Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Reexamination Certificate
1998-08-12
2001-05-08
Snay, Jeffrey (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
C422S082020, C436S146000
Reexamination Certificate
active
06228325
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to improved methods and apparatus for the determination of the total concentration of organic carbon compounds in aqueous process streams and in bulk solutions. The invention is especially adapted for use in measuring carbon in deionized water or deionized water with dissolved carbon dioxide, which is often used in the manufacture and processing of electronic components, fine chemicals and pharmaceuticals. The present invention in one embodiment includes the measurement of the temperature and conductivity of an aqueous sample, the oxidation of the organic components of the sample stream, and the sensitive and selective detection of carbon dioxide utilizing a selective carbon dioxide gas permeable membrane and conductometric detection to determine the level of organic carbon in the sample. In a preferred embodiment for some applications, accurate conductometric detection of carbon can be carried out utilizing a single conductivity cell.
2. Background Art
The measurement of the total organic carbon (TOC) concentration and total carbon (organic plus inorganic) concentration in water has become a standard method for accessing the level of contamination of organic compounds in potable waters, industrial process waters, and municipal and industrial waste waters. In addition to widespread terrestrial applications, the measurement of TOC is one of the primary means of determining the purity of potable and process waters for manned space-based systems including the space shuttle, the proposed space station and for future manned explorations of the moon and planets.
The United States Environmental Protection Agency recently promulgated new rules aimed at reducing the levels of disinfectant by-products in drinking water. Formed from the reaction of chlorine and other disinfectants with naturally occurring organic matter, disinfectant by-products are potentially hazardous compounds including trihalomethanes (CHCl
3
, CHBrCl
2
, etc.), haloacetic acids, and other halogenated organic species. The new rules also require monitoring the levels of natural organic material in raw water, during the treatment process and in the finished water by measurement of total organic carbon concentration.
Very pure water is used for the manufacture of electronic components, and also in certain processes involving fine chemicals and pharmaceuticals. The water required for such uses is often deionized and carbon based impurity concentration in the parts per billion or even parts per trillion range must be monitored.
A variety of prior art approaches for measuring the total organic carbon content of water have been proposed. For example, See U.S. Pat. Nos. 3,958,941 of Regan; 3,224,837 of Moyat; 4,293,522 of Winkler; 4,277,438 of Ejzak; 4,626,413 of Blades, et al. and 4,666,860 of Blades, et al.; and 4,619,902 of Bernard.
Representative of the devices described in these references are the methods disclosed in U.S. Pat. No. 3,958,941 of Regan. In Regan an aqueous sample is introduced into a circulating water stream that flows through a reaction chamber where the sample is mixed with air and exposed to ultraviolet (U.V.) radiation to promote the oxidation of organic compounds found in the sample to form carbon dioxide. The carbon dioxide formed in the reaction chamber is then removed from solution by an air stripping system and introduced into a second chamber containing water that has been purified to remove ionic compounds. The conductivity of the water in the second chamber is measured, and any increase in conductivity is related to the total concentration of carbon dioxide following oxidation in the first reactor. In Ejzak, persulfate is added to an aqueous sample stream prior to oxidation of the stream using ultraviolet radiation in a series of reactors. Ejzak also describes the use of an inorganic carbon stripping process—before oxidation of the organic carbon—that includes the addition of phosphoric acid to the sample stream. After oxidation, the sample stream is passed into a gas-liquid separator where the added oxygen acts as a carrier gas to strip carbon dioxide and other gases from the aqueous solution. In the preferred embodiment, the gas stream is then passed through an acid mist eliminator, a coalescer and salt collector, and through a particle filter prior to passage into an infrared (IR) detector for the measurement of the concentration of carbon dioxide in the gas stream.
The methods and apparatus disclosed by Ejzak provide improvements over the teachings of Regan; however, the Ejzak device requires extensive manual operation and is also generally unsatisfactory. The Ejzak device requires three external chemical reagents; oxygen gas, aqueous phosphoric acid and an aqueous solution of sodium persulfate. Both the phosphoric acid and persulfate solutions must be prepared at frequent intervals by the operator due to the relatively high rate of consumption. The Ejzak device requires dilution of the sample if the solution contains high concentrations of salts in order to ensure complete oxidation of the sample and to eliminate fouling of the particle filter located prior to the IR carbon dioxide detector. As with Regan, relatively large sample sizes are required—typically 20 &mgr;L of sample for accurate measurement at 0.5 mg/L total organic carbon—and the carbon dioxide formed in the oxidation chamber is removed using a gravity dependent technique that cannot be easily used in space-based operations.
Another improved method and apparatus for the measurement of total organic carbon in water is disclosed in U.S. Pat. No. 4,293,522 of Winkler. In Winkler, an oxidizing agent, molecular oxygen, is generated in-situ by the electrolysis of water. Organic compounds are subsequently oxidized to form carbon dioxide by the use of U.V. radiation and the in-situ generated oxygen. The irradiation and electrolysis processes are both accomplished in a single oxidation chamber. Winkler does not teach that the aqueous sample stream be acidified to assist in the removal of carbon dioxide from solution, and in fact teaches against the use of acid. Therefore, this method and apparatus cannot be used for the measurement of organic compounds in basic aqueous samples. The oxidation chamber of Winkler uses a solid electrolyte to separate the two electrodes employed for the electrolysis of water. The solid electrolyte described by Winkler is composed of an organic polymer which, upon exposure to oxygen, ozone and U.V. radiation, will undergo limited oxidation to form carbon dioxide, therefore resulting in unacceptable background levels of organic compounds in the sample stream, particularly at low organic compound concentrations.
The Winkler patent describes a conductometric carbon dioxide detection system wherein the sample stream exiting the oxidization chamber is maintained in an equilibrating relationship with a stream of deionized water. The two flowing streams are separated by a gas permeable membrane that permits the concentration of carbon dioxide to equilibrate between the streams. The concentration of the carbon dioxide generated in the oxidation chamber is thereafter determined by measuring the conductance of the deionized water stream. However, the use of two continuously flowing and recirculating streams with separate pumps on either side of the membrane as taught by Winkler introduces precise operating parameters into the detection process that require frequent calibration adjustments, such as adjustments necessitated by ionic contamination from the circulatory pump. Using one pump for the sample stream and a different pump for the deionized water stream can produce varying differential flow rates which introduce additional errors into the system. The use of a membrane as taught in the Winkler patent allows the passage of acid gases other than carbon dioxide, thereby interfering with the measurement of carbon dioxide. The device described in Winkler uses a large volume batch process which would also be very time-consuming to operate, t
Godec Richard D.
Kosenka Paul P.
O'Neill Kevin J.
Petropavlovskikh Viatcheslav A.
Andover-IP-Law
Sievers Instruments, Inc.
Silverstein David
Snay Jeffrey
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