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There is increasing interest in developing new fluidic devices with and without moving parts for crystallization. The goal is to gain better control of particle size distribution of produced crystals. Recently, the feasibility of using a planar fluidic oscillator for crystallization was demonstrated by Pandit and Ranade (Pandit, A. V.; Ranade, V. V. Fluidic Oscillator as a Continuous Crystallizer: Feasibility Evaluation. Ind. Eng. Chem. Res.2020, 59(9), 3996–4006). A novel “loop setup” using a fluidic oscillator was used for carrying out seeded antisolvent crystallization of paracetamol in a methanol–water system. Because of the novel mode of operation, the conventional models are not directly applicable for interpreting the reported data on the influence of key operating parameters such as residence time, supersaturation ratio, and seed particle size distribution (PSD). In this study, a rigorous mathematical model was developed to simulate the antisolvent crystallization experiments of Pandit and Ranade. A generalized multistage model comprising mass balances, population balances, and crystallization kinetics was developed. A population balance model (PBM) was formulated in terms of the standard method of moments (MOM). A predefined log-normal distribution function with moment-based parameters (mean, μ, and variance, σ2) was used to predict PSD. The model was used to fit relevant kinetic parameters using the experimental data reported by Pandit and Ranade. A new parameter characterizing the effectiveness of mixing in the fluidic oscillator is defined. An empirical relation between this mixing parameter and other parameters is proposed. The developed model and results will be useful for extending applications of the fluidic oscillator and other fluidic devices for antisolvent crystallization.

Crystallization is an important separation unit operation accounting for nearly 90% of organic molecules in the pharmaceutical and fine chemical industries. Recently, continuous crystallization was demonstrated to have several advantages over the conventional batch crystallization in terms of improved product consistency, reduced labor costs/economic footprint, and better process control. Continuous stirred tank crystallizers, however, are limited in mixing/heat transfer capabilities and have issues like cyclical oscillations in product quality. Tubular crystallizers can mitigate these issues and, however, suffer from issues related to particle settling and blockages. Fluidic oscillators with one or more feedback channels are gaining popularity in recent years due to the advent of microfluidics. Jet oscillations in fluidic oscillators were shown to consistently provide vigorous mixing and heat transfer above a critical Reynold’s number. In the present study, the feasibility of the fluidic oscillator as a continuous crystallizer was evaluated to mitigate challenges faced by previous continuous crystallization technologies. A novel “loop setup” was proposed for continuous crystallization and was investigated using the seeded antisolvent crystallization of paracetamol in a methanol–water system. The effects of key operating conditions of residence time, supersaturation ratio, operational mode, fluidic device, device orientation, and seed size were investigated. Throughout the study, it was observed that the loop setup gave product particle size distributions consistent with enhanced mixing behavior. Further, it was demonstrated that the proposed continuous crystallizer was better in terms of scale up in comparison with batch crystallizers. The presented results and approach will be useful to develop fluidic oscillators as a useful platform for continuous crystallization.

In this work, a computational fluid dynamics (CFD)-assisted optimization study has been carried out, implementing geometric design modifications in a biomass cook stove (BCS) to achieve uniform air–fuel distribution. The work has been divided into two parts. The first part deals with the numerical investigations of fluid phase hydrodynamics and air–fuel homogeneous phase combustion. Simulations have been performed for a wide range of air velocities to predict the roles of primary and secondary airflow in improving the spatial airflow uniformity inside the BCS. The homogeneous combustion simulations show linear dependence of power and temperature on the air velocity and air-to-fuel ratio. The results indicate that the most optimized power output and temperature values are achieved when the grate is placed at a height of 25 mm, and the orifice plate with 15 holes of 10 mm each is located at a height of 105 mm from the bottom of the cook stove.

