Modeling of transient heterogeneous two-dimensional catalytic packed bed reactor

A two-dimensional transient catalytic packed bed model, incorporating all transport parameters and resistances, along with boundary conditions based on a catalytic single pellet has been developed. Thermal conduction through the solid phase is included in the model. The overall steady state reactor performances of packed bed reactor using a model proposed in this study are compared with those from different models which are often used for a packed bed reactor. The model presented is very useful in the presence of internal temperature and concentration gradients in the catalyst pellets. The dynamic behavior in feed temperature change is examined during ethane hydrogenolysis. A transient thermal runaway is observed by feed temperature decrease. The sensitivities of the computation to each physical parameter and the effects of some simplifying assumptions in the model are also analyzed. The magnitude and position of hot spot in catalytic packed bed reactor are relatively sensitive to thermal parameters and characteristic parameters of a catalyst pellet.     

Isobutane dehydrogenation reaction in a packed bed catalytic membrane reactor

A packed-bed catalytic ceramic membrane reactor (PBCMR) was used for the isobutane dehydrogenation reaction. The experimental results have shown that through the use of the membrane reactor one can attain better conversions and yields than in a conventional reactor operating under the same outlet pressure and temperature, and feed composition conditions.     

Hydrogen sulfide removal by catalytic oxidative absorption method using rotating packed bed reactor

Using catalytic oxidative absorption for H_2S removal is of great interest due to its distinct advantages. However,traditional scrubbing process faces a great limitation in the confined space. Therefore, there is an urgent demand to develop high-efficiency process intensification technology for such a system. In this article, H_2S absorption experimental research was conducted in a rotating packed bed(RPB) reactor with ferric chelate absorbent and a mixture of N_2 and H_2S, which was used to simulate natural gas. The effects of absorbent p H value, gas–liquid ratio, gravity level of RPB, absorption temperature and character of the packing on the desulfurization efficiency were investigated. The results showed that H_2S removal efficiency could reach above 99.6% under the most of the experimental condition and above 99.9% under the optimal condition. A long-time continuous experiment was conducted to investigate the stability of the whole process combining absorption and regeneration. The result showed that the process could well realize simultaneous desulfurization and absorbent regeneration, and the H_2S removal efficiency kept relatively stable in the whole duration of 72 h. It can be clearly seen that high gravity technology desulfurization process, which is simple, high-efficiency, and space intensive, has a good prospect for industrial application of H_2S removal in confined space.     

Control of a nonadiabatic packed bed reactor under periodic flow reversal

A full parametric study of the open-loop behavior of a packed bed reactor-recuperator system operating under periodic flow reversal produced a series of parametric maps which slow regions of operating conditions for which the system exhibits runaway, stable operation or extinction of the reaction. The reaction is CO oxidation over a Pt/alumina catalyst. A set of optimal operating conditions in terms of cycle time and heat transfer coefficient can be directly extracted from the parametric maps. A preliminary study on the control of periodic flow reversal tested and compared two strategies. 1) feedback PID control of the exit CO concentration and 2) model based feedforward control.     

Catalytic hydrogenation in a packed bed bubble column reactor

The cocurrent downflow contactor reactor (CDCR) has been found to give low mass transfer resistances both in slurry and packed bed catalytic operation. The hydrogenation of propan-2-ol solutions of itaconic acid in the range 100–300 kPa and 20–70°C and of soyabean oil in the range 100–500 kPa and 130–160°C was studied using slurry (5% w/w Pd/C) and packed bed (3% w/w Pd/Al₂O₃ Raschig ring) catalyst. Mass transport and kinetic parameters were evaluated for both operational modes and while the slurry CDCR gave better mass transfer properties than the packed bed CDCR, the latter gave better mass transfer than conventional reactors and superior selectivity to the slurry CDCR. As has been observed with the slurry CDCR, the packed bed CDCR was found to operate under surface reaction rate control with negligible transport resistances. This was particularly evident for soyabean oil hydrogenation, which is well known to be transport controlled in conventional reactors.     

