Effects Of Stirring Rate Research Articles

Water extraction of pyrolysis oil: The first step for the recovery of renewable chemicals

The interest in biomass as a source of renewable energy and chemicals has been increasing in keeping up with the transition to a sustainable bio-based economy. An important initial step of chemicals recovery from biomass-derived pyrolysis oil is water extraction where most of polar compounds are isolated in the aqueous phase. This study was done to investigate the effects of stirring rate and water-to-oil ratio on the extraction capability (distribution coefficient and yield), water content, and atomic composition of both aqueous and organic phases. The results show that the stirring rate above 300rpm has no influence on the equilibrium. Increasing the water-to-oil ratio dilutes the aqueous phase without changing the atomic distribution. Forest residue-derived pyrolysis oil should be extracted at a water-to-oil ratio of 0.65–0.7, whereas pine-derived pyrolysis oil is preferably extracted at the lowest feasible water-to-oil ratio where complete phase separation occurs, which is 0.5 in this study.

Effects of stirring rate for thermal runaway reaction in cumene hydroperoxide manufacturing process using calorimetric techniques

Oxygen (O2) or air is widely applied globally to yield cumene hydroperoxide (CHP) in a cumene oxidation tower. In previous studies, CHP has been identified as a thermally hazardous chemical. This study was used to evaluate thermal hazard of CHP in cumene using differential scanning calorimetry and vent sizing package 2 (VSP2). Self-accelerating decomposition temperature (SADT), self-heating rate, exothermic onset temperature (T0), critical temperature (Tc), time to maximum rate (TMR), activation energy (Ea), etc., were employed to prevent and protect thermal runaway reaction and explosion in the manufacturing process and/or storage area. The reaction order (n) of CHP was evaluated to be 0.5 in this study. The Ea was determined to be 122 kJ mol−1 by VSP2. High volume of CHP with 0 rpm of stirring rate by VSP2 was more dangerous than a low one. Control of stirring rate should be a concern in process safety management program. In view of proactive loss prevention, inherently safer handling procedures and storage situations should be maintained in the chemical industries.

Study on Free Lipase‐Catalyzed Ethanolysis for Biodiesel Preparation in an Oil/Water Biphasic System

AbstractUsing free lipase as the catalyst for biodiesel production has drawn increasing attention in recent years due to its advantages of lower cost and faster reaction rate compared to immobilized lipase. Our previous study showed that free lipase NS81006 could effectively catalyze the methanolysis of renewable oil. Ethanol, derived from renewable biomass, has a greater potential for biodiesel production. In this paper, ethanol was explored for the first time as the acyl acceptor for free lipase‐mediated biodiesel preparation. The effect of stirring rate, water content, molar ratio of ethanol to oil and ethanol adding strategy was investigated systematically during the process of free lipase NS81006‐catalyzed ethanolysis. An ethyl ester yield of 90% was obtained under the optimized conditions. Further study showed that the free lipase could be repeatedly used by simple separation of the water phase from the oil phase and there was no obvious loss in lipase activity after five repeated uses.

Effect of stirring rate on the microstructure and microhardness of Ni–CeO2 nanocomposite coating and investigation of the corrosion property

The nickel–ceria nanocomposite coatings have been pulse electrodeposited from a Watts-type electrolyte containing nano-sized ceria particles have been synthesized by high energy ball milling technique. The influence of the stirring rate of the plating bath on the microstructure and hardness of nickel–ceria nanocomposite coating has been investigated and the corrosion property of the nanocomposite coatings has also been studied. Experimental results show that both the co-deposition of ceria particles in the Ni matrix and microhardness of the composite coating increase up to the stirring rate of 450rpm. Beyond this stirring rate the co-deposition of ceria particles decreases in the Ni matrix resulting in a decrease in the hardness of the composite coating. Another reason of decreasing hardness of the composite coating is the agglomerations of ceria particles that take place after the stirring rate of 450rpm. Higher corrosion resistance has been found for the nickel–ceria nanocomposite coating electrodeposited from electrolyte with the stirring rate of 450rpm.

