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.     

Continuous‐Flow Surface Aeration Systems

An aeration process in an activated sludge plant is a continuous‐flow system. In this system, there is a steady input flow (flow from the primary clarifier or settling tank with some part from the secondary clarifier or secondary settling tank) and output flow connection to the secondary clarifier or settling tank. The experimental and numerical results obtained through batch systems can not be relied on and applied for the designing of a continuous aeration tank. In order to scale up laboratory results for field application, it is imperative to know the geometric parameters of a continuous system. Geometric parameters have a greater influence on the mass transfer process of surface aeration systems. The present work establishes the optimal geometric configuration of a continuous‐flow surface aeration system. It is found that the maintenance of these optimal geometric parameters systems result in maximum aeration efficiency. By maintaining the obtained optimal geometric parameters, further experiments are conducted in continuous‐flow surface aerators with three different sizes in order to develop design curves correlating the oxygen transfer coefficient and power number with the rotor speed. The design methodology to implement the presently developed optimal geometric parameters and correlation equations for field application is discussed.     

Membrane reactor immobilized with palladium‐loaded polymer nanogel for continuous‐flow Suzuki coupling reaction

A catalytic membrane reactor, which was immobilized with palladium‐loaded nanogel particles (NPs), was developed for continuous‐flow Suzuki coupling reaction. Palladium‐loaded membranes were prepared by immobilization of NPs, adsorption of palladium ions, and reduction into palladium(0). The presence of palladium in the membrane was confirmed by the scanning electron microscopy; palladium aggregation was not observed. The catalytic activity of the membrane reactor in continuous‐flow Suzuki coupling reaction was approximately double that of a comparable reactor in which palladium ions were directly adsorbed onto an aminated membrane. This was attributed to the formation of small palladium particles. The reusability in the continuous‐flow system was higher than that in a batch system, and the palladium‐loaded membrane reactor had high long‐term stability. © 2014 American Institute of Chemical Engineers AIChE J, 61: 582–589, 2015     

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     

Two‐phase model for continuous final‐stage melt polycondensation of poly(ethylene terephthalate). III. Modeling of multiple reactors with multiple reaction zones

A steady‐state two‐phase model has been developed for a continuous finishing stage of the melt polycondensation process that consists of two rotating‐disk reactors in series. Each reactor has multiple reaction zones with different types of rotating disks to establish plug flow profiles and to facilitate the removal of volatile reaction byproducts. The effect on reactor performance of varying the mass transfer parameter was found to be small for the reaction conditions used. The simulation results show that the use of two reactors offers increased flexibility in reactor operations to obtain the desired polymer properties. Although the proposed model has not been fully validated with experimental or plant data, it has illustrated that the complex multizone reactor system can be easily modeled by the two‐phase modeling technique and that added physical insights can be made through numerical model simulations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1088–1095, 2003     

Study on the enzymatic hydrolysis of racemic methyl ibuprofen ester

The hydrolysis of racemic methyl ibuprofen ester in the presence of lipase from Candida rugosa was investigated in shake flasks. Experiments were performed to study the effect of temperature, pH and shaking speed on the reaction rate. Different hydrophobic co‐solvents were screened for the highest reaction rate and the presence of enzyme inhibition by substrate and products was examined. A kinetic expression was then proposed to describe the reaction. Kinetic parameters were determined for the optimum operating conditions and the proposed model was verified with the experimental results. Next, this reaction was scaled up to a fed batch stirred tank reactor. Batch reactor and fed batch reactor configurations were compared for better conversions. The effects of aqueous phase hold‐up, substrate concentration and feed flow rate on the conversion of the reaction were also studied. Higher conversions were obtained in a fed batch reactor when compared with the batch reactor. In the fed batch reactor, increased conversions were observed with lower feed flowrates and high aqueous phase hold‐up. © 2001 Society of Chemical Industry     

Application of Monod kinetics on cascade reactors‐in‐series

Mass balance equations for biomass and substrate are numerically solved to determine the effects of different variables on suspended growth systems. The longitudinal biomass gradient was taken into account. Monod kinetics and mathematical models of reactors‐in‐series are used to represent the actual conditions resulting from varying degrees of wastewater quality. An attempt has been made to determine the effluent concentration as a function of two parameters, ie a dimensionless time and a dimensionless substrate concentration of the incoming wastewater. Computer techniques are applied to express the results generally. By means of the numerical approach, the variation of the ratio between the hydraulic residence time of a given reactor and that of an equivalent plug‐flow tank without longitudinal biomass gradient was investigated. Results were expressed in form of nomograms to characterize the plug‐flow activated sludge systems and to provide the basis for design. Experimental data reported in the literature were also evaluated to demonstrate the cases where the existing classical solution to the problem differs from the exact results based upon Monod‐type substrate removal. © 2000 Society of Chemical Industry     

Comparison of Heterogeneous Catalyst Activities in Various Reactor Types and Reaction Conditions

A comprehensive reactor analysis package is provided that will enable more accurate comparison of catalyst activity in various reactor types and reaction conditions. Conservation of mass was applied to formulate the performance equations for catalytic batch, plug flow, continuous stirred tank, and pulse reactors. The weight hourly space velocity was correlated with the conversion and the reaction rate in many integral forms. The apparent reaction rate constant can be obtained from kinetic data for each reactor type.     