Modeling and simulation of non-isothermal catalytic packed bed membrane reactor for H2S decomposition

The recovery of H₂ from H₂S is an economical alternative to the Claus process in petroleum and minerals processing industries. Previous studies [React. Kinet. Catal. Lett. 62 (1997) 55; Catal. Lett. 37 (1996) 167] have demonstrated that catalytic decomposition of H₂S over bimetallic sulfide can proceed at relatively higher rates than over mono-metallic systems due to chemical synergism although conversions are still thermodynamically limited. In the present study, the performance of a catalytic membrane reactor containing a packed bed of Ru–Mo sulfide catalyst has been investigated with a view to improving H₂ yield beyond the equilibrium ceiling. A system of differential equations describing the non-isothermal reactor model has been solved to examine the effect of important hydrodynamic and transport properties on conversion. The results were obtained using a Pt-coated Nb membrane tube as the catalytic reactor enclosed in a quartz shell cylinder. Reynolds number for shell and tube side (Re^s and Re^t) as well as the modified wall Peclet number, Pe_m, dramatically affect H₂S conversions. Membrane reactor conversion rose monotonically with axial distance exceeding the equilibrium conversion by as much as eight times under some conditions.     

Cationic polymerization in rotating packed bed reactor: Experimental and modeling

On the basis of analysis of key engineering factors predominating in cationic polymerization, butyl rubber (IIR) as an example was synthesized by cationic polymerization in the high‐gravity environment generated by a rotating packed bed (RPB) reactor. The influence of the rotating speed, packing thickness, and polymerization temperature on the number average molecular weight (M_n) of IIR was studied. The optimum experimental conditions were determined as rotating speed of 1200 r min^?1, packing thickness of 40 mm and polymerization temperature of 173 K, where IIR with M_n of 289,000 and unimodal molecular weight distribution of 1.99 was obtained. According to the experimental results and elementary reactions, a model for the prediction of M_n was developed, and the validity of the model was confirmed by the fact that most of the predicted M_ns agreed well with the experimental data with a deviation within 10%. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Liquid-liquid heterogeneous mixing efficiency in a rotating packed bed reactor

Mixing of two immiscible liquids consists of two sections that are liquid-liquid dispersion and mass transfer intraphase or interphase. It plays a crucial role in the liquid-liquid heterogeneous reactions. Here, the liquid-liquid heterogeneous mixing efficiency in RPB reactor is experimentally assessed by a consecutive-competitive chemical probe system. The diameters of dispersed phase droplets in RPB were measured and a correlation to predict the mean diameters were obtained. Based on the dispersed phase size and mass transfer characteristic, a model for predicting the segregation index of liquid-liquid heterogeneous mixing in RPB was established with a deviation <20%. Based on this model, the characteristic time of liquid-liquid heterogeneous mixing in RPB is determined to be in the range of 0.01–1 s. RPB exhibits a great process intensification potential for heterogeneous mixing process.     

Electrochemical treatment of human wastes in a packed bed reactor

There is an increasing interest in the use of electrochemical methods for dealing with pollution problems. This paper deals with the mass balance and the use of a packed bed reactor for the electrochemical incineration of human wastes. Parametric studies were carried out to determine the effect of: (i) anodic particle size, (ii) flow rate of faeces/urine mixture, (iii) height of packed bed, (iv) current density and (v) cathode to anode spacing arrangement, on the rate of oxidation of human waste. It is shown that particles of Ebonex (0.5–1.0 mm diam.) coated with a catalyst layer, comprising SnO₂/Sb₂O₃, a solution flow rate of 0.9–1.4 cm s^–1 through the packed bed based on the cross sectional area of the reactor, a bed height of 5–8 cm and a current density based on the geometric area of the particles of 5 mA cm^–2 comprise an optimum set of parameters for the scale-up of a packed-bed electrochemical reactor system. A preliminary design for the further scale up of the process is also described.     