Adsorption of food dyes acid blue 9 and food yellow 3 onto chitosan: Stirring rate effect in kinetics and mechanism

Adsorption of food dyes acid blue 9 and food yellow 3 onto chitosan was studied. Stirring rate influence on kinetics and mechanism was verified. Infra-red analysis was carried out before and after adsorption in order to verify the adsorption nature. Adsorption experiments were carried out in batch systems with different stirring rates (15–400rpm). Kinetic behavior was analyzed through the pseudo-first-order, pseudo-second-order and Elovich models. Adsorption mechanism was verified according to the film diffusion model and HSDM model. Pseudo-second-order and Elovich models were satisfactory in order to represent experimental data in all stirring rates. For both dyes, adsorption occurred by film and intraparticle diffusion, and the stirring rate increase caused a decrease in film diffusion resistance. Therefore, the film diffusivity increased the adsorption capacity and, consequently, intraparticle diffusivity increased. In all stirring rates, the rate-limiting step was film diffusion. Adsorption of acid blue 9 and food yellow 3 onto chitosan occurred by chemiosorption.

Gastroretentive microballoons of metformin: Formulation development and characterization.

The present study involves preparation and evaluation of floating microballoons with metformin as model drug for prolongation of gastric residence time. The microballoons were prepared by the solvent evaporation method using polymers hydroxypropylmethyl cellulose and ethyl cellulose. The shape and surface morphology of prepared microballoons were characterized by optical and scanning electron microscopy, respectively. In vitro drug release studies were performed and drug release kinetics was evaluated using the linear regression method. Effects of stirring rate during preparation, polymer concentration, solvent composition and dissolution medium on the size of microballoons, and drug release were also observed. The prepared microballoons exhibited prolonged drug release (8 hours) and remained buoyant for >10 hours. The mean particle size increased and the drug release rate decreased at higher polymer concentration. No significant effect of the stirring rate during preparation on drug release was observed. In vitro studies demonstrated diffusion-controlled drug release from the microballoons.

Emulsifier-Free, Organotellurium-Mediated Living Radical Emulsion Polymerization of Styrene: Effect of Stirring Rate

The effect of stirring rate on control/livingness and particle formation in emulsifier-free organotellurium-mediated living radical emulsion polymerization (emulsion TERP) of styrene at 60 °C was i...

Head Space Solid Phase Micro-Extraction (HS - SPME) of volatile organic compounds produced by Sporidiobolus salmonicolor (CBS 2636)

The aim of the present study was the assessment of volatile organic compounds produced by Sporidiobolus salmonicolor (CBS 2636) using methyl and ethyl ricinoleate, ricinoleic acid and castor oil as precursors. The analysis of the volatile organic compounds was carried out using Head Space Solid Phase Micro-Extraction (HS - SPME). Factorial experimental design was used for investigating extraction conditions, verifying stirring rate (0-400 rpm), temperature (25-60 ºC), extraction time (10-30 minutes), and sample volume (2-3 mL). The identification of volatile organic compounds was carried out by Gas Chromatography with Mass Spectrum Detector (GC/MSD). The conditions that resulted in maximum extraction were: 60 ºC, 10 minutes extraction, no stirring, sample volume of 2.0 mL, and addition of saturated KCl (1:10 v/v). In the bio-production of volatile organic compounds the effect of stirring rate (120-200 rpm), temperature (23-33 ºC), pH (4.0-8.0), precursor concentration (0.02-0.1%), mannitol (0-6%), and asparagine concentration (0-0.2%) was investigated. The bio-production at 28 ºC, 160 rpm, pH 6,0 and with the addition of 0.02% ricinoleic acid to the medium yielded the highest production of VOCs, identified as 1,4-butanediol, 1,2,2-trimethylciclopropilamine, beta-ionone; 2,3-butanodione, pentanal, tetradecane, 2-isononenal, 4-octen-3-one, propanoic acid, and octadecane.

Removal of safranin from aqueous solutions by NaOH‐treated rice husk: thermodynamics, kinetics and isosteric heat of adsorption

