Band 20, Heft 11

The mixing performance in a miniature conical counter-rotating twin-screw extruder was investigated by means of experimental technique and computational fluid dynamics (CFD) simulation. An on-line experimental device based on the fluorescence detection was built to study the residence time distribution (RTD). Polypropylene was selected as the flow material and the blend of Polypropylene and anthracene was used as the tracer. This on-line detection device has good reproducibility. The hydrodynamics in the extruder was simulated by the finite element method (FEM) combined with the mesh superposition technique (MST). The particle tracking technique was carried out to evaluate the RTD and mixing efficiency. The effect of screw speed and feed rate on the hydrodynamics and mixing performance was investigated. The velocity magnitude and local shear rate tend to become smaller from inlet to outlet due to the decreasing diameters of screws. The mean length of stretch increases exponentially from inlet to outlet and the mean value of time averaged mixing efficiency remains positive along the axial direction.

Microbial fuel cells (MFCs) can be used to produce clean energy from organic wastes. Various biomasses for MFCs can be used as biofuel materials. Moss ( Bryophyta ) is a source of biomass materials and can be used as an alternative fuel for microbial fuel cells. In this study, moss-enriched MFCs were produced by using moss as a biofuel source and aluminum and silver as an electrode. As a result of the good electrochemical performance of the metal electrodes (aluminum and silver), higher power density than previous studies involving moss was obtained, with the highest power density in this study being 20 mW/m 2 . Moreover, in this study, bacterial activity, biofilm formation, soil utilization, pH change, and corrosion were investigated in MFCs and the effects of MFC on power density were discussed. The addition of soil increased the corrosion rate and internal resistance while reducing the power density. As a result of the addition of soil, the power density dropped to 16.13 mW/m 2 . The corrosion rate was lower than industrial corrosion. Changes in pH confirmed that organic material dissolved and chemical reactions took place. Scanning electron microscope (SEM)-Energy dispersive spectroscopy (EDS) analyzes showed the presence of Bacillus and Coccus bacteria species on the electrode surfaces. These bacteria were acted as biocatalysts by forming a biofilm on the electrode surfaces.

Photochemical processes in thin surface layers of solutions of compounds of the copper subgroup elements leading to the formation of dispersed metal particles on the surface of dielectrics are investigated. It is shown that dispersed particles of elemental gold are formed on dielectrics moistened with AuCl 3 solution and exposed to sunlight. At the same time, there is no need to use any chemical reducing agents. On cotton fabrics moistened with solutions of AgNO 3 , CuBr 2 , when exposed to sunlight, silver and copper monohalides are formed, respectively. These processes take place with the participation of terminal cellulose molecules and also do not require the use of chemical reducing agents. In addition, it was found that copper monohalides can be converted into elemental copper particles by a photochemical reaction involving ascorbic acid. Examples of metallization of a number of dielectrics using photochemical activation using sunlight are given.

In this study, the kinetic degradation of the anti-inflammatory drug Ibuprofen in aqueous solution by heterogeneous TiO 2 photocatalytic was investigated. The data obtained were used for training an artificial neural network. Preliminary experiments of photolysis and adsorption were carried out to assess their contribution to the photocatalytic degradation. Both, direct photolysis and adsorption of Ibuprofen are very low-efficient processes (15,83% and 23,88%, respectively). The degradation efficiency was significantly elevated with the addition of TiO 2 Catalyst (>94%). The photocatalytic degradation followed a pseudo-first-order reaction according to the L-H model. The hydroxyl radicals and photo-hole (h + ‏) were found to contribute to the Ibuprofen removal. The higher the initial concentration of Ibuprofen resulted in the lower percentage of degradation. This can be credited to the fact that the created photon and radicals were constant. The higher the initial concentration of Ibuprofen the fewer radicals were shared for each Ibuprofen molecular and so the lower percentage of degradation. The maximum photoactivity from the available light is accomplished when the concentration of catalyst reaches to 1 g/L (0.8 g), which was adopted as the optimal amounts. Compared to the removal of ibuprofen, the mineralization was relatively lower. This decrease is due to the organic content of the treated solution, which is mainly composed of recalcitrant intermediate products. The network was planned as a Levenberg-Marquardt algorithm with three layer, four neurons in the input layer, fourteen neurons in the hidden layer and one neuron in the output layer (4:14:1). The artificial neural network was trained until the MSE value between the simulated data and the experimental results was 10 −5 . The best results ( R 2  = 0.999 and MSE = 1.5 × 10 −4 ) were obtained with a log sigmoid transfer function at hidden layer and a linear transfer function at output layer.

