Ultrasound to increase

Simal, S., Benedito, J., Sanchez, E.S., and Rossello, C. 1998. Use of ultrasound to increase mass transport rates during osmotic dehydration. J. Food Engineer. 36, 323-336. 

There are a number of examples of the use of ultrasound to increase the productivity of food products through the enhancement of efficiency of whole cells without disrupting the cell walls. A simple example of this is in the use of low-power ultrasonic activation of a liquid nutrient media to enhance the rate of growth of algal cells. Essentially this results in an increase in the production of protein (up to three-fold) and represents a real possibility for the production of food materials from unusual sources for human or animal consumption [18]. 

The weld depths penetration for gold-nickel alloy and tantalum cylinders have been well controlled by an entirely contactless ultrasound method. Nevertheless, the development of signal and image processing will allow to increase the resolution of the ultrasonic images. Moreover, in order to be able to size quite well the lacks of weld penetration, the simulation of the interaction beam-defect is presently developed in our laboratory. 

Ultrasound can thus be used to enhance kinetics, flow, and mass and heat transfer. The overall results are that organic synthetic reactions show increased rate (sometimes even from hours to minutes, up to 25 times faster), and/or increased yield (tens of percentages, sometimes even starting from 0% yield in nonsonicated conditions). In multiphase systems, gas-liquid and solid-liquid mass transfer has been observed to increase by 5- and 20-fold, respectively [35]. Membrane fluxes have been enhanced by up to a factor of 8 [56]. Despite these results, use of acoustics, and ultrasound in particular, in chemical industry is mainly limited to the fields of cleaning and decontamination [55]. One of the main barriers to industrial application of sonochemical processes is control and scale-up of ultrasound concepts into operable processes. Therefore, a better understanding is required of the relation between a cavitation coUapse and chemical reactivity, as weU as a better understanding and reproducibility of the influence of various design and operational parameters on the cavitation process. Also, rehable mathematical models and scale-up procedures need to be developed [35, 54, 55]. 

In order to increase the overall extraction efficiency during SFE sonication has been applied [352]. Ultrasound creates intense sinusoidal variations in density and pressure, which improve solute mass transfer. Development of an SFE method is a time-consuming process. For new methods, analysts should refer the results to a traditional sample preparation method such as Soxhlet or LLE. 

In the experiment involving oxidative enzyme HRP (EC 1.11.1.7, RZ 1.9, 240 purpuro gallin (units/mg)) [89] for the enzymatic treatment and ultrasonic waves of 423 kHz and 5.5 W, the phenol degradation rate was found to increase. The ultrasound assisted biodegradation method has been found to be more efficient method than the sonolysis and enzyme treatment when operated individually. 

Ultrasonic irradiation has been shown in laboratory studies [73] to increase dye exhaustion, enabling salt levels to be reduced. However, it seems doubtful whether the higher effectiveness is sufficient to merit development to overcome the problems involved in scaling-up the ultrasonic equipment to bulk-scale processing. For example, in one experiment using 5% salt at 65 °C, ultrasound treatment increased the dye exhaustion from 77% to 82%. 

Microwave heating has already been used in combination with some other (unconventional activation processes. Such a combination might have a synergic effect on reaction efficiencies or, at least, enhance them by combining their individual effects. Application of MW radiation to ultrasound-assisted chemical processes has been recently described by some authors [18, 19]. Mechanical activation has also been successfully combined with MW heating to increase chemical yields of several reactions [1]. 

One impediment of universally applying PET in the area of packaging is its gas-barrier properties. These can be slightly improved by measures to increase the density (crystallinity) during blow molding, for example, by treatment with ultrasound. Ultrasonic treatment during injection reduces the gas permeability to a certain extent [34],... 

Since 1945 an increasing understanding of the phenomenon of cavitation has developed coupled with significant developments in electronic circuitry and transducer design (i. e. devices which convert electrical to mechanical signals and vice versa). As a result of this there has been a rapid expansion in the application of power ultrasound to chemical processes, a subject which has become known as Sonochemistry . 

