WO1990010217A1 - Method for measuring low levels of ammonia in process gas streams - Google Patents

Method for measuring low levels of ammonia in process gas streams Download PDF

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Publication number
WO1990010217A1
WO1990010217A1 PCT/US1990/000865 US9000865W WO9010217A1 WO 1990010217 A1 WO1990010217 A1 WO 1990010217A1 US 9000865 W US9000865 W US 9000865W WO 9010217 A1 WO9010217 A1 WO 9010217A1
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Prior art keywords
ammonia
gas stream
process gas
chromatographic column
hydrogen sulfide
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PCT/US1990/000865
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French (fr)
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James Joseph Karr
Roger Blaine Searle
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Atochem North America, Inc.
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Publication of WO1990010217A1 publication Critical patent/WO1990010217A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0054—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/281—Sorbents specially adapted for preparative, analytical or investigative chromatography
    • B01J20/282—Porous sorbents
    • B01J20/285—Porous sorbents based on polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3202—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the carrier, support or substrate used for impregnation or coating
    • B01J20/3204—Inorganic carriers, supports or substrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
    • B01J20/3242—Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
    • B01J20/3268—Macromolecular compounds
    • B01J20/3272—Polymers obtained by reactions otherwise than involving only carbon to carbon unsaturated bonds
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/62—Detectors specially adapted therefor
    • G01N30/64—Electrical detectors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • B01J2220/80—Aspects related to sorbents specially adapted for preparative, analytical or investigative chromatography
    • B01J2220/86—Sorbents applied to inner surfaces of columns or capillaries
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/62—Detectors specially adapted therefor
    • G01N30/64—Electrical detectors
    • G01N2030/642—Electrical detectors photoionisation detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/88—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86
    • G01N2030/8809—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86 analysis specially adapted for the sample
    • G01N2030/8859—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86 analysis specially adapted for the sample inorganic compounds
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/88—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86
    • G01N2030/8809—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86 analysis specially adapted for the sample
    • G01N2030/8872—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86 analysis specially adapted for the sample impurities
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/88—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86
    • G01N2030/8886—Analysis of industrial production processes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/04—Preparation or injection of sample to be analysed
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Definitions

