Increasing Stirring Speed Research Articles

REACTION CONDITIONS IN VITRO AFFECT RATE OF LIPASE‐CATALYZED HYDROLYSIS OF OLIVE OIL

ABSTRACTAn in vitro procedure that approximates many of the conditions prevailing in the human duodenum was further refined and used to study the effect of dietary fibers on the rate of lipase‐catalyzed hydrolysis of olive oil. Increasing bile salt concentration over the range of 2–8 mM caused a marked increase in the rate of lipid hydrolysis, both in the presence and absence of red wheat bran. Stirring speed (20–90 rpm) had no significant effect on the rate of lipolysis in the absence of fiber, whereas in the presence of fiber an increase in stirring speed was often accompanied by an increase in the rate of lipolysis. Fiber inhibition was sometimes observed regardless of stirring speed. Sequence of addition of reactants influenced the rate of lipolysis. Attention to these variables is clearly important if meaningful, reproducible results are desired.

Dissolution Kinetics of Phosphate Ore in SO2-Saturated Water

SO[sub 2] gas produced with the roasting of sulfur minerals has substantially caused air pollution. SO[sub 2] has been used only for the production of H[sub 2]SO[sub 4] for a long time in the past. However, at present, this side product is being used for the extraction of ores and the production of some chemicals. In this study, the dissolution of phosphate ore from Mazidagi-Mardin, Turkey, the products formed, and the dissolution kinetics were investigated in SO[sub 2]-saturated water. In experiments, particle size, stirring speed, solid/liquid ratio, and temperature were chosen as parameters. It was determined by X-ray diffractometer that the final solid product contains CaHPO[sub 4][center dot]2H[sub 2]O, Ca[sub 3](SO[sub 3])[sub 2][center dot]SO[sub 4][center dot]12H[sub 2]O, and CaSO[sub 4][center dot]2H[sub 2]O. It was observed that the dissolution rate increased with the increase in stirring speed and reaction temperature, and with the decrease in particle size and solid/liquid ratio. A semiempirical mathematical model in the following form, including the effect of the parameters was established to express the dissolution kinetics of phosphate ore: [minus]ln(1 [minus] X) = 35.874D[sup [minus]0.512]w[sup 0.380][center dot](S/L)[sup [minus]0.825]e[sup [minus]2575/Tt0.781], where X is the conversion fraction of the ore, w is stirring speed, D is particle size,more » and S/L is the solid/liquid ratio in weight. The activation energy for the process was found to be 21,408.55 J/mol.« less

Study on polyamide microcapsules containing oily liquids.

Oily liquids were microencapsulated within polyphthalamide membranes with dodecyl sulphonate sodium (DSS) as an emulsifier. The mean diameter and the distribution, as well as the zeta-potential, of the microcapsules were analysed. It was found that the mean diameter decreases with an increase in stirring speed and emulsifier concentration during the emulsification step. The addition of DSS to aqueous phase resulted in a decrease in zeta-potential of the microcapsules.

Microencapsulation of indomethacin by gelatin-acacia complex coacervation in the presence of surfactants.

Gelatin-acacia microcapsules containing indomethacin were prepared by a complex coacervation method. To improve the wetting of hydrophobic core material different surfactants, cationic benzalkonium chloride, anionic sodium lauryl sulphate (SLS) or non-ionic polysorbate 20, were used. The effects of surfactants on microencapsulation were investigated at concentrations below, at and above their critical micelle concentration (CMC) using three different stirring speeds (200, 310 and 420 rpm). A considerable fraction of the core was leached out during the dehydration of microcapsules with isopropanol when the capsules were prepared without surfactant, and especially with SLS. SLS was noted to be an unsuitable surfactant for this process of microencapsulation, and this was considered to be due to ionic complexes, solubilization of gelatin and too-effective spreading of small coacervate droplets. Benzalkonium chloride enhanced encapsulation at concentrations below and at CMC, but above CMC the encapsulation was slightly decreased due to too-effective spreading of coacervate. Polysorbate 20 enhanced encapsulation with all the concentrations allowing for the formation of intact-walled microcapsules. All the microcapsules reduced in size with increasing stirring speed. The two lowest concentrations of benzalkonium chloride and all the concentrations of polysorbate 20 increased microcapsule size due to a greater amount of the colloids being available in formation of thicker walled microcapsules. The dissolution of unencapsulated indomethacin was very slow, but the drug was released quickly from all the microcapsules whether or not any type of surfactant was used. A hydrophilic wall of gelatin-acacia microcapsules in itself ensured quick wetting of hydrophobic indomethacin.

