A preliminary evaluation of a continuous‐flow reactor for liquid–liquid–solid phase‐transfer catalyzed synthesis of n‐butyl phenyl ether

This study evaluates the feasibility of using a continuous‐flow stirred vessel reactor (CFSVR) to synthesize n‐butyl phenyl ether (ROPh) from n‐butyl bromide (RBr) and sodium phenolate (NaOPh) by liquid–liquid–solid phase‐transfer catalysis (triphase catalysis). The factors affecting the preparation of triphase catalysts, the etherification reaction in a batch reactor, and the performance in a CFSVR were investigated. The kinetic study with a batch reactor indicated that when the initial concentration of NaOPh or RBr was high, the conversion of RBr would depend on the initial concentration of both RBr and NaOPh. The reaction can be represented by a pseudo‐first‐order kinetic model when the concentration of NaOPh is in proper excess to that of RBr, and the apparent activation energy is 87.8 kJ mol^?1. When the etherification reaction was carried out in the CFSVR, the catalyst particles did not flow out of the reactor, even at a high agitation speed. The conversion of RBr in the CFSVR was, as predicted, lower than that in the batch reactor, but was higher than the theoretical value because the dispersed phase is not completely mixed. Copyright © 2004 Society of Chemical Industry     

Continuous‐Flow Di‐N‐Alkylation of 1H‐Benzimidazole in a Fixed‐Bed Reactor

A new process for a continuous‐flow di‐N‐alkylation of 1H‐benzimidazole to 1H‐benzimidazole‐3‐ium iodide by methylene iodide in the presence of potassium carbonate in a fixed‐bed reactor is presented. The synthesis was transferred from batch to continuous operation with similar yields and conversion rates. Moreover, the influence of temperature and residence time in the continuous flow setup was characterized; optimized conditions led to a doubling of yield. In addition, the continuous flow allowed for a better control of the two‐step reaction by adding an additional tube reactor after the fixed bed that further enhanced the overall performance. With this, the continuous‐flow system presented itself as superior due to higher available temperatures and a better controllability.     

The STAR configuration for methanol synthesis in reversed flow reactors

Although the transient reversed flow operation of a fixed bed reactor for methanol synthesis was shown to be an economically attractive alternative for the traditional steady state technology, it suffers from strongly varying exit concentrations upon flow reversal. These not only disturb the operation of downstream equipment but also significantly decrease the time averaged conversion to methanol. To avoid this drawback, the STAR reactor concept is introduced. It operates in a fully transient mode, but combines the attractive features of the reversed flow reactor operation with practically constant exit concentrations. Extensive simulation work shows that the conversions obtained exceed those of the single reversed flow reactor by at least 5 percent.     

Modeling a dense polymeric catalytic membrane reactor with plug flow pattern

A theoretical study on a tubular membrane reactor assuming isothermal operation, plug flow pattern and using a dense polymeric catalytic membrane is performed. The reactor conversion for an equilibrium gas-phase reaction generically represented by AB is analyzed, considering the influence of the product’s sorption and diffusion coefficients. It is concluded that the conversion of such a reaction can be significantly improved when the overall diffusion coefficient of the reaction product is higher than the reactant’s one and/or the overall sorption coefficient is lower, and for Thiele modulus and contact time values over a threshold. Though a sorption coefficient of the reaction product lower than that of the reactant may leads to a conversion enhancement higher than that one obtained when the reaction product diffusion coefficient is higher than that of the reactant, the contact time value for the maximum conversion is much higher in the first case. In this way, a higher diffusion coefficient for the reaction product should be generally preferable, because it leads to a lower reactor size. The performance of a dense polymeric catalytic membrane reactor depends in a different way on both sorption and diffusion coefficients of reactants and products and then a study of such a system cannot be based only on their own permeabilities. Favorable combinations of diffusion and sorption coefficients can affect positively the reactor’s conversion.     

Theoretical and experimental analysis of methane steam reforming in a membrane reactor

Thermal effects on methane steam reforming process were analyzed, in a Pd-Ag (23wt%) membrane reactor as a function of several parameters, such as temperature, reactant and sweep-gas flow rate, and reactant molar ratio. Heat transfer from the oven was very important for the outlet methane conversion, which also depends on the temperature profile along the reactor. In particular, when the reactant flow rate was high the conversion degree decreased because the energy supplied was not sufficient to maintain the temperature in the reactor. A non-isothermal mathematical model was presented which reproduced the experimental data.     

