Pyrolysis of Wood: Unlocking Hidden Potential of Waste Wood

Pyrolysis of wood is a fascinating thermal conversion process. Now it is gaining more and more attention due to its potential in converting waste wood into valuable biochar. The main product, biochar, can be used as a substitute for traditional charcoal. It can also be used in fields such as soil improvement, carbon sequestration, biochar animal feed, etc. This sustainable approach not only reduces wood waste, but also contributes to environmental protection and resource utilization. 

Pyrolysis of Wood
Pyrolysis of Wood

The Essence of Pyrolysis of Wood

At its core, pyrolysis of wood is a thermal conversion process that occurs in the absence of oxygen. It involves a complex series of chemical reactions. The primary reaction mechanism of a wood charcoal making machine is as follows:

  1. Drying: Through heating, at temperatures not higher than 150 ° С, the moisture of wood is evaporated. During this stage, the composition of the wood remains almost unchanged.
  2. Decomposition: At 150°С to 270°С, hemicelluloses and individual fragments of lignin in wood begin to decompose. And low molecular weight products like carbon oxides and methanol are formed. At 270° С to 450° С, cellulose, and lignin in wood undergo intense decomposition. As a result, abundant products of disassociation and char residue are formed.
  3. Calcination: At 450°С–550 °С, the residual functional groups are cleaved from the carbon skeleton. Thus, the impurities of charcoal are further discharged to form high-quality charcoal.
  4. Cooling: If the hot charcoal is discharged directly from the charcoal kiln, it will absorb oxygen from the air, and thus spontaneous combustion occurs. Therefore, the hot charcoal needs to be cooled before it can be released from the kiln.

Accessible Wood Raw Materials and Feeding Requirements

Waste wood

The wood selected for pyrolysis is generally wood waste rather than trunks that have greater utilization value. This helps to reduce the pyrolysis project cost and obtain the maximum benefit.

Wood waste from logging or pruning
Wood waste from logging or pruning of trees: These wastes usually include branches, bark, tree tops, branches, leaves, etc. They are the parts that have no direct use value in logging or pruning activities.
Wood scraps waste during wood processing
Wood scraps waste during wood processing: These wastes usually include wood chips, sawdust, wood shavings, etc. They are usually a by-product of wood processing or a substandard product.

Requirements for pyrolysis feeding

The moisture and particle size of wood have important effects on the pyrolysis process and the quality of the product. In general, the moisture of wood of pyrolysis is best kept below 15%, and the feed size is preferably 8 mm-12 mm.

Charcoal Making Machine for Pyrolysis of Wood

Products of Pyrolysis of Wood

Picture Product Characteristic Application
biochar biochar A highly porous and stable carbon-rich solid material It can be used as fuel.
It can improve soil fertility and water retention, thus improving agricultural yields.
Its carbon sequestration properties contribute to mitigating climate change by locking carbon in the soil for hundreds of years.
Biochar animal feed can reduce methane gas emissions from ruminants by regulating the digestive capacity of livestock.
bio-oil bio-oil A complex mixture of organic compounds It has the potential as a renewable industrial fuel.
It contains many organic molecules with high energy density, which can be used as chemical feedstocks.
wood vinegar A mixture of organic substances such as acetic acid, formic acid, and acetone It can be used for making pesticides, fungicides, wood preservatives and so on.


Benefits of Pyrolysis of Wood

biochar as sustainable energy
Sustainable Energy Production: Wood pyrolysis plays an important role in sustainable energy production. Its products, biochar, bio-oil, and syngas, provide a renewable alternative to conventional fossil fuels. This helps to reduce greenhouse gas emissions and dependence on finite resources.
waste wood management
Waste Management: Different from traditional incineration and landfill treatment, pyrolysis provides a new solution for waste biomass treatment. It helps reduce environmental pollution caused by landfills and incineration. It also promotes a circular economy.
climate change mitigation of wood pyrolysis
Climate Change Mitigation: The production and application of biochar in agriculture play a vital role in carbon sequestration. By incorporating biochar into soils, we can sequester carbon for extended periods. This helps mitigate climate change and improve soil health.

Factors Affecting the Pyrolysis of Wood

When it comes to factors that affect wood pyrolysis efficiency and product distribution, temperature, pressure, and catalysts are the three main concerns.


Temperature is one of the most important factors in the pyrolysis of wood. Generally, with the increase in temperature, the pyrolysis reaction rate will increase, but too high temperature may also lead to side reactions. It may reduce the yield of the target product. Studies have shown that the optimum temperature range for wood pyrolysis is between 300°C and 500°C. In this range, major components such as lignin, cellulose, and hemicellulose can be effectively converted into biochar and bio-oil, while reducing undesirable gases and ash generation.


Pressure can affect the rate of pyrolysis reaction and product distribution. Increasing pressure will reduce the solid product’s yield and help increase the yield of liquid products and gas products. However, excessive pressure can lead to limited mass transfer during the reaction, thus reducing the reaction rate. At present, most wood pyrolysis reactions are carried out under normal pressure to get biochar.


The catalyst plays a key role in pyrolysis of wood. It can increase the reaction rate and has an effect on the selectivity of the product. The acid catalyst is mainly used to promote the production of liquid bio-oi. The alkaline catalyst may increase the yield of solid biochar and improve its properties, making it more suitable for active carbon or other uses. The alkaline catalyst also helps to reduce tar production, thus reducing carbon accumulation and clogging problems in equipment. Therefore, when selecting a catalyst, it is necessary to make a reasonable choice according to the type and distribution of the desired product.

wood pyrolysis to make biochar

Future Development of Pyrolysis of Wood

With the increasing demand for sustainable energy, wood pyrolysis technology will continue to be widely concerned and applied. To better achieve the efficient use of biomass resources, its future development direction will involve improvement and innovation in different aspects. The following are some possible improvements and innovations:

Optimization of pyrolysis reaction conditions

Optimize pyrolysis reaction conditions

Future research will continue to seek optimal pyrolysis reaction conditions. including more appropriate temperature, pressure, etc. Through more accurate control of reaction conditions, the wood will undergo multiple pyrolysis stages at different temperatures. This facilitates finer product control of the proportional distribution of biochar, bio-oil, and syngas.


Research more efficient catalysts

Catalysts play a key role in the wood pyrolysis process. The use of new catalysts in a biomass pyrolysis plant, such as nanocatalysts and composite catalysts can increase the yield of the target product and reduce the generation of by-products. Thus it brings improvement in the economic value of the overall product.

bio-oil treatment technology

Develop bio-oil treatment technology

Bio-oil, a renewable liquid fuel, holds significant development potential. Yet, challenges in stability and energy density persist. Future efforts will focus on increasing the purity of bio-oil through efficient separation and purification techniques. Attention will also be paid to optimizing its stability to make it more suitable for use as a biofuel and chemical feedstock.


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