A study of mass transfer in a packed bed reactor by electrochemical technique

Electrochemical method was used to study the mass transfer between the solid particles and the flowing liquid in a packed bed. From the limiting current of a single active particle immersed in inactive glass particles of the same size and shape, the mass transfer coefficients can be derived.Various size and shape of packing particles were used. The experimental results indicate that smaller packing particles have higher mass transfer coefficient. In the meantime, spherical packing particles have higher mass transfer coefficients than cylindrical particles of the same equivalent diameter. However they approach each other when liquid flowing velocity is increased.The wall-effect of the reactor on mass transfer was also observed.     

固定床反应器在病毒性疫苗研究中的应用

固定床反应器在病毒性疫苗的研究中已经得到广泛的应用。固定床反应器能在较小的体积中得到较高的细胞密度和病毒滴度。本文主要介绍固定床反应器在病毒性疫苗研究中的应用及其优势和存在的主要问题。     

An Ru-based catalytic membrane reactor for dry reforming of methane—its catalytic performance compared with tubular packed bed reactors

The methane reforming with CO₂ seems to be a promising reaction system useful to reduce the greenhouse contribution of both gases into the atmosphere. On this basis, and considering the potentiality of this reaction system, the dry reforming reaction has been carried out in an Ru-based ceramic tubular membrane reactor, in which two Ru depositions have been performed using the co-condensation technique. Experimental results in terms of CH₄ and CO₂ conversion versus temperature during time are presented, as well as product selectivity and carbon deposition. These experiments have also been carried out using a traditional reactor. A comparison with literature data regarding dry reforming reaction is also provided. Experimental evidence points out a good catalyst activity for the methane dry reforming reaction, confirming the potentiality of a catalytic membrane applied to the reaction system.     

Methanol steam-reforming in a catalytic fixed bed reactor

Designing an appropriate methanol steam reformer requires detailed knowledge about the processes within such a reactor. Thus, the axial temperature and concentration gradients and catalyst ageing were investigated. It was found that for a fresh catalyst load, the catalyst located in the reactor entrance was most active during the experiment. The activity of this part of the catalyst bed decreased after some time of operation due to ageing. With further operation, the most active zone moved through the catalyst bed. From the results concerning hydrogen production and catalyst degradation, the necessary amount of catalyst for a mobile PEMFC-system can be estimated.     

Tomographic measurement of breakthrough in a packed bed adsorber

The tomographic measurement technique enables the measurement of local water vapour concentrations at the exit of a packed bed adsorber using near infra-red. This is realized by extending the adsorption column with a hollow glass cylinder that serves as the measurement cross-section. The glass is transilluminated from three directions with three light-sheets. The light absorption by water vapour is measured with three InGaAs photodiode arrays and these projections are used for the tomographic reconstruction of the concentration fields. For low water vapour concentrations () an error below 8% is reported. Concentration field measurements during adsorption show the early breakthrough near the column wall due to channeling effects at a low ratio between tube and particle diameter.     

Modelling of non-catalytic gas—solid reactions—II. Transient simulation of a packed bed reactor

A Transient model for packed bed non-catalytic reactors, which avoids many of the simplifying assumptions of the earlier models, has been developed. The model includes the effects of inter- and intra-pellet transfer resistances and the additional effects of axial dispersion in the bulk fluid. The solution procedure to the system of equations is based on the orthogonal collocation method. The effects of various parameters on the temperature rise encountered in the bed and the possibility of reducing this rise by perturbing the inlet concentration and temperature of the gas are examined.     

Generalized criteria for parametric sensitivity and temperature runaway in catalytic reactors

Instability in the steady state operation of fixed bed catalytic reactors may arise from various sources, the most probable being parametric sensitivity as a consequence of the heterogeneity of the system, leading to temperature runaway, outside of the region of multiple steady states. A technique has been developed for predicting regions of temperature runaway in heterogeneous fixed bed reactors, which is not dependent on temperature gradients. The relationship between this form of instability and that due to multiple steady states is examined.