Analysis of a discontinuously operated chromatographic reactor

The principle of a discontinuously operated chromatographic reactor was studied experimentally and theoretically. The heterogeneously catalysed hydrolysis of methyl formate was chosen as a model reaction. An acidic ion exchange resin was used as catalyst and adsorbent. The relevant adsorption equilibrium constants were available from a previous study. In this work the reaction rates were quantified on the basis of batch reactor experiments. Subsequently, systematic experiments were carried out using a fixed bed. The influence of temperature, residence time, feed concentration and cycle time on the reactor performance was studied. It was attempted to analyse the observations using a simplified pseudo-homogeneous cell model. Since the model was found to be capable of describing the reactor behaviour over a wide parameter range, it was applied to perform extensive parametric calculations. Besides the achievable conversion other objective functions such as recoveries and production rates were also analysed. From the results obtained a few generally applicable rules to evaluate the potential of discontinuously operated chromatographic reactors could be derived.     

Simultaneous methanol removal and destruction from wastewater in a trickle-bed reactor

The stripping of methanol from wastewater was studied in a trickle-bed reactor packed with a mixture of hydrophobic catalyst and hydrophilic support. The process involves air stripping of methanol followed by a gas phase oxidation of methanol into CO₂ and H₂ O over a platinum catalyst. At temperatures between 25 and 70°C, the overall rate was found to be controlled by the stripping step. Since the oxidation results in a lower concentration of methanol in the gas phase, the increased driving force for interfacial mass transfer leads to higher overall methanol removal efficiency.     

Scaling and sensitivity analysis of a reverse flow reactor

Scaling analysis is presented as a systematic procedure to analyze and understand the operation of a complex process such as the autothermal reverse flow reactor (RFR). The reactor is complex from an operational point of view due to its hybrid and periodic nature. An adequate model of the RFR involves highly nonlinear equations. Using simple mathematical operations, these model equations are non-dimensionalized, scaled to order 1 and used to determine the contributions of the controlling physical phenomena taking place in it. The scale factors lead to several analytical expressions useful for suggesting efficient operational strategies for the RFR. Based on a specified error tolerance, we also illustrate how model approximation can be carried out and justified. The sensitivity of important operational parameters that determine sustainability (i.e., maximum temperature and overall conversion) to variables such as reactor length, switching time and mass transfer rate are also analyzed for the pseudo-steady-state condition. The results obtained prove that prudent ways of operating an RFR can be determined through scaling and sensitivity analysis.     

Combustion of toluene-hexane binary mixtures in a reverse flow catalytic reactor

This work is focused on the application of reverse flow reactors to the combustion of lean mixtures of aliphatic and aromatic hydrocarbons in air. For this purpose, hexane and toluene were chosen as model compounds. The combustion of binary mixtures of these compounds (up to 500 ppmV total hydrocarbon concentration) over a commercial Pt/Al₂O₃ catalyst in reverse flow reactors has been studied both experimentally, in a bench-scale unit, and by simulations, using a heterogeneous mono-dimensional dynamic model, good correspondence being observed between both approaches.As general trend, it was observed that the behaviour of the reactor is determined mainly by the combustion enthalpies and reactivities of toluene and hexane. Hence, increasing total concentration and increasing fraction of toluene (the most reactive compound) lead to more stable operation. Regarding the kinetic inhibition effects, in the conditions studied no influence on the reactor performance was observed, probably because the hydrocarbons combust in different reactor zones. This behaviour can be extended to the combustion of aromatic and C₅-C₈ alkanes, characterised by their relatively low concentrations (determined by their vapour pressure) and high reaction rates.     

Oxidation of cyanide in a hydrocyclone reactor by chlorine dioxide

The greatest amounts of cyanide-containing wastes are produced by precious metals milling operations, the electroplating industry and coal processing or coking effluents processes. Because of high toxicity and to comply with federal and state regulations, the treatment of wastewater is required before safe discharge of cyanide wastes. In this regard, the gas-sparged hydrocyclone (GSH) has been tested as a reactor for the treatment of cyanide solutions for cyanide destruction by oxidation with the use of chlorine dioxide gas (ClO₂). The results show oxidation efficiencies of free cyanide approached 99% at all pH values in 5 min. The use of NaCl was also considered for the generation of chlorine dioxide. Excellent performance appears to offer operational and cost advantages over conventional processes.     

