Volume 22, Issue 6

This work reports a CFD-DEM study on the segregation and mixing of binary mixtures of particles in a bubbling fluidized bed. A simplified mixing index was applied to determine the instantaneous mixing state in the bed, with which the effects of superficial gas velocity and initial packing state on the fluidization behavior were further discussed. For the well-mixed initial conditions, the mixing index decreases with fluidization time until a dynamic equilibrium between segregation and mixing is achieved. In contrast, the mixing index first increases and then decreases with fluidization time for completely-segregated initial conditions. However, the final equilibrium between segregation and mixing will not be affected by initial packing states for a given superficial gas velocity. Moreover, the bubbling behavior shows a marked impact on segregation and mixing, i.e., mixing is enhanced during the formation and grow-up of bubbles, while segregation is strengthened during the eruption of bubbles. This makes it possible to improve the fluidization of binary mixtures of particles based on the bubbling behaviors in the fluidized bed.

Tributyl aconitate is a new type of alternative plasticizer to phthalates. Amberlyst-15 was used to catalyze the esterification of aconitic acid and n -butanol for the preparation of tributyl aconitate in a cyclic fixed-bed reactor. The influence of the reaction conditions on the conversion was investigated. The results showed that the conversion of aconitic acid increased significantly with the rise of temperature and catalyst loading. The reaction conditions were optimized as: temperature: 115 °C; initial mass ratio of AA and n -butanol: 1:4; catalyst loading: 25 %; reaction absolute pressure: 85 kPa; volume flow rate: 30 mL min −1 . Thermodynamics and kinetics of the reaction was studied. The non-ideality of the reaction system was rectified using the UNIFAC group contribution method. The kinetic process was simulated using the pseudo-homogeneous (PH) model, Eley-Rideal (E-R) model, and Langmuir-Hinshelwood-Hougen-Watson (LHHW) model. The results revealed that the E-R model exhibited superior suitability in simulating the kinetic process.

A laboratory scale continuous flow stirred tank reactor (CFSTR) has been developed for ultrasound-assisted Fenton degradation of Rhodamine B dye in simulated wastewater and its performances have been studied in the present work. The sono-reactor was made of glass, 6 cm in diameter and 17.5 cm in height; fitted with a cooling water jacket. The volume was about 0.4 L and the flow rate of dye solution was 20 mL min −1 . Ultrasound was provided with a 120 W probe-type sonicator. The hydrodynamic characteristics were studied by RTD studies and CFD analysis in COMSOL Multiphysics software. The CFD analysis showed the reactor to be behaving like a CSTR with bypassing leading to a short residence time. The optimum treatment conditions in this reactor for degrading Rhodamine B solution were determined using Response Surface Methodology. A model equation correlating the decolorization percentage with the initial dye concentration, H 2 O 2 and Fe 2+ dosage (Fenton’s reagent) was developed which can predict the decolorization with a high degree of accuracy. Under optimum conditions, the percent decolorization was 55 and the corresponding COD removal was 15 %. A continuous sono-Fenton reactor, if scaled up properly, can be useful for degradation of dark coloured refractory organics in wastewater where photo-Fenton reaction is ineffective.

The superficial gas velocity (Ug) values of 1.0, 1.5 and 2.0 cm s −1 showed a diesel consumption of 59.70, 58.20 and 65.20 %, respectively. The productivity of the airlift bioreactors (ALBs) was 0.030, 0.026 and 0.034 g L −1  d −1 , respectively. During 10 days of operation, the emulsification index ( E 24 % ) values for Ug 1.0, 2.0 and 2.0 cm s −1 were 15.79, 15.07 and 12.85 %, respectively. Likewise, an increase in the degradation and suspended solids was observed when increasing the Ug from 1.0 to 2.0 cm s −1 of the ALBs, whereas a decrease in emulsification index E 24 % was observed for an Ug of 2.0 cm s −1 . According to the results, the Ug of 2.0 cm s −1 was the most effective for increasing the degradation of diesel and growth of the consortium among the Ug evaluated. Furthermore, the reduction of E 24 % in this Ug suggests that the consortium uses a mixed form of hydrocarbon consumption, both by direct contact and in emulsified form.

