Chemviron Carbon Greening of Aerosol Propellants
Develop a system enabling the use of a benign gas as a propellant.
Since the demise of chlorofluorocarbons (CFCs), the majority of aerosol propellants have been based on light hydrocarbon components such as propane, butane and iso-butane. Although combinations of these materials have suitable vapour pressure characteristics, they are also classified as Volatile Organic Compounds (VOCs) which contribute both to low-level (tropospheric) ozone and global warming (greenhouse gas) effects. Hydrocarbon propellants come from oil feedstocks and are highly flammable, with significant safety and health issues. Residual hydrocarbons pose a significant problem for recycling of the canisters.
These gases also have very high global warming potentials and their use is limited to non-flammable or non-toxic propellants. Compressed gas propellants, such as carbon dioxide and nitrogen on the other hand are low-cost, low-toxicity, non-flammable, inert materials ideally suited to the environment. However, when deployed in aerosol canisters the pressure in the container falls rapidly as the contents are used and causes undesirable changes in the rate of discharge and spray characteristics, resulting in low customer appreciation.
Gas storage and aerosol dispensing systems have been developed based upon adsorbed permanent gases. The capability of activated carbon to condense or immobilise gases was exploited, resulting in increased gas storage and delivery capacity compared to usual storage containers. Adsorption onto a material’s porous structure densifies the gas to the point that it achieves a quasi-liquid state. Consequently a carbon-filled container can physically deliver more gas than a non-carbon filled container despite the volume lost to the carbon skeleton.
For the aerosol can and related devices (such as the foghorn), carbon dioxide is usually the preferred gas when used in conjunction with a selected activated carbon.
The activated carbon used for aerosol applications is manufactured from sustainable resources such as coconut shells, the carbonisation and subsequent activation of which produces more energy than the process itself uses. This allows a process of manufacture that doesn’t require external energy input and uses all by-products.