Robust control of a reverse-flow reactor

This paper is focused on the design of a robust controller for a catalytic fixed-bed reactor with periodical inversion of the flow direction (reverse-flow reactor, RFR). The analogy between the RFR operated at infinite switching frequency and the countercurrent reactor is the basis of the simplified mathematical model of the reactor.The control system uses dilution and internal electric heating to ensure complete conversion of the reactants and to prevent overheating of the catalyst. As the state of the system is not fully available, apart from some temperature measurements, an observer is designed and used in the control algorithm. This is a typical case of nonlinear system with uncertainties. Following the procedure described in detail by Fissore [2008. Robust control in presence of parametric uncertainties: observer-based feedback controller design. Chemical Engineering Science, in press, doi:10.1016/j.ces.2007.12.019.], the extended model for the process is setup, thus taking into account all the simplifications of the model and linking performance and robustness to the control law, which is a simple state feedback. Simulations with randomly varying feeding concentration have been carried out in order to demonstrate the effectiveness of the proposed control system.     

Repetitive model predictive control of a reverse flow reactor

This paper deals with the control of a catalytic reverse flow reactor (RFR) used for methane combustion. The periodic flow reversals effected on the system makes it both continuous and discrete in nature (i.e., a hybrid system). Control of this system is challenging due to the unsteady state behavior of the process along with its mixed discrete and continuous behavior. Although model predictive control (MPC) is proven to be a powerful technique for several processes it becomes less effective in systems such as the RFR where the model prediction errors and the effect of disturbances on the plant output repeat from time to time. In such cases, control can be improved if the repetitive error pattern is exploited. A novel repetitive model predictive control (RMPC) strategy, that combines the basic concepts of iterative learning control (ILC) and repetitive control (RC) along with the concepts of MPC, is proposed for such systems. In the proposed strategy, the state variables of the model are reset periodically along with predictive control action such that the process follows the reference trajectory as closely as possible. The results obtained prove that the RMPC approach provides an excellent performance for the control of the RFR.     

Dynamical behaviour of the Belousov-Zhabotinsky reaction in a fed-batch reactor

In this study, we report the experimental and numerical investigation of the behaviour of a spontaneously oscillatory reaction in a fed-batch reactor (FBR). We use a cerium catalysed BZ model with a modified Oregonator mechanism. In fed-batch mode, we observe phase-locked, quasiperiodic and period-doubling responses, depending on the amplitude and period of the replacement cycle. A series of single pulse experiments is used to construct phase transition curves, from which limit point (Arnold tongues) and period-doubling bifurcation boundaries can be constructed. Experimental boundaries are compared with boundaries determined numerically using a path following analysis. The results are used to determine the variation, in terms of the mean rate of production of the oxidised catalyst, with the operating conditions of the FBR for a fixed residence time.     

Non-ideal reactor network synthesis through IDEAS: Attainable region construction

The attainable region (AR) for non-ideal reactor networks is constructed for the first time using the Infinite DimEnsionAl State-space (IDEAS) framework. The axial dispersion model is used to represent a non-ideal reactor, and it is shown that the IDEAS framework and associated Shrink-wrap algorithm are applicable to this model. A case study demonstrates that the AR for a reactor network featuring non-ideal dispersion models is larger than the AR for a reactor network featuring only ideal CSTR/PFR models.     

Control of a reverse flow reactor for VOC combustion

A flow reversal reactor for VOC combustion is controlled by the linear quadratic regulator (LQR), which uses dilution and internal electric heating as controls to confine the hot spot temperature within the two temperature limits, in order to ensure complete conversion of the VOC and to prevent overheating of the catalyst. Three phases of operation, i.e., dilution phase, heating phase and inactive phase, are identified. In dilution and heating phases, the cost functions of the LQR control are defined in quadratic forms. In the inactive phase, the controllers are inactivated. A linear model is derived by linearization of a countercurrent pseudo-homogeneous model at two nominal operating conditions in the dilution phase and the heating phase, respectively. The feed concentration and the temperature profile are estimated on-line by using a high-gain observer with three temperatures measurements and are used in the LQR feedback control. Experiments are carried out on a medium-scale reversed flow reactor to demonstrate the proposed LQR control strategy. Results show that the LQR controller is highly efficient in maintaining normal operation of the reactor.     