A porous draft tube (DT) with suitable converging and diverging angles having varying porosity is newly introduced in a spouted bed (SB) for manipulating the fluid exchange rate from the spout to the annular region and thus to enhance the fluid residence time in the annular region. A comparative study of the exchange of the spouting gas (argon) into the bed of zirconia and glass beads in a conventional, nonporous, and porous DT-fitted SB with different converging and diverging angles of 9 and 18° is reported here. Computational fluid dynamics simulation using “Fluent, v-15.0” was performed to identify hydrodynamic phenomena inside the DT as well as in the bed for converging and diverging porous DT designs. Experimental findings for the efficient combination of converging and diverging angles have been compared with the simulation results.

In this study, we have developed a novel model to include the spatial heterogeneity for the combustion of volatiles in the presence of oxygen inside a biomass cookstove (BCS). Three-dimensional computational fluid dynamic simulations of BCS were done to evaluate the dynamics of spatial heterogeneity incurred during biomass combustion. The proposed methodology prescribes the mass release rate of the fuel as a dynamic boundary condition that evolves as per the changing temperature in the void spaces of the packed bed. The temporally evolving mass release rate due to the change in temperatures of the void spaces is calculated iteratively and set as the inlet boundary condition on the particle surfaces using an empirical correlation. The validation studies showed that the time-averaged outlet temperatures predicted from the model are in good agreement with the experimentally obtained values.

This investigation is focused on designing an effective strategy for the real-time monitoring of biopharmaceutical crystallization using focused beam reflectance measurement (FBRM). Lysozyme, rHu insulin, and vitamin B12 were selected as model biopharmaceutical molecules for the study. Under selected experimental conditions, lysozyme exhibits polymorphism with tetragonal and needle-shaped crystals, rHu insulin forms rhombohedral crystals, and vitamin B12 forms polyhedral-shaped crystals. Focused beam reflectance measurements were performed to obtain the real time chord length distribution (CLD) of crystals obtained using static and dynamic conditions. Mathematical models were developed for converting CLD data obtained using FBRM measurements into the useful crystal size distribution (CSD) data for low (tetragonal, rhombohedral and polyhedral) and high aspect ratio crystals (needle). For high-aspect-ratio crystals, both width-based and length-based models were developed for capturing the CSD. The model validation was performed by comparing the model CSD with the CSD obtained using microscopic image analysis. Developed models effectively capture the CSD for variable shape crystals of lysozyme, rHu insulin, and vitamin B12. It was demonstrated that in the case of high-aspect-ratio crystals, there is an intrinsic limitation in using FBRM for length-based crystal size measurement.

Glycerol is a valuable feedstock, produced in biorefineries as a byproduct of biodiesel production. Esterification of glycerol with acetic acid yields a mixture of mono-, di-, and triacetins. The acetins are commercially important value-added products with a wide range of industrial applications as fuel additives and fine chemicals. Esterification of glycerol to acetins substantially increases the environmental sustainability and economic viability of the biorefinery concept. Among the acetins, diacetin (DA) and triacetin (TA) are considered high-energy-density fuel additives. Herein, we have studied the economic feasibility of a facility producing DA and TA by a two-stage process using 100,000 tons of glycerol per year using Aspen Plus. The capital costs were estimated by Aspen Process Economic Analyzer software. The analysis indicates that the capital costs are 71 M$, while the operating costs are 303 M$/year. The gross profit is 60.5 M$/year, while the NPV of the project is 235 M$ with a payback period of 1.7 years. Sensitivity analysis has indicated that the product price has the most impact on the NPV.

In the present paper we report a novel and green approach for the selective synthesis of sulfoxide from sulfide using ultrasound. Use of aqueous media and easily separable and recyclable reagents makes this process green. Hydrogen peroxide is used as an oxidizing agent. Ultrasound is used to enhance the rates of reaction and selectivity of the oxidation reaction toward the desired product (sulfoxide). The effect of various parameters such as the presence and absence of ultrasound, initial concentration of the reactants, reaction temperature, molar ratio of the reactant to the oxidizing agent, mode of addition of the oxidizing agent, presence and absence of -cyclodextrin, and amount of -cyclodextrin has been studied. The optimum operating conditions found for the oxidation reaction on the laboratory scale were equally effective at a scaled up version of the reaction.

