Scale Continuous Microwave Dry‐Media Reactor – Part II: Application to Waxy Esters Production

The solvent free esterification reaction between stearic acid and stearyl alcohol has been examined with a montmorillonite clay as catalyst. To aim for industrial application the system has been studied on reaction rate, product purity, catalyst behavior and water removal as function of the process conditions. To avoid an etherification side reaction and to aim for the highest reaction rate, the temperature should be strictly maintained at 170 °C. This is provided on larger scale by the application of microwave heating. Although the examined Brønsted acid clay was found to lose its catalytic activity at very low water activities, a yield of 95 % pure stearyl stearate can be obtained by simply filtering of the clay without solvent extraction or distillation. The “waxy” esterification reaction was investigated with the pilot plant continuous microwave dry‐media reactor (CMDR). The reaction time needed for 95 % yield was reduced by a factor 20–30 in comparison with industrial conventional reactors. This was due to the more homogeneous heat transfer of microwaves, which allows to reach a higher bulk temperature.     

Heat Dispersion Effects on the Functional Characteristics of Industrial‐scale Adiabatic Membrane Reactors

The influence of heat dispersion on the performance of adiabatic industrial‐scale membrane reactors is studied in this work. The results presented are from the application of the model to a membrane reactor that is introduced in an IGCC plant, to control carbon dioxide emissions. The performance of this reactor equipped with highly selective membranes is studied in detail. The thermal phenomena that take place in the interior of the membrane reactor have a considerable influence on the operation of the reactor thus the assumption of isothermal operation is not valid. The omission of thermal dispersion results on the underestimation of the system operation and the total gaseous fluxes that permeate through the membrane. The temperature distribution in the membrane reactor differs significantly from the calculated distribution predicted from the model that ignores thermal dispersion effects.     

Steady‐State Modeling and Simulation of an Axial‐Radial Ammonia Synthesis Reactor

A two‐dimensional model was developed for an axial‐radial ammonia synthesis reactor of the Shiraz petrochemical plant. In this model, momentum and continuity equations as well as mass and energy balance equations are solved simultaneously by orthogonal collocation on the finite element method to obtain pressure, velocity, concentration and temperature profiles in both axial and radial directions. For the catalyst particle, the effectiveness factor is calculated by solving a two‐point boundary value differential equation. The boundary conditions for the Navier‐Stokes and continuity equations are obtained by using equations representing the phenomena of gases splitting or joining in different streams and going through holes in a thin wall. The results of the mathematical model have been compared with the plant data and a good agreement is obtained.     

Contribution to the Qualification of Technical Microwave Systems and to the Validation of Microwave‐Assisted Reactions and Processes

New insights into the energy efficiency of reactions in a microwave field and the development of a concept to transfer thermally heated reactions to microwave‐assisted reactions are reported utilizing commercial modular microwave systems. Particularly, questions on the qualification of technical microwave systems and their measurement and monitoring technology as well as on the validation of chemical reactions and processes are discussed. For that purpose, some technical microwave systems of different manufacturers were tested. The applicability for the implementation of chemical reactions and processes was determined. Conversions and yields of some reactions were compared by the dependence of irradiation modus, temperature and temperature measurement method.     

Modeling of Emulsion Copolymerization of 2‐Hydroxyethyl Methacrylate and Styrene

A mathematical model is developed to describe the reaction behavior of emulsion copolymerization systems where significant polymerization occurs in both the latex particle and aqueous phases. 2‐Hydroxyethyl methacrylate (HEMA) and styrene system was used to illustrate the development of a batch reactor. The model considers the gel and glass effects and monomer transfer. The principal model parameters are taken from the literature. Copolymerization reactivity ratios were estimated using a nonlinear least‐squares procedure. Model predictions have been compared with experimental data on monomer conversion.     

Performance Evaluation of a Novel Concept “Open Plate Reactor” Applied to Highly Exothermic Reactions

The implementation of chemical reactions in batch or semibatch reactors is strongly limited by the constraints linked to the dissipation of the heat generated by the reactions. A novel concept of heat exchanger reactors offers enhanced thermal performances in a continuously operating reactor. A study program is proposed to assess the feasibility and potentialities of this concept. Two kinds of reactions are carried out to characterize simultaneously the reactor performances in terms of reaction and heat exchange: the oxidation of sodium thiosulfate by hydrogen peroxide and an acidobasic reaction (NaOH/H₂SO₄). The resultant experimental data emphasize a significant thermal efficiency: the reactant concentrations and therefore the heat generation can be increased without risk of thermal runaway.     

Modeling the Heat and Mass Transfer in Microwave Drying of White Oak

A 2D comprehensive heat and mass transfer model was developed to simulate the free liquid, vapor, and bound water movement in microwave drying of white oak specimens. The experimental and model results showed that, for white oak, moisture movement was easily impeded and high gradient of internal vapor pressure occurred. The internal vapor pressure was affected by sample dimension (length and thickness). At the same input power density, the internal pressure generated in the core increased with the sample length and thickness. However, as compared with sample length, sample thickness has less effect on the pressure gradient because of the high ratio of permeability between longitudinal and transverse directions.     

Modeling of the Residence Time Distribution and Application of the Continuous Two Impinging Streams Reactor in Liquid‐Liquid Reactions

The two‐phase monosulfonation of toluene, as an example of liquid‐liquid reactions, has been conducted in a continuous two impinging stream reactor (TISR). The extent of reaction under different operating conditions has been determined. A comparison has been made between the performance capability of the TISR and that of continuous stirred tank reactors (CSTR). Under identical conditions, including mean residence time, temperature, feed compositions and phase ratio, the impinging stream reactor has shown a higher efficiency. Finally, a stochastic model, based on Markov chain processes has been developed for the TISR, which describes the flow pattern and the residence time distribution (RTD) within the reaction system. The RTD model, combined with the kinetic expression, has been applied to calculate the conversion of toluene in the reactor. The predicted values for toluene conversion have been compared with those determined experimentally.     