  • the present invention relates to a method of separating and measuring the concentration of ammonia in a process gas stream.
  • Hydrogen sulfide process gas streams are found in oil refineries and other chemical manufacturing plants. Although these streams are predominantly hydrogen sulfide, other gases, such as oxygen, nitrogen, carbon dioxide, water, olefins, hydrocarbons, ammonia, mercaptans, sulfides and amines, may be present. It is particularly troublesome when the ammonia concentrations are above 500 parts per million (ppm) because a reaction occurs with carbon dioxide resulting in the.,formation of solid ammonium bicarbonate which accumulates and eventually clogs the process pipes. The ammonium bicarbonate formation generally occurs when the hydrogen sulfide gas stream temperature is lowered for i liquefaction purposes. It is therefore advantageous to measure the ammonia levels in the process gas streams so that the formation of ammonium bicarbonate, can be monitored .
  • gases such as oxygen, nitrogen, carbon dioxide, water, olefins, hydrocarbons, ammonia, mercaptans, sulfides and amines
  • the excited nitrogen dioxide almost instantaneously relaxes to the ground state resulting in a photoemission which is measured by an optical detector.
  • the output from the optical detector is proportional to the ammonia concentrations.
  • other nitrogen-containing compounds if present, they will also contribute to the formation of nitrogen dioxide, and an accurate measurement of the ammonia concentrations cannot be made. Since the hydrogen sulfide process streams often contain amines, accurate measurements of the ammonia levels cannot be made using this technique.
  • photoionization gas chromatography techniques have been shown to be useful in detecting low levels of ammonia in an inert carrier gas, there has been no suggestion to use these techniques for the online measurement of ammonia levels in process gas streams containing ammonia and carbon dioxide so that the formation of ammonium bicarbonate can be monitored.
  • the present invention provides for a method of separating and measuring the concentration of ammonia in a process gas stream comprising ammonia and carbon dioxide.
  • a sample of the process gas stream is first mixed with a carrier gas in a heated qhamber.
  • the mixture of the process gas stream and the carrier gas is then passed through a chromatographic column under conditions sufficient to separate it into its gaseous components.
  • Each of the gaseous components is discharged from the column within a predetermined time period after its introduction.
  • the separated gaseous components leaving the chromatographic column are then passed into a photoionization detector having an ultraviolet lamp capable of ionizing ammonia, whereby the current produced by the ammonia ions is proportional to the ammonia concentration in the process gas stream.
  • Figure 1 is a plan view illustrating a system for carrying out the process of the present invention.
  • Figure 2 is a graph of chromatogram peak height versus ammonia concentration for the Example.
  • FIG. 1 a typical hydrogen sulfide process gas stream found in a refinery or other chemical manufacturing plant.
  • This gas stream is generally identified as 10.
  • the gas stream 10 is predominantly hydrogen sulfide, it also contains ammonia and carbon dioxide which react to form solid ammonium bicarbonate.
  • the ammonium bicarbonate accumulates in the process pipes and can eventually damage the process equipment.
  • An exemplary process gas stream contains at least about 85% (vol.) hydrogen sulfide, about 5-10% (vol.) carbon dioxide and ppm levels of ammonia.
  • the hydrogen sulfide gas stream 10 may also trace amounts of elemental nitrogen, hydrocarbons, water, amines and other compounds.
  • the process of the present invention is illustrated with a hydrogen sulfide gas stream, it should be understood that it may be used with any gas stream where ammonium bicarbonate formation is a problem and ammonia detection is required.
  • a gas sample from the process stream 10 is removed via the conduit 12 and supplied to a sampling valve 14.
  • the conduit 12 may be internally coated with Teflon® to reduce adsorption losses.
  • the sampling valve 14 is computer controlled so that gas samples may be withdrawn from the process stream automatically at selected intervals.
  • the gas sample used in the present invention ranges between about 50 to about 1,000 microliters ( ⁇ l) and preferable about 200 ⁇ l.
  • An outlet conduit 16 is also connected to the sample valve 14 for returning portions of the withdrawn gas sample to the gas stream 10.
  • the gas sample valve 14 is attached to a gas chromatograph, such as Hewlett Packard GC Model 5890.
  • the gas sample from the sample valve 14 is then supplied via the conduit 20, within the gas chromatograph 18, to a mixing chamber 22.
