Volume 16, Issue 8 -

To take into account the impact of hydrodynamics on their behavior, chemical reactors are traditionally modeled as an association of smaller ideal reactors: perfectly stirred or plug flow reactors. This modeling is mainly based on the reactor hydrodynamics but sometimes also on phenomena governing the considered process such as heat or mass transfer or chemical reaction. The approaches encountered in the literature start from the most basic one in which the whole reactor is considered as an ideal reactor, up to a very fine discretization using Computational Fluid Dynamics (CFD). In between, the reactor can be described as an association of a small number of ideal reactors: this is the systemic approach. Another intermediate approach has also been recently developed: the compartmental method, where all compartments are assumed to be perfectly mixed. In the compartment method, the compartment number is significantly more important than in the systemic approach - but lower than for CFD. Furthermore, these compartments are chosen to be relevant regarding their position in space as opposed to systemic models in which, in most of cases, only the global physical behavior is taken into account. Compared to CFD, compartment models are less computationally demanding while taking into account the most important flow features. The present review describes the different types of modeling commonly used in chemical reaction engineering during the last 60 years from the systemic approach to CFD, with a focus on the attractive compartmental modelling. In particular, the methodologies encountered to determine the compartment structure are detailed, as well as the different possibilities to determine the turbulent fluxes between compartments.

This work focuses on Two Phase Anaerobic Digestion – a novel approach to split reactions’ chain in two separated tanks, each with specialized microbe community to achieve the best possible efficiency for each part of conversion. More specifically, the article tackle the topic of evaluation the possibility to adapt a mathematical model, previously dedicated for Autogenerative High Pressure Digestion (AHPD), to make use of it in simulation of Temperature Phased Anaerobic Digestion (TPAD) process. A comprehensive study of available solutions for biogas production simulation in conventional and TPAD configuration is additionally performed. Basing on its results, a reference model from literature, for comparison purpose is selected. Revisions and modifications, necessary to adjust previously developed model, to TPAD process, are described. Also, additional improvements like redesigned pH calculating algorithm is presented. Finally, the comparison between model predictions, a reference model and pilot-scale data is carried out. The results show that our current model needs further optimization, however even at this stage it provides acceptable results in short-range simulations (not longer than 42 days). Further works should focus on process stability improvement, especially in the thermophilic stage of biogas production. There's an opportunity for innovation as the research shows that requirement of accurate, large-scale optimized TPAD process model, is still not fulfilled.

A new mesoporous silica SBA-16 (called SP-16) was prepared by the direct hydrothermal method using Pluronic F127 (triblock copolymer; EO106PO70EO106) as surfactant and TEOS (tetraethyl orthosilicate) as silica source. The catalyst property of the SBA-16 was attained by loading the STA (Silicotungstic acid) active compound. The loading contents of STA were determined between 5 % and 40 % based on weight ratio of W and Si (W/Si). Catalytic activities and sustainability of SP-16 (10–20 %, W/Si) catalysts were determined by esterification (liquid phase reaction methanol and acetic acid) reactions at 343-353K, under autogenic pressure, 1/1–1/2 feed molar ratios (methanol/acetic acid) and in the presence of 0.4 g catalyst in the semi-batch reactor for 6 - 24h. Acetic acid conversion values of 10 and 20 % catalysts with 1/1 molar ratio at the end of 24h were obtained as 32–52.9 % and 47–60 %, respectively. On the other hand, when 1/2 molar ratio at 353K was used, 20 % catalyst showed 82.2 % conversion. Moreover, a second reaction experiment of 10 % catalyst was also carried out in identical conditions in the presence of catalyst recovered after the first methyl acetate reaction. The first and second reaction results of 10 % catalyst indicated that catalytic activity and sustainability were preserved for both 6 and 24h analyses. The physical properties of the materials obtained were investigated by Nitrogen sorption at 77K (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy(FT-IR), Multiple Internal Reflection (DRIFT), Thermo-gravimetry/Differential thermal analysis(TG/DTA), Scanning electron microscope (SEM) and MAPPING analysis methods.

2-nitro-4-methylsulfonylbenzoic acid (NMSBA) can be produced by oxidizing 2-nitro-4-methylsulfonyltoluene (NMST) with air catalyzed by Co/Mn/Br and phosphotungstic acid(HPW) loaded on activated carbon. This paper reports that the catalytic ability of the HPW@C catalyst in the oxidation of NMST to NMSBA can be improved by treating the activated carbon with ZnCl 2 solution. The best modification condition with ZnCl 2 solution is impregnating the carbon sample in 0.1 mol/L solution for 6 h followed by calcination at 600 °C for 4 h. The increase of the surface area and the acidic groups on the carbon surface enhances the catalytic ability of the HPW@C catalyst. The mesopores play an important role in the catalytic oxidation of NMST to NMSBA.

The kinetic effects of H 2 addition on the thermal characteristics of laminar methane diffusion flames were numerically studied using a detailed chemical kinetics consisting of 53 species and 325 reactions. The variations in the heat release properties and relevant key reactions with H 2 addition were analyzed. Results show that the reactions of H + O 2 + H 2 O ⇔ HO 2 + H 2 O (R35), H + HO 2 ⇔ OH + OH (R46), H + CH 3 (+ M) ⇔ CH 4 (+ M) (R52) and OH + H 2 ⇔ H + H 2 O (R84) present important roles in the global heat release and the contributions of these reactions significantly increased as H 2 is added to CH 4 stream. Moreover, the increase rate of contribution of R84 with H 2 addition is much larger than those of the reactions of R35, R46 and R52. The H and OH are the two most important radicals for heat release in the combustion process of CH 4 -H 2 diffusion flame. The reaction of R84 is one of the main contributors for production of H radical and the contribution of R84 significantly increased with H 2 addition, while the reaction of H + O 2 ⇔ O + OH (R38) dominates the contribution of production of OH, which contributes more than 50 %, no matter whether H 2 is added to CH 4 stream.

