Scale-up Criteria Research Articles

Progress after three years of BioMinE—Research and Technological Development project for a global assessment of biohydrometallurgical processes applied to European non-ferrous metal resources

BioMinE is an integrated project under the sixth framework programme of research supported by the European Commission, which started in November 2004 and will last until October 2008 (Ref. NMP2-CT-2005-500329). It is dedicated to the evaluation of biohydrometallurgy to improve the exploitation of the European non-ferrous metal resources in a sustainable way. At the end of 2007, the Consortium of BioMinE comprised 37 partners from industry (13 including 6 Small or Medium Enterprises), research organisations (8), universities (15), and government (1). The participants are from 13 EU member states and from Serbia and South Africa (INCO Countries). For more details see http://biomine.brgm.fr. The three main kinds of resources considered for bioleaching studies are: - Copper polymetallics (concentrates and tailings), - Zinc polymetallics (zinc and zinc polymetallic concentrates) - Secondary wastes (tailings, rock and metallurgical wastes, etc.) For each of these resources, amenability studies of application of bioleaching technologies by various approaches have been undertaken or still ongoing. Further processing assessment will be conducted up to the demonstration scale. Technological improvements have been made to apply bioleaching in the context of the European resources in terms of complexity and sustainability requirements. The relevant fundamental studies covering bio-prospecting, molecular ecology, biochemistry, and genetics areas aimed at improving the understanding and the control of the selected technologies have given original results. Much progress has also been obtained in the use of the microbial sulfate-reducing process to polish effluents and to recover metals from leachates containing low concentrations of metals. The finding of micro-organisms thriving at low and high temperature, respectively 8 and 65 °C, leads to an extension of the application range of the process. It has been also observed that this process could be pushed down to pH 4.5 and 4 creating opportunities of selective metal recovery as metal sulphides. It has also been demonstrated that sulphate can be removed at high concentrations, as well as arsenic or selenium. The next step in this work is pilot testing. This will allow to determine scale-up criteria and to assess the residual metal concentration under actual conditions. The pilot-scale demonstration operations, as well as the techno-economic and comparative sustainability assessments will be achieved during 2008, the last year of the project. The prototypes of the learning objects for training about biohydrometallurgy accessible by internet have been elaborated. A public output of this work is accessible at http://wiki.biomine.skelleftea.se/wiki. The basic knowledge thus delivered is aimed at disseminating the understanding of the origins and use of biohydrometallurgy. Contacts with mining operators in Europe have been taken and collaboration schemes have been established in various ways according to the respective contexts. When a high potential of technical involvement could be foreseen, a direct participation of the mining operators in the project was favoured, this led to integrate KGHM (Pol), Boliden (Sw) and Copper Institute of Bor (Serbia) into the consortium of partners. When no direct technical commitment was conceivable at the first stage, collaboration was established with companies with the most urgent requirement to have access to the relevant resource.

Scaling Up the Spray Drying Process from Pilot to Production Scale Using an Atomized Droplet Size Criterion

The purpose of this study was to investigate the possibility of producing identical powders in pilot and production scale spray drying equipment by matching the droplet size distributions produced by two differently sized atomizers. Particles were prepared by spray drying solutions of acetaminophen and polyvinylpyrrolidone K-30. The success of the up-scaling was evaluated by comparing the powders in terms of particle size distribution (laser diffraction), crystallinity (XPRD) and morphology (SEM). Furthermore, the influence of process parameters on other product characteristics such as stability and residual volatile content was also evaluated. The spray drying experiments resulted in spherical, amorphous particles with volumetric median diameters of typically 4-10 microm for pilot scale and 4-30 microm for production scale. The results showed that particles with similar morphology and crystallinity could be produced in the two applied spray dryers. However, scale-up based purely on matching droplet size distributions was not feasible. The scale-up criterion did not account for the differences between the droplet-drying gas mixing and residence time distribution within the two spray dryers. Therefore, production scale experiments are required in order to obtain similar product characteristics as in pilot scale.