  • a syringe injection port 24 is also coupled to the mixing chamber 22 so that the gas samples may be manually inserted into the chromatograph 18.
  • the mixing chamber 22 is also heated to a temperature between about 100 to about 225°C and preferably about 200°C.
  • An inert gas such as helium or nitrogen, is mixed with the gas sample in the mixing chamber 22.
  • the inert gas stored in a cylinder 26, having a pressure regulator 28, is supplied to the gas chromatograph 18 via the conduit 30.
  • Gas controls 32 are provided on the chromatograph 18 for regulating the carrier gas flow. The flow rate is adjusted so that the chromatograph column head pressure is between about 5 to about 30 psig (pounds per inch ⁇ gauge) and preferably about 18 psig.
  • the gas chromatograph 18 also contains a control panel 34 with a display 36.
  • the heated mixture of the carrier gas and the sample gas is introduced via the conduit 38 to the chromatographic column 40.
  • the chromatographic column 40 is a fused silica capillary having an inside diameter of about 0.53 mm. This capillary is also internally coated with about 5 to about 8 microns of 007 methyl silicone. Chromatographic columns of this type are available from Quadrex Corporation, New Haven, Connecticut. In order to adequately separate the gaseous mixture into its component parts, the column length is between about 50 to about 200 meters and preferably about 125 meters.
  • the chromatographic column 40 is housed within a chromatographic oven 42 maintained at a temperature between about 40 to about 100°C and preferably about 40°C. Within the column 40, the gaseous mixture is separated into its component parts and sequentially discharged from the chromatograph 18 via the conduit 44.
  • the separated components are then supplied to a photoionization detector 46 which is used to measure the concentration of ammonia.
  • the photoionization detector such as model 4430 from Owens-Illinois, Austin, Texas, is equipped with an ultraviolet lamp having an emission of between about 10 to about 11 electron volts (eV) .
  • the photoionization detector is also heated and maintained at a temperature between about ambient to about 250°C and preferably about 150°C
  • the separated gaseous components are then passed in front of the UV lamp and ionized if they have an ionization potential equal to or less than the lamp voltage. Since ammonia has an ionization potential of about 10.15 eV, it is ionized by the UV light and accelerated by a polarizing voltage onto a collector.
  • the collector produces a current that is proportional to the concentration of ammonia in the process gas stream 10.
  • other gaseous components such as many hydrocarbons like ethane, have ionization potentials well above the UV lamp voltage and they do not contribute to the current signal.
  • the current flow measured by an electrometer is then supplied via the cable 50 to a computing integrator/strip chart recorder 52, such as Hewlett Packard model no.
  • the concentrations of each of the ionized species can be determined from a calibration curve.
  • the calibration curve is established from known concentrations of ammonia in hydrogen sulfide.
  • the time period during which the individual gaseous component enter the photoionization detector 46 can be determined after several trial runs. Based on this information, the photoionization detector 46 can be programmed so that certain components, such as the major component hydrogen sulfide, may bypass the ionization chamber and be vented from the detector 46 via outlet 48. This is particularly useful for preventing the photoionization detector 46 from being saturated from the major component of the gaseous mixture whose concentration need not be measured.
  • the concentration of ammonia in the hydrogen sulfide process gas stream can be monitored to determine when ammonia levels reach the point where ammonium bicarbonate formation is possible. Then, corrective measures may be taken to avoid damage to the process equipment.
  • Example Known concentrations of ammonia in hydrogen sulfide were manually injected into the equipment illustrated in Figure 1.
  • the sample sizes varied between 50 ⁇ l to 200 ⁇ l.
  • Each injected sample was then mixed with helium in a mixing chamber maintained at 200°C.
  • the helium gas flow was controlled so that the chromatograph column pressure was 18 psig.
  • a 125 meter fused silica capillary having an inside diameter of 0.53 mm and internally coated with 007 methyl silicone was used as the column.
  • the chromatograph oven containing the column was maintained at 40°C.
  • the eluted components were then passed to the photoionization detector (10.0 eV lamp) maintained at 150°C.
  • the peak height of the eluted ammonia was obtained from the chromatogram and plotted against the known concentration as shown in Figure 2.
  • the graph shown in Figure 2 can be used as a calibration curve for measuring ammonia levels in a hydrogen sulfide process gas stream.

