Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0039—Inorganic membrane manufacture
  • B01D67/0046—Inorganic membrane manufacture by slurry techniques, e.g. die or slip-casting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0039—Inorganic membrane manufacture
  • B01D67/0041—Inorganic membrane manufacture by agglomeration of particles in the dry state
  • B01D67/00416—Inorganic membrane manufacture by agglomeration of particles in the dry state by deposition by filtration through a support or base layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0081—After-treatment of organic or inorganic membranes
  • B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/02—Inorganic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/02—Inorganic material
  • B01D71/024—Oxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
  • C01B13/02—Preparation of oxygen
  • C01B13/0229—Purification or separation processes
  • C01B13/0248—Physical processing only
  • C01B13/0251—Physical processing only by making use of membranes
  • C01B13/0255—Physical processing only by making use of membranes characterised by the type of membrane
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2323/00—Details relating to membrane preparation
  • B01D2323/15—Use of additives
  • B01D2323/18—Pore-control agents or pore formers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/04—Characteristic thickness
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2210/00—Purification or separation of specific gases
  • C01B2210/0043—Impurity removed
  • C01B2210/0046—Nitrogen

Definitions

• the present invention relates to a method for manufacturing a dense and crack-free ceramic membrane which selectively transports oxygen when it is subjected to an oxygen partial pressure gradient.
• Such supported film-based membranes consisting of mixed-conducting oxides, have a range of technological applications including oxygen separation, electrochemical membranes reactors and power generation.
• Ceramic membranes consisting of mixed-conducting oxides allow the selective transport of oxygen when subjected to an oxygen partial pressure gradient, and this ability allows the production of 100% pure oxygen as e.g. described in European Patent Application No. 95100243.5 (EP-A-663230), US Patent 5,108,465, US Patent 5,516,359, US Patent 5,447,555 and US Patent 5,240,480.
• Oxygen supplied from compressed air for example, is dissociated on the surface of the mixed- conducting membrane, and it becomes incorporated into the bulk of the oxide, in the form of an oxygen anion. The oxygen is able to move within the oxide lattice via oxygen ion vacancies.
• a pair of oxygen anions at the surface are able to be recombined and be oxidised to molecular oxygen, which desorbs. If a membrane of the mixed-conducting material is subjected to an oxygen partial pressure gradient, oxygen is able to be selectively transported from the high partial pressure side of the membrane to the low partial pressure side.
• the oxygen transported through the membrane may be the desired product, or alternatively, it may be used for the production of synthesis gas as described in US Patent 5,356,728, for partial oxidation of hydrocarbons as in European Patent Application No 90134083 8 (EP-A-438902) and US Patent 5.714,091 or power generation applications as in International Patent Applications Nos PCT NO97/00170, PCT NO97/00171 and PCT/NO97/00172 (Norsk Hydro ASA)
• the partial pressure gradient across the membrane may be generated by either supplying compressed air to one side of the membrane, or by reducing the oxygen pressure at the other side of the membrane The latter could be achieved by pumping, if pure oxygen is the desired product, or by exposing one side to the membrane to a gas which has a low oxygen pressure, for example methane, in a partial oxidation reactor
• the flux of oxygen through such a membrane is determined by the ambipolar conductivity of the membrane material, the oxygen partial pressure gradient and the thickness of the membrane Therefore, the flux of oxygen through the membrane may be increased by reducing the thickness of the membrane When the thickness of a ceramic membrane is reduced below approximately 100 ⁇ m, handling of the membrane becomes difficult because of its mechanical weakness This limit on thickness is higher if the membrane is to be subjected to a total pressure gradient, rather than only an oxygen partial pressure gradient
• membranes consisting of a dense film or coating on a porous substrate may be prepared.
