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CN-121986261-A - Detection of trace amounts of gas components in a gas sample

CN121986261ACN 121986261 ACN121986261 ACN 121986261ACN-121986261-A

Abstract

The present invention relates to a method for detecting a reactive gas component in trace amounts as contained in a gas sample by using a gas chromatograph in fluid communication with a detector sensitive to the gas component. Sequentially performing the steps of (i) feeding a carrier gas doped with an amount of the active gas component to the gas chromatograph for a doping time, (ii) feeding a carrier gas not doped with the active gas component to the gas chromatograph for a flushing time, and (iii) adding the gas sample to the carrier gas of step (ii) and feeding the resulting mixture to the gas chromatograph.

Inventors

  • Owen Barendrecht
  • Karsten Fan Buhler

Assignees

  • AC分析控制有限公司

Dates

Publication Date
20260505
Application Date
20240801
Priority Date
20230809

Claims (13)

  1. 1. A method for detecting a trace level of a reactive gas component as contained in a gas sample by using a gas chromatograph in fluid communication with a detector sensitive to the reactive component, wherein the steps of: (i) Feeding a carrier gas doped with an amount of the reactive gas component to the gas chromatograph for a doping time; (ii) Feeding the carrier gas, which is not doped with the active gas component, to the gas chromatograph for a flushing time, and (Iii) Adding the gas sample to the carrier gas of step (ii) and feeding the resulting mixture to the gas chromatograph.
  2. 2. The method of claim 1, wherein the flush time is between 10 seconds and 300 seconds.
  3. 3. The method of any one of claims 1 to 2, wherein step (i) is performed within 600 seconds after step (iii) is performed.
  4. 4. A process according to any one of claims 1 to 3, wherein the reactive gas component is ammonia, hydrogen sulfide, hydrogen cyanide, carbon monoxide, carbon dioxide, oxygen, hydrogen, fluorine, chlorine, sulfur dioxide, formaldehyde, formic acid, hydrogen chloride and water, and mixtures thereof.
  5. 5. The method of any one of claims 1 to 4, wherein the sample gas consists of more than 50% by volume of hydrogen, carbon monoxide, carbon dioxide, methane, ethane, propane, butane, air, nitrogen, helium, ethylene, propylene, or mixtures thereof.
  6. 6. The method of claim 5, wherein the sample gas consists of more than 80% by volume of hydrogen or propylene and the reactive gas component is at least one or more selected from the group consisting of ammonia, hydrogen sulfide, formic acid, sulfur dioxide, formaldehyde, oxygen, carbon monoxide, carbon dioxide, hydrogen chloride, and water.
  7. 7. The method of claim 6, wherein the sample gas consists of more than 99% hydrogen by volume.
  8. 8. The method of any one of claims 1 to 7, wherein the trace level of the gas component in the gas sample is less than 100 ppm.
  9. 9. The method of any one of claims 1 to 8, wherein the pressure of the gas sample in step (iii) is between 10 kPa and 500 kPa.
  10. 10. The method according to any one of claims 1 to 9, wherein gas sampling valve injection is used.
  11. 11. A gas chromatography system comprising a gas chromatography column having an upstream end and a downstream end, a detector fluidly connected to the downstream end of the gas chromatography column, a first switch valve fluidly connected to a second switch valve, each switch valve having a different switch valve position, Wherein the first switching valve has an inlet for a carrier gas, an inlet for a dopant carrier gas, and an outlet for the carrier gas or for the dopant carrier gas depending on the position of the first switching valve, Wherein the outlet for the carrier gas or for the dopant carrier gas is fluidly connected to the inlet for the second on-off valve, Wherein the second on-off valve is further provided with an inlet for a gas sample, a sample loop, an outlet to an exhaust conduit and a second on-off valve outlet fluidly connected to the upstream end of the gas chromatography column, and Wherein the first and second switching valves have switching valve positions (i) to (iii) at which there are (I) Fluid communication between the inlet for a doping carrier gas and the upstream end of the gas chromatography column via the second on-off valve outlet, (Ii) Fluid communication between the inlet for carrier gas and the upstream end of the gas chromatography column via the second on-off valve outlet, and (Iii) Fluid communication between the inlet for carrier gas, the sample loop and the upstream end of the gas chromatography column via the second on-off valve outlet.
  12. 12. The gas chromatography system of claim 11, wherein the first switch valve has an outlet for a carrier gas fluidly connected to an inlet for a doping carrier gas via a flow path comprising a furnace comprising a permeate tube containing an active component, and wherein the inlet for a doping carrier gas is fluidly connected to the outlet for a doping carrier gas.
  13. 13. The gas chromatography system according to any one of claims 11 to 12, wherein the exhaust conduit is provided with a back pressure regulator.

