Volume 19, Issue 3

An efficient immobilized denitrification bioreactor functioning under anaerobic conditions was developed by combining bacterial immobilization technology with iron-carbon (Fe–C) particles. The effects of key factors on nitrate (NO 3 − –N) removal efficiency were invested, such as the carbon-nitrogen ratio (C/N), pH and hydraulic retention time (HRT). Experimental results show that 100.00% NO 3 − –N removal efficiency and a low level of nitrite (NO 2 − –N) accumulation less than 0.05 mg L −1 were obtained under the condition of a C/N ratio of 3, pH 7.0 and HRT of 6 h. Meteorological chromatographic analysis showed that the final product of denitrification was mainly nitrogen (N 2 ). The main component of precipitation formed in the bioreactor was characterized as Fe 3 O 4 by X-ray diffraction. High-throughput sequencing analysis indicated that the dominant bacterial class in the Fe–C bioreactor was Gammaproteobacteria , while the dominant genera were Zoogloea and Azospira , the relative abundances of which were as high as 23.25 and 15.43%, respectively.

The hydrogen removal and carbon formation effects in dense palladium (Pd)-based membrane reactors for dry reforming of methane (DRM) performance is numerically analyzed in this study. The steady-state membrane reactor operation is described using a three-dimensional, heterogeneous, non-isothermal mathematical model. Based on the numerical simulation results for reaction temperature and pressure varied in the 400–600 °C and 1–30 atm ranges, methane conversion and hydrogen yield were found enhanced using the membrane reactor. However, carbon formation, which affects catalyst activity and limits the benefits of using a membrane reactor is also enhanced. A parametric study using reaction pressure as the primary parameter for the membrane reactor operation found that the CH 4 conversion, hydrogen yield, H 2 recovery, and carbon formation can be enhanced by increasing the reaction temperature, inlet CO 2 /CH 4 ratio, and sweep gas flow rate. With the enhanced H 2 removal, carbon formation is also enhanced. Because membrane permeance is inversely proportional to the membrane thickness, membrane thickness can be used as a parameter to control the carbon formation under given operating conditions.

The isolated mixed region (IMR) is gradually formed during stirring and reduces the mixing efficiency. The unsteady-state formation process of the IMR was modeled and its formation mechanism was analyzed. The rotating frequency of the impeller was optimized using the chaos mathematical theory to improve the stirring efficiency without increasing the power consumption. The calculated results demonstrate that the IMR is a coherent structure, and its formation process is based on the free shear effect of the mixed layer. The chaotic stirring method can accelerate the momentum dissipation process by 37% by eliminating the IMR, and increase the speed by up to 31%. Therefore, chaotic mixing can eliminate the IMR in a shorter time and lower the power consumption.

Clogging behavior of powder particles in packed bed is a longstanding engineering challenge in many industrial processes, of particular interests to ironmaking reactors. In this work, a CFD-DEM model was developed to investigate the powders clogging in a packed bed with lateral inlet. The flow and clogging of powders of varying gas velocities flowing through the packed bed were studied. The results showed that two kinds of clogging powders inside the porous can be observed. One is mainly due to mechanical interactions between powder particles, which can create arches on packed bed and stop the flow. When the powders form a bridge across the pore throat of the orifice, the bottleneck of void space becomes the starting point for blockage formation. The other represents a part of clogging powders which is due to drag force and friction between one small particle rolling very slowly on the surface of large particles whose spacing is close to the diameter of powders. The powders distribution, mechanical behavior and pressure drop were also discussed. The findings of this work provides a fundamental understanding on clogging behavior of powders in a packed bed with lateral inlet, and is useful for industry processes’ understanding and optimization.

This study was performed to determine the efficiency of the electro/persulfate process to remove basic violet 16 (BV16) dye and COD from aqueous solutions. The present study was experimentally performed on a laboratory scale. The effect of pH on the process was investigated independently, and after performing the experiments, the effect of voltage (volts), the dose of persulfate (g/L), initial concentration of BV16 dye, and electrolysis time was investigated with the model presented by Box Behnken design, and optimal conditions for BV16 dye removal was obtained. Under optimal conditions, COD removal efficiency and toxicity changes during the process were calculated, and the effect of distance between electrodes and surface of electrodes on process efficiency was investigated. By-products of oxidative degradation were determined with LS-MS. The amount of electrical energy consumed by the process was investigated by voltage changes and then the kinetics of the process was investigated by a pseudo-first-order model. The results showed that the electro/persulfate process in optimal conditions including pH of 5, a voltage of 11.43 V, persulfate dose of 0.09 g/L, initial BV16 concentration of 45 mg/L, and electrolysis time of 48.5 min could provide BV16 dye removal efficiency of 95% and COD removal efficiency of 57.14%. Findings of electrical energy consumption showed that with increasing voltage, the efficiency of the process increased, but the amount of energy consumption also increased. Under optimal conditions, increasing distance between the electrodes was led to a decrease in removal efficiency, but the removal efficiency increased with the increasing surface of the electrodes. Based on the kinetic results, the electro/persulfate process followed pseudo-first-order kinetics with R 2  = 0.9956. The present study showed that the electro/persulfate process as a useful technique has high efficiency in removing BV16 dye and its toxicity from aqueous solutions and can be effective and useful in removing the COD of solution.