Thus, even if a bubble does not undergo transient collapse, extremely high temperatures and pressures are developed within the bubbles as they oscillate from R to R j. It is these large temperatures and pressures within the bubble which are thought to contribute to the significant increases in chemical reactivity observed in the presence of ultrasound. This does suppose however, that the reactant species is sufficiently volatile to enter the bubble. If it is not, increased chemical reactivity can only be assumed to have occurred due to increased molecular interaction within the liquid due to the large build up of pressure at the bubble wall. If the bubble is not to completely collapse then this will be equal to the liquid pressure at the liquid-bubble wall interface. 

On the other hand stable cavitation (bubbles that oscillate in a regular fashion for many acoustic cycles) induce microstreaming in the surrounding liquid which can also induce stress in any microbiological species present [5]. This type of cavitation may well be important in a range of applications of ultrasound to biotechnology [6]. An important consequence of the fluid micro-convection induced by bubble collapse is a sharp increase in the mass transfer at liquid-solid interfaces. In microbiology there are two zones where this ultrasonic enhancement of mass transfer will be important. The first is at the membrane and/or cellular wall and the second is in the cytosol i. e. the liquid present inside the cell. 

Applying ultrasound to the cylinder, no matter what the position, led to a significant decrease in the melt viscosity (0-60%), and increase in flow rate, the magnitude of... 

Ultrasound has also been used to effect changes in the composition of a deposit during plating. For example it is particularly advantageous to increase the proportion of iron in nickel-iron alloy deposits thereby giving cheaper coatings. For a deposit produced in the presence of 24.8 kHz ultrasound, the deposit increased from 3.5 % for the silent system to 19.2 %. Using 37.9 kHz ultrasound, the deposit was 18.8% [41]. 

Low-energy ultrasound was employed to increase by up to 70% the production of shikonin (Fig. 4) in cell cultures of the medicinal herb Lithospermum erythrorhizon. Shikonin exhibits a variety of effects, which includes anti-inflammatory, antigonadotropic and human immunodeficiency virus type 1 (HIV-1) suppression activities. 

Peterson and Scarrah 165) reported the transesterification of rapeseed oil by methanol in the presence of alkaline earth metal oxides and alkali metal carbonates at 333-336 K. They found that although MgO was not active for the transesterification reaction, CaO showed activity, which was enhanced by the addition of MgO. In contrast, Leclercq et al. 166) showed that the methanolysis of rapeseed oil could be carried out with MgO, although its activity depends strongly on the pretreatment temperature of this oxide. Thus, with MgO pre-treated at 823 K and a methanol to oil molar ratio of 75 at methanol reflux, a conversion of 37% with 97% selectivity to methyl esters was achieved after 1 h in a batch reactor. The authors 166) showed that the order of activity was Ba(OH)2 > MgO > NaCsX zeolite >MgAl mixed oxide. With the most active catalyst (Ba(OH)2), 81% oil conversion, with 97% selectivity to methyl esters after 1 h in a batch reactor was achieved. Gryglewicz 167) also showed that the transesterification of rapeseed oil with methanol could be catalyzed effectively by basic alkaline earth metal compounds such as calcium oxide, calcium methoxide, and barium hydroxide. Barium hydroxide was the most active catalyst, giving conversions of 75% after 30 min in a batch reactor. Calcium methoxide showed an intermediate activity, and CaO was the least active catalyst nevertheless, 95% conversion could be achieved after 2.5 h in a batch reactor. MgO and Ca(OH)2 showed no catalytic activity for rapeseed oil methanolysis. However, the transesterification reaction rate could be enhanced by the use of ultrasound as well as by introduction of an appropriate co-solvent such as THF to increase methanol solubility in the phase containing the rapeseed oil. 

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