Description

Detection of trace amounts of gas components in a gas sample The present invention relates to a method for detecting a reactive gas component in trace amounts as contained in a gas sample by using a gas chromatograph in fluid communication with a detector sensitive to the reactive gas component. The invention also relates to a gas chromatography system suitable for the method. Many analyses within gas chromatography can result in system losses due to reactive gas components, i.e., components of interest, reacting with or adsorbing onto active sites in the gas chromatography system. Adsorption or reactivity of the components of interest can lead to poor detection limits, reproducibility, linearity, and equimolar performance, especially at lower concentration levels. The level of adsorption of a component of interest will depend on the component itself, as well as the activity of the different surfaces that are in contact with the component during transport through the gas chromatography system. Common practice within gas chromatography is to treat these surfaces by using a coating such as Sulfinert to minimize such active surfaces. But even after these treatments the active surface may remain. The presence of such remaining active surfaces is particularly problematic when measuring low levels of active components, such as ammonia or hydrogen sulfide, in a hydrogen or propylene gas sample. The active surface may be passivated by multiple injections of a sample or calibration standard containing a certain amount of the component of interest. The problem with this method is that it takes time before the actual sample analysis can be performed. Further, it is sometimes still not determined whether and for how long all of the active surfaces have been passivated. This method is also not applicable when the concentration of the component of interest to be measured is extremely low. US 2012/013987 describes a chromatography method in which the active component is first measured in a first carrier gas, then the sample is measured using a different carrier gas flushing system, and then a different carrier gas. US5612489 describes a method of passivating active surfaces in a gas chromatography system by doping a carrier gas with a passivating component. The passivating component may be a component of interest. A problem with performing passivation by the component of interest is that it increases baseline noise and also creates problems when performing sample injection by valve switching. When measuring very low concentrations of the component of interest in the sample, peaks of the component of interest are found to be unquantifiable. This method is also difficult to implement when sample injection is performed using valve switching, so-called gas sampling valve injection (GSV-injection). It is an object of the present invention to provide a method for detecting trace amounts of reactive gas components as contained in a gas sample, which avoids the drawbacks of the prior art methods. This is achieved by the following method. A method for detecting a reactive gas component, such as a trace level contained in a gas sample, by using a gas chromatograph in fluid communication with a detector sensitive to said reactive gas component, wherein the following steps are performed in sequence, wherein: (i) Feeding a carrier gas doped with a certain amount of active gas component to a gas chromatograph for a certain doping time; (ii) Feeding a carrier gas not doped with an active gas component to a gas chromatograph for a purge time, and (Iii) Adding a gas sample to the carrier gas in step (ii) and feeding the resulting mixture to a mid-gas chromatograph. Applicants have found that with this method an improved signal to noise ratio can be achieved, enabling low levels of reactive gas components in the sample gas to be measured. Furthermore, the method has good linearity. Without wishing to be bound by the following theory, applicants believe that in step (i), the carrier gas doped with a certain amount of active gas component is first fed into the gas chromatograph and the active sites in the system will be chemically bonded. In addition, there will be some amount of unbound active gas component in the gas chromatograph system of which the gas chromatograph is a part. By performing step (ii), unbound active gas components are purged from the gas chromatography system while chemically bound active gas components on the active sites remain. By subsequently performing step (iii), the reactive gas species of the sample will not interact with the reactive surface due to the presence of chemically bonded reactive gas species on the reactive sites. In the present specification, the sequence of steps (i) to (ii) is referred to as batch carrier doping. As explained, the components of interest present in the sample gas will reach the detector largely unaffected by the adsorption loss, producing a normal positive peak. This peak will have