The crystalline modification of succinic acid by variations in crystallization conditions

The crystallinity of samples of beta -succinic acid crystallized from aqueous solution has been observed to be influenced by the initial supersaturation and agitation intensity. Samples were prepared under controlled conditions from three initial supersaturations and at four stirrer speeds. For any initial supersaturation level the crystallization onset temperature decreased with increasing stirrer speed. This effect was attributed to a decrease in the width of the metastable zone. The increase in sample crystallinity as indicated by X-ray powder diffractometry was considered to result from differences in the predominating growth mechanism caused by variations in the supersaturation level for crystal growth. Scanning electron microscopy indicated a change in surface rugosity and a habit change for crystals prepared under one set of extreme conditions.

半溶融撹はん凝固したＡＺ９１Ｄマグネシウム合金の組織と機械的性質

Changes in microstructure and viscosity with both stirring conditions and a fraction of solid have been investigated in order to obtain fundamental aspects of various poroperties of a semi-solid stir-cast AZ91D magnesium alloy. Mechanical stirring was conducted during cooling of a liquid phase into mushy zone at a given temperature. Tensile test was performed for as-cast and T6-treated specimens. The primary α phase in specimens changed from the rosettelike α phase, whose dendrite arms were bent by stirring, to spheroid during the isothermal stirring. The spheroidization of the primary α phase and the decrease in their size were accelerated with the increase in stirring speed, stirrer width and the fraction of liquid. The stirring torque during the isothermal holding decreased in accordance with the spheroidization of the α phase. 0.2% proof stress of as-cast specimens was higher than the minimum value specified in JIS because of a fine eutectic phase crystallized by rapid cooling. Tensile properties of both as-cast and T6-treated samples had a tendency to decrease with increasing the fraction of solid. Tensile stress increased with the T6 heat treatment and the increment became higher with the fraction of solid being lower during isothermal stirring.

Effect of stirring on morphology and properties in a catalyst cured epoxy system

AbstractThis article describes the effect of stirring on epoxy network morphology and physical properties. Several different mechanical stirrer speeds, from 45 rpm to 800 rpm, were employed for the mixing of diglycidyl ether of bisphenol A resin with 2‐ethyl‐4‐methyl imidazole catalytic curing agent. The investigation indicated that the glass transition temperature, room temperature density, low temperature relaxation, tensile mechanical properties in the rubbery state, and nodular morphology are significantly affected by the stirrer speed used. Transmission electron microscopy has revealed that the extent of homogeneity for the dispersion of nodule domain in the low crosslinking matrix improved with increasing stirrer speed. However, an optimum stirrer speed condition is needed for achieving the most homogeneous system. In addition, it is shown that the room temperature tensile mechanical properties are independent of the mixing condition. This independence is ascribed to the fact that the glassy state mechanical properties are closely related to the intermolecular forces rather than to the network structure.

