Conceptual design, simulation and experimental validation of divided wall column: application for non-reactive and reactive mixture

Les colonnes à cloison et la distillation réactive présentent de nombreux avantages. Si ces deux concepts sont couplés, cela conduit à un procédé intensifié appelé : colonne à cloison réactive. Ce nouveau procédé intensifié constitue le principal objet d’étude de cette thèse. Dans une première partie, une procédure de design d’une colonne à cloison basée sur le modèle FUGK a été proposée. Dans cette procédure les aspects technologiques et hydrodynamiques sont abordés. Ces paramètres de design obtenus sont ensuite utilisés pour réaliser une simulation rigoureuse et une optimisation de cette colonne en utilisant le logiciel ProSim. Afin de tester cette procédure, des mélanges idéaux et non idéaux ont été utilisés. Il a été montré que cette procédure de design aboutit rapidement aux paramètres de pré design qui permettent d’initialiser de manière satisfaisante la simulation rigoureuse. Dans un second temps, un pilote d’une hauteur de 4m a été conçu, monté et testé au laboratoire. Des résultats expérimentaux ont été obtenus qui valident la procédure sur des mélanges non réactifs en termes de profils de composition et de température ainsi que sur les compositions et les débits de sortie du procédé. Enfin, dans une dernière partie, cette procédure a été adaptée à des mélanges réactifs en combinant les approches de R. Thery et al (2005) et celle de Triantafyllou et al (1992). Ces ultimes développements ont été testés sur la production d’acétate de méthyl par estérification du méthanol par l’acide acétique à la fois d’un de vue expérimental et théorique. ABSTRACT : Divided wall column and reactive distillation have many advantages. If a divided wall column and a reactive distillation are integrated, they leads to a higher integrated process is a reactive divided wall column. However reactive divided wall column has still a new research area. First of all, the thesis proposed a procedure for design of divided wall column, which based on the FUGK model. Both technological and hydrodynamic aspects in the divided wall column are considered in the procedure. Design parameters are then provided to the rigorous simulation and optimization in the ProSimplus software. In order to test this procedure, both ideal and non-ideal ternary mixtures are chosen to be separated in a divided wall column. The results show that the procedure can determine parameters quickly in the case studies and can give a good initialization for rigorous simulation. Secondly, a pilot plant has been design, built and operated in our laboratory (LGC, Toulouse, France, 2013). The pilot plant will provide necessary experimental evidence to validate the previous procedure. Ternary mixture and four-component mixture of alcohols have been used in our pilot plant in steady state conditions. The results show that the composition of products, composition and temperature profile along the column are in very good agreement with simulation results. Finally, a conceptual design method for reactive divided wall column is presented. The pre-design method of R. Thery et al., (2005) and a modified shortcut method for reactive divided wall column that is based on the classical shortcut adapted to a non-reactive divided wall column by C. Triantafyllou and R. Smith (1992) are applied. To verify, simulation and experiment are considered. The methodology has been illustrated for the synthesis of Methyl Acetate from Methanol and Acetic Acid

An investigation of the interactions between system characteristics and controllability for reactive distillation systems

Reactive distillation is an emerging process intensification technology, although its operation and control are complex due to the interactions between reaction and separation within the column. In this work, the impact of reaction and separation, as well as design parameters, on the controllability of reactive distillation processes is investigated, using a systematic methodology developed. Case studies of industrial interest are considered, varying in the key (reaction, separation and design) parameters, in order to investigate the relative impact of the latter on the controllability of the reactive distillation systems. It is shown that the system with slower kinetics demonstrates an increased difficulty in rejecting feed disturbances for both one point (V-only) and two-point (LV) control configurations. Even when linear model predictive control (MPC) is considered based on a state-space representation of the model, the system with slower reaction kinetics is still more difficult to control, for both set point change and load disturbance. It is also shown that revision of the optimal steady state design variables, such as the total number of stages, may be beneficial for the controllability of the process. The importance of maintaining feed ratio in stoichiometric processes is identified and discussed, as failure to do so may result in failure to maintain both product purities when two point control is considered