ABSTRACTSafranin is a widely used, cationic, azine synthetic dye, and because of various adverse properties any effluent streams require treatment prior to discharge. The correct disposal of synthetic dye wastewater after proper treatment is difficult because of the dye properties and their resistance to degradation processes. Adsorption is often an effective, economical and useful process for the treatment of dye effluents. The potential use of rice husk, a plentiful waste agricultural product, to remove safranin from aqueous solution by a batch adsorption process was evaluated. Rice husk was transformed into an effective adsorbent material by treating with sodium hydroxide (NaOH). During the treatment process, the effects of stirring rate, temperature, pH, initial dye concentration and sorbent dose were studied. The maximum dye adsorption was obtained at pH 8. The Langmuir isotherm model was a good representation of the equilibrium data, and the maximum monolayer adsorption capacity obtained was 37.97 mg g−1 at 303 K. The mean free energy (E) estimated from the Dubinin–Radushkevich (D–R) model indicated that the main mechanism governing the sorption process was chemical ion‐exchange. The kinetic data were shown to be represented by the pseudo‐second‐order model and the intraparticle diffusion model. The Arrhenius and Eyring equations were used to evaluate the activation parameters. The activation energy was estimated to be 46.57 kJ mol−1. Gibbs' free energy was spontaneous for all interactions, and the adsorption process exhibited endothermic enthalpy values. The isosteric heat of adsorption, determined using the Clausius–Clapeyron equation, increased directly in relation to the surface loading showing its strong dependence on surface coverage. Results suggest that NaOH‐treated rice husk is a potential low‐cost adsorbent for safranin removal from aqueous solution. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Adsorption Thermodynamics and Kinetics of Malachite Green onto Ca(OH)2-Treated Fly Ash

Fly ash, an industrial by-product abundant in India, was treated with alkali and tested as a low-cost adsorbent for the removal of malachite green from an aqueous solution in a batch adsorption procedure. Effects of stirring rate, temperature, pH, initial dye concentration, contact time, and adsorbent dose were investigated. The adsorption was found to be strongly dependent on pH of the medium and the adsorption capacity decreased with an increase in temperature. The Langmuir isotherm model showed a good fit to the equilibrium adsorption data at all temperatures. The mean free energy (E) estimated from the Dubinin-Radushkevich model indicated that the adsorption mechanism was chemical ion exchange. The kinetic data were found to follow the pseudo second-order kinetic model. The rate constant decreased with the increase in temperature indicating the exothermic nature of adsorption. Intraparticle diffusion was not the sole rate-controlling factor. The Arrhenius and Eyring equations were used to evaluate the...

Dye/water separation through supported liquid membrane extraction

The separation of synthetic dye Rhodamine 6G (R6G) and water was investigated using blended organic liquids in a supported liquid membrane (SLM) extraction system. Liquid membrane (LM) components include octyl alcohol (OcOH) as the dye extractant and a polysiloxane liquid as the stabilizing agent. Initial permeation results revealed the suitability of poly (phenyl methyl) siloxane (PPMS) over poly (octyl methyl) siloxane as the blending agent. The most acceptable condition for dye extraction was determined at feed solution pH≅1, wherein highest distribution coefficient, KD (OcOH/H2O)=18, was attained. Though permeability decreased at optimal blending condition of 1:1 (w/w) OcOH/PPMS, SLM longevity was exhibited with>98% LM retention after 15h operation in contrast to pure OcOH SLM system (>60% LM loss). Equilibrium experiments reveal that dye extraction followed Langmuir adsorption principle. The dye transport was elucidated using mass transfer analysis wherein it showed a decrease in overall coefficient (ko) at increasing feed concentrations. This was a direct consequence of KD decline, which becomes more apparent at higher concentrations when SLM saturation point is approached. At varied hydrodynamic conditions, improved ko values were observed up to Reω=10,000 when minimal variation in film resistance is attained. Beyond this condition, ko becomes independent from stirring rate effect nonetheless SLM stability is compromised due to shear-induced LM losses.

MODELING PROCESS DYNAMICS USING A NOVEL NEURAL NETWORK ARCHITECTURE: APPLICATION TO STIRRED CELL MICROFILTRATION

A novel neural network architecture is presented for dynamic process modeling, using stirred cell microfiltration of bentonite suspensions as a model system. Unlike previous studies that include time explicitly as a network input and have a single output at that time, the network architecture presented contains the process variables as inputs and many outputs representing the output (filtrate flux in this case) at different selected times. The network is shown to represent the stirred cell microfiltration of bentonite suspensions over a range of pressures (0.2–1.5 bar), initial concentrations (0.5–2.0 g/L), stirrer tip speeds (0.04–0.17 m/s), membrane resistances (3.09 × 1010–6.85 × 1010 m−1), pH values (2.5–10.4), and temperatures (20°–24°C) with good accuracy (R2 = 0.91 on network test data). With this network architecture, it becomes easy to track the time dependence of the relative effect of the various process parameters on the system output. Thus, for example, the network weights show that the effect of stirring rate on flux increases as time progresses, while the opposite effect is seen for membrane resistance, as expected.

