CFC Chlorofluorocarbons

Overview

Chlorofluorocarbons (CFCs) are fully halogenated hydrocarbons containing only carbon, chlorine, and fluorine atoms. These synthetic compounds revolutionized refrigeration and air conditioning from the 1930s through the 1980s due to their excellent thermodynamic properties, chemical stability, and non-toxic nature. However, their atmospheric persistence and severe ozone depletion potential led to their global phaseout under the Montreal Protocol.

CFCs represent the first generation of synthetic refrigerants that replaced hazardous substances like ammonia, sulfur dioxide, and methyl chloride in mainstream applications. Their development by Thomas Midgley Jr. at General Motors in 1928 marked a paradigm shift in refrigeration safety and reliability.

Molecular Structure and Nomenclature

Chemical Composition

CFCs are saturated aliphatic compounds where all hydrogen atoms have been replaced by chlorine or fluorine atoms. The general chemical formula is:

CClₓFᵧ (for single-carbon compounds) C₂ClₓFᵧ (for two-carbon compounds)

Where x + y equals the total number of bonds available on the carbon skeleton.

Refrigerant Numbering System

The ASHRAE refrigerant numbering system for CFCs follows this format:

R-ABC

Where:

• A = Number of carbon atoms minus 1 (omitted if zero)
• B = Number of hydrogen atoms plus 1
• C = Number of fluorine atoms

The number of chlorine atoms is determined by difference after accounting for carbon valence.

Example: R-12 (CCl₂F₂)

• A = 0 (one carbon, 0 is omitted)
• B = 1 (zero hydrogens + 1 = 1)
• C = 2 (two fluorine atoms)
• Chlorine atoms = 4 - 2 = 2

Common CFC Refrigerants

R-11 (CCl₃F) - Trichlorofluoromethane

Molecular Properties:

Thermodynamic Characteristics:

• Low pressure refrigerant (operates below atmospheric at typical evaporator conditions)
• Excellent for large centrifugal chillers
• High molecular weight provides good compressor efficiency
• Low latent heat requires large mass flow rates

Historical Applications:

• Large centrifugal water chillers (100-10,000 tons)
• Low-temperature industrial refrigeration
• Foam blowing agent
• Aerosol propellant

Operating Considerations:

• Evaporator operates in vacuum at standard air conditioning temperatures
• Air and moisture ingress major concern
• Requires purge systems for non-condensables
• Oil return challenges due to low refrigerant velocities

R-12 (CCl₂F₂) - Dichlorodifluoromethane

Molecular Properties:

Thermodynamic Characteristics:

• Medium pressure refrigerant
• Excellent volumetric efficiency
• Good coefficient of performance
• Favorable pressure-temperature relationship
• Compatible with mineral oils

Historical Applications:

• Domestic refrigerators and freezers
• Automotive air conditioning
• Medium-sized commercial refrigeration
• Reciprocating and scroll compressors
• Transport refrigeration
• Industrial process cooling

Saturation Properties (Selected Points):

R-12 was the most widely used CFC refrigerant, considered the industry standard for decades. Its balanced properties made it suitable for a vast range of applications.

R-113 (CCl₂FCClF₂) - 1,1,2-Trichloro-1,2,2-trifluoroethane

Molecular Properties:

Historical Applications:

• Very large centrifugal chillers
• Industrial solvent
• Electronics cleaning
• Precision cleaning applications
• Aerospace applications

Operating Characteristics:

• Very low pressure operation (below atmospheric)
• Highest molecular weight of common CFCs
• Excellent for very large capacity systems
• Superior chemical stability
• Non-flammable solvent properties

R-114 (CClF₂CClF₂) - 1,2-Dichloro-1,1,2,2-tetrafluoroethane

Molecular Properties:

Historical Applications:

• Military and naval refrigeration systems
• Heat pumps
• Medium-temperature applications
• Centrifugal chillers
• Specialized industrial processes

Unique Characteristics:

• Long atmospheric lifetime (300 years)
• Exceptionally stable molecule
• Low toxicity
• Good thermal stability at high temperatures
• Used in binary refrigerant blends

R-115 (CClF₂CF₃) - Chloropentafluoroethane

Molecular Properties:

Historical Applications:

• Low-temperature refrigeration
• Cascade systems (low stage)
• Cryogenic applications
• Component in azeotropic blends (R-502)
• Ultra-low temperature freezers

Operating Characteristics:

