Stirred Tank Process Research Articles

Influence of process variables on foaming ability of surfactants: Experimental study and dimensional analysis

By applying the dimensional analysis approach to a lab-scale stirred tank process, the influence of process parameters on the foamability of three model surfactants: SLES, Tween 20 and Brij L23 is investigated and modelled. For validation of process law, the theoretical approach is complemented with an experimental work varying process parameters such as agitator rotational speed rate (N), mixing time (tm) and bottom clearance (Cb). The foam rate of expansion of surfactant solutions is correlated with success to two dimensionless numbers: the Reynolds number and the mixing time number. Reynolds number is observed as mainly governing the amount of formed foam. A clear difference between the intermediate flow regime (Re<105) and the turbulent one (Re>105) is observed leading to a different process law for each regime. Master curves are finally drawn and can be used for helping to predict final foam volumes in the studied experimental domain according to both dimensionless numbers.

New micronutrient biocomponents based on blackcurrant seeds pomace – Bench-scale kinetic studies

In the present work new universal bench-scale plant for biosorption, useful in production of new micronutrient biocomponents, was described. The new installation enabling working in a fixed bed or stirred tank batch mode. Reactors may also be used in serial or parallel mode, which gives many application possibilities. Copper ions were selected as a sorbate for kinetic modelling. The results of the adsorption capacities of Cu(II) were 13.9 mg/g for fixed bed and 12.8 mg/g for stirred tank. During biosorption of Cu(II) ions from aqueous solution ion exchange and release of Ca(II), K(I), Mg(II), and Na(I) were observed. For kinetics description of stirred tank process pseudo-1st-and pseudo-2nd order models were used. For fixed bed process the Thomas, Yoon-Nelson, Adams-Bohart and Wolborska models were used. The use of blackcurrant seed residues as biosorbents enables the generation of new products from waste biomass, which can become an alternative to the traditional fertilizers with microelements. The presented technology is an attempt to reduce environmental impact of the conventional micronutrient fertilizers, which contain toxic chelators such as EDTA. Minimization of waste and maximization of product output makes it an efficient tool supporting cleaner production.

Modelling the chemical free neutralization of caustic peeled tomato slurry as a continuously stirred tank

The purpose of this investigation was to use membrane filtration to neutralize a waste stream from the chemical peeling of tomatoes and to model this process. The waste exiting the peeler/scrubber unit is decanted to separate skins and seeds from the aqueous portion of the waste stream. This aqueous suspension represents the inefficiency in over peeling of tomatoes. Recycling the slurry would reduce waste generated from the peeling operation thereby increasing process efficiency. A constant volume dilution (CVD) membrane filtration process was designed to perform a chemical-free neutralization of the tomato slurry. Through the CVD process, the active alkali of the slurry was reduced from 0.7 to less than 0.01mol/L and electrical conductivity of the suspension decreased from 27 to less than 0.1mS/cm. Additionally, electrical conductivity and active alkali were found to have a linear relationship (r2=0.9962) showing that one value can adequately predict the other in this system. All of the indicators of neutralization fit log-linear to the derived stirred tank processes model with significant correlation coefficients. This work shows that a CVD process using membrane technology has the potential to reclaim tomato waste from caustic peeling and that the filtration can be adequately modelled.

ChemInform Abstract: Membranes and Crystallization Processes: State of the Art and Prospects

AbstractReview: 101 refs.