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Abstract

Ammonia levels in a process gas stream (10) containing carbon dioxide and ammonia are separated and measured with a gas chromatograph (18) containing a photoionization detector (46). The ammonia levels in the process stream are monitored so that the formation of ammonium bicarbonate within the process pipes can be detected.

Description

Method For Measuring Low Levels of Ammonia in Process Gas Streams
Background of the Invention The present invention relates to a method of separating and measuring the concentration of ammonia in a process gas stream.
Hydrogen sulfide process gas streams are found in oil refineries and other chemical manufacturing plants. Although these streams are predominantly hydrogen sulfide, other gases, such as oxygen, nitrogen, carbon dioxide, water, olefins, hydrocarbons, ammonia, mercaptans, sulfides and amines, may be present. It is particularly troublesome when the ammonia concentrations are above 500 parts per million (ppm) because a reaction occurs with carbon dioxide resulting in the.,formation of solid ammonium bicarbonate which accumulates and eventually clogs the process pipes. The ammonium bicarbonate formation generally occurs when the hydrogen sulfide gas stream temperature is lowered for i liquefaction purposes. It is therefore advantageous to measure the ammonia levels in the process gas streams so that the formation of ammonium bicarbonate, can be monitored .
Wet chemical methods are available for measuring ammonia levels, but these techniques require large gas samples, i.e. 500 cn , which are sparged through an absorbing reagent. The reagents are then treated to adjust pH or develop a color which can be measured by a pH meter or colorimeter, respectively, to determine the ammonia concentrations. Unfortunately, the need for sparging and the use of liquid reagents make this technique unsuitable for automated online measurements. Ammonia levels can also be measured using chemiluminescent detection techniques, such as those described in U.S. Patents 4,018,562 and 4,351,801. These techniques involve the combustion of a sample containing ammonia in an oxygen atmosphere whereby metastable nitrogen dioxide is formed. The excited nitrogen dioxide almost instantaneously relaxes to the ground state resulting in a photoemission which is measured by an optical detector. The output from the optical detector is proportional to the ammonia concentrations. However, if other nitrogen-containing compounds are present, they will also contribute to the formation of nitrogen dioxide, and an accurate measurement of the ammonia concentrations cannot be made. Since the hydrogen sulfide process streams often contain amines, accurate measurements of the ammonia levels cannot be made using this technique.
In an article entitled, "Applications of a Photoionization Detector in Gas Chromotography, " American Laboratory. 8(10), pp. 71-75 (1976), J. N. Driscoll suggests that ammonia at parts per billion levels in an inert carrier gas can be detected with a photoionization detector. The article also reports that the detection limit for ammonia using an experimental photoionization gas chromatography detector was 200 picograms.
Although photoionization gas chromatography techniques have been shown to be useful in detecting low levels of ammonia in an inert carrier gas, there has been no suggestion to use these techniques for the online measurement of ammonia levels in process gas streams containing ammonia and carbon dioxide so that the formation of ammonium bicarbonate can be monitored.
Summary of the Invention The present invention provides for a method of separating and measuring the concentration of ammonia in a process gas stream comprising ammonia and carbon dioxide. A sample of the process gas stream is first mixed with a carrier gas in a heated qhamber. The mixture of the process gas stream and the carrier gas is then passed through a chromatographic column under conditions sufficient to separate it into its gaseous components. Each of the gaseous components is discharged from the column within a predetermined time period after its introduction. The separated gaseous components leaving the chromatographic column are then passed into a photoionization detector having an ultraviolet lamp capable of ionizing ammonia, whereby the current produced by the ammonia ions is proportional to the ammonia concentration in the process gas stream.
Brief Description of the Drawing Figure 1 is a plan view illustrating a system for carrying out the process of the present invention. Figure 2 is a graph of chromatogram peak height versus ammonia concentration for the Example.
Detailed Description of the Preferred Embodiments Turning now to Figure 1, the process of the present invention will be described using a typical hydrogen sulfide process gas stream found in a refinery or other chemical manufacturing plant. This gas stream is generally identified as 10. Although the gas stream 10 is predominantly hydrogen sulfide, it also contains ammonia and carbon dioxide which react to form solid ammonium bicarbonate. The ammonium bicarbonate accumulates in the process pipes and can eventually damage the process equipment. An exemplary process gas stream contains at least about 85% (vol.) hydrogen sulfide, about 5-10% (vol.) carbon dioxide and ppm levels of ammonia. The hydrogen sulfide gas stream 10 may also trace amounts of elemental nitrogen, hydrocarbons, water, amines and other compounds. Although the process of the present invention is illustrated with a hydrogen sulfide gas stream, it should be understood that it may be used with any gas stream where ammonium bicarbonate formation is a problem and ammonia detection is required.