Water Gas shift reaction (WGS) kinetics are prominent in reactions involving hydrocarbons. Often the rate expressions developed for WGS have narrow application for wider experimental conditions. On the other hand, DFT based microkinetic models developed for WGS can predict the experimental trend, however, developing rate expressions for the same can be difficult owing to the validity of different approximations and assumptions. In this context, R dot approach has been used in this study to develop rate expressions for WGS over Pt, Rh. Using this approach, the rate determining steps of the mechanisms proposed, validation with experimental data and most abundant reaction intermediate (MARI) analysis was carried out. Based on the interpreted results it has been seen that the R dot approach was able to predict the experimental trend to good degree of accuracy in line with the predictions of quasi steady state (QSS) approach.

In this work, production of ethyl acetate (EtAc) using Fischer esterification between acetic acid (AcOH) and ethyl alcohol (EtOH) is presented. Batch kinetics was developed with EtOH as the limiting reactant to avoid the problems associated with unreacted ethanol in the final product. Regression was performed to estimate the parameters of the Langmuir Hinshelwood type kinetic equation. Reaction mass obtained during kinetics was subjected to separation and purification. Molecular sieves (MS) were used to remove water. Distillation (simple and extractive distillation – with entrainer, dimethyl sulfoxide, DMSO) was used to obtain almost pure AcOH, EtOH, EtAc and DMSO. Future work in reactive separation environment is indicated. Use of EtOH as the limiting reactant, use of MS for water removal and complete separation sequence are important features of this work.

The challenges posed by volatile organic compound (VOC) emissions in iron ore sintering flue gas are significant. La-based perovskite catalysts offer a promising solution for efficiently degrading VOCs. In this study, a series of LaBO 3 (B = Cu, Fe, Cr, Mn, Co) perovskite catalysts were synthesized using the sol-gel method. The influence of various B-site elements on the catalyst’s structure and surface chemical properties was thoroughly examined. Simulations were conducted to assess the VOC reduction capabilities of these catalysts under conditions mimicking sintering flue gas composition. It was found that the crystallite size of the perovskite catalyst decreases as the ionic radius of the B-site elements increases, while the specific surface area, total pore volume, and average pore size increase correspondingly. Notably, LaCoO 3 and LaMnO 3 demonstrated exceptional activity, attributed primarily to their elevated surface oxygen concentration and oxygen migration capability, positioning them as highly promising materials for further development. Furthermore, a proposed mechanism elucidates the La-based perovskite catalytic reduction of toluene, wherein lattice oxygen and adsorbed oxygen undergo mutual conversion during the oxidation process. This mechanism aligns with the L-H and M-v-K models, providing a comprehensive understanding of the catalytic process.

This study examined the effect of the Sr concentration in SrK/CaO catalysts based on oyster shells for the transesterification of canola oil. The CaO support was obtained by mixing 800 °C calcined oyster shell and limestone. Then, K and Sr were impregnated simultaneously at three different Sr/(Sr + K) molar ratios, 0.2, 0.3, and 0.4, and calcined at 800 °C. XRD, SEM, and Hammett indicators were used to characterize the catalysts. The reaction conditions were 60 °C, 1 h, met/oil = 12.5, and a catalyst loading of 7 wt%. The results showed that a Sr/(Sr + K) = 0.3 produces larger K 2 Sr(CO 3 ) 2 crystals that contribute synergistically to the catalytic activity. At Sr/(Sr + K) > 0.3, the K and Sr are segregated, decreasing the alkaline character and activity. Also, the optimization of WCO transesterification conditions was carried out by Box–Behnken response surface design with SrK/CaO-0.3 catalyst. The theoretical optimal conditions were 70 °C, 1.5 h, and a met/oil = 10, which achieved 79 % of biodiesel yield. Nonetheless, the produced WCO biodiesel did not present acceptable quality, and this reactive system increased the lixiviation of the active phases.

A computational fluid dynamics coupled population balance model (CFD-PBM) was used to numerically simulate the fluid dynamics of bubble swarms in a bubble column containing non-Newtonian fluids. The effects of superficial gas velocity ( U g ), the consistency index ( K ), and the flow index ( n ) on bubble size distribution (BSD), gas holdup, and fluid dynamic viscosity in a bubble column were analyzed at both local and overall scales. As U g increases, the bubble breakup occurs excessively, the gas holdup increases, and the dynamic viscosity decreases. K and n were used to characterize the rheological properties of power law fluid. As K increases, fluid viscosity increases, bubble breakup rate decreases, gas holdup in the top zone is slightly lower than in the middle zone, and dynamic viscosity increases. Within the range of n from 0.45 to 1.07, when n is smallest, the relative frequency of bubbles smaller than the initial size is relatively large, and the overall and local gas holdup are the highest. When n  = 1.07, the fluid exhibits shear-thickening properties, and the dynamic viscosity variations are significant.