Impact of Fluid Flow on Free Radical Polymerization in a Batch Reactor

In this work, the mixing process on a batch reactor is analyzed for the thermal synthesis of poly(acrylamide-co-sodium 2-acrylamide-2-methylpropane sulfonate) initiated by ammonium persulfate. The analysis is achieved by using tracer technology and computational fluid dynamics (CFD). ANSYS Fluent® software is used for numerical simulations. By studying the mixing time in the reactor, the injection point and the stirring speed are determined so that the kinetics of copolymerization is improved

Study of a torus bioreactor for the enzymatic elimination of phenol

Phenols are priority pollutants that are commonly found in a large number of industrial wastewaters. Different processes are currently available for the elimination of phenol from wastewater but present some disadvantages like low efficiency, high energy-consumption, the necessity of acclimatisation of the sludges or the limitation of the treatment capacity. The need to find alternatives has made the enzymatic processes a good option. In the last two decades, several processes were implemented with different enzymes from plants and microorganisms, including peroxidases from several sources, as the horseradish peroxidase.Also, different enzyme configurations, free or immobilised enzyme and different supports for immobilisation have been studied. Substantial attention has been devoted to the covalent immobilisation of enzymes on porous insoluble supports such as glass, alumina, silica, and chitosan.The main novelty of this work is the utilisation of a torus reactor for the removal of organic contaminants from wastewaters. This reactor, which can be considered as a loop reactor, presents some advantages over other stirred tank reactors.The goal of this work is the study of the hydrodynamics of a torus reactor for its further application in the enzymatic elimination of phenol and the coupling of the kinetics and the modelisation.In a first step, the enzymatic elimination of phenol was experimentally studied in the torus reactor. In order to compare the performances, several assays were also carried out with a stirred reactor. A high degree of conversion was obtained for the enzymatic elimination of phenol in both reactors with the tested quantities of phenol. It was concluded that, keeping a ratio of 1:1 between the phenol and the H2O2 initial molar quantities, the highest final reaction conversion was obtained. Using the torus reactor was obtained 97% of phenol conversion when the optimal concentrations of substrates were usedIn order to improve economically the process, the enzyme should be used in a continuous regime over a long time period to exploit it completely. For this reason it was necessary to immobilise the enzyme. This work presents a new configuration that has never been tested: the horseradish peroxidase supported on Eupergit.In a second step, the characterisation using the CFD of the flow-field in a torus reactor of 100 ml, similar to the experimental reactor, was carried out for two different configurations, batch and continuous operating modes. Moreover, the scale-up of the volume of the torus reactor was carried out using CFD for a 300 ml reactor.Finally, the enzymatic reaction of phenol with the HRP was modelled using the CFD coupled to the kinetic model of the enzymatic reaction to the flow simulation. These results allowed the possibility of optimising and scaling-up the process using the CFD modelisation.Los compuestos fenólicos son contaminantes prioritarios que se encuentran comúnmente en una gran cantidad de efluentes industriales. Diferentes procesos están disponibles actualmente para la eliminación de fenol desde dicho efluentes pero los mismos presentan algunas desventajas como pueden ser una baja eficiencia, un mayor consumo de energía, la producción de lodos conteniendo hierro o limitaciones en la capacidad de tratamiento. La necesidad de encontrar alternativas a estos problemas ha hecho del proceso enzimático una buena opción. En las últimas dos décadas, varios procesos han sido implementados utilizando diferentes enzimas extraídas de plantas y microorganismos como pueden ser las peroxidasas de diversas fuentes, incluyendo la horseradish peroxidasa.Diferentes configuraciones de enzimas, libre e inmovilizada y diferentes soportes para la inmovilización han sido también estudiados. Sustancial atención ha sido dedicada a la inmovilización de enzimas por enlace covalente sobre soportes porosos insolubles tales como vidrio, aluminio, sílice y chitosan. El objetivo de este trabajo es el estudio de la hidrodinámica dentro de un reactor tórico para su posterior aplicación en la eliminación enzimática de fenol y el acople entre las cinéticas y la modelización.En una primera etapa, la eliminación enzimática de fenol es estudiada experimentalmente en el reactor tórico. Con el objetivo de comparar el rendimiento de dicho reactor, varios ensayos se realizaron en un reactor agitado tradicional. Un alto grado de conversión de fenol ha sido obtenido para la eliminación enzimática de fenol en ambos reactores para las cantidades estudiadas de fenol. Ha sido observado que es necesario mantener una relación de 1:1 entre la concentración inicial de fenol y la de peróxido de hidrógeno para lograr la mayor conversión de fenol. Usando el reactor tórico ha sido obtenido un 97% de conversión de fenol cuando las concentraciones óptimas de substratos y enzimas fueron utilizados. Con el objetivo de mejorar económicamente el proceso y hacerlo factible para su uso a escala industrial, la enzima debería ser utilizada en un proceso en continuo sobre un largo período de tiempo para explotarla completamente. Por esta razón, ha sido necesario inmovilizar la enzima. Este trabajo muestra una nueva configuración que no ha sido aún probada: la horseradish peroxidase soportada en Eupergit. Asimismo, la caracterización usando CFD del campo de flujo de un reactor tórico similar al experimental de 100 ml ha sido realizada para un reactor trabajando de forma batch y continua. Un escalado en el volumen del reactor tórico ha sido realizado utilizando CFD para un reactor de 300 ml. Finalmente, la reacción enzimática de fenol con HRP has sido modelada acoplando el modelo cinético obtenido experimentalmente con las simulaciones del campo de flujo dentro del reactor. Estos resultados permitirán la optimización y el escalado del proceso usando CFD

