Sonocrystallization: effect on lactose recovery and crystal habit

Sonocrystallization is the use of power ultrasound to control the crystallization process, commonly used during the nucleation phase of crystallization. However, in the present study a different approach has been tried, in which the whole process of lactose crystallization from model reconstituted lactose solutions was completed rapidly with the aid of ultrasound, in the presence of 'ethanol' as an anti-solvent, at temperature of 30+/-2 degrees C (ambient temperature). The lactose recovery and crystal properties from sonicated samples were compared with non-sonicated samples. For optimization of sonocrystallization process for rapid lactose recovery, variations in the time of sonication, lactose concentration, protein concentration and pH were tried. A lactose recovery of 91.48% was obtained in 5 min of sonication time, from a reconstituted lactose solution (17.5% w/v, pH 4.2) as against 14.63% under only stirring. Lactose recovery decreased with lowering of pH from 4.2 to 2.8. The protein showed maximum influence on lactose recovery even at concentration of 0.2% w/v. A rapid process of crystallization gave a better uniformity in crystal size distribution of lactose samples.     

Ultrasonically controlled particle size distribution of explosives: a safe method

Size reduction of the high energy materials (HEM's) by conventional methods (mechanical means) is not safe as they are very sensitive to friction and impact. Modified crystallization techniques can be used for the same purpose. The solute is dissolved in the solvent and crystallized via cooling or is precipitated out using an antisolvent. The various crystallization parameters such as temperature, antisolvent addition rate and agitation are adjusted to get the required final crystal size and morphology. The solvent-antisolvent ratio, time of crystallization and yield of the product are the key factors for controlling antisolvent based precipitation process. The advantages of cavitationally induced nucleation can be coupled with the conventional crystallization process. This study includes the effect of the ultrasonically generated acoustic cavitation phenomenon on the solvent antisolvent based precipitation process. CL20, a high-energy explosive compound, is a polyazapolycyclic caged polynitramine. CL-20 has greater energy output than existing (in-use) energetic ingredients while having an acceptable level of insensitivity to shock and other external stimuli. The size control and size distribution manipulation of the high energy material (CL20) has been successfully carried out safely and quickly along with an increase in the final mass yield, compared to the conventional antisolvent based precipitation process.     

Lactose hydrolysis and beta-galactosidase activity in sonicated fermentation with Lactobacillus strains

Milk fermentation with four Lactobacillus strains, including L. delbrueckii subsp. bulgaricus B-5b, L. helveticus LH-17, L. delbrueckii subsp. lactis SBT-2080 and L. acidophilus SBT-2068, was carried out under sonicated conditions. Under continuous sonication, viable cell count decreased or grew less than in conventional fermentation, but it increased considerably in static incubation after sonication. Sonication caused beta-galactosidase release from lactic acid bacteria cells to the culture medium, thus resulting in higher total beta-galactosidase activity. However, lactose hydrolysis was enhanced only when beta-alactosidase was effectively released. With L. delbrueckii subsp. bulgaricus B-5b and L. helveticus LH-17. the degrees of lactose hydrolysis achieved were about 75% which is much higher than those in conventional fermentation (below 40%). Results presented here showed that a high viable cell count and a high degree of lactose hydrolysis could be simultaneously achieved by a suitable sonication method.     

Effect of process parameters on the recovery of lactose in an antisolvent acetone/acetone-ethanol mixture: A comparative study based on sonication medium

Recovery of lactose from the whey using sonocrystallization was studied experimentally. The effect of sonication medium and irradiation power levels was evaluated using three different ultrasonic equipments. Effects of various parameters such as sonication time, pH of the medium, antisolvent (acetone and acetone-ethanol mixture) and concentration of lactose were determined. The optimal parametric conditions were analyzed using differential scanning calorimetry, thermogravimetric analysis, particle size distribution, and zeta potential measurements. Overall, the highest lactose recovery was obtained using a mixture of acetone and ethanol as antisolvent in bath sonication as well as atomization process.     