Scale‐up of Escherichia coli growth and recombinant protein expression conditions from microwell to laboratory and pilot scale based on matched kLa

Fermentation optimization experiments are ideally performed at small scale to reduce time, cost and resource requirements. Currently microwell plates (MWPs) are under investigation for this purpose as the format is ideally suited to automated high-throughput experimentation. In order to translate an optimized small-scale fermentation process to laboratory and pilot scale stirred-tank reactors (STRs) it is necessary to characterize key engineering parameters at both scales given the differences in geometry and the mechanisms of aeration and agitation. In this study oxygen mass transfer coefficients are determined in three MWP formats and in 7.5 L and 75 L STRs. k(L)a values were determined in cell-free media using the dynamic gassing-out technique over a range of agitation conditions. Previously optimized culture conditions at the MWP scale were then scaled up to the larger STR scales on the basis of matched k(L)a values. The accurate reproduction of MWP (3 mL) E. coli BL21 (DE3) culture kinetics at the two larger scales was shown in terms of cell growth, protein expression, and substrate utilization for k(L)a values that provided effective mixing and gas-liquid distribution at each scale. This work suggests that k(L)a provides a useful initial scale-up criterion for MWP culture conditions which enabled a 15,000-fold scale translation in this particular case. This work complements our earlier studies on the application of DoE techniques to MWP fermentation optimization and in so doing provides a generic framework for the generation of large quantities of soluble protein in a rapid and cost-effective manner.

Scale-up of a fixed bed electrochemical reactor consisting of parallel screen electrode used for p-aminophenol production

The behavior of a fixed bed consisting of amalgamated copper screens has been investigated for the electrolytic reduction of nitrobenzene to p-aminophenol under potentiostatic condition (controlled potential). The preparative electrolysis of nitrobenzene was carried out using supporting electrolytes consisting of 2 M H 2SO 4 in a solution of 50% 2-propanol/50% water (v/v). The criterion for scale-up ( ɛ n ) was determined through application of one-dimensional model. The polarization curves that describe the reduction of nitrobenzene to p-aminophenol were obtained experimentally by using a pilot scale for different nitrobenzene concentrations and flow rates of catholyte. It was found that the effectiveness factor ( ɛ n ) increases with increasing flow rate, and decreasing nitrobenzene concentration. An optimum thickness of bed equal to 0.6 cm was obtained, in which the effectiveness factor not less than 0.588, to ensure a well distribution of current and potential.

Scale-Up of Solids Distribution in Slurry, Stirred Vessels Based on Turbulence Intermittency

Scale-up criteria for obtaining the same vertical concentration profile of particles in agitated, dilute suspensions are considered. Previous experiments in two sizes of high aspect ratio vessels stirred by multiple impellers (either pitched blade or Rushton turbines) gave n = 0.93 in the scale-up relationship 32 ND n = constant. This result is intermediate between constant power per unit volume (n = 2/3) and constant tip speed (n = 1), although closer to the latter. It is now suggested that intermittent turbulent fluctuations greater than their average values play a part in maintaining vertical concentration gradients. An analysis of solids suspension by intermittent turbulence gives n ≈ 0.93. This value is also supported by additional experimental data as well as by new CFD results.

CFD modelling and scale-up of Confined Impinging Jet Reactors

Confined Impinging Jet Reactors (CIJRs) are appealing devices for precipitation of nanoparticles because of their high mixing efficiency. In fact, since precipitation processes are generally very fast, mixing plays a crucial role and it is of great importance to operate under very fast mixing conditions. In this work mixing and reaction in CIJRs are studied by means of Computational Fluid Dynamics (CFD). Mixing at the molecular level is modelled with a presumed Probability Density Function (PDF) approach: the Direct Quadrature Method of Moments coupled with the Interaction by Exchange with the Mean (DQMOM-IEM) model. The influence of operating conditions and reactor geometry on mixing is also evaluated and a scale-up criterion for CIJRs is developed, showing that scaling up by means of CFD is a practicable path, worth of further investigation.