Control of drug loading efficiency and drug release behavior in preparation of hydrophilic-drug-containing monodisperse PLGA microspheres

We prepared monodisperse poly(lactide-co-glycolide) (PLGA) microspheres containing blue dextran (BLD)--a hydrophilic drug--by membrane emulsification technique. The effects of electrolyte addition to the w(2) phase and significance of the droplet size ratio between primary (w(1)/o) and secondary (w(1)/o/w(2)) emulsions during the preparation of these microspheres was examined. The droplet size ratio was evaluated from the effect of stirring rate of the homogenizer when preparing the primary emulsion. The drug loading efficiency of BLD in these microspheres increased with stirring rate. It increased to approximately 90% when 2.0% NaCl was added to the w(2) phase. Drug release from these microspheres was slower than that when they were prepared without electrolyte addition. Despite the very high efficiency drug release was gradual because BLD was distributed at the microspheres core. Relatively monodisperse hydrophilic-drug-containing PLGA microspheres with controlled drug loading efficiency and drug release behavior were prepared.

Microencapsulated n-Octadecane with styrene-divinybenzene co-polymer shells

Microcapsules containing n-Octadecane using styrene (St)-divinybenzene (DVB) co-polymer shells were synthesized by suspension-like polymerization. The effects of stirring rates and monomers/n-Octadecane mass ratios on the average diameter and phase change properties of microencapsulated n-Octadecane (MicroC18) were investigated. The surface morphology, diameters, phase change properties and thermal decomposition temperature of MicroC18 were investigated by using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electronic Microscope (SEM), Differential Scanning Calorimeter (DSC), and Thermogravimetric Analysis (TGA). The average diameters of MicroC18 decreased with an increase of stirring rate. When the monomers/n-Octadecane mass ratio of 1:1 is used, the enthalpy of MicroC18 reaches the highest-126 J/g. Surfaces of majority of MicroC18 show large concaves because of the production of reserved expansion space in the process of micro-encapsulation. The thermal decomposition temperature of MicroC18 is about 230 °C which is higher than that of MicroC18 using melamine-formaldehyde shell.

Effect of silicone oil fraction and stirring rate on methane degradation in a stirred tank reactor

AbstractBACKGROUND: Methane is an important greenhouse gas and its biological oxidation constitutes a cost‐effective alternative for low concentration emissions. Nevertheless, due to its low aqueous solubility (similar to oxygen), gas mass transfer is often the limiting step. Two‐phase partition bioreactors (TPPBs), have been proposed to increase the biodegradation of poorly soluble compounds. In this work, the effect of stirring rate and silicone oil fraction on abiotic volumetric oxygen transfer coefficient kLa and methane elimination capacity (EC) by a methanotrophic consortium in a stirred tank was studied.RESULTS: In abiotic conditions, the kLa increased when increasing both factors. Nevertheless, a negative effect on kLa was observed with silicone oil at the highest stirring rate (800 rpm). During methane biodegradation experiments, EC also improved when increasing both factors, but contrary to abiotic kLa, it was not affected at the highest stirring rate. While stirring rate was the dominant variable determining methane biodegradation, the effect of oil fraction was only significant above 200 rpm. A maximum EC improvement of 700% was observed when increasing stirring rate from 200 to 800 rpm with 10% of silicone oil.CONCLUSIONS: Increasing both stirring rate and oil fraction enhanced EC. The results were different from those observed with kLa suggesting that kLa is not sufficient to describe properly the mass transfer in TPPB because other factors (interfacial contact between the phases and physicochemical properties of organic phase) should be considered. Copyright © 2010 Society of Chemical Industry

Reduction Kinetics of Chromium(VI) by S(-II) in Alkalescent Aqueous Media

Batch experiments were performed to study the reaction kinetics of chromium( VI) and S(-II) in alkalescent aqueous media with high reactant concentrations. Effects of stirring rate, pH, initial Cr(VI) concentration, temperature and inert substance concentration on Cr(VI) reduction were experimentally investigated. Apparent reaction kinetics were obtained. The apparent activation energy(E(a)) of the reaction was ca. 30.9 kJ . mol(-1) at temperature range of 303-333 K and the reaction showed positive salt effect in the low inert substance concentration media of 0.025-0.25 mol/L, suggesting that the actual reactants might be HCrO(4)(-) and HS(-).