Ultrasonically improved semi-hydrogenation of alkynes to (Z-)alkenes over novel lead-free Pd/Boehmite catalysts

This paper reports the application of ultrasound in the semi-hydrogenation of alkynes over two novel Pd/Boehmite catalysts. The semi-hydrogenations of phenylacetylene, diphenylacetylene and 2-butyne-1,4-diol have either been investigated in an ultrasonic bath under atmospheric hydrogen pressure, or in an ultrasonic horn reactor under 0.1–0.5 MPa hydrogen pressure. Alkyne hydrogenation was suppressed by sonication under atmospheric hydrogen pressure, but promoted by sonication under 0.1 MPa of hydrogen pressure. Sonication increased selectivity towards the semi-hydrogenated products in both cases. Catalyst loading, hydrogen pressure, temperature and the presence of quinoline, all impacted on hydrogenation rate, activity and selectivity to semi-hydrogenated products. Palladium leaching from the catalyst was evaluated in ethanol and hexane both under plain stirring and sonication.     

Cavitation field analysis for an increased efficiency of ultrasonic sludge pre-treatment using a novel hydrophone system

The generation of cavitation fields for the pre-treatment of anaerobic sludge was studied by means of a novel acoustic measuring system. The influence of different reactor dimensions (i.e., choosing reaction chamber widths of 40, 60 and 80 mm) on the cavitation intensity was determined at various solid contents, flow rates and static pressures. Results suggest that the cavitation intensity is significantly reduced by the sonication of liquids with a high solid content. By increasing the pressure to 1 bar, the intensity of bubble implosions can be enhanced and the sound attenuation in the solid fraction is partly compensated compared to ambient pressure. However, a further increase in pressure to 2 bars has a detrimental effect due to the suppression of powerful bubbles. A reduction of the reactor gap permits an intensification of the treatment of waste activated sludge (WAS) by concentrating the ultrasound power from 6 to 18 dB. This effect is less relevant in digested sludge (DS) with its markedly lower total solids content (2.2% vs. 6.9% of solids in WAS). Increasing the flow rate, resulting in a flow velocity of up to 7 m/min, has no influence on the cavitation intensity. By adapting the reactor design and the static pressure to the substrate characteristics, the intensity of the sonication can be notably improved. This allows the design of sonication devices that are suitable for the intensive treatment of wastewater sludge.     

Mechanistic investigations in sono-hybrid techniques for rice straw pretreatment

This paper reports comparative study of two chemical techniques (viz. dilute acid/alkali treatment) and two physical techniques (viz. hot water bath and autoclaving) coupled with sonication, termed as sono-hybrid techniques, for hydrolysis of rice straw. The efficacy of each sono-hybrid technique was assessed on the basis of total sugar and reducing sugar release. The system of biomass pretreatment is revealed to be mass transfer controlled. Higher sugar release is obtained during dilute acid treatment than dilute alkali treatment. Autoclaving alone was found to increase sugar release marginally as compared to hot water bath. Sonication of the biomass solution after autoclaving and stirring resulted in significant rise of sugar release, which is attributed to strong convection generated during sonication that assists effective transport of sugar molecules. Discrimination between individual contributions of ultrasound and cavitation to mass transfer enhancement reveals that contribution of ultrasound (through micro-streaming) is higher. Micro-turbulence as well as acoustic waves generated by cavitation did not contribute much to enhancing of mass transfer in the system.     

High undercooling of bulk water during acoustic levitation

The experiments on undercooling of acoustically levitated water drops with the radius of 5-8 mm are carried out, and the maximum undercooling of 24 K is obtained in such a containerless state. Various factors influencing the undercoolability of water under acoustic levitation are synthetically analyzed. The experimental results indicate that impurities tend to decrease the undercooling level, whereas the dominant factor is the effect of ultrasound. The stirring and cavitation effects of ultrasound tend to stimulate the nucleation of water and prevent further bulk undercooling in experiments. The stirring effect provides some extra energy fluctuation to overcome the thermodynamic barrier for nucleation. The local high pressure caused by cavitation effect increases the local undercooling in water and stimulates nucleation before the achievement of a large bulk undercooling. According to the cooling curves, the dendrite growth velocity of ice is estimated, which is in good agreement with the theoretical prediction at the lower undercooling. The theoretical calculation predicts a dendrite growth velocity of 0.23 m/s corresponding to the maximum undercooling of 24 K, at which the rapid solidification of ice occurs.     

