The Effect of Size and Concentration of Nanoparticles on the Mass Transfer Coefficients in Irregular Packed Liquid–Liquid Extraction Columns

This investigation explored the effects of nanofluids on mass transfer enhancement using an irregularly packed liquid–liquid extraction column and the chemical systems of water–acetic acid–toluene. SiO₂ nanoparticles with sizes of 10, 30, or 80 nm are dispersed in toluene–acetic acid to produce nanofluids with different volume fractions of 0, 0.01, 0.05, and 0.1 vol.%. The effects of nanoparticle size and concentration on dispersed phase mass transfer coefficient were discussed based on the experimental data. This is for the first time that the effect of nanoparticle size is studied in liquid–liquid extraction systems. It was found that the mass transfer enhancement was more significant in nanofluids with smaller particles. It was also observed that mass transfer coefficient is larger in nanofluids compared to that in dispersed phase without nanoparticles, with a peak enhancement at a nanoparticle volume fraction of 0.05 vol.% for 10-nm particles and 0.01 vol.% for 30- and 80-nm particles. The maximum mass transfer coefficient enhancement was approximately 42% at 0.05% concentration of nanoparticles using smaller particles (10 nm). Finally, a novel correlation for prediction of effective diffusivity in the presence of nanoparticles has been proposed, which is a function of nanoparticle size and its concentration. The main advantage of this approach is that the principal effect of these two parameters is considered in correlation without which the experimental data could not be fitted with an acceptable accuracy.     

Mass transfer into/from nanofluid drops in a spray liquid‐liquid extraction column

The performance of a spray liquid‐liquid extraction column at two mass‐transfer directions was experimentally studied in the presence of silica nanoparticles. Toluene‐based nanofluid drops containing 0.0005–0.01 vol % silica nanoparticles were dispersed in aqueous phase and acetic acid (AA) transfer between phases was investigated. The experiments were performed at fixed volumetric flow rates of dispersed and continuous phases. Maximum enhancement of 47.4% and 107.5% in overall mass‐transfer coefficient, respectively, for mass‐transfer direction of dispersed to continuous phase and vice versa were achieved for drops with 0.001 vol % silica nanoparticles. These enhancements can be referred to Brownian motion of nanoparticles and induced microconvection. The results showed that nanoparticles are more effective in augmenting AA transfer from continuous to dispersed phase. Probable reason is that smaller diameter and lower internal turbulence of drops in this transfer direction increase dispersed phase resistance potential to be manipulated by Brownian motion of nanoparticles. © 2015 American Institute of Chemical Engineers AIChE J, 62: 852–860, 2016     

Bubble/droplet formation and mass transfer during gas–liquid–liquid segmented flow with soluble gas in a microchannel

Microchannels have great potential in intensification of gas–liquid–liquid reactions involving reacting gases, such as hydrogenation. This work uses CO₂–octane–water system to model the hydrodynamics and mass transfer of such systems in a microchannel with double T‐junctions. Segmented flows are generated with three inlet sequences and the size laws of dispersed phases are obtained. Three generation mechanisms of dispersed gas bubbles/water droplets are identified: squeezing by the oil phase, cutting by the droplet/bubble, cutting by the water–oil/gas–oil interface. Based on the gas dissolution rate, the mass transfer coefficients are calculated. It is found that water droplet can significantly enhance the transfer of CO₂ into the oil phase initially. When bubble‐droplet cluster are formed downstream the microchannel, droplet will retard the mass transfer. Other characteristics such as phase hold‐up, bubble velocity and bubble dissolution rate are also discussed. The information is beneficial for microreactor design when applying three‐phase reactions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1727–1739, 2017     

Effect of silica nanoparticles on the phase inversion of liquid-liquid dispersions

The effect of silica nanoparticles on phase inversion of liquid-liquid dispersions in a stirred vessel was investigated. The studied systems were toluene dispersed in water and vice versa. In the first set of experiments, phase inversion behavior of systems without Silica nanoparticles was evaluated and subsequent experiments were conducted in the presence of the nanoparticles. For this purpose, Silica nanoparticles of different concentrations (0.01, 0.03, 0.05, 0.07 wt%) were dispersed in water. The nanofluid stability was examined using an ultraviolet-visible (UV-vis) spectrophotometer. The results indicated that increase in silica nanoparticle concentrations up to 0.07 wt% led to increase in agitation speed of phase inversion 43–53.5% and 38.5–45% in the case of O/W and W/O dispersions, respectively. Consequently, the tendency of dispersions to inversion diminished as nanoparticle concentrations increased. Finally, 0.05 wt% of silica nanoparticle was selected as the optimum on the range studied.     