Morphology and clavulanic acid production of Streptomyces clavuligerus: Effect of stirrer speed in batch fermentations

Streptomyces clavuligerus ATCC 20764 was grown from spore-inocuia on a glycerol, malt extract, bacteriological peptone medium in 5-L batch fermentations at 490, 990, and 1300 rpm. Dry cell weights, clavulanic acid production, and the morphological parameters main hyphal length, total hyphal length, number of tips, and hyphal growth unit were measured. Growth and productivity were hardly dependent on stirrer speed. After early growth fragmentation of long, highly branched mycelia to shorter, less branched fragments occurred. This was followed by regrowth and, at 1300 rpm, a second fragmentation phase. The effect of increasing stirrer speed was to accelerate the initial fragmentation phase. It was clearly possible to obtain the same biomass concentration and clavulanic acid liter, with different morphologies depending on stirrer speed. This shows that for this fermentation at least there is no direct link between morphology and productivity and, hence, that it might be possible to manipulate them independently to improve fermentor performance.

Characterization of a Macrocycle-Mediated Dual Module Hollow Fiber Membrane Contactor for Making Cation Separations

Abstract Separation of metal cations in aqueous solution by a macrocyclemediated Dual Hollow Fiber Membrane Contactor is described. The advantages of this type of supported liquid membrane configuration include easily accessible source, receiving and membrane phases; transport rates competitive with those of other types of membranes; and the potential for continuous operation. The new system was investigated to determine the effect of aqueous solution flow rate and membrane solvent stirring rate on Na+ and K+ transport using dicyclohexano-18-crown-6 as the carrier. The results demonstrated that transport increases with increasing stirring speed, but remains constant with increased aqueous flow rate through the fibers within the range of four to twelve m1/min. The membrane solvents hexane, toluene, octane, 1-octanol, 4-methyl-2-pentanone, octanal, and 2-octanone were tested for their ability to preserve membrane integrity in the presence of aqueous solutions of low pH, and to maximize transport. Of these s...

The effect of agitation, purge time, and nonsimultaneous addition of acid and initiator on xanthated cellulose–polystyrene graft copolymer

AbstractConversion to polymer and molecular weight of grafted copolymer in the graft copolymerization of styrene initiated by the xanthate method is strongly dependent on reaction conditions even in the range of agitation speed when the effect of diffusion of monomer is neglected. When sulfuric acid and hydrogen peroxide are added simultaneously after 15 min of purging with nitrogen 99.99%, conversion and molecular weight vary little with stirring speed. Both parameters decrease with increasing stirring speed when H2 SO4 is added 1 min earlier than H2O2 and nitrogen is purged 15 min before starting the reaction. Both parameters increase when H2SO4 and H2O2 are added simultaneously after 60 min of purging with nitrogen. Highest conversion is observed when both reagents are added after 15 min of purging with nitrogen. Molecular weight is the highest at 310 rpm when H2SO4 is added 1 min earlier than H2O2, and at 1100 rpm when nitrogen is purged for 60 min.

Triphase catalysis. I. Kinetics and mechanism of alkylation of phenylacetonitrile with alkyl halides catalyzed by aqueous naoh and polymer‐supported benzyltriethylammonium chloride

AbstractThe alkylation and cycloalkylation of phenylacetonitrile (PAN) with excess of 1‐bromobutane and 1,4‐dibromobutane respectively catalyzed by aqueous NaOH and insoluble polystyrene‐bound benzyltriethylammonium chloride were studied and the rates depend upon several experimental parameters. The rate of cycloalkylation of PAN is five times faster than the alkylation and the former proceeds even in the absence of the solid catalyst. Both alkylation and cycloalkylation gave higher rates in reverse addition method than in direct addition. Deprotonation of PAN by hydroxide ion takes place without participation of the polymeric catalyst. The electrostatic force between the positive charge on the nitrogen atom of catalyst and carbanion is responsible for alkylation of active nitrile with polystyrene‐bound phase‐transfer catalyst. The rates of both the reactions increase with increased stirring speed, ring substitution, hydroxide ion concentration and catalyst amount and decrease with increased particle size and the degree of cross‐linking of the polymer. Apparent activation energies for the reactions were calculated. The kinetic results are discussed in terms of mass transfer and a combination of intraparticle diffusion and intrinsic reactivity limitations of the rates.

