A FUNDAMENTAL ANALYSIS OF CONTINUOUS FLOW BIOREACTOR AND MEMBRANE REACTOR MODELS WITH TESSIER KINETICS

In this research we analyze the steady-state operation of a continuous flow bioreactor, with or without recycle, and an idealized or nonidealized continuous flow membrane reactor. The model extends to include a fixed bed reactor where a fraction of the biomass is detached by the flow. The reaction is assumed to be governed by Tessier growth kinetics. We show that a flow reactor with idealized recycle has the same performance as an idealized membrane reactor and that the performance of a nonidealized membrane reactor is identical to that of an appropriately defined continuous flow bioreactor with nonidealized recycle. The performance of all three reactor types can therefore be obtained by analyzing a flow reactor with recycle. The steady states of the recycle model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained.     

ANALYSIS OF SUBSTRATE CONVERSION IN ABUBBLE COLUMN BIOREACTOR WITH A MEMBRANE FILTER FOR CONTINUOUS CULTURE

The steady-state performance, mainly with respect to substrate conversion, of a bubble column bioreactor with substrate limited microbial growth and cell recycle through a membrane filter is investigated numerically. The dispersion model and the Monod equation are employed for describing flow behaviour and cell growth rate in the reactor, respectively. Moderate longitudinal mixing causes a favourable effect on the substrate conversion. Such an effect is enhanced with increasing recycle ratio and separator concentration efficiency. There exists an optimum Peclet number to maximize the substrate conversion. The relation between the critical recycle ratio at which the optimum Peclet number becomes zero and the corresponding exit substrate concentration is presented.     

微气泡耦合生物反应器的研究进展

微气泡具有气液接触面积大、气体溶解速率快、上升速度慢和水中停留时间长等理化特征,非常适合于高气液传质效率需求的生物发酵过程。本文介绍了能够耦合生物反应器的几种微气泡发生装置,分别为微气泡分散器、微孔膜、流体振荡器耦合微孔膜和微气泡曝气搅拌桨;并简述了微气泡发生装置耦合搅拌式生物反应器、气升式生物反应器和生物膜反应器在生物反应过程的应用进展;最后回顾了二氧化碳微气泡在生物反应器的应用研究进展。指出微气泡耦合生物反应器的研究仍处于起步阶段,在放大规律和能耗方面仍处于研究空白。微气泡耦合生物反应器的发展对工业生物技术、石油化工、污水处理和资源再利用等的发展具有重要的意义。     

Application of hydrogen-permselective Pd-based membrane in an industrial single-type methanol reactor in the presence of catalyst deactivation

This work presents application of palladium-based membranes in a conventional single-type methanol reactor. A novel reactor configuration with hydrogen-permselective Pd and Pd–Ag membrane are proposed. In this configuration the reacting synthesis gas is fed to the shell side of reactor while the high pressure product is routed from recycle stream through tubes of the reactor in a co-current mode with reacting gas. The reacting gas is cooled simultaneously with recycle gas in tube and saturated water in outer shell. The permselective palladium layer on inner tube allows hydrogen to penetrate from the tube side to the reaction side. In this work, the results of two types of novel membrane reactors are compared with a conventional methanol synthesis reactor at identical process conditions. Also the effect of key parameters such as membrane thickness, reaction and tube side pressure, ratio of tube side flow rate to reaction side flow rate on performance of reactor are investigated. The steady-state and quasi-steady-state simulations results show that there are favorable profiles of temperature and methanol mole fraction along the reactor in proposed reactor relative to conventional reactor system. Therefore using this novel configuration in industrial single-type methanol reactor improves methanol production rate.     

Emulsion polymerization kinetics and reactor design. IV. Continuous-flow operation with recycling

A new mathematical model with a correction for radical capturing efficiency in a continuous emulsion polymerization with recycle flow has been proposed. These performance equations predict the conversion as well as molecular weight distribution of the polymer product during the continuous-flow operation. Experimental results obtained with vigorous mixing associated with a premixer are in best agreement with the theoretical prediction. In certain situations, the recycling provides a means for obtaining a higher degree of back-mixing with a normal flow reactor. However, it is difficult to obtain a high conversion of monomer by a continuous emulsion polymerization operation even with a long residence time. Theoretical and experimental average degrees of polymerization of polymer leaving the reactor are progressively displaced toward smaller values with greater mean residence time. According to the calculations based on our kinetic model the ratio M?_w/M?_n in the continuous emulsion polymerization remains constant regardless of mean residence time.     