Naphtha catalytic reforming is a key process for oil refining in terms of production of gasoline with a high octane number. In the present research, the gradual and sudden effect of operating conditions changes on the products of the catalytic reforming unit and the octane number, as well as how to neutralize their negative effects were investigated. Also, kinetic parameter optimisation and unit operation optimisation, using the Levenberg–Marquardt algorithm were performed. For these purposes, a suitable dynamic model was solved within a three-lump kinetic network that included a model of the reactors, furnaces, and catalyst deactivation functions. In addition, two cases were considered for operationalizing the optimization to maintain the octane number at its highest value during the catalyst lifetime. In the first case, the optimization parameters were the inlet temperature of the three reactors along with the recycle flow rate; in the second case, the optimised parameters were the inlet temperature of the three reactors, the recycle rate, and the feed flow rate.

The 3D virtual full-loop CFD simulation method with two-fluid model (TFM) was developed to model an industrial two-stage FCC reaction–regeneration system. The virtual connections (mass, species, and energy) between riser reactors, disengager, stripper, and regenerator were realized by defining user-defined functions (UDFs) for boundary conditions according to the reality. Five correction factors were used to correct the reaction rates in the 14-lump FCC reaction kinetics, and two correction factors were used to correct the FCC reaction heat in the first and second riser reactors. As a result, the whole FCC reaction–regeneration system was successfully modeled in one single CFD case. A thorough and comprehensive view of the performance of reaction–regeneration system was obtained by the 3D virtual full-loop CFD simulation, which is helpful for the operating and optimization of FCC unit. The major predicted results were in a good agreement with the industrial data. The effects of operating conditions were also investigated by changing regenerated temperature, catalyst to oil (CTO) ratio, and process capacity.

Esterification of acetic acid and methanol to produce methyl acetate and water has been studied in a continuous packed bed catalytic reactive distillation column. Indion 180, an ion-exchange resin solid catalyst has loaded in an equivalent Katapak-S into the reactive section of the column. The experiments were conducted under different operating conditions of reboiler temperature, total feed flow rate of the reactants, methanol to acetic acid mole ratio, feed location of acetic acid and methanol with respect to reactive section, reflux ratio and catalyst amount to investigate the composition of distillate and reboiler respectively. The maximum methyl acetate composition and acetic acid conversion is obtained at reboiler temperature of 80 °C, reflux ratio of 2, total feed flow rate of 16.3 g/min, catalyst loading of 60 g and mole ratio of methanol to acetic acid is 1. From the experimental investigations, it is found that the composition of the methyl acetate in the distillate is 95% by mole at an optimized experimental condition. The experimental data has been compared with equilibrium and non-equilibrium model predictions and found that non-equilibrium model is able to predict the experimental data reasonably good. The calculated error from equilibrium model relative to experimental data is 4.71% and rate based model relative to experimental data is 0.61%. It is observed that the error is less in rate based model compared to equilibrium model.

As an important part of laboratory-on-a-chip (LOC) and micro-total analysis system (μTAS), micromixers are widely used in the fields of biological analysis and chemical synthesis. Most of them are used for the pretreatment of the detection and analysis system to realize the full mixing between the sample and the target to improve the accuracy of the inspection system. A new type of 3D-SAR micromixer with cross-channel structures was put forward after the systemic simulation by using CFD software. The mixing performance and mechanism of 3D-SAR micromixer with/without cross-mixing channel has been investigated with different Reynolds numbers (Re). The results show that the 3D-SAR micromixer with or without cross-mixing channel structures are of excellent mixing performance when the Re was high (Re > 50), and the mixing index is close to 1. While the concentration stratification of the two fluids in the cross-mixing channel (CMC) 3D-SAR micromixer is obviously better than that of no-cross-mixing channel (NCMC) 3D-SAR micromixer when Re is low (Re < 10). It is because the two fluids in the cross-mixing channel rotate counterclockwise at the mixing unit, which induces a vortex and increases the contact area between the two fluids. The mixing performance is greatly improved, and the mixing index at the outlet is more than 0.9. Meanwhile, in order to optimize the higher pressure drop of the CMC micromixer, a new 3D-SAR micromixer with the unbalanced-cross-mixing channel (UCMC) is proposed based on the CMC structure. This channel structure can meet the requirements of high mixing index and low-pressure drop at the same time, which is helpful to design and manufacture of new type micromixer.

The present work was aimed at evaluating the roles of zinc chloride impregnation states on specific surface and dielectric properties in microwave-assisted activated carbon preparation. Activated carbons were synthesized using castor shell at dry impregnation ratios of 1 and 2 (material-to-activator), and in suspensions of distilled water and zinc chloride, at power intensity of 800 W and irradiation time of 5 min. The activated carbons exhibit an improvement in dielectric properties and specific surface with increasing impregnation ratio. Palm kernel shell was employed for comparison to verify the effect of power intensity. At 800 W, the magnitudes of surface area are 1684 m 2 /g and 1150 m 2 /g for castor shell- and palm kernel shell-based activated carbons, respectively. A high specific surface brings about a greater methylene blue adsorption for possible applications in wastewater treatment.