Method for analyzing impurities in carbon dioxide

A method for monitoring contaminants in a carbon dioxide stream that is directed to a workpiece, comprising the steps of:

• a) identifying a reference value, wherein said reference value indicates that the dissolved contaminants will precipitate and deposit onto the workpiece in acceptably low levels, by detecting the number of particles of at least a portion of the dissolved contaminants in a calibration process which includes the steps of:
• i) sampling at least a potion of an acceptable carbon dioxide stream to form an acceptable carbon dioxide sample;
• ii) modifying the conditions of the acceptable carbon dioxide sample to form an aerosol of gaseous carbon dioxide and precipitated contaminants, whereby at least a portion of the contaminants are in the form of suspended droplets;
• and
• iii) detecting the number of particles of at least a portion of the acceptable carbon dioxide sample with at least one particle counter;
• thereby identifying said reference value;
• b) subsequently directing a carbon dioxide stream to the workpiece;
• c) sampling said carbon dioxide stream to identify at least one measured value, wherein said measured value indicates whether contaminants will precipitate from the carbon dioxide stream and deposit onto the workpiece in an acceptably low level, by detecting the number of particles of an essentially equal portion of the dissolved contaminants as employed to determine the reference value in a monitoring process which includes the steps of:
• i) sampling at least a portion of said carbon dioxide stream to form a carbon dioxide sample;
• ii) modifying the conditions of the carbon dioxide sample to form an aerosol of gaseous carbon dioxide and precipitated contaminants;
• and
• iii) detecting the number of particles in the portion of the carbon dioxide sample with at least one particle counter;
• thereby identifying said measured values;
• and
• d) comparing the measured values with the reference value to determine the number of dissolved particles that will precipitate from the subsequently directed carbon dioxide and deposit onto the workpiece is an acceptably low level, thereby monitoring contaminants of the carbon dioxide stream.

A system for continuously detecting contaminants dissolved in a carbon dioxide stream flowing through a solvent feed line, comprising:

• a) a sampling means for removing a sample stream, wherein said sample stream is at least a portion of the carbon dioxide stream flowing through the solvent feed line;
• b) a modification means in fluid communication with the sampling means, wherein said modification means modifies the conditions of the sample stream to form an aerosol of gaseous carbon dioxide and suspended contaminants;
• c) at least one contaminant measurement zone in fluid communication with the modification means;
• and
• d) at least one particle counting means, wherein said particle counting means can detect at least a portion of the suspended contaminants in the contaminant measurement zone with at least one particle counter.