Band 19, Heft 5

Axial-radial flow plate reactors have been recently considered as efficient and practical types of reactors for methanol synthesis. Generally, an axial–radial reactor (AR) consists of two main parts namely the axial section and the radial section and the vast majority of the feed enters the radial section. Moreover, the structure of AR has a space above the axial part, which can add an adiabatic bed in the system. In this study, the performance of two novels AR configurations is investigated to improve the effectiveness of the axial–radial plate reactor. In the first configuration, the optimum length of the adiabatic bed is calculated and the adiabatic bed is located above the axial section inside the AR and is named IAAR. Therefore, in IAAR the feed of the axial section just enters the adiabatic bed and warms up. On the other configuration, the adiabatic bed with the optimum length is placed outside the reactor and is named OAAR. Therefore, in OAAR the total feed passes through the adiabatic bed, highly warms up, then cools to the optimum temperature in a heat exchanger, and finally enters AR. Two-dimensional mathematical modeling via orthogonal collocation on the finite element method is developed to compare the performance of two configurations. The results show that the maximum proportion of methanol produces in IAAR, which is approximately 3.8% higher than that produced in conventional AR due to utilizing an adiabatic bed inside the AR and superior gas distribution in the process. Momentum, mass, and heat equations are calculated and molar flow rates, mole fractions and temperatures are depicted along the radius and the length of the three configurations.

In this paper, We arrange the obstacles based on the Koch fractal principle (OKF) in the micromixer. By changing the fluid flow and folding the fluid, a better mixing performance is achieved. We improve the mixing efficiency by placing OKF and changing the position of OKF, then we studied the influence of the number of OKF and the height of the micromixer on the mixing performance. The results show that when eight OKF are staggered in the microchannel and the height is 0.2 mm, the mixing efficiency of the OKF micromixer can reach 97.1%. Finally, we compared the velocity cross section and velocity streamline of the fluid, and analyzed the influence of OKF on the concentration trend. Through analysis, it is concluded that OKF can generate chaotic convection in the fluid, and enhance the mixing of fluids by generating vortices and folding the fluid. It can effectively improve the mixing efficiency of the micromixer.

In this study, activated carbon was developed from saw-dust by pyrolysis. The activated carbon was characterized for elemental composition, morphology and surface chemistry. The potential of the prepared activated carbon for the removal of methylene blue (MB) from aqueous solution was investigated. Batch adsorption experiments were conducted to evaluate the adsorption isotherm, kinetic and thermodynamic of MB onto saw-dust activated carbon. The MB removal efficiency was 99.2% and the Lamgmuir isothermal model having correlation coefficient ( R 2 ) of 0.98 gave the best fit. The kinetics of MB adsorption onto activated carbon was described with the pseudo second order model indicates the dominance of chemisorption mechanism. Thermodynamic parameters showed that the adsorption of MB on saw dust activated carbon adsorbent was endothermic in nature and a non-spontaneous process. The activation energy of 34.7 kJ/mol further reveals that the adsorption process was chemisorption. Generally, the results suggest that the saw-dust activated carbon is a viable adsorbent for effective removal of MB from wastewater effluent contaminated with dye.

Revalorization of mining residues is of central concerns to the mining industry and the environment. Specifically, environmental management of residual products from the exploitation of chrysotile in the Thetford Mines region is one of the government concerns in Quebec and Canada. This work uses mining wastes in a second resource generation for production of magnesium from cheap and health-friendly mineral sources; the goal being to produce chrysotile-depleted pre-concentrates for a use as precursors in the leach off extraction of magnesium. The concentration of lizardite/antigorite from chrysotile containing serpentine rock mine tailings originating from the Carey Mine site in East-Broughton (Québec) was carried out using a suite of hydrocyclone, settling/decantation and magnetic separations. Four size classes of the mining residue, namely (−3150,+1580), (−1580, +600), (−600, +300) and (−300, +150) μm, were tested with an aim to reduce the level of objectionable asbestos fibers to allow access to the safer Mg-bearing minerals contained in the mine waste sources. The asbestos fibers clean-up consisted of subjecting the sieved fractions to two hydrocyclone steps, six settling/decantation steps and two magnetic separation steps. The best results were achieved when the hydrocyclone separators led to Mg recovery of 85% (±4) for the coarsest size fraction size. Both hydrocyclone underflow streams underwent settling/decantation separations. The settling tests lasted 30 min and led to Mg recoveries of 82.5% (±1.8) of Mg in the ultimate concentrate. SEM characterizations revealed that it was possible to reduce substantially the amount of chrysotile fibers to render the coarse-sized fraction in the mining waste usable while significantly lowering the health risk of the fibers. A two-step magnetic separation was applied to the final settling/decantation underflow to remove magnetic minerals such as magnetite from the lizardite/antigorite concentrate. The final quasi-non-magnetic chrysotile-depleted lizardite/antigorite concentrate allowed sample recovery of 62.5% (±0.9) wt. of Mg. These preliminary results are intended as a first compulsory step in support of viable restoration and sustainable development scenarios for the Thetford Mines mining sites as second-breath sources for valuable magnesium.

