Pyrolysis and the Production of Biochar

In a previous post, we introduced pyrolysis, which can be defined as a "process of thermochemical decomposition with the application of heat and in absence of oxygen."

This long definition is necessary, because the term "combustion" cannot be used when talking about pyrolysis, as combustion only happens in presence of oxygen. In other terms, pyrolysis reproduces in a very short time a process that in nature requires thousands of years, which is the irreversible transformation of organic material in fossil fuels.

Depending on the quantity of energy applied and on the final temperature, there will be different types of fuels from pyrolysis, liquid, gaseous, or solid form, such as biochar, biofuels, methane, hydrogen, carbon monoxide and dioxide.

At low temperatures (up to 450°C), pyrolysis will mainly produce biochar and charcoal. High temperatures (above 800°C) will produce gasses, while intermediate temperatures will mainly generate biofuels.

The two solid materials generated by the thermal decomposition process, charcoal and biochar, have very different uses. While charcoal is used as a domestic fuel, the high porosity of biochar makes it particularly suitable as fertilizer.

Biochar was not discovered by Industrial Revolution: this type of vegetal coal (as well as the pyrolysis process to produce it) was already known by populations in the Amazon area, and was called terra preta (black soil) by Portuguese explorers.

Another advantage of biochar is the so-called carbon sequestration, whereby CO2 is accumulated underground instead of being released in the atmosphere.