Preamble : Readers should be aware that the abbreviation PFCs is being used for two different classes of classes of products.
PFCs (perfluorocarbons), covered by the Kyoto Protocol, are organofluorine compounds that contain exclusively carbon and fluorine. Examples are CF4 (tetrafluoroethane) and C2F6 (hexafluoroethane or perfluoroethane). These substances have high global warming potential but do not bioaccumulate and are considered to be of low order of toxicity. They are gases or volatile liquids.
While other compounds which contain atoms other than carbon and fluorine are also sometimes called PFCs, they should in effect be considered specifically as fluorocarbon derivatives. Examples are PFOA (perfluorooctanoic acid: C8HF15O2) and PFOS (perfluorooctanesulfonic acid : C8HF17O3S ). These are typically surfactants with long carbon chains, with uses in fluoropolymer preparations and for water repellancy.
The properties of these substances – bioaccumulation and stability – means that voluntary and regulatory measures are being taken to control their use and minimize their emissions to the environment.
1) IPCC Fourth Assessment Report GWP values
Due to their high GWP, PFCs are included in the “HFCs, PFCs and SF6” basket of the Kyoto Protocol.
Natural geological emissions have been responsible for the PFCs that have accumulated in the atmosphere over a very long time. However, the largest current source is aluminium production, releasing CF4 and C2F6 as by-products.
With the phase-out of ozone depleting substances, PFCs have been introduced into several specialised applications. The low volume level of use is associated with the fact that PFCs are relatively expensive products and are only selected if they are absolutely necessary for performance, system efficiency or safety. The manufacturing cost of PFCs is related to high material costs and processes that have limited scope for scale-up; the cost of manufacturing is much less sensitive to scale than that of HCFCs and HFCs.
The industrial use is mainly linked to the electronics industry, as PFCs offer a unique combination of properties: they are inert, good dielectrics, non-flammable, non-toxic and compatible with a broad range of materials. Semiconductor manufacturing processes utilise PFC gases as a fluorine source for chemical vapour deposition chamber cleaning and specialised plasma etching. PFC liquids C5F12and C6F14 are traditionally used as direct contact immersion cooling liquid for high power electronics, mainly as replacement for CFC-113, with required good dielectric characteristic at optimum material compatibility and thermal stability.
C3F8 has been developed as an inerting agent for a number of speciality refrigerant formulations. These formulations are primarily for use in existing CFC-based equipment and have a significant benefit of requiring the very minimum of retrofit adjustments. Whilst there are many new ODP-free refrigerants available (mainly HFC-134a) which perform well in newly designed equipment, their use in existing equipment is limited due to the high cost of retrofit.
In summary, only niche market applications for PFCs have developed following the European CFC phase-out since 1995. Today, the market is already in mature status and the EC HCFC phase-out regulation (EC 2037/2000) will not have a significant impact on the inert PFC liquids.
Primary aluminium manufacturing – PFC by-product emissions will decline due to already available process optimisation technologies.
Semiconductor manufacturing – the industry’s goal for global PFC emission reduction will reduce the total emissions by 10% (MMTCE) by 2010 (baseline 1995). This goal is embraced by European semiconductor manufacturers (Memorandum of Agreement signed 1998) and is equivalent to a reduction of more than 95% for each electronic component made3.
Refrigerant blends – use of C3F8 (in for example R-403A/B, R-412A) to render HCFC blends non-flammable will decline because HCFCs will discontinue by end 2009, as required by EC2037/2000. PFCs are also used in small amounts in specialist blends with HFCs but the quantities are small compared to releases from the semiconductor and aluminium industries.