Band 13, Heft 1 -

In this study, performance of Ni/γ-Al 2 O 3 catalysts which is prepared under the influence of magnetic field (MF) was investigated in partial oxidation of methane (POM) reaction to syngas. The results showed that the Ni based catalyst which was prepared by calcinations with the MF, as compared with ordinary calcinations, increased in CO selectivity and H 2 yield. Based upon XRD and TEM characterization results, a catalyst that was prepared by calcinations with MF, the average size of particles decreased from 4–12 to 2–8 nm, showing the effect of MF in improved dispersion of Ni oxide catalysts. Also, the TGA characterization demonstrated enhanced anti-carbon deposit ability

The influence of potassium addition to the vanadia supported on the microemulsion-mediated TiO 2 nanoparticles in propane oxidative dehydrogenation was studied. Raman spectroscopy demonstrated that the addition of potassium caused enhanced dispersion of vanadia species on the support surface. Also, potassium existence affects the H 2 temperature programmed reduction maximum reduction temperature and shifted it to 520°C, which was in accordance with its lesser catalytic activity. Nevertheless, a propylene selectivity enhancement was observed by potassium addition. In spite of the fact that the catalytic performance loss was not severe in vanadia-supported TiO 2 anatase, potassium addition led to improve the catalyst lifetime. After deactivation test, potassium-containing vanadia catalyst possessed lower surface area loss (i.e. from 52 to 49 m 2 g −1 ). Average crystallite size of potassium-containing vanadia catalyst exhibited lower decrease than that of potassium-free vanadia catalyst after deactivation test. According to Raman spectra, deactivation phenomena had influenced the population of vanadia species so that monovanadates decreased and polyvanadates increased.

Effect of titania loading on physical–chemical properties and bifunctional catalytic activity of phosphate–vanadia-impregnated silica–titania was investigated. Different concentrations of titanium were impregnated into fumed silica, followed by impregnation of vanadium and phosphoric acid simultaneously onto the prepared silica–titania. Results revealed that Ti amount did not have significant effect on crystallinity, surface area and particle size of the resulted materials. However, quantity of tetrahedrally coordinated Ti species increased with increasing Ti content in the sample. Pyridine adsorption study showed the presence of both Brønsted and Lewis acid sites in all the samples even in the titanium-free phosphate–vanadia-impregnated silica sample. The catalytic testing showed that phosphate–vanadia-impregnated silica–titania with the molar ratio of Si:Ti=33:1 was the best bifunctional catalyst in the transformation of 1-octene to 1,2-octanediol using aqueous hydrogen peroxide as oxidant.

This paper presents the magnetohydrodynamic (MHD) boundary layer stagnation point flow with diffusion of chemically reactive species undergoing first-order chemical reaction over a permeable stretching sheet in presence of partial slip. With the help of similarity transformations, the partial differential equations corresponding to momentum and the concentration equations are transformed into non-linear ordinary differential equations. Numerical solutions of these equations are obtained by shooting method. It is found that the horizontal velocity increases with the increasing value of the ratio of the free stream velocity and the stretching velocity. Velocity decreases with the increasing magnetic parameter when the free-stream velocity is less than the stretching velocity but the opposite behavior is noted when the free-stream velocity is greater than the stretching velocity. Due to suction, fluid velocity decreases at a particular point of the surface. With increasing velocity slip parameter, velocity increases when the free-stream velocity is greater than the stretching velocity. But the concentration decreases in this case. Concentration decreases with increasing mass slip parameter.

The present paper deals with the effect of surface heat and mass transfer on magnetohydrodynamic flow of Powell–Eyring fluid over a vertical stretching sheet. The effects of thermophoresis, Joule heating and chemical reaction are also considered. The governing non-linear partial differential equations of the model are transformed into coupled non-linear ordinary differential equations using a similarity transformation and solved numerically by Runge–Kutta method and analytically by homotopy analysis method (HAM). The convergence is carefully checked by plotting ℏ$$\hbar $$-curves. For different dimensionless parameters, numerical and analytical calculations are carried out and an investigation of the obtained results shows that the flow field is influenced considerably by the buoyancy ratio and thermal radiation, chemical reaction and magnetic field parameters. A totally analytical and consistently applicable solution is derived which agrees with numerical results.

