Perfluorocarbons and its uses
Perfluorocarbons, sometimes referred to as fluorocarbons or PFC¹s, are organofluorine compounds that contain only carbon and fluorine bonded together in strong carbonfluorine bonds. Perfluorocarbons have chemical inertness and thermal stability.
Perfluorocarbon liquids are colorless. They have high density, up to over twice that of water, due to their high molecular weight. Very low intermolecular forces gives the liquids low viscosities (compared to liquids of similar boiling points), low surface tension and low heats of vaporization. They have particularly low refractive indices too. They are not miscible with most organic solvents (e.g., ethanol, acetone, ethyl acetate and chloroform), but are miscible with some hydrocarbons (e.g., hexane in some cases). They have very low solubility in water, and water has a very low solubility in them (on the order of 10 ppm). However, they are relatively good solvents for gases, again because of the very low intermolecular forces. The number of carbon atoms in the perfluorocarbon molecule largely defines most physical properties. The greater the number of carbon atoms, the higher the boiling point, density, viscosity, surface tension, critical properties, vapor pressure and refractive index. Gas solubility decreases as carbon atoms increase.
Medical Applications
Perfluorocarbons have many medical uses. Medical applications require high purity perfluorocarbons. Impurities with nitrogen bonds can have high toxicity; hydrogen-containing compounds (which can release hydrogen fluoride) and unsaturated compounds must also be excluded. Infrared spectroscopy, nuclear magnetic resonance and cell cultures can be used to test the perfluorocarbon.
Perfluorocarbons are commonly used in eye surgery as temporary replacements of the vitreous humor in retinal detachment surgery. The dense perfluorocarbon liquid, typically n-perfluorooctane, is injected into the eye, to push out vitreous liquid trapped behind the retina, and to aid removal of membranes (essentially scar tissue).
Perfluorocarbons are also used in contrast-enhanced ultrasound to improve ultrasound signal backscatter. The perfluorocarbons used in the microbubbles are gases at body temperature (though they may be liquids at room temperature). The gas-filled microbubbles oscillate and vibrate when a sonic energy field is applied and characteristically reflect ultrasound waves. This distinguishes the microbubbles from surrounding tissues. Their stability, inertness, low diffusion rate and solubility increase the duration of contrast enhancement as compared to microbubbles containing air.
Perfluorocarbons can also be used in magnetic resonance imaging (MRI), though this is not as common. Usually MRI is set up to detect hydrogen nuclei, but it is also possible to use MRI for 19-fluorine nuclei. As there is no fluorine in the human body naturally, it is very easy to determine exactly where the sample has gone. Perfluorocarbons can be introduced into the blood in an emulsion, or neat in the lungs.
In radiographic imaging, the perfluorocarbon derivative perfluorooctyl bromide (PFOB) is employed, as this is more opaque to X-rays.
Perfluorocarbons dissolve relatively high concentrations of gases, for example, 100 ml of perfluorodecalin at 25°C will dissolve 49 ml of oxygen at STP. Therefore, pefluorocarbons have been used in “liquid breathing” where the perfluorocarbon is breathed into the lungs instead of air.
The ability to dissolve high concentrations of oxygen has also led to the use of perfluorocarbons in so-called “artificial blood” as oxygen therapeutics which function as artificial erythrocytes, serving to transport and deliver oxygen in the body
Perfluorocarbons accelerate nitrogen washout after venous gas emboli. Success in the treatment of decompression sickness has been shown in rat, swine, and hamster models. This treatment shows great potential as a future adjunctive therapy for decompression sickness in humans.
Non-Medical Applications
Electrical and electronic applications. Perfluorocarbons have highdielectric strengths and high insulating properties, and so can be used indirect contact with high voltage components, either as dielectric fluids,dielectric gases, or as coolants.
Perfluorcarbon tracers. Perfluorocarbons can be detected at extremely lowlevels using electron capture detectors or negative ion mass spectroscopy. They can be released at a certain point and the concentration measured in the surrounding area. Perfluorocarbon tracers (PFTs) have been used to map oil fields, study building ventilation, track pollution, detect cable oil leaks, and even recover ransom money.
Cosmetics. Inspired by the medical applications, several companies incorporate perfluorocarbons in their cosmetic formulations, claiming the oxygen dissolved in the perfluorocarbon has an anti-aging effect on the skin.
Fluorous biphase catalysis. In this application, a perfluorocarbon is used to dissolve a catalyst with a perfluoroalkyl group, while the substrate is dissolved in an organic solvent. At elevated temperature, the perfluorocarbon and organic solvent become miscible, and so the mixture becomes homogeneous, facilitating the reaction. Upon cooling, the two phases separate, allowing the catalyst to be recovered from the perfluorocarbon, and the product from the organic solvent.