In the present work, experiments have been performed for leaching (recovery) of uranium from MgF2(byproduct from the uranium ore recovery process) under various conditions of leach acid concentration with and without the presence of ultrasound, under different energy dissipation rates (different rotational speeds of conventional stirring by impeller), and on different MgF2particle size distributions. The enhancement of the leaching rate due to ultrasound is found to occur in two steps:  (1) MgF2particle fragmentation leading to high specific solid−liquid interfacial area and by increase in the surface diffusional rate of the reactive species; (2) enhancement in the convective diffusivity of the leach acid solvent through micropores of the MgF2agglomerate structure due to convective motion created by the cavitation phenomena (shock wave propagation, microjet formation) at the solid−liquid interface. Thus, the overall recovery has been increased by the application of ultrasound with several additional advantages such as low leach acid concentration and decrease in the leaching operation time. The energy dissipation rate with the use of ultrasound was very high, yet, at an equivalent energy dissipation rate in the form of conventional stirring, leaching rates or the final extent of the leaching could not be matched. This indicated that the scale (time and spatial) of energy dissipation has important effect on the overall leaching rate. Kinetics shows that the leaching operation can be explained as a classical shrinking core kinetics phenomenon with pore diffusion resistance as the rate-limiting step.

A comprehensive computational fluid dynamics CFD model was developed in the present study to gain insight into the solid suspension in a stirred slurry reactor. The preliminary simulations highlighted the need for the correct modeling of the interphase drag force. A two-dimensional model problem was then developed using CFD to understand the influence of free stream turbulence on the particle drag coefficient. The proposed correlation was then incorporated in a two-fluid model (Euler−Euler) along with the standard k−ε turbulence model with mixture properties to simulate the turbulent solid−liquid flow in a stirred reactor. A multiple reference frame approach was used to simulate the impeller rotation in a fully baffled reactor. A computational model was mapped on to a commercial CFD solver FLUENT6.2 (of Fluent Inc., USA). The model predictions were compared with the published experimental data of Yamazaki et al. [Powder Technol.1986, 48, 205] and Godfrey and Zhu [AIChE Symp. Ser.1994, 299, 181]. The predicted results show reasonably good agreement with the experimental data. The computational model and results discussed in this work would be useful for extending the applications of CFD models for simulating large stirred slurry reactors.

Ultrasound was used in the presence of hydrogen peroxide as the oxidant to synthesize benzaldehyde from benzyl alcohol. A commercially available homogeneous catalyst (heteropolyacid) and a phase-transfer catalyst (PTC) were used for the reaction. The effects of various parameters, such as solvent, amount of PTC, bulk temperature, mechanical agitation, concentration of hydrogen peroxide, amount of aqueous phase, amount of homogeneous catalyst, and benzyl alcohol concentration, on the extent of reaction have been studied. The kinetics of the reaction has also been studied. Enhancements in rates and selectivity of the benzaldehyde were observed in the presence of ultrasound as compared to their silent counterpart. The increased rates of reaction and selectivity are explained on the basis of ultrasonically generated cavitational effects. The work presented here clearly highlights the methodology to be followed for investigating the optimum extent of intensification achieved as a result of the use of ultrasound as compared to the conventional methods and should be followed by the design engineers to investigate a particular application in question.

Gas−liquid flows in a stirred vessel exhibit different flow regimes and demonstrate complex interaction of transport processes with varying spatio-temporal scales. The knowledge of key space and time scales of fluid dynamics is important for designing and enhancing the performance of gas−liquid stirred reactor. The present study uses simple, robust, and nonintrusive experimental techniques (torque and pressure sensors) to characterize the fluid dynamics in a gas−liquid stirred vessel. Time series obtained from the pressure and torque sensors were analyzed to develop criteria for flow regime identification. Further analyses of torque and pressure time series were done to extract valuable information of different time scales of fluid dynamics. The detailed analysis of torque and wall pressure fluctuations provided not only an insight into the fluid dynamics but also a possible opportunity to on-line monitoring of gas−liquid flows in stirred vessel.