Prediction of average droplet size in flowing immiscible polymer blends

The paper is focused on calculation of the average droplet size in immiscible blends during their steady flow. Available theoretical and experimental results of studies of the droplet breakup and coalescence are utilized to derive the equations describing dynamic equilibrium between the droplet breakup and coalescence. New expression for the coalescence efficiency, reliably reflecting recent theoretical results, is proposed. The equation for the average steady droplet size, controlled by the stepwise breakup mechanism and coalescence of droplets with not very different sizes, is derived for blends containing up to 10–20 vol % of the droplets. For blends with above approximate 20 vol % of the droplets, the breakup by the Tomotika mechanism and coalescence in highly polydisperse system is modeled. Results of the derived equations are compared with experimental data; qualitative agreement is found for the dependence of the droplet size on the amount of the dispersed phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45250.     

Fabrication and Thermal Properties of Polyimide/Ba0.77Sr0.23TiO3 Nanocomposites

Polyimides (PIs) are considered to be one of the most important engineering materials. The nano-particle of barium strontium titanate (BST) with formulation of Ba_0.77Sr_0.23TiO₃ was synthesized by the sol-gel method. In this process, different contents of BST suspensions in polyamic acid (PAA) solution were imidized by heat treatment to form PI/BST nanocomposites. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), simultaneous thermal analysis (STA), scanning electron microscope (SEM), and transmission electron microscopy (TEM) were used to characterize the structure and properties of the obtained nanocomposites. It was found that the BST nanoparticles sized 32–40 nm were dispersed homogeneously in the polyimide matrix without aggregation. The ζ potential of PI/BST 33 vol.% was decreased in contrast with that of the pure polyimide. The coefficient of thermal expansion (CTE) of PI/BST 33 vol.% was measured between 36°C and 600°C. CTEs comparison showed about 80% decrease in the CTE value of the nanocomposite in respect to the pure polyimide in a wider temperature range.     

Synthesis and encapsulation of magnetite nanoparticles in PLGA: effect of amount of PLGA on characteristics of encapsulated nanoparticles

Oleic acid-coated superparamagnetic iron oxide nanoparticles (Fe₃O₄) encapsulated within poly(d,l-lactide-co-glycolide) (PLGA) particles were prepared by the w/o/w emulsion technique using poly(vinyl alcohol) as a dispersant. The concentration of PLGA in the oil phase was varied (5, 15, 30, 45, and 60?mg/ml) at constant magnetite concentration in the oil phase (5?mg/ml) to study the properties of composite Fe₃O₄–PLGA nanoparticles. Even though PLGA concentration varied widely in the oil phase, the weight percent of 7–16?nm diameter magnetite in the particles varied only from 56 to 62?% (23–28?vol.%). The obtained composite nanoparticles were essentially spherical with magnetite spatially uniformly dispersed in individual PLGA particles, as measured by transmission electron microscopy (TEM). Also, the magnetite concentration in each particle did not vary widely as determined qualitatively via microscopy. Hydrodynamic diameters of the composite nanoparticles as measured by dynamic light scattering increased by approximately 10?% with added magnetite, with a smaller relative increase in diameter measured by TEM. The zeta potential of the particles was about ?26?mV, independent of Fe₃O₄ loading. Relatively high saturation magnetizations (36–45?emu/g) were measured for these highly loaded particles, with the latter value only 7?emu/g lower than the value measured for the oleic acid-coated particles alone.     

A study on hydrodynamic characteristics in a Φ38 pulsed extraction column by four‐sensor optical fiber probe

Accurate prediction of dispersed phase droplet behavior is crucial to the design and scaling‐up of an extraction column. In this article, the dispersed droplet velocity algorithm and the diameter algorithm in a liquid–liquid two‐phase flow have been developed based on the bubble velocity model in gas–liquid two‐phase flow of Lucas [Measurement Science & Technology. 749, 758(2005)] and Shen [International Journal of Multiphase Flow. 593, 617(2005)]. Hydrodynamic characteristics, including droplet diameter, holdup and droplet velocity, were measured using a self‐made four‐sensor optical fiber probe in a 38 mm‐diameter pulsed sieve‐plate extraction column. Water and kerosene were used as continuous and dispersed phases, respectively. The influences of the pulsed intensity, the continuous and dispersed phase superficial velocities on the hydrodynamic characteristics were investigated. The experimental results show that it is reliable to use a four‐sensor optical probe to measure the hydrodynamic characteristics of a pulsed extraction column. © 2016 American Institute of Chemical Engineers AIChE J, 63: 801–811, 2017     

Novel continuous process for methacrolein production in numerous droplet reactors