The effects of modes of hydrogen input and reactor configuration on reaction rate and H2 efficiency in the catalytic hydrogenation of alkynol to alkenol

Hydrogenation often involves three phases where hydrogen-on-demand is the typical mode of operation in industrial scale reactors. In research labs and publications, however, continuous hydrogen flow has been used. This paper investigates the effect of such modes of operation on reaction rate using a selective hydrogenation of 3-butyn-2-ol over Pd/Al₂O₃ to obtain 3-buten-2-ol as the model reaction. The two modes of operation were first tested in a commercial PARR stirred tank reactor and then repeated in an oscillatory baffled reactor (OBR) in order to validate the experimental results. Our investigation demonstrates that an enhanced reaction performance and 10 times better H₂ efficiency were obtained when the pressure was maintained constant during the reaction by feeding gas as required, ie hydrogen-on-demand mode. The method of a continuous flow of hydrogen in hydrogenation means that excess hydrogen is vented out when operating at ambient pressures or builds up at elevated pressures. Our work also enables a comparison of reactor designs on reactor performance, and three times higher H₂ efficiency and 2.3 times shorter residence time were achieved when using the OBR instead of the PARR due to its enhanced and uniform mixing, regardless of the mode of operation.     

Minimum tank volumes for CFST bioreactors in series

The primary reactor type currently used in the production of microorganisms or microbial products is the stirred tank reactor (STR). If operated on a continuous flow basis (CFSTR) they become similar in performance to the primary reactor configuration used in most of the chemical industry. In this work, microbial kinetics are considered in the design of CFSTRs in series. An equation is derived to predict the minimum possible total residence time to achieve any desired substrate conversion. The equation permits the use of a wide variety of growth kinetic models and is applied here to Monod, substrate inhibition and product inhibition cases. For the majority of cases, it is found that three optimally designed CFSTRs in series provide close to the minimum possible residence time for any desired substrate conversion. A comparison to the use of a PFR is made for cases of both no-recycle and biomass recycle to the CFSTR train. It is found that three CFSTRs, which are not equi-volume, provide the same required total mean residence time as a PFR for Monod kinetics, but are significantly superior (i.e., less total volume required) to a PFR for substrate-inhibited growth.     

Continuous hydrolysis of olive oil by lipase in microporous hydrophobic membrane bioreactor

Continuous hydrolysis of olive oil byCandida cylindracea’s lipase was studied in a microporous hydrophobic membrane bioreactor. Olive oil and buffer solution, fed continuously through two compartments partitioned by membrane, caused reaction at the interface of lipase-adsorbed membrane and buffer solution. Fatty acid was obtained in a single phase without being mixed with components of other phases. At all mean residence times, countercurrent flow mode was superior to cocurrent one. The lipase was adsorbed onto the membrane, and its adsorption was suggested to be partially specific from the experiments with enzymes having various levels of purity. The percent hydrolysis depended hyperbolically on the interfacial enzyme concentration. The hydrolysis seemed to be limited by diffusion of fat or fatty acid through the micropores of the membrane at higher interfacial enzyme concentrations. The lipase was stabilized significantly by glycerol added to the buffer solution. Satisfactory performance of the membrane bioreactor was obtained in a longterm continuous operation which lasted for 24 days by feeding buffer-glycerol (18.0%) solution over the adsorbed lipase. The operational half-life of the adsorbed enzyme was 15 days at 40 C.     

Mixing performance comparison of milliscale continuous high‐shear mixers

Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.

     

Modeling of poly(ethylene terephthalate) reactors: 4. A continuous esterification process

A mathematical model has been developed for the direct, continuous esterification process. Influence of process and operational variables, including temperature distribution, residence time distribution, bis(hydroxyethyl)terephthalate recycle, pressure, and ethylene glycol (EG) to terephthalic acid ratio on the reactor performance have been investigated in a range as close to industrial practice as possible. The variables influencing the amount of EG reflux (which governs the energy economy) and side products (which govern the product quality) have been discussed. This investigation provides an analysis of a continuous, direct esterification process, and the results indicate strategies for optimizing productivity and product quality.     