Exploring the Steady Operation of a Continuous Pilot Plant for the Di‐Nitration Reaction

Continuous‐flow synthesis of the selective herbicide pendimethalin was demonstrated in both a laboratory‐scale and a pilot‐scale reactor using only concentrated nitric acid as nitrating agent. The di‐nitration reaction follows second‐order kinetics where the reaction is first order with respect to both reactant and nitric acid. The pinched‐tube reactor was chosen for pilot‐scale reactor fabrication due to its excellent mixing and mass transfer characteristics compared to a straight‐tube reactor. The estimated mass transfer coefficient showed similar nature in the laboratory‐scale and the pilot‐scale pinched‐tube reactor, ensuring similar performance at the pilot scale. Di‐nitration in continuous flow, inline quenching, extraction, and phase separation are some of the salient features of the developed pilot plant. The importance of the start‐up time for achieving steady state in the flow system at the large scale is highlighted.     

Investigation of natural convection heat transfer in a unique scaled‐down dual‐channel facility

Multiphase Reactors Engineering and Applications Laboratory (mReal) has designed and constructed a scaled‐down dual‐channel facility to investigate plenum‐to‐plenum natural circulation heat transfer through two channels for coolant flow that would be encountered during a loss of flow accident in the prismatic modular reactor (PMR). Heat transfer characterization of the current facility has been investigated under different upper plenum and cooled channel outer surface temperatures using sophisticated flush mounted heat transfer sensors. Results show a reduction in the values of local heat‐transfer coefficient and Nusselt number along the heated channel with increasing outer surface temperatures. One significant observation was the heat transfer reversal close to heated channel exit, where the heat flows from gas to the channel wall. This flow reversal is attributed to recirculation at the heated channel exit to the upper plenum. The average heat transfer results, when compared with previous literature, showed a similar qualitative trend. © 2016 American Institute of Chemical Engineers AIChE J, 63: 387–396, 2017     

Decomposition of formic acid in a photocatalytic reactor with a parallel array of four light sources

The performance of a photocatalytic reactor system with a parallel array of four 6 W blacklight blue fluorescent lamps (wavelength: 300–400 nm) was investigated, based on the decomposition of formic acid in an aqueous solution. An aqueous solution of formic acid (7.8–22.0 gm^?3) was recirculated between the photocatalytic reactor and perfectly‐mixed flow container. The results show that the UV‐light that penetrated through the wall of a glass tube and then passed through the flowing liquid solution accelerated the photocatalytic reaction occurring on the neighboring glass tubes, which greatly contributed to an increase in the reactor activity. This confirms that the arrangement of several light sources in parallel which uses effectively a three‐dimensional space can lead to increased reactor activity and an increase in decomposition rates. A significant reduction in the reaction rate due to a film‐diffusional resistance in the vicinity of the titanium dioxide film was observed. © 2002 Society of Chemical Industry     

Pollutant destruction in a reverse-flow chromatographic reactor

A reverse-flow chromatographic reactor (RFCR) is a packed reactor in which the flow direction is reversed periodically and in which one of the reactants is strongly adsorbed on the catalyst. We study the performance of a RFCR used to destruct a pollutant A by a reaction with a reactant B, the emission level of which is subject to even stricter restrictions. Due to safety considerations, this reactant B is introduced in the center of the reactor. The RFCR operation enables a reduction of the regulated effluent products well below the minimum attainable under a steady-state operation of the same packed-bed reactor. Moreover, it can respond effectively to any perturbations in the pollutant feed rate and/or concentration. When the environmental regulations on the emission of B are stricter than those of A, it is often advantageous to feed slightly less B than the amount needed for complete conversion of A. We present a methodology for finding the operating conditions that lead to the minimal level of weighted emission of both A and B. A continuous feed of the reactant B is superior to operation in which the same amount of B is fed during each semi-cycle but in a non-continuous fashion.     

Synthesis gas production from natural gas in a fixed bed reactor with reversed flow

The feasibility of producing synthesis gas by partial oxidation of natural gas on a Ni-catalyst in a fixed bed reactor with reversed flow was investigated by means of simulation. A one dimensional reactor model of the non-steady state heterogeneous type, accounting for internal diffusional limitations, was applied. A double temperature peak is observed just after flow reversal, influencing the selectivities at the exit through enhanced steam reforming reactions. The second peak gradually decreases in importance with time during the semi-cycle. The influence of several operating conditions on the reactor performance was studied. Most of the coke deposited in a semi-cycle can be removed after flow reversal. This observation opens new perspectives for the reversed flow operation.     

Flow,Solidification, and Solute Transport in a Continuous Casting Mold with Electromagnetic Brake

A three‐dimensional mathematical model is developed to study coupled turbulent flow, heat, solute transport, and solidification in a slab continuous caster with electromagnetic brake. Based on the analogy analysis, all the governing equations can be expressed as a general differential equation and be solved by a general numerical method. Numerical results show that a small corner‐vortex appears near the free surface due to the interaction between the moving solidified shell and the upward flow. Influenced by the fluid flow, the temperature and solute distribution can also be divided into the upper and lower recirculation zones but the distribution of carbon concentration is opposite to that of temperature. The three‐dimensional magnetic field can effectively damp the local flow and affect heat and solute transfer in the mold.     

