Influence Of Agitation Rate Research Articles

Mass transfer studies in RDC column by the coupling effects of perforated structure and reactive extraction of Mo(VI) and W(VI) from sulfate solution

Solvent extraction of molybdenum (VI) and tungsten (VI) by synergism of the mixture of D2EHPA and TBP were conducted in the RDC extractor with perforated structure. The initial aqueous pH, extractant concentration, ammonium hydroxide concentration as a stripping agent, and synergistic enhancement factor were optimized in the initial experiments before collecting column data. In the RDC column, the influence of agitation rate and inlet phase velocities were examined on the hydrodynamic velocities, mass transfer data, and distribution coefficients. The finding data indicated that the impact of agitation speed on the distribution coefficients of molybdenum and tungsten is considerable in comparison the inlet phase flow rates. Published empirical models for estimating the slip and characteristic velocities were compared with the solvent extraction data, and the modified models were presented by considering the reactive extraction. Mass transfer performance based on the dispersed phase was studied by applying the axial dispersion model. Column performance enhances the increment of the operational variables such as agitation speed, inlet solvent phase flow rate, and inlet aqueous phase flow rates, but the variations of agitation speed and solute transfer direction have a high impact on this phenomenon. The previous models for estimating the mass transfer coefficients were compared with the present work. The published models failed to acceptable estimate the mass transfer evaluation due to column geometry and reactive extraction systems. Finally, the new models were proposed by using the dimensionless analysis methods for obtaining the enhancement factor in both extraction and stripping stages.

In vitro release studies of furosemide reference tablets: influence of agitation rate, USP apparatus, and dissolution media.

Furosemide is a diuretic drug widely used in chronic renal failure. The drug has low solubility and permeability, which cause clinical problems. Studying the in vitro release performance elucidates the rate and extent of drug dissolved from dosage forms under different conditions. Furosemide reference tablets were tested using USP Apparatuses 1 and 2 as well as the flow-through cell method (USP Apparatus 4), a dissolution apparatus that simulates the human gastrointestinal tract better than the other methods. Dissolution profiles were created with USP Apparatuses 1 and 2 at 25, 50, and 75 rpm and 900 mL of 0.1 M hydrochloric acid, acetate buffer (pH 4.5), and phosphate buffer (pH 6.8). USP Apparatus 4 with a laminar flow of 16 mL/min and 22.6 mm cells was used. Drug dissolution was quantified at 274 nm for 60 min. Mean dissolution time, dissolution efficiency, time to 50% dissolution, and time to 80% dissolution data were used to compare dissolution profiles. Additionally, zero-order, first-order, Higuchi, Hixson-Crowell, Makoid-Banakar, and Weibull models were used to adjust furosemide dissolution data. Between USP Apparatus 1 and 2, significant differences were observed in almost all parameters at 50 and 75 rpm (p < 0.05). A similar dissolution profile (f2 > 50) with a pharmacopoeial dissolution method (USP Apparatus 2 at 50 rpm and 900 mL of phosphate buffer pH 5.8) and USP Apparatus 4 (laminar flow of 16 mL/min, 22.6 mm cells, and pH 6.8) was observed. The Weibull function was the best mathematical model to describe the in vitro release performance of furosemide in the three USP dissolution apparatuses. These results could be used to manufacture better furosemide dosage forms and decrease the negative clinical impact of current furosemide formulations.

Improving the cost effectiveness of enhanced green fluorescent protein production using recombinant Escherichia coli BL21 (DE3): Decreasing the expression inducer concentration.

Green fluorescent protein (GFP) is a globular protein used as biosensor and biomarker in medical and industrial fields. However, due to the expensive production costs of expressing proteins using high-cost inducers like isopropyl-β-d-1-thiogalactopyranoside (IPTG), the number of GFP applications are still scarce. This work studied the production of enhanced GFP (EGFP) using Escherichia coli BL21 (DE3) [pLysS; pET28(a)], aiming to increase its yield and reduce costs. First, the influence of agitation rate, induction time, and concentration of IPTG in the production of EGFP was evaluated, but only the first two parameters were significant. Subsequently, aiming to reduce costs related to the use of inducer, the IPTG concentration (0.005, 0.010, and 0.025mM) was decreased and, interestingly, the production levels were maintained or increased. These results show that a proper choice of production conditions, particularly through the decrease of inducer concentration, is effective to reduce the upstream production costs and guarantee high EGFP expression.