Liquid‐Solid Mass Transfer Behavior of a New Stirred‐Tank Reactor with a Packed Bed Fixed to its Wall

Rates of liquid‐solid mass transfer at a packed bed of Raschig rings fixed to the wall of a stirred tank were measured by a technique which involves the diffusion‐controlled dissolution of copper in acidified dichromate. Variables studied were impeller rotation speed, impeller geometry, Raschig ring diameter, bed thickness, presence of baffles, physical properties of the solution, and effect of superimposed flow. Mass transfer data for the batch reactor were correlated by a dimensionless equation. For a given set of conditions, the radial‐flow impeller was found to produce higher rates of mass transfer than the axial‐flow impeller. The presence of baffles increased the rate of mass transfer inside the bed. Applications of the suggested reactor in conducting different diffusion‐controlled liquid‐solid reactions were evaluated.     

BATCH REACTION WITH REGULAR PARTIAL REPLACEMENT—A FORM OF SEMICONTINUOUS OPERATION

A mathematical model is derived to describe the semicontinuous process of first-order batch reaction with regular partial replacement and the steady-state performance of such a system is shown to depend on the frequency and degree of replacement. A useful analogy is also shown to exist between the system and a recycle plug flow reactor. The practical significance of this mode of operation is then briefly discussed.     

Einfluss der Reaktorkonfiguration auf die Enantioselektivität einer kinetischen Racematspaltung

The optical purity of a product at the reactor outlet depends not only on the enantioselectivity of the catalyst, but also on the reactor configuration. Different reactor configurations are compared with respect to the enantiomeric excess (ee) at a respective conversion that can be achieved in a kinetic resolution of a racemate. For batch, fed‐batch and plug flow reactors enantioselectivities (E value) of 35 are sufficient to achieve high enantiomeric excess. For a continuously operated stirred tank reactor high ee values are only obtained for E values higher than 190.     

Measurement of intrinsic rates for homogeneous gas‐phase reactions at high temperatures

A coiled quartz tubular reactor has been designed to measure the intrinsic reaction kinetics for homogeneous reactions at high temperatures up to 1100°C. Actual gas residence times were less than 100 ms. A simple and well‐studied test reaction (i.e., the decomposition of nitrous oxide, N₂O), with published intrinsic kinetics, was used to verify the operation of the experimental reactor. For this system, Peclet numbers (Pe = uL/DL) computed from experimental conversion data were greater than 1000, indicating that the plug flow assumption could be used with this reactor system to determine intrinsic rate expressions with errors of less than 5% for the conditions studied.     

The behaviour of an intermeshing twin screw extruder with catalyst immobilised screws as a three-phase reactor

The characteristics of an intermeshing co-rotating twin screw extruder were investigated as a three-phase reactor using a model reaction. The kinetics of the reaction and base line data were obtained using a high pressure stirred tank reactor. The feasibility of immobilisation of palladium on the surface of the screws as the catalyst was also studied. The behaviour of the extruder in batch and continuous mode and with slurry and non-slurry solutions was investigated. The results confirmed the superiority of the intermeshing co-rotating twin screw extruder as a novel three-phase reactor compared to the stirred tank reactor as a traditional three-phase reactor. The residence time distribution measurements indicated that the behaviour of the extruder approached perfect plug flow reactor with increasing viscosity of reaction solution.     

Effect of third-phase properties on benzyl-n-butyl ether synthesis in phase transfer catalytic system

The production of benzyl-n-butyl ether from benzyl chloride and n-butanol is studied in phase transfer catalytic system. A third phase is formed when polyethylene glycol (PEG) and dodecane are used as the phase transfer catalyst (PTC) and an organic solvent, respectively. The production rate at the three-phase system is higher by seven times than that at the two-phase system. The ether production rate and its selectivity are dependent on the initial concentration of n-butanol. These are affected by the properties of the third phase, especially the concentrations of n-butanol and water in the third phase.

n-Butanol reacts with benzyl chloride and potassium hydroxide simultaneously. The reaction between n-butanol and potassium hydroxide occurs in the aqueous phase. Then, the selectivity of ether on a basis of initial n-butanol is below 0.6 in a stirred tank batch reactor. The selectivity is much improved at 0.9 by using a static triphase batch reactor in which the organic and aqueous phases are separated by the third phase. The interphase mass transfer can be accelerated by ultrasonic device.     

