HFCs Application in Propellants
HFCs are chemical substances, short for hydrofluorocarbons, which can cause global warming when used in large quantities as refrigerants.
This article mainly introduces another important use of hydrofluorocarbons, which is the propellant used in aerosol products.
Propellants are the source of aerosol spray power and can also serve as solvents or diluents for drugs. Propellants are mostly liquefied gases with a boiling point lower than room temperature at normal pressure and a high vapor pressure. When the valve is opened, the pressure suddenly drops, the propellant vaporizes rapidly, and the drug in the container is sprayed out in a mist by the pressure of the propellant.
Propellants General Classification
Fluorochloroalkanes, such as Freon, are characterized by low boiling point, slightly higher vapor pressure than atmospheric pressure at room temperature, easy to control, stable properties, not easy to burn, high density after liquefaction, tasteless, basically odorless, and low toxicity;
Hydrocarbons: mainly include propane, n-butane and isobutane, etc;
Compressed gas: such as carbon dioxide, nitrogen, carbon monoxide, etc.
Propellants Requirements
Propellants need to meet the following characteristics and requirements:
- Vapor pressure: The vapor pressure at room temperature should be greater than atmospheric pressure;
- Safety: Non-toxic, non-sensitizing, non-irritating, non-flammable and non-explosive;
- Stability: Stable, does not react with drugs, etc;
- Physical properties: Colorless, odorless, tasteless;
- Economical: Cheap and easy to obtain.
HFC Substitutes For CFC Propellant
HFC-134a
HFC 134a has zero ODP value and low GWP value, does not produce photochemical smog, is chemically inert, toxicologically safe, has passed the expanded toxicity test of the International Medical Aerosol Toxicity Test Alliance (IPACT-I), is the main substitute for CFCs in medical aerosols , and can be used as a fuel for MDI (used to treat asthma and chronic respiratory disorders).
Pharmaceutical administration departments have approved MD1 with HFC 134a as a propellant in more than 40 countries.
HFC-152a
The environmental characteristics of HFC-152a are similar to those of HFC-134a, especially its greenhouse effect potential is lower (GWP=140), and it does not produce photochemical smog, so it does not belong to “volatile organic compounds” (VOC). The disadvantage is that it is flammable. HFC-152a has been produced on a large scale at home and abroad.
HFC-227ea
Its chemical name is 1,1,1,2,3,3,3-heptafluoropropane. Its environmental characteristics are similar to those of HFC-134a, but its GWP value is higher. It is non-toxic, non-combustible, safe to use, and has also passed the IPACT-I expanded toxicity test.
Because it has more suitable vapor pressure, liquid density, low surface tension, oxygen solubility and dipole moment than HFC134a, as well as higher viscosity and better solubility, it is more suitable as a propellant for MDI. In many new medical spray products, it has been used to replace HFC-134a as a propellant, or a mixture of the two.
DME
Although dimethyl ether (DME) is not a hydrofluorocarbon, it plays an important role in aerosol products, so it is briefly introduced here. Dimethyl ether has excellent solvent properties and water solubility and can be used as a propellant for water-based aerosols. This type of water-based aerosol reduces the amount of flammable organic solvents, which is undoubtedly beneficial to reducing VOC emissions and the resulting photochemical smog.
Dimethyl ether is flammable, but its use in water-based aerosols can greatly reduce flammability. The propellant formula of dimethyl ether and various hydrofluorocarbons (such as HFC134a and HFC-227ea) has been commercialized in large quantities and is safer to use.
Summary
The propellant is one of the components of aerosol. It can sometimes be used as a solvent or diluent for the main drug. The nature and dosage of the propellant are related to the size of the aerosol particles, dryness, wetness, etc.
The propellant can be compressed gas such as nitrogen, carbon dioxide or nitrous oxide, but most of them use liquefied gases such as chloroalkanes with boiling points lower than room temperature, such as trichloromonofluoromethane, difluoromethane, trichlorotetrafluoroethane, etc. If the effect of using only one fluorochloroalkane propellant is not satisfactory, two or more fluoroalkanes can be mixed to make a mixed propellant with the required vapor pressure.
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