Prop ellant Injection A brief history of pressurized filling Over the years, a surprising number of volatile organic compounds (VOCs) have been used as aerosol propellants. Those that are liquids at room temperatures have ranged from n.pentane (-5 psi-g. at 70°F) to carbon dioxide (837 psi-g. at 70°F). Those such as nitrogen, compressed air (CAIR), oxygen and argon have critical temperatures below -310°F. They cannot be liquefied above that cryogenic temperature, even at pressures up to 50,000 psi-g. Around 1965, the aerosol industry arbitrarily decided that volatile compounds boiling above 105°F would be classified as propellants (methylene chloride boils at 103.57°F). Some exotic propellants have been commercialized in aerosol forms. DuPont’s C-318 (octafluorocyclobutane, 25.1 psi-g at 70°F) was once used as a food propellant, always with nitrous oxide. It allowed more product to be used in any given can size. Vinyl chloride (monomer, 34 psi-g. at 70°F) was used around 1960 in paints, hair sprays and shave creams until it was discovered to be a mild animal carcinogen. While no one was harmed, torts were pursued by lawyers for over 30 years. As late as about 1995, non-flammable sulfur hexafluoride (321 psi-g at 70°F) was being used in at least two automotive products. Still later, it was found to have a Global Warming Potential (GWP) of about 25,000, meaning that the escape of one pound into the atmosphere would be the equivalent of injecting 25,000 pounds of carbon dioxide. Ethylene oxide, a flammable sterilant and toxic gas (7.3 psi-g at 70°F) has been packaged in small aerosol containers for use in hospitals and clinics. Similarly, methyl bromide (marginally flammable, 27.9 psi-g at 70°F) has been filled into special Crown cans as a toxic insect fumigant for tomato greenhouses, flour mills and bakeries. It is arguably the most intensive solvent ever put in an aerosol dispenser. It is poured into the bottomless, inverted can after which the base is attached by double seaming, using a special sealing compound. There is no top opening. To operate the unit, a special valve is attached, puncturing the top of the can. Lastly, in the early 1950s, sulfur dioxide (34.4 psi-g at 70°F) was aerosolized as a refrigerant refill. This was a case which the propellant was also the product. To illustrate the versatility of the aerosol system, laboratory work has shown that perfectly dry solutions of hydrogen chloride (HCl) in petroleum distillates were very effective in removing lime and rust stains from sinks, tubs and toilets, but the odor, toxicity and acidity with water precluded commercialization. Aerosols containing anhydrous ammonia (114 psi-g at 70°F and 317 psi-g at 130°F) were also prepared as a potential coolant additive for early refrigeration systems, but the pressure was excessive. They were never commercialized. The first aerosol propellant to be banned was vinyl chloride monomer (VCM) in about 1960. This was an industry ban, precluding the need for any government intervention. However, the U.S. Environmental Protection Agency (EPA) and U.S. Food & Drug Administration (FDA) did issue regulations banning chlorofluorocarbon (CFC) propellants in April, 1978 after determining that they could diminish the planet’s stratospheric ozone layer. Europe followed some ten years later, and a few countries were still using CFCs as late as about 2010. The ban included CFCs 11, 12, 113 and 114. Later amendments 42 Spray October 2014 Table 1 PROPELLANT PRESSURE psi-g 70° F PRESSURE psi-g 130° F. SOLVENCY Propane 109 257 Poor Iso-Butane 31.1 97.1 Poor n-Butane 16.7 67.0 Sl. Better iso-Pentane -3.5 18. Poor n.Pentane -5.0 11. Sl. better Dimethylether (DME) 63. 174.6 Excellent HFC-134a 70. 199. Fair HFC-152a 62.6 174.5 Good HFO-1234yf 87.8 205.9 Good Solstice HFO-1234ze 45.3 140. Good Solstice PF 2.2 29. Excellent Carbon Dioxide 837. n/a. Good Nitrous Oxide 720. n/a Good Nitrogen n/a. n/a. Poor Compressed Air (CAIR) n/a. n/s. Poor Oxygen n/a. n/a. Poor Argon n/a. n/a. V. Poor NOTE: DuPont’s HFO-1234yf has been developed principally as an air-conditioner coolant. HFC-134a uses are extremely limited due to its high GWP (also HFC-227ea). “n/a.” (Not Applicable): Non-liquifiable, since above the critical temperature, or triple point. Solstice PF is 1-Chloro-3,3,3-trifluoroprop-1-ene from Honeywell Fluorine Chemicals.
Spray Oct 2014
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