旋转泡沫填料反应器的研究进展

旋转泡沫填料反应器是一种新型多相搅拌釜式反应器,其将传统的搅拌桨替换成圆环型泡沫填料,可有效强化反应器内多相间传质混合过程,且多孔填料可作为催化剂载体,能减小多相催化反应中固体催化剂的使用量,具有替换传统多相搅拌釜式反应器和浆态反应器的潜力,将有较好的应用前景。本文详细阐述了旋转泡沫填料反应器的结构和反应器内多相流动形式,着重介绍了反应器内多相流动特性的研究进展及反应器内传质性能的研究现状,并与传统的多相反应器传质性能进行比较;从应用方面分析了反应器用于葡萄糖催化氧化、苯乙烯催化加氢等多相过程的强化方式及优势,通过对比得出旋转泡沫填料反应器能有效降低化工过程中物耗、提高物料的利用率;介绍了与旋转泡沫填料反应器类似的其他多孔式搅拌桨反应器的研究进展,分析了这类反应器的优势,并对其性能进行对比;最后,对旋转泡沫填料反应器研究的不足及未来的发展进行了阐述和展望。     

Pure hydrogen generation in a fluidized bed membrane reactor: Application of the generalized comprehensive reactor model

A generalized comprehensive model was developed to simulate a wide variety of fluidized-bed catalytic reactors. The model characterizes multiple phases and regions (low-density phase, high-density phase, staged membranes, freeboard region) and allows for a seamless introduction of features and/or simplifications depending on the system of interest. The model is implemented here for a fluidized-bed membrane reactor generating hydrogen. A concomitant experimental program was performed to collect detailed experimental data in a pilot scale prototype reactor operated under steam methane reforming (SMR) and auto-thermal reforming (ATR) conditions, without and with membranes of different areas under diverse operating conditions. The results of this program were published in Mahecha-Botero et al. [2008a. Pure hydrogen generation in a fluidized bed membrane reactor: experimental findings. Chem. Eng. Sci. 63(10), pp. 2752-2762]. The reactor model is tested in this second paper of the series by comparing its simulation predictions against axially distributed concentration in the pilot reactor. This leads to a better understanding of phenomena along the reactor including: mass transfer, distributed selective removal of species, interphase cross-flow, flow regime variations, changes in volumetric flow, feed distribution, and fluidization hydrodynamics. The model does not use any adjustable parameters giving reasonably good predictions for the system of study.     

Transient operation of a catalytic liquid-liquid plug flow reactor for kinetics measurements

A centrifugal partition chromatograph (CPC) was used as a liquid-liquid catalytic reactor for the isomerisation of hexen-3-ol into ethylpropylketone with a water soluble rhodium catalyst. Global mass transfer coefficients were measured and shown to depend on both the nature of the solute and the flow rate. Liquid-liquid partition isotherms were also determined with the CPC using elution chromatography. Finally, a reactor model was derived to account for the experimental results obtained both under stationary and transient (pulse) conditions. A parameter sensitivity evaluation is also presented.     

Modeling of a novel membrane reactor to integrate dehydrogenation of ethylbenzene to styrene with hydrogenation of nitrobenzene to aniline

The catalytic dehydrogenation of ethylbenzene to styrene is coupled with the catalytic hydrogenation of nitrobenzene to aniline in a simulated integrated reactor formed of two fixed beds separated by a hydrogen-selective membrane, where both hydrogen and heat are transferred across the surface of membrane tubes. A pseudo-homogeneous model of the two fixed beds predicts the performance of this novel configuration first proposed by Moustafa and Elnashaie [Simultaneous production of styrene and cyclohexane in an integrated membrane reactor. Journal of Membrane Science 178 (1), 171-184]. Both co-current and counter-current operating modes are investigated and the simulation results are compared with corresponding predictions for an industrial adiabatic fixed bed reactor operated at the same feed conditions. The conversion of ethylbenzene and the yield of styrene in the membrane reactor are predicted to exceed by a wide margin those in the industrial adiabatic fixed bed reactor. Aniline is also produced as an additional valuable product in a favorable manner, and autothermality is achieved within the reactor. The results suggest that coupling of these reactions could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.     

