Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C13/00—Details of vessels or of the filling or discharging of vessels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/22—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to internal surfaces, e.g. of tubes
  • B05D7/227—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to internal surfaces, e.g. of tubes of containers, cans or the like
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2203/00—Vessel construction, in particular walls or details thereof
  • F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
  • F17C2203/0602—Wall structures; Special features thereof
  • F17C2203/0607—Coatings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2203/00—Vessel construction, in particular walls or details thereof
  • F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
  • F17C2203/0634—Materials for walls or layers thereof
  • F17C2203/0636—Metals
  • F17C2203/0639—Steels
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2203/00—Vessel construction, in particular walls or details thereof
  • F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
  • F17C2203/0634—Materials for walls or layers thereof
  • F17C2203/0636—Metals
  • F17C2203/0646—Aluminium
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2221/00—Handled fluid, in particular type of fluid
  • F17C2221/03—Mixtures
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2221/00—Handled fluid, in particular type of fluid
  • F17C2221/03—Mixtures
  • F17C2221/032—Hydrocarbons
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2260/00—Purposes of gas storage and gas handling
  • F17C2260/05—Improving chemical properties

Definitions

• the present invention relates to coating gas cylinders to improve the stability of gas mixtures contained therein.
• GB-A-2075366 disclosed the use of a layer of an inert water-insoluble organic polymeric material with at least 75% of the layer formed from a monomer containing hydrophilic chemical groups to reduce carbon dioxide bubble nucleation on the internal walls of a container for liquid carbonated beverages.
• the coatings would be of use, if applied to the internal surface of a metal gas cylinder, to maintain the standard of a calibration gas mixture within the cylinder. It refers to the use of poly(vinyl alcohol) (“PVA”) as a suitable hydrophilic polymer but states that PVA must be insolubilized by, for example, cross-linking before it is suitable for use.
• PVA poly(vinyl alcohol)
• JP-A-55115694 discloses the coating of internal surfaces of gas cylinders with poly(trifluorochloroethylene) ("PCTFE”) to stabilize calibration gas mixtures and JP-A-54134070 discloses the coating of the internal surfaces of gas cylinders with a wax also to stabilize calibration gas mixtures.
• the exemplified waxes are Japan wax, ceresin wax, paraffin wax and silicon wax.
• PCTFE and the exemplified waxes are hydrophobic and are non-polar (i.e. non-water-wettable) and were used only to prevent contact between the gas and cylinder walls.
• the present invention is directed to stabilizing gas mixtures in a gas cylinder and has particular, but not exclusive, application to the storage of calibration gases. It has been found that stability of gas mixtures is significantly improved by coating the internal surfaces of gas cylinders with a film of a polar (i.e. water-wettable) film-forming polymer whereby non-polar organic molecules will not adhere to the polymer film.
• a polar film-forming polymer whereby non-polar organic molecules will not adhere to the polymer film.
• a metal gas cylinder having an internal, gas-contacting surface coated with a film of a polar film-forming polymer, whereby non-polar organic molecules will not adhere to the polymer film.
• the polar polymer prevents, or at least tends to inhibit, condensation of polar organic compounds and nitrogen oxides on, or reaction of compounds with, the internal, gas-contacting surface of the cylinder.
• the polar polymer is water-soluble, whereby it can be applied to the internal cylinder wall by contacting the wall surface with an aqueous solution of the polymer to coat the wall with the solution, and drying the coating to evaporate water from therefrom to leave a film on the wall surface. This process may be repeated to build up a second layer, or even more layers, on the gas-contacting surface.
• the water-soluble polymer has multiple hydroxyl groups and suitably is a polymer of an alcohol, a glycol, or a polyhydroxyalcohol, for example poly(ethylene glycol) or, especially, (uncrosslinked) PVA.
• the metal of the cylinder usually will be aluminium but may be, for example, steel.
• the present invention also includes a metal gas cylinder, the cylinder having an internal, gas-contacting surface coated with a film of a polar film-forming polymer, and the cylinder containing a calibration-gas mixture.
• the present invention also includes the use of a polar polymer to coat the internal, gas-contacting surface of a gas cylinder in a gas-calibration method.
• Polyvinyl alcohol having a molecular weight of 25,000 in the form of chips was dissolved in hot water and allowed to cool. It is preferable to make the solution as concentrated as possible as the water has to be dried off later. It was found to be possible to dissolve 15% by weight (w/w) of PVA in water.
• a quantity of the cooled solution was poured into a standard high quality aluminium gas cylinder in an amount sufficient to wet the entire internal, gas-contacting surface of the cylinder.
• a torch was used to inspect the inside of the cylinder to ensure that the whole surface has been fully coated with the solution.
