An Introduction To The Rapid Expansion On Supercritical Fluid

By Author: Sharon
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Application of supercritical fluid technology has been gradually extraction, chemical reaction extended to the more traditional areas of fine particles prepared by the new area. Supercritical fluid method of preparation of fine particles divided into two: one for the RESS method (Rapid Expansion of Supercritical Solution); two methods for the GAS (Gas Anti-Solvent).They are developed over a decade of supercritical fluid of new applications, the purification, separation of material has the advantages of conventional methods can not match.

Rapid expansion of supercritical solution (RESS) combined with liquid - liquid extraction (based on differences in physical solubility) and distillation (based on material differences between volatility) features, by adjusting the temperature and pressure to change the materials solubility in SCF.RESS process is characterized by: fast delivery disturbance, high solute supersaturation, the former lead to uniform medium solute components, forming a narrow particle size distribution, which lead to fine particles of. This article focuses on the rapid expansion of supercritical solution (RESS) ...
... fine particles prepared by the application.

RESS fine particles prepared mainly by using the solubility of the solute and supercritical fluid density relationship, as from the rapid expansion of supercritical fluid state to a low pressure, low temperature gas state, a sharp decline in the solubility of the solute, the change to the rapid nucleation and Solute grow into particles and deposition .Only when the solid solute in supercritical solvent in a certain solubility in the process of rapid expansion to form a stable solid - liquid state RESS process can proceed smoothly. So for different solutes, need different supercritical solvents. Has studied the RESS process solvents CO2, CHF3, C2H4, C3H6 (propylene), C5H12, H2O, C2H5OH, etc .Powder size and shape influence factors are: dissolution temperature, dissolved pressure (both of which can control the solubility of the solute), pre-expansion temperature, the temperature after expansion (collection room temperature), pre-expansion pressure (the pressure is generally not equal to dissolve), after inflation pressure (collection chamber pressure), solute solubility, shape and size of the nozzle geometry, jet length and super-critical solution.

Preparation of Fine Particles RESS device consists of four modules: freezing unit, pump unit, dissolve unit and collection unit. Supercritical fluid extraction device is composed by the four units, two of the same first three modules can be generic, are from the air tank, refrigerator, pressure pump and extractor component. But the fourth unit, collection unit is completely different. Extraction device from the separation tank, buffer tank and the rot meter composition of fine particles prepared by the collecting chamber devices, nozzles, flow meters and other components. Nozzle is to collect a key component of the cell.

Now there are two types of more that capillary nozzle and the nozzle plate of porous sintered materials can be quartz glass or stainless steel. In the porous sintered plate nozzle device for controlling the flow rate of supercritical fluid in the sintered plate before and after the placement of different diameter throttle. The results show that, using porous sintered plate nozzle available capillary nozzle diameter smaller than the fine particles, the smaller the aperture plate and sintered, the smaller the average particle size of powder obtained.

Note that the super-critical solution pressure in the nozzle jet flash drop throttling process will lead to a sharp temperature drop, so the nozzle and heating measures must be taken to avoid nozzle clogging.

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