Dynamic On‐Line Reoptimization Control of a Batch MMA Polymerization Reactor Using Hybrid Neural Network Models

A hybrid neural network model based on‐line reoptimization control strategy is developed for a batch polymerization reactor. To address the difficulties in batch polymerization reactor modeling, the hybrid neural network model contains a simplified mechanistic model covering material balance assuming perfect temperature control, and recurrent neural networks modeling the residuals of the simplified mechanistic model due to imperfect temperature control. This hybrid neural network model is used to calculate the optimal control policy. A difficulty in the optimal control of batch polymerization reactors is that the optimization effort can be seriously hampered by unknown disturbances such as reactive impurities and reactor fouling. With the presence of an unknown amount of reactive impurities, the off‐line calculated optimal control profile will be no longer optimal. To address this issue, a strategy combining on‐line reactive impurity estimation and on‐line reoptimization is proposed in this paper. The amount of reactive impurities is estimated on‐line during the early stage of a batch by using a neural network based inverse model. Based on the estimated amount of reactive impurities, on‐line reoptimization is then applied to calculate the optimal reactor temperature profile for the remaining time period of the batch reactor operation. This approach is illustrated on the optimization control of a simulated batch methyl methacrylate polymerization process.     

Hydrodynamics in an Internal Loop Airlift Reactor with a Convergence‐Divergence Draft Tube

Gas holdup and liquid circulation of one conventional draft tube and three different convergence‐divergence draft tubes in an internal loop airlift reactor were investigated. Experiments were carried out in two‐phase systems with air‐water and air‐CMC (carboxyl methyl cellulose) solution and three‐phase system with air‐water‐resin particles. The two‐phase drift‐flux model was used to estimate gas holdup for three‐phase Newtonian and two‐phase non‐Newtonian systems. It is shown that gas holdup in convergence‐divergence draft tubes is higher than that in a conventional draft tube and increases with superficial gas velocity. Variation of the structural parameters of convergence‐divergence draft tubes has little effect on gas holdup in the two‐phase and three‐phase system. The mathematical model, which is based on a drift‐flux model, was developed to describe the liquid circulation velocity in the reactor satisfactorily.     

Development of a Continuous Segmented Flow Tubular Reactor and the “Scale‐out” Concept – In Search of Perfect Powders

The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production.     

Particle‐Scale Investigation of Heat Transfer in Radiation‐Driven Char Gasification

A model of the steam gasification of a single char particle driven by high‐intensity radiation was developed and experimentally verified with available measurements in the literature. This was used to explore the sensitivity of the particle surface temperature and heat‐transfer mechanisms to variations in particle diameters, radiative heat flux, and the concentration of the gasification agent H₂O under typical conditions for solar gasification reactors. The results highlight the importance of the particle diameter in influencing solar‐to‐chemical energy conversion efficiency and assist in the selection of appropriate feedstock particles to match the conditions in specific solar gasification reactors.     

Semi‐Empirical Equations for the Residence Time Distributions in Disperse Systems – Part 1: Continuous Phase

Residence time distributions (RTD) are often described on the basis of the dispersion or the tanks in series models, whereby the fitting is not always good. In addition, the underlying ideas of these models only roughly characterize the real existing processes. Two semi‐empirical equations are presented based on characteristic parameters (mean, minimum, maximum residence time) and on an empirical exponent to permit better fitting. The determination of the parameters and their influence on the RTD are discussed. The usefulness of the models is shown in this first part for single‐phase systems and for the continuous phase of multiphase systems using data from literature for laminar and turbulent flows in different apparatuses. A comparison with the results of other models is also done.     

Fischer‐Tropsch Synthesis: Modeling and Performance Study for Fe‐HZSM5 Bifunctional Catalyst

A water‐cooled fixed bed Fischer‐Tropsch reactor packed with Fe‐HZSM5 catalyst has been modeled in two dimensions (radial and axial) using the intrinsic reaction rates previously developed at RIPI. The reactor is used for production of high‐octane gasoline from synthesis gas. The Fischer‐Tropsch synthesis reactor was a shell and tube type with high pressure boiling water circulating on the shell side. By the use of a two‐dimensional model, the effects of some important operating parameters such as cooling temperature, H₂/CO ratio in syngas and reactor tube diameter on the performance capability of the reactor were investigated. Based on these results, the optimum operating conditions and the tube specification were determined. The model has been used to estimate the optimum operating conditions for the pilot plant to be operated in RIPI.     

Catalytic Oxidation of Methanol to Formaldehyde in a Continuous Fluidized‐Bed Reactor

Partial oxidation of methanol to formaldehyde by using a mixture of ferric and molybdenum oxides as the reaction catalyst at 280–330 °C has been studied in a continuous fluidized bed reactor. The reactor was a cylindrical tube of 20 mm in i.d. and 36 mm in o.d. placed vertically and connected to a truncated coneshaped cyclone separator. The catalyst was prepared by the precipitation method using aqueous solutions of ammonium heptamolybdate and ferric nitrate. The effect of certain parameters, such as temperature, superficial gas velocity and feed flow rates, on the extent of oxidation reaction has been investigated. The maximum size of the catalyst particles was 990 μm, therefore, neither external nor internal diffusion was expected to be effective in the process. The experimental data were correlated with three classes of hydrodynamic models presented for fluidized systems. The best correlation was obtained with compartment type models.