A continuous process for methacrolein production was constructed by filling w/o Pickering emulsions in a column reactor. Ionic liquid (IL-[HDEA]Ac) with secondary amine was designed to catalyze propionaldehyde condensation with formaldehyde through the Mannich reaction. Emulsion droplets encapsulated with IL aqueous solution were stabilized with modified SiO₂ nanoparticles and dispersed in cyclohexane, which could be observed as numerous reactors. The properties of SiO₂ stabilizer, such as wettability, surface groups, and the effect on interfacial tension were investigated. The characteristics of emulsion influenced by stabilizer properties and content were systematically studied. The droplet size, IL concentration and liquid hourly space velocity were optimized. The droplets were evaluated at 0.5 hr⁻¹ for 150 hr without IL leakage and obvious activity decreasing, indicating the excellent stability of the emulsion system. The continuous process showed a 1.25-fold enhancement in catalysis efficiency and less equipment compared to batch process.     

On the Use of Ruthenium Dioxide in 1-n-Butyl-3-Methylimidazolium Ionic Liquids as Catalyst Precursor for Hydrogenation Reactions

The H₂ reduction of RuO₂ hydrate “dissolved” in 1-n-butyl-3-methylimidazolium ionic liquids with different counterions, hexafluorophosphate (BMI ? PF₆), tetrafluoroborate (BMI ? BF₄) and trifluoromethane sulfonate (BMI ? SO₃CF₃), is a simple and reproducible method for the preparation of ruthenium nanoparticles of 2.0–2.5?nm diameter size and with a narrow size distribution. The Ru nanoparticles were characterized by TEM and XRD. The isolated Ru nanoparticles are reoxidized in air, whereas they are less prone to oxidation when imbibed in the ionic liquids. These nanoparticles are active catalysts for the solventless or liquid–liquid biphasic hydrogenation of olefins under mild reaction conditions (4 atm, 75°C). The catalytic system composed of nanoparticles dispersed in BMI ? PF₆ ionic liquid is very stable and can be reused several times without any significant loss in the catalytic activity. Total turnover numbers greater than 110 000 (based on total Ru) or 320 000 (corrected for exposed Ru atoms) were attained within 80?h for the hydrogenation of 1-hexene.     

Corrosion inhibition of carbon steel under two‐phase flow (water‐petroleum) simulated by turbulently agitated system

The corrosion of carbon steel in single‐phase (water with 0.1N NaCl) and two immiscible phases (kerosene‐water) using turbulently agitated system was investigated. The experiments were carried out for Reynolds number (Re) range of 38 000 to 95 000 using circular disc turbine agitator at 40°C. In two‐phase system, test runs were carried out in aqueous phase (water) concentrations of 1% vol, 5% vol, 8% vol, and 16.4% vol mixed with kerosene at various Re. The effect of Re, percent of dispersed phase, dispersed droplet diameter, and number of droplets per unit volume on the corrosion rate were investigated and discussed. Test runs were carried out using two types of inhibitors: sodium nitrite of concentrations 20, 40, and 60 ppm and sodium hexapolyphosphate of concentrations 485, 970, and 1940 ppm in a solution containing 8% vol aqueous phase (water) mixed with kerosene (continuous phase) at 40°C for the whole range of Re. It was found that increasing Re increased the corrosion rate and the presence of water enhanced the corrosion rate by increasing the solution electrical conductivity. For two‐phase solution containing 8% vol and 16% vol of water, the corrosion rate was higher than single phase (100% vol water). The main parameters that play the major role in determining the corrosion rate in two phases were concentration of oxygen, solution electrical conductivity, and the interfacial area between the two phases (dispersed and continuous). Sodium nitrite and sodium hexapolyphosphate were found to be efficient inhibitors in two‐phase solution for the investigated range of Re.     

CHARACTERISTICS OF MICROMETER AND SUBMICROMETER SIZE O/W EMULSIONS PRODUCED BY RAMOND SUPERMIXER®

A novel motionless mixer named the Ramond Supermixer® (RSM®) was employed to produce O/W emulsions composed of micrometer and submicrometer-size droplets. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Pressure drop, droplet size distribution, Sauter mean diameter (d ₃₂), and geometric standard deviation of the droplet size distribution (σ_g) were investigated under the various combinations of process variables; superficial liquid velocity, number of mixing units, number of passages through RSM®, dispersed phase viscosity (η_d), continuous phase viscosity (η_c), and dispersed phase volume fraction. Different modes of droplet size variations with process variables were obtained, with respect to micrometer- and submicrometer-size ranges, and theoretical explanations are forwarded. For the micrometer-size range, maximum droplet diameter (d _max) was proportional to d ₃₂. For the submicrometer-size range, d _max varied with d ₃₂ in the range of 1.53–2.19-fold, and a correlation is proposed with K (=η_d/η_c); d ₃₂ and σ_g were well correlated with the process variables. Furthermore, a semi-empirical mechanistic model was developed for the formation of droplets obtained under inertial sub-range to interpret the effect of process variables.     