Leaching of FeS in aqueous chlorine solution

FeS leaching was carried out in aqueous chlorine solution at low temperatures (12–40°C) and ambient pressure ( ⋍610 mm Hg in Erzurum). The effects of particle size, reaction time, solid to liquid ratio, gas flow rate, temperature, and speed of stirring were investigated. The sulfide ion in the FeS was oxidized to sulfate and elemental sulfur during the leaching. Most of the oxidized sulfide ion was found in the solution as sulfate. All of the elemental sulfur was oxidized to sulfate as the reaction progressed to completion. The dissolution rate increased with increase in stirring speed and temperature, and with decrease in particle size, but it was not affected by the flow rate of Cl 2 and the solid to liquid ratio under the conditions covered in this study. The data were well correlated by the shrinking core-diffusion (through the fluid film) control model. The activation energy was calculated as 18.9 kJ mol −1.

Minimum seed crystal size for secondary nucleation of potassium alum in a stirred-vessel crystallizer.

The minimum seed crystal size or the minimum size, usually defined as the critical size greater than which seed crystals can produce secondary nuclei, was measured for potassium alum secondary nucleation using a seeded stirred-vessel crystallizer. The value was lowered with increasing stirrer speed both for stainless steel and acrylic resin impellers. The former impeller gave a smaller minimum size than the latter. The minimum size was newly interpreted as a measure of difficulty of nucleation, by defining it as the seed size at which the nucleation rate, being increased as the seed crystals grow, reached a certain detectable level. The behavior of the experimental results and literature data (effects of stirrer speed, supersaturation, impeller materials, impurities and system size) for laboratory crystallizers were reasonably but qualitatively explained in terms of secondary nucleation caused by crystal-impeller collisions. It was concluded that nucleation data obtained in a laboratory, using a small crystallizer, would be difficult to apply to industrial crystallizers because crystal-impeller collisions are unlikely to occur in large-scale industrial systems.

Graft Copolymerization of Methyl Acrylate by Ceric Ion in the Presence of a Controlled Amount of Oxygen

Abstract Methyl acrylate (MA) was grafted onto dissolving pulp by eerie sulfate in the presence of a controlled amount of oxygen. the magnitude and location of the maximum on the conversion vs the agitation speed curve are dependent on reaction conditions. the concentration of eerie sulfate and the reaction time are the most important determinants. the type of stirrer has only limited influence. the Ce(IV) consumption rises with increasing stirring speed due to higher diffusion of oxygen to active centers and is higher than for the oxidation of cellulose. the difference in Ce(IV) consumption for grafting and oxidation is not directly related to the amount of homopolymer because the grafting efficiency is independent of agitator speed. the rate of grafting is proportional to the amount of monomer to the second power, as a result of reaction of primary radicals with oxygen. Adding the MA later than the eerie sulfate causes a considerable increase in the induction period but no increase in the conversion. Hypothetical conversion curves are presented.

Semicontinuous emulsion polymerization of vinyl acetate. IV. Homopolymerization with poly(vinyl alcohol)

AbstractIn semicontinuous emulsion polymerization of vinyl acetate the system behaves as a flooded system in the first moment of the process. Then the polymerization rate becomes proportional to the introduced monomer. At moderate feed rate the polymerization rate is controlled by the addition rate. At a critical addition rate transition to a flooded system takes place. The conversion and particle diameter decrease with increasing stirring speed.

Grafting of vinyl monomers by the xanthate method

The removal of oxygen from swollen pulp is very difficult. At least 1–2 h of purging with oxygen-free nitrogen or argon is required as well as efficient mixing and a low concentration of pulp (not higher than 1%). During the grafting reaction, in which the xanthate cellulose is a part of the redox system, the concentration of oxygen falls to zero and stabilizes at this level even if air is purged through the system or a higher rate of stirring is applied. Primary sulfur radicals created in the reaction of the xanthated groups with H2O2 are further oxidized by H2O2 or by particles of oxygen dissolved in the reaction mixture. The observed increase in reaction caused by an increase in stirring speed is due to the higher rate of diffusion of hydrophobic monomers as well as the diffusion of oxygen to active centers at high stirring speed. The low rate of grafting at lower agitation speeds is caused by agglomeration of monomer molecules to bigger particles and, as a result, decreased diffusion of monomer to active centers. Above 300 rpm, the effect of monomer diffusion diminishes and further increase in conversion is caused only by a higher rate of oxygen diffusion to active centers from reaction mixture or passing gas. However, above a certain level of oxygen, the effect of termination by oxygen prevails and the rate of reaction decreases. Additives increase the conversion in the lower range of agitation speed only. The application of additives and agitation are two equivalent methods, both of which lead to an increase in conversion in the lower range of stirring speed.

