Why is oxygen-deficient heating applied to wood in the traditional process of charcoal making? What are the specific chemical reaction principles involved in this process?

In the traditional process of charcoal making, oxygen-deficient heating of wood is a crucial step. This operation not only affects the quality of the charcoal but also determines its combustion performance and uses. So, why is an oxygen-deficient environment used? What chemical reactions occur during this process?

First, oxygen-deficient heating prevents the wood from completely burning. In the presence of sufficient oxygen, wood will completely burn to produce carbon dioxide and water, which obviously cannot yield charcoal. By controlling the oxygen supply, the wood undergoes pyrolysis at high temperatures, releasing volatile components and leaving behind a carbon-rich solid material, which is charcoal.

Second, this process involves complex chemical reactions. In the initial stage of heating, the moisture in the wood evaporates first. As the temperature rises, the cellulose, hemicellulose, and lignin in the wood begin to decompose, producing a series of volatile compounds such as methane, methanol, acetic acid, etc. The release of these volatile substances gradually transforms the wood into a porous, carbon-rich structure.

Specifically, the pyrolysis reactions mainly include the following stages:

1. Dehydration stage (100-200℃): The moisture in the wood evaporates.
2. Primary pyrolysis stage (200-280℃): Hemicellulose begins to decompose, releasing volatile substances.
3. Main pyrolysis stage (280-500℃): Cellulose and lignin decompose extensively, producing charcoal and volatile products.
4. Carbonization stage (above 500℃): The residual carbon further reorganizes to form a stable charcoal structure.

Through oxygen-deficient heating, the wood is ultimately transformed into high-carbon-content charcoal, which has a high calorific value, low ash content, and excellent combustion performance. This traditional craft not only reflects the wisdom of the ancients but also provides valuable experience for modern carbon material science.