Protonation of norharmane as a sonochemical dosimeter for organic media. The effect of temperature

The sonolysis of different organic and aqueous media in the presence of norharmane produce its protonation. This simple and reversible reaction is particularly suitable as a dosimetric reaction in order to measure the relative amount of cavitation induced by the ultrasonic irradiation in non aqueous solutions. The protonation rate increases when small amounts of chloroform are added to the solution. The frequency (20 and 475 kHz) and temperature effects on the reaction rate are also studied. Our results show that sonication of aqueous solutions at high frequency leads to a strongly oxidant medium.     

Sonocrystallisation of lactose in concentrated whey

Whey concentrated to 32% lactose was sonicated at 30 °C in a non-contact approach at flow rates of up to 12 L/min. Applied energy density varied from 3 to 16 J/mL at a frequency of 20 kHz. Sonication of whey initiated the rapid formation of a large number of lactose crystals in response to acoustic cavitation which increased the rate of crystallisation. The rate of sonocrystallisation was greater than stirring for approximately 180 min but slowed down between 120 and 180 min as the metastable limit was reached. A second treatment with ultrasound at 120 min delivering an applied energy density of 4 J/mL stimulated further nuclei formation and the rate of crystallisation was maintained for >300 min. Yield on the other hand was limited by the solubility of lactose and could not be improved. The crystal size distribution was narrower than that with stirring and the overall crystal size was smaller.     

Preparation of nanoparticles of poorly water-soluble antioxidant curcumin by antisolvent precipitation methods

The objective of this study was to enhance the solubility and dissolution rate of a poorly water-soluble antioxidant, curcumin, by fabricating its nanoparticles with two methods: antisolvent precipitation with a syringe pump (APSP) and evaporative precipitation of nanosuspension (EPN). For APSP, process parameters like flow rate, stirring speed, solvent to antisolvent (SAS) ratio, and drug concentration were investigated to obtain the smallest particle size. For EPN, factors like drug concentration and the SAS ratio were examined. The effects of these process parameters on the supersaturation, nucleation, and growth rate were studied and optimized to obtain the smallest particle size of curcumin by both the methods. The average particle size of the original drug was about 10–12 μm and it was decreased to a mean diameter of 330 nm for the APSP method and to 150 nm for the EPN method. Overall, decreasing the drug concentration or increasing the flow rate, stirring rate, and antisolvent amount resulted in smaller particle sizes. Differential scanning calorimetry studies suggested lower crystallinity of curcumin particles fabricated. The solubility and dissolution rates of the prepared curcumin particles were significantly higher than those the original curcumin. The antioxidant activity, studied by the DPPH free radical-scavenging assay, was greater for the curcumin nanoparticles than the original curcumin. This study demonstrated that both the methods can successfully prepare curcumin into submicro to nanoparticles. However, drug particles prepared by EPN were smaller than those by APSP and hence, showed the slightly better solubility, dissolution rate, and antioxidant activity than the latter.     

An investigation of the crystallization kinetics of zeotype SAPO-34 crystals synthesized by hydrothermal and sonochemical methods

The kinetics study of SAPO-34 crystallization from a gel containing morpholine as a structure directing agent (SDA) was investigated by means of X-ray diffraction (XRD) patterns in order to determine the kinetics parameters, i.e. induction times, rate constants, frequency factors, and activation energies for the induction and growth stages. The kinetics data of growth period were determined by using the Avrami–Erofeev nucleation growth model. SAPO-34 molecular sieves were synthesized by using both sonochemical-assisted hydrothermal and conventional hydrothermal heating at temperatures of 180, 200, and 220 °C to elucidate the influence of crystallization method on the crystallization kinetics of SAPO-34. The activation energy values indicated that the crystal growth mechanism was enhanced for samples synthesized sonochemically, whereas the induction energy was not greatly affected by using sonication process. Also, the kinetic compensation effect (KCE) was considered in order to obtain the isokinetic temperature.     

