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Dichlorodifluoromethane

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Dichlorodifluoromethane
Di structure.png
General
Systematic name dichlorodifluoromethane
Other names

Freon
Freon-12
R12
Chlorofluoromethane
Fluorocarbon 12
halocarbon 12

Molecular formula CCl2Fl2
Molar mass Molar mass::120.93 g/mol
Appearance clear gas
CAS number CAS number::75-71-8
Properties
Density and phase 6.25 kg/m3 (1.013 bar at boiling point), gas
Density and Phase cont. 1486 kg/m3 (1.013 bar at boiling point), liquid
Solubility in water 0.286 g/l at 20 °C
Melting point Melting point::−157.7°C
Boiling point Boiling point::−29.8°C
Viscosity 0.01168 cPcP at 0°C
Structure
Dipole moment 0.51 D
Hazards
MSDS Material safety data sheet
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Disclaimer and references

Dichlorodifluoromethane is a gas that is widely used as a refrigerant and aerosol spray propellant, which is better known as Freon. This helpful tool was very prevalent in air-conditioning systems for vehicles for years, yet today is being restricted due to it's ozone-depleting nature. Although considered "non-toxic" it's liquid form can be very dangerous. However, it's clear, ether-scented, gas form can be inhaled in large concentrations before it affects the body. However, if it is inhaled in dangerous amounts, it can affect the heart and Central Nervous System.

Properties

Dichloroflouromethane is a clear, noncombustible, non-acidic gas. It is known to aquire a strong scent of ether. [1] Freon has a molecular weight of 120.93 g/mol. In the liquid phase it’s density at 1.013 bar at boiling point is 1486 kg/m3. At 15 degrees Celsius or 59 degrees Fahrenheit it is measured 292 vol/vol. It’s boiling point at 1.013 bar is -29.8 degrees Celsius. Latent heat of evaporation (1.013 bar at boiling point) is 166.95 kJ/kg. The critical temperature is 112 degrees Celsius and the critical pressure 41.15 bar. Gas density of Freon at boiling point 1.012 bar is 6.25kg/m3. The density at the same bar at 15 degrees Celsius is 5.11kg/m3. Compressibility factor is 0.995. Specific gravity (air=1) at 21 degrees Celsius is 4.2 Specific volume of dicholorodifluoromethane at 21 degrees Celsius is 0.195 m3/kg. The heat capacity at 30 degrees Celsius is 0.074 kJ/(mol.K). At constant volume at 30 degrees Celsius the heat capacity is 0.065 kJ/(mol.K). Ratio of specific heats (Gamma:Cp/Cv –constant pressure, constant volume) at 30 degrees Celsius, still remaining at 1.013 bar is 1.138889. Viscosity at waters freezing point (0 degrees Celsius) for Freon is 0.0001168 Poise. Dicholrodifluoromethane’s thermal conductivity at 0 degrees Celsius is 9.46 mW/(m.K). [2] Heat adds to the instability of reactivity. Contact between dichlorodifluoromethane and very reactive metals such as sodium, potassium, calcium, powdered aluminum, zinc, and magnesium is very dangerous and not advised. When Freon decomposes it creates dangerous products. Hydrogen chloride, phosgene, and hydrogen fluoride- toxic gases may be in fires where dichlorodifluoromethane is burnt. [3]

Synthesis

Dichlorodifluoromethane can be constructed in laboratories or factories by reacting carbon tetrachloride (CCl4) and hydrogen fluoride gas (H2F2) with the use of a catalyst. The most common catalyst used is antimony pentafluoride (SbF5) Two of the chlorines in the carbon are replaced by two fluorines from the hydrogen fluoride in this reaction, thus creating dichlorodifluoromethane. [1]