• the film will act as a functional layer for the selective transport of oxygen and the substrate will provide mechanical strength to the film.
• the connected porosity of the substrate allows the transport of gas either to or from the membrane
• a layer which is less than 10 ⁇ m in thickness is generally referred to as a film, whereas thicker layers are termed coatings
• CND chemical vapour deposition
• PND physical vapour deposition
• ESP electrostatic spray pyrolysis
• sol-gel techniques Two distinct processes are referred to as sol-gel techniques
• in-situ formation of a sol occurs in the liquid phase, usually through an alkoxide precursor
• the sol which has formed is then deposited onto the substrate by spin coating or dipping
• the solution containing a polymeric precursor is deposited onto the substrate, and then a further treatment (hydrolysis or thermal) leads to the formation of the film
• the substrate and the film or coating is represented by the formula AxA'x'A"x"ByB'y'B"y"Oz ⁇ d
• the present invention describes a method by which membranes for oxygen transport applications may be prepared by the deposition of a layer of oxide particles onto a porous substrate with bi- or multimodal distribution of poresizez.
• the oxide particles are deposited from a colloidal dispersion by a capillary action and dip-coating processes. Subsequent thermal treatment of the substrate and the deposited layer leads to the formation of a dense film or coating supported on the substrate, which retains open porosity which allows gas transport to and from the interior surface of the film.
• the method according to the present invention involves the deposition of a layer of oxide particles onto a porous substrate. Subsequent sintering of the coated substrate results in the formation of a coating of high density, which is free of cracks.
• the coating is prepared in the form of a colloidal dispersion or slip (a slip is defined as a dispersion of a powder in a liquid).
• a slip is defined as a dispersion of a powder in a liquid.
• L 2 Cav mary is the thickness of the layer
• pc ap ary is the capillary suction pressure of the substrate
• t is the immersion time
• ⁇ is the viscosity
• V is the solid volume fraction
• K is the permeability
• P is the porosity and the subscripts refer to the slip, the deposited layer and the substrate [M. Tiller and C. Tsai, J. Amer. Ceramic Soc, 69, 882-887 (1986)].
• the capillary pressure pc ap , ⁇ iary is approximated by the Laplace equation:
• a limiting thickness will be reached when all of the pores in the substrate are saturated with liquid and it is dependant on the solid volume in the slip; the pore volume of the substrate and the thickness of the substrate. This limit may only be exceeded if a continuous flux of the dispersion medium was able to pass through the substrate. This may be achieved if either a pressure was applied to the slip or a reduced pressure was applied to the opposite side of the substrate.
• L d ⁇ is the thickness of the liquid layer produced when withdrawing the substrate from the slip; £/ is the withdrawal speed; r[ dv is the dynamic viscosity of the slip; y S ⁇ ⁇ is the surface tension, p Shp is the density of the slip and g is the acceleration due to gravity. Therefore, the thickness of the layer deposited on the substrate, and hence the thickness of the sintered film, is controlled by the physical characteristics of the substrate, the slip, and by the process conditions, in terms of dip time and withdrawal rate.
• This method allows the preparation of dense crack-free films, with thickness' ranging from 5 to 70 ⁇ m.
• the deposition of the green film is carried out in a rapid, single process step, and unlike spin coating methods, multiple coating steps are not required to develop thick films.
• the typical thickness of films prepared by spin-coating of polymeric precursors is 0.1-0.2 ⁇ m.
• up to 10 layers may be deposited before cracking becomes problematic. Therefore, the maximum thickness of film that may be deposited is of the order of 1 to 2 ⁇ m. For some applications, this is adequate.
• grain growth due to sintering, in a thin coating or film may lead to the development of holes in the membrane.
• the powder that is used to produce the slip has a similar thermal history as the substrate. This ensures that the green film and the substrate exhibit the same sintering characteristics during densification of the film