Improving methane production from wheat straw by digestate liquor recirculation in continuous stirred tank processes

Wheat straw is an abundant, cheap substrate that can be used for methane production. However, the nutrient content in straw is inadequate for methane fermentation. In this study, recycling digestate liquor was implemented in single-stage continuous stirred tank processes for enrichment of the nutrient content of straw with the aim of improving the methane production. The VS-based organic loading rate was set at 2 g/(L d) and the solid retention time at 40 days. When wheat straw alone was used as the substrate, the methane yields achieved with digestate liquor recycling was on average 240 ml CH4/g VS giving a 21% improvement over the processes without recycling. However, over time, the processes suffered from declining methane yields and poor stability evidenced by low pH. To maintain process stability, wheat straw was co-digested with sewage sludge or supplemented with macronutrients (nitrogen and phosphorous). As a result, the processes with digestate liquor recycling could be operated stably, achieving methane yields ranging from 288 to 296 ml CH4/g VS. Besides, the processes could not be operated sturdily with supplementation of macronutrients without digestate liquor recycling. The highest methane yield (296 ± 16 ml CH4/g VS) was achieved by co-digestion with sewage sludge plus recycling of digestate liquor after filtration (retention of nutrients and microorganisms). This was comparable to the maximum expected methane yield of 293 ± 13 ml CH4/g VS achieved in batch test. The present study therefore demonstrated that digestate liquor recycling could lead to a decreased dilution of vital nutrients from the reactors thereby rendering high process performance and stability.

High methane yields and stable operation during anaerobic digestion of nutrient-supplemented energy crop mixtures

The feasibility of digesting energy crops supplemented with macro- and micronutrients instead of manure, without the commonly applied long hydraulic retention time (HRT), was investigated in long-term, single-stage continuous stirred tank processes. The crops used were mixtures of sugar beets, maize and whole crop triticale. The organic loading rate (OLR) measured as a total solid (TS) was 1.5–5.5 kg m−3 d−1 and the HRT from 30 to 40 days. The results showed high methane yields, comparable to those in batch digestion, and high stability. The digestion of beets only was most stable, and showed the highest average TS-based methane yield (383 ± 26 m3 kg−1) at an OLR of 4.5 kg m−3 d−1 and a HRT of 40 days. No significant difference in methane yield was found for all the crop mixtures during stable operation. Nutrient addition therefore showed the same stimulatory and stabilising effects as manure with high methane yields achieved at relatively short HRTs.

High level arsenic resistance in bacteria present in biooxidation tanks used to treat gold-bearing arsenopyrite concentrates: A review

The microbial consortium used in continuous-flow, stirred tank processes to treat gold-bearing arsenopyrite concentrates became adapted to high concentrations of arsenic over a number of years. The dominant microorganisms, Acidithiobacillus caldus and Leptospirillum ferriphilum, were found to contain two sets of arsenic resistance genes. One set of ars genes was present in all isolates of a species irrespective of whether they were highly arsenic resistant or not. A second set of ars genes was present on Tn21-like transposons and was found in all strains tested that had been adapted to high concentrations of arsenic. The arsenic resistance transposons present in At. caldus and L. ferriphilum were closely related, but sufficiently different for them to have been acquired independently rather than having been passed from one bacterium to the other. The transposons were transpositionally active in Escherchia coli and were shown to confer higher levels of arsenic resistance than the chromosomally-located ars genes where it was possible to test this. Transposons containing arsenic resistance genes that were identical or closely related to the transposon from L. ferriphilum, originally found in South Africa, were also found in both L. ferrooxidans and L. ferriphilum isolates from South America and Europe. An arsB gene knockout of At. caldus was produced by homologous recombination that demonstrated both the ability of the chromosomal ars genes to confer low levels of arsenic resistance in At. caldus and the development of a genetic system for the creation of knock-out mutants.

Construction of arsB and tetH Mutants of the Sulfur-Oxidizing Bacterium Acidithiobacillus caldus by Marker Exchange

Acidithiobacillus caldus is a moderately thermophilic, acidophilic bacterium that has been reported to be the dominant sulfur oxidizer in stirred-tank processes used to treat gold-bearing arsenopyrite ores. It is also widely distributed in heap reactors used for the extraction of metals from ores. Not only are these bacteria commercially important, they have an interesting physiology, the study of which has been restricted by the nonavailability of defined mutants. A recently reported conjugation system based on the broad-host-range IncW plasmids pSa and R388 was used to transfer mobilizable narrow-host-range suicide plasmid vectors containing inactivated and partially deleted chromosomal genes from Escherichia coli to A. caldus. Through the dual use of a selectable kanamycin resistance gene and a hybridization probe made from a deleted portion of the target chromosomal gene, single- and double-recombinant mutants of A. caldus were isolated. The functionality of the gene inactivation system was shown by the construction of A. caldus arsB and tetH mutants, and the effects of these mutations on cell growth in the presence of arsenic and by means of tetrathionate oxidation were demonstrated.

