Effects Of Agitation Speed Research Articles

Kinetics study on reactive extraction of hydroxy-(2-methyl-phenyl)-acetic acid enantiomers from organic solution by HP-β-CD

Kinetics data is important for the reliable scale-up of a lab-scale process and for selection, design and operation of related equipment. This paper reports on the kinetics study for reactive extraction of hydroxy-(2-methyl-phenyl)-acetic acid (HA) enantiomers by hydroxypropyl-β-cyclodextrin (HP-β-CD) from the organic phase to the aqueous phase. The theory of extraction with chemical reaction was used. The effects of agitation speed, interfacial area, pH value of aqueous phase, initial concentration of HA enantiomers and initial concentration of extractant on the specific rate of extraction were investigated. The reactions have been found to be first order in HA and second order in HP-β-CD with the forward rate constants of 4.873×10−4m6/(mol2s) for R-HA and 4.343×10−4m6/(mol2s) for S-HA, respectively.

Effects of agitation speed on the ex vivo expansion of cord blood hematopoietic stem/progenitor cells in stirred suspension culture

The mononuclear cells were cultivated in stirred flasks at different agitation speeds of 30 rpm, 45 rpm, 60 rpm and 80 rpm. At the agitation speed of 30 rpm, total cells achieved higher expansion folds and the CFC density increased. When at higher agitation speed of 60 rpm or 80 rpm, the number of cells dropped rapidly and characteristics of hematopoietic stem/progenitor cells (HSPCs) were not maintained. Moreover, the culture duration of 6–9 days was better for HSPCs ex vivo expansion. These data indicated that HSPCs should be cultured at relatively low agitation speed and for a short-term period when cultured in stirred suspension system.

Drying Kinetics of Oil Palm Frond Particles in an Agitated Fluidized Bed Dryer

The drying kinetics of oil palm frond particles in a laboratory-scale agitated fluidized bed dryer were investigated under various operating conditions: inlet air temperature (50–80°C), superficial air velocity (0.6–1.0 m/s), bed load (200–300 g), and agitation speed (300–500 rpm). To study the effects of these variables on the drying time and drying rate, an experimental design using Taguchi orthogonal array was employed. Based on analysis of variance (ANOVA), the results indicated that inlet air temperature greatly affected the drying rate, followed by superficial air velocity and bed load. The effect of agitation speed on the drying rate was found to be small. The experimental drying kinetics data were compared with the values obtained from three different models, namely, the Page model, modified quasi-stationary method (MQSM), and a new composite model. It was found that the proposed new model could satisfactorily predict the complete drying rate curve for the drying of oil palm fronds.

Comparative Study of RANS and LES Simulation Methods for Analysis of Turbulence in a Tubular Stirred Reactor

Selecting a right simulation method is important for accurately predicting flow field in stirred reactor. The Reynolds-Averaged Navier-Stokes (RANS) approach with standard model and large eddy simulations (LES) method were both used to analyze the turbulent flow field in a tubular stirred reactor for leaching. Calculations were performed to study the effects of agitator speed and flux on the turbulent flow field. The velocity at different axial sections gained by the two methods was compared. Results showed that the eddy current, especially in the back of impellor, predicted by LES was better than that by standard model. At the same time，the average relative error of the mean residence time and the mixing time of the former reduced 5% and 13% respectively than that of the latter.

Optimal conditions for mycelia biomass and extracellular polysaccharides of Grifola frondosa: Effect of agitation speed, inoculum ratio and initial pH

Grifola frondosa, a medicinal and edible mushroom, has shown different bioactive compounds, such as polysaccharides with anticancer and other therapeutic properties. In the present research, the mycelia of G. frondosa were cultivated in shaking flasks to investigate the effects of agitation speeds, inoculum ratios, and initial pH on pellet morphology, biomass, and extracellular polysaccharide (EPS) production. Furthermore, mathematical models for optimizing the three factors for biomass and EPS production were developed. The results show that the culture parameters including agitation speed, inoculum ratio, and initial pH influenced pellet morphology, biomass, and EPS production. The optimal conditions for biomass and EPS production were agitation speed at 105 and 111 rpm, inoculum ratio 3.1 and 3.3%, and initial pH 5.5 and 5.6, respectively. Under these conditions, the predicted maximum biomass and EPS were 5.28 and 2.35 mg/ml, respectively. The findings may be useful for future development of fermentation techniques for the production ofG. frondosa products. Key words: Grifola frondosa, biomass, extracellular polysaccharides, optimization.