Feasibility of novel integrated dividing-wall batch reactive distillation processes for the synthesis of methyl decanoate

YesThe production of methyl decanoate (MeDC) through esterification of decanoic acid (DeC) with methanol by reactive distillation is operationally challenging and energy-intensive due to the complicated behaviour of the reaction system and the difficulty of retaining the reactants together in the reaction region. Methanol being the lightest component in the mixture can separate itself from the reactant DeC as the distillation proceeds which will cause a massive reduction in the conversion of DeC utilizing either a batch or continuous distillation process. Aiming to overcome this type of the potential problem, novel integrated divided-wall batch reactive distillation configuration (i-DWBD) with recycling from the distillate tank is established in this study and is examined in detail. This study has clearly demonstrated that the integrated divided-wall batch reactive distillation column (i-DWBD) is superior to the traditional conventional batch distillation (CBD) and both the divided-wall (DWBD), and split reflux divided-wall (sr-DWBD) batch reactive distillation configurations in terms of maximum achievable purity of MeDC and higher conversion of DeC into MeDC. In addition, significant batch time and energy savings are possible when the i-DWBD is operated in multi-reflux mode

Sustainable Catalytic Processes for the Synthesis and Use of Organic Carbonates

The present study is focused on the development and improvement of sustainable catalytic processes for the synthesis of organic carbonates. In particular, the condensation reaction between carbon dioxide and several alcohols and diols has been investigated using a new generation of mesoporous nanosilicas functionalized by the insertion of amino groups on the catalyst surface. This reaction were performed in a high-pressure batch vessel (autoclave). Moreover, the carbonate interchange reaction (CIR) of the simplest linear organic carbonate, dimethyl carbonate (DMC) with several alcohols has been implemented by means of a new lab-scale reactive distillation system. In this new system, the distilled mixture is continuously passed over molecular sieves able to promote a selective adsorption of methanol (co-product of the reactions) while DMC is continuously refluxed back into the reaction batch. In this way, we were able to promote an efficient shift of the reaction equilibria toward the formation of the desired products. This system allowed us to achieve up to 90% isolated yield of pyrocatechol carbonate (PCC), a new and previously scarcely investigated carbonate. The PCC has been used as a new and more efficient carbonate source for the selective synthesis of symmetric carbonates and for the synthesis of glycerol carbonate (GlyC). GlyC has been also used as glycidol intermediate, for the condensation reaction with catechol in order to obtain the efficient synthesis of 2-hydroxymethy-1,4-benzodioxane (HMB) an important intermediate for the pharma industry. Finally, some of the synthesized carbonates were tested for the gas-phase phenol alkylation showing an interesting reactivity that could be properly modulated by changing the reaction conditions and the catalyst acid-base properties

Catalysis & Kinetics of Non-Phosgene Route to Synthesis of Dimethyl Carbonate (DMC)