Leptospirilli from different continents have acquired related arsenic-resistance transposons

The microbial consortium in continuous-flow, stirred tank processes used to treat gold-bearing arsenopyrite concentrates in South Africa has become adapted to high concentrations of arsenic over several years. The dominant microorganisms, Acidithiobacillus caldus and Leptospirillum ferriphilum, were found to contain two sets of arsenic-resistance genes. One set was present in all isolates of a species irrespective of whether they were highly arsenic resistant or not, while a second, transposon-located set was present in only those strains that had been adapted to high concentrations of arsenic. The arsenopyrite treatment tanks from Tamboraque (near Lima, Peru) have not been inoculated with an arsenic-adapted consortium from South Africa. Isolation of a Leptospirillum ferrooxidans from the Tamboraque consortium allowed us to determine whether these microorganisms had acquired similar arsenic-resistance mechanisms as contained on the transposons in the highly arsenic resistant South African cultures. Several isolates of both L. ferriphilum and L. ferrooxidans from Europe as well as a “Leptospirillum ferrodiazotrophum” were also screened to detect whether they contained similar arsenic-resistance transposons even though they had not been selected for enhanced arsenic resistance. Transposons containing arsenic-resistance genes that were identical or closely related to those from South Africa were found in both L. ferrooxidans and L. ferriphilum isolates from South America and Europe. The widespread occurrence of arsenic-resistance transposons suggests that it should be possible to select for highly arsenic resistant biomining microorganisms from many different sources and therefore, unnecessary to use pre-adapted arsenic resistant consortia.

Production of [formula omitted]- [formula omitted]-fluoroleucine ethyl ester by enzyme mediated dynamic kinetic resolution: Comparison of batch and fed batch stirred tank processes to a packed bed column reactor

Immobilized Candida antarctica lipase B has been shown to form the pharmaceutically important ( S ) - γ -fluoroleucine ethyl ester intermediate from the ring opening of an azlactone with ethanol, providing 79% yield and 78% enantiomeric excess (ee) for a stirred tank batch process demonstrated at multi kilogram scale. A kinetic analysis of the reaction system was defined which included the selective enzyme mediated dynamic kinetic ethanolysis, the background hydrolysis to acid and the non selective ethanolysis to racemic ester. This was used to generate a kinetic model which made excellent predictions of the reaction behavior. This kinetic model was then used to develop two new optimized processes. A fed batch stirred tank process was developed that increased productivity four fold compared to the original batch process, while maintaining a similar product ee value. Additionally, a plug flow column reactor process was developed that significantly improved productivity via a 20 fold reduction in the enzyme deactivation rate observed in the batch processes. As a result, the plug flow reactor generated a 20 fold reduction in enzyme to substrate ratio and an increased product yield ( > 90%) and ee (86%) over the initial batch process, producing an effective and economical process for large-scale production.

Related Arsenic Resistance Transposons Occur in Leptospirilli Isolated from Different Continents