Uses

Dichlorodifluoromethane is used in refrigerators as a coolant

In the mid-1980s Freon production climaxed, creating the gas for its many helpful uses. Some of its uses are refrigerants, propellants, and blowing agents. Its main use, refrigeration, is the transfer of heat from a cooler area to a warmer area. By pumping dichlorodifluoromethane, the low boiling gas around a closed circuit, the refrigerant evaporates in the coils, absorbing heat energy (Qc) from the refrigerator. The gas is then compressed, creating an elevated boiling point outside of the ice box which releases the heat into the air. This process is called the Clausius-Rankine cycle. The coefficient of performance for the Clausius-Rankine cycle is byabs (Qc/W). This is the amount of energy removed divided by the amount of work it took to remove the energy. R-12’s ability to remove a lot of energy per cycle is vital. Any car built before 1994 most likely uses R-12 for it’s air conditioning system. However use of Freon in cars was prohibited after 1994 as enforced by the Montreal protocol. Before 1990, CFC-12 was a very desirable blowing and propelling agent due to its non- reactive, and non-toxic nature. R-12 was even used on the space shuttles to blow foam insulation in critical areas of the ship. CFC 12 was even used to help cool down those with jungle fever. However, care must be taken because too much Freon can cause frostbite.[2] It has also been used as aerosol propellant for hair sprays, insecticides, paints, adhesives, and cleaners. It also acts as a foaming agent for the shipping of plastics. Due to its almost non-toxic nature, it was even used in the food preservation business- even as simple as chilling cocktail glasses. It’s been involved in important tasks, such as propelling rockets and freezing sections of tissue; along with manufacturing paints and varnishes, assisting in the purification of water, and detecting leaks. [3]

Consumption Patterns

From 1984-1986 the typical uses for dichlorodifluoromethane were: Freon 12 refrigerants, 39%; Foam Blowing Agents, 17%; Solvents, 14%; Fluoropolymers, 14%; Sterilant gas, 2%; Aerosol propellants, 2%; Food freezant, 1%; Other, 8%; Exports, 3% (1985); and for Fluorocarbons (1986). By 1991, Refrigeration/ air conditioning rose to 43%; blowing agents to 20%; polymer precursors, 13%; solvent cleaning, 12%; aerosol propellants, 2%; medical equipment sterilization, 3%; and other 7%.[4]

Specific Dangers

Description

Some major hazards of Dichlorodifluoromethane are that it decomposes when it is heated and its toxicity 1000ppm. It also has a risk of corrosion in the presence of water. [2] Exposure to Freon 12 can occur through inhalation or contact with the skin or eyes. After watching it's affects on animals, it became apparent that at high concentrations Freon could be used a narcotic and an asphyxiant. The effects of direct eye contact with liquid dichlorodifluoromethane is normally not substantial, however if the eyes are kept from shutting, temporary eye freezing may occur. While testing human reaction, high concentration of Freon 12 caused narcosis, unconsciousness, cardiac arrhythmia, cardiac arrest, and/or asphyxiation. Inhalation of 10,000 ppm of dichlorodifluoromethane for 2.5 hours caused a 7 percent reduction in average psychomotor skills; however, at 1,000 ppm for 8 hours/day, 5 days/week, for a total of 17 repeated exposures, no strange responses were observed. Many nonoccupational deaths have been reported from the sniffing of fluorochlorinated hydrocarbon aerosols, dichlorodifluoromethane being one of them; cause of death in these cases is believed to be cardiac arrhythmia caused by sharpening of the myocardium to epinephrine. Exposure to 40,000 ppm for 8 minutes caused generalized sensory losses, ringing in the ears, paranoia, and garbled speech; at 110,000 ppm for 11 minutes, there were cardiac arrhythmias, amnesia, and a noticeable decrease in consciousness.[3]


Safety Procedures

Fire Safety

When fighting a fire involving Freon 12, only necessary people should be kept near. Being at the maximum distance possible away in an upwind area is the best option. Isolate areas ½ mile in every direction from the fire if a large transportation vehicle is involved. Avoiding low areas and ventilating closed spaces is very important to the safety of emergency personnel. If cylinders of Freon are present, they may explode in the fire. If it is possible to remove them from the fire area safely, it is strongly advised. If that is not a safe option,cool the containers with water continually, even after the fire has been out for a considerable time. If a rising sounds from a venting safety device is heard or if there is discoloration on the container due to fire personnel should quickly flee from the container. Self-contained breathing apparatuses and full sets of protective clothing are vital to fighting fires involving dichlorodifluoromethane.