Continuous production of penicillin-g by penicillium chrysogenum cells immobilized on celite biocatalyst support particles

Celite R-630, a commercially available catalyst support, was used successfully in the batch and continuous production of Penicillin-G by mycelial cells of Penicillium chrysogenum. As an extension of previous work, the productivity of a 1.2 L three phase fluidized bed bioreactor using the Celite support was compared directly with the same reactor in which cells had been immobilized inside a larger carrageenan support matrix. With Celite particles, maximum yields and specific reaction rates for continuous reactor runs were 0.11 g Pen-G (K⁺)/g lactose and 0.05 mmol Pen-G/h/g protein respectively. These results were similar to those obtained with carrageenan beads. However, on a reactor volume basis, Celite was five times more productive than carrageenan. Results are discussed in terms of the potential for using Celite in industrial bioreactor systems.     

Segmented thin-gap flow cells for process intensification in electrosynthesis

Design calculations are presented for a single-pass high-conversion electrochemical reactor suitable for process intensification in electroorganic synthesis. The key feature of the design is the use of a segmented working electrode, combined with a small anode—cathode gap. Each working electrode segment is operated at an optimal local current density, defined with respect to the local diffusion—limited current density of the reacting species. Two reactor configurations are considered:(i) an adiabatic reactor, and (ii) an isothermal reactor with integrated heat exchange. Calculated results for the devices in a classical electroorganic synthesis system, the methoxylation of 4-methoxy-toluene, are presented and the general features and performance characteristics of the cell are compared with those of a more conventional capillary-gap cell, currently used industrially. For an electrode gap of 0.1 mm, the average current density attainable in the novel design is of the order of 2700 A m⁻² in the adiabatic reactor and of the order of 7100 A m⁻² in the isothermal reactor, respectively, 5 and 14 times higher than the current densities applied in the current industrial process. In addition to process intensification, other advantages of the proposed technology are the absence of reactant recycle, short residence times and plug flow of the reagents, all of which contribute to improved process selectivity.     

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.     

Influence of reaction temperature on direct esterifications in a continuous recycling process between terephthalic acid and ethylene glycol

Simulations were carried out with a continuous recycle esterification model for the terephthalic acid–ethylene glycol (TPA–EG) system proposed previously. The influence of reaction temperatures, recycle ratios, and residence times on the oligomer characteristics was examined and the following results were obtained: (1) The main reactions proceed more under higher reaction temperatures, but the side reactions on diethylene glycol (DEG) proceed further than do the main reactions. (2) The higher residence time ratio of the first reactor to the total results in the proceeding of esterifications, which becomes remarkable as the temperature becomes high. (3) As the recycle ratio becomes high, the esterfications proceed, but in the very high degree of esterification, the tendency is reversed. (4) The characteristics of oligomer are almost the same at the same degree of esterification, independent of the reaction conditions. © 1994 John Wiley & Sons, Inc.     

Continuous solid-state fermentation as affected by substrate flow pattern

The performance of continuous solid state bioreactors having two different solid substrate flow patterns, namely plug flow and completely mixed flow, is quantified for both steady-state and transient operation using a simple mathematical model. The core assumption is that each substrate particle acts as an infinitesimal bioreactor. The residence time distribution of the particles is considered in the formulation of the equations for the mixed-flow bioreactor and the error that results from neglecting it is investigated by comparing the simulation results with those of a completely mixed, continuous bioreactor for submerged liquid fermentation (a chemostat). The model is extended to include autolysis, inter-particle inoculation and contamination. Plug flow is shown to have superior performance when high product concentration is needed, if autolysis or other undesirable late emerging phenomena occur, and when non-sterile fermentation using slow-growing microorganisms is undertaken.     