A virucidal face mask based on the reverse-flow reactor concept for thermal inactivation of SARS-CoV-2

While facial coverings reduce the spread of SARS-CoV-2 by viral filtration, masks capable of viral inactivation by heating can provide a complementary method to limit transmission. Inspired by reverse-flow chemical reactors, we introduce a new virucidal face mask concept driven by the oscillatory flow of human breath. The governing heat and mass transport equations are solved to evaluate virus and CO₂ transport. Given limits imposed by the kinetics of SARS-CoV-2 thermal inactivation, human breath, safety, and comfort, heated masks may inactivate SARS-CoV-2 to medical-grade sterility. We detail one design, with a volume of 300 ml at 90°C that achieves a 3-log reduction in viral load with minimal impedance within the mask mesh, with partition coefficient around 2. This is the first quantitative analysis of virucidal thermal inactivation within a protective face mask, and addresses a pressing need for new approaches for personal protective equipment during a global pandemic.     

Mathematical modelling of a reverse flow reactor with catalytic surface dynamics

This paper studies a system of partial differential equations modelling the behaviour of a reverse flow reactor. For the parameters appropriate for the oxidation of ammonia on a Pt/Al₂O₃ catalyst in a typical laboratory set-up, the reactor may be split into regions where approximate formulas that determine its behaviour are deduced. Numerical calculations are presented and can be used to compare with the analytical formulas. The physical insight gained from the asymptotic analysis suggests a new switching strategy which is the subject of numerical experiments. The switching strategy is found to be efficient at minimising the ammonia exiting the reactor after reversal.     

Experimental studies and modeling of a fixed bed reactor for Fischer-Tropsch synthesis using biosyngas

The aim of this work was to study the Fischer-Tropsch (FT) synthesis of a model biosyngas (33% H₂, 17% CO and 50% N₂) in a single tube fixed-bed FT reactor. The FT reactor consisted of a shell and tube with high-pressure boiling water circulating throughout the shell. A spherical unpromoted cobalt catalyst was used with the following reaction conditions: a wall temperature of 473 K, a pressure of 20 bars and a gas hour space velocity (GHSV) of 37 to 180 NmL.g_cat^− 1.h^− 1. The performance of the FT reactor was also validated by developing a 2D pseudo-homogeneous model that includes transport equations and reaction rate equations. Good agreement between the model predictions and experimental results were obtained. This developed model was extended to predict and quantify the influence of the FT kinetics as well as determine the influence of the tube diameter and the wall temperature. The predicted behaviors for CO and H₂ conversion, productivity of hydrocarbons (mainly CH₄ and C₅₊) and fluid temperature along the axis of the reactor have been analyzed.     

Optimization of a flow reversal reactor for the catalytic combustion of lean methane mixtures

This paper describes a parametric study of a catalytic flow reversal reactor used for the combustion of lean methane in air mixtures. The effects of cycle time, velocity, reactor diameter, insulation thickness, thermal mass and thermal conductivity of the inert sections are studied using a computer model of the system. The effects on the transient behaviour of the reactor are shown. Emphasis is placed on the effects of geometry from a scale-up perspective. The most stable system is obtained when the thermal mass of the inert sections is highest, while thermal conductivity has only a minor effect on reactor temperature. For a given operation, the stationary state depends on the combination of velocity and switch time. Provided that complete conversion is achieved, highest reactor temperature is achieved with the highest switch time. The role of the insulation is not only to prevent heat loss to the environment, but also to provide additional thermal mass. During operation heat is transfer to and from the insulation. The insulation effect leads to higher reactor temperature up to a maximum thickness. The insulation effect diminishes as the reactor diameter increases, and results in higher temperatures at the centreline.