Effect of ultrasonic-induced selenium crystallization behavior during selenium reduction

In this work, the crystallization process of selenium was accelerated by ultrasonic wave. The effects of ultrasonic waves and conventional conditions of selenium crystallization were compared to understand the effects of different conditions on crystallization, including ultrasonic time, ultrasonic power, reduction temperature, and H₂SeO₃ concentration. The mechanism of ultrasound affecting selenium crystallization was also investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that ultrasonic time, ultrasonic power, and reduction temperature significantly influenced the crystallization process and morphology of selenium. Ultrasonic time had a large effect on the completeness (all products have been crystallized) and integrity of the crystallization of the products. Meanwhile, ultrasonic power and reduction temperature had no effect on the completeness of crystallization. However, it had a significant effect on the morphology and integrity of the crystallized products, and different morphologies of the nano-selenium materials could be obtained by changing the ultrasonic parameters. Both primary and secondary nucleation are important in the process of ultrasound-accelerated selenium crystallization. The cavitation effect and mechanical fluctuant effects generated by ultrasound could reduce the crystallization induction time and accelerate the primary nucleation rate. The high-speed micro-jet formed in the rupture of the cavitation bubble generated is the most important reason to influence the secondary nucleation of the system.     

The effect of static pressure on the inertial cavitation threshold

The amplitude of the acoustic pressure required to nucleate a gas or vapor bubble in a fluid, and to have that bubble undergo an inertial collapse, is termed the inertial cavitation threshold. The magnitude of the inertial cavitation threshold is typically limited by mechanisms other than homogeneous nucleation such that the theoretical maximum is never achieved. However, the onset of inertial cavitation can be suppressed by increasing the static pressure of the fluid. The inertial cavitation threshold was measured in ultrapure water at static pressures up to 30?MPa (300 bars) by exciting a radially symmetric standing wave field in a spherical resonator driven at a resonant frequency of 25.5 kHz. The threshold was found to increase linearly with the static pressure; an exponentially decaying temperature dependence was also found. The nature and properties of the nucleating mechanisms were investigated by comparing the measured thresholds to an independent analysis of the particulate content and available models for nucleation.     

Facile synthesis of mesoporous ZSM-5 aided by sonication and its application for VOCs capture

Application of ultrasound power to the mother liquor is popular pretreatment for zeolite synthesis which offers a simple way of accelerating crystallization process and finetuning the properties of nanocrystalline zeolites. In this work, sonication-aided synthesis of mesoporous ZSM-5 at low temperature and ambient pressure was systematically studied, in an attempt to reach efficient and benign synthesis of zeolites with hierarchical pore structure, which has wide applications as catalysts and sorbents. The effects of sonication duration, power density, sonication temperature and seeding on the crystallization of ZSM-5 were investigated. The obtained samples were characterized by XRD, SEM, BET and VOCs capture. High quality mesoporous ZSM-5 can be obtained by a facile 5 d synthesis at 363 K, much faster than conventional hydrothermal synthesis. The reduced synthesis time was mainly attributed to the enhanced crystallization kinetics caused by the fragmentation of seeds and nuclei, while sonication radiation had little impact on the nucleation process. Compared with control sample, mesoporous ZSM-5 prepared by sonochemical method had higher surface area and mesoporosity which demonstrated improved adsorption performance for the capture of isopropanol.     

