Photocatalytic degradation of methyl tert‐butyl ether (MTBE) in contaminated water by ZnO nanoparticles

BACKGROUND: Over the past several decades methyl tert‐butyl ether (MTBE) as additive to gasoline, intended to either boost ratings of fuel or to reduce air pollution, has been accepted worldwide. Since MTBE has high water solubility, the occurrence of fuel spills or leaks from underground storage tanks or transferring pipeline has led to the contamination of natural waters. In this study the degradation of aqueous MTBE at relatively high concentrations was investigated by a UV‐visible/ZnO/H₂O₂ photocatalytic process. The effects of important operational parameters such as pH, amount of H₂O₂, catalyst loading and irradiation time were also investigated. Concentration of MTBE and intermediates such as tert‐butyl formate and tert‐butyl alcohol were measured. RESULTS: Time required for complete degradation increased from 20 to 150 min when the initial concentration was increased from 10 to 500 mg L^?1. The first‐order rate constants for degradation of MTBE were estimated to be 0.183–0.022 min^?1 as the concentration increased from 10 to 500 mg L^?1. Study of the overall mineralization monitored by total organic carbon analysis showed that at an initial concentration of 100 mg L^?1 MTBE complete mineralization was obtained after 100 min under UV‐visible/ZnO/H₂O₂ photocatalysis. CONCLUSION: The data presented in this paper clearly indicated that UV‐visible/ZnO/O₂ as an advanced oxidation process provides an efficient treatment alternative for the remediation of MTBE‐contaminated waters. Copyright © 2008 Society of Chemical Industry     

Kinetics of TSCD zinc oxide nano-layer growth by modified diffuse-interface model

Deposition of zinc oxide films from aqueous solutions containing complex Zn²⁺ ions on soda-lime substrates were studied by two-stage chemical deposition (TSCD) process. It was shown that the film thickness can be controlled by the number of dipping stages. Nano-layers were produced with less than nine times dipping stages. Greater dipping numbers resulted in film thickness exceeding 100 nm. The growth rate obeyed double-stage zeroth order with respect to the concentration and first order with respect to the temperature. This rate was proportional to the difference between the temperature of the hot water and the substrate. Overall activation energy of 17.20 ± 0.42 kJ mol⁻¹ and frequency factor of 2.81 ± 0.07 μm s⁻¹ was determined for ZnO deposition. These values were attributed to two resistances. One resistance corresponded with film heat transfer mechanism. The other was attributed to species attachment to the solid substrate. A modification to the diffuse-interface kinetic model was devised for explanation of the latter. EDAX (electron dispersive elemental analysis), XRD (X-ray diffraction) and SEM (scanning electron microscopy) were used to characterize the layer formed. These methods showed that the product consisted solely of pure elliptical ZnO grains.     

Gasification of heavy fuel oils: A thermochemical equilibrium approach

Combustion of heavy fuel oils is a major source of production of particulate emissions and ash, as well as considerable volumes of SO_x and NO_x. Gasification is a technologically advanced and environmentally friendly process of disposing heavy fuel oils by converting them into clean combustible gas products. Thermochemical equilibrium modeling is the basis of an original numerical method implemented in this study to predict the performance of a heavy fuel oil gasifier. The model combines both the chemical and thermodynamic equilibriums of the global gasification reaction in order to predict the final syngas species distribution. Having obtained the composition of the produced syngas, various characteristics of the gasification process can be determined; they include the H₂:CO ratio, process temperature, and heating value of the produced syngas, as well as the cold gas efficiency and carbon conversion efficiency of the process. The influence of the equivalence ratio, oxygen enrichment (the amount of oxygen available in the gasification agent), and pressure on the gasification characteristics is analyzed. The results of simulations are compared with reported experimental measurements through which the numerical model is validated. The detailed investigation performed in the course of this study reveals that the heavy oil gasification is a feasible process that can be utilized to generate a syngas for various industrial applications.     

