Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
  • G01N31/12—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using combustion
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
  • G01N31/005—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods investigating the presence of an element by oxidation

Definitions

• the present invention relates to a system for measuring nitrogen content. More particularly, the present invention provides an analytical method and apparatus for measuring nitrogen content in aqueous samples such as waste water.
• Total Combined Nitrogen Content means the amount of nitrogen existing with other chemical elements in certain organic and inorganic compounds.
• Total Kjeldahl Nitrogen means the amount of nitrogen existing in certain organic compounds and in ammonia and ammonium compounds.
• Nitrite Nitrogen means nitrogen existing in inorganic compounds containing the nitrite (NO 2 ⁇ ) ion.
• Nitrate Nitrogen means nitrogen existing in inorganic compounds containing the nitrate (NO 3 ⁇ ) ion.
• Combined Nitrate-Nitrite Nitrogen Content is the amount of nitrogen existing in a mixture of nitrites and nitrates without distinguishing from the parent species.
• NO x means gaseous oxides of nitrogen. Quantitatively determining the amount of nitrogen in a mixture is among the most important of analytical measurements. In waste water treatment -X
• a commonly known procedure for analysis of organically-bound nitrogen is the Kjeldahl method.
• the sample is heated in concentrated sulfuric acid containing a catalyst. This procedure converts the nitrogen to ammonia.
• ammonia is distilled into a dilute boric acid solution, which is then titrated with acid.
• chemiluminescent detection equipment for detecting organically-bound nitrogen has been developed. These chemiluminescent detectors are based on the reaction of nitric oxide with ozone to form metastable or excited nitrogen dioxide (NO 2 *). Almost instantaneously, the excited nitrogen dioxide relaxes to its ground state with a resulting photo-emission ( ⁇ ) ,as represented by the following reactions:
• the chemiluminescent nitrogen detectors are commonly known as NO/NO x detectors and are used to detect ambient NO and NO x concentrations in the air. Such NO/NO x concentration detectors are presently made by several companies, but they are limited in that they are able to detect nitrogen only as NO/NO x gases in gaseous samples. Alone, they cannot be utilized with liquid or solid organic compound samples.
• a chemiluminescent nitrogen detection apparatus and method for samples in a phase other than gas has been disclosed in U.S. Patent 4,018,562 issued to Parks et al. Parks et al.
• a system including an inert gas, such as helium or argon, a source of oxygen, a furnace or other pyrolyzing means connected to receive the carrier gas (helium or argon), the oxygen and a sample containing nitrogen.
• the furnace pyrolyses the sample to convert the sample to oxides of nitrogen.
• the product gases from the furnace are then provided to a dryer.
• a reaction chamber of a chemiluminescent detector is connected to an output of the dryer.
• An ozone generator is connected to the reaction chamber and generates ozone from oxygen received from the oxygen source. The reaction chamber receives the gases from the dryer and the ozone from the ozone generator.
• the present invention provides an apparatus and method for determining Total Combined Nitrogen Content and/or Combined Nitrate-Nitrite Nitrogen Content in a liquid system.
• the apparatus comprises an oxidation tube, a nitrate-nitrite reaction chamber, a dryer and a detection apparatus.
• the oxidation tube having an oxidation catalyst receives a carrier gas including oxygen and a sample from the liquid system.
• the oxidation tube converts the liquid sample to a product gas that includes nitrogen dioxide and nitric oxide.
• the nitrogen dioxide is then converted to nitric oxide in the reaction chamber.
• the reaction chamber includes a liquid chemical reduction agent, preferably vanadium and sulfuric acid.
• the nitric oxide is provided to the dryer where the nitric oxide is dried sufficiently for the detection apparatus, such as a chemiluminescent detector.
• the present system can be used to determine the Combined Nitrate-Nitrite Nitrogen Content in the liquid system.
• a second liquid sample is injected into the reaction chamber and converted to a second portion of nitric oxide.