Light emitting diodes and an infrared bulb as light sources of a fixed‐film tubular photobioreactor for conversion of hydrogen sulfide to elemental sulfur

The effect of light quality on the performance a fixed‐film continuous‐flow photobioreactor for removal of hydrogen sulfide from synthetic industrial wastewater and conversion of it to elemental sulfur was investigated. Sixteen 150 mm long and 1.6 mm internal diameter (id) Tygon tubes formed the active part of the reactor. At the same light intensity, reactor performance in terms of optimal sulfide loading rates was compared between an infrared bulb and light emitting diodes (LEDs). The LEDs provided light within the peak absorption wavelength range of green sulfur bacteria (GSB) and were used as a light source for the GSB with the goal of reducing the cost of the required light. Though the reactor sustained higher sulfide loading rates using LEDs than when using an infrared bulb at equal light intensities, the infrared bulb has the potential to be more efficient overall. Copyright © 2004 Society of Chemical Industry     

Effects of carboxylic additives on the polymerization characteristics of nylon‐6 reactors with diffusional water removal

The effects of carboxylic acid on the polymerization characteristics of nylon‐6 were investigated in reactor models that consist of a continuous‐flow stirred tank reactor (CSTR) and a tubular reactor with a diffusional water‐removal system, which are connected in series. Mathematical models for the CSTR and the tubular reactor were established and solved by numerical methods. In the CSTR, with an increase of the feed acetic acid content, the monomer conversion, and the molecular weights are increased. In the tubular reactor, the acid behaves like a catalyst and a modifier at the same time in the polymerization of nylon 6. The effects of the feed acetic acid content and the diffusional water removal on the zeroth, first, and second moments and the polydispersity index of the polymer were investigated. The polydispersity index is greatly affected by the feed content of carboxylic acid in the CSTR, but it finally approaches to values of ～ 2 in the tubular reactor. The diffusional water removal is found to have little effect on the polydispersity index of the polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1226–1237, 2001     

Esterification of Acetic Acid and Ethanol in a Flow‐Through Membrane Reactor Coupled with Pervaporation

The esterification of acetic acid is an important industrial process for the synthesis of ethyl acetate. A membrane reactor with a sulfonated polyethersulfone/polyethersulfone/non‐woven fabrics composite catalytic coupled with a poly(vinyl alcohol) pervaporation membrane was applied in continuous esterification of ethanol with acetic acid in a flow‐through mode. High equilibrium conversion was obtained for esterification in a closed‐loop mode. For the pervaporation‐assisted esterification in this mode, the experimental conversion was very close to the theoretical value.     

Alkylation of phenol with tert‐butyl alcohol over a catalyst synthesized from coal fly ash

The alkylation of phenol with tert‐butyl alcohol was carried out in a continuous flow reactor over a catalyst synthesized from fly ash. The activity of the synthesized catalyst was compared with those of other conventional zeolite catalysts such as 13X (NaX) and Hβ. Of all the catalysts tested, zeolite Hβ showed the highest activity in phenol conversion followed by the synthesized zeolite (HZOP‐31). The activity of commercial 13X zeolite was found to be same as that of HZOP‐31. Ce‐exchanged catalyst (CeZOP‐31) showed even better performance than 13X in the alkylation of phenol. The effects of different parameters such as reactant mole ratio, temperature and space velocity on phenol conversion and tert‐butyl phenol selectivity were studied. The effect of mass transfer resistance was found to be negligible within the feed rate range and particle size range studied. The apparent activation energy for the reaction of tert‐butyl alcohol over HZOP‐31 was determined as 30.1 kJ mol^?1. Copyright © 2006 Society of Chemical Industry     

Electrochemical degradation of pulp and paper industry waste‐water

BACKGROUND: Conventional biological waste‐water treatment techniques are insufficient to degrade large quantities of dissolved lignin discharged by small‐scale paper mills. The current investigation is aimed at comparing the overall performance of basic electrochemical reactor configurations such as batch, batch recirculation, recycle and single pass systems, in removing the organic part of waste‐water from a small‐scale, agro‐based paper industry. The effect of current density, supporting electrolyte concentration, duration of electrolysis, specific electrode surface and fluid flow rate on the removal of pollutants and energy consumption are critically evaluated. The improvement in biodegradability of the effluent during treatment is also noticed. RESULTS: The batch recirculation mode of operation was found to be superior in comparison with a batch system using the same specific electrode surface for both COD removal (73.3 vs. 64%) and capacity utilization (rate constant 1.112 × 10^?3 vs. 1.049 × 10^?3 cm s^?1). The pollutant removal performance of the batch recirculation system improved considerably with increase in the circulation flow rate. At the best operating point in the recycle system, 59% of COD was removed, corresponding to a current efficiency of 68.9% and specific energy consumption of 18.46 kWh kg^?1. The biodegradability index of the waste‐water was improved from 0.18 ± 0.01 to 0.36 ± 0.01. CONCLUSION: A recycle reactor was the best configuration, because of its flexibility of operation. Circulation flow rate and withdrawal flow rate enable the control of transfer coefficients and treatment duration respectively. Electrochemical treatment not only removes the bulk of the organic matter, but also makes the remaining pollutants more easily biodegradable. Copyright © 2009 Society of Chemical Industry     

