Volume 17, Issue 9 -

The mixing of fluids in wavy micromixer and wavy micromixer with obstacles on its side walls has been numerically investigated. The effect of frequency of wavy channel on mixing performance is studied over a range of Reynolds number from 0.1 to 45. Various performance characteristics viz. the mixing index, pressure drop, performance index, and pumping power are used to analyze the overall mixing performance. The results show that the wavy micromixer with obstacles produces better mixing performance than the wavy micromixer. Also, the mixing index is sensitive to the wavy frequency of the channel. The wavy micromixer exhibits the smallest pressure drop as compared to micromixer with obstacles in all cases.

Ammonium jarosite sediment is a by-product of hydrometallurgical process used to extract zinc metal, which, which contains heavy metal ions and raises severe environmental concerns The transformation of jarosite sediment into high-value-added sulfide products through simple processing is a cost-effective and efficient strategy to overcome environmental and waste management issues. Herein, the influence of sulfur on thermal decomposition of ammonium jarosite is investigated in reducing atmosphere. The results reveal that the presence of sulfur promoted the decomposition of ammonium jarosite and szomolnokite and iron oxide phases have been observed after being heat treated at 300 °C. Moreover, after heat treatment at 700 °C, the decomposition of jarosite/sulfur mixture resulted in the formation of pyrrhotite phase, which can be used as a raw material for sulfuric acid production. Lastly, the activation energy of pyrrhotite formation has been estimated by using KAS equation and found to be 216.2 kJ/mol in reducing atmosphere.

Our rigorously validated Computational Fluid Dynamics (CFD) model (Basha et al. 2016) was previously used to predict the effects of gas sparger designs and internals configurations on the local hydrodynamics in a pilot-scale and a conceptual large-scale slurry bubble column reactors (SBCRs) (Basha and Morsi 2018). In this study, the CFD model was used to predict the effect of incorporating the F-T reaction kinetics on the local hydrodynamics in the pilot-scale (0.3-m ID, 3-m height) and the overall performance of the pilot-scale and an industrial-scale (5.8-m ID, 42-m height) SBCRS, both operating under F-T conditions with iron catalyst. In the pilot-scale SBCR, the CFD simulations were carried out with catalyst concentrations of 5, 10 and 15 vol% and three H 2 /Co ratios of 1, 1.5 and 2, at temperature of 443 K, pressure of 20.5 bar and a superficial gas velocity of 0.24 m/s. The predictions showed that the presence of chemical reactions decreased the gas holdup and the Sauter mean bubble diameters along the reactor height by an average of 15.4 % and 17.63 %, respectively and strengthened the liquid circulations near the reactor wall. The predictions also showed that the CO and H 2 conversions increased with increasing the catalyst concentration, and the pilot scale SBCR could produce a maximum of 1.87 tons/day of C 5 + products at a catalyst concentration of 15 vol%. In the commercial-scale SBCR, the CFD simulations were conducted at a catalyst loading of 10 vol% at a temperature of 528 K, pressure of 29 bar and four superficial gas velocities of 0.12, 0.24, 0.3 and 0.4 m/s. The calculations were completed, however, the contours of the local hydrodynamics were not extracted due to computational and memory limitations associated with generating graphics of such a large and complex reactor geometry. The predictions showed that the CO conversions were 48 %, 59 %, 58 % and 55 %; the H 2 conversions were 36 %, 51 %, 56 % and 54 % and the C 5 + products yields were are 275, 576, 627 and 654 ton/day at the superficial gas velocities of 0.12, 0.24, 0.3 and 0.4 m/s, respectively. When comparing the CFD model predictions with those of the 1-D empirical model developed by Sehabiague et al. (Sehabiague et al. 2015) at a superficial gas velocity of 0.24 m/s and catalyst loading of 10 %, the CFD model was found to predict lower CO conversion, higher H 2 conversion and higher C 5 + yield.

The photocatalytic degradation of hexylpyridinium bromide (HPyBr) from an aqueous solution was studied by focusing on comparison of the photoactivity of ZnO and TiO 2 P25. The process was carried out under different experimental conditions. The results showed that there is no adsorption of pollutant by both catalysts in the dark. The efficiency of P25 Degussa and ZnO photocatalysts were compared, and the photocatalytic kinetics study showed that ZnO is more efficient than TiO 2 P25. The HPyBr photodegradation was found to follow a pseudo-first order kinetics, and the higher rates constants were obtained at the alkaline medium for ZnO (pH = 11, k app = 9.61 × 10 –2  min −1 ) and at acidic medium for TiO 2 P25 (pH = 3, k app = 1.28 × 10 –2  min −1 ). The Langmuir–Hinshelwood model was found suitable to explain the rate constant data for the ionic liquid degradation by both catalysts. The presence of carbonate ions at alkaline medium was found to reduce the HPyBr degradation for ZnO and to enhance the HPyBr degradation for TiO 2 , this enhancement in TiO 2 /CO 3 2- /UV system was confirmed by the addition of • OH and h vb + scavengers. According to TOC and COD results, HPyBr mineralization was faster in ZnO/UV system than in TiO 2 /UV system.

The performance of a steam methane reforming (SMR) reactor is optimized by using the theory of finite time thermodynamics in this paper. The maximum hydrogen production rate (HPR) and the corresponding optimal exterior wall temperature (EWT) and the optimal pressure of the reaction mixture (PRM) profiles in the SMR reactor are obtained by using nonlinear programming method. In the optimization process, the fixed inlet mole flow rate of components, the thresholds of the state variables and the conservation equations are taken as the constraints. The performance of the optimal reactor is compared with that of the reference reactor with a linear EWT profile. The results show that the HPR of the optimal reactor increases by about 11.8 %. The optimal EWT profile is alike with the linear EWT profile. The HPR increases with the increase of the inlet temperature of reaction mixture and the decrease of the inlet PRM. The influence of the TRM on the HPR is smaller than that of the PRM. The results obtained herein are helpful to the optimal design of practical tubular reactors.