• Suitable for temperatures below -40°C
• High pressure operation
• Component of R-502 (48.8% R-115 / 51.2% R-22)
• Extremely long atmospheric persistence
• Limited standalone use

Thermodynamic Performance Analysis

Vapor Compression Cycle with R-12

For a standard vapor compression cycle operating between evaporator and condenser temperatures:

Given Conditions:

• Evaporator temperature: 0°C (273.15 K)
• Condenser temperature: 40°C (313.15 K)
• Subcooling: 5 K
• Superheat: 10 K

State Points:

Performance Metrics:

• Refrigeration effect: qₑ = h₁ - h₄ = 188.6 - 64.6 = 124.0 kJ/kg
• Compressor work: wc = h₂ - h₁ = 218.4 - 188.6 = 29.8 kJ/kg
• COP = qₑ / wc = 124.0 / 29.8 = 4.16
• Carnot COP = Tₑ / (Tc - Tₑ) = 273.15 / 40 = 6.83
• Efficiency ratio = 4.16 / 6.83 = 60.9%

Comparative Performance

CFC Refrigerants Performance Comparison (Standard Rating Conditions):

Note: Rating conditions - Evaporator: -15°C, Condenser: 30°C, 5K subcooling, 10K superheat

Ozone Depletion Mechanism

Stratospheric Chemistry

CFCs are chemically inert in the troposphere due to the absence of hydrogen atoms and strong C-F and C-Cl bonds. This stability allows them to migrate to the stratosphere (15-50 km altitude) where ultraviolet radiation breaks the C-Cl bonds:

Step 1: Photodissociation

CCl₂F₂ + hν (UV) → CClF₂• + Cl•

The photolysis occurs at wavelengths below 220 nm, abundant in the stratosphere but filtered by ozone in the troposphere.

Step 2: Catalytic Ozone Destruction

Cl• + O₃ → ClO• + O₂ ClO• + O → Cl• + O₂ Net: O₃ + O → 2O₂

A single chlorine atom can destroy 100,000 ozone molecules through this catalytic cycle before being deactivated.

Step 3: Chlorine Reservoir Formation

Cl• + CH₄ → HCl + CH₃• ClO• + NO₂ → ClONO₂

These reservoir species temporarily sequester chlorine but can be reactivated.

Ozone Depletion Potential (ODP)

ODP quantifies the relative ability of a substance to destroy stratospheric ozone compared to R-11 (defined as 1.0).

Factors Affecting ODP:

1. Number of chlorine atoms per molecule
2. Atmospheric lifetime
3. Molecular weight (affects transport to stratosphere)
4. Photodissociation rate in stratosphere

CFC ODP Values:

The lower ODP of R-113 and R-115 results from reduced stratospheric chlorine yield, not fewer chlorine atoms.

Antarctic Ozone Hole

The most severe ozone depletion occurs over Antarctica during austral spring (September-November) due to unique atmospheric conditions:

1. Polar Stratospheric Clouds (PSCs): Form at temperatures below -78°C, providing surfaces for heterogeneous reactions that convert reservoir species to reactive chlorine
2. Polar Vortex: Isolates Antarctic air mass, preventing mixing with mid-latitude air
3. Sunlight Return: Spring sunlight photolyzes chlorine compounds, triggering rapid ozone destruction
4. Surface Chemistry: PSC particles enable: ClONO₂ + HCl → Cl₂ + HNO₃

CFC-derived chlorine levels in the stratosphere peaked around 2000 at approximately 3.6 ppbv (parts per billion by volume).

Montreal Protocol and Phaseout

International Framework

The Montreal Protocol on Substances that Deplete the Ozone Layer, signed in 1987, represents the most successful international environmental agreement. It mandated the phased elimination of CFC production and consumption.

Timeline for Developed Countries (Article 5.1 Non-Parties):

Timeline for Developing Countries (Article 5 Parties):

Essential Use Exemptions

Limited CFC production continued post-phaseout for essential uses where no technically or economically feasible alternatives existed:

Approved Essential Uses:

1. Metered dose inhalers (MDIs) for asthma medication
2. Laboratory and analytical applications
3. Critical defense applications
4. Space vehicle applications

Medical MDI use of CFCs (primarily R-12 and R-114) continued until HFA (hydrofluoroalkane) propellants became available in the early 2000s.

