Modeling of Mass Transfer and Reactions with the Moment Method

In chemical engineering field, mass transfer and reaction process models are needed in many stages of process research and design. These models usually consist of systems of partial differential equations. The focus of this work is to study the moment method as a numerical tool to solve different mass transfer and reaction models, which can be utilized to simulate a number of chemical engineering processes e.g. chromatography, adsorption, extraction etc. The implementation procedures, the features of the moment method are introduced with different application cases in this work. The moment transformation procedure, as the key step of the moment method is discussed in great detail when the moment method is applied to solve the chromatographic model. The important features of the moment method revealed in this work include: 1) Similar with other higher order methods, the moment method reaches desired accuracy with decreased number of variables and reduced computational load; 2) The moment method predicts the chromatographic effluent curve moments with good accuracy, because the moment method is to minimize the errors in the column profile moments; 3) Based on the moment method, the spatial PDE solution inherently conserves mass if 0th order moment is included into the set of equations. Different mass transfer and reaction processes are modeled in this work. From modeling point of view, these models are highly similar to each other except some minor details e.g. boundary conditions. This characteristic naturally is beneficial for the implementation of modeling tasks

Process equipment modeling using the moment method

Process equipment models are needed in all stages of chemical process research and design. Typically, process equipment models consist of systems of partial differential equations for mass and energy balances and complicated closure models for mass transfer, chemical kinetics, and physical properties. The scope of this work is further development of the moment method for modeling applications that are based on the one-dimensional axial dispersion model. This versatile model can be used for most process equipment, such as chemical reactors, adsorbers and chromatographic columns, and distillation and absorption columns. The moment method is a numerical technique for partial differential equations from the class of weighted residual methods (WRM). In this work it is shown with examples how the moment method can be applied to process equipment modeling. The examples are: catalyst activity profiles in fixed-bed reactors, dynamic modeling of chemical reactors and fixed-bed adsorbers with axial dispersion, and steady-state and dynamic modeling and simulation of continuous contact separation processes with or without axial dispersion. An innovative field of application of the moment method is continuous-contact separation processes. The advantage of the moment method, compared to the state-of-the-art nonequilibrium stage model, is that the same level of numerical accuracy can be achieved with fewer variables. In addition, the degree of axial dispersion can be controlled precisely since only physical axial dispersion is introduced via the axial dispersion coefficient. When using axial dispersion models, special attention has to be paid to the boundary conditions. Using the moment transformation it is shown that the Danckwerts boundary conditions are appropriate for time-dependent models in closed-closed geometries. An advantage of the moment method, compared to other weighted residual methods such as orthogonal collocation on finite elements, is the ease with which boundary conditions are specified. The boundary conditions do not arise as additional algebraic equations. Instead, they simply appear as additive source terms in the moment transformed model equations. The second part of this thesis deals with the detailed closure models that are needed for process modeling. Relevance of some of the closure models is scrutinized in particular with two test cases. The first test case is gas-liquid mass transfer coefficients in trickle-bed reactors. It is shown that the correlation of Goto and Smith is appropriate for gas-liquid mass transfer coefficients in industrial trickle-bed reactors. The second test case is vapor-liquid equilibrium model parameters for binary systems of trans-2-butene and cis-2-butene and five alcohols. The Wilson model parameters for all binary systems are fitted against measurements with a total pressure apparatus. The measured pressure-composition profiles are compared against predictions by the UNIFAC and UNIFAC-Dortmund methods

Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration

Problems related to the design and control of a mobile planetary vehicle to implement a systematic plan for the exploration of Mars are reported. Problem areas include: vehicle configuration, control, dynamics, systems and propulsion; systems analysis, terrain modeling and path selection; and chemical analysis of specimens. These tasks are summarized: vehicle model design, mathematical model of vehicle dynamics, experimental vehicle dynamics, obstacle negotiation, electrochemical controls, remote control, collapsibility and deployment, construction of a wheel tester, wheel analysis, payload design, system design optimization, effect of design assumptions, accessory optimal design, on-board computer subsystem, laser range measurement, discrete obstacle detection, obstacle detection systems, terrain modeling, path selection system simulation and evaluation, gas chromatograph/mass spectrometer system concepts, and chromatograph model evaluation and improvement