Direct Observation of Crystallization of Polybutene-1 Under Low Shear Rate Flow

The isothermal crystallization process of polybutene-1 melt under shear flow was investigated with an optical microscope and a device (shear flow direct observation system, SF-DOS) newly developed by our group. The nucleation rate and growth rate of polybutene-1 were studied under slow shear rates (0–0.1 s^?1) at high crystallization temperature (102–108°C) with the SF-DOS. The nucleation remains heterogeneous. The number of nuclei after long times increased and induction time decreased by increasing the shear rate. Anisotropic and distorted spherulites were observed under shear flow, while the spherulites in the static condition were isotropic. It was clearly observed that the spherulites were rotating under shear. The average growth rates were enhanced by increasing shear rates, which acts as the main factor affecting the overall crystallization kinetics. Finally, the crystallization kinetics were analyzed on the basis of the secondary nucleation theory of Hoffman and Lauritzen. Even under very low shear rates, the product of lateral‐surface free energy σ _s and fold-surface free energy σ _e was found to be reduced as shear rate increased.     

单斜辉石固溶体CaMgSi2O6-NaAlSi2O6的合成机理研究

 研究了压力和温度对单斜辉石的结晶和晶粒纤维编织的影响。在较低的晶化温度下压力对单斜辉石结晶的影响很明显，这种影响随温度升高而减弱。然而，压力对单斜辉石晶粒纤维编织的影响正相反，在相同的高温下，较高压力下晶化的单斜辉石晶粒纤维比较低压力下得到的晶粒纤维粗壮，而且编织紧密。     

Mechanical denaturation of high polymers in solutions XXIX. Stress-induced crystallization of poly(vinyl alcohol) from its aqueous solution under steady-state flow

The crystallization of poly(vinyl alcohol), derived from its aqueous solution was carried out under a steady-state flow. The effect of the rate of stirring on the crystallization and details of several phenomena observed in stirred solutions during crystallization are presented. Moreover, the structure of crystallized poly(vinyl alcohol) was studied with use of an electron microscope. Evidence is presented for a crystal morphology that includes smooth fibrils and the absence of lamellar overgrowth, i.e., no shish kebabs.     

Respective contribution of cavitation and convective flow to local stirring in sonoreactors

The knowledge of respective parts of convection and cavitation to the stirring induced by ultrasound at one exact position into a sonoreactor is useful for all processes implementing surfaces exposed to sonication. PIV measurement allows real fluid motion determination, whereas the electrochemical technique gives an equivalent flow velocity considered as the sum of all stirring contributions to the electrode. Thus, by a simple subtraction between real fluid velocity and equivalent flow velocity, it is possible to identify the contribution of each phenomenon. Applied to low frequency reactors, it had been observed that cavitation is the preponderant phenomenon, with a contribution of stirring close to the electrode always more than 90%. High frequency reactors, frequently known to produce less cavitation, have shown that at the focal zone, if it concerns HIFU, cavitation becomes preponderant and reaches similar values to those close to the ultrasonic horn in low frequency sonoreactors.     

Effect of gold nanoparticle size on acoustic cavitation using chemical dosimetry method

When a liquid is irradiated with high intensities of ultrasound irradiation, acoustic cavitation occurs. Acoustic cavitation generates free radicals from the breakdown of water and other molecules. Cavitation can be fatal to cells and is utilized to destroy cancer tumors. The existence of particles in liquid provides nucleation sites for cavitation bubbles and leads to decrease the ultrasonic intensity threshold needed for cavitation onset. In the present investigation, the effect of gold nanoparticles with appropriate amount and size on the acoustic cavitation activity has been shown by determining hydroxyl radicals in terephthalic acid solutions containing 15, 20, 28 and 35 nm gold nanoparticles sizes by using 1 MHz low level ultrasound. The effect of sonication intensity in hydroxyl radical production was considered.The recorded fluorescence signal in terephthalic acid solutions containing gold nanoparticles was considerably higher than the terephthalic acid solutions without gold nanoparticles at different intensities of ultrasound irradiation. Also, the results showed that the recorded fluorescence signal intensity in terephthalic acid solution containing finer size of gold nanoparticles was lower than the terephthalic acid solutions containing larger size of gold nanoparticles. Acoustic cavitation in the presence of gold nanoparticles can be used as a way for improving therapeutic effects on the tumors.