Supercritical Water Gasification: Practical Design Strategies and Operational Challenges for Lab-Scale, Continuous Flow Reactors

Optimizing an industrial-scale supercritical water gasification process requires detailed knowledge of chemical reaction pathways, rates, and product yields. Laboratory-scale reactors are employed to develop this knowledge base. The rationale behind designs and component selection of continuous flow, laboratory-scale supercritical water gasification reactors is analyzed. Some design challenges have standard solutions, such as pressurization and preheating, but issues with solid precipitation and feedstock pretreatment still present open questions. Strategies for reactant mixing must be evaluated on a system-by-system basis, depending on feedstock and experimental goals, as mixing can affect product yields, char formation, and reaction pathways. In-situ Raman spectroscopic monitoring of reaction chemistry promises to further fundamental knowledge of gasification and decrease experimentation time. High-temperature, high-pressure spectroscopy in supercritical water conditions is performed, however, long-term operation flow cell operation is challenging. Comparison of Raman spectra for decomposition of formic acid in the supercritical region and cold section of the reactor demonstrates the difficulty in performing quantitative spectroscopy in the hot zone. Future designs and optimization of SCWG reactors should consider well-established solutions for pressurization, heating, and process monitoring, and effective strategies for mixing and solids handling for long-term reactor operation and data collection