The kinetics of esterification reaction between acetic acid and methanol was studied with the Indion 180 catalyst in the temperature range between 323.15 and 353.15K, and the catalyst loading between 0.01 g/cc to0.05 g/cc. The effects of temperature, catalyst loading, size of the catalyst and agitation speed on the reaction rate were investigated. The experimental results have shown the negligible effect of mass transfer resistances on the reaction rate. A second order kinetic rate expression was used to correlate the experimental data. An activity based kinetic model was also developed for the esterification process, which was validated against experimental results. The activity based model is found advantageous as it involves only two reaction rate parameters which were determined based on the kinetic rate parameters of the concentration based model. The comparison of the model predictions with the experimental results for different temperature and catalyst loading conditions has shown the better suitability of the activity based kinetic model for the esterification process with Indion 180 catalyst.

Photocatalytic degradation of diazinon in the aqueous solution using UV light and MgO nanoparticle (NPs) immobilized on the concrete was investigated. Prepared catalyst was characterized using TEM, XRD, SEM, and EDX techniques. The results showed that the average particle size of immobilized MgO NPs was 38.3 nm and NPs appropriately was coated on the concrete surface. The performance of degradation and mineralization of diazinon was evaluated by HPLC and TOC techniques, respectively. The effect of operational parameters including pH value, initial pesticide concentration, and contact time were studied on the removal and mineralization of diazinon by a photocatalytic process. The results showed that the MgO NPs and UV light had little effect in removing pesticide when used individually. On the other hand, diazinon can be effectively degraded by immobilized MgO NPs in the presence of UV light. Degradation products of diazinon using the proposed photocatalytic technique were identified by the GC-MS analysis. The maximum diazinon removal (99.46 %) was obtained under the conditions; pH 7, diazinon concentration of 5 mg/L, and contact time of 120 minutes. Also, the lowest energy consumption conditions were as follow; pH 7, diazinon concentration of 5 mg/L, and contact time of 30 minutes.

The saponification reactor, otherwise called the crutcher is a dual purpose unit operational vessel that serves for reactor and mixer in the production of soapy detergent. Little or no efforts have been made by available literatures to work on the crutcher agitation concepts and geometry which determines the rate of reaction and degree of homogeneity of reactor mixture in the crutcher as used in the currently most widely applied semi-boiled process. This paper presents for the first time the standard optimum agitation conditions for effective performance of a crutcher for semi-boiled laundry soap production. A standard reactor volume to diameter of 0.17 m 3 /m and height to diameter ratio of 1.2 ratios on 7 % over design, agitator speeds of 0.75 rps (paddle), motor power of 10.5 W and torque of 2.24 Nm with impeller to reactor diameter of 1/3 and teflon shaft centralizer have been developed. The introduction of “bottom scrapper” component to the agitation unit in a cone bottomed cylindrical batch reactor would enhance mixing and heat transfer, eliminate recycling unit and the application of under steam bubbling for effective cone content mixing. Also, the introduction of 4 baffles on 0.5 × 10 –2  m clearance from impeller blades would promote efficient mixing and heat transfer. The overall conditions developed ensured effective mixing, heat transfer and high rate of reaction.

This study was aimed to evaluate the characteristics of chitosan from Pessu river crab shell and its derivatives as prospective adsorbent. The synthesized chitosan (CH) was modified with 10 % (w/v) oxalic acid (CHOx), while the composites (CHOx-ANL 1 , CHOx-ANL 2 and CHOx-ANL 3 ) were designated according to the amount of activated neem leave (ANL). The materials were characterized by Fourier transform infrared (FTIR), energy-dispersive X-ray (EDAX), X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), thermal gravimetric (TGA) and methylene blue dye adsorption. The FTIR spectra of chitosan samples show the characteristics of primary and secondary amine/amide groups. The SEM images exhibit a tight, porous and fractured surface, which is covered with activated neem leave for the composites. The BET surface area of chitosan materials is in the increasing order of, CH < CHOx-ANL 1  < CHOx-ANL 2  < CHOx < CHOx-ANL 3 . CHOx-ANL 3 displays a higher surface area of 389 m 2 /g, and 70.9 % mesoporosity. Despite its lower surface area of 258 m 2 /g (65.4 % mesoporosity), CHOx-ANL 1 exhibits a greater methylene blue adsorption of 90.8 mg/g at dye concentration of 300 mg/L. The possible removal mechanisms include ionic interaction between dye molecules and functional groups, and surface adsorption due to the textural properties of chitosan samples. Chitosan from Pessu river crab shell and its derivatives are promising adsorbent candidate for dyes and heavy metals removal from water.

The back pressure of a gas–liquid swirl ejector is a critical parameter that affects the flow regime and entrainment performance of the system. In the case of a weak swirl injection, the motive jet carries relatively higher axial momentum thus remains in a single phase and the liquids appear glassy. With increasing in the back pressure of the bubble flow, the suction rate drops rapidly. For a strong swirl injection, the liquid jet is disintegrated due to higher angular momentum and the spray is atomized. Augmentation in the back pressure also causes the reduction in the suction rate but it tends to grow more gradual than the weak swirl injection. As a result, the suction rate of the strong swirl is greater than that of the weak swirl in the majority of the back-pressure range. However, owing to the high transition pressure, only the weak swirl entrains the air in the bubble flow regime at low back pressure. The relationship between the suction and the swirl intensity is not fixed and is influenced by the back pressure.