Phase-transfer catalytic dichlorocyclopropanation of styrene under the influence of ultrasound conditions – A kinetic study

The kinetics for dichlorocyclopropanation of styrene with an excess of chloroform were studied under phase-transfer catalysis and ultrasound irradiation conditions using aqueous sodium hydroxide as the base and benzyltriethylammonium bromide as a catalyst. The reaction was carried out at 35°C under pseudo-first order conditions by keeping aqueous sodium hydroxide and chloroform in excess and was monitored by gas chromatography (GC). The effects of agitation speed, quaternary ammonium salts, amount of catalyst, amount of sodium hydroxide and temperature on the kinetics of the conversion were investigated.

OPTIMIZATION OF AGITATION AND INCUBATION PERIOD ON PRODUCTION OF MANNANASE BY BACILLUS VELEZENSIS NRC-1 USING BENCH-SCALE BIOREACTOR

The effect of agitation speed and incubation period on the production of mannanase enzyme by Bacillus velezensis NRC-1 using bench-scale bioreactor at 45oC was investigated. Results revealed that the increase in agitation speed from 200 to 800 rpm resulted in a significant increase in mannanase production to 21.04 U/mL. The increase in agitation speed affected dissolved oxygen (DO) concentration which in turn affected cell growth and mannanase production. The maximum mannanase production in the bioreactor was attained after 72 h of incubation at 45 oC. Mannanase activity in the bioreactor (21.04 U/mL) while much higher than that obtained from the shake flask fermentation (15.6 U/mL) also the incubation period decreased from 7 days in shake flask fermentation to 3 days in bioreactor.

Kinetics of vanadium leaching from black shale in non-oxidative conditions

The leaching kinetics of vanadium from black shale under non-oxidative conditions was presented and compared with that under oxidative conditions. The effects of agitation speed, sulphuric acid concentration, temperature and particle size were determined. The morphology of the solid particles during leaching indicated that no product layer formed on the particles. The grain model with pore diffusion control provided a good description of vanadium leaching kinetics. The model gave an activation energy of 55·6 kJ mol−1, and reaction order 0·37 with respect to sulphuric acid due to diffusion and chemical reactions occurring in parallel in the porous solids. The linear relationship KD∝1/r02 found for the apparent rate constant, where r0 is initial particle radius, also supported a diffusion controlled process. The apparent activation energy was 40% larger for leaching under non-oxidative conditions than for leaching under oxidative conditions, indicating that an oxidising atmosphere had a positive effect on vanadium leaching.

An investigation of agitation speed as a factor affecting the quantity and monomer distribution of alginate from Azotobacter vinelandii ATCC® 9046

Alginate is a copolymer of β-D: -mannuronic and α-L: -guluronic acids. Distribution of these monomers in the alginate structure is one of the important characteristics that affect the commercial value of the polymer. In the present work, the effect of agitation speed in the range of 200-700 rpm on alginate production by Azotobacter vinelandii ATCC(®) 9046 was investigated at a dissolved oxygen tension of 5% of air saturation. Experiments were conducted in a fermentor operated in batch mode for 72 h while the production of biomass and alginate, the consumption of substrate and the change in culture broth viscosity and monomer distribution of the polymer were monitored. Results showed that the growth rate of the bacteria increased from 0.165 to 0.239 h(-1) by the increase of mixing speed from 200 to 400 rpm. On the other hand, alginate production was found to be the most efficient at 400 rpm with the highest value of 4.51 g/l achieved at the end of fermentation. The viscosity of culture broth showed similar trends to alginate production. Viscosity was recorded as 24.61 cP at 400 rpm while it was only 4.26 cP at 700 rpm. The MM- and GG-block contents were almost equal in most of the culture times at 400 rpm. On the other hand, GG-blocks dominated at both low and high mixing speeds. Knowing that GG-blocks make rigid and protective gels with divalent cations, due to the higher GG-block content, the gel formation potential is higher at 200 rpm as well at 700 rpm, which might originate from the unfavorable environmental conditions that the bacteria were exposed to.