Optimization and design of reactive crystallization process

Crystallization is an important process used in a wide range of industries, which has made it the main process in the primary manufacturing stage, and thereby the quality of crystals produced has a major impact on downstream processes such as filtration, milling and drying, as well as transport and storage processes. Organic reactive crystallization, which is widely used in the production of active pharmaceutical ingredients (APIs), has many unique features that make it different from cooling or anti-solvent crystallization, even leading to some concepts and methods not directly applicable to this process. A survey of the literature reveals that previous research on reactive crystallization has mainly been conducted for inorganic materials which are known to be simpler than crystallization of organic materials. For example, it is known that compared with inorganic materials, organic materials tend more to aggregation and form amorphous. In addition, the published literature in this research area is often concerned with laboratory scale crystallization, rather than industrial scale processes. The focus of this research project is to carry out research on the process design, optimization, simulation and scale-up of organic reactive pharmaceutical crystallization. The objective is to research the process and crystallizer design which takes advantage of the features of the reactive crystallization process and on simulation, optimization and scale-up techniques with the aim of manufacturing high quality products measured by the products’ crystallinity, stability, purity, and processability. Process analytical technology (PAT) is used as a supporting tool to achieve the above stated objectives. An off-patent drug, sodium cefuroxime which is considered as a second generation antibiotic, is used as the case study drug. Firstly, on-line Attenuated Total Reflection-Fourier Transform InfraRed spectroscopy (ATR-FTIR) was used to monitor the change in the supersaturation in order to optimize the flow rate of the anti-solvent during the anti-solvent re-crystallization process of sodium cefuroxime. The solubility of sodium cefuroxime under various temperatures T, pH values and solvents was measured and correlated in models. The effect of the anti-solvent (95% ethanol) flow rate on crystallinity was examined and the results showed that appropriate anti-solvent flow rate could improve the stability of sodium cefuroxime. The optimized anti-solvent re-crystallization process provided a new method to obtain high-quality seeds of sodium cefuroxime. Secondly, Process Analytical Technology (PAT) based on Focused Beam Reflectance Measurement (FBRM) was used to optimize the parameters of the reactive synthesis process of sodium cefuroxime, such as the feed order, the reaction temperature, the stirring speed, the feed rate/speed and the amount of seeds. An impinging jet mixer, which could provide rapid mixing effectiveness of reactants, was applied and optimized. After that, the optimized process was scaled-up from 1L to 10L with a volumetric scaling-up factor of 10. The product had superior crystallinity, uniform size distribution, higher stability and purity, which indicated that this optimization methodology and impinging jet mixer design could be applied in other similar reactive crystallization processes. Finally, Process Analytical Technology (PAT) including Ultraviolet–Visible Spectrometry (UV) and FBRM was used to study the reaction kinetics and the mechanism of crystal growth in the reactive synthesis process of sodium cefuroxime. A process and crystallizer was designed based on the data obtained above. This process provided two reactors in series for conducting a rapid reactive crystallization process of pharmaceutical compounds in continuous mode. It involved a tank reactor with the use of an impinging jet mixer and stirrer to create intensive mixing of the reactants before nucleation and a tubular reactor with suitable length to avoid back mixing of the products. The results showed that by using this process, the product had uniform size distribution, higher stability and superior crystallinity, in both laboratory scale and 50L scaled-up processes

Applications of CFD Simulations on Microfluidic Systems for Nanoparticle Synthesis

Microfluidics has been extensively investigated as a unique platform to synthesize nanoparticles with desired properties, e.g., size and morphology. Compared to the conventional batch reactors, wet-chemical synthesis using continuous flow microfluidics provides better control over addition of reagents, heat and mass transfer, and reproducibility. Recently, millifluidics has emerged as an alternative since it offers similar control as microfluidics. With its dimensions scaled up to millimeter size, millifluidics saves fabrication efforts and potentially paves the way for industrial applications. Good designs and manipulations of microfluidic and millifluidic devices rely on solid understanding of fluid dynamics. Fluid flow plays an important role in heat and mass transfer; thereby, it determines the quality of the synthesized nanoparticles. Computational fluid dynamics (CFD) simulations provide an effective approach to understand various effects on fluid flows without carrying out complicated experiments. The goal of this project is to utilize CFD simulations to study flow behaviors inside microfluidic and millifluidic. Residence time distribution (RTD) analysis coupled with TEM characterization was applied to investigate the effect of reagent flow rates on particle sizes distribution. Droplet-based microfluidics, as a solution to intrinsic drawbacks associated with single-phase microfluidics, depends on proper manipulation of the flow to generate steady droplet flow. The droplet / slug formation process inside a millifluidic reactor was investigated by both experiments and numerical simulations to understand the hydrodynamics of slug breaking. Geometric optimization was carried out to analyze the dependency of slug sizes on geometric dimensions. Numerical simulations were also performed to quantify the mixing efficiency inside slugs. This work provides insight to understand fluid flow inside microfluidic and millifluidic systems. It may benefit the design and operations of novel microfluidic and millifluidic systems

Numerical Study of Mixing of Different Newtonian and Non-Newtonian Fluids in Stirred Tank