Decolorization of organic dyes by Irpex lacteus in a laboratory trickle‐bed biofilter using various mycelium supports

BACKGROUND: Dyes used in textile industries and released to their wastewaters are serious ecological problems as they are hard to degrade by common means used in wastewater treatment plants. White‐rot fungi can biodegrade textile dyestuffs using their extracellular enzyme system. However, it is difficult to keep them in functional form in conventional wastewater treatment systems, because of their specific nutritional and physiological requirements. Selection of a suitable bioreactor type and mode of operation are crucial for successful implementation of white rot fungi in waste water treatment processes. RESULTS: Both Remazol Brilliant Blue R (RBBR) and Reactive Orange 16 (RO16) were decolorized efficiently in the trickle‐bed reactor. A degree of decolorization exceeding 80% was achieved within 2 days with all mycelium carriers and both dyes. In reactors packed with plastic kitchen scourers and luffa sponge slices the decolorization degree reached 90% within 2 days. The initial rate of decolorization of RBBR dye was notably higher than the rate of RO16 decolorization. The lowest liquid hold‐up value (1–1.5%) was achieved in the reactor packed with the plastic kitchen scourers, the largest hold‐up value (3–5%) was observed in the reactor filled with luffa sponge. The longest mean retention time, 430 s, was achieved in the reactor with the luffa carrier at a liquid flow rate of 6.81 cm³ min^?1; the shortest mean retention times (10–20 s) were achieved in the reactor filled with the plastic kitchen scourers. Broad liquid residence time distributions were observed in tracer experiments at all volumetric flow rates. CONCLUSIONS: The ability of I. lacteus to secrete laccase and manganese peroxidase enzymes in a trickle‐bed bioreactor with three mycelium carriers was proved and quantified experimentally. The decolorization capability of the I. lacteus mycelium was only marginally influenced by the kind of carrier used. Basic operational characteristics of the reactor—residence times, axial dispersion and liquid hold‐up—were determined at various liquid flow rates. Copyright © 2009 Society of Chemical Industry     

Application of KHX Impeller in a Low-shear Stirred Bioreactor☆

In our previous work, a low-shear stirred bioreactor was explored. With a pitched blade turbine impeller downflow (PBTD) used, the shear stress generated is high compared with that in some low shear ax...     

Simultaneous removal of organic substances and nitrogen using amembrane bioreactor seeded with anaerobic granular sludge under oxygen-limited conditions

An innovative process, the oxygen-limited membrane bioreactor seeded with anaerobic granular sludge, wasproposed and its performance investigated for concurrent removal of organic substances and nitrogen from synthetic domestic wastewaters. An air diffuser was installed just above the granular sludge bed to supply air to the reactor at an intermittent mode. The internal recycle from the upper part of the reactor to the bottom was introduced to provide the granular sludge bed under the oxygen-limited conditions. The oxygen addition rates were controlled at 3-4 g O₂ 1⁻¹d⁻¹. The total COD removal efficiency of more than 94% was achieved throughout the whole operation period. N was removed through the simultaneous nitrification and denitrification process that took place in the granular sludge bed. TN levels decreased with the decrease of ammonium levels, indicating that nitrification was the rate-limiting step. The TN removal efficiency reached 80-91% at an hydraulic retention time of 15 h. Nitrate was scarcely detected and nitrite was the main NO_x-N species in the effluent, indicating that nitrite oxidizers were inhibited in the system.     

The reversed two-environment model of micromixing and growth processes

A reversed two-environment model of micromixing in a flow reactor in which the feed enters a maximum mixedness environment and then passes to a segregated environment is presented. The performance equations for an arbitrary residence time distribution are developed and employed to analyse the behaviour of growth processes in a continuous stirred tank reactor under intermediate states of micromixing. The results, which are bounded by the two extremes of micromixing, indicate that micromixing is important in growth processes and that segregation appears to reduce the rate of cell production.     

Oxidation of ethanol vapors in a spiral bioreactor

A fixed film spiral bioreactor containing immobilized activated sludge microorganisms has been used to degrade ethanol vapors. The effect of air flow rate, and ethanol feed concentration on elimination capacity has been investigated. Air flow rate is varied in the range from 2?34 to 40?0 dm³ min^?1. Ethanol feed concentration is varied in the range from 600 to 7000 ppmv. In the concentration range studied, the elimination capacity increased proportionately with an increase in feed concentration. However, the elimination capacity decreased significantly at flow rates greater than 20 dm³ min^?1 owing to insulfficient residence time. The maximum elimination capacity observed was 185 g ethanol h^?1 m^?3 of reactor volume. Critical ethanol loading, defined as the maximum loading to achieve greater than 99% elimination at various residence times have been determined. These data are extremely useful in designing bioreactor for large scale applications.