A gas sample from the process stream 10 is removed via the conduit 12 and supplied to a sampling valve 14. The conduit 12 may be internally coated with Teflon® to reduce adsorption losses. The sampling valve 14 is computer controlled so that gas samples may be withdrawn from the process stream automatically at selected intervals. The gas sample used in the present invention ranges between about 50 to about 1,000 microliters (μl) and preferable about 200 μl. An outlet conduit 16 is also connected to the sample valve 14 for returning portions of the withdrawn gas sample to the gas stream 10. The gas sample valve 14 is attached to a gas chromatograph, such as Hewlett Packard GC Model 5890. The gas sample from the sample valve 14 is then supplied via the conduit 20, within the gas chromatograph 18, to a mixing chamber 22. A syringe injection port 24 is also coupled to the mixing chamber 22 so that the gas samples may be manually inserted into the chromatograph 18. The mixing chamber 22 is also heated to a temperature between about 100 to about 225°C and preferably about 200°C. An inert gas, such as helium or nitrogen, is mixed with the gas sample in the mixing chamber 22. The inert gas stored in a cylinder 26, having a pressure regulator 28, is supplied to the gas chromatograph 18 via the conduit 30. Gas controls 32 are provided on the chromatograph 18 for regulating the carrier gas flow. The flow rate is adjusted so that the chromatograph column head pressure is between about 5 to about 30 psig (pounds per inch^ gauge) and preferably about 18 psig. The gas chromatograph 18 also contains a control panel 34 with a display 36.
The heated mixture of the carrier gas and the sample gas is introduced via the conduit 38 to the chromatographic column 40. The chromatographic column 40 is a fused silica capillary having an inside diameter of about 0.53 mm. This capillary is also internally coated with about 5 to about 8 microns of 007 methyl silicone. Chromatographic columns of this type are available from Quadrex Corporation, New Haven, Connecticut. In order to adequately separate the gaseous mixture into its component parts, the column length is between about 50 to about 200 meters and preferably about 125 meters. The chromatographic column 40 is housed within a chromatographic oven 42 maintained at a temperature between about 40 to about 100°C and preferably about 40°C. Within the column 40, the gaseous mixture is separated into its component parts and sequentially discharged from the chromatograph 18 via the conduit 44.
The separated components are then supplied to a photoionization detector 46 which is used to measure the concentration of ammonia. The photoionization detector, such as model 4430 from Owens-Illinois, Austin, Texas, is equipped with an ultraviolet lamp having an emission of between about 10 to about 11 electron volts (eV) . The photoionization detector is also heated and maintained at a temperature between about ambient to about 250°C and preferably about 150°C The separated gaseous components are then passed in front of the UV lamp and ionized if they have an ionization potential equal to or less than the lamp voltage. Since ammonia has an ionization potential of about 10.15 eV, it is ionized by the UV light and accelerated by a polarizing voltage onto a collector. The collector produces a current that is proportional to the concentration of ammonia in the process gas stream 10. However, other gaseous components, such as many hydrocarbons like ethane, have ionization potentials well above the UV lamp voltage and they do not contribute to the current signal.
The current flow measured by an electrometer is then supplied via the cable 50 to a computing integrator/strip chart recorder 52, such as Hewlett Packard model no.
3396A, which produces a chromatogram 54 of the gaseous components which have been ionized. Based on the peak height of the curves on the chromatogram, the concentrations of each of the ionized species can be determined from a calibration curve. In the present invention, the calibration curve is established from known concentrations of ammonia in hydrogen sulfide.
The time period during which the individual gaseous component enter the photoionization detector 46 can be determined after several trial runs. Based on this information, the photoionization detector 46 can be programmed so that certain components, such as the major component hydrogen sulfide, may bypass the ionization chamber and be vented from the detector 46 via outlet 48. This is particularly useful for preventing the photoionization detector 46 from being saturated from the major component of the gaseous mixture whose concentration need not be measured.
Based on the information contained on the chromatogram 54, the concentration of ammonia in the hydrogen sulfide process gas stream can be monitored to determine when ammonia levels reach the point where ammonium bicarbonate formation is possible. Then, corrective measures may be taken to avoid damage to the process equipment.
The following Example is presented to further illustrate the present invention and is not intended to be a limitation thereof.
Example Known concentrations of ammonia in hydrogen sulfide were manually injected into the equipment illustrated in Figure 1. The sample sizes varied between 50μl to 200μl. Each injected sample was then mixed with helium in a mixing chamber maintained at 200°C. The helium gas flow was controlled so that the chromatograph column pressure was 18 psig. A 125 meter fused silica capillary having an inside diameter of 0.53 mm and internally coated with 007 methyl silicone was used as the column. The chromatograph oven containing the column was maintained at 40°C. The eluted components were then passed to the photoionization detector (10.0 eV lamp) maintained at 150°C. The peak height of the eluted ammonia was obtained from the chromatogram and plotted against the known concentration as shown in Figure 2.
The graph shown in Figure 2 can be used as a calibration curve for measuring ammonia levels in a hydrogen sulfide process gas stream.
Various changes and modifications can be made to the above-described embodiments without departing from the spirit and scope of the present invention.