The behavior of pilot trickle-bed reactor under periodic operation

Hydrogenation of olefins presented in pyrolysis gasoline to prevent gum-formation and catalyst deactivation in subsequent processes is usually adopted in trickle-bed reactor. To overcome external limitations and to improve operation safety, a periodic liquid feed modulation can be used. The goal of this work was to evaluate scale-up criteria from laboratory measurement to experiments in bench and pilot trickle-bed reactor. Toluene solution of styrene and/or dicyclopentadiene hydrogenation on palladium egg-shell type catalyst was chosen as model reactions. Hydrodynamic parameters, namely, wetting efficiency and pressure drop were evaluated both for continuous bench and periodic operated pilot-scale reactors. Experiments confirmed presumptions of influence of catalyst wetting in bench reactor and increase of pilot reactor productivity of styrene hydrogenation by 30% for periodic operation in comparison with steady state one.

Scale‐up criteria of square tank surface aerator

Oxygen transfer rate and the corresponding power requirement to operate the rotor are vital for design and scale-up of surface aerators. Present study develops simulation or scale-up criterion correlating the oxygen transfer coefficient and power number along with a parameter governing theoretical power per unit volume (X, which is defined as equal to F(4/3)R(1/3), where F and R are impellers' Froude and Reynolds number, respectively). Based on such scale-up criteria, design considerations are developed to save energy requirements while designing square tank surface aerators. It has been demonstrated that energy can be saved substantially if the aeration tanks are run at relatively higher input powers. It is also demonstrated that smaller sized tanks are more energy conservative and economical when compared to big sized tanks, while aerating the same volume of water, and at the same time by maintaining a constant input power in all the tanks irrespective of their size. An example illustrating how energy can be reduced while designing different sized aerators is given. The results presented have a wide application in biotechnology and bioengineering areas with a particular emphasis on the design of appropriate surface aeration systems.

Hydrodynamics and scale up in Rushton turbine flotation cells: Part 2. Flotation scale-up for laboratory and pilot cells

A series of flotation experiments was carried out in three Rushton turbine cells of volumes 2.25, 10 and 50 dm 3 using hydrophobic quartz particles to determine a set of scale-up criteria that would produce the same size-by-size flotation rate constants. Flotation was performed at a constant Sauter mean bubble diameter over a range of superficial gas velocities and impeller rotational speeds. The overall flotation rate constant increased linearly with increasing superficial gas velocity (and hence bubble surface area flux). The rate constant also increased linearly with increasing energy dissipation, until a maximum value was reached. A further increase in energy dissipation had little effect on the rate constant. The dependency of the rate constant on energy dissipation is a reflection of the size range and hydrophobicity of the particles used in this study. Good agreement was obtained between the experimental results and those predicted by a fundamental flotation model using experimentally measured values for mean energy dissipation and the Sauter mean bubble diameter. The bubble velocity was adjusted to obtain the best fit of the experimental data. This inferred bubble velocity was found to increase with increasing superficial gas velocity and decrease with increasing impeller rotational speed. To achieve scale-up of the flotation rate constants, maintaining a constant bubble surface area flux was used as one criterion. The other operating variable was the impeller rotational speed, which, for successful scale-up was adjusted so that N 3 D was constant over the cell volume range. This enabled the measured mean energy dissipation for the three cells to be held constant as the cell volume increased.

Scale up of a viscous fungal fermentation: Application of scale‐up criteria with regime analysis and operating boundary conditions