Regulatory Framework in United States

Clean Air Act Section 608:

• Prohibits venting CFCs during service, maintenance, or disposal
• Mandates technician certification (Type I, II, III, Universal)
• Requires use of certified recovery/recycling equipment
• Establishes maximum penalties for violations ($37,500 per day per violation as of 2020)

EPA Regulations:

• 40 CFR Part 82 Subpart F: Recycling and emissions reduction
• 40 CFR Part 82 Subpart G: Significant New Alternatives Policy (SNAP)
• Recordkeeping requirements for refrigerant purchases and usage

Replacement Refrigerants and Conversion Strategies

Direct Replacement Options

R-11 Replacements:

R-12 Replacements:

Retrofit Considerations

System Compatibility Assessment:

1. Lubricant Compatibility:

   • CFCs used mineral oil or alkylbenzene
   • HFC replacements require polyolester (POE) or polyalkylene glycol (PAG)
   • Oil change typically necessary (minimum 95% conversion)
   • Residual mineral oil affects miscibility and return

2. Material Compatibility:

   • Elastomers: Different swelling characteristics
   • Desiccants: XH-7 or XH-9 required for HFCs (replace XH-5)
   • Expansion devices: May require resizing due to different pressure-temperature relationships

3. System Modifications:

Performance Expectations:

• R-134a in R-12 systems: 5-10% capacity reduction typical
• Energy efficiency: Generally comparable or slightly lower
• Discharge temperatures: 5-10°C higher with R-134a
• Operating pressures: R-134a operates at slightly higher pressures

Legacy Equipment Management

Servicing Existing CFC Systems

Refrigerant Supply Challenges:

• New CFC production prohibited since 1996 (developed countries)
• Reclaimed and recycled CFCs only legal source
• Prices increased 1000-2000% since phaseout
• Counterfeit refrigerants concern in some markets

Reclaimed Refrigerant Standards:

Per AHRI Standard 700-2016, reclaimed refrigerants must meet virgin product specifications:

Economic Analysis

Cost-Benefit of Retrofit vs. Continued Service:

Factors Favoring Retrofit/Replacement:

1. CFC refrigerant costs exceeding $50-150/kg
2. Frequent refrigerant additions (leak rate >10% annually)
3. Equipment age >20 years
4. High energy consumption (EER <8)
5. Availability of utility incentives
6. Upcoming major maintenance requirements

Factors Favoring Continued Service:

1. Tight system with minimal leakage
2. Recent major component replacements
3. Adequate refrigerant inventory
4. Specialized application with limited replacement options
5. Short remaining service life (≤5 years)

Payback Calculation Example:

Retrofit 100-ton R-11 centrifugal chiller to R-123:

• Retrofit cost: $80,000
• Annual CFC cost avoided: $12,000
• Energy savings: $3,000/year
• Simple payback: 80,000 / 15,000 = 5.3 years

Decommissioning Procedures

EPA Requirements for Equipment Disposal:

1. Refrigerant Recovery:

   • Recover to EPA-mandated levels before disposal
   • High-pressure equipment: 0 psig (vacuum)
   • Low-pressure equipment (R-11): 25 mmHg absolute
   • Very high-pressure equipment: 0 psig

2. Documentation:

   • Maintain records of refrigerant recovery
   • Report to refrigerant tracking systems if required
   • Document final disposition of equipment

3. Recovery Equipment Requirements:

   • Must be certified to AHRI Standard 740
   • Regular calibration and maintenance
   • Separate equipment for different refrigerant classes

Environmental Impact and Atmospheric Recovery

Global Atmospheric Trends

Chlorine Loading:

• Peak stratospheric chlorine: ~3.6 ppbv (2000)
• Current levels: ~3.1 ppbv (2023)
• Pre-industrial baseline: ~0.6 ppbv
• Projected return to baseline: 2060-2070

CFC Concentrations in Atmosphere:

Note: ppt = parts per trillion by volume

Ozone Layer Recovery

Montreal Protocol Success Indicators:

1. Antarctic ozone hole stabilized in size (not growing)
2. Mid-latitude ozone showing recovery (0.5-3% per decade)
3. Stratospheric chlorine declining
4. UV-B radiation increases halted

Projected Recovery Timeline:

• Arctic ozone: Return to 1980 baseline by 2030-2040
• Mid-latitudes: Return to 1980 baseline by 2040-2050
• Antarctic ozone hole: Return to 1980 baseline by 2060-2070

Without the Montreal Protocol, atmospheric models project:

