Use of High Pressure Homogenizers

The production of small droplets (submicron) requires application of high energy-emulsification is generally inefficient, as illustrated below. 

The intensity of the process or the effectiveness in making small droplets is often governed by the net power density [fi(t)]. 

Break up of droplets will only occur at high s, which means that the energy dissipated at low levels is wasted. Batch processes are generally less eflBcient than continuous processes. This shows why with a stirrer in a large vessel, most of the energy applied at low intensity is dissipated as heat. In a homogenizer, p is simply equal to the homogenizer pressure. 

Several procedures may be applied to enhance the efficiency of emulsification when producing nano-emulsions One should optimise the efficiency of agitation by increasing 6 and decreasing the dissipation time. The emulsion is preferably prepared at high volume faction of the disperse phase and diluted afterwards. However, very high rj) may result in coalescence during emulsification. Addition of more surfactant creates a smaller and possibly diminishes recoalescence. A surfactant mixture that shows a reduction in y compared with the individual components can be used. If possible, the surfactant is dissolved in the disperse phase rather than the continuous phase this often leads to smaller droplets. 

It may be useful to emulsify in steps of increasing intensity, particularly with emulsions having a highly viscous disperse phase. 

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Meuser, F. and German, H. 1984. Use of high-pressure homogenization for the production of starch from maize. Starch/Stdrke 36, 116-121. 

Four methods may be applied for the preparation of nanoemulsions (covering the droplet radius size range 50-200 nm) use of high pressure homogenizers (aided by appropriate choice of surfactants and cosurfactants) application of the phase inversion composition method apphcation of the phase inversion temperature (PIT) concept dilution of a microemulsion. 

Low-viscosity concentrates (-10% to 20%) of fabric softeners such as imidazoline derivatives and other diaUcyl ammonium compounds have been prepared by making use of high-pressure homogenization [15] fatty alcohols, aliphatic fatty acids, and fatty acid methyl esters [16] paraffin oils and paraffin waxes [17] ionogenic and nonionogenic emulsifiers (such as ethoxylated nonylphenol... 

Haynes, A. (2005) The use of high pressure spectroscopy to study catalytic mechanism, in Mechanisms in Homogeneous Catalysis, A Spectroscopic Approach (ed. B. Heaton), Wiley-VCH Verlag GmbH, Weinheim, pp. 107-50. 

S. Brdsel and H. Schubert Investigation of the Role of Surfactants in Mechanical Emulsification Using a High-Pressure Homogenizer with an Orifice Valve. Chem. Eng. Process. 38, 533 (1999). 

The most recently developed homogenizer is the so-called cell bomb, which makes use of high pressure and decompression to disrupt cells. In this... 

Brosel, S., and Schubert, El. (1999). Investigations on the role of surfaetants in mechanical emulsification using a high-pressure homogenizer with an orifiee valve. Chem. Eng. Processing. 38, 533-540. 

Table 1 Encapsulation efficiency and entrapped volumes of vesicles prepared using a high-pressure homogenizer...

These homogeneous metal complex-catalyzed reaction processes have several disadvantages a low reaction rate, required use of high pressure, and involvement of an energy intensive step for catalyst recovery. Immobilization of... 

A mechanical, nonsolvent-based method using a high-pressure homogenizer in the presence of SDS is also described. A maximum recovery yield of 98% was achieved by homogenizing the cells at 400 kg/cm in 5% SDS solution [81]. 

Another option is extractive crystallisation. Here, the tendency of particular aqueous-solvent mixtures such as water-propanol, water-amines, water-micelles, water-polar polymers to split into two liquid phases upon small variations in temperature is used to dehydrate solutions of crystallisable solutes. At low temperatures, these systems form homogeneous mixtures, whereas at high temperatures, a solvent rich phase is created. The aqueous solute becomes concentrated in a smaller volume and consequently crystallises, whereas the pure solvent is recycled. Also, alternative schemes may be used depending on the exact phase behaviour of the component. For instance, a solute such as amino acids and peptides may crystallise from an aqueous solution upon introducing a fully miscible component, such as in water-ethanol mixtures. In a second stage, after the separation of the crystals, the conditions may be altered to induce an L - L phase split that allows easy recovery of the auxiliary component. Maurer and co-workers [25] described the use of high pressure CO2 in water-alkanol systems. At low pres-... 

Haynes A (2005) The use of high pressure infrared spectroscopy to study catalytic mechanisms. In Heaton B (ed) Mechanisms in homogeneous catalysis a spectroscopic approach. Wiley, Weinheim, pp 107-150... 

There are mainly two different principles of high-pressure homogenization used piston-gap principle (e.g. APV Gaulin ) and the interaction chamber principle (e.g. Microfluidics ). Homogenization can be carried out continuously and discontin-uously. 

Production of nano-emulsions using (a) High-pressure homogenizers and (b) the phase inversion temperature (PIT) principle. 

Abrasion in the disruption unit of high pressure homogenizers can be avoided using the High Pressure Post Feeding (HPPF) valve setting, as proposed by [81]. Here, the fluid which contains the abrasive material is added into the jet forming directly after the orifice valve (see Fig. 13) [81, 82]. 

Brmez WJ, Roig-Sagues AX, Hernandez MM, Guamis B. 2007. Inactivation of Staphylococcus spp. strains in whole milk and orange juice using ultra high pressure homogenization at inlet temperatures of 6 and 20°C. Food Control 18 1282-1288. 

Kumar S, Thippareddi H, Subbiah J, Zivanovic S, Davidson PM, Harte F. 2009. Inactivation of Escherichia coli k-12 in apple juice using combination of high-pressure homogenization and cMtosan. J Food Sd 74 8-14. 

It may be clear that general conclusions cannot easily be drawn, since several of the mechanisms mentioned may come into play. Some experimental results will briefly be mentioned. Goulden and Phipps and Walstra used a high-pressure homogenizer and compared various (up to 0.4) at constant initial me, regime TI,... 

High-pressure recombination. The use of high-pressure recombination in homogeneous reactors would eliminate the need for continuous letdown of the radiolytic gases and continuous feed-pump operation. To investigate the possibilities of high-pressure recombination, tests [41] were made with a loop built at ORNL. 

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