• the nitric oxide is again provided to the dryer for drying.
• the second portion of nitric oxide is received and then measured by the detection apparatus to determine the Combined Nitrate-Nitrite Nitrogen Content.
• Figure 1 is a mechanical schematic drawing of a nitrogen analyzer according to the present invention.
• Figure 2 is a partial sectional view of an oxidation tube
• Figure 3 is a partial sectional view of a nitrate-nitrite reaction chamber
• Figures 4A and 4B are side elevational views of the reaction chamber in operation.
• a nitrogen measuring system is indicated generally at 10 in Figure 1.
• the system 10 includes a catalytic oxidation (combustion) tube 12, a nitrate- nitrite ("N-N") reaction chamber 14, drying means indicated generally at 16, and a detector 18, such as a conventional gas chromatograph or a NO/NO x chemiluminescent detection apparatus herein depicted.
• the system 10 quantitatively determines the Total Combined Nitrogen Content and the Combined Nitrate Nitrite Nitrogen Content in an aqueous system from different samples. From these determinations, the Total Kjeldahl Nitrogen can be calculated as the difference between Total Combined Nitrogen Content and Combined Nitrate-Nitrite Nitrogen Content.
• the catalytic oxidation tube 12 is illustrated in detail in Figure 2.
• the catalytic oxidation tube has a first inlet 22 connected to an oxygen source 20 to supply metered oxygen.
• oxygen is used throughout the measuring system 10 as the carrier gas. Therefore, it should be understood that applicable components of the system 10 are made from material suitable for carrying oxygen as well as NO x to be described below.
• an aqueous sample containing nitrogen is injected into the catalytic oxidation tube 12 with a microsyringe 13 through a second inlet 24 to pyrolyze the sample in an oxygen atmosphere to form oxides of nitrogen, mostly nitric oxide.
• oxides of nitrogen mostly nitric oxide.
• approximately 5-10% by volume of the product gas is typically nitrogen dioxide.
• the catalytic oxidation tube 12 is made from quartz and has an upper expansion zone 26 to minimize the pressure increase due to evaporation of water and to keep the evaporated sample in the oxidation tube 12. At a lower end 28 of the oxidation tube 12, the tube 12 is narrowed or reduced at a narrowing point 30.
• a platinum catalyst 32 is packed in the large cross-sectional area of upper expansion zone 26 above the narrowing point 30 to maximize the contact area between the sample and the catalyst surfaces, and thus, minimize localized cooling, while in the small cross-sectional area of lower end 28, the platinum catalyst is packed in order to enhance oxidation.
• the catalytic oxidation tube 12 has a wall thickness of 1.5 millimeters ("mm") and is approximately 260 mm in length with the upper expansion zone approximately 110 mm in length and the narrowed cross-sectional area approximately 150 mm in length.
• the outside diameter at the upper end of the catalytic oxidation tube is approximately 22 mm, while the outside diameter near an outlet end 34 of the narrowed cross-sectional area 28 is approximately 11 mm.
• oxygen is supplied from the oxygen source 20 to the catalytic oxidation tube 12 at a flow rate of approximately 200 milliliters per minute with the tube heated to approximately 850°C. All nitrogen compounds are quickly oxidized in the catalytic oxidation tube to NO/NO 2 according to the following equation:
• the ratio of NO and NO 2 is determined by the type of nitrogen species, oxygens partial pressure, and effective temperature. In the embodiment illustrated, a 40 micro liter sample is used.
• the product gas, water vapor and carrier gas are discharged from the catalytic oxidation tube 12 through the outlet 34 and carried by a suitable line 36 to a condenser 38.
• the condenser 38 removes a substantial amount of water vapor from the product gas discharged from the catalytic oxidation 12.
• NO 2 is soluble in water
• nitric acid (HNO 3 ) formed in the condenser 38 is also provided to the reaction chamber 14 for conversion to NO.
