Supercritical carbon dioxide spray process

UNICARB [Union Carbide carbon dioxide] A process for spray painting objects using supercritical carbon dioxide as the solvent. Developed by Union Carbide Company and workers at Johns Hopkins University. 

The flavour and modern phytopharmaceutical industries have made big changes to the traditional pharmaceutical extraction processes. Whereas ethanol was really the only significant solvent apart from water used by the traditional pharmaceutical extractors, solvents such as hexane and acetone have been used by flavour companies to make soft-extract oleoresins for natural flavour components. Sub- and supercritical carbon dioxide and also some fluorohydrocarbons are now used to produce some very high-quality extracts. Modern concentration and drying processes such as reverse osmosis, spray-drying and freeze-drying... 

Corrigan OI, Crean AM. Comparative physicochemical properties of hydro-cortisone-PVP composites prepared using supercritical carbon dioxide by the GAS antisolvent recrystallization process, by coprecipitation and spray drying. Int J Pharm 2002 245 75-82. 

Supercritical carbon dioxide is also useful in a variety of applications as a replacement for organic solvents. Union Carbide markets a process for spray-painting in... 

SAA, supercritical assisted atomization This process is based on the solubilization of a fixed amount of supercritical carbon dioxide in the liquid solution then the ternary mixture is sprayed through a nozzle, and as a consequence of atomization, solid particles are formed ]. 

Nicotine is obtained from tobacco plants by extraction or steam distillation. Particularly suitable for this, just as for caffeine, is destraction with supercritical carbon dioxide. [567] Nicotine-rich Mapacho is cultivated for this purpose in the USA but also the waste from tobacco processing is a suitable source. The annual worldwide production for pharmaceutical purposes reaches a total of around 35-40 tonnes, whereof most is attributed to nicotine replacement therapy (nicotine containing patches, nasal spray, chewing gum, lollipops) for smoking cessation. 

In the second method the solution is sprayed through a nozzle into compressed carbon dioxide the process is termed as precipitation with compressed antisolvent (PCA) [33] and liquid or supercritical antisolvents can be employed. In the case of continuous flow of the solution and of the antisolvent the process is termed also as aerosol solvent extraction system (ASES) [34], in the case of countercurrent flow and supercritical antisolvent precipitation (SAS) in the case of co-current flow [35]. 

Another method that utilized low-temperature processing without an aqueous phase involved supercritical fluid extraction techniques (Randolph et al, 1994). The polymer, which was dissolved in an organic solvent, was sprayed into a continuous phase of supercritical carbon dioxide. The carbon dioxide acts as a nonsolvent for the polymer phase and extracts the organic solvent. The microsphere size should correlate to the density of the carbon dioxide phase (e.g., more dense, larger microspheres). This process should also provide a high encapsulation efficiency and improved protein stability. 

Another type of atomization employed for pharmaceuticals is supercritical fluid nebulization. The process uses carbon dioxide as an aerosolization aid, which permits drying at lower temperatures than is usually needed in conventional spray drying (55). Within the atomization system, supercritical carbon dioxide is intimately mixed with aqueous solutions containing API, often proteins or peptides. The outcome is the formation of microbubbles, which are rapidly dried in <5 sec, resulting in dried particles predominately <3 pm in diameter (56,57). This method is generally applied for the production of materials for pulmonary use or to achieve increased bioavailability (58). 

A schematic diagram of this process is shown in Figure 2. A solution of drug dissolved in a suitable solvent is sprayed into a continuum of supercritical carbon dioxide (10). The nozzle is typically a fine capillary tube, which generates droplets in the supercritical medium. The technique has been used to prepare polymers and proteins from both organic and organic-water solvents (11). 

With the principle of this process being antisolvent addition, the process does not differ significantly from the SAS technique. As in SAS process, the drug or polymer solution is sprayed into a bulk of SCF, typically carbon dioxide, for a fixed period of time. This step is then followed by passing supercritical carbon dioxide to extract and remove the solvent and dry the precipitated product (18). Reports on the application of this technique focus on particle size reduction (18-22). 

The basic idea of the gas-assisted spray process consists of an enrichment of the polymer with supercritical carbon dioxide (scCOa) which leads to a decrease in viscosity and surface tension. The eiuichment of the polymer with SCCO2 in the spray process occurs upstream the nozzle in a static mixer under high pressure conditions. Downstream the nozzle ambient conditions exist, thus the prior phase equilibrium is disturbed. Therefore, the amount of CO2 that is dissolved in the polymer decreases dramatically. This is followed by a spontaneous gas emission in the polymer. Hence, the atomization of the polymer is assisted by the expanding gas which also leads to a decline of the temperamre based on the Joule Thompson Effect. However, to date there is no detailed knowledge of the fundamental mechanisms to form sprays and particles by this gas-assisted high-pressure spray process. 

The investigated spray process is based on the dissolution of supercritical carbon dioxide (SCCO2) into the liquid which shall be atomized. Therefore, CO2 is one of the central substances within this project. The carbon dioxide is provided by YARA with a purity of 99.9% (v/v). The critical temperature of CO2 is 304.13 K the critical pressure amounts 7375 MPa. The solubility of CO2 in water is in the order of 2-5 wt.% at 313 K and a pressure range of 2-15 MPa [5]. The solubility of CO2 in polymers is in the range of 10 wt.% at 353 K and 14 MPa [6]. 

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