The scale up of the novel, pharmaceutically important pneumocandin (B(0)), from the filamentous fungus Glarea lozoyensis was successfully completed from pilot scale (0.07, 0.8, and 19 m(3)) to production scale (57 m(3)). This was accomplished, despite dissimilar reactor geometry, employing a combination of scale-up criteria, process sensitivity studies, and regime analysis using characteristic time constants for both oxygen mass transfer and bulk mixing. Dissolved oxygen tension, separated from the influence of agitation by gas blending at the 0.07 m(3)-scale, had a marked influence on the concentrations of pneumocandin analogs with different levels of hydroxylation, and these concentrations were used as an indicator of bulk mixing upon scale up. The profound impact of dissolved oxygen tension (DOT) (low and high levels) on analog formation dictated the use of constant DOT, at 80% air saturation, as a scale-up criterion. As a result k(L)a, Oxygen uptake rate (OUR) and hence the OTR were held constant, which were effectively conserved across the scales, while the use of other criterion such as P(g)/V(L), or mixing time were less effective. Production scale (57 m(3)) mixing times were found to be faster than those at 19 m(3) due to a difference in liquid height/tank diameter ratio (H(L)/D(T)). Regime analysis at 19 and 57 m(3) for bulk mixing (t(c)) and oxygen transfer (1/k(L)a) showed that oxygen transfer was the rate-limiting step for this highly shear thinning fermentation, providing additional support for the choice of scale-up criterion.

Development and commercial demonstration of the BioCOP™ thermophile process

The paper describes the engineering development of the BioCOP™ Process, from pilot-scale to full-scale commercial demonstration at the Chuquicamata Mine in Chile, with a design production rate of 20 000 t copper per annum. BioCOP™ Process is owned by BHP Billiton. The BioCOP™ Process has been specifically developed for treatment of concentrates not suitable for commercial smelting due to the content of deleterious elements, such as arsenic, which is harmful to the environment. The process utilises thermophilic microorganisms operating at temperatures up to 80 °C to leach copper sulphide mineral concentrates. The copper is subsequently recovered by conventional solvent extraction and electrowinning, producing a high value copper metal product. The paper describes the importance of staged development to ensure correct definition of scale-up criteria for commercial plant design. The design and operation of the Commercial Demonstration Plant is also described a “World First” for bioleaching using thermophilic microorganisms for commercial treatment of primary copper sulphide concentrates.

Fluid mixing in shaken bioreactors: Implications for scale-up predictions from microlitre-scale microbial and mammalian cell cultures

Pressures on pharmaceutical companies to speed bioprocess development have led to significant interest in small scale, parallel experimentation. A particular focus is cell cultivation and the optimisation of protein synthesis because of the number of biological and engineering variables involved. In this work, we briefly review the current understanding of mixing and mass transfer phenomena in shaken bioreactors with a view to defining criteria for the scale-up of results obtained in shaken microwell systems to conventional laboratory scale. Scale-up approaches are illustrated for two different cell cultures. The first involves an automated microscale process ( 1000 μ l ) for the aerobic fermentation of E. coli JM107:pQR706 overexpressing transketolase (TK) which is subsequently used for asymmetric carbon–carbon bond formation. The kinetics of both the fermentation and bioconversion stages are first quantified as a function of fermentation medium composition (LB or LB-glycerol) and shaking frequency with oxygen transfer rates being identified as rate limiting in certain cases. Successful scale-up of the microwell process (in terms of maximum cell growth rate, biomass yield and specific TK activity) to a 1.4 l scale mechanically stirred bioreactor is then demonstrated based on experiments performed at constant k L a values. The second process investigated involved antibody production in suspension cultures of VPM8 hybridoma cells. Initial results suggest that experiments performed at constant mean energy dissipation rates provide a satisfactory basis for scale translation from shaken microwells ( 800 μ l ) to conical flasks (100 ml) and are indicative of results obtained in a mechanically stirred bioreactor (3.5 l). Overall this work provides an initial insight into the engineering characterisation of shaken bioreactors and how key parameters may be used to define suitable scale-up criteria for different cell cultures.

