Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Reexamination Certificate
2001-09-11
2004-12-14
Gakh, Yelena G. (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
C422S050000, C422S062000, C422S082010, C422S082020, C422S083000, C422S090000
Reexamination Certificate
active
06830730
ABSTRACT:
BACKGROUND OF THE INVENTION
Sulfur in motor fuels such as gasoline and diesel fuel is an important pollutant. Its concentration has been regulated over the past several years so as not to exceed levels in the range of 500 parts per million (ppm). In order to ensure that the regulated concentration levels are not exceeded, petroleum products are subjected to both laboratory and on-stream analysis during their processing and production. At these concentrations, one of the preferred methods of analysis is x-ray fluorescence spectrometry, described in ASTM methods D
2622
and
4294
incorporated herein by reference, which is well-suited to direct analysis of liquid samples. However, recent government regulations worldwide will reduce the acceptable sulfur contents of gasoline and diesel fuel to below 50 ppm with specific regulatory levels set at 30 and 15 ppm in the next two or three years. It is doubtful whether x-ray fluorescence is sensitive enough to reliably monitor sulfur at 15 ppm, see ASTM Research Report D.02-1456, incorporated herein by reference. There is also a need to monitor total nitrogen, in the ppm range, in liquids such as beverages and fuels. X-Ray fluorescence is not suitable for measuring nitrogen content.
Other more sensitive laboratory methods are “pyro-UV fluorescence” for sulfur, according to ASTM method D
5453
incorporated herein by reference, “pyro-chemiluminescence” for nitrogen, according to ASTM method D
4629
incorporated herein by reference, and “pyro-electrochemical” for either or both sulfur and nitrogen, described in ASTM methods D
6366
and
6428
also incorporated by reference herein. In all these methods a small fixed volume of sample is thermally oxidized (“pyrolyzed”) and the combustion products are analyzed for SO
2
or NO. Ultraviolet fluorescence for SO
2
and chemiluminescence for NO both have detection limits of 1 ppb or less, so the sensitivity is good enough to monitor low ppm levels of sulfur or nitrogen in liquids even allowing for the dilution inherent in the pyrolysis step. Similarly, the sensitivity of electrochemical detectors, although not as good as UV fluorescence or chemiluminescence, should be adequate to measure low ppm levels of sulfur and/or nitrogen in liquids, after pyrolysis. However, electrochemical detectors have the great advantages of simplicity and low cost.
Known systems for employing these methods, however, have many drawbacks that are avoided by the present disclosure. In particular, known systems fail to guarantee the quality of the pyrolysis, and as a consequence, reproducible and reliable results may not be obtained and sooting may occur. In employing these analysis methods, a dryer is utilized after pyrolysis to insure the quality of the analysis is not adversely affected by the presence of too much water vapor. However, the dryer arrangement employed in known systems is either costly requiring the use of a separate vacuum pump or may fail to prevent the collapse of the sample dryer inner tube.
SUMMARY OF THE INVENTION
The present invention overcomes the drawbacks of known analysis methods by providing reliable and cost-effective on-stream analysis methods and apparatuses for measuring chemical components, including the measurement of total sulfur and nitrogen contents and other components that may be monitored. The present invention accomplishes these objectives by, in certain embodiments, providing reproducible and reliable pyrolysis products and/or by providing an improved dryer design. On-stream analyzers preferably operate automatically and reliably and therefore may include many features, components and improvements that enable the erstwhile laboratory method to function successfully as an on-stream analyzer. Such improvements and additional features are described below.
On-stream analysis for monitoring pollutant levels is of particular importance in many industrial applications. For example the monitoring of sulfur and nitrogen is of concern within the petroleum and beverages industry, however other applications are contemplated by the present disclosure. For simplicity, we refer primarily to monitoring sulfur, although it is contemplated and within the scope of the present invention that the disclosed methods and apparatuses may also be employed for the analysis of other chemical components which may be measured by measuring their pyrolysis products and are capable of detection according to the techniques disclosed herein.
According to the ASTM method, a fixed volume, usually 5-20 microliters, of liquid sample is injected into the pyrolyzer along with an inert carrier gas, usually argon at a flow rate of about 130-160 sccm (standard cubic centimeters per minute) and including some oxygen, about 10-30 sccm. The liquid vaporizes and then reaches the combustion zone where another flow of oxygen, about 450-500 sccm, the “pyrolysis-gas”, is introduced and effects complete thermal oxidation at 1050° C. The reactor is a quartz tube heated by a tube furnace. The flow rate of liquid sample should never exceed about 4 &mgr;l/s (microliters/second), otherwise the combustion process will be starved of oxygen and soot formation (or “sooting”) will occur, that is, the internal surfaces downstream of the hot zone will be covered with soot. The ASTM methods specify a flow rate of 1 &mgr;l/s. The gas output from the pyrolyzer is a mixture of the inert carrier gas (about 20 vol %), unconsumed oxygen (about 60 vol %), carbon dioxide, CO
2
(about 10 vol %), water vapor (about 10 vol %) and ppm levels of SO
2
. The dewpoint is 45-50° C., so the gas lines are usually heat traced and/or the water vapor content is reduced to prevent condensation. Water vapor can be reduced without affecting the SO
2
content by means of a permeation dryer which operates on the principle of absorption-desorption of water vapor through a membrane (a rapid process having first order chemical kinetics), such as the “NAFION” membrane dryer, commercially available from Perma Pure, Inc. The conditioned gas mixture is then fed to the SO
2
detector. A typical 20 &mgr;l sample takes some 20 seconds to inject and passes through the pyrolyzer and other gas sample plumbing in about one minute. The SO
2
concentration at the detector starts at zero just before the injection, rises to a maximum and then falls off to zero. The rates of rise and fall depend on the various flow rates and gas mixing, and on any molecular exchange reactions that the SO
2
undergoes at surfaces it comes into contact with. The detector response ideally follows this same profile. The actual detector response will be less than ideal, so additional broadening of the time profile will occur. In practice, the whole SO
2
signal from a given injection will extend over 2-5 minutes. This signal is integrated and is directly proportional to the total amount of sulfur in the original sample. As long as the sample volume remains constant, the SO
2
signal is, therefore, proportional to sulfur content of the original sample. “Continuous” analysis is accomplished by automating the sample injection procedure.
It is therefore an object of the present disclosure to provide reproducible and reliable pyrolysis byproducts for use in an on-stream analyzer by, in certain embodiments, controlling the volume of a liquid sample dispensed for injection into a pyrolyzer so that it is constant and repeatable. Also, the injection rate is preferably controlled below the upper limit set by “sooting” and above a lower limit below which the analysis takes too long. In practice, there are closer tolerances set not only on the sample injection rate but also on the flow rates of the input gases. If the detector background signal is negligible, the size of the integrated signal, e.g. SO
2
or other chemical signal, would depend only on the total sample volume injected (and its sulfur or other chemical content). Variations in injection rate and in flow rates of the input gases will cause changes in dilution of the SO
2
or other components to be measured in the output gas but this would not matter as long
Gakh Yelena G.
SpectrolAnalytical Instruments
Vinson & Elkins L.L.P.
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