Coal Tar

Part of Petroleum and Tar

Producing coal tar through destructive distillation of coal — a gateway to industrial chemistry.

Why This Matters

Coal tar is one of the most chemically complex and useful substances a rebuilding community can produce. When coal is heated in the absence of air (destructive distillation), it breaks down into three major products: coal gas (a flammable fuel), coal tar (a thick dark liquid), and coke (a solid carbon fuel). Of these, coal tar is the most versatile — it contains hundreds of chemical compounds that serve as waterproofing agents, wood preservatives, antiseptics, adhesives, and the raw materials for an entire chemical industry.

Historically, coal tar was considered a waste product of gas works and coking operations. Then, in the mid-1800s, chemists discovered that its components could be separated by distillation into fractions with extraordinary properties. From coal tar came carbolic acid (the first surgical antiseptic), creosote (the most effective wood preservative ever developed), naphthalene (moth repellent), and eventually the entire synthetic dye industry. Coal tar literally launched industrial chemistry.

For a rebuilding community, coal tar production represents a critical transition from biological chemistry (working with plant and animal products) to industrial chemistry (working with mineral and synthetic products). Even the simplest coal tar separation provides waterproofing, preservation, and medical materials that are difficult or impossible to obtain from biological sources alone.

Requirements for Coal Tar Production

Coal Source

Not all coal is equally suitable for tar production:

Coal Type	Tar Yield	Notes
Bituminous (soft coal)	High (3-8%)	Best for tar production; black, layered, burns with yellow flame
Sub-bituminous	Moderate (2-4%)	Acceptable; brown to black
Lignite (brown coal)	Low (1-2%)	Poor tar yield; better used as direct fuel
Anthracite (hard coal)	Very low (<1%)	Too thoroughly carbonized; almost no volatiles left
Cannel coal	Very high (10-15%)	Excellent but rare; produces the most tar

Finding Coal

Coal deposits are often visible as black seams in cliff faces, riverbank cuts, and hillside exposures. Look for areas with black shale, and ask about any location where dark rock burns. Surface coal was known and used in many regions long before mining technology existed.

Equipment

At minimum, you need:

1. A retort — a sealed vessel that can withstand high heat. Options:
   • Thick-walled ceramic pot with a sealed lid and exit tube
   • Metal pipe section with capped ends and an exit tube
   • Purpose-built brick or clay oven with a sealed chamber
2. An exit tube — metal pipe, ceramic tube, or bamboo section to carry gases and tar vapor away
3. A condensing arrangement — the tube passing through water or simply being long enough to cool
4. A collection vessel — any container to catch the liquid tar
5. A heat source — a fire capable of bringing the retort to red heat (700-900°C)

The Production Process

Small-Scale Retort Method

For initial experiments and small production:

1. Crush the coal into pieces roughly 2-5 cm across — smaller pieces heat more evenly
2. Pack the retort loosely — coal needs some air space for gases to escape through
3. Seal the retort leaving only the exit tube open
4. Angle the exit tube downward from the retort to the collection vessel
5. Optionally pass the exit tube through a water-filled trough for condensation
6. Build a fire around the retort and bring to high heat gradually over 1-2 hours

What happens during heating:

Temperature Range	What Occurs
100-200°C	Water driven off as steam
200-350°C	Light tar begins to distill; yellowish smoke appears
350-500°C	Main tar production phase; thick brown-black liquid condenses
500-700°C	Coal gas production peaks; gas is flammable
700-900°C	Final volatile removal; coke formation completes

7. Maintain high heat for 4-8 hours depending on retort size — coal must be thoroughly “cooked”
8. Collect the condensate — a dark, oily liquid with a strong, characteristic smell
9. Allow to cool completely before opening the retort
10. Remove the coke — the solid residue is an excellent high-temperature fuel

What You Collect

The condensate is a mixture of:

• Coal tar (heavy, dark, sinks to bottom) — the primary product
• Ammoniacal liquor (watery, lighter, floats on top) — contains dissolved ammonia and other water-soluble compounds
• Some tar may remain as thick residue in the exit tube — warm the tube to recover it

Separate the tar from the aqueous layer by decanting — carefully pour off the lighter liquid, or use a reed/tube to siphon it from the top.

