Europaisches Patentamt 287 730 J European Patent Office 2) Publication number: 0 A1 Office europeen des brevets EUROPEAN PATENT APPLICATION © Application number: 87303659.4 © mtci.*: G01N 27/56 © Date of filing: 24.04.87 @ Date of publication of application: © Applicant: UOP INC. 26.10.88 Bulletin 88/43 25 East Algonquin Road Oes Plaines Illinois 6001 7-501 7(US) © Designated Contracting States: BE DE ES FR GB IT NL SE © Inventor: Petty-Weeks, Sandra Louise 15271 White Oak Drive West Chicago Illinois, 60185(US) © Representative: Brock, Peter William UOP Processes International Corporation 48 Leicester Square London WC2H 7LW(QB) Method and apparatus for detecting hydrogen-containing hydrogen-positive gases. © Apparatus and method for detecting and mea- Fig suring hydrogen and gaseous compounds capable of dissociating into or combining with hydrogen ions using a novel solid electrolyte membrane which comprises a three-component blend prepared by admixing an organic polymer or copolymer, such as poly(vinyl alcohol), with an inorganic compound, such as a phosphoric acid, and an organic com- pound selected from a group of polymers and copolymers having monomer units containing nitro- gen, oxygen, or sulfur atoms, such as poly(vinyl pyrrolidone). CO LLJ Xerox Copy Centre 0 287 730 GAS- "METHOD AND APPARATUS FOR DETECTING HYDROGEN-CONTAINING OR HYDROGEN-REACTIVE ES" inven- This invention relates to electrochemical mea- membrane is used in and part of the present that surement and detection of hydrogen or substances - tion. This membrane embodies the discovery a thin film capable of reacting with hydrogen. More specifi- macroscopically homogeneous polymer- fabricated from admix- cally, it relates to the use of a novel solid proton- blend membrane may be an such sulfuric conducting electrolyte membrane and a catalyst in 5 ture of an inorganic compound, as or detecting the presence in a sample gas of hy- acid or phosphoric acid, with an organic polymer selected drogen or gases capable of dissociating to yield or copolymer and an organic compound to combine with hydrogen ions, including oxygen, from a group of polymers and copolymers having sul- and measuring the quantity present relative to a monomer units containing nitrogen, oxygen, or known reference substance. The solid electrolyte w fur atoms, where the three components are at least This membrane is capable of membrane may be formed by blending an in- partially compatible. in detec- organic compound, an organic polymer or acting as a proton conductor a hydrogen is converted into copolymer, and an organic compound selected tor where molecular hydrogen of the membrane, protons are from a group of polymers and copolymers having protons on one side and monomer units containing nitrogen, oxygen, or sul- 15 then transported through the membrane, pro- fur atoms, or by compositing a membrane compris- tons are recombined with electrons to form molec- The membrane is ing these components with a porous support. This ular hydrogen on the other side. invention also involves the use of a reference sub- also useful in detection of gases capable of dis- with ions. stance in gaseous or solid form. sociating into or combing hydrogen U.S. Patent 4,500,667 (Polak and Beuhler) de- 20 In addition, the three components utilized to scribes proton-conducting membranes. make the membrane may be composited with or U.S. Patent 4,024,036 (Namamura et al) de- on a porous support to form a supported mem- well scribes a proton permselective solid state member brane which possesses increased strength as of capable of exhibiting ionic conductivity. as being a protonic conductor. Examples ma- U.S. Patent 3,265,536 (Miller et al), 4,306,774 25 terial used for such porous support include glass (Nicholson), 3,276,910 (Grasselli et al), and cloths, polysulfone and ceramics. 4,179,491 (Howe et al) deal with substances ca- The invention utilizes a concentration cell pable of conducting hydrogen ions. whose electrolyte is said membrane or supported An article by Lundsgaard, J.S., et al, "A Novel membrane. A membrane is mounted in a sample Hydrogen Gas Sensor Based on Hydrogen 30 cell or membrane housing having a sample gas URANYL Phosphate," Solid State Ionics 7 (1982) chamber and a reference chamber, which cham- 53-56, North Holland Publishing Co., describes ex- bers are separated by a partition comprising the contains the periments done using a substance which conducts membrane. The sample gas chamber hydrogen ions. gas sample of interest, which must include a com- A hydrogen detector using more complex 35 ponent capable of dissociating to form hydrogen methods than that of the invention may be seen in ions or capable of combining with hydrogen ions. U.S. Patent 4,373,375 (Terhune et al) and on page In the other chamber is a reference gas whose 8 of Platinum Metals Review 27.1 (January 1983), composition is known or a solid reference sub- Johnson