Atmospheric acid leaching mechanisms and kinetics and rheological studies of a low grade saprolitic nickel laterite ore

Improved atmospheric acid leaching (AL) of complex, low grade nickel (Ni) laterite ores warrants greater knowledge of the exact processes underpinning Ni and pay metal cobalt (Co) extraction rates, acid consumption and pulp handleability. In this study, the influence of agitation rate (600–1000rpm) and temperature (70 and 95°C) on the isothermal, batch acid leaching and rheological behaviour of saprolitic Ni laterite slurry (40wt.% solid) was investigated over 4h at pH1. The leaching behaviour was distinctly incongruent and reflected strong temperature-dependent Ni/Co extraction, acid consumption and the proliferation of gangue minerals' constituent elements (e.g., Na, Mg, Al, Fe). Whilst the total mass of acid consumed per ton of dry ore processed was greater at higher temperature, the total kg acid consumed per kg Ni and Co extracted was markedly lower. In all cases, the slurries displayed time-dependent, non-Newtonian, shear thinning rheological behaviour. The pulp viscosities and shear yield stresses were generally greater at lower than at higher temperature, with both increasing dramatically in the course of 4h leaching. Agitation rate in the range 600–1000rpm had no noticeable impact on Ni and Co leaching rates, confirming the insignificance of volume diffusion limitation. Although high pulp shear viscosities in the range 37–120mPas were observed in the course of leaching, they did not have an impact on Ni and Co leaching mechanisms and kinetics from the saprolitic laterite ore. The mechanism of saprolitic laterite ore leaching appears to follow a chemical reaction controlled, shrinking core model with apparent activation energies of 75.5±3.8 and 81.2±4.1kJ/mol, respectively, for the release of Ni and Co.

Commercial Coffee Wastes as Materials for Adsorption of Heavy Metals from Aqueous Solutions

This work aims to study the removal of Cu(II) and Cr(VI) from aqueous solutions with commercial coffee wastes. Materials with no further treatment such as coffee residues from café may act as adsorbents for the removal of Cu(II) and Cr(VI). Equilibrium data were successfully fitted to the Langmuir, Freundlich and Langmuir-Freundlich model (L-F). The maximum adsorption capacity of the coffee residues can reach 70 mg/g for the removal of Cu(II) and 45 mg/g for Cr(VI). The kinetic data were fitted to pseudo-first, -second and -third order equations. The equilibrium was achieved in 120 min. Also, the effect of pH on adsorption and desorption was studied, as well as the influence of agitation rate. Ten cycles of adsorption-desorption were carried out revealing the strong reuse potential of these low-cost adsorbents; the latter was confirmed from a brief economic approach.

The production of hemicellulases by Thermomyces lanuginosus strain SSBP: influence of agitation and dissolved oxygen tension.

Shake-flask cultivation of T. lanuginosus strain SSBP on coarse corn cobs yielded beta-xylanase levels of 56,500 nkat/ml at 50 degrees C, whereas other hemicellulases (beta-xylosidase, beta-glucosidase, and alpha-L-arabinofuranosidase) were produced at levels less than 7 nkat/ml. Cultivation on D-xylose yielded much lower levels of xylanase (350 nkat/ml), although other hemicellulase levels were similar to those produced on corn cobs. The influence of agitation rate and dissolved oxygen tension (DOT) on hemicellulase production was studied further in a bioreactor. On xylose, xylanase activities of 4,330 nkat/ml and 4,900 nkat/ml were obtained at stirrer speeds up to 1,400 rpm to control DOT. At a constant stirrer speed of 400 rpm, xylanase activities of 10,930 nkat/ml and 15,630 nkat/ml were obtained when cultivated on xylose and beechwood xylan respectively, despite DOT levels below 5% for the duration of fermentation. The results indicate that there is an interaction between agitation rate and DOT, impacting on xylanase and accessory enzyme production. Higher agitation rates favoured the production of xylosidase, arabinofuranosidase and glucosidase by T. lanuginosus strain SSBP, whereas the lower agitation rates favoured xylanase production. Rheological difficulties precluded cultivation on corn cobs in the bioreactor. Volumetric xylanase productivities of 1,060,000 nkat/l x h and 589,000 nkat/l x h obtained on beechwood xylan and xylose indicate that T. lanuginosus strain SSBP is a hyperxylanase producer with considerable industrial potential.