• Stratospheric chlorine would have reached 17 ppbv by 2050
• Global ozone depletion of 50% by 2050
• Arctic ozone hole comparable to Antarctic hole
• UV radiation increases causing millions of additional skin cancer cases

Technical Specifications Summary

Physical Properties Comparison

Safety Classification

Per ASHRAE Standard 34, all CFCs are classified as A1:

• A: Lower toxicity (permissible exposure limit ≥400 ppm)
• 1: No flame propagation at 60°C, 101.3 kPa

Occupational Exposure Limits:

Cardiac Sensitization: CFCs can sensitize the heart to epinephrine, potentially causing cardiac arrhythmia at high concentrations (>10,000 ppm). This effect limits occupational exposures during maintenance activities in confined spaces.

Historical Significance

Industry Impact

CFCs enabled the widespread adoption of refrigeration and air conditioning technology from the 1930s through 1980s:

Key Milestones:

• 1928: Thomas Midgley Jr. synthesizes dichlorodifluoromethane (R-12)
• 1930: DuPont commercializes CFCs under trade name “Freon”
• 1935: R-11 introduced for centrifugal chillers
• 1940s-1950s: CFCs replace ammonia and SO₂ in most applications
• 1960s: Explosive growth in residential and automotive air conditioning
• 1974: Molina-Rowland hypothesis on ozone depletion published
• 1987: Montreal Protocol signed
• 1996: CFC production banned in developed countries

Market Dominance: At peak usage (early 1980s):

• R-12: ~500,000 metric tons/year global production
• R-11: ~300,000 metric tons/year global production
• Combined CFC production: ~1.1 million metric tons/year

Lessons Learned

The CFC experience provides critical lessons for refrigerant selection:

1. Long-term environmental assessment: Atmospheric lifetime and environmental impact must be evaluated before widespread adoption
2. Chemical stability trade-off: Compounds that are chemically stable in systems may persist in the environment
3. Global cooperation: International agreements can successfully address global environmental threats
4. Transition planning: Adequate transition periods and alternatives are essential for successful phaseout
5. Continuous improvement: Each generation of refrigerants addresses previous issues while introducing new considerations

Current Status and Future Outlook

Remaining Applications

Legitimate CFC use in 2024 is limited to:

• Servicing existing equipment (using reclaimed refrigerants only)
• Essential use exemptions (laboratory, analytical standards)
• Feedstock use (chemical synthesis where CFCs are destroyed)

Global Reclaimed Refrigerant Market:

• Annual reclaimed CFC supply: ~5,000-10,000 metric tons
• Primary sources: Equipment decommissioning, recovered refrigerants
• Quality concerns necessitate AHRI 700 certification
• Prices: $30-150/kg depending on refrigerant type and purity

Enforcement and Illegal Trade

Enforcement Challenges:

1. Continued illegal CFC production detected in East Asia (2018-2019)
2. Counterfeit refrigerant cylinders
3. Cross-border smuggling to avoid phaseout compliance
4. Mislabeled refrigerants

Detection Methods:

• Atmospheric monitoring networks
• Cylinder sampling and analysis
• Isotopic fingerprinting
• Import/export tracking systems

Environmental Legacy

While CFC emissions have largely ceased, their environmental impact continues:

• R-115 concentrations still slowly increasing due to 1,020-year lifetime
• Stratospheric chlorine will remain elevated for decades
• Antarctic ozone hole will persist until at least 2060
• Climate impact continues (high GWP values)

Total Climate Impact: CFCs contribute approximately 12% of historical radiative forcing from long-lived greenhouse gases, despite representing a small fraction of emissions by mass.

References and Standards

Key Standards:

• ASHRAE Standard 34: Designation and Safety Classification of Refrigerants
• AHRI Standard 700: Specifications for Refrigerants
• ASHRAE Standard 15: Safety Standard for Refrigeration Systems
• ISO 817: Refrigerants - Designation and Safety Classification

Regulatory Documents:

• Montreal Protocol on Substances that Deplete the Ozone Layer
• Clean Air Act Section 608 (40 CFR Part 82)
• EPA Significant New Alternatives Policy (SNAP) Program
• UNEP Ozone Secretariat Technical Reports

Scientific Assessment:

• WMO/UNEP Scientific Assessment of Ozone Depletion (published every 4 years)
• IPCC Climate Change Reports
• ASHRAE Handbook - Fundamentals (Chapter on Refrigerants)