THE USE OF STABLE ISOTOPES OF CO2 TO VALIDATE CYLINDER PREPARATION

Abstract

A quality control method for the preparation of dry compressed gas cylinder including passivating and/or preparing the compressed gas cylinder with the technique to be validated, filling the passivated/prepared compressed gas cylinder with gaseous carbon dioxide to a normal working pressure, wherein the gaseous carbon dioxide has a known .sup.18O isotope ratio, maintaining the pressurized gas cylinder at ambient temperature for a first predetermined period of time, and gradually emptying the pressurized gas cylinder, while simultaneously measuring the .sup.18O isotopic ratio, wherein a predetermined variation in the measured isotopic ratio of .sup.18O indicates a properly prepared cylinder.

Claims

1. A quality control method for the preparation of dry compressed gas cylinder comprising: a) passivating and/or preparing the compressed gas cylinder with the technique to be validated, b) filling the passivated/prepared compressed gas cylinder with gaseous carbon dioxide to a normal working pressure, wherein the gaseous carbon dioxide has a known .sup.18O isotope ratio, c) maintaining the pressurized gas cylinder at a first temperature for a first predetermined period of time, d) gradually emptying the pressurized gas cylinder, while simultaneously measuring the .sup.18O isotopic ratio, wherein a predetermined variation in the measured isotopic ratio of .sup.18O indicates a properly prepared cylinder.

2. The quality control method of claim 1, wherein the predetermined variation in the measured isotopic ratio of .sup.18O of a standard deviation of less than 0.1, indicates a properly prepared cylinder.

3. The quality control method of claim 1, wherein the gaseous carbon dioxide has a natural .sup.18O isotope ratio.

4. The quality control method of claim 1, wherein the first predetermined period of time is between 6 hours and 100 days.

5. The quality control method of claim 1, wherein the first predetermined period of time is 75 days or greater.

6. The quality control method of claim 1, further comprising: c1) inverting and/or agitating the cylinder, thereby ensuring complete mixing.

7. The quality control method of claim 1, further comprising: c2) heating the cylinder for a second predetermined period of time, at a second predetermined temperature based on the metallurgy of the cylinder.

8. The quality control method of claim 7, wherein the second predetermined temperature is less than 177 C, for an aluminum cylinder.

9. The quality control method of claim 7, wherein the second predetermined temperature is less than 260 C, for a steel cylinder.

10. The quality control method of claim 7, wherein the second predetermined period of time is between 2 days and 60 days.

11. The quality control method of claim 7, wherein the second predetermined period of time is greater than 5 hours.

12. Storing isotopically prepared mixtures in a prepared compressed gas cylinder validated by the quality control method of claim 1.

13. Calibrating an analyzer using the isotopically prepared mixture of claim 12 as the calibration mixture.

14. Storing corrosive gas mixtures in a prepared compressed gas cylinder validated by the quality control method of claim 1.

15. The method of claim 1, wherein the compressed gas cylinder internal passivation comprises the reaction product of a silicon-containing material and an oxygen-containing material and an amount of the reactive gas adsorbed on the reaction product.

16. The method of claim 15, wherein the silicon-containing material is selected from the group consisting of compounds within the general formula (II): SiR.sup.1R.sup.2R.sup.3R.sup.4 (II) wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are the same or different and are independently selected from the group consisting of hydrogen, halogen, amine, alkyl, aryl, halogenated alkyl, and halogenated aryl.

17. The method of claim 15, wherein the silicon-containing material is elected from the group consisting of silane, methylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, and mixtures thereof.

18. The method of claim 15, wherein the oxygen-containing compound is selected from the group consisting of moisture, molecular oxygen, metal oxides, and mixtures thereof.

19. The method of claim 1, wherein the compressed gas cylinder internal passivation comprises simultaneously exposing the cylinder to a desiccating temperature and a vacuum for a defined period of time.