Computational Fluid Dynamics Study of a Styrene Polymerization Reactor

The computational fluid dynamics (CFD) approach was adopted to simulate benzoyl peroxide (BPO)‐initiated styrene polymerization in a laboratory‐scale continuous stirred‐tank reactor (CSTR). The CFD results revealed the effects of non‐homogeneity and the short‐circuiting of the unreacted styrene and initiator on the reactor performance. The study also investigated the effects of the impeller speed and the residence time on the conversion and the flow behavior of the system. The CFD simulation showed that intense mixing remained confined to a small region near the impeller. With increasing impeller speed, it was found that the perfectly mixed region near the impeller expanded, thus reducing non‐homogeneity. Different contours were generated and exhibited the effect of the mixing parameters on the propagation rate and styrene conversion. The monomer and initiator conversions predicted with the CFD model were compared to those obtained with a CSTR model. The CFD model accounts for the non‐ideality behavior of the polymerization reactor, and hence conversion predictions are more realistic.     

Single and Multiphase Catalytic Oxidation of Benzyl Alcohol by Tetrapropylammonium Perruthenate in a Mobile Microreactor System

A mobile microreactor system, with flow and temperature control for organic synthesis, is described. The system can be used anywhere a venting outlet is available. The microreactors can be operated in different flow patterns (continuous flow, stop‐flow, or programmed‐flow) providing reaction times from a few minutes to a few hours. The system was tested for the catalytic oxidation of benzyl alcohol to benzaldehyde by tetrapropylammonium perruthenate (TPAP) with N‐methyl‐morpholine‐N‐oxide in the liquid phase under stop‐flow mode and on supported TPAP with oxygen under continuous flow mode. The conversion of benzyl alcohol in the microreactor was close to that of a small batch reactor for the liquid phase reaction. For the multiphase reaction, a conversion of 30–40 % was obtained with residence times below 1 min.     

Gas holdup in a two‐phase reversed flow jet loop reactor

Experimental investigations have been carried out in Reversed Flow Jet Loop Reactor (RFJLR) to study the influence of liquid flow rate, gas flow rate, immersion height of two‐fluid nozzle in reactor and nozzle diameter on gas holdup without circulation, that is, gas–liquid mixture in draft tube only (E_gd) and gas holdup with circulation loop (E_g). Also critical liquid flow rate required for transition from draft tube to circulation loop has been determined. Gas holdup was measured by isolation valve technique. Gas holdup in draft tube and circulation loop increased with increase in liquid flow rate and gas flow rate. It is observed that the increased flow rate is required for achieving a particular value of gas holdup with larger nozzle diameter. Nozzle at the top edge of draft tube have higher gas holdup as compared to other positions. It has been noted that, no significant recirculation of gas bubbles into the top of draft tube from annulus section has been observed till a particular liquid flow rate is reached. A plot of gas holdup with no circulation and with circulation mode determines minimum liquid flow rate required to achieve complete circulation loop. Critical liquid flow rate required to achieve complete circulation loop increases with increase in gas flow rate and is minimum at lowest immersion height of two‐fluid nozzle.     

Modelling and simulation of trickle‐bed reactors using computational fluid dynamics: A state‐of‐the‐art review

Trickle‐bed reactors (TBRs), which accommodate the flow of gas and liquid phases through packed beds of catalysts, host a variety of gas–liquid–solid catalytic reactions, particularly in the petroleum/petrochemical industry. The multiphase flow hydrodynamics in TBRs are complex and directly affect the overall reactor performance in terms of reactant conversion and product yield and selectivity. Non‐ideal flow behaviours, such as flow maldistribution, channelling or partial catalyst wetting may significantly reduce the effectiveness of the reactor. However, conventional TBR modelling approaches cannot properly account for these non‐ideal behaviours owing to the complex coupling between fluid dynamics and chemical kinetics. Recent advances in the application of computational fluid dynamics (CFD) to three‐phase TBR systems have shown promise of achieving a deeper understanding of the interactions between multiphase fluid dynamics and chemical reactions. This study is intended to give a state‐of‐the‐art overview of the progress achieved in the field of CFD simulation of TBRs over the past two decades. The fundamental modelling framework of multiphase flow in TBRs, advances in important constitutive models, and the application of CFD models are discussed in detail. Directions for future research are suggested.