Performance of an adiabatic controlled cycled stirred tank reactor (2023)

The use of heat exchanger/reactors (HEX/reactors) is a promising way to overcome the barrier of poor heat transfer in batch reactors. However to reach residence time long enough to complete the chemistry, low Reynolds number has to be combined with both a plug flow behaviour and the intensification of heat and mass transfers. This work concerns the experimental approach used to characterize an innovative HEX/reactor. The pilot is made of three process plates sandwiched between five utility plates. The process stream flows in a 2mm corrugated channel. Pressure drop and residence time distribution characterizations aim at studying the flow hydrodynamics. Identified Darcy correlations point out the transition between laminar and turbulent flow around a Reynolds number equal to 200. Moreover the flow behaves like a quasi-plug flow (Pe>185). The heat transfer and mixing time have also been investigated. The ratio between the reaction kinetics and the mixing time is over 100 and the intensification factor ranges from 5000 to 8000kWm⁻³K⁻¹. As a consequence, no limitations were identified which allows the implementation of an exothermic reaction. It has been successfully performed under severe temperature and concentration conditions, batchwise unreachable. Thus, it highlights the interest of using this continuous HEX/reactor.

The temperature control strategy of a fed-batch reactor has been presented. The fed-batch operation is very useful to increase the productivity in some type of batch reactors but may incur in reactant overdose, which in case of exothermic reaction would result in possible runaway condition. The main problem is to get the best feeding profile (temporal trajectory) to minimize the reaction time with a temperature constraint. The genetic algorithm (GA) has been used for this task and the profile obtained has been used to drive a pilot scale experimental reactor. This work also demonstrates the usefulness of the GA in parameter estimation of first principle models.

In this work, a study of a batch and semibatch reactor has been carried out based on a very exothermic reaction between thiosulfate and hydrogen peroxide. The experiments were carried out in a glass-jacketed reactor of 5 l, provided with different sensors and a data acquisition system. Thermal and kinetic studies were carried out previously using an adiabatic batch reactor. Then, these results have been used for experiments in semibatch mode of operation with heat transfer. Several experiments have been carried out at different operating conditions (addition flow, initial temperature, initial concentration of reagents…). In batch and adiabatic mode of operation, experimental measures of the reaction mass temperature provided concentration profiles of reagents and products which have been compared to those determined by simulation. In semibatch mode of operation, temperature profiles have also been simulated and validated with experimental results. An algorithm describing the mathematical model has been developed and implemented in a software module written in FORTRAN 77 language. With this mathematical model it has been possible to obtain concentration and heat profiles for the semibatch mode of operation.

Data from simulation studies of the hydrogen peroxide-sodium thiosulphate and hydrogen peroxide-potassium dichromate reactions were employed to select experimental parameters for the study of metastable states in stirred reactors using microprocessor control. The peroxide-thiosulphate system was found to closely approximate the simulation results and microprocessor control within the metastable region was achieved using a simple proportional+integral (PI) control algorithm. With the peroxide-chromate reaction, existing kinetic data had to be corrected for pH effects to enable accurate simulation. The existence of metastable states in this system was demonstrated experimentally, and microprocessor control within the metastable region was again possible using the same PI control algorithm.

The dynamic study of an agitated insulated vessel was performed using the pulse test method. Adequate pulse characteristics which will disturb a first- and a second-order system in a single pulse test were found by analysing the effects of pulse height and duration, integration step size in computation and the type of approximation used on the accuracy of the results. The theoretical multivariable matrix for the system was found and the best manipulated-controlled variable couples were determined by Bristol's technique.

The multiple steady states of conversion in the model of non-ideal CSTR's in series have been studied for irreversible, homogeneous exothermic reaction of first order. The influences of the parameters p and n and those of some kinetic parameters on the occurrence of multiple conversions for a given residence time are presented. The existence of steady-state multiplicity of conversion in each CSTR is shown to be independent of n and depen largely on the values of E/RT₀ (activation energy), b/T₀ (heat of reaction), and p. For certain parametric values, more than three steady states can exist in such a model.

Microporous and Mesoporous Materials, Volume 255, 2018, pp. 211-219

The energetic performances of pure silica CFI and DON-type zeolites (zeosils) were studied by intrusion-extrusion experiments in water and LiCl aqueous solutions at different concentrations. For both zeosils, characterized by a 1D channel system with 14MR pore openings, when water is used as nonwetting liquid a perfect reversible spring behavior is observed with an intrusion pressure of 75 and 26MPa, respectively. The lower value for the DON-type structure is probably due to a larger pore aperture. The intrusion pressures in both cases rise considerably with the LiCl concentration, but the doubling of the salt concentration from 10 to 20M leads only to a slight increase of the intrusion pressure. The maximal stored energy achieves 14.6 and 6.8J/g for CFI and DON-type zeosil-based systems, respectively. The zeolite samples were characterized before and after intrusion-extrusion experiments by XRD, SEM, N₂ adsorption-desorption, TG and NMR analysis in order to get a better understanding of the influence of these intrusion-extrusion experiments on the CFI and DON-type structures.

