Refrigeration – Cryogenic treatment of gas or gas mixture – Solidification
Reexamination Certificate
2001-06-22
2002-06-18
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Solidification
C062S617000
Reexamination Certificate
active
06405560
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for analysing impurity levels in liquid carbon dioxide (CO
2
).
2. Description of the Prior Art
Previous methods of separating impurities from liquid CO
2
rely primarily on High Pressure Liquid Chromatography (HPLC) to separate out the constituents of impurities contained in the liquid CO
2
, for analysis of the impurity levels. The equipment necessary to carry out these methods is expensive and has an inherent lower resolution, quantification, and accuracy than that which is required for many applications. Also, some impurities may not be able to be separated using this technique, rendering the HPLC method useless for detecting the presence of these impurities. Furthermore, the equipment has to be calibrated frequently, usually just prior to use.
SUMMARY OF THE INVENTION
It is an object of the invention to mitigate and/or obviate the drawbacks of the prior art mentioned above, and provide an easy to use and inexpensive apparatus for determining the impurity levels in liquid CO
2
.
In the invention, CO
2
snow (frozen CO
2
) is used as a medium to determine non-volatile impurities in the CO
2
snow, and consequently determine the purity of the liquid CO
2
. Liquid CO
2
is expanded in specially designed primary and secondary nozzles to produce low-density and low-velocity CO
2
snow. The impurities initially contained in the liquid CO
2
are trapped inside of the frozen CO
2
, which is preferably collected in a clean container. According to one preferred embodiment, the container is emptied on top of a high purity surface. The impurities are concentrated on the surface, since these impurities are non-volatile and do not escape with the CO
2
gas formed as the CO
2
snow is heated by the ambient temperature to its sublimation point. After all of the CO
2
snow has sublimed, the surface can be analysed by standard methods to determine quantity and composition of the impurities. The determination and quantification of non-volatile impurities, such as organic oils and greases, in the CO
2
supply that feeds, for example, cleaning systems utilizing liquid CO
2
,is thus made possible.
The system according to the invention has a primary nozzle and a secondary nozzle. The primary nozzle is connected to a liquid CO
2
source via one or more small orifices having a suitable shape, for example substantially round, a slit or an annulus shape (an annular slit). Liquid CO
2
is expanded after the orifices, and the expansion causes the liquid to freeze into snow particles. The primary nozzle is arranged to project the snow particles at a certain angle into the secondary nozzle. The snow particles collide with each other and the walls of the secondary nozzle, and the secondary nozzle geometry is designed to cause the snow to have multiple collisions with these walls. The collisions reduce the velocity of the snow and cause many snow particles to stick together further reducing the snow velocity. Thus, the snow is easily collected in a container for analysis. The container is emptied onto a high purity surface, and as the snow sublimes from the surface, the non-volatile impurities remain on the surface and accumulate in high concentrations.
The advantage of this system is the simplicity of use and low cost, since it does not require expensive analytical equipment. This simple and inexpensive method enables part-per-billion (ppb) resolution of non-volatile impurities.
Further features of the invention will be described or will become apparent in the course of the following detailed description.
REFERENCES:
patent: 3124442 (1964-03-01), Rich
patent: 4337071 (1982-06-01), Yang
patent: 5566553 (1996-10-01), Gibot et al.
patent: 5868003 (1999-02-01), Simas et al.
patent: 6023941 (2000-02-01), Rhoades
patent: 6116049 (2000-09-01), Filipczak
Bowers Charles W.
Krone-Schmidt Wilfried
Armstrong R. Craig
Capossela Ronald
Eco-Snow Systems, Inc.
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