A multi-fiber handling device for in vivo solid phase microextraction–liquid chromatography–mass spectrometry applications

Solid phase microextraction, an in vivo and ex vivo sample preparation method, continues to capture growing interest among researchers for bioanalytical applications. When coupled with liquid chromatography mass spectrometry, the procedure often involves large numbers of fibers in, for example, both pharmacokinetic and pharmadynamic studies as well as other bioapplications. In this regard, appropriate and adequate precaution will be critical in preventing the fibers firstly from any possible external contamination and damage to maintain high analytical data integrity. In addition, improving the offline desorption of fibers specifically for in vivo SPME will not only help in improving data quality, but will also significantly decrease the overall analysis time. This article introduces a prototype multi-fiber handling device capable of simultaneous extraction/desorption of multiple solid phase microextraction (SPME) fibers on a 96-deep well plate format. This device thus provides an alternative approach to improving higher sample throughput for in vivo SPME liquid chromatography mass spectrometry applications. The portable design of the device ensures effective protection and prevention of fibers against damage and possible contamination and thus maintains analytical data reliability. To ensure its suitability for parallel extraction/desorption, the device was carefully evaluated using four benzodiazepines (diazepam, nordiazepam, oxazepam and lorazepam) as model drugs by monitoring inter- and intra-well variability. The effect of agitation speed on data precision and accuracy, effect of device weight on data precision, and comparison of the overall performance of the device with traditional manual desorption approach were also assessed. Results obtained from evaluation of the device with particular focus on the desorption process indicated that the weight of the device has no effect on the reliability and reproducibility of data acquired using the device. The average amount of diazepam obtained for 20 selected wells with and without device was 48.8pg and 49.4pg, respectively. Intra-, inter-well, and inter fiber variations recorded were all ≤13% indicating an excellent precision and reproducibility can be attained with the device.

Numerical Simulation of Turbulent Mixing for Dislocated Blades in a Stirred Tank

Mixing efficiency is an important parameter in the design of many industrial processes in stirred tanks. In this study, CFD technology was used to simulate the mixing process inside the stirred tank with dislocated blades and standard turbine. Calculations were performed to study the effects of agitator speed and the configuration of impellers on mixing efficiency. The results showed that the flow field in the stirred tank with the dislocated blades is better than the standard turbine, and the flow number of the dislocated blades had been improved while the power number had been reduced. According to calculation results of Wr, we found the mixing efficiency of the dislocated blades had been improved about 4 times than that of standard turbine.

Kinetics of vanadium dissolution from black shale in pressure acid leaching

The leaching kinetics of vanadium from black shale in the sulphuric acid–oxygen system is presented. The effects of agitation speed, leaching temperature in the range of 110–150 °C, sulphuric acid concentration, oxygen partial pressure and particle size on the rate of vanadium leaching were determined. The results indicate that the rate is nearly independent of agitation above 200 rpm and increases with increasing temperature, sulphuric acid concentration and oxygen partial pressure. As leaching occurs, there is a progressive dissolution of a vanadium-bearing alumino-silicate phase, while the inert quartz phase assembles onto the mineral surface and remains as an “ash” layer. The leaching kinetics was analyzed by using a new variant of the shrinking core model (SCM) in which both the interfacial transfer and diffusion across the product layer affect the leaching rate. The determined activation energy was found to be 40.14 kJ/mol and the reaction orders with respect to sulphuric acid concentration and oxygen partial pressure were 0.61 and 1.67, respectively. A semi-empirical rate equation was derived to describe the process.

Effects of constant and shifting dissolved oxygen concentration on the growth and antibiotic activity of Xenorhabdus nematophila

To evaluate the effects of dissolved oxygen (DO) control strategy on cell growth and the production of antibiotic (cyclo(2-Me-BABA-Gly)) by Xenorhabdus nematophila. The effects of different agitation speeds and DO concentrations on cell growth and antibiotic activity of X. nematophila YL001 were examined. Experiments showed that higher agitation speeds and DO concentrations at earlier fermentation stage were favorable for cell growth and antibiotic production. At mid- and later-stage, properly decreasing DO concentration can strengthen cell growth and antibiotic production. Based on the kinetic information about the effects of agitation speeds and DO concentrations on the fermentation, the two-stage DO control strategy in which DO concentration was controlled to 70% in the first 18 h, and then switched to 50% after 18 h, was established to improve the biomass and antibiotic activity. By applying this DO-shift strategy in X. nematophila YL001 fermentation, maximal antibiotic activity and biomass reached 252.0 ± 6.10 U/mL and 30.04 ± 2.50 g/L, respectively, thus was 18.99% and 15.36% more than in the cultures at constantly 50% DO.