Intensified continuous three-phase catalytic reactors working in high-pressure and -temperature conditions are particularly effective at coping with mass transfer limitations during three-phase catalytic reactions. They are highly nonlinear, multivariable systems and behave differently from conventional batch, fed-batch or continuous non-intensified reactors. This paper deals with an integration of real-time optimization and model predictive control (RTO–MPC) of an intensified continuous three-phase catalytic reactor. A steady-state model developed by regression method is used in optimization layer and gives the reference trajectory for control layer. At control layer, a linear MPC is proposed based on identified state space model. The performance of RTO–MPC is illustrated by simulation

Studies have been made on the kinetics accompanied with mass transfer for the pyruvic acid/tributylamine (TBA)/n-butyl acetate system to investigate the effectiveness of reactive extraction for the separation of pyruvic acid from the aqueous solution. In the present work, kinetic studies, needed for the design of a recovery unit, were carried out using aqueous solution of pyruvic acid. TBA (conc. range 0.420–2.099 kmol/m 3 ) dissolved in n-butyl acetate (conc. range 50–90%) was used as an extractant. The effect of reactant concentration, the effect of stirring speed and the effect of phase volume ratio on the extraction process were investigated. The kinetic parameters such as reaction order and rate constant were calculated. Kinetic measurements showed that the reaction is of second order occurring in the diffusion film and was found to be independent of hydrodynamic conditions. Rate constant was evaluated to be 0.419m3mol−1S−1$0.419\,{{\rm{m}}^3}{\rm{mo}}{{\rm{l}}^{- 1}}{{\rm{S}}^{- 1}}$.

Analysis of efficient production of ethyl acetate utilizing a C atalytic M embrane M icro- R eactor (CMMR) was theoretically investigated and verified using published results for the esterification reaction. Grafted sulfonic groups in the pores of a polyethersulfone membrane catalyzed the reaction. Theoretical analysis of the catalytic membrane reactor was achieved through development of a lumped parameter model to describe the CMMR behavior and performance. The developed model was solved numerically for different design and operating conditions using MATLAB Simulink software. The model parameters were verified and validated using the experimental results to achieve a reliable tool for design, replication, scaling-up, and optimization. The approach to maximum conversion was simulated. Cumulative yield per unit time was investigated to determine the optimum process time. Membrane regeneration was conducted and the regeneration time was determined as well in order to reuse the membrane for other cycles. Reactor scaling-up was studied using the model for process design.

Structured Pd/Al 2 O 3 catalysts were fabricated by impregnating Pd onto Ni and Cu foams coated with Al 2 O 3 layers. By testing the adhesion stability and catalytic activity in the combustion of methane, the superior performance of Ni-foam-supported Pd/Al 2 O 3 catalyst was demonstrated, to its counterpart powder catalysts. The resultant structured catalysts enable the fabrication of lamellar microreactor systems. It is found that the metal foams influence the activity of catalyst layer, due to the diffusive penetration of metallic atoms into catalysts from metal foams. The Ni foam is beneficial for enhancing the activity of Pd/Al 2 O 3 catalyst, while the Cu foam plays a negative role. The investigation to the model powder catalysts doped with Ni and Cu verified the modification of Ni and Cu to the physicochemical properties of Pd/Al 2 O 3 catalyst, thereby the catalytic performances. Thus, it can be expected that the performance of structured catalysts may be improved by rationally designing and selecting proper supports.

Soot formed during the rich combustion of fossil fuels is an undesirable pollutant and health hazard. A newly developed Monte Carlo method is used to simulate the soot formation in a counterflow diffusion flame of ethylene. The simulation uses a new reaction mechanism available in literature, which focuses on modeling the formation of large polycyclic aromatic hydrocarbons (PAHs) up to coronene (C 24 H 12 ). Nascent soot particles are assumed to form from the collision of eight different PAH molecules. Soot surface growth includes the hydrogen-abstraction-C 2 H 2 -addition mechanism and the condensation of the PAHs. Soot coagulation is in the free-molecular regime because particles are small (not more than a hundred nanometer). The coupling between vapor consumption and soot formation is handled by an interpolative moment method. Soot particle diffusion is found negligible throughout the counterflow flame, except for a very narrow region right around the stagnation plane. The soot particle size distribution (PSD) generally exhibits a bimodal shape. The first peak corresponds to a large number of nascent particles, while the second peak results from the competition between nucleation and coagulation. Surface growth affects the PSD quantitatively, but does not change the modality. A comparison with experimental data is also provided.

