (ZnO-Ag). These synthesized nanoparticles were examined to convert glucose to formic acid at different temperatures. Physical properties and morphology of the synthesized nanoparticles were analyzed using XRD, DLS, and SEM techniques. Increasing the temperature to 200 ºC caused increase of the glucose conversion to formic acid, which in the presence of ZnO-Ag nanoparticles and at temperature of 200 ºC, conversion was about 75%. But during reaction time in the presence of ZnO-Ag nanoparticles, that amount of conversion dropped to about 68%. These results showed that formic acid can be decomposed and eliminated in the presence of ZnO-Ag nanoparticles as catalysts during reaction.