20. The method of claim 19, wherein the vacuum is less than 20 microns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0015] FIG. 1 illustrates the .sup.18O ratio remaining constant over the entire cylinder contents,

[0016] FIG. 2 illustrates the .sup.13C ratio remaining constant over the entire cylinder contents,

[0017] FIG. 3 illustrates the stability of a pure CO.sub.2 containing compressed gas cylinder over a 1 year period, and

[0018] FIG. 4 also illustrates the stability of a pure CO.sub.2 containing compressed gas cylinder over a 1 year period.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0019] A quality control method of validating cylinder preparation of compressed gas cylinders suitable to provide stability of isotopically prepared gas mixtures is proposed. The quality control method could also be advantageously used to validate cylinders for use in the storage of corrosive and/or reactive gas mixtures, since such mixtures are very sensitive to trace moisture.

[0020] The ability of CO.sub.2 and H.sub.2O to undergo an exchange reaction in a compressed gas cylinder was validated by adding a known quantity of .sup.18O enriched H.sub.2O (at 98+% atom purity to a compressed gas cylinder, which was processed using a cylinder prep protocol via a syringe).

[0021] CO2 may be derived from many sources such as naturallimestone, combustion-based: bio-mass-derived stock, geo-fuels etc. Herein, this class is defined as having CO2 with isotope ratios within the natural abundance spectrum. This covers a fairly wide range. For example, where heavy water is used to cause species to exchange with the CO2 from the natural abundance source yields CO2 that has isotope ratios that are manipulated. These CO.sub.2's may be used as test material to determine the quality of cylinder prep.

[0022] A sufficient quantity of gaseous CO.sub.2, whose isotopic values were known, was then added to the cylinder. The cylinder was then inverted/agitated several times to ensure complete mixing. After a set number of hours of heating at a prescribed temperature, the cylinder was left to sit at room temperature for a period exceeding 75 days. To stop any further isotopic exchange, the CO.sub.2 was passed through a H.sub.2O getter (VICI model #T100-2). The dried CO.sub.2 was then transfilled into a specially prepared cylinder. The isotopic values were then measured. The change in isotopic values can be seen in Table two, which clearly demonstrates the change of .sup.18O isotopic values.

.SUP.18.OCO.SUB.2 .Values Before and after Isotopic Exchange

[0023]

TABLE-US-00002 TABLE 2 Starting value Value after exchange .sup.18OCO.sub.2 signature 23.16 vs VPDB +109 vs VPDB

[0024] Trace moisture is known to desorb from cylinder walls below approximately 3 bar (45 psi), therefore if there is residual moisture remaining in the compressed gas cylinder the CO.sub.2 isotopic ratios will change as the cylinder is depleted.

[0025] As a non-limiting example, a cylinder was prepared using appropriate cylinder preparation, filled to 34 bar (500 psi) with gaseous CO.sub.2. The .sup.18O and .sup.13C isotopic ratios were measured vs. VPDP as the cylinder was depleted at a rate of approximately 50 mL/min. FIG. 1 illustrates that the .sup.13C and .sup.18O ratios remained constant over the entire cylinder contents validating the absence of residual moisture in the cylinder.

[0026] Further verification of the absence of residual moisture in the cylinder can be illustrated by measuring the stability of the CO.sub.2 isotopic concentration over an extended period. The stability of a pure CO2 containing compressed gas cylinder over a 1 year period is indicated in FIG. 3 and FIG. 4.

[0027] In one embodiment, a quality control method for the preparation of dry compressed gas cylinder is provided. The first step of this method is passivating and/or preparing the compressed gas cylinder to be validated. This may be any method known in the art.

[0028] In one non-limiting example, the passivation may comprise lining the cylinder with the reaction product of a silicon-containing material and an oxygen-containing material and an amount of the reactive gas adsorbed on the reaction product. The silicon-containing material may be selected from the group consisting of compounds within the general formula (II): SiR.sup.1R.sup.2R.sup.3R.sup.4 (II) wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are the same or different and are independently selected from the group consisting of hydrogen, halogen, amine, alkyl, aryl, halogenated alkyl, and halogenated aryl. The silicon-containing material may be selected from the group consisting of silane, methylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, and mixtures thereof. The oxygen-containing compound may be selected from the group consisting of moisture, molecular oxygen, metal oxides, and mixtures thereof. Passivation of this type is fully described in U.S. Pat. Nos. 7,156,225, 7,229,667, 7,794,841, 7,799,150, 7,832,550, 7,837,806, 7,850,790, and 8,288,161 the entire disclosure of which are incorporated herein by reference.