The heat conduction performance of the methanol synthesis reactor is significant for the development of large-scale methanol production. The present work has measured the temperature distribution in the fixed bed at air volumetric flow rate 2.4–7 m 3 · h −1 , inlet air temperature 160–200°C and heating tube temperature 210–270°C. The effective radial thermal conductivity and effective wall heat transfer coefficient were derived based on the steady-state measurements and the two-dimensional heat transfer model. A correlation was proposed based on the experimental data, which related well the Nusselt number and the effective radial thermal conductivity to the particle Reynolds number ranging from 59.2 to 175.8. The heat transfer model combined with the correlation was used to calculate the temperature profiles. A comparison with the predicated temperature and the measurements was illustrated and the results showed that the predication agreed very well with the experimental results. All the absolute values of the relative errors were less than 10%, and the model was verified by experiments. Comparing the correlations of both this work with previously published showed that there are considerable discrepancies among them due to different experimental conditions. The influence of the particle Reynolds number on the temperature distribution inside the bed was also discussed and it was shown that improving particle Reynolds number contributed to enhance heat transfer in the fixed bed.

A facile and general strategy was successfully developed for the surface modification of hydrophobic Fe 3 O 4 magnetic nanoparticles with various sizes (4–17 nm). The results show that the magnetic and hydrophobic properties are sensitive to the nanoparticle size. For example, the contact angle (CA) of the sample increases as the particle size increases. Using these surface modification techniques allowed the coating of water droplets with highly hydrophobic Fe 3 O 4 nanoparticles to form magnetic liquid marbles through a mechanical method. The behavior of these liquid marbles under the action of a magnetic field revealed that their potential value in electronic, biomedical, self-cleaning, and biochemical applications.

Synthesis of GVL (γ-valerolactone) via hydrogenation of aqueous LA (levulinic acid) with H 2 over heterogeneous catalyst (Ru/C) was investigated. In the first part, a study of the influence of various operating conditions was conducted including that of temperature (90–180°C), stirring rate (500–1200 rpm), catalyst loading (0.1–2.0 g), hydrogen pressure (0.4–2.8 MPa) and initial LA concentration (0.5–2 M). In the second part, influence of supercritical CO 2 (scCO 2 ) on hydrogenation rate and GVL yield were investigated. Hydrogenation of aqueous LA under scCO 2 and under N 2 atmosphere was carried out in batch reactor at 150°C and was compared with the case when no additional gases were present. The result indicated that the use of scCO 2 had no beneficial effect neither in terms of LA conversion nor hydrogenation rate when the amount of hydrogen was relatively low compared to the stoichiometry. This effect was mitigated when more hydrogen was present.

The control of the aeration time and the dissolved oxygen in a reactor plays an important role in the management of the plant and the reduction of energy consumption. For this, two full-scale municipal wastewater treatment plants were chosen. The first plant (Choutrana II) designed for 600,000 population-equivalents (p.e), consists of a primary treatment step (screening, grit and grease removal), followed by four parallel oxidation ditches with a total volume of 60,000 m 3 . Aeration is ensured by air diffuser. The second plant (Menzel Bourguiba) designed for 140,000 p.e consists of a primary treatment stage (screening, grit and grease removal), followed by anoxic tanks and two aerobic reactors with a total volume of 14,000 m 3 . Aeration is ensured by six surface aerators which are operated episodically to create aerobic and anoxic conditions. Currently, the aeration management is controlled by a timer with a maintained oxygen concentration at a given level in the aerobic reactor. The nitrogen removal is done during air-on and air-off periods. The process can be seen as a succession of aeration periods followed by an anoxic period. This category of plant operation is far from the optimal and raises energy consumption and operative costs. The purpose of this study is to implement a new strategy to control aeration taking into account the variation of the daily organic load received by plants (feedforward control) and to create favorable conditions for nitrification and denitrification steps (feedback control). The Activated Sludge Model 1, which is calibrated and validated by respirometry tests, is used. Simulation results show the potentialities of the chosen strategy, which could save 28% of aeration energy and could adjust the aerobic and anoxic times. As first results, daily aeration time could be considered enough to produce treated water conform to standard terms. For Choutrana II plant, the results obtained have allowed to achieve a nitrogen removal rate of 85% and an output concentration between 6 and 12 mg/L. Rates of nitrification and denitrification were estimated at 4 mg NO 3 -N/L/h and 6 mg NH 4 -N/L/h, respectively. At the same time, aeration periods (on/off) are connected with daily organic load received by the plant and created favorable conditions for nitrification–denitrification. A good agreement between input biological loads, aeration profile and nitrogen removal is approved.