The plate-fin heat exchanger has been widely applied in the field of air separation and aerospace due to its high specific surface area of heat transfer. However, the low heat transfer efficiency of its plate bundles has also attracted more attention. It is of great significance to optimize the structure of plate-fin heat exchanger to improve its heat transfer efficiency. The plate bundle was studied by combining numerical simulation with experiment. Firstly, according to the heat and mass transfer theory, the plate bundle calculation model of plate-fin heat exchanger was established, and the accuracy of the UDF (User-Defined Functions) for describing the mass and heat transfer was verified. Then, the influences of fin structure parameters on the heat and mass transfer characteristics of channel were discussed, including the height, spacing, thickness and length of fins. Finally the influence of various factors on the flow field performance under different flow states was integrated to complete the optimal design of the plate bundle.

The transfer of particles in laminar and turbulent flows has many applications in combustion systems, biological, environmental, nanotechnology. In the present study, a Combined Baffles Quick-Separation Device (CBQSD) is simulated numerically using the Eulerian-Lagrangian method and different turbulence models of RNG k - ε , k - ω , and RSM for 1–140 μm particles. A two-way coupling technique is employed to solve the particles’ flow. The effect of inlet flow velocity, the diameter of the splitter plane, and solid particles’ flow rate on the separation efficiency of the device is examined. The results demonstrate that the RSM turbulence model provides more appropriate results compared to RNG k - ε and k - ω models. Four thousand two hundred particles with the size distribution of 1–140 µm enter the device and 3820 particles are trapped and 380 particles leave the device. The efficiency for particles with a diameter greater than 28 µm is 100%. The complete separation of 22–28 μm particles occurs for flow rates of 10–23.5 g/s, respectively. The results reveal that the separation efficiency increases by increasing the inlet velocity, the device diameter, and the diameter of the particles.

The aim of this study is to verify the ability of some photochemical processes in the absence of light (Fenton) and in its presence (photolysis/UV, photo-Fenton/UV and photo-Fenton/Solar) to obtain total decolorization and mineralization of an diazo dye in aqueous solution: the Evans Blue (abbreviated as EB). Batch experiments were carried out to evaluate, on the first stage, the influence of different processes on EB decolorization and mineralization. During the second stage the optimal operational conditions like: H 2 O 2 dosage, EB concentration and source of light were investigated. The reaction efficiencies have been compared for the same system in the dark or under the assistance of an artificial or solar light source. The obtained results showed that color removal followed the increasing order: photolysis/UV (18.2%) < Fe(II)/H 2 O 2 (64.12%) < Fe(II)/H 2 O 2 /UV 365 nm (83.4%) < Fe(II)/H 2 O 2 /solar light (86.3%) < Fe(II)/H 2 O 2 /UV 254 nm (99.9%) with a reaction time of 60 min This improvement could be related to a better production of radicals OH • . In another hand, The efficiency of substrate mineralization in each process has been comparatively discussed by total organic carbon (TOC) and total chemical oxygen demand content of EB solutions.

One of the most significant aspects in selective catalytic reduction (SCR) of nitrogen oxides (NO x ) is developing suitable catalysts by which the process occurs in a favorable way. At the present work SCR reaction by ammonia (NH 3 -SCR) was conducted using Co-Mn spinel and its composite with Fe-Mn spinel, as nanocatalysts. The nanocatalysts were fabricated through liquid routes and then their physicochemical properties such as phase composition, degree of agglomeration, particle size distribution, specific surface area and also surface acidic sites have been investigated by X-ray diffraction, Field Emission Scanning Electron Microscope, Energy-dispersive X-ray spectroscopy, energy dispersive spectroscopy mapping, Brunauer–Emmett–Teller, temperature-programmed reduction (H 2 -TPR) and temperature-programmed desorption of ammonia (NH 3 -TPD) analysis techniques. The catalytic activity tests in a temperature window of 150–400 °C and gas hourly space velocities of 10,000, 18,000 and 30,000 h −1 revealed that almost in all studied conditions, CoMn 2 O 4 /FeMn 2 O 4 nanocomposite exhibited better performance in SCR reaction than CoMn 2 O 4 spinel.

MCM-22 was synthesized by using silicic acid powder as a silica source under the static hydrothermal condition and characterized by X-ray diffraction, nitrogen adsorption-desorption isotherms, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, and temperature-programmed desorption of ammonia. The liquid phase benzylation of benzene with benzyl alcohol to diphenylmethane was investigated over H-MCM-22. The effects of reaction parameters on the conversion of benzyl alcohol and product distribution were determined. Under optimal reaction conditions, diphenylmethane yield of 92.1% was achieved for 99.3% conversion of benzyl alcohol in 3 h of reaction period. The reusability of the catalyst was also investigated after calcination of the catalyst in stagnant air at 500 °C for 4 h. The results show that the organic species produced during the reaction deposited in the catalyst lead to the deactivation of the catalyst and the calcination of the deactivated catalyst causes catalyst dealumination.