Mixing has the most common occurrence in process industries like chemical, food and polymer and plays a significant part in overall success of the processes. Stirred tanks are commonly used for mixing various types of Newtonian and non-Newtonian liquids. Impeller is the movable part and is used as the rotating device in stirred tank systems for achieving mixing. An impeller while it rotates imparts shear force in the vicinity along the peripheral zone. Literature is rich with information on various experimental and theoretical findings on the hydrodynamics and mixing behaviour of Newtonian fluids in stirred tank systems. However, with non-Newtonian fluids, limited published literature is available on the hydrodynamic behaviour of the mixing process in stirred vessels. A few available experimental works in literatures successfully explained the mixing process in a non-Newtonian system using Rushton turbine (impeller commonly used in industry). But unavailability of the theoretical prediction of the same is basically explains the motivation behind the study on the mixing of non-Newtonian fluids in stirred tank with Rushton turbine. For mixing highly viscous liquids, helical ribbon impellers are most suited. In this thesis work, it was aimed to study the computational aspects of the hydrodynamic performance of helical ribbon impeller in a highly viscous non-Newtonian system and comparing the results with helical screw ribbon impeller through computational fluid dynamics (CFD) simulation. Entropy generation minimization study is an integral part of this thesis work. Mostly, the earlier works involve use of analytical expressions from basics of mass, energy and entropy balance which has got certain limitations because of many assumptions. Here, we aimed for a detailed numerical study on the same. Also, the understanding of residence time distribution (RTD) study in a stirred tank system gives an idea on the distribution of flow structure. Although, this particular aspect has been studied by various research groups, however, some of the experimental data are not compared with numerical findings for validation. In this work it was aimed to predict RTD numerically especially by using swept volume of the impeller into consideration. A computational fluid dynamics study using Ansys Fluent was carried out to determine the mixing performance of a tank stirred with Rushton turbine. The predicted profiles of the velocity components were validated with literature data. The non-parametric Spearman’s rank order test was used to find the interaction of velocity profiles with the impeller Reynolds number and flow behavior index. The characteristic performance parameters such as power number and flow number of the impeller were predicted. The variations of entropy generation due to only viscous dissipation with Reynolds number, tank geometry, etc. were calculated for the isothermal tank. The entropy generation minimization (EGM) approach was used to optimize the performance of the non-isothermal continuous stirred tank with respect to the system parameters like inlet Reynolds number, impeller speed, and impeller clearance and impeller blade width. The numerical study of the stirred tank with helical ribbon (HR) and helical ribbon with screw (HRS) impellers was carried out successfully. The CFD models were successfully validated with the experimental power number given in literature. The power constant for Newtonian fluid (Kp) and non-Newtonian fluid (Kp(n)) were calculated and compared successfully with the literature data. The Metzner Otto or geometry constant, Ks were computed following four different methods and the best one was identified by predicting successfully the generalized power curve. The flow numbers of HRS impeller were predicted for wide range of impeller Reynolds number. The non-dimensional mixing times were varied in scattered way with impeller Reynolds number, and the dispersive flow away from the impeller shaft was observed. The entropy generations were increased with the impeller Reynolds number, and an empirical model of entropy generation with impeller Reynolds number was developed. The non-isothermal stirred tank with HR and HRS impellers were optimized employing the entropy generation minimization technique. The hydrodynamic and the residence time distribution (RTD) behavior of the viscous Newtonian fluid was studied using a tracer age distribution function, I(θ). The experimental tracer age distribution functions were predicted by CFD tools using tracer injection and swept volume methods. The predicted results were found in good agreement with the literature data. The mixing behaviour was changed from dispersion to ideal mixing state with increasing the tank Reynolds number and impeller rotations. The mixing performance parameters like holdback, segregation, number of ideal continuous stirred tank in series equivalent to single actual continuous stirred tank were also calculated to identify the necessary flow parameters and their magnitude to obtain the ideal flow distribution in the tank

Micromixing in chemical reactors : test reactions

Tese de doutoramento. Engenharia Química. Faculdade de Engenharia. Universidade do Porto. 200

