High-pressure valve homogenizers

Figure 6. Technical schematics of the three most often used homogenization devices (a) highspeed blender, (b) high-pressure valve homogenizer, and (c) colloid mill.

Experiments have shown that the smallest droplet size that can be achieved using a high-pressure valve homogenizer increases as the disperse phase volume fraction increases (52). There are a number of possible reasons for this, (1) increasing the viscosity of an emulsion may suppress the formation of eddies responsible for breaking up droplets, (2) if the emulsifier concentration is kept constant, there may be insufficient emulsifier molecules present to completely cover the droplets, and (3) the rate of droplet coalescence is increased. 

Recently, these sampUng problems have been addressed in the development of an FTIR method for the determination of fat and protein in raw meat [32]. The use of a custom-designed high-pressure valve homogenise was found to ehminate the requirement for filtration of meat suspensions prior to IR analysis. The homogenates obtained were injected directly into a heated (65°C) flow-through transmission cell, with a 0.037-mm pathlength. The accuracy and reproducibility of the FTIR method were reported to be superior to those of the reference chemical methods... 

A homogenize is a high pressure positive pump with three, five, or seven pistons, that is driven by a motor and equipped with an adjustable homogenizing valve. Smoother flow and greater capacity are obtained with more pistons, which force the product iato a chamber that feeds the valve. In design and operation, it is desirable to minimize the power requirements for obtaining an acceptable level of homogenization. At 17.2 MPa (2500 psi) and a volume of 0.91 t/h (2000 lb/h), a 56-kW (75-hp) motor is required. 

High pressure homogenizers are especially suitable for the emulsification processes in the food, pharmaceutical and bioprocess industries. A general disadvantage of these type of reactors is that there is no precise control over the cavitationally active volume and the magnitude of the pressure pulses that will be generated at the end of the cavitation events (cavitational intensity), unless the valve seat designs are substantially modified. 

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). 

Homogenization A method of atomization and thereby emulsification of one liquid in another in which the liquids are pressed between a finely ground valve and seat under high pressure (e.g., up to 5,000 psi). 

Homogenisation processes now extend up to 1500 bar differential pressures. As the materials to be homogenized exhibit varying properties with respect to viscosity, corrosiveness and abrasiveness the high pressure components, such as homogenising pumps and valves, need very careful design and choice of materials. 

---