Safety Precautions

• Coal tar contains carcinogenic compounds (benzene, polycyclic aromatic hydrocarbons). Minimize skin contact; wear gloves if available
• Coal gas is flammable and toxic (contains carbon monoxide). Work outdoors with good ventilation
• The retort operates at very high temperatures — maintain safe distance, use long tools
• Hot tar causes severe burns — handle only after cooling

Larger-Scale Beehive Method

For communities needing regular production:

1. Build a beehive oven — a dome-shaped brick structure roughly 2 m in diameter
2. Include a sealed charging door at the top or side
3. Install an exit pipe at the lowest point, running downhill to a collection pit
4. Load coal through the charging door
5. Ignite the coal and burn briefly, then seal the door to exclude air
6. The oven’s own heat drives distillation; gases and tar exit through the pipe
7. After 24-48 hours, the process is complete
8. Open the oven to remove coke; collect tar from the pit

This method produces larger quantities and yields both good coke (for metalworking fuel) and significant volumes of tar.

Immediate Uses of Crude Coal Tar

Without any further processing, crude coal tar is useful for:

Waterproofing

• Apply heated coal tar to wooden structures, barrel exteriors, boat hulls, and fence posts
• Coal tar penetrates wood deeply and provides excellent water resistance
• Superior to pine tar for below-ground applications (fence posts, pilings)
• One application can protect wood for 10-20 years

Road and Path Surfacing

• Mix coal tar with gravel or crushed stone to create a waterproof surface
• Spread while warm; compact with a roller or heavy traffic
• This is essentially the original macadam/tarmac road surface
• Far superior to bare earth or gravel alone for wet climates

Roofing Compound

• Apply hot coal tar to flat roofs, especially over felt or woven fabric
• Build up layers: tar, fabric, tar, fabric, tar
• Creates a waterproof membrane that lasts years
• Traditionally called “tar and gravel” roofing

Pest Control

• Coal tar applied to fence posts, building foundations, and granary bases deters insects and rodents
• The strong smell repels many animals
• Apply in a band around the base of structures

Further Processing: Distillation

Coal tar can be separated into fractions by careful distillation (see Coal Tar Distillation for detailed methods). The key fractions and their uses:

Fraction	Boiling Range	Primary Use
Light oil	80-170°C	Solvent, fuel, raw material for further chemistry
Middle oil (carbolic)	170-230°C	Contains phenol — antiseptic, disinfectant
Heavy oil (creosote)	230-270°C	Wood preservative — the best available
Anthracene oil	270-350°C	Lamp fuel, lubrication
Pitch (residue)	>350°C	Waterproofing, caulking, adhesive

Yield Expectations

From 1,000 kg of good bituminous coal, expect approximately:

Product	Approximate Yield
Coke	650-750 kg
Coal tar	30-80 kg
Coal gas	300-350 m³
Ammoniacal liquor	50-100 liters

The coke alone makes the process worthwhile for metalworking communities — it burns hotter and cleaner than raw coal. The tar and gas are valuable bonuses.

Storing Coal Tar

• Container: Metal or ceramic vessels with tight lids. Coal tar attacks some plastics and dissolves rubber
• Shelf life: Essentially indefinite — coal tar does not spoil or degrade significantly
• Temperature: Store in a cool, dark place. Coal tar remains liquid above ~20°C and thickens in cold weather
• Fire safety: Coal tar is flammable. Store away from heat sources and open flames
• Health: Avoid prolonged skin contact and inhalation of warm tar fumes

Coal tar production is a transformative capability for a rebuilding community. It represents the crossing point from purely biological resources into the world of industrial chemistry. Even the most basic coal tar production yields waterproofing, preservation, and fuel products that dramatically improve infrastructure longevity. With further distillation, it opens the door to antiseptics, solvents, and eventually the entire chemical industry that powered the modern world.