One chemical industry that was ubiquitous in earlier times (1920's) was the wood distillation industry. The principle product, after processing, was a charcoal with low yields of chemical products. The wood used for distillation was air dried for 6 to 18 months. Artificial drying methods were later developed to shorten the drying time and better control the moisture content.
During distillation, wood is placed inside an oven and heating started. When wood is heated above 270C, it begins a process of decomposition called carbonization. If air is absent, the final product is charcoal (since there is no oxygen present to react with the wood). If air, which contains oxygen is present, the wood will catch fire, and burn when it reaches a temperature of 400-500C. The final product is wood ash.
If wood is heated while away from air, moisture is first driven off, and until this is complete, the wood temperature remains at 100-110C. When the wood is dry, its temperature rises to about 270C, it spontaneously decomposes, and heat is emitted. This is the well-known reaction that takes place during charcoal burning.
The first distillate (condensation from the gases) is almost entirely water and it is not until about the 4th hour that the liquor slowly darkens and contains increasing amounts of acid. The crude condensate produced from the distillation of wood is called Pyroligneous Acid.
The crude Pyroligneous Acid is then refined by fractional distillation to separate a food grade version that is suitable for use in health products.
