Coal Tar Distillation

Part of Petroleum and Tar

Distilling coal tar into useful chemical fractions — antiseptics, preservatives, solvents, and pitch.

Why This Matters

Crude coal tar straight from the retort is already useful for waterproofing and preservation, but it is a complex mixture of over 200 chemical compounds, each with different properties and applications. Separating coal tar into its component fractions through distillation unlocks specific, high-value products that crude tar cannot match: carbolic acid (phenol) for surgical disinfection, creosote for unmatched wood preservation, light oils for solvents and fuel, and refined pitch for the best caulking and waterproofing available.

This distillation represents one of the earliest practical steps into industrial chemistry. The same principles — heating a liquid to specific temperatures and collecting what evaporates — apply to alcohol distillation, petroleum refining, essential oil extraction, and eventually every branch of chemical manufacturing. A community that masters coal tar distillation has the foundational skills and equipment to tackle progressively more sophisticated chemical processes.

From a survival standpoint, the carbolic acid fraction alone is worth the entire effort. Before antibiotics, carbolic acid (phenol) was the most effective antiseptic available — it transformed surgery from a death sentence into a life-saving practice. Access to even crude carbolic acid dramatically improves a community’s medical capabilities.

Equipment for Distillation

The Still

You need a vessel that can be sealed and heated, with a way to collect vapor:

Option 1: Metal pot still

• A large metal pot (copper, iron, or steel) with a tight-fitting lid
• A copper or metal tube exiting the lid, angled downward
• The tube passes through a water-cooled condenser (a bucket of cold water, or a coiled tube submerged in a water trough)
• Condensed liquid drips into a collection vessel

Option 2: Ceramic retort

• A purpose-built ceramic vessel with an integral spout
• The spout connects to a condenser tube
• Less efficient than metal but functional

Option 3: Improvised still

• A sealed metal container (drum, large can) with a pipe fitting welded or sealed into the lid
• Any arrangement that captures vapor and directs it through cooling to a collection point

Supporting Equipment

Item	Purpose	Alternatives
Thermometer	Monitor distillation temperature	Experienced operators judge by vapor appearance and smell
Collection vessels	Separate fractions	Any clean containers — glass, ceramic, or metal
Heat source	Controllable fire	Wood fire with damper; charcoal brazier is easier to control
Condenser	Cool vapor to liquid	Tube through cold water; longer air-cooled tube; wet cloth on tube
Stirring rod	Prevent bumping	Long metal or wooden stick (for initial mixing only)

The Distillation Process

Preparation

1. Filter the crude tar through coarse cloth to remove solid debris (wood fragments, coal particles)
2. Charge the still — fill no more than two-thirds full to leave room for foaming and vapor
3. Connect all tubing and check seals — any leak wastes product and creates fire/fume hazards
4. Fill the condenser with cold water; arrange collection vessels in order
5. Label collection vessels clearly — you will switch between them at specific temperature points

Distillation Sequence

Heat the still gradually and collect fractions at the following temperature ranges:

Fraction 1: Water and Light Volatiles (up to 80°C)

• The first material to come off is residual water and very light compounds
• This fraction is mostly waste — discard or save the water for cleaning (it contains traces of ammonia)
• Appearance: Cloudy, thin liquid

Fraction 2: Light Oil / Benzol Fraction (80-170°C)

• A yellowish to pale brown liquid with a strong, distinctive smell
• Contains benzene, toluene, and xylene (collectively called “BTX” or “light oil”)
• Uses:
  • Solvent — dissolves grease, tar, wax, and resin from surfaces and equipment
  • Fuel — burns with a hot, clean flame; excellent for lamps
  • Paint thinner — thins pitch and tar-based coatings for easier application
  • Degreasing agent — for cleaning metal parts before soldering or welding

Health Hazard

Light oil fractions contain benzene, which is toxic and carcinogenic with prolonged exposure. Use in well-ventilated areas. Avoid breathing vapors. Minimize skin contact. Never use as a hand-cleaning solvent despite its effectiveness.

Fraction 3: Middle Oil / Carbolic Oil (170-230°C)

This is the most medically valuable fraction.

• A dark yellow to brown liquid with a sharp, medicinal smell
• Contains phenol (carbolic acid) — the compound that revolutionized surgery
• Also contains cresols and xylenols — related antiseptic compounds
• Uses:
  • Surgical antiseptic: Diluted to 2-5% solution in water for wound cleaning and surgical instrument sterilization
  • General disinfectant: Diluted solution for cleaning surfaces, latrines, and sickrooms
  • Livestock treatment: Dilute solutions treat skin parasites (mange, ringworm)
  • Embalming/preservation: Preserves biological specimens

Preparing carbolic acid for medical use:

1. Collect the middle oil fraction (170-230°C distillate)
2. Allow to cool — phenol crystals may form as white/pinkish solid
3. If crystals form, filter them out — this is relatively pure phenol
4. Dissolve crystals in water at 2-5% concentration for antiseptic use
5. If no crystals form, use the entire fraction diluted 1:20 in water as crude carbolic solution

Phenol Burns

Concentrated phenol causes chemical burns on contact with skin. Always dilute before use. If pure phenol contacts skin, wash immediately with large amounts of water, then with alcohol or glycerin if available. Even a 5% solution can cause irritation with prolonged exposure.