Claims

We claim:
1. A method of separating and measuring the concentration of ammonia in a process gas stream comprising ammonia and carbon dioxide, said method comprising the steps: mixing a sample of the process gas stream with a carrier gas in a heated chamber; passing the mixture of the process gas stream and the carrier gas through a chromatographic column under conditions sufficient to separate the mixture into its gaseous components, each of said gaseous components being discharged from said column within a predetermined time period after introduction of the mixture into said column; and passing the separated gaseous components into a photoionization detector having a UV lamp capable of ionizing ammonia, whereby the current produced by the ammonia ions is proportional to the ammonia concentration in said process stream.
2. A method according to claim 1 wherein said process gas stream further comprises hydrogen sulfide as the major component.
3. A method according to claim 2 wherein said process
S gas stream comprises at least about 85% by volume hydrogen sulfide.
4. -method according to claim 2 wherein said UV lamp has a predominant emission of between about 10 to about 11 eV.
5. A method according to claim 4 wherein said chromatographic column comprises a capillary internally coated with methyl silicone.
6. A method according to claim 5 wherein said capillary is fused silica having an internal diameter of about 0.53 millimeter and a length of at least about 50 meters.
7. A method according to claim 6 wherein said capillary has a length of between about 50 and about 200 meters.
8. A method according to claim 6 wherein the methyl silicone coating has a thickness between about 5 to about 8 microns.
9. A method according to claim 8 wherein the chromatographic column head pressure is between about 5 to about 30 psig.
10. A method according to claim 5 wherein said heated chamber is maintained at a temperature between about 100 to about 225°C, said chromatographic column is maintained at a temperature between about 40 to about 100°C and the photoionization detector is maintained at a temperature between about room temperature to about 250°C.
11. A method according to claim 2 wherein said carrier gas is selected from the group consisting of helium and nitrogen.
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PCT/US1990/000865 1989-02-22 1990-02-14 Method for measuring low levels of ammonia in process gas streams WO1990010217A1 (en)

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Cited By (3)

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WO1994012860A2 (en) * 1992-12-03 1994-06-09 Photovac Incorporated System for the detection of noxious contaminants in beverage and potable water containers
CN104807964A (en) * 2015-04-24 2015-07-29 西安热工研究院有限公司 On-line detection device and method for gas-liquid transfer method escaping ammonia
CN109444348A (en) * 2018-12-24 2019-03-08 海宁市英德赛电子有限公司 A kind of high-purity ammon products detection system and its detection method

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994012860A2 (en) * 1992-12-03 1994-06-09 Photovac Incorporated System for the detection of noxious contaminants in beverage and potable water containers
WO1994012860A3 (en) * 1992-12-03 1994-08-04 Photovac Inc System for the detection of noxious contaminants in beverage and potable water containers
CN104807964A (en) * 2015-04-24 2015-07-29 西安热工研究院有限公司 On-line detection device and method for gas-liquid transfer method escaping ammonia
CN109444348A (en) * 2018-12-24 2019-03-08 海宁市英德赛电子有限公司 A kind of high-purity ammon products detection system and its detection method

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