CHOOSING THE RIGHT PROPELLANT
for technical aerosols
SOLUTIONS FOR THE FUTURE
LIQUEFIED GASES FOR AEROSOLS
Isobutane has almost fallen into disuse because of its -83°C boiling point. It tends to be replaced by butane-propane. The sale of isobutane aerosols in superstores, supermarkets, DIY outlets, and small specialist outlets is prohibited. For example, gas aerosols for portable camping stoves are no longer found. The aerosol Butagaz, after being packaged in Korea, has disappeared from our stores.
The boiling point of butane propane is -44°C, therefore it is always supplied in a mixture with butane, the boiling point of which is 0°C.
Advantages: available, inexpensive (because the BP mixture is just LPG especially deodorised for this application).
Large gas reserve in aerosols, good solubility in most products, low internal pressure of 2.5 bars so that lower-cost 12-bar cans can be used.
Extremely low active product/propellant ratio.
Disadvantages: Flash point -58°C, extremely flammable.
Declared Volatile Organic Compound (VOC).
Storage in limited quantities. New SEVESO III regulations,
ICPE Sections 4320/4321.
Storage in supermarkets and DIY outlets is prohibited. Future regulations to come in small specialist outlets.
Overestimated insurance premiums, as this is the primary cause of fire claims (usually related to handling).
Butane-propane would also present pathological risks in toxicological terms; its penetration into the organism is liable to react with proteins or nucleic acids to produce various toxic metabolites that spread into human organs.
CFC production was banned in 1995.
HCFC production was banned more gradually starting in 2007; some HCFC had low ODP but significant GWP.
These gases were naturally replaced by HFCs, and mainly by HFC 134 A, boiling point -25°C, and, above all, non-flammable.
EU Regulation 517/2014 of 16 April 2014 on fluorinated greenhouse gases (F. Gas Directive) will ban atmospheric discharges of fluorinated gases with a GWP greater than 150. This is the case for HFC 134 A.
This ban will take effect on 1 January 2018.
Aerosol fillers and packagers naturally turned to HFC 152 A, which has a GWP of 124 that is below the limit (150). Although HFC 152 A is extremely flammable (-50°C), its boiling point at -25°C, which is strictly equivalent to that of HFC 134 A, did not require the products to be reformulated.
This solution is not destined for a long future. The parties (197 countries) in the Montreal Protocol (1987), who recently met in July 2016 in Vienna, are going to set the end date for all HFCs.
COP 22 has decided to ban all HFCs in the near future, including HFC 152 A and all those with global warming potential. This agreement was signed by 197 countries (bearing in mind that the GWP of an HFC is 14,000 times higher than that of CO2). Reference UNFCCC COP 22.
The recent choice of certain aerosol packagers to offer an alternative to HFC 134 A by replacing it with HFC 152 A will therefore not be a long-lasting solution.
A fourth generation of fluorinated gases is appearing: hydrofluoroolefins, known as R 1234 ze. This liquefied gas has an ODP of 0 and negligible GWP for a similar boiling point to HFC 134 a (-19°C).
Its cost is currently very high, but this should change if its use becomes widespread as a refrigerant in air conditioning systems and in the foaming of polyurethane.
Dimethyl ether or methoxymethane has fallen out of use by fillers and packagers of technical aerosols. With a boiling point of -24°C and flashpoint of -41°C, it is not an advantageous replacement for butane-propane in terms of cost. It does however have remarkable solvent power, a significant gas reserve, and excellent solubility in water.
Methoxymethane (DME) is still widely used in the cosmetics sector: hair sprays, styling gels, and shaving foams.
DME has existed for a very long time. The very well-known Start Pilote aerosols contain only DME.
Because DME is an isomer of ethanol, large quantities obtained from biomass could become available in the coming years, making this a bio-sourced propellant of great interest.
COMPRESSED GASES FOR AEROSOLS
CO2, or carbonic anhydride, is the ideal gas because it comes from natural sources. CO2, also called R 744 in refrigeration, is an atmospheric gas, so it is available in air, just like argon, helium, oxygen, and nitrogen. CO2 was used as the reference in establishing the global warming potential
(GWP) of other gases. Example CO2 GWP = 1 - HFC 134a GWP = 1430
CO2 produced by photosynthesis, which is the source of life on earth, is available in underground reservoirs. This non-flammable, non-explosive, non-combustible, inert, food-grade, medical, bacteriostatic compressed gas has just one drawback: it is not easily miscible in most of the products being packaged if they have a high viscosity.
In traditional impact gassing techniques, the pressure required would be too high and would damage the cans.
Advantages: non-flammable, non-explosive, non-combustible
Propellant authorised for agri-food applications (CO2 is used for the gasification of carbonated drinks, and for
the inerting and bacteriostatic protection of vacuum-packed foods).
Disadvantages: CO2 is incompatible in pressurised cans with water or traces of water.
Advantage or disadvantage: The marketing choice: only a very low percentage of compressed gases go into aerosols, therefore they contain a very high quantity of product. This can be an advantage or a disadvantage with regard to the final price.
NITROGEN PROTOXIDE N2O
Nitrogen protoxide is widely used in the medical sector.
Used as an aerosol propellant, it is partially soluble in water (unlike CO2), which makes it more widely usable in applications such as aqueous formulations, whipped cream, detergents, etc.
It is a non-flammable gas and an oxidizer when pure, but not in the presence of water.
N2O has a GWP (global warming potential) 298 times higher than CO2, but because of the very low percentage of compressed gases used in aerosols (2 to 3%), the long-term impact is negligible
(especially if compared to butane-propane, which has GWP 300,000 times higher than CO2).
Nitrogen, a naturally occurring gas like carbonic anhydride, is an ideal gas in environmental terms.
It makes up 78.06% by volume of the air around us.
Nitrogen is produced by the liquefaction of air.
As a compressed gas, it is non-flammable and inert, but in view of its extremely low boiling point (-195°C) it nevertheless requires specially adapted facilities, in particular for the supply of the packaging machines.
The use of nitrogen is common for very large production runs, for example to make atomisers or hair spray. It is a perfect gas for aqueous formulations with a high percentage of active matter, if packaged in a gasser shaker.
Choosing the right propellant is a strategic choice based on the
current or future environmental regulations
TEC INDUSTRIES INVENTION PATENT 904 019 684
Publication No. 0.407.308 A1
Fineness of spray with a non-flammable compressed gas