The substitution of unwanted solvents (CFC's, other organic solvents, water) by supercritical carbon dioxide (scCO_2) is still of great interest. The advantages of scCO_2 are well known (clean, easy to regenerate and non-toxic), but many promising applications fail to enter the industrial production level because of high investment costs and the inflexibility of the technique bound on the batch process. In many cases the ability of a continuous mass transport of solids from ambient to high pressure would make the processes faster, easier to control and with less energy demand for pressurization. A good example is the admission of dyestuff (disperse dye as powder/particles) in a high pressure vessel, for the dyeing of textiles or synthetic fibers in scCO_2. Today, the whole amount of needed dyestuff has to be put as a batch in a pressure vessel, prior to the beginning of the process. Other applications are the admission of valuable solid substances inside high pressure vessels for the production of pharmaceutical or chemical products. A technical solution for powdery solids has been invented by the Technical University of Hamburg-Harburg (Prof. R. Eggers). Its name is "FES" (Feststoff-Eintrag-System = Solids admission system). Powdery material (e.g. dyestuff), which is stored in a small container, can be quasi-continuously transported from ambient pressure (storage container) into the supercritical fluid (inside the high pressure vessel). This is done by small transport-holes in an shaft, which is horizontally moved through a vertically mounted pressure vessel. In a cooperation of the TUHH (Prof. R. Eggers) and Siegfried Kempe GmbH (Germany) the FES has been constructed, build and successfully tested at industrial scale. It was integrated in a pilot plant for industrial dyeing of polyester fibers. The main advantages are a homogeneous loading of the scCO_2, a better control of the dyeing process and, as a result of these effects, shorter process times. Additionally the invention can save 30 to 50% of dyestuff due to a better utilization of the solid material.
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