[0029] In another non-limiting example, the passivation may comprise heating the cylinder to a desiccating temperature while being exposed to a vacuum for a defined period of time. The desiccating temperature may be less than 70 C. The vacuum may be less than 20 microns, preferably less than 10 microns. The defined period of time may be less than 24 hours, preferably less than 15 hours. The defined period of time may be more than 6 hours.

[0030] The next step of this method is filling the passivated/prepared compressed gas cylinder with gaseous carbon dioxide to a normal working pressure. The gaseous carbon dioxide to be used will have been tested and will have a known .sup.18O isotope ratio. The .sup.18O isotope ratio may be that which is naturally occurring, that is to say within the natural abundance spectrum. Sources of such carbon dioxide may be limestone caves. Such carbon dioxide may also be derived from combustion of hydrocarbons, biomass derived sources, etc. The .sup.18O isotope ratio may also be manipulated and customized. One non-limiting example would be where heavy water is used to cause species to exchange with the CO2 from the natural abundance source yields CO2 that has isotope ratios that are manipulated.

[0031] The pressurized gas cylinder is then maintained at a first temperature, typically ambient temperature, for a first predetermined period of time. This first predetermined period of time may be 100 days or less. This first predetermined period of time may be 75 days or more. This first predetermined period of time may be between 6 hours and 100 days. This first predetermined period of time may be between 2 days and 75 days. The first predetermined period of time may be less than 1 day.

[0032] After this first predetermined period of time, the pressurized gas cylinder is gradually emptied, while simultaneously measuring the .sup.18O isotopic ratio. From this measurement, a predetermined variation in the measured isotopic ratio of .sup.18O is determined. It is this variation that may indicate a properly prepared cylinder.

[0033] If the predetermined variation in the measured isotopic ratio of .sup.18O reveals a standard deviation of less than 0.5, this may indicate a properly prepared cylinder. If the predetermined variation in the measured isotopic ratio of .sup.18O reveals a standard deviation of less than 0.1, this may indicate a properly prepared cylinder. If the predetermined variation in the measured isotopic ratio of .sup.18O reveals a standard deviation of less than 0.05, this may indicate a properly prepared cylinder.

[0034] In some embodiments, additional steps may also be performed. During the step of maintaining the pressurized gas cylinder at the first (i.e. ambient) temperature for a first predetermined period of time, the cylinder may be inverted and/or agitated, in order to endure more complete mixing.

[0035] During the step of maintaining the pressurized gas cylinder at the first (i.e. ambient) temperature for a first predetermined period of time, the cylinder may be heated for a second predetermined period of time, at a second predetermined temperature which may be based on the metallurgy of the cylinder. The second predetermined temperature may be less than 177 C for an aluminum cylinder. The second predetermined temperature may be less than 260 C for a steel cylinder.

[0036] The second predetermined temperature may be dependent on valve components, such as the seat material for the valve or the safety relief device. The safety relief device may be a fusible alloy plug or a rupture disc. Such safety devices are mandatory in North America. Therefore, in instances where the entire cylinder is contained within the oven, the second predetermined temperature may be less than 70 C. This second predetermined period of time may be greater than 20 minutes. This second predetermined period of time may be greater than 5 hours. This second predetermined period of time may be between 2 days and 60 days.

[0037] Once the preparation of a cylinder has been thus validated, isotopically prepared mixtures may be stored in this cylinder. The isotopically prepared mixture thus stored, may be a calibration mixture which then may then be used for the purpose of calibrating an analyzer. Once the preparation of a cylinder has been thus validated corrosive gas mixtures and/or reactive gas mixtures may be stored in this cylinder.

[0038] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.