Hydrodynamics and droplet size distribution of liquid–liquid flow in a packed bed reactor with orifice plates

A packed bed reactor with orifice plates (PBR@OP) was designed by adding orifice plates periodically in packed beds. Hydrodynamics and droplet size distribution in PBR@OP were experimentally investigated using fatty acid methyl esters (FAME)/water as the model liquid–liquid system. In PBR@OP, the flow pattern was close to plug flow. Droplets with Sauter mean diameter (d₃₂) of 150–550 μm were generated. The pressure drop of orifice, flow velocity and plate spacing were key parameters to control the droplet size. The reactor performance was evaluated by analyzing a FAME epoxidation process. At the same d₃₂ and residence time, the length and total pressure drop of PBR@OP were about 1/3 and 1/4 of those of PBR without orifice plates, respectively. Furthermore, a semi-empirical correlation describing the d₃₂ change in PBR@OP was developed, revealing a relative mean deviation of 8.64%. PBR@OP presents a cost-effective option for the intensification of liquid–liquid medium rate reactions.     

On the mean drop size of toluene/water dispersion in the presence of silica nanoparticles

An experimental study of mean drop size (d₃₂) has been conducted in a horizontal mixer–settler for toluene/water system. The effects of feed holdup and agitation speed on d₃₂ were investigated in the absence and presence of silica nanoparticles. In order to study the influence of silica nanoparticles, different amounts of them (0.005, 0.01, 0.03 and 0.05 wt.%) were dispersed in water using ultrasonic vibration. The stability of nanofluids was evaluated by means of an UV–vis spectrophotometer. It was found that introducing silica nanoparticles in the system can decrease d₃₂ up to ∼21% in different operating conditions. Furthermore, presence of silica nanoparticles lowers the increasing influence of feed holdup and decreasing influence of agitation speed on d₃₂. Initially, an empirical correlation for predicting d₃₂ was proposed from experimental results of pure system. After that, new general correlations were proposed for systems containing different concentrations of silica nanoparticles which included the term of weight fraction of silica nanoparticles being in good agreement with experimental data.     

A toughened epoxy resin by silica nanoparticle reinforcement

Within this study the influence of adding 5 vol % of silica nanoparticles, obtained via a sol–gel process, on an Araldite‐F epoxy was investigated. To characterize toughening effects, compact tension specimens were used to obtain K_IC and G_IC. Additionally, tensile strength and E‐Modulus were measured as well as differential scanning calorimetry and dynamic mechanical thermal analysis were carried out to evaluate the influence on the thermal properties of the epoxy because of addition of the particles. Electronic microscopy was used to check dispersion quality and fracture surfaces, in transmission mode and scanning mode, respectively. The addition of 5 vol %. silica‐nanoparticles could improve the stiffness and the toughness of an epoxy resin at the same time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1849–1855, 2006     

The tough microcapsules of acrylic acid–styrene–isoprene–styrene quadrablock copolymer shell via Pickering emulsion technique

Pickering emulsion technique has been demonstrated a simple method to fabricate the microcapsules. However, the resulted microcapsules are often fragile. This limits their applications. Here, we report that the microcapsules with the nanostructured shell of poly(acrylic acid‐b‐styrene‐b‐isoprene‐b‐styrene) (ASIS), which is of high toughness and elasticity, could be fabricated via Pickering emulsions using ASIS nanoparticles as stabilizing particles. The surfactant‐free ASIS latex (with theoretical molecular weight for each block: 1.5k–15k–55k–10k) was synthesized by reversible additional fragmentation transfer (RAFT) emulsion polymerization using amphiphilic macro‐RAFT agent [poly(acrylic acid)₂₀‐b‐polystyrene₅ trithiocarbonate] as both reactive surfactant and polymerization mediator. It was found that the ASIS nanoparticles were able to self‐assemble on oil/water interface to stabilize Pickering emulsion of hexadecane in the pH range from 8 to 12. The droplet diameter was finely tuned from 17 to 5 µm by increasing the ASIS particle levels from 0.13 to 12 wt % based on the mass of the ASIS aqueous dispersions. With toluene as a coalescing aid, the capsules with a coherent and nonporous shell were obtained with the dispersed phase volume percentage as high as 50%. The toluene treated capsules were so mechanically strong to survive the utrasonic treatment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46700.     

