Temperature plays a crucial role in determining the properties of biochar.
When the pyrolytic temperature rises, the yield of sludge biochar decreases.
The pH value of the biochar shifts from acidic to alkaline as the temperature increases.
Higher temperatures significantly improve the specific surface area of the biochar.
As the temperature rises, the degree of aromatization and stability of the biochar also increase.
This means that the biochar becomes more aromatic and stable at higher temperatures.
On the other hand, the amount of oxygen functional groups in the biochar decreases with increasing temperature.
The properties of biochar can vary depending on the feedstock biomass and the process conditions used in its production.
Different types of biomass, such as pine wood, wheat straw, green waste, and dried algae, can be used to produce biochar.
The highest treatment temperature (HTT) and residence time during the pyrolysis process can also affect the properties of the biochar.
Some of the properties influenced by temperature and process conditions include the fixed carbon content, pH in solution, higher heating value, and BET surface area.
The fixed carbon content of the biochar increases with higher temperatures and longer residence times.
The pH in solution, higher heating value, and BET surface area of the biochar also increase with increasing pyrolysis temperature.
When biochar is added to soil, it initially reduces the rate of carