Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means
  • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
  • G01N25/22—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures
  • G01N25/28—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly
  • G01N25/30—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly using electric temperature-responsive elements
• • 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
  • G01N33/004—CO or CO2
• • 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 generally to gas sensors and, more particularly, to carbon monoxide sensors.
• Carbon monoxide sensors are used in a wide variety of applications, including the monitoring of heating installations that employ fossil fuels as an energy source and the monitoring of exhaust fumes from internal combustion engines. Two additional applications involve self-cleaning ovens and fuel cells.
• self-cleaning ovens include a cleaning cycle that removes carbonaceous residues through a high-temperature burning at a high-power capacity for a fixed amount of time. Because the high-temperature burning consumes a relatively large quantity of energy, there is a need for efficient self-cleaning cycles that automatically shut off the oven as soon as the burning process is complete. One way to accomplish this would be to monitor the carbon monoxide evolution during the heating cycle. Specifically, it is known that a typical dirty oven, when being cleaned at temperatures exceeding 800°F, will begin to emit carbon monoxide at a temperature of about 550°F. The amount of carbon monoxide being emitted will peak at around 800°F at a value of about 1500 ppm.
• carbon monoxide sensors include infrared adsorption sensors and thin film metal oxide technology, such as tin oxide sensors.
• the infrared adsorption sensors are inappropriate for the household oven market due to their high cost and low sensitivity.
• the thin film metal oxide sensors are also inappropriate for use in monitoring self-cleaning oven cycles because they generally don't work well in a humid environment. Further, metal oxide sensors take a long time to regenerate.
• Fuel cells are known devices that convert chemical energy of a fuel to electrical energy.
• Each fuel cell includes a pair of electrodes arranged across an electrolyte. The surface of one electrode is exposed to hydrogen or a hydrogen-containing gaseous fuel and the surface of the other electrode is exposed to an oxygen-containing oxidizing gas. Electrical energy is produced at the electrodes through electrochemical reactions.
• an adsorbent is used on the surface of the anode that is exposed to hydrogen or the hydrogen-containing gaseous fuel.
• One known problem associated with fuel cells is the poisoning of this adsorbent by the adsorption of carbon monoxide.
• One embodiment of the present invention satisfies the aforenoted need by providing a carbon monoxide sensor that includes a sensing element, a temperature sensor for measuring the temperature of the sensing element and a signal processing module coupled to the temperature sensor.
• the sensing element includes an adsorbent dispersed over a support material.
• the adsorbent is capable of exothermically adsorbing carbon monoxide.
• the senor also includes a heating element. Specifically, the heating element heats the sensing element to a temperature that is at least as high as the desorption temperature of the adsorbed carbon monoxide, resulting in a desorption of the adsorbed carbon monoxide and a regeneration of the adsorbent.
• the preferred adsorbents are monovalent silver (Ag + ), monovalent copper (Cu + ) and mixtures thereof.
• the support material may be zeolite, alumina, silica gel, carbonaceous materials or mixtures thereof.
• the sensor may include a permeable membrane support substrate disposed on a front side of the sensing element or upstream of the heating element, temperature sensor and heating element.
• the sensor may include a protective membrane disposed behind the sensing element, temperature sensor and heating element.
• a reference element includes a non-adsorbing material that does not adsorb carbon monoxide.
• a second temperature sensor is in contact with the reference element. This second temperature sensor is coupled to the processing module and sends signals indicative of the temperature of the reference element to the processing module.
• a heating element may also be provided for the reference element, or a single heating element may be employed for both the sensing element and reference element.
• the present invention also provides a method of detecting a presence of carbon monoxide in a gas.
• the method includes exposing a sensing element to a gas that may or may not include carbon monoxide.