Analysis of chromatograph systems using orthogonal collocation

Research is generating fundamental engineering design techniques and concepts for the chromatographic separator of a chemical analysis system for an unmanned, Martian roving vehicle. A chromatograph model is developed which incorporates previously neglected transport mechanisms. The numerical technique of orthogonal collocation is studied. To establish the utility of the method, three models of increasing complexity are considered, the latter two being limiting cases of the derived model: (1) a simple, diffusion-convection model; (2) a rate of adsorption limited, inter-intraparticle model; and (3) an inter-intraparticle model with negligible mass transfer resistance

Minor Whey Protein Purification Using Ion-Exchange Column Chromatography

This thesis is concerned with application of mechanistic models for recovery and purification of two minor milk proteins to develop an efficient and robust process. A fundamental and quantitative understanding of the underlying mechanisms assists to evaluate chances and challenges in non-linear chromatography. The first chapter considers adsorption isotherm data of two minor whey proteins on cation exchanger under various conditions and used as the basis to develop a predictive approach for correlating adsorption behavior using a mechanistic isotherm model. The SMA isotherm model explicitly considers the contributions of protein-adsorbent and protein-protein interactions in the simulation of salt gradients in ion exchange chromatography.Sensitivity and robustness analysis by factorial design of experiments within this framework showed to be highly consistent and even allowed for upscale predictions with an excellent quality. In the next part of the thesis, the nonlinear gradient elution was to be optimized by three process factors the length of gradient, final salt concentration at the end of gradient and flow velocity. Predictions based on response surface modeling (RSM) approach were applied to reveal significant process factors. The optimal operating point was then determined by calibrated mechanistic model within and outside the design space. The operating conditions containing optimal information were experimentally verified which confirmed simulations accuracy. The third chapter considers the effects of scale-up and operating conditions on dynamic adsorption of proteins. For two columns having similar bed height, flow distribution properties was observed under non-binding conditions. Elution profiles were employed to determine dominant mass transport mechanisms. Breakthrough profiles were compared at different flow rates and protein loading concentrations.The efficiency of the columns in terms of HETP and dynamic binding capacity were calculated and compared for two columns. The outcomes resulting from the application of mechanistic models to the purification of lactoperoxidase and lactoferrin in this thesis exploit the platform for the next step towards the recovery of high-value proteins at industrial scales

Modelling and control of crystal purity, size and shape distributions in crystallization processes

Crystallization is a key unit operation used for obtaining purified products by many process industries. The key properties of the crystalline products, such as size and shape distribution, purity and polymorphic form are controlled by the crystallization process. All these properties impact significantly the downstream operations such as drying or filtration. Therefore, monitoring and controlling this process is fundamental to ensure the quality of the final product. Process analytical technology (PAT) brings numerous new methods and opportunities in the process analytics and real time process monitoring systems, which can be integrated into the control algorithm and provide high level optimal control strategies as well as deeper understanding of the process. Process monitoring helps develop mathematical models which can, in one hand, help in better understanding the processes and consecvently the development and application of advanced control methods in order to achieve better product quality. In this work, image processing and image analysis based direct nucleation control (IA-DNC) is developed in order to investigate the evolution of the crystal properties, such as crystal size, and crystal shape distribution. The IA-DNC approach is also compared to alternative DNC techniques, in which particle number were measured by Focused Beam Reflectance Measurement (FBRM) in order to control crystal size. A control approach is introduced that control the nucleation and disappearance of crystals during cooling and heating segments related to the changes of the number of counts (measured by Particle Vision Measurment, so called PVM or combination of FBRM and PVM). The approach was applied to investigate crystallization of compounds with different behavior: potassium dihydrogen phosphate (KDP) water, contaminated KDP -water and Ascorbic acid water systems. The results demonstrate the application of imaging technique for model-free feedback control for tailoring crystal product properties. The second main aim of the thesis is to investigate and control crystallization processes in impure media in the presence of multiple impurities, with an impact on the crystal shape via growth kinetics. The broad impact of the crystal growth modifiers (impurities) on the growth kinetics is observed in real time by using in situ video imaging probe and real-time image analysis. A morphological population balance model is developed, which incorporates a multi-site, competitive adsorption mechanism of the impurities on the crystal faces. The kinetic parameters of primary nucleation, growth and impurity adsorption for a model system of potassium dihydrogen phosphate crystallization in water in the presence of two impurities, were estimated and validated with experimental results. It was demonstrated that the model can be used to describe the dynamic evolution of crystal properties, such as size and aspect ratio during crystallization for different impurity profiles in the system. Manual, feedback and hybrid feedback-feedforward control techniques are developed and investigated numerically for continuous processes, while model-based and model-free control approach for crystal shape are developed for batch processes. The developed morphological population balance model is implemented and applied in the model-based control approaches, which are suitable to describe multicomponent adsorption processes and their influence on the crystal shape. Case studies show the effectiveness of crystal growth modifiers based shape control techniques. Comparison of different control approaches shows the effectiveness of the techniques. The third part of the thesis deals with purification of crystals when adsorption of impurities on crystal surfaces and its incorporation into crystals are considered. A purification method, called competitive purity control (CPC) is proposed and investigated. A morphological population balance model, including nucleation, growth and competitive impurity adsorption kinetics is developed to describe the case when multiple impurities can adsorb competitively on the crystal surface. The model is also combined with liquid phase chemical reaction model, in order to investigate the purity control case when an additive is introduced in the system that reacts with the impurity forming a non-adsorbing reaction product. Both competitive purity control approaches proposed: the adsorption based competitive purity control (A-CPC) and the reaction based competitive purity control (R-CPC); are investigated using detailed numerical simulations then compared with the alternative widely used purification method, called recrystallization. In the last contribution chapter, an integrated process optimization of a continuous chemical reactor and crystallizer is performed and studied numerically. The purpose of this study is to show the way in which the byproduct produced in the chemical reactor may affect the crystallization process and how its negative effect can be reduced by applying integrated process optimization. Sensitivity analysis of the system was performed by considering the flow rate and the concentration of substances in the input stream of the chemical reactor as manipulated process variables. Model based integrated process optimization and the sensitivity analysis in order to obtain improved quality product in terms of crystal size, shape and purity