A simplified model of peroxidase‐catalyzed phenol removal from aqueous solution

A number of investigations have demonstrated the potential of applying peroxidase enzymes to remove aromatic compounds from wastewater. The efficiency of alternative peroxidase enzymes could be compared on a kinetic basis using a versatile model which may be calibrated in a straightforward manner. A model of the peroxidase‐catalyzed removal of aqueous aromatic compounds has been developed. This model is calibrated using readily available spectrophotometric and mathematical techniques and is shown to accurately predict aqueous phenol removal at 25 °C and neutral pH over the course of batch reactions both in the presence and absence of polyethylene glycol, a protective additive. © 1999 Society of Chemical Industry     

Novel two‐stage phenol–formaldehyde resol resin synthesis

The synthesis of phenol–formaldehyde resol resins was carried out in two stages to facilitate the start of a conventional batch process. In the first stage, the starting material solution was preprocessed in a continuous‐flow stirred‐tank reactor with a 5‐min residence time. In the second stage, synthesis was continued in a batch reactor. Samples were analyzed by titrimetric methods, gas chromatography, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. Most of the starting materials were consumed in the preprocessing reactor, which allowed better control of the reactivity of the prepolymer solution in the second stage. The methylolation and condensation reactions proceeded steadily during the production process in the batch reactor. The results of the study indicated that dividing a conventional one‐stage batch process into two stages could facilitate the control of the initial stages of resol production. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:371–379, 2007     

Numerical investigation of continuous processes for catalytic hydrogenation of nitrile butadiene rubber

Dynamic behavior of continuous processes was numerically investigated for the catalytic hydrogenation of nitrile butadiene rubber, based on developed models, which took into account the coupling between kinetics and mass transfer. The evolution of hydrogenation reaction trajectories in both cases were analyzed. It is proposed that the coupling behavior between the catalytic hydrogenation and mass transfer was completely determined by the ability of the catalyst in activating hydrogen, carbon‐carbon double bond loading level and the relative capacity of reaction to mass transfer as well as the residence time in the reactor. Four dimensionless parameters were derived to characterize these aspects. The effects of operation conditions on the hydrogenation processes were investigated. The application of the ideal flow models to non‐ideal flows was in addition discussed. It is suggested that the optimal reactor for such a hydrogenation system would be a plug flow reactor with an instantaneous well‐mixing component in the inlet of it, and a reasonable approach to the proposed optimal reactor should be with the flow behavior of at least three continuous stirred tank reactors in series. Further research directions are suggested.     

Removal of aqueous phenol and 2‐chlorophenol with purified soybean peroxidase and raw soybean hulls

In this study, the removal of phenol and 2‐chlorophenol using soybean seed‐hulls in the presence of hydrogen peroxide is demonstrated. The performance of a stirred membrane reactor containing soluble purified SBP was compared with a batch stirred reactor containing raw soybean seed‐hulls. The purified enzyme reactor proved to be ineffective while excellent results were obtained with the crude seed‐hulls for the removal of phenol and 2‐chlorophenol. Four sequential batch reactors containing raw seed‐hulls achieved greater than 96% removal of phenol with a retention time of 20 min in each reactor. A single batch reactor containing raw seed‐hulls was effective in removing greater than 98.5% of 2‐chlorophenol (initially at 1000 ppm) in less than 15 min. The performance of these reactors is comparable to existing HRP‐based technology. The stability of the soybean peroxidase (SBP) enzyme was also examined in the presence of detergents (SDS, Tween 20 and Triton X‐100). Low concentrations of the detergents significantly increased the enzyme activity and higher concentrations of detergents (up to 20% w/v) did not inactivate the SBP enzyme. These results demonstrate that SBP has good potential for the treatment of phenol contaminated solutions. © 1999 Society of Chemical Industry     

Anaerobic digestion of liquid dairy manure using a sequential continuous‐stirred tank reactor system

BACKGROUND: Anaerobic digestion of liquid manure from flush dairy operations is an alternative to manure management practices with environmental benefits and producing biogas. A unique sequential reactor system was used to study the anaerobic digestion (AD) of flush dairy manure with the aim of determining (1) the effects of organic strength of the influent on AD performance; (2) whether phase separation is beneficial to treatment and AD design; and (3) whether there is any difference between completely mixed and plug‐flow approaches to implementing the AD process. RESULTS: The influent with high organic strength resulted in higher levels of biogas production and chemical oxygen demand (COD)/solids removal. When the manure stream is used as influent for the anaerobic digestion, the phenomenon of two‐stage anaerobic digestion process does not exist because the stream contained high levels of alkalinity and volatile fatty acids. The biogas production and COD/solids destruction achieved by plug‐flow and completely mixed reactor were very similar when treating the liquid manure stream. CONCLUSION: The organic strength of the influent significantly influenced AD performance. The plug‐flow reactor and the completely mixed reactor had a similar AD performance. For the type of manure and organic loading rate investigated, the results give indications for designing an AD process in flush dairy operations. Copyright © 2007 Society of Chemical Industry