• the sensing element includes an adsorbent dispersed over a layer of a support material.
• the adsorbent is capable of exothermally adsorbing carbon monoxide.
• the method also includes adsorbing at least a portion of the carbon monoxide in the gas onto the adsorbent, thereby resulting in an increase in the temperature of the sensing element due to the exothermal adsorption.
• An increase in the temperature of the sensing element can be used as an indication of a presence of carbon monoxide in the gas being tested.
• FIG. 1 is a schematic cross-sectional view of an exemplary carbon monoxide sensor of one embodiment of the present invention.
• FIG. 1 illustrates schematically one embodiment of a carbon monoxide sensor 10 made in accordance with the present invention and coupled to a processing module 12.
• the carbon monoxide sensor 10 includes a protective membrane cover 14 and a permeable membrane 16, which faces the air flow indicated generally by the arrows 18.
• a carbon monoxide adsorbing layer 20 is disposed between the protective membrane 14 and a temperature probe or sensor 22.
• the carbon monoxide adsorbing layer 20 comprises an adsorbent dispersed over a support material.
• a preferred adsorbent is monovalent copper compounds due to their low cost.
• silver compounds and mixtures of monovalent copper and monovalent silver compounds can also serve as useful adsorbents in the carbon monoxide sensor of the present invention.
• Suitable support materials include high surface area materials such as zeolites, alumina, silica gel, carbonaceous materials, and others.
• the supported Cu + and/or Ag + are selective for carbon monoxide in the presence of oxygen, carbon dioxide, methane, nitrogen and other chemical species.
• a NaY-supported CuCI at a loading of 0.554 g CuCI/g NaY will adsorb one millimole of carbon monoxide per gram of adsorber at a concentration of about 100 ppm.
• the heat of adsorption has been measured to be -48.8 kJ/mole of CO.
• Good selectivity is observed for carbon monoxide over carbon dioxide, oxygen, methane and nitrogen.
• a highly dispersed Cu + can adsorb carbon monoxide and provide a temperature rise of 0.1 °C assuming an adsorption time of five seconds. This temperature rise can be used for the sensing of carbon monoxide.
• a heating element 24 is provided. As shown in FIG. 1 , the temperature sensor 22 and heating element 24 are coupled to the processing module 12.
• the temperature sensor 22 and the heating element 24 are preferably provided in the form of a microbridge structure due to their small size, low cost and high reliability. The details of the microbridge structures will not be repeated here as they are well known to those skilled in the art (see, e.g., U.S. Pat. Nos. 4,478,077; 4,501 ,144; 4,624,137; 4,651,564; 4,683,159; and 4,696,188).
• a reference element 26 can be provided.
• the reference element 26 comprises non-carbon monoxide adsorbing material.
• a second temperature sensor or reference temperature sensor 28 detects the temperature of the reference element 26.
• the reference temperature sensor 28 is also in communication with the processing module 12.
• any increase in the ambient temperature can be detected by the reference temperature sensor 28 and the ambient increase in temperature can be deducted from the increase in temperature of the sensing element 20 as sensed by the temperature sensor 22.
• a separate heating element 30 can also be provided for the reference element 26 or a single element can be provided for purposes of heating the sensing element 20 and reference element 26.
• the electronics used to implement the present invention are known to those skilled in the art.
• the temperature sensor 22 and heating elements 24, 30 are preferably provided in a micro- bridge structure.
• the carbon monoxide sensor 10 of the present invention can be manufactured using known microelectromechanical systems (MEMS) technology.
• MEMS microelectromechanical systems

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
• Physics & Mathematics (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Medicinal Chemistry (AREA)
• Food Science & Technology (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
• Investigating Or Analyzing Materials Using Thermal Means (AREA)

Priority Applications (2)

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Publications (2)

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• 2000
  • 2000-11-28 US US09/724,536 patent/US6474138B1/en not_active Expired - Fee Related
• 2001
  • 2001-11-28 WO PCT/US2001/044767 patent/WO2002044702A2/en not_active Ceased
  • 2001-11-28 JP JP2002546197A patent/JP2004532971A/ja active Pending
  • 2001-11-28 EP EP01995269A patent/EP1337839A2/en not_active Withdrawn

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