• the method is not restricted to deposition of films on the surface of substrates with a planar geometry, as a film may be deposited onto any surface of the substrate that is accessible to the colloidal dispersion.
• This example shows the preparation of ceramic substrate of high porosity.
• the porous substrate was prepared by the following method.
• a mixed-conducting oxide powder, of composition La 2 NiO prepared by spray pyrolysis of metal nitrate salts at 700°C, was calcined at 1050°C for 20 hours.
• This powder was dry ball-milled with an equal volume of mono-disperse polymethacrylmethacrylate (PMMA) polymer spheres, with a diameter of 7 ⁇ m.
• PMMA mono-disperse polymethacrylmethacrylate
• the polymer acted as a pore former, which leads to the formation of a well-defined, open pore structure.
• the polymer-oxide powder was pressed into discs using a uni-axial press.
• the ceramic/polymer pellets were heated at 0.5°C/min to a temperature of 500°C, to remove the polymer by combustion.
• the oxide pellets were then heated at 5°C/min to an initial sintering temperature, in the range of 1 100 to 1300°C, for a period of four hours, before cooling to room temperature.
• the substrate After sintering at 1 100°C for four hours, the substrate had a relative pore volume of 0 65, with a bimodal pore size distribution
• the primary pores (2 ⁇ m) were formed by the removal of the polymer spheres and accounted for approximately 60% of the porosity (see Figure 1)
• This example shows the preparation of colloidal slip for coating porous substrate
• the colloidal dispersion or slip was made from the same oxide powder that had been used to form the porous substrate described in Example 1.
• the La 2 NiO 4 powder (20 g) was mixed with ethyl acetate (20 g), Paraloid B-66 polymer (0 55 g) and Paraloid B-72 polymer (0.55 g) (Rohm and Haas Nordiska AB)
• the resulting slurry was ball milled in a polyethylene container with zirconia milling media, for 24 hours
• the solid content of the colloidal dispersion was 12 volume %
• This example shows deposition of La 2 NiO 4 coating onto a porous La 2 NiO 4 substrate using dip coating.
• the coating was deposited by dipping the substrate into the slip, for periods of time of up to one minute. After the dipping process, the coated substrate was dried and slowly heated to 500°C to remove the polymer binder from the coating and the substrate After a thermal treatment of 1100°C, the coating was porous and it exhibited the same structure as the framework of the substrate (see Figure 3) EXAMPLE 4
• This example shows control of pore size distribution and shrinkage in porous substrates
• This example shows sintering of film on a porous substrate
• the microstructure of the framework of the porous substrate and the film, after thermal treatment at 1100°C are the same
• the elimination of the secondary pores in the substrate during sintering matches the sintering of the deposited film
• the coated substrate was heated to 1300°C to densify the film This is a temperature that, in the absence of a pore former, would result in the sintering of a powder compact to a density exceeding 95% of the theoretical density Sintering at 1300°C leads to a high density film supported on a substrate, which retains a high degree of interconnected porosity, to allow gas transport to and from the film Therefore, it is possible to prepare a dense, crack-free film on the porous substrate (see Figures 7 and 8)

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Organic Chemistry (AREA)
• Analytical Chemistry (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Diaphragms For Electromechanical Transducers (AREA)

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• 1999
  • 1999-02-19 NO NO19990811A patent/NO315549B1/no unknown
• 2000
  • 2000-02-18 EP EP00906783A patent/EP1156868B1/en not_active Expired - Lifetime
  • 2000-02-18 JP JP2000599493A patent/JP2002537088A/ja active Pending
  • 2000-02-18 DE DE60001541T patent/DE60001541T2/de not_active Expired - Fee Related
  • 2000-02-18 DK DK00906783T patent/DK1156868T3/da active
  • 2000-02-18 AT AT00906783T patent/ATE233590T1/de not_active IP Right Cessation
  • 2000-02-18 US US09/913,795 patent/US6613384B1/en not_active Expired - Fee Related
  • 2000-02-18 PT PT00906783T patent/PT1156868E/pt unknown
  • 2000-02-18 ES ES00906783T patent/ES2193939T3/es not_active Expired - Lifetime
  • 2000-02-18 WO PCT/NO2000/000061 patent/WO2000048717A1/en not_active Ceased
  • 2000-02-18 AU AU28343/00A patent/AU2834300A/en not_active Abandoned

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