Scale-up of L-lactic acid production by mutant strain Rhizopus sp. MK-96-1196 from 0.003 m 3 to 5 m 3 in airlift bioreactors

In order to study the feasibility of commercial-scale L-lactic acid production by Rhizopus sp. MK-96-1196 using large scale airlift bioreactors (ALBs), a scale-up study from 0.003 m3 to 5 m3 ALB was carried out using oxygen transfer rate (OTR) as the scale-up criterion. Enhanced L-lactic acid production was achieved at OTRs higher than 0.28 (g-O2/l/h) irrespective of the scale of the bioreactor in question: in the range of 0.003 m3 to 5 m3, more than 90 g/lL-lactic acid was produced with a yield of approximately 80%, based on the initial glucose concentration. In future research, we plan to design an ALB greater than 3000 m3 (working volume: 2000 m3) for further studies on the production of L-lactic acid in large quantities.

Scale-up criteria for an injector with a confined mixing chamber during precipitation with a compressed-fluid antisolvent

Four scaling criteria were used to scale-up the precipitation with a compressed-fluid antisolvent (PCA) process from the laboratory to the pilot plant scale using an injector with a confined mixing chamber. The scale-up criteria consisted of maintaining either: (1) constant Reynolds numbers, (2) constant axial velocity, (3) constant residence time and suspension density, or (4) a constant energy dissipation rate, as process scale was changed. Experiments were conducted in a semi-continuous PCA flow apparatus and the biodegradable polymer poly ( l-lactic acid) (PLLA) was used as the model solute. Successful scale-up was based on maintaining measured particle size distributions for PLLA microparticles as process scale was increased. The scale-up criteria of maintaining constant Reynolds numbers or constant axial velocities were not sufficient to ensure equivalent process performance during scale-up. Scale-up at constant Reynolds number resulted in a 40% increase in the average PLLA diameter with a feed concentration of 0.125 wt% PLLA, and a 36% increase in the average diameter was calculated when the feed concentration was increased to 0.25 wt% PLLA. Scale-up maintaining a constant axial velocity resulted in a 32% increase in the average PLLA diameter with a feed concentration of 0.125 wt% PLLA. The shift in the PLLA particle size distributions towards larger size fractions with this criteria was attributed to a low energy dissipation rate in the confined mixing chamber, which directly affected mixing quality and secondary nucleation mechanism(s) in the confined mixing chamber. Scaling the injector with a constant residence time and suspension density, or a constant energy dissipation rate resulted in similar PLLA particle size distributions at each scale of operation, and was attributed to maintaining comparable mixing quality and similar precipitation kinetics with a change in process scale.

Transcriptional and metabolic response of recombinant Escherichia coli to spatial dissolved oxygen tension gradients simulated in a scale‐down system

Escherichia coli, expressing recombinant green fluorescent protein (GFP), was subjected to dissolved oxygen tension (DOT) oscillations in a two-compartment system for simulating gradients that can occur in large-scale bioreactors. Cells were continuously circulated between the anaerobic (0% DOT) and aerobic (10% DOT) vessels of the scale-down system to mimic an overall circulation time of 50 s, and a mean residence time in the anaerobic and aerobic compartments of 33 and 17 s, respectively. Transcription levels of mixed acid fermentation genes (ldhA, poxB, frdD, ackA, adhE, pflD, and fdhF), measured by quantitative RT-PCR, increased between 1.5- to over 6-fold under oscillatory DOT compared to aerobic cultures (constant 10% DOT). In addition, the transcription level of fumB increased whereas it decreased for sucA and sucB, suggesting that the tricarboxylic acid cycle was functioning as two open branches. Gene transcription levels revealed that cytrochrome bd, which has higher affinity to oxygen but lower energy efficiency, was preferred over cytochrome bO3 in oscillatory DOT cultures. Post-transcriptional processing limited heterologous protein production in the scale-down system, as inferred from similar gfp transcription but 19% lower GFP concentration compared to aerobic cultures. Simulated DOT gradients also affected the transcription of genes of the glyoxylate shunt (aceA), of global regulators of aerobic and anaerobic metabolism (fnr, arcA, and arcB), and other relevant genes (luxS, sodA, fumA, and sdhB). Transcriptional changes explained the observed alterations in overall stoichiometric and kinetic parameters, and production of ethanol and organic acids. Differences in transcription levels between aerobic and anaerobic compartments were also observed, indicating that E. coli can respond very fast to intermittent DOT conditions. The transcriptional responses of E. coli to DOT gradients reported here are useful for establishing rational scale-up criteria and strain design strategies for improved culture performance at large scales.

