Reagentless oxidation reactor and methods for using same

Details Reagentless oxidation reactor and methods for using same Reagentless oxidation reactor and methods for using same

1998-05-11

2001-02-06

Soderquist, Arlen (Department: 1743)

Chemical apparatus and process disinfecting, deodorizing, preser

Analyzer, structured indicator, or manipulative laboratory...

Means for analyzing liquid or solid sample

C422S076000, C422S077000, C422S078000, C422S080000, C436S145000, C436S146000, C436S150000

Reexamination Certificate

active

06183695

ABSTRACT:

FIELD OF THE INVENTION
The present invention principally relates to an improved apparatus and method for in situ generation, i.e., without the need for adding chemical oxidizing agents, or enhancement of oxidizing conditions used to promote oxidation of organic compounds to form carbon dioxide, and the use of the same in connection with high-accuracy determination of even extremely low levels of organic and/or inorganic carbon compounds both in flowing aqueous streams and in bulk solutions. This invention has particular utility in determining and monitoring carbon levels in ultrapure water intended for such highly impurity-sensitive applications as in the manufacture of semiconductors. This invention also has utility in such other applications as monitoring various stages of water purification systems and municipal drinking waters.
BACKGROUND OF THE INVENTION
The measurement of the total organic carbon (TOC) concentration, total inorganic carbon (TIC) concentration, and total carbon (TC) concentration in water has become a standard method for ascertaining the level of contamination by organic and inorganic carbon 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 for 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 other planets.
A variety of prior art approaches for measuring the total organic carbon content of water have been proposed, for example, in U.S. Pat. No. 3,958,941 (Regan); U.S. Pat. No. 3,224,837 (Moyat); U.S. Pat. No. 4,293,522 (Winkler); U.S. Pat. No. 4,277,438 (Ejzak); U.S. Pat. Nos. 4,626,413 and 4,666,860 (Blades et al.); U.S. Pat. No. 4,619,902 (Bernard); U.S. Pat. No. 5,275,957 (Blades et al.); and U.S. Pat. Nos. 5,132,094 and 5,443,991 (Godec et al.), each of which is incorporated herein by reference.
Representative of the devices described in these references are the methods described in U.S. Pat. No. 3,958,941 (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 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 concentration of carbon dioxide formed in the first reactor. The conduction measurement can be used, therefore, to determine the concentration of organic compounds in the original sample.
But, the Regan device is slow, cannot be used for the continuous monitoring of TOC concentration in flowing aqueous streams, cannot be scaled down without increasing interference from commonly-occurring contaminants, such as NO
2
, SO
2
and H
2
S, to unacceptable levels, and is therefore generally unsatisfactory. In addition, Regan does not disclose that an aqueous solution of acid must be added to the sample stream to reduce the pH to a value of less than about 4 to insure a reasonable removal rate of carbon dioxide using the air stripping system described. The oxidation method disclosed by Regan is unsatisfactory for the measurement of refractory compounds, particularly urea. In Regan, an aqueous sample of 20 to 100 mL containing 0.5 mg/L organic carbon is required to generate sufficient carbon dioxide for accurate detection, thus limiting the utility of the device for the measurement of sub-part per million levels of TOC in smaller sample sizes. Finally, in practice, the Regan system requires frequent recalibration-typically once per day—due to variations in background conductivity. Also, the concentration of total organic carbon in the calibration standard must be approximately equal to the concentration of organic carbon in the sample. Because of this, recalibration is required when analyzing aqueous samples containing higher or lower levels of organic carbon when compared with the calibration standard.
Another method and apparatus for the measurement of organic content of aqueous samples is that described in U.S. Pat. No. 4,277,438 (Ejzak). Ejzak describes a multistage reactor design which provides for the addition of oxygen and a chemical oxidizing agent, preferably sodium persulfate, to the 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 or carbon dioxide in the gas stream.
The methods and apparatus disclosed by Ejzak provide certain improvements over the Regan patent; however, the Ejzak device requires extensive manual operation and is generally unsatisfactory for other reasons as well. Thus, 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 insure complete oxidation of the sample and to eliminate fouling of the particle filter located prior to the IR carbon dioxide detector. As in the Regan patent, relatively large sample sizes are required—typically 20 mL 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.
Still another method and apparatus for the measurement of total organic carbon in water is disclosed in U.S. Pat. No. 4,293,522 (Winkler). In Winkler, an oxidizing agent, specifically molecular oxygen, is generated in situ by the electrolysis of water. Organic compounds are subsequently oxidized to form carbon dioxide by a combination of exposure to U.V. radiation and the in situ-generated oxygen. Winkler does not teach or suggest, however, that the aqueous sample stream be acidified to assist in the removal of carbon dioxide from solution. On the contrary, Winkler teaches away from the use of acid. Therefore, the Winkler method and apparatus cannot be used for high accuracy measurement of very low levels of organic compounds in basic aqueous samples. Also, 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, under exposure to oxygen, ozone and U.V. radiation, will undergo oxidation to form carbon dioxide, therefore resulting in unacceptable and misleading background levels of carbon and/or organic compounds in the sample stream. These background levels of carbon and/or organic compounds, though typically small, become proportionally very large and increasingly significant sources of error at very low organic compound concentrations in the sample.
Winkler also describes a conductometric carbon dioxide detection system wherein the sample stream exiting the oxidizing chamber must be held in an equilibriating relationship to a stream of deionized wat

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