PGSS procedure
The PGSS process (Particle from Gas Saturated Solutions) is a high-pressure method for generating particles. In principle, any number of liquefiable solids can be mixed and processed into free-flowing powder. Here are supercritical fluids used as auxiliaries. These adjuvants are used to slightly to highly viscous substances such. B. to spray chocolate, glue or paint and to solidify. Gas-containing melts are homogenized and pulverized by mixing the liquefied individual components with compressed carbon dioxide and then, e.g. B. be relaxed via a nozzle . The melt is thereby torn into tiny droplets. The finest powder forms, which opens up new applications due to its specifically adjustable size (nano- to micrometer), morphology and composition.
The PGSS process can be operated both continuously and discontinuously (batchwise).
application
This new process is particularly in demand in the food industry and in medicine, as it offers the possibility of producing microcapsules . The aim of this encapsulation is not only to protect the powder but also to release the active ingredient in a controllable manner.
As a micronization process, the PGSS process is in direct competition with cryogenic (with liquid gases / cold) grinding and spray drying . Due to the high pressures and temperatures required, the PGSS process initially appears to be economically disadvantaged in terms of operating costs. The gas requirement for PGSS, however, at around 1–10 kg / kg of product, is usually significantly lower than with other processes for solids conversion. The production costs of the PGSS process are often significantly lower than those of the classic processes.
Nevertheless, the PGSS process has so far only made limited use of the industry. A market obstacle usually proves to be that there are large depreciated plants for the classic processes, which from an economic point of view also allow production using greater energy and raw material consumption.
Procedure
The two starting materials (encapsulation material and core substance) are stored separately from one another in the heatable storage containers, temperature controlled and, if necessary, melted. The substances are compressed by high-pressure pumps and conveyed into a static mixer . A temperature-controlled mostly supercritical gas is also pumped into the static mixer via another high-pressure pump. When flowing through the static mixer, the material flows are intensively mixed and a dispersion is formed. When mixed, part of the gas dissolves in the composite components. Depending on the phase behavior, the encapsulation and / or core material can also be dissolved in the gas. After flowing through the static mixer, the dispersions formed reach an atomizing device, where they are expanded to ambient pressure in a spray tower . The strong shear action of the nozzle device and the releasing and expanding gas lead to the formation of droplets. The effective cooling of the droplets is achieved by the Joule-Thomson effect that occurs when the gas is expanded . If the temperature drops below the solidification temperature of the capsule material, composite formation occurs. The resulting product collects in the lower part of the spray tower and can be removed there. The gas to be cleaned is sucked off by means of a fan, passed through a cyclone and / or a filter and released into the environment.
See also
literature
- Henning Gunnar Brandin: Production of powdery composites using high pressure spraying. Dissertation, Univ. Bochum, 2005, Cuvillier, 2006, ISBN 978-3-86537-922-1 .
- Tobias Wendt: Production of liquid-containing powdery composites using a high-pressure spray process for applications in the food sector. Dissertation, Univ. Bochum 2007, Cuvillier, 2007, ISBN 978-3-86727-156-1 .
- Michael Zacherle: Spraying of substances dissolved in supercritical gases and characterization of the products obtained. Diploma thesis, Univ. Karlsruhe, 1994, online at zacherle.de, accessed on April 2, 2017.