Converting CO2 into value-added chemicals or fuels is one of the major sustainability challenges facing human society. Catalytic manufacture of dimethyl carbonate, a green chemical, using CO2 as a starting material attracts increasing attention, because it provides an alternative environmentally friendly route. However, several fundamental issues need to be investigated to improve this technology: (a) development of heterogeneous catalyst with high activity, selectivity and stability; (b) kinetics and mechanism of transesterification required to provide a basis for catalyst improvement and design of suitable reactors. In this thesis, a study on transesterification of alkyl carbonates has been presented using two types of catalysts: Metal Oxides (e.g. CaO) and Double metal cyanides. In one part, transesterification using CaO catalyst is presented to address the significant effect of catalyst pre-treatment using reactants on catalytic activity. Upon CaO pretreatment with methanol, the transesterification activity (TOF) increased significantly. In sharp contrast, pretreatment with cyclic carbonates resulted in a prolonged induction time and rate inhibition. Additionally, various characterization (SEM, CO2-TPD, XRD, FT-IR, XANES and 13C-NMR) was done on fresh CaO and treated CaO to explore the factors affecting catalytic activity. It is detected that strong basic sites have close correlation with catalytic activity. Furthermore, the formation of Ca(OCH3)2 is a key step during the pre-treatment process. Detailed investigations on catalyst recycle, effects of substrate types and reaction parameters (reactant concentrations, temperature and catalyst loading) on conversion, selectivity and initial rates are reported. The experiments revealed that with CaO as catalyst, significant contribution of the reaction is due to homogeneous catalysis from sparingly soluble CaO under reaction conditions. Therefore, an approach to analyze simultaneous homogeneous-heterogeneous catalytic transesterification has been discussed. Based on experimental concentration-time data in batch slurry reactor, detailed kinetic modeling of transesterification of propylene carbonate to DMC in both homogeneous phase as well as heterogeneous phase is reported using both empirical power law and microkinetic (based on molecular level description of catalytic cycle) models, during which corresponding rate parameters for each model were fitted and determined. In another part of the thesis, a truly heterogeneous double metal cyanide catalyst system is reported which eliminates the problems of leaching observed in metal oxide (CaO) catalysts. It is observed that transesterification of various cyclic carbonates, such as ethylene carbonate, propylene carbonate, and 1, 2-butalene carbonate to dimethyl carbonate can occur over double metal cyanide complex with high activity, selectivity and stability. Detailed investigation of the morphology and structure of the catalysts are done through different characterization techniques (BET, SEM, TEM, XRD, XPS, TGA, FT-IR and UV-Vis). Studies on different reaction parameters (catalyst loading, initial methanol/PC molar ratio, temperature and different cyclic carbonates) and surface characterization enabled the establishment of activity-performance correlation for cyclic carbonate conversion. Further, kinetic modeling using Fe-Mn double metal cyanide complex is reported in which different kinetic models based on different reaction mechanisms are discriminated to fit with the experimental data. The kinetic studies in this work provide guidance for postulating reaction mechanisms and better insight into activation mode of reactants. In the last, a brief study of transesterification of DMC with phenol for synthesis of diphenyl carbonate (a key intermediate for polycarbonates) is presented. This is an example of a highly equilibrium limited reaction which gives very low reactant conversions (< 3-5%) in batch reactors. The preliminary results presented demonstrate that with simultaneous removal of a co-product methanol, significantly higher reactant conversions can be achieved. The preliminary study suggest that reactive distillation approach can be effectively used to achieve high conversion in DPC synthesis. The methodologies developed in this work will provide insights on rational design of catalysts for ring-opening reactions as well as understanding of the reaction mechanism and catalytic cycles

Methodologies for the optimisation, control and consideration of uncertainty of reactive distillation

The work presented in this thesis is motivated by the current obstacles hindering the implementation of reactive distillation in industry, mainly related to the complexities of its design and control, as well as the impact of uncertainties thereupon. This work presents a rigorous methodology for the optimal design and control under uncertainty of reactive distillation. The methodology can also be used to identify and investigate mitigation strategies for process failures arising due to design and/or operation deficiencies under changed processing conditions, based on the evaluation of different design and/or control alternatives. The first step of the methodology is the simultaneous (MINLP) optimisation of the design and operation of a reactive distillation process superstructure, used to explore the possible steady-state design alternatives available, including ancillary equipment such as pre- and side-reactors, side-strippers and additional distillation columns, based on product-related constraints and a detailed objective cost function. The next step is the investigation of the dynamic control performance of this optimal system, where conventional and advanced process control strategies are considered in order to investigate how robust the system is towards operational disturbances, or whether revising the optimal steady-state design is required. As the optimisation depends heavily on accurate data for reaction kinetics and separation performance, the final step of the methodology is the evaluation of the impact of parameter uncertainty on the performance of the optimal controlled system, including redesigning the controlled system if required. The methodology is demonstrated using a number of industrially relevant case studies with different reaction and separation characteristics in order to investigate how these determine the design and control of an economically attractive and rigorous reactive distillation process. It is demonstrated that the process characteristics have a significant impact on the design of the system, and that auxiliary equipment may be required to meet production specifications and/or to ensure robust controlled behaviour. It is also shown that, under parameter uncertainty, an optimal controlled system may nevertheless face performance issues, and revising the design and/or operation of the process may be required in order to mitigate such situations