• the N-N reaction chamber 14 is shown in detail in Figure 3.
• the N-N reaction chamber 14 comprises a glass vessel 40 partially filled with an aqueous reagent 41 containing vanadium (III) and sulfuric acid (H 2 SO 4 ) ( Figures 4A and 4B).
• the reagent may comprise 0.1% to 5% vanadium-chloride by volume in water, while the sulfuric acid may comprise 5% to 60% by volume in water.
• the reagent 41 comprises two percent vanadium-chloride and twenty percent sulfuric acid by volume in water.
• the N-N reaction chamber 14 includes a first inlet 42 for the reagent and the product output from the catalytic oxidation tube 12.
• the aqueous reagent 41 is maintained between 60°C and 90°C, preferably at 80°C, while a flow of oxygen from the catalytic combustion tube 12 continuously sparges the reaction chamber 14.
• the N-N reaction chamber 14 includes a second inlet 44 for injection of a second sample into the N-N reaction chamber with a microsyringe 43. The second sample is used to determine Combined Nitrate-Nitrite Nitrogen Content.
• the N-N reaction chamber 14 has an inner sleeve 46, spaced apart and generally shaped to conform to a lower portion 48 of the N-N reaction chamber 14.
• the inner sleeve 46 is partially submerged in the reagent 41 ( Figure 4 A) with the submerged portion having holes 50 to allow gas and reagent 41 to pass therethrough.
• the inner sleeve 46 is sealed annularly to an inner wall 52 of the N-N reaction chamber below the reagent and carrier gas inlet 42, whereas the inner sleeve is sealed to the N-N reaction chamber wall above an outlet 54. Since the inner sleeve 46 is sealed annularly to the inner wall 52, the oxygen carrier gas and product output from the condenser 38 flows through the N-N reaction chamber 14 by passing through the holes 50 in the inner sleeve 46.
• the N-N reaction chamber 14 is made of Pyrex and is concentric having an outside diameter approximately 25 mm, while the inner sleeve 46 is positioned within the N-N reaction chamber 14 and has an outside diameter of approximately 15 mm.
• the N-N reaction chamber 14 has sufficient cross-sectional area such that when the sample is injected into the reagent from the microsyringe 43, the second sample falls into the reagent 41 without contacting the sides of inner sleeve 46.
• quick reaction with the reagent 41 is provided by minimizing the reagent volume, which is approximately 6 milliliters.
• the N-N reaction chamber 14 is mounted in a heated aluminum block 51. When operated to determine Combined Nitrite-Nitrate Nitrogen Content, the aqueous nitrogen containing sample is injected into inlet 44 with the microsyringe 43 to fall to the reagent solution 41, as illustrated in Figure 4A.
• the outlet port 54 from the N-N reaction chamber 14 is connected to the drying means 16 comprising a condenser 60, a gas/liquid separator 62 and a dryer 64.
• the NO and the oxygen carrier gas flows from the outlet 54 of the N-N reaction chamber 14 to the condenser 60.
• the condenser 60 condenses liquid present in the NO and oxygen carrier gas from the N-N reaction chamber 14.
• a suitable fan 63 can be provided to aid in condensation of water vapor from the NO and oxygen carrier gas.
• the condenser 60 is further connected to the gas/liquid separator 62.
• the gas/liquid separator 62 separates the liquid condensed by condenser 60.
• a drain outlet 65 of the gas/liquid separator 62 is provided to discharge continuously the separated liquid.
• An outlet 66 from the gas/liquid separator 62 is connected to the dryer 64.
• the dryer 64 is a permeation dryer having an inlet 70 connected to an oxygen supply 72 and a ventilation port 74. Since the dryer 64 principally functions to remove water vapor from, the oxygen carrier gas and NO flowing from the liquid/gas separator 62, a second condenser 76 similar to condenser 60, can be coupled between the liquid/gas separator 62 and the dryer 64 to insure liquid water does not enter the dryer 64.