Packed-bed reactor for the integrated biodegradation of cyanide and formamide by immobilised Fusarium oxysporum CCMI 876 and Methylobacterium sp. RXM CCMI 908

Experiments were carried out to develop the technological basis for the integrated biodegradation of cyanide and formamide. The ability of both Fusarium oxysporum CCMI 876 and Methylobacterium sp. RXM CCMI 908 to transform cyanide and formamide was analysed and characterised. The K m i for cyanide hydratase in the immobilised Fusarium oxysporum CCMI 876 was 19 ± 4 mM of cyanide and the V max i was 21 ± 5 μmol min −1 g −1 (DW) cells. For the entrapped Methylobacterium sp. RXM CCMI 908 the values of the apparent reaction kinetics were K m i = 1.7 ± 0.3 mM of cyanide and the V max i = 20 ± 2 μmol min −1 g −1 (DW) cells. These data were used to design and operate a two-catalyst system to balance cyanide and formamide transformations and assess the system stability. The cyanide was degraded by Fusarium oxysporum CCMI 876 at a rate of 0.059 mM h −1 leading to 96% cyanide conversion and leaving a residual 0.21 mM. Average 3.76 mM of formamide and 0.34 mM of formate were formed. This effluent is contacted with Methylobacterium sp. RXM CCMI 908 which used 84% of formamide. Then this compound drops to an average value of 0.62 mM. In parallel, formate builds up to nearly 12-fold the initial concentration, correlating with the amount of formamide used. The two systems were merged in a single system which design involved a scale-up criterion and the degradation profiles along the system were determined.

Optimization and scale up of industrial fermentation processes

To increase product yields and to ensure consistent product quality, key issues of industrial fermentations, process optimization and scale up are aimed at maintaining optimum and homogenous reaction conditions minimizing microbial stress exposure and enhancing metabolic accuracy. For each individual product, process and facility, suitable strategies have to be elaborated by a comprehensive and detailed process characterization, identification of the most relevant process parameters influencing product yield and quality and their establishment as scale-up parameters to be kept constant as far as possible. Physical variables, which can only be restrictedly kept constant as single parameters, may be combined with other pertinent parameters to appropriate mathematical groups or dimensionless terms. Process characterization is preferably based on real-time or near real-time data collected by in situ and on-line measurements and may be facilitated by supportive approaches and tools like neural network based chemometric data analysis and modelling, clarification of the mixing and stream conditions through computational fluid dynamics and scale-down simulations. However, as fermentation facilities usually are not strictly designed according to scale-up criteria and the process conditions in the culture vessels thus may differ significantly and since any strategy and model can only insufficiently consider and reflect the highly complex interdependence and mutual interaction of fermentation parameters, successful scale up in most cases is not the result of a conclusive and straight-lined experimental strategy, but rather will be the outcome of a separate process development and optimization on each scale. This article gives an overview on the problems typically coming along with fermentation process optimization and scale up, and presents currently applied scale-up strategies while considering future technologies, with emphasis on Escherichia coli as one of the most commonly fermented organisms.

Ultrasound‐Supported Catalysis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Effect of Scaleup and Aggregation on the Use of Well Tests To Identify Geological Properties