Exposure Limits

Exposure limits have been set by health administrations. The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) is 1000 parts per million (ppm) parts of air for an 8-hour time-weighted average (TWA) concentration for dichlorodifluoromethane. The National Institute for Occupational safety and health (NIOSH) has established a recommended exposure limit (REL) for Freon 12 at 1000 ppm as a TWA for up to 10-hours during a 40-hour work week. This is based to avoid narcotic effects and possible asphyxia from vapor. The American Conference of Government Industrial Hygienists (ACGIH) has created a threshold limit value (TLV) for 1000ppm as a TWA for a normal 8-hour work day for a 40-hour workweek. This limit is based on the risk of cardiac sensitization and systematic injury. A pre-placement evaluation of one’s medical needs is advised before hiring a future employee. It is important to be aware of possible medical conditions that could be aggravated by exposure to Freon 12.The health care professional consider the work conditions, the persons health history and how the person may react before hiring. Health interviews and physical examinations should be performed regularly during service as directed by the national, state, or local standard. Where no standards exist, if there is a minimal danger, checks should be performed every three to five years or as often as medical experts recommend. Further examinations are expected if an employee shows signs of symptoms of dichlorodifluoromethane exposure. The affects on the heart and Central Nervous System should be monitored quickly and efficiently, recognizing hazardous effects cause by Freon. Their health status should be compared to the average health of the population and the individual. No biological monitoring test has been created and approved for dichlorodifluoromethane. Thus, no study of tissues and bodily fluids has been placed into a normal practice.

Personal Hygiene

If liquid Freon 12 touches the skin, workers should cleanse the areas directly with lots of lukewarm water. If clothes become contaminated they should be taken off and not put on again until all of the dichlorodifluoromethane has evaporated. Before eating, smoking, going to the restroom, putting on make-up, or taking medication; a worker should rigorously wash their hands, forearms, and face with soap and water. Workers should also not do these activities in areas where Freon is stored.

Storage

A cool, dry, open area is the ideal place to store the dichlorodifluoromethane. The storage cylinders should be very tight and labeled as OSHA’s Hazard Communication Standard requires. It should be kept at a safe distance from all flammable sources, including chemically active metals- especially sodium, potassium, calcium, magnesium, zinc, and aluminum in the powder form. Workers should be careful to avoid physical damage to the containers.

Spills and Leaks In the case of a leak or spill, persons without protective gear should not be permitted in contaminated areas until they have been fully cleaned. The next procedures should be acted out in the case of a spill or leak: 1. Make safety personnel aware of the situation. 2. Remove all heat sources and flammable items. 3. Air out the area 4. If safe, stop the leak. Do not allow the gas to reach the atmosphere. 5. If the leak cannot be stopped, funnel into a combustion chamber to destroy by fire. 6. See if local and state air pollution control authorizes burning.[3]

History

Before Dupont’s discovery of dichlorodifluoromethane, later named Freon, the only available refrigerants were NH3, SO2, and CH3Cl. All had considerable drawbacks, thus Freon was quickly accepted. Most were toxic, so the main goal of new refrigerant possibilities was to make them non-toxic. Chlorofluorocarbons, with increased C-F bonding, decrease in toxicity along with decreasing in boiling point. With two C-F bonds, dichlorodifluoromethane boils around -29.8C and is not toxic. In fact, to prove its non-toxicity, Thomas Midgley Jr., the CFC-12 discoverer, filled his lungs with Freon and extinguish a candle at a meeting for the American Chemical Society in 1930. Interestingly enough, the only time Freon is dangerous is when it is exposed to flame because it may decompose into its individual parts or into phosgene (CCl2O)- a chemical warfare agent. In the 1890’s, Belgian chemist Fredric Swarts had already found an effective fluorine exchange catalyst. Using SbF3Br2 and some reaction manipulation, the Frigidaire team was creating dichlorodifluoromethane in the lab. This is the equation used by Midgeley and his team:

    CCl4 + HF –SbF3Cl2 (catalyst) →   CFCl3 + CF2Cl2 (Freon-12) + HCl 

In 1976, Dr. Michael Dove of the University of Nottigham found that HF was actually in equilibrium with SbCl5. Fluorene, in this reaction, is exchanged for Cl and SbCL5 becomes SbFxCL5-x. However, the additional F is very difficult to add to SbF5. It was also established that each fluorine in SbFx could be exchanged for a chlorine atom in chlorocarbons. SbF5 was found more effective in fluorinating than SbFCl4. Temperature also adds to the effective nature. [4]

Polar Ozone Loss and CFC Regulations

Dichlorodifluoromethane may be destroying the ozone.