• An outlet 78 of the dryer 64 is connected through suitable tubing 80 as one input to a reaction chamber 82 of the chemiluminescent detector apparatus 18.
• the drying means 16 functions to receive a nitric oxide and oxygen mixture, dries the mixture by removal of water vapor, and lowers the dew point of the carried gases below a predetermined temperature level, a level that has been determined should not exceed the operating temperature of the reaction chamber 82.
• Oxygen from the oxygen source 72 is also supplied through tubing 86 to an ozone generator 88.
• the ozone generator 88 generates a supply of ozone which is applied through tubing 90 as a second input to the reaction chamber 82.
• the mixing of NO with ozone causes a reaction that forms metastable or excited nitrogen dioxide (NO 2 * ). Almost instantaneously, the excited nitrogen dioxide relaxes to its ground state with a resulting photo-emission ( ⁇ ), the following reactions occurring:
• the detector module 18 detects the light emission ( ⁇ ) which is proportional to the amount of NO, which in turn is proportional to the nitrogen content of the sample. Depending on whether the aqueous sample was injected into the system at the oxidation tube 12 or at the N-N reaction chamber, the amount of NO detected will be proportional to the Combined Total Nitrogen Content or the Combined Nitrate-Nitrite Nitrogen Content, respectively.
• An ozone scrubber 94 is connected to the reaction chamber and removes any remaining ozone upon completion of the reaction before venting the nitrogen dioxide through an outlet 96.
• the various modules and units identified in the schematic block diagram can conveniently be comprised of the following commercially available equipment:
• Dryer 64 Model MD-250-24
• the gas/liquid separator 62 is of conventional design.
• the gas/liquid separator 62 can be similar in shape to the gas/liquid separator (P/N 512-100) available from Rosemount Analytical Inc., Dohrmann Division, Santa Clara, CA.
• the distance 67 between the drain 65 and the lower level of the liquid must be sufficient to accommodate the operating pressure of the present system.
• the nitrogen detection system 10 illustrated in Figure 1 operates with positive pressure from the oxygen source 20 to carry the product gases throughout the system.
• a vacuum pump 98 can be connected to the system to increase sensitivity by driving the product gases through the system.
• the present invention provides a convenient and versatile system for measuring Total Combined Nitrogen Content and Combined Nitrate-Nitrite Nitrogen Content in an aqueous sample.
• the Total Combined Nitrogen Content and Combined Nitrate-Nitrite Nitrogen Content in an aqueous sample.
• Nitrogen Content is measured by pyrolyzing the sample in a catalytic oxidation tube, the output of which is connected to an N-N reaction chamber.
• the N-N reaction chamber converts NO 2 to NO with a liquid chemical reduction agent comprising vanadium and sulfuric acid that is then mixed in a reaction chamber with ozone to form metastable nitrogen dioxide, which then relaxes to its ground state with a resulting photo-emission is measured by a detector such as a chemiluminescent detector.
• the chemiluminescent detector provides a signal proportional to the Total Combined Nitrogen content contained in the aqueous sample.
• the present invention can be used to determine the combined Nitrate-Nitrate Nitrogen Content in the aqueous sample by injecting a second sample directly into the N-N reaction chamber containing the same liquid chemical reduction agent, the resulting NO produced being carried to and measured by the detector, as previously described. From these determinations, the Total Kjeldahl Nitrogen can be calculated as the difference between the Total Combined Nitrogen Content and the Combined Nitrate-Nitrite Nitrogen Content.

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• 1993
  • 1993-09-13 EP EP93921515A patent/EP0660927A1/de not_active Withdrawn
  • 1993-09-13 WO PCT/US1993/008593 patent/WO1994007134A1/en not_active Application Discontinuation
  • 1993-09-13 JP JP6508216A patent/JPH08501393A/ja active Pending

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