Kinetic Intersections as a Source of Information on Rate Coefficients

C

Process development using oscillatory baffled mesoreactors

PhD ThesisThe mesoscale oscillatory baffled reactor (meso-OBR) is a flow chemistry platform whose niche is the ability to convert long residence time batch processes to continuous processes. This reactor can rapidly screen reaction kinetics or optimise a reaction in flow with minimal waste. In this work, several areas were identified that could be addressed to broaden the applicability of this platform. Four main research themes were subsequently formulated and explored: (I) development of deeper understanding of the fluid mechanics in meso-OBRs, (II) development of a new hybrid heat pipe meso-OBR for improved thermal management, (III) further improvement of continuous screening using meso-OBRs by removing the solvent and employing better experiment design methodologies, and (IV) exploration of 3D printing for rapid reactor development. I. The flow structures in a meso-OBR containing different helical baffle geometries were studied using computational fluid dynamics simulations, validated by particle image velocimetry (PIV) experiments for the first time. It was demonstrated, using new quantification methods for the meso-OBR, that when using helical baffles swirling is responsible for providing a wider operating window for plug flow than other baffle designs. Further, a new flow regime resembling a Taylor-Couette flow was discovered that further improved the plug flow response. This new double vortex regime could conceivably improve multiphase mixing and enable flow measurements (e.g. using thermocouples inside the reactor) to be conducted without degrading the mixing condition. This work also provides a new framework for validating simulated OBR flows using PIV, by quantitatively comparing turbulent flow features instead of qualitatively comparing average velocity fields. II. A new hybrid heat pipe meso-OBR (HPOBR) was prototyped to provide better thermal control of the meso-OBR by exploiting the rapid and isothermal properties of the heat pipe. This new HPOBR was compared with a jacketed meso-OBR (JOBR) for the thermal control of an exothermic imination reaction conducted without a solvent. Without a solvent or thermal control scheme, this reaction exceeded the boiling point of one of the reactants. A central composite experiment design explored the effects of reactant net flow rate, oscillation intensity and cooling capacity on the thermal and chemical response of the reaction. The HPOBR was able to passively control the temperature below the boiling point of the reactant at all conditions through heat spreading. Overall, a combined 260-fold improvement in throughput was demonstrated compared to a reactor requiring the use of a solvent. Thus, this ii wholly new reactor design provides a new approach to achieving green chemistry that could be theoretically easily adapted to other reactions. III. Analysis of in situ Fourier transform infrared (FTIR) spectroscopic data also suggested that the reaction kinetics of this solventless imination case study could be screened for the first time using the HPOBR and JOBR. This was tested by applying flow-screening protocols that adjusted the reactant molar ratio, residence time, and temperature in a single flow experiment. Both reactor configurations were able to screen the Arrhenius kinetics parameters (pre-exponential factors, activation energies, and equilibrium constants) of both steps of the imination reaction. By defining experiment conditions using design of experiments (DoE) methodologies, a theoretical 70+% reduction in material usage/time requirement for screening was achieved compared to the previous state-of-the-art screening using meso-OBRs in the literature. Additionally, it was discovered that thermal effects on the reaction could be inferred by changing other operating conditions such as molar ratio and residence time. This further simplifies the screening protocols by eliminating the need for active temperature control strategies (such as a jacket). IV. Finally, potential application areas for further development of the meso-OBR platform using 3D printing were devised. These areas conformed to different “hierarchies” of complexity, from new baffle structures (simplest) to entirely new methods for achieving mixing (most complex). This latter option was adopted as a case study, where the passively generated pulsatile flows of fluidic oscillators were tested for the first time as a means for improving plug flow. Improved plug flow behaviour was indeed demonstrated in three different standard reactor geometries (plain, baffled and coiled tubes), where it could be inferred that axial dispersion was decoupled from the secondary flows in an analogous manner to the OBR. The results indicate that these devices could be the basis for a new flow chemistry platform that requires no moving parts, which would be appealing for various industrial applications. It is concluded that, for the meso-OBR platform to remain relevant in the next era of tailor-made reactors (with rapid uptake of 3D printing), the identified areas where 3D printing could benefit the meso-OBR should be further explored