Method for analyzing impurities in carbon dioxide

#Carbon dioxide normally supplied to food and beverage customers must meet a set of purity specifications known as Enhanced Ingredient Grade (EIG). Carbon dioxide of this purity is sufficient for use in food and beverages, and most plants can produce it.

#Some applications require carbon dioxide of higher purity than EIG. For example, supercritical fluid extraction and supercritical fluid chromatography require small amounts of higher purity carbon dioxide. Examples of the types of higher purity carbon dioxide include Supercritical Fluid Extraction (SFE) and Supercritical Fluid Chromatography (SFC) grades. These grades of carbon dioxide are generally supplied in cylinders.

#Additional applications requiring high purity and ultra-high purity (UHP) carbon dioxide have recently been developed. These include pharmaceutical processing, semiconductor processing (photoresist removal and wafer cleaning), micro-electromechanical systems (MEMS) drying, and metal target cleaning.

#FIG. 1 is a schematic diagram illustrating one embodiment of the present invention, wherein the suspended particles are detected with a particle analyzer.

#FIG. 2 is a schematic diagram illustrating one embodiment of the present invention, wherein a first analyzer prevents a particle analyzer from being overwhelmed by suspended particles.

#FIG. 3 is a graph illustrating the path-dependent nature of aerosol formation.

#The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

#The present invention generally relates to applications that use carbon dioxide. Preferably, the application uses carbon dioxide at a pressure lower than about 10,000 psia. More preferably, the application uses carbon dioxide at a pressure less than about 4,000 psia. The invention is particularly well suited for applications that use carbon dioxide in a supercritical, critical, or subcritical phase. Carbon dioxide has a supercritical temperature of 31° C. and a supercritical pressure of 1070 psia, a triple point pressure and temperature of 75 psia and −57° C. respectively, and its sublimation temperature at ambient pressure is approximately −78° C.

#Examples of applications which use carbon dioxide include electronics applications, such as photoresist stripping and deposition; pharmaceutical applications, such as nanoparticle formation; and the processing of micro-electro-mechanical systems (MEMS). Applications may also use carbon dioxide in a two-phase state, such as carbon dioxide snow cleaning applications. Snow cleaning applications typically expand carbon dioxide to close to ambient pressure in order to form solid carbon dioxide “snow” and carbon dioxide gas, which is then used in the cleaning applications.