• the gas cylinder was then be inverted to allow the excess solution to drain off and dry gas gently blown through the gas cylinder in order to evaporate water from the coating. This resulted in a gas cylinder which has a complete polymer film over the whole of its internal, gas-contacting surface.
• the whole process may be repeated in order to build up a second coating layer.
• further layers may be applied if desired.
• Gas cylinders coated as described above provide for extremely stable storage of mixtures within the gas cylinder. This is particularly important where the gas mixture is used in a calibration method and is therefore stored for a considerable period of time.
• the present invention derives its improved properties as follows.
• An uncoated metal cylinder is covered with oxygen atoms at its surface and the surface may be slightly polar, especially if the oxide layer is thin and new.
• larger organic molecules such as xylene tend to stick to, or condense on, the surface, thereby reducing the concentration of the molecules in the gas space in the cylinder.
• the use of a polar polymer coating as proposed in the present invention, and particularly one which has multiple OH groups, causes the organic molecules to be repelled and thus prevents or inhibits the loss of the organic molecules from the gas space in the cylinder.
• Nitric oxide mixtures are present in nitrogen because, in air, the nitric oxide reacts to form nitrogen dioxide.
• the problem is that there are still traces of oxygen in nitrogen and the aluminium surface of the gas cylinder can promote a reaction.
• Nitric oxide can be lost in two ways from an uncoated gas cylinder. In one mechanism, the nitric oxide reacts with gaseous oxygen, in which case the concentration of NO is lowered but the total NO x remains constant. In the second mechanism, the NO seems to react with the aluminium surface of an aluminium cylinder, but is retained so that the levels of NO and NO x both fall.
• the metal surface of the gas cylinder either acts directly or as a catalyst in the mechanism, particularly in the case of an aluminium cylinder. Coating the surface of the cylinder with a substance which is not an oxide allows the concentration of NO to be stabilised.
• OH groups can form a useful key to which other reactive compounds such as silanols could attach. This facilitates the provision of water-repellant coatings or other tailor made coatings for particular applications.
• the present invention whilst described above with particular reference to aluminium gas cylinders, can also be applied to gas cylinders of other materials, for example steel.
• the concentrations (ppb) of NO and NO x in gas mixtures stored the coated cylinders are compared with the concentrations (ppb) of NO and NO x in gas mixtures from the same source stored in the uncoated cylinders.
• NO loss in the uncoated cylinders was between 15 and 30% within 21 ⁇ 2 months.
• the gas mixture stored in the coated (invention) cylinders was stable to ⁇ 1.5% over a period of up to 11 ⁇ 2 years.
• Nitric Oxide Mixture Stability Nitric Oxide Mixtures in PVA Coated Cylinders Cylinder # Days After Fill NO Analysis NO x Analysis 6732 0 520 520 6 518 518 20 520 520 140 520 520 2413 0 497 not measured 4 503 not measured 13 504 503 164 504 504 197 494 501 555 493 494 Nitric Oxide Mixtures in Uncoated Cylinders Cylinder # Days After Fill NO Analysis NO x Analysis 2331 0 520 not measured 26 422 not measured 64 355 not measured 69 349 349 2333 0 805 not measured 7 750 not measured 29 704 not measured 58 673 not measured 67 680 not measured 72 682 808
• Hydrocarbons are often unstable and sometimes lost either when transfilled from one cylinder to another or when stored over a long period in a gas cylinder, especially at very low concentration. Component loss could be due to physical absorption onto metal surfaces or through chemical reaction and decomposition.
• the four hydrocarbons the results for which are shown in Table 2 are chosen to be a fair representation of those that are often stable (e.g. propane) and those that are often unstable (e.g. isoprene and the C 8 and C 9 compounds).
• the "Stability Ratio” is the quotient of the chromatographic peak area of a master cylinder component on day 0 and the chromatographic peak area of a target cylinder component on day x.
• the “Reference Component” is a component that may be regarded as stable (such as propane).
• the “Normalised Stability Ratio” is the quotient of the Stability Ratio of a component on day x and the stability ratio of the Reference Component on day x. In an ideal cylinder all the values would be 1.00. Because of the decay shown by gas stored in the uncoated cylinders, no further measurements were made for those cylinders after 35 days. However, measurements were made for the coated cylinders for 394 days.

Landscapes

• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)
• Investigating Or Analysing Materials By The Use Of Chemical Reactions (AREA)
• Sampling And Sample Adjustment (AREA)
• Paints Or Removers (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=10798661

Family Applications (1)

Country Status (4)

Cited By (1)

Family Cites Families (3)

• 1996
  • 1996-08-19 GB GB9617368A patent/GB9617368D0/en active Pending
• 1997
  • 1997-08-19 DE DE69736094T patent/DE69736094T2/de not_active Expired - Lifetime
  • 1997-08-19 ES ES97306321T patent/ES2262171T3/es not_active Expired - Lifetime
  • 1997-08-19 EP EP19970306321 patent/EP0824970B1/de not_active Expired - Lifetime

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