Modélisation numérique d’écoulement diphasique compressible et transport réactif en milieux poreux - Applications à l'étude de stockage de CO2 et de réservoir de gaz naturel.

Human activity in the subsurface has rapidly been expanding and diversifying (waste disposal, new mining technologies, high-frequency storage of energy), while the public and regulatory expectations keep growing. The assessment of each step of underground operations requires careful safety and environmental impact evaluations. They rely on elaborate simulators and multiphysics modeling. With its process-based approach, reactive transport simulation provides an effective way to understand and predict the behavior of such complex systems at different time and spatial scale.This work aims at incorporating a compressible multiphase flow into conventional reactive transport framework by an operator splitting approach. A multiphase flow module is developed in the HYTEC reactive transport software. A new approach is then developed to fully couple multiphase multicomponent compressible flow, the complex thermodynamic description of the fluid properties, with existing reactive transport codes. The method is implemented in HYTEC. Some validation is provided, before application to the simulation of underground storage of CO2 and associated impurities.Les activités humaines dans la subsurface se développent rapidement (stockage de déchets,nouvelles techniques minières, stockage à haute fréquence de l’énergie), alors que dans le même temps les attentes du public et des autorités s’intensifient. L’évaluation de chaque étape de ces opérations souterraines repose sur des études détaillées de la sûreté et des impacts environnementaux.Elles reposent sur des simulateurs élaborés et sur de la modélisation multiphysique. Avec leur approche orientée processus, les simulations en transport réactifs proposent une méthode efficace pour comprendre et prévoir le comportement de ces systèmes complexes, à différentes échelles de temps et d’espace.Le but de ce travail est d’intégrer la résolution de l’écoulement diphasique compressible dans le cadre de codes de transport réactifs à l’aide d’une méthode de séparation d’opérateurs. Un module multiphasique a été créé dans le code de transport réactif HYTEC. Une nouvelle approche a ensuite été développée pour coupler écoulement multicomposant multiphasique compressible, description de propriétés thermo-dynamiques complexes pour les fluides, avec des codes de transport réactif. La méthode a été intégrée dans HYTEC. Des cas de validation sont proposés, puis des exemples d’application pour la simulation du stockage souterrain de CO2 et des impuretés associées

Development of an efficient method for simulating fixed-bed adsorption dynamics using Ideal Adsorbed Solution Theory

Otto-von-Guericke-Universität Magdeburg, Fakultät für Verfahrens- und Systemtechnik, Dissertation, 2016von M. Sc. Héctor Octavio Rubiera LandaLiteraturverzeichnis: Seite 195-22

Development of 2D- and 3D-BTEM for pattern recognition in higher-order spectroscopic and other data arrays

Ph.DDOCTOR OF PHILOSOPH