Scaling of turbulence characteristics in a turbine-agitated tank in relation to agitation rate

The influence of agitation rate on scaling in a turbine-agitated tank is examined using constant temperature anemometry measurements. Measurements in the high-intensity impeller zone are compared with measurements in the bulk zone for four agitation rates. The mean velocity of the flow was found not to be constant when scaled with V tip. This is contrary to assumptions and measurements reported in the literature. The energy spectra in the impeller zone scale by the energy dissipation length scales and so did also the low wavenumbers of the spectra in the bulk zone. A small region of the energy spectra in the impeller zone are scaled by Kolmogorov's scales. In the bulk zone, the low-energy range of high wavenumbers of the energy spectra scale with Kolmogorov's scales. The ratios of energy dissipation rate and the ratios of turbulent kinetic energy in the impeller zone versus the bulk zone, show a linear increase as the agitation rate is increased. This indicates that changing the agitation rate affects flow conditions in the impeller zone more than in the bulk zone.

Influence of agitation rate on growth and ribonuclease production by free and immobilizedAspergillus clavatus cells

Aspergillus clavatus spores have been immobilized in poly(vinyl alcohol) criogel (PVAC) for ribonucleae (RNase) production. The enzyme productivity and growth of free (FC) and immobilized cells (IC) were studied in a bioreactor with agitation under different cultivation conditions. The influence of some medium compunds, aeration, and agitation speeds were investigated. Production of RNase was stimulated by the presence of reducing glucose, peptone, and soybean concentrations in the medium. From 42,000 to 45,000 U/L were produced by IC using optimized batch fermentation conditions. The RNase prouction by IC was 2.3 and 2.5 times greater than the same by FC in a bioreactor and control flasks, respectively.

The influence of agitation rate on xanthan production by Xanthomonas campestris

The influence of agitation rate on Xanthan production in a baffled stirred tank reactor is reported. To separate the hydrodynamic effect of agitator speed on any slime layer from the influence on oxygen mass transfer, oxygene-enriched air was used. Furthermore, the influence of agitation speed on the molecular weight distribution was studied

Kinetics and mechanism of dissolution of synthetic molybdenum disulphide MoS 2 in bromate solutions Part II: Kinetics of molybdenum disulphide dissolution in the MoS 2KBrO 3H 2SO 4H 2O system

The dissolution of synthetic molybdenum disulphide MoS 2 in aqueous potassium bromate solution in the presence of sulphuric acid was investigated. The influence of agitation rate, temperature, concentration of KBrO 3 and H 2SO 4, MoS 2 specific surface and addition of MoO 3 and Br − ions on the course of the dissolution process was determined. The dissolution of MoS 2 as a function of time shows a monotonically decreasing rate with no induction period. The agitation rate has no effect on MoS 2 dissolution in the system studied in the range 300–1550 min −1. The reaction rate constants depend on temperature, KBrO 3 and H 2SO 4 concentrations and MoS 2 specific surface. The apparent activation energy determined as 32.3 kJ/mol is too large for reactions controlled by diffusion through a layer of reacted solid body and at the same time relatively low, although possible, for reactions proceeding in the kinetic region. Considering the good agreement of experimental data with a Shrinking Core Model equation for reactions controlled by the chemical process and the independence of the reaction rate of agitation rate, it is possible to accept that reactions proceed in the kinetic region.