Miscellaneous Uses
Perfluorocarbons are being used in refrigerating units as replacements for CFCs (chlorofluorocarbons), often in conjunction with other gases, and as “clean” fire extinguishers. They are used in plasma cleaning of silicon wafers. Perfluorocarbons are also used in high end racing ski waxes due to their hydrophobic nature, which is responsible for reduced friction in wet snow conditions.
sir i have a question. perfluorocarbons is a greenhouse gas, so how to destroy or neutralized the gas?
Since you are asking about the global warming potential of perfluorocarbon gases, I assume you are most concerned about their largest global application – refrigerant gases.
Refrigerant gases are, by law in most countries, required to either be recovered from unwanted refrigeration equipment and recycled or destroyed. But, invariably, some of the gases will leak or otherwise be released to the atmosphere. So the short answer to your question is to choose a refrigerant gas that has as low of a global warming potential as possible combined with the lowest atmospheric lifetime so that it is easily broken down into harmless components by sunlight, oxygen, and a host of other naturally occurring atmospheric chemicals.
Refrigerant gases have come under very close scrutiny in the last 40 years, first because of their ozone depletion potential (ODP), then for their global warming potential (GWP).
Hydrochlorofluorocarbon (HCFC) gases have been used in refrigeration since the1930s. In 1974, it was found that HCFCs were depleting the ozone layer. One of the largest volume CFC gases was HCFC-22 (HCClF2). It has since been phased out as a refrigerant gas in most countries and the ozone layer has started to recover. HCFC-22 also has the disadvantages of a high GWP and a long lifetime in the atmosphere (see Table 1). The long lifetime of HCFC-22 means that it can spend a lot of time in the atmosphere doing damage to the ozone and increasing global warming.
HCFC’s have since been largely replaced with hydrofluorocarbon (HFC) gases. For example, R-134a (CF3CFH2) has been used for the last 20 years, especially in automobile air conditioners. It has no ODP (contains no chlorine atoms), so is safe for the ozone. But it does have a large GWP and a long atmospheric lifetime (see Table 1), which is a problem.
In the last year, the US EPA and the EU have approved a new type of refrigerant called hydrofluoroolefin (HFO) gases. These new gases have no ODP, very low GWP, and a very short atmospheric lifetime (see Table 1). So in the near future, you will start to see a new gas called HFO-1234yf (CH2=CFCF3) showing up in cars in the US and EU. Most likely, the rest of the world will follow the US and the EU.
So, in conclusion, we don’t have to actively try to destroy perfluorocarbon gases if we selectively choose to use only zero ODP, low GWP, and short atmospheric lifetime perfluorocarbon gas products.
I recently came across a NASA study which looked at using PFCs as a potential tool for terraforming Mars due to its super greenhouse properties, exceptionally long lifespan, and since it is non-harmful to life.
The concept involved building factories to produce the gas on Mars, however, I am wondering if the required PFCs could instead be manufactured elsewhere. My question is whether PFCs can be created and stored and transported efficiently as a liquid, and if so, what are the handling requirements? Similarly, what would be needed to then convert this into a gas once it arrived on Mars?
Thanks!
Another key benefit of effective gas detection and the use of fixed refrigerant detection devices is the opportunity to reduce overall operating costs. This is due to many factors – such as the discovery of extreme energy consumption thanks to inefficient refrigeration systems. Some systems also help you to top-up your refrigerant gases on a timely basis. This includes gases such as: Carbon Dioxide, Ammonia, hydrocarbons, halocarbons (all Freon gases) – HFC’s, HCFC’s, CFC’s that are common in businesses that utilise long-term freezing solutions – such as food processors in meat processing plants or those who use the cold storage e.g. for fruit processing /distribution, fishing companies, large chain retail markets and many other food-related industries. The refrigerant gas detection industry is well served by new technologies and these easily refillable gas solutions.
The only emission is gas used to blow brine to storage, which is typically treated with a small sweetening pot located on the water tank vent. Most systems include a sweet gas purge system using either city gas or bottled nitrogen. After vessels are depressurized sweet gas is purged through the vessels, normally several times, before the vessels are opened. Naturally the operator should still wear proper safety equipment as if he were working in a hydrogen sulfide environment. Reducing employee exposure to hydrogen sulfide can be a valuable benefit of desiccant dehydration.
If there are many areas of extreme thermal variance (this includes heaters or air conditioners) you should avoid placing your detector near these ‘hotspots’. Keep your sensors cabling routed inside of the premises, and well away from overhead cables that reside inside the buildings. Allow for sufficient warm-up time before the device begins to work correctly.