When Freon 12 is released into the environment as emissions as it is produced, stored, transported, used as a refrigerant, foam blowing agent, solvent, or chemical intermediate in the production of fluoropolymers. Dichlorodifluoromethane is created in large quantities. All of the Freon made is eventually absorbed into the atmosphere and the level of chemicals has been building up throughout the years. It also can affect the soil. Although it does not seem to degrade anything and is virtually harmless at the trophospheric level, in the stratosphere, it can cause damages. Freon 12 is stable in water; it’s only removal process-vaporization. It is then able to enter water from the atmosphere when the concentration of dichlorodifluoromethane in the water is parallel with the concentration in the air. The ocean furthers its travels by carrying it far below the surface in the current. Due to the process of photolysis- a process in which ozone- harming chlorine atoms are released into the atmosphere- restrictions on dichlorodifluoromethane have been implemented. [5]

Environmental Requirements

The U.S. Environmental Protection Agency (EPA) has created standards for emergency plans, reporting contaminant leaks, community right-to-know, and correct disposal of substances which may change as time progresses. Thus, it is advised to determine current standards from time to time in the case of new information. For emergency plans, the EPA does not subject dichlorodifluoromethane to specific requirements for emergencies under the Superfund Amendments and Reauthorization Act (SARA) (Title II) in 42 USC 11022. As defined by the EPA, a “hazardous substance release” is defined by “any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment ( including the abandonment or discarding of contaminated containers) of hazardous substances.” Employees are expected by law to notify the proper Federal, State, and local powers that be. 2.5 tons of dichlorodifluoromethane is the reportable quantity. If an equal or greater amount is released in a 24-hour period that will affect people outside the facility, employees must notify the National Response Center without delay at (800) 424-8802 or (202) 426-2675 for Washington D.C. Those who own or run facilities in SIC codes 20-39 that employ ten or more people and that produce more than 25,000 pounds or more per year of dichlorodifluoromethane or utilize 10,000 pounds or more per year are required by EPA to submit what is called a Toxic Chemical Release Inventory form (Form R) stating the annual total of facility-released Freon. EPA considers ignitable, corrosive, reactive, or toxic substances as hazardous in 40 CFR 261.21-261.24. Under the Resource Conservation and Recovery Act (RCRA). Freon has been named hazardous waste No. U075. It is fine for land disposal only if the concentration does not increase over 7.2 mg/kg. [3]

Restrictions on Freon

Freon 12 restriction began in 1979 with an EPA ban on aerosol propellants. The later discovery of the 1985 ozone hole increased restriction. In the fall of 1987 in Montreal, Canada, an international treaty to control Freon was signed. Industrial nations stopped production in 1996 and “developing” countries were supposed to stop by 2010. Another treaty was signed in Kyoto, Japan. However the U.S. refused to sign until further evidence for the greenhouse gas theory was shown.[3]

Videos

References

  1. Dichlorodifluoromethane R-12 CCl2F2 CFC StarTec LLC Accessed 1/24/11.
  2. 2.0 2.1 Gas Encyclopaedia AIR LIQUIDE Group Accessed 1/24/11.
  3. 3.0 3.1 3.2 3.3 3.4 Occupational Safety and Health Guideline for Dichlorodifluoromethane United States Department of Labor 1996.
  4. Dichlorodifluoromethane Aaron Vorderstrasse, Western Oregon University,Monmouth, Oregon Accessed 1/24/11.
  5. Spectrum Chemical Fact Sheet Spectrum Laboratories Accessed 1/24/11.

Additional Information