Acidithiobacillus caldus and Leptospirillum ferriphilum dominate the microbial consortium used in continuous-flow, stirred tank processes used to treat gold-bearing arsenopyrite concentrates in South Africa. These microorganisms were adapted to high concentrations of arsenic over several years and both types of microorganisms were found to contain two sets of arsenic resistance genes. One set was present on all isolates of a species irrespective of whether they were highly arsenic resistant or not, while a second, transposon-located set was present in only those strains that had been adapted to high concentrations of arsenic. We isolated a Leptospirillum ferrooxidans from the microbial consortium present in arsenopyrite treatment tanks from Tamboraque (near Lima, Peru) that had not been inoculated with an arsenic-adapted consortium from South Africa. This allowed us to determine whether these microorganisms had acquired similar arsenic resistance mechanisms as contained on the transposons in the highly arsenic resistant South African cultures. Several isolates of both Leptospirillum ferriphilum and L. ferrooxidans from Europe as well as a "Leptospirillum ferrodiazotrophum" were also screened to detect whether they contained similar arsenic resistance transposons even though they had not been selected for enhanced arsenic resistance. Transposons containing arsenic resistance genes that were identical or closely related to those from South Africa were found in both L. ferrooxidans and L. ferriphilum isolates from South America and Europe. The widespread occurrence of arsenic resistance transposons suggests that it should be possible to select for highly arsenic resistant biomining microorganisms from many different sources and therefore, unnecessary to acquire pre-adapted arsenic resistant consortia.

Wave microcarrier cultivation of MDCK cells for influenza virus production in serum containing and serum-free media

A process for equine influenza virus vaccine production using a microcarrier system (Cytodex 1) in a 2 L Wave bioreactor is described. Growth of Madin Darby canine kidney (MDCK) cells in serum containing GMEM medium (SC) is compared to growth in serum-free Ex-Cell MDCK medium (SF) without washing steps and medium exchange before infection. Cultivations with microcarrier concentrations of 2 and 4 g/L for both media are shown. Metabolic data from carbon and amino acid metabolism are discussed. Additionally, in roller bottle experiments the influence of multiplicity of infection (moi) and trypsin concentration on the HA value was investigated. Analysis of HA and TCID 50 at 37 °C showed a stable HA of maximum 2.6 log HA/100 μL for 2 weeks. Peak TCID 50 titers of 10 7.7 viruses/mL were achieved 20 h post infection, but infectivity was below detection limit after 150 h. Cell attachment onto microcarriers under serum-free conditions was improved by Ca 2+ addition and by cell harvesting without trypsin using only an EDTA/PBS solution. For the wave cultivation maximum virus titers of 2.3–2.6 log HA units/100 μL were reached from infection with a moi of 0.05. However, in SF medium pH dropped to less than pH 6.8 which resulted in lower HA titers of 1.7 log HA units/100 μL. For the higher microcarrier concentration (4 g/L) medium exchange steps (500 mL) were needed for both media. Omission of the washing step and medium exchange before infection in SF medium clearly simplified the influenza production process; however, for higher virus yields a better pH control of the wave bioreactor would be required. Higher cell densities (2.8 × 10 6 cells/mL for 2 g/L microcarrier) and better attachment compared to stirred tank bioreactors showed, that the wave bioreactor is a good alternative to stirred tank processes for expanding production capacities in case of a pandemic.

Design Considerations for the Batch Capture of Proteins from Raw Whole Milk by Ion Exchange Chromatography

AbstractThe on‐farm extraction of proteins directly from raw whole milk is a promising approach for the production of minor, high‐value proteins from conventional milk and for the production of recombinant proteins from the milk of transgenic animals. The main advantage of the stirred tank process is that protein extraction is rapid and is achieved in a single step without the need for a pre‐treatment. It also includes the minimization of microbial growth and the potential for batch traceability between individual animals and final product lots.

Isolation of parametric faults in continuous-time multivariable systems: a sampled data-based approach

A novel approach is proposed towards on-line and real-time detection and isolation of parametric faults in a multivariable linear continuous-time (CT) system. The problem of fault detection and isolation (FDI) is formulated in terms of a CT state space model. Since parameters in a CT model usually have simple relationships with physical parameters of the system, isolating parametric faults in the CT model can lead to the isolation of undesired changes in the physical parameters. Isolating parametric faults is very challenging, because even in a linear time-invariant system, the fault model can be time-varying and random. To obtain a constant fault model, many existing parametric FDI schemes have to make unrealistical assumptions. Our proposed FDI approach can generate an optimal primary residual vector (PRV), in which the fault model is constant without making any assumptions. To isolate faults, the PRV is transformed into a set of structured residual vectors (SRVs), where one SRV is made insensitive to a specified subset of faults, but most sensitive to other faults. The proposed approach is successfully applied to detection and isolation of undesired changes in the physical parameters of a simulated continuously stirred tank process.