Fraction 4: Heavy Oil / Creosote Oil (230-270°C)

• A dark brown to black, oily liquid with a strong tarry smell
• Contains creosote compounds — the most effective wood preservatives known
• Uses:
  • Wood preservation: Applied by brush or soaking, creosote penetrates wood deeply and prevents rot, insect damage, and fungal growth for decades
  • Railroad tie treatment (historically): Creosote-treated timbers lasted 30-50 years vs. 5-7 years untreated
  • Fence posts and pilings: Soak the burial portion in hot creosote for several hours
  • Rope treatment: Soaking rope in creosote prevents rot in marine and outdoor use

Applying creosote to wood:

1. Heat the creosote to 60-80°C (warm, not boiling) — this thins it for better penetration
2. Apply liberally with a brush, or soak small pieces directly in the hot creosote
3. For maximum protection, apply 2-3 coats, allowing each to soak in
4. The wood will darken significantly and develop a characteristic smell
5. Allow to dry for several days before placing in service

Fraction 5: Anthracene Oil (270-350°C)

• Very dark, thick liquid
• Contains anthracene and other polycyclic compounds
• Uses:
  • Lamp fuel — burns with a smoky but hot flame
  • Lubricant base — thick enough for heavy bearing applications
  • Further chemical processing (if capabilities exist)
• Less immediately useful than fractions 3 and 4 but worth collecting

Residue: Coal Tar Pitch (remains in still)

• Black, solid or semi-solid material left after all volatile fractions have been driven off
• This is refined pitch — superior to crude tar for:
  • Boat caulking (see Boat Caulking)
  • Road surfacing
  • Waterproof coating for roofs, foundations, and cisterns
  • Adhesive for heavy-duty bonding
• Remove from the still while warm (it solidifies when cool)
• Store as solid blocks — remelt when needed

Yield Expectations

From 100 kg of crude coal tar, approximate fractional yields:

Fraction	Yield (kg)	Yield (%)
Water + light volatiles	2-5	2-5%
Light oil (benzol)	2-5	2-5%
Middle oil (carbolic)	8-12	8-12%
Heavy oil (creosote)	10-15	10-15%
Anthracene oil	5-10	5-10%
Pitch (residue)	55-65	55-65%

The pitch residue is always the largest fraction, which is convenient — pitch has many uses and stores well.

Tips for Better Distillation

Temperature Control

Without a thermometer, experienced operators recognize fractions by:

Indicator	Fraction Being Collected
Steam, thin wisps	Water (below 100°C)
Pale yellow vapor, light smell	Light oil (80-170°C)
Sharper, medicinal smell; thicker vapor	Middle oil (170-230°C)
Heavy, tarry smell; dark condensate	Heavy oil (230-270°C)
Very thick, slow condensate	Anthracene oil (270-350°C)
Condensation stops	All volatiles collected; pitch remains

Preventing Problems

Problem	Cause	Prevention
Foaming/bumping	Heating too fast; still too full	Heat gradually; fill only 2/3
Mixed fractions	Not switching vessels at correct point	Monitor temperature/vapor carefully
Low yield	Insufficient heat; leaky connections	Increase heat; seal all joints
Fire	Flammable vapors igniting	Ensure condenser works; no open flame near collection point
Still cracking	Thermal shock or overpressure	Heat gradually; ensure exit tube is clear

Re-Distillation

For purer products, collected fractions can be re-distilled:

1. Take the middle oil fraction (170-230°C)
2. Re-distill, collecting only the 180-195°C cut
3. This narrower fraction is richer in phenol
4. Allow to cool — phenol crystallizes at 41°C
5. Collect crystals for the purest carbolic acid available

Safety Summary

Hazard	Mitigation
Fire/explosion	Work outdoors; keep flames away from collection vessels; have sand ready
Toxic fumes	Adequate ventilation; work upwind; never in enclosed spaces
Chemical burns	Avoid skin contact with middle oil and pitch; dilute before handling
Carcinogens	Minimize exposure to light oil (benzene); wash hands after handling any fraction
Heat burns	Handle hot pitch and still components with long tools; never rush cooling

Coal tar distillation is the gateway technology that connects simple charcoal-making and tar production to the entire field of industrial chemistry. The products are immediately and practically useful — antiseptics save lives, creosote preserves infrastructure, pitch seals boats and roofs, and solvents enable further chemical work. Master this process, and your community has taken the first concrete step from the wood age into the chemical age.