Morphology enhancement of TiO2/PVP composite nanofibers based on solution viscosity and processing parameters of electrospinning method

In this work, different sol solutions with various titanium tetraisopropoxide (TIP)/glacial acetic acid ratios in 2‐propanol with 5 wt % poly(vinyl pyrrolidone) (PVP) (M_w = 360,000 g/mol) were prepared and electrospun. Composition of the prepared sols and as‐spun TiO₂/PVP nanofibers were determined by Fourier transform infrared and Raman spectroscopy methods. Morphology of the electrospun TiO₂/PVP nanofibers was studied by scanning electron microscopy and transmission electron microscopy (TEM) techniques. Rheometry measurements of the sol solutions showed decrease of viscosity upon the addition of TIP to the polymer solutions with constant polymer and acid concentrations. The sol solution having the lowest viscosity (at shear rate 10 s^?1) but the highest TIP/glacial acetic acid ratio showed beaded nanofibers morphology when electrospun under 10 and 12 kV applied voltage while injection rate, needle tip to collector distance, and needle gauge were kept constant. However, smooth electrospun TiO₂/PVP composite nanofibers with the average nanofibers diameters (148 ± 79 nm) were achieved under the same condition when applied voltage increased to 15 kV. TEM micrographs of the electrospun TiO₂/PVP nanofiber showed that the TiO₂ particles with continuous structure are formed at the middle of the nanofiber and distributed along its axis. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46337.     

Influence of Gating System,Sand Grain Size,and Mould Coating on Microstructure and Mechanical Properties of Thin-Wall Ductile Iron

 In this study, the effect of gating systems, mould coating and sand grain size on metallurgical and mechanical properties of TWDI casting were investigated. Two different gating systems; stepped and tapered runners, were used to cast strip samples. The thicknesses of the samples cast were 2.3, 3.3, 4.5, 5.4, 6.5, 7.5 and 8.5 mm. The samples were cast in CO2/silicate process moulds of two different sand grain sizes of 151 and 171 according to the AFS standard. To assess the effect of mould coat on the properties of TWDI, half of the moulds were coated with graphite-based zircon whilst the rest were left uncoated. The carbon equivalent (CE) of the molten metal prepared was 4.29% and poured at the temperatures of 1450°C. The microstructure of the cast specimens was analyzed by optical and scanning electron microscopes. Clemex Image Analyzer (CIA) was used to evaluate graphite nodule count, graphite nodules area fraction, roundness and diameter of the nodules of the TWDI cast samples. Brinell hardness and tensile tests were also conducted on all the samples. The results show that by using stepped runner gating system with uncoated and coarse sand grain size mould, roundness and graphite nodule counts decrease. However, graphite nodules diameter and area fraction increase. The results also show that finer sand grain size and coated mould produce longer distance of molten metal travel.     

Intensification of continues biodiesel production process using a simultaneous mixer- separator reactor

Nowadays, Biodiesel as an alternative, sustainable and less toxic fuel has been accepted by both researchers and industry. Developing process intensification reactors with the aim of reaching more efficient process has captured the attention of many researchers recently. In order to examine a novel reactor for biodiesel production using Waste Cooking Oil as a cost-effective feedstock, and KOH as an efficient homogeneous catalyst, the present study was developed to investigate three effective parameters (Oil flow rate, catalyst concentration and reaction temperature) focusing on transesterification reaction yield in the Simultaneous Mixer-Separator (SMS) reactor, designed and fabricated exclusively for biodiesel production at Tarbiat Modares University (TMU). As the findings indicated, rising the flow rate presented an increasing trend up to 15 mL/min and a decreasing trend was found after this level. Also, catalyst concentration up to 1% w/w showed an increasing trend which was significant. Analysis of reaction temperature showed that at 60^°C the maximum yield is obtained. Furthermore, 15 mL/min oil flow rate, 1% w/w KOH concentration and 60^?C were selected as the optimal reaction conditions for continuous biodiesel production. At this point, the produced biodiesel followed by the purification step reached the yield of 96%. The produced biodiesel physicochemical properties were found to meet ASTM D6751 standard. All in all, continuous production capability, higher productivity, simultaneous separation of products, and the successful handling of waste resources distinguish the SMS reactor as a potential and efficient process intensification reactor.     

A review on 3D micro-additive manufacturing technologies

New microproducts need the utilization of a diversity of materials and have complicated three-dimensional (3D) microstructures with high aspect ratios. To date, many micromanufacturing processes have been developed but specific class of such processes are applicable for fabrication of functional and true 3D microcomponents/assemblies. The aptitude to process a broad range of materials and the ability to fabricate functional and geometrically complicated 3D microstructures provides the additive manufacturing (AM) processes some profits over traditional methods, such as lithography-based or micromachining approaches investigated widely in the past. In this paper, 3D micro-AM processes have been classified into three main groups, including scalable micro-AM systems, 3D direct writing, and hybrid processes, and the key processes have been reviewed comprehensively. Principle and recent progress of each 3D micro-AM process has been described, and the advantages and disadvantages of each process have been presented.