On‐line acoustic attenuation spectroscopy of emulsions stabilized by vinyl alcohol–vinyl acetate copolymers: a model system for the suspension polymerization of vinyl chloride

AbstractBACKGROUND: Poly[(vinyl alcohol)‐co‐(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis (DH) and average degree of polymerization (DPw), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin.RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on‐line with an agitated laboratory reactor. The emulsions were stabilized by PVA with DH values between 73 and 88 mol% and DPw values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size.CONCLUSION: On‐line acoustic spectroscopy appears to be a suitable technique for the real‐time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant‐stabilized emulsions. Copyright © 2009 Society of Chemical Industry

Application of the factorial design of experiments to biodiesel production from lard

Synthesis of biodiesel from lard was carried out using potassium hydroxide as a catalyst. A 3 2 factorial design of experiments was used. The effects of agitation speed and catalyst concentration were studied. A regression model was obtained to predict the methyl ester concentration and adequately describe the experimental range studied. According to this study, the most suitable operational conditions were an agitation speed of 600 rpm, and 0.9 wt.% catalyst concentration. Furthermore, the product characterization was set out to meet the requirements laid down by the European Standard for biodiesel fuel (EN 14214).

Important Parameters of Epoxidation of 1,4‐bis(allyloxy)butane in Aqueous‐Organic Phase Transfer Catalytic System

AbstractThe epoxidation of 1,4‐bis(allyloxy)butane to give 1‐allyloxy‐4‐glycidoloxybutane and 1,4‐bis(glycidoloxy)butane was investigated. The reaction was carried out with 30 wt % hydrogen peroxide under phase transfer catalysis (PTC) conditions in the presence of sodium tungstate(VI) dihydrate and orthophosphoric(V) acid (WO42–/PO43–). Methyltrioctylammonium chloride (Aliquat 336) was used as the phase transfer catalyst. The effect of agitation speed and reaction temperature on the yield of epoxidation products was determined.

Flooding characteristics in a Hanson mixer-settler extraction column

The flooding behavior of a pilot scale Hanson mixer-settler extraction column with seven stages has been investigated using three different liquid–liquid systems. The effects of agitation speed, phase flow rates, and interfacial tension on flooding velocities and holdup at flooding have been investigated and found to be significant. The experiments showed that flooding occurred by phase inversion under the selected operating conditions. Two precise empirical correlations for flooding velocities and holdup at flooding are derived in terms of the operating variables, column geometry and physical properties of the liquid–liquid systems.

KINETIC STUDY OF SYNTHESIZING 1-PHENYl-3-PROPYL ETHER UNDER LIQUID-LIQUID PHASE-TRANSFER CATALYTIC CONDITIONS

The etherification of 1-bromo-3-phenylpropane with phenol to synthesize 1-phenyl-3-propyl ether by phase-transfer catalytic conditions was successfully carried out in an alkaline solution of KOH/organic solvent two-phase medium. In this work, quaternary ammonium salts acted as the phase-transfer catalysts. The main purpose of this study was to investigate the kinetic behavior, mechanism, and activation energy of the reaction system. A rational mechanism for the etherification is proposed according to the experimental evidence. The reaction follows a pseudo first-order rate law. A pseudo steady-state hypothesis (PSSH) was proposed to describe the kinetic behaviors from which the apparent rate constant of the two-phase reaction (kapp) was obtained via experimental data. Kinetics of the reaction including the effects of agitation speed, amount of potassium hydroxide, volume of water, temperature, amount of tetrabutylammonium bromide, quaternary ammonium salts, volume of chlorobenzene, and organic solvents on the reaction rate were investigated in detail. Rational explanations to account for the unique results, especially for the water volume effect on the reaction rate, are also provided.

Catalytic studies of lipase on FAME production from waste cooking palm oil in a tert-butanol system

In this present work, fatty acid methyl ester (FAME) was produced from waste cooking palm oil (WCPO) by lipase-catalyzed reaction. The catalytic activities of several commercial lipases and different organic solvent were screened. Novozyme 435 was found to be more effective in catalyzing the transesterification of WCPO with methanol. tert-Butanol was used as the reaction medium, which eliminated both negative effect caused by excessive methanol and glycerol as the byproduct. Several variables such as effect of methanol/oil molar ratio, effect of lipase quantity and effect of agitation speed (rpm) were examined in a batch system. Transesterification of WCPO can reach up to 88% FAME yield under optimum condition (methanol/oil molar ratio 4:1, 4% Novozyme 435 based on oil weight, 200 rpm and 12 h reaction time). Kinetics of lipase-catalyzed transesterification of WCPO in tert-butanol system was also investigated. A model based on Ping Pong Bi Bi with only inhibition by methanol was found to fit the initial rate data and the kinetics parameters were evaluated by non-linear regression analysis.

Mass transfer coefficients in a hanson mixer-settler extraction column

The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Grober equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.