Matthey, London. Three references show- stance which exhibits a substantially constant of the ing hydrogen detectors which use an entirely dif- 40 known hydrogen partial pressure during use ferent principle than the present invention are U.S. invention. Molecular transport through the mem- Patents 4,324,760 and 4,324,761 (Harris) and an brane should be sufficiently slow so that gases will article on page 29 of the August 1972 Instrumenta- not mix by diffusing through it. tion Technology. A catalytic agent for promotion of dissociation U.S. Patent 4,040,929 (Bauer et al) shows the 45 to hydrogen ions or combination with hydrogen use of a solid reference in an oxygen sensor. ions is in intimate contact with the membrane on The present invention provides methods and the sample gas side. Another catalytic agent is also reference side. It apparatus for detecting gaseous hydrogen, hydro- provided in a like manner on the that the catalytic be gen ion, dissociable hydrogen compounds, and is not necessary same agent substances capable of combining with hydrogen so used on both sides. Means for forming electrical ion, in order to indicate the presence or absence of contact and transferring electrons to and from an these substances and, where desired, provide external circuit are provided on each side of the quantitative information on the amount present. electrolyte in intimate contact with the catalytic A novel three component solid electrolyte agents. The cell electromotive force (EMF) Is mea- 0 287 730 sured across said means for forming electrical con- a solid electrolyte (ionic conductor) and conducting tact and provides an indication of the presence of electrodes are attached to both sides of the ionic hydrogen or gases capable of combining with it in conductor, an EMF is generated which is related to the sample gas and/or a quantitative measure of the partial pressures as follows: the amount of such which is present. A preferred embodiment of the method of the ** - ^ invention may be summarized as a method for Eo+-sr detection, in a gas sample, of a gaseous compo- nent which is capable, in the of a cata- presence where R is the gas constant, T is absolute tem- of to ions 10 lytic agent, dissociating yield hydrogen perature, F is the Faraday constant, Eo is the such method or of combining with hydrogen ions, standard oxidation-reduction potential difference, first comprising contacting said gas sample with a EMF is electromotive force, and n is the number of surface of a thin film polymer-blend membrane and electrons per molecule of product from the overall detecting an EMF signal between means for for- cell reaction. electrical connection with two 75 ming separate por- If the system described by the above equation tions of effective to the a catalytic agent promote behaves nonideally, the partial pressures must be dissociation and combination of ions, hydrogen replaced by fugacites. Another factor which may of is in contact where a first portion catalytic agent need to be considered in regard to a particular with said first surface and second of a portion system is the rate of dissociation to form the ions is in contact with a second surface 20 catalytic agent which pass through the solid electrolyte. This may said membrane which membrane isolates said of be a limiting factor to the transfer of ions through from reference substance and has gas sample a the electrolyte. The rate of dissociation can be said second surface to the reference sub- exposed calculated by means of the equilibrium constant for stance, said membrane comprising a blend of three the dissociation reaction. which 25 components, components are an organic The magnitude of EMF produced is generally polymer or copolymer, an inorganic compound se- in accordance with the parameters discussed here- of acids, lected from a group consisting phosphoric in: the Nernst equation and, where applicable, the acids, and salts of sulfuric acid, heteropoly dissociation equilibrium constant. However, re- and heteropoly acids, an organic compound se- quired practice in measuring concentration is to from of and lected a group polymers copolymers 30 periodically calibrate the measuring apparatus by units having monomer containing nitrogen, oxygen, use of samples whose composition is known. Thus, is or sulfur atoms, which organic compound com- exact adherence to theoretical relationships is not with said and said or- patible inorganic compound required of commercially used methods and ap- and the EMF ganic polymer correlating resulting paratus. The primary commercial requirement is existence amount of said signal with the or gas- 35 repeatability. eous component. It has now been discovered that a macro- device be used to automati- A calculating may scopically homogeneous thin film polymer-blend calculate concentrations, or calculation cally may membrane may be fabricated by admixing the or- be This device accomplished manually.