Summary This paper discusses specific issues encountered when pressure tests are analyzed in reservoirs with complex geological properties. These issues relate to questions concerning the methodology of scaleup, the degree of aggregation, and the reliability of conventional methods of analysis. The paper shows that if we desire to use pressure-transient analysis to determine more complex geological features such as connectivity and widths of channels, we need a model that incorporates reservoir heterogeneity. This complexity can lead to significantly more computational effort in the analysis of the pressure transient. The paper demonstrates that scaleup criteria, based on steady-state procedures, are inadequate to capture transient pressure responses. Furthermore, the number of layers needed to match the transient response may be significantly greater than the number of layers needed for a reservoir-simulation study. The use of models without a sufficient number of layers may lead to interpretations that are in significant error. The paper compares various vertical aggregation methods to coarsen the fine-grid model. The pressure-derivative curve is used as a measure of evaluating the adequacy of the scaleup procedure. Neither the use of permeability at a wellbore nor the average layer permeability as criteria for the aggregation was adequate to reduce the number of layers significantly. Introduction The objectives of this paper are to demonstrate the impact of the detailed and small-scale heterogeneities of a formation on the flow characteristics that are obtained from a pressure test and how those heterogeneities affect the analysis of the pressure test. The literature recognizes that special scaleup procedures are required in the vicinity of wells located in heterogeneous fields. Our work demonstrates that these procedures apply only to rather small changes in pressure over time and are usually inadequate to meet objectives for history-matching well tests. Using a fine-scale geological model derived by geological and geophysical techniques, this work systematically examines the interpretations obtained by various aggregation and scaleup techniques. We will demonstrate that unless care is taken, the consequences of too much aggregation may lead to significant errors on decisions concerning the value of a reservoir. Current scaleup techniques presume that spatial (location of boundaries, location of faults, etc.) variables are maintained. In analyzing a well test, however, one of our principal objectives is to determine the relationship between the well response and geometrical variables. We show that a limited amount of aggregation will preserve the spatial and petrophysical relationships we wish to determine. At this time, there appears to be no method available to determine the degree of scaleup a priori. Because the objective of well testing is to estimate reservoir properties, the scaleup process needs to be made a part of the history-matching procedure. By assuming a truth case, we show that too much vertical aggregation may lead to significant errors. Comparisons with traditional analyses based on analytical techniques are made. Whenever an analytical model is used in the analysis, unless otherwise stated, we use a single-layer-reservoir solution.

Scale-up Methods for Fast Competitive Chemical Reactions in Pipeline Mixers

An experimental study investigated the scale-up methods for fast competitive/consecutive reactions in static mixers. Twelve-element Kenics helical element mixers of 1/8-, 1/4-, and 1/2-in.-diameters were tested using the fourth Bourne reaction system as a test reaction. The fourth Bourne reaction is a parallel reaction system where the acid-catalyzed hydrolysis of 2,2-dimethoxypropane (DMP) is conducted in parallel with the neutralization of HCl with NaOH. With very rapid mixing, the HCl catalyst is neutralized by NaOH and minimal hydrolysis of DMP occurs. The main feed contained 200 mol/m3 of DMP and 210 mol/m3 of NaOH (5% stoichometric excess relative to HCl in the side stream). The side stream, which was introduced through two radial cylindrical feed ports at the midpoint of the third mixer element, contained 2000 mol/m3 of HCl. The two streams were combined in the mixer at a volumetric flow ratio of 10:1, main to side. By analysis of the reactor effluent for DMP hydrolysis products of acetone and methanol, the effectiveness of the mixer−reactor in promoting the acid−base reaction was quantified. The parameters used to evaluate the static mixer performance at different sizes are (1) the Reynolds number (experiment Re varied from 550 to 17 000), (2) the turbulent energy dissipation rate, and (3) the residence time in the mixer. At low flow rates and low energy dissipation, micromixing controlled and equal power dissipation was an acceptable scale-up criterion. At high flow rates and high energy dissipation, mesomixing controlled and equal residence time was the proper scale-up criterion. The recommended scale-up procedure is as follows: (1) Maintain geometrical similarity. (2) Maintain the following parameters constant: (A) ratio of the main to side feed rates, (B) ratio of the main to side feed velocities, (C) ratio of the reagent concentration in the main and side feeds, (D) number of mixing elements in the mixer, and (E) side feed orientation and location relative to the mixing elements. (3) Analyze the experimental data to determine the controlling mixing mechanism, either micromixing or mesomixing: (A) for micromixing control, scale-up using equal power dissipation; (B) for mesomixing control, scale-up using equal mixer residence time.