The present study deals with the time-dependent natural convective supercritical third-grade fluid flow past a vertical cylinder. A new thermodynamic model for the supercritical carbon di-oxide (CO 2 ) has been derived. In this model the thermal expansion coefficient is characterized as a function of pressure, temperature and compressibility factor. This model uses the Redlich-Kwong equation of state (RK-EOS). The numerically calculated thermal expansion coefficient values of CO 2 are validated with available experimental results. The governing non-linear coupled partial differential equations are solved by using Crank-Nicolson method. The obtained numerical data is described in terms of velocity, temperature, skin-friction and Nusselt number through the graphs and tables for the different set of physical parameters. It is observed that the unsteady velocity is an increasing function of reduced pressure and reduced temperature; whereas it is a decreasing function with respect to third-grade fluid parameter. The temperature field is enhanced near the critical point for the increasing values of third-grade fluid parameter. In supercritical fluid region for the increasing values of reduced pressure and reduced temperature, the skin-friction values are magnified against time. Also, the average heat transfer rate decreases for increasing values of third-grade fluid parameter.

The application of nanoparticles in dye degradation is one of the trending arenas of research in the present day world. In this work, we report a novel route to synthesise MgO/TiO 2 metal oxide nanocomposite by microemulsion technique and its application in photocatalytic dye degradation. Oil in water microemulsion was prepared using Span 80 and Tween 80 as surfactants whose proportion was regulated using hydrophilic and lipophilic Balance (HLB). The obtained microemulsion was then mechanically stirred and calcined to obtain the nanocomposite. The as-prepared nanocomposites were characterized using X Ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The prepared nanoparticles exhibited remarkable potential to degrade azo dye (Methyl red) under UV-Visible light irradiation. The effect of catalyst in the degradation was studied for different concentrations of dye (20, 40, 60, 80, 100 mg/L) and different loadings of the catalyst (0.4, 0.6, 0.8, 1.0, 1.2 g/L) so as to determine the optimum catalyst load. The consistency of the obtained data was compared with the first order reaction rate expression. Quasi steady state model was used in fitting the data and the kinetic constants were evaluated. Also, the degradation efficiency of MgO/TiO 2 nanocomposite was compared with the degradation efficiency of TiO 2 nanoparticles synthesized by microemulsion method.

The computational fluid dynamics (CFD) combined with a population balance model (PBM) was applied to simulate gas-liquid dispersion in a stirred tank with low and high gas loadings. The model predictions were validated by using the data in the literature. The simulation results show that the flow patterns and gas dispersion characteristics are very different in the stirred tank for low and high gas loadings. A typical two-loop flow pattern forms as that in single-phase stirred tank for low gas loadings, while a triple-loop flow pattern, with two recirculation loops above and one below the impeller is found in the tank for high gas loadings. Shaft power input of impeller agitation plays a major role for gas dispersion with low gas loadings. For high gas loadings, the potential energy due to gas sparging has significant effect on gas dispersion and can not be neglected. Compared to low gas loading, high gas loading causes average gas holdup increased in the stirred tank, while relative local gas holdup in the lower circulation-loop region and near-wall region reduced. The ability of impeller agitation for gas dispersion reduces with high gas loadings, and mean bubble size becomes larger and the volume-averaged bubble size distribution is wider.

In the present paper focused on flow and mass transfer of Prandtl fluid over a Riga plate. The effects of chemical reaction and solutal slip are taken into the account. The governing partial differential equations are reduced into a set of coupled non linear ordinary differential equations using suitable similarity transformations. These equations are then solved using Runge-Kutta-Fehlberg-45 method. Behaviour of emerging parameters are presented graphically and discussed for velocity and concentration distribution. Numerical values of reduced skin friction coefficient and Sherwood number are shown in table and are discussed. From the plotted results it can be observed that the solutal boundary layer thickness decreases for larger values of chemical reaction parameter and Schmidt number. Also, momentum boundary layer thickness rise with stronger modified Hartman number.

The edible plant oil production factories consume high amounts of water and contaminate the water resources. This type of wastewater consists of high chemical oxygen demand (COD) which should properly be treated by an efficient technique. Furthermore, it is containing some chemicals obtained from several sources such as H 3 PO 4 (from hydration section), NaOH (from neutralization section) and citric acid (from nickel removal section). The conventional techniques cannot efficiently treat it which is full of COD. Therefore, the electro-Fenton process as a rapid, compact and efficient one has been encouraged to be applied. For this purpose, 47 experiments were designed and carried out using iron electrodes to evaluate the effects of five significant independent variables such as reaction time (min), pH, current density (mA/cm 2 ), volume ratio of H 2 O 2 /wastewater (ml/l) and H 2 O 2 /Fe 2+ molar ratio on the COD removal. Response surface methodology (RSM) was employed to assess individual and interactive effects of the parameters. The optimum conditions were experimentally obtained at reaction time of 87.33 min, pH of 3.03, current density of 57 mA/cm 2 , H 2 O 2 /wastewater volume ratio of 2.13 ml/l and H 2 O 2 /Fe 2+ molar ratio of 3.61 for COD removal of 62.94 %.