Legal alert: Another chapter in “arranging for disposal”

Crystallization is one of the major unit operations of chemical process industries and plays a key role for particulate solids production in the pharmaceutical, chemical, electronic, minerals sectors. Most of the current crystallization processes are performed under batch or continuous mode based on a stirred tank process; the need for breakthrough technologies has been highlighted by numerous authors and reports. Membranes are one of the potentially attracting strategies in order to achieve this target. Nevertheless, a relatively limited number of publications have been reported on membranes and crystallization processes, compared to other unit operations. This study intends to provide a state-of-the-art review of the different approaches combining membranes and crystallization processes. Hybrid and integrated systems are discussed and the different role and function potentially provided by dedicated membrane materials are analyzed. Based on the results and analyses gained through the different approaches that have been tested, unexplored issues and open questions have been listed. The research efforts which are required in order to make membranes processes for crystallization/precipitation an industrial reality are finally discussed.

Generation of oil emulsion for stirred tank processes

The presence of oil emulsion required in some processes occurring in stirred tanks, commonly used in various technologies, can be obtained either by high pressure injection of oil to the tank; or, by the impeller generating a higher shear rate in the tank, filled up with a carrier liquid to which the oil was poured. A simplified mathematical model for both methods has been derived, together with formulae to calculate the size of the oil droplet produced. The formulae show that the droplets get smaller with increasing oil density, carrier liquid density and viscosity, and with decreasing surface tension. The droplets diminish with increasing impeller diameter and speed, when a stirred tank is used, or diminish with atomized oil pressure. Theoretical results are compared to some measured data. The advantage of the injection method has been proven by experiments on a selective agglomeration of coal at a batch laboratory scale. In comparison to the impeller method, the injection method allowed the reduction of the total processing time by about 80%.

Indirect adaptive pole-assignment controllers with direct implementations

A new strategy involving the cancellation of system poles and controller zeros is proposed for the indirect adaptive pole-assignment controllers. The resulting controllers can be implemented without solving simultaneous equations. A new method of eliminating the offset due to reference input without an explicit integrator is also proposed. The new strategies can be applied to pole assignment controllers of both general-feedback structure and error-driven structure. The results obtained from the simulations and trials on a stirred tank process verify that the controllers work well.

Multivariable pole-zero placement self-tuning controller†

Abstract A computationally efficient pole-zero placement self-tuning control algorithm for multi-input-multi-output servo systems is developed. It is effectively an implicit algorithm in the sense that the controller design step is trivial. Moreover, the controller is obtained as a left matrix-fraction and so can be immediately implemented. Although the algorithm is restricted to stable plants, it is applicable to non-minimum-phase plants and can also handle unknown but bounded pure time delays. Results obtained from computer simulations of the algorithm, as well as by trials on an actual stirred-tank process, are presented.

New applications of digital simulation in chemical plant construction

Use of digital simulation for process design, for finding the best run of a plant, for designing the automatic control system, Formation of a model collection of chemical processes. Generation of the model structure, supply of the structure with valid parameters, control of the simulation run are implemented in a display-screen version. Examples: Design a multicontrol loop System for distillation column. Layout of a stirred tank process.

The application of robust and non‐interacting control schemes to a heat‐exchanger stirred tank process

AbstractAn experimental study involving the digital computer implementation of four multivariable control schemes to a heat‐exchanger stirred process has been performed. The control schemes varied in their complexity and in the amount of process information required for their design. The analysis of the experimental data shows how each controller handled the asymmetric non‐linearity and dead times inherent in the process. The development of the theory shows why the best control was not always achieved with the most sophisticated controller. The controllers are suitable for industrial applications.