Microporous and Mesoporous Materials, Volume 267, 2018, pp. 235-241

We describe a fast photocalcination process to prepare highly ordered silica mesoporous films through the use of a low-pressure amalgam arc (λ: 185/254 nm). Because radiant power is 2–3 times higher than conventional low-pressure UV lamps, the elimination of the PEO-b-PPO-b-PEO copolymer template in the 2D hexagonal hybrid film has been completed within 50 min, without damage to the mesostructure. The degradation kinetics are impacted by film thickness and irradiance, but hardly copolymer concentration. Compared to thermocalcination, a narrower pore size distribution and lower energy consumption have been found. Photodegradation mostly originates from a photoablation mechanism induced by radiation at 185 nm, while oxidation due to photogenerated reactive oxygen species plays a minor role. Photocalcination has been combined with an initial photoinduced mesostructuration (detailed in Part 1: Microporous Mesoporous Mater., 257 (2017) 42–50), resulting in an unprecedented “all UV” method to mesoporous silica films. The final process relies on dual wavelength photoactivation: UV_B to form the hybrid copolymer/silica network, a flash intermediate thermal consolidation, and UV_C to decompose the copolymer chains.

Computer Aided Chemical Engineering, Volume 38, 2016, pp. 1027-1032

Continuous Pharmaceutical Manufacturing (CPM) is a strategy which can secure the economic competitiveness hampered by the innate drawbacks of batch production: this mature technology is the current norm for therapeutic molecules, but its key advantages are frequently outweighed by poor mixing and heat transfer, limited scalability and low Overall Equipment Effectiveness (OEE). Moreover, in an environment of expanding economic pressure from generics manufacturers, ever-increasing R&D costs and high societal demand for sustainability and waste minimisation, systematic evaluation of continuous process alternatives in early design stages is critical toward ensuring feasibility and profitability. Artemisinin is an essential anti-malarial substance in high global demand, with many recent advances toward its continuous synthesis. This paper presents a comprehensive analysis of a wide range of solvents for continuous artemisinin recovery. Continuous crystallisation has been simulated using predictive UNIFAC modelling for artemisinin solubility; several technical and green chemistry metrics (product recovery, E-factor) have then been employed in order to comparatively evaluate solvent performance and elucidate relative advantages. Ethyl acetate emerges as a promising crystallisation candidate antisolvent: with high potential product recoveries and good E-factor values, it has a potential to enhance process sustainability via increased material efficiency and reduced waste generation. The clear identification of strong CPM advantages indicates the merit of investigating solvent compatibility in upstream (continuous flow chemistry) as well as downstream (product formulation) operations, toward pursuing the global optimisation of novel, integrated CPM processes.

Chemical Engineering Science, Volume 144, 2016, pp. 446-448

Journal of Magnetism and Magnetic Materials, Volumes 358–359, 2014, pp. 183-191

In the current study, sway of nanofluid on peristaltic transport of a hyperbolic tangent fluid model in the incidence of tending magnetic field has been argued. The governing equations of a nanofluid are first modeled and then simplified under lubrication approach. The coupled nonlinear equations of temperature and nano particle volume fraction are solved analytically using a homotopy perturbation technique. The analytical solution of the stream function and pressure gradient are carried out using perturbation technique. The graphical results of the problem under discussion are also being brought under consideration to see the behavior of various physical parameters.

Computer Aided Chemical Engineering, Volume 38, 2016, pp. 1045-1050

The global pharmaceutical industry faces high R&D, regulatory and cost pressure which can be alleviated by the advent of Continuous Pharmaceutical Manufacturing (CPM). Embarking upon demonstrating and commissioning continuous processes is not trivial: judicious product selection and process design is quintessential for viable investments. Technological as well as economic considerations must be inseparably combined, but a quantitative method for elucidating only the most viable candidates has yet to emerge. This study illustrates how systematic statistical analysis can support business decisions and process R&D for the synthesis and design of continuous pharmaceutical processes. A systematic statistical evaluation of UK economic data has been performed to identify viable drug substances (DS) and drug products (DP) for continuous manufacturing. Product classification and ranking is employed to select those with the highest demand, and statistical hypothesis testing explores causality and correlations of key parameters. Molecular weight and complexity have been correlated with trade and value statistics, indicating that amides, lactones, antibiotics and hormones have high CPM potential.