A new single-phased thermosetting resin (propargyloligosilazane, POSZ) was prepared through Hofmann alkylation of oligosilazane with propargylbromide; the propargyl content in POSZ was controlled by monitoring the amount of propargylbromide in synthesis. The characterizations showed that POSZ has ideal rheology during material processing, the thermal curing temperature could be lowered when isocyanate was used as crosslinking agent, and the thermally cured POSZ can be pyrolyzed into anti-oxidative ceramic at a high yield of >70%. For POSZ-matrixed carbon-fabric laminate composite, it possessed high mechanical properties and retained the original shape with the increase of temperature as high as 800 °C. The POSZ-matrixed laminate has the mechanical properties combining polymer character at room temperature and ceramic character at high temperature, and it will find many prospective high temperature applications in need of polymer and ceramic properties simultaneously.

The oxidation of rabeprazole sulfide is a key step in the synthesis of rabeprazole, a drug for the treatment of stomach acid-related disorders. The current rabeprazole production process adopts one pot batch process, which has low reaction efficiency and poor stability. A continuous process can greatly improve the production efficiency and solve the above problems. Therefore, the reaction parameters of rabeprazole in microreactor were explored through laboratory experiments to explore the possibility of continuous production of rabeprazole. Rabeprazole sodium was synthesized by using rabeprazole thioether as a raw material and sodium hypochlorite solution as the oxidant. Oxidation, quenching, acid-base regulation and extraction were completed continuously in the microreactor. Rabeprazole solution with a purity of 98.78% (±0.13%) can be obtained continuously in 56 s, whereas intermittent production lasted for at least 2 h. Thus, the microreactor can effectively improve the oxidation synthesis efficiency of rabeprazole, and provide reference for the realization of other reactions in the microreactor.

A numerical study of the gas–liquid two-phase flow and mass transfer in a square microchannel with a T-junction is carried out in this work. Through numerical simulation methods, the flow patterns of bubble flow, slug flow and annular flow are determined. By proposing a new flow pattern conversion relationship with different media and different speeds, 100 sets of CO 2 -water flow patterns and 100 sets of CO 2 -ethanol flow patterns are obtained. The effects of surface tension on flow pattern, bubble length and liquid plug length are studied. The pressure distribution and pressure drop are analyzed, and mass transfer is obtained through slug flow simulation, and the influencing factors of gas–liquid mass transfer are studied. The results show that the effect of surface tension on the length of the bubble and the length of the liquid plug is completely opposite, the pressure distribution is stepped, and the pressure drop increases with the increase of the gas–liquid velocity. In addition, it was found that the volumetric mass transfer coefficients of the bubble cap and the liquid film gradually decreased with time, and eventually stabilized. The increase in bubble velocity accelerates the mass transfer rate, while the increase in unit cell length slows the mass transfer rate. However, the influence of film thickness and liquid film length on mass transfer varies with time.

Micromixers are key components of microfluidic systems for sample analysis, bioreactors, drug delivery, and many other applications. To date, numerous passive micromixer designs have been proposed. Among those, several designs with complex design structures have been demonstrated to be efficient. In the present work, the authors try to propose a new efficient design with low complexity in terms of fabrication. The new design is two-layer and is based on the split and recombination (SAR) and vortex mixing principles. It is suggested to fabricate the new design in polydimethylsiloxane (PDMS) using the soft lithography technique. This new design is chosen among three new designs simulated using the computational fluid dynamics (CFD) software ANSYS Fluent 17.0. The three new designs are named ND1, ND2, and ND3 and their mixing performances are evaluated numerically using mixing index (MI) and mixer effectiveness (ME) quantities at four different Reynolds (Re) numbers in the range of 0.1–100. Calculated values are compared with those obtained for the classical Y-shaped (CY) micromixer. Flow and mixing patterns are computed by solving the continuity, Navier–Stokes, and the convection–diffusion equations. CFD results for the CY micromixer are compared with available experimental and numerical data and reasonable agreement is observed. According to the results, ND3 has the highest performance (ME up to 36.86 percent/mm) among the investigated micromixer designs in the entire range of Re numbers. The maximum pressure drop (35099.9 Pa at Re = 100 for ND3) is still in the range of acceptable pressure drops reported in the literature. ND3 can be used as an efficient substitute for CY. Although ND3 is highly efficient (MI up to 99.52%) at Re numbers lower than 0.3 or higher than 50, its performance at the intermediate Re numbers (0.3 < Re < 50) is poor and unacceptable (MI as low as 44%). This can be simply improved by adding extra mixing units to provide adequate mixing also at the intermediate Re numbers.