High pressure micronization

The processes of high-pressure micronization which have been studied intensively by numerous groups are ... 

One goal of RESS/CSS, the anti-solvent processes such GAS, and the PGSS process, is to obtain submicron- or micron-sized particles. Technological features of the various high-pressure micronization processes are summarised and compared in Table 9.8-4 [58]. 

Weidner, E. High-pressure micronization for food applications. The Journal of Supercritical Fluid 47 (2009) 556-565. 

Spray-type collectors In this system water is sprayed or cascaded onto the contaminated air directly or through packed towers, and the fumes or dust are washed away by absorption. These collectors are used extensively on the treatment of fumes of all types and have low pressure drops and hence low power requirements compared to induced spray. A development of this collector is the venturi scrubber, which injects high-pressure water into a venturi through which the fume-laden air is passing. The intimate contact of the two ensures absorption and removal from the air stream. These collectors are used in fume removal and have efficiencies of more than 99 per cent on sub-micron particles. 

Over the years the performance standards of hydraulic equipment have risen. Whereas a pressure of about 1000 psi used to be adequate for industrial hydraulic systems, nowadays systems operating with pressures of 2000-3500psi are common. Pressures above 5000psi are to be found in applications such as large presses for which suitable high-pressure pumps have been developed. Additionally, systems have to provide increased power densities, more accurate response, better reliability and increased safety. Their use in numerically controlled machine tools and other advanced control systems creates the need for enhanced filtration. Full flow filters as fine as 1-10 micron retention capabilities are now to be found in many hydraulic systems. 

On the basis of the above data it has been hypothesized that the conductivity of PFCM is due not to the contact between the filler particles but the current passes across the thin (less than 1 -2 microns) polymer interlayers. The conductivity arises when a spontaneous pressure exceeding the threshold value develops in the material. The overstresses apparently arise as a result of PP crystallization in the very narrow gaps between the filler particles [312], Since crystallization must strongly affect the macromolecular conformation whereas the narrowness of the gap and fixed position of molecules on the filler prevent it, the heat released in the process of crystallization must, in part, be spent to overcome this hindrance, whereby a local high pressure may arise in the gap. This effect is possible only where there are gaps of the size comparable with that of macromolecules. The small gap thickness will also hamper pressure relaxation, since the rate of flow from such a narrow clearance should be negligibly small. 

A commercial HPLC system and columns capable of performing ultra high-pressure LC were recendy introduced at PITTCON 2004 (ACQUITY Ultra Performance LC System by Waters). This HPLC system was designed to take full advantage of the potential of novel, sub-2-micron particles to give scientists chromatographic run times that are up to 9 times shorter than current fast HPLC systems, up to 2 times better peak capacity or resolution, and 3 times better routine sensitivity. 

High-pressure diesel fuel pumps are not tolerant of dirt, debris, and organic deposits and can be seriously damaged by fuel contaminants. The barrel and plunger clearance is within a 1 to 2 micron tolerance. This tolerance is necessary to ensure that fuel injection pressures are maintained with minimal leakage past the plunger shaft. For this reason, thorough and complete filtration of fuel is required before the fuel reaches the injection pump. 

It is seen from Table (3) that an open tubular column with an I 0 of about 86 micron and 20 meters long, operating at an inlet pressure of only 1 ps.i. can complete the very difficult separation in about a week. A very long analysis time, perhaps, but not much longer than would be required by an optimized packed column and in this case the separation is earned out with a simple tube to coat and with no high pressure pump required. 

The substance which has to be micronized is filled into a thermostatted feed vessel (A) (Figure 9.8-6). The solution from (A) is transferred into the thermostatted autoclave (C) after evacuation. The compressible medium is supplied by a high-pressure pump (B). The pressure in the autoclave is increased to a certain value, and the high-pressure circulation pump (D), connected with the autoclave, is installed to increase the efficiency of dissolving of the solute by circulating the liquid phase. The gas-saturated mixture is rapidly depressurized through a nozzle. In the spray-tower the solvent is set free, and the formed solid particles of the substance under consideration (>10 pm) are collected in the vessel at the bottom. The temperature in the spray can be measured and recorded via two thermoelements. 

In the last few years, an increasing trend towards new high pressure applications could be observed in R D, all of them in a certain way taking advantage of the remarkable properties of fluids at near critical or supercritical conditions. At the same time the demand for high pressure pilot units for these new" applications like Supercritical Fluid Reactions, HP-Micronization, HP-Spray Drying and HP-Sterilization increased. In order to also supply customized... 

The multipurpose high pressure pilot unit in picture 4 is built for HP-Spray Drying, HP-Micronization and for SFE of solid products. As can be seen on the corresponding flow sheet (figure 2), the C02 circulation system and the separation module are exactly the same as in the multipurpose SFE unit. However, the column and the product pump had to be adapted to the requirements of the "new" application. 

---