Electrochemical Determination of Phenothrin in Agricultural Formulations, Vegetables, and Storage Bags of Wheat and Rice by Differential Pulse Adsorptive Stripping Voltammetry (DP-AdSV)

An electroanalytical method has been developed for the determination of the pesticide phenothrin by differential pulse adsorptive stripping voltammetry on a hanging mercury drop electrode in universal buffer as supporting electrolyte. The best adsorption conditions were found to be pH 6.0, an accumulation potential of −0.6 V, and an accumulation time of 75 s. Effects of stirring rate, scan rate, pulse amplitude, and purge time were examined for the optimization of instrumental conditions. Calibration curve is linear in the range 2 × 10−9 to 2 × 10−7 mol l−1 with a detection limit of 1.9 × 10−10 mol l−1. The correlation coefficient and relative standard deviation were 0.995% and 1.1%. The method is applied to the determination of the phenothrin in agricultural formulations, vegetables, and storage bags of wheat and rice under Food Corporation of India’s storage system.

Modelling of zinc (II) transport through a PC-88A supported liquid membrane

Zinc has been permeated through a flat-sheet supported liquid membrane, using 2-ethylhexylphosphoric acid mono-2-ethylhexyl ester (PC-88A) in kerosene. Liquid–liquid experiments were conducted as a function of aqueous pH (1–6) to establish optimum conditions for both extraction and stripping of the metal. A mass-transfer model was developed to predict the extent of Zn(II) permeation through the supported liquid membrane (SLM) under different experimental conditions. The effect of stirring rate, carrier concentration and temperature upon metal transport has been evaluated. The metal flux has been derived taking into account stagnant layer aqueous diffusion and liquid membrane diffusion as controlling factors. The overall transport evaluated from the proposed resistances model was in reasonable agreement with those obtained from experimental data. Under the studied experimental conditions the resistance of the intrinsic organic phase is masked by the aqueous stagnant layer resistance; therefore the Zn (II) transport through the liquid membrane is mainly controlled by the hydrodynamic of the system.

Mechanism for the release of the industrial biocide CMI from clathrate crystal

This paper investigated the effect of stirring rate on the behavior and mechanism of the release of the biocide CMI from clathrate crystals, with TEP as the host. During the process of releasing CMI (guest) from TEP–CMI crystals in solvent mixtures of methanol and water, the TEP host structure transformed into a stable form including solvent molecules as guests. At high stirring rates, CMI concentration increased quickly with time and attained higher concentrations than at low stirring rates. TEP concentration also increased quickly with time and after the appearance of a peak, it attained a lower value than that at low stirring rates. With increases in the stirring rate, the peak occurred earlier and the height of the peak increased. At a high stirring rate (450 rpm), the crystals were dispersed completely in the solution and a true equilibrium was established between the crystals and the solution, while lower stirring rates were considered to result in quasi-equilibrium. This may have been due to the disturbance of the diffusion of CMI molecules from TEP–CMI crystals by the new phase of TEP–SOL crystals precipitating on the surface of the agglomerated TEP–CMI crystals. The concentration attained was expressed as a function of the solvent composition. The change in concentration during the dissolution process and the equilibrium concentration in the presence of the two solid phases were elucidated using a model containing the dissociation constants of the solids.

Investigation of reduction kinetics of Cr2O72− in FeSO4 solution

Abstract The kinetics of reduction of potassium dichromate (K 2 Cr 2 O 7 ) by Fe 2+ ions in sulfuric acid (H 2 SO 4 ) solution have been investigated under well-defined hydrodynamic conditions. The reaction has been monitored potentiometrically by measuring volt values between saturated calomel electrode and a Pt electrode. The effect of stirring rate, particle size, temperature, Fe 2+ and H + concentrations have been studied. It was found that the reaction kinetic model achieved in the study was chemical reaction control model. The reaction has been analyzed using kinetic equation t = τ (1 − (1 − x ) 1/3 ). The rate has been found proportional to [Fe 2+ ] 0.5 [H + ] 0.5 and the apparent activation energy has been determined as 46.18 kJ mol −1 .