Preparation and characterization of surface modified silicon carbide/polystyrene nanocomposites

A simple method is reported to coat silicon carbide (SiC) nanoparticles with polystyrene (PS) to improve the interfacial adhesion between polymer matrix and SiC nanoparticles. The morphology of untreated SiC nanoparticles, PS coated SiC (p‐SiC) nanoparticles, SiC/PS nanocomposites, and p‐SiC/PS nanocomposites are observed. The HRTEM image of p‐SiC shows that the thickness of PS on the surface of SiC is about 1.5–2.0 nm, which is consistent with the TGA results. With 24.7 vol % untreated SiC nanoparticles dispersed into PS matrix, the thermal conductivity (λ) of the SiC/PS composites increases by about 192%. However, when the same volume fraction of p‐SiC nanoparticles is used, the increase is about 353%. This big difference could be attributed to the promoted dispersion of the p‐SiC in the PS matrix. The measurements of glass transition (T_g), dielectric constant (ε), and tensile strength at break (σ_b) also support this explanation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of TiO2 and polymer nanocomposite films with high refractive index

Novel nanocomposite films of TiO₂ nanoparticles and hydrophobic polymers having polar groups, poly (bisphenol‐A and epichlorohydrin) or copolymer of styrene and maleic anhydride, with high refractive indices, high transparency, no color, solvent‐resistance, good thermal stability, and mechanical properties were prepared by incorporating surface‐modified TiO₂ nanoparticles into polymer matrices. In the process of preparing colloidal solution of TiO₂ nanoparticles, severe aggregation of particles can be reduced by surface modification using carboxylic acids and long‐chain alkyl amines. These TiO₂ nanoparticles dispersed in solvents were found not to aggregate after mixing with polymer solutions. Transparent colorless free‐standing films were obtained by drying a mixture of TiO₂ nanoparticles colloidal solution and polymer solutions in vacuum. Transmission electronic microscopic studies of the films suggest that the TiO₂ nanoparticles of 3–6 nm in diameter were dispersed in polymer matrices while maintaining their original size. Thermogravimetric analysis results indicate that the nanocomposite film has good thermal stability and the weight fraction of observed TiO₂ nanoparticles in the film is in good accordance with that of theoretical calculations. The refractive index of nanocomposite films of TiO₂ and poly(bisphenol‐A and epichlorohydrin) was in the range of 1.58–1.81 at 589 nm, which linearly increased with the content of TiO₂ nanoparticles from 0 to 80 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

One‐pot synthesis of a few nanocomposites with poly(N‐vinylcarbazole) and CdS,Ag, Pd50–Ag50, and Pt50–Ru50 nanoparticles with γ irradiation

The one‐pot synthesis of nanocomposites of a conductive poly(N‐vinylcarbazole) (PVK) with CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles was performed with γ irradiation in a tetrahydrofuran–water mixture (3/1 vol %). For comparison, the CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles were also prepared with γ irradiation with polyvinylpyrrolidone as a stabilizer. Ultraviolet–visible spectroscopy, transmission electron microscopy, X‐ray diffraction analysis, and photoluminescence spectroscopy were used for the characterization of CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles and nanocomposites of PVK with CdS, Ag, Pd₅₀–Ag₅₀, and Pt₅₀–Ru₅₀ nanoparticles. The absorption spectrum of the CdS‐nanoparticle‐based composite revealed a quantum confinement effect. The emission spectrum of the composite with CdS nanoparticles and PVK indicated the block effect of PVK for surface recombination. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1809–1815, 2006     

Characteristics of SiCf/SiC hybrid composites fabricated by hot pressing and spark plasma sintering

Abstract

Abstract

SiC fibre reinforced SiC–matrix ceramic composites were fabricated by electrophoretic deposition (EPD) combined with ultrasonication. Fine β-SiC powder and Tyranno-SA fabrics were used as the matrix and fibre for reinforcement, respectively. Different amounts of fine Al₂O₃–Y₂O₃ were added for liquid phase assisted sintering. For EPD, highly dispersed slurry was prepared by adjusting the zeta potentials of the constituent particles to ?+40 mV for homogeneous deposition. The composite properties were compared after using two different consolidation methods: hot pressing for 2 h at 20 MPa and spark plasma sintering (SPS) for 3 min at 45 MPa at 1750°C to minimise the damage to the SiC fibre. The maximum flexural strength and density for the 45 vol.-% fibre content composites were 482 MPa and 98% after hot pressing, respectively, whereas those for SPS were 561 MPa and 99·5%, indicating the effectiveness of SPS.