Effect of Agitation Intensity on the Dissolution Rate of Indomethacin and Indomethacin-Citric Acid Compressed Discs

AbstractThe dissolution rates of indomethacin (IMC) and indomethacin-citric acid (monohydrate) 1:1 mixtures under various hydrodynamic conditions were determined in a phosphate buffered medium Dissolution profiles of the γ form of IMC were nonlinear the rates decreasing with time The dissolution rates increased with increasing stirring speed In contrast α-IMC gave linear dissolution profiles the rates being higher and more sensitive to agitation intensity than those obtained using the γ-form. The slope of a log dissolution rate versus log stirring speed plot had a value of 0.598 for γ-IMC and 0.171 for γ-IMC Indomethacin dissolution rates from the mixed discs were 5-10 times lower than those of pure γ-IMCin the stirring speed range 180-60 rpm respectively The dissolution profiles of IMC showed positive curvature at low stirring speed while at high stirring speed the dissolution profiles became linear The slope of the log dissolution rate versus log stirring speed plot was nonlinear and ranged from >1 at l...

Polyarylates. III. Kinetic studies of interfacial polycondensation

AbstractThe kinetics of interfacial polycondensation of bisphenol A with isophthaloyl chloride and terephthaloyl chloride in dichloromethane with triethylbenzylammonium chloride (TEBAC) as the catalyst was investigated via measurements of bisphenolate concentration by UV. The reaction was found to be second order with respect to bisphenolate. The dependence of the rate constant on stirring speed, amount of TEBAC, and reaction temperature was studied. The rate constant was increased with an increase of stirring speed, quantity of TEBAC added, as well as the reaction temperature. The activation energy was found to be 7.7 kcal/mol at a stirring speed of 700 rpm in the presence of 0.160 of TEBAC. The role of TEBAC was found to be interesting. It did not alter the equilibrium (the partition coefficient remained the same in the presence of TEBAC), but it did enhance the transfer rate of bisphenolate.

Coarsening during stircasting

A difference in coarsening of Al-6Cu alloy and the organic substance neopentylalcohol (NPA) was observed during stircasting. It was found that the coarsening of Al-6Cu is independent of the applied stirring speed, whereas the coarsening of NPA was found to increase with increasing stirring speed. It appears that this difference can be explained by the influence of convection around the suspended primary particles, which have a different morphology in Al-6Cu and NPA in the early stages of the solidification during stircasting.

Theoretical and experimental investigations on macrosegregation caused by mixing in the liquid bulk melt

An improved model describing the macrosegregation caused by mixing in the liquid bulk melt is presented. This model includes the mass transfer between the interdendritic liquid and the bulk melt which takes place additionally to the mass transfer via the boundary layer in front of the dendrite tips. Further, laboratory experiments on macrosegregation of iron‐carbon alloys are described. The experiments were carried out in a unidirectional solidification device with 1,5 kg melts. During the solidification process the liquid melt was stirred by a ceramic blade stirrer with rotational speeds between 180 and 720 min−1. The melts were supperheated above the liquidus temperature by amounts between 3 and 80 K. The solidification velocities were 2 to 6 mm/min. The experiments could satisfactorily be described by the model using an exchange factor α for the amount of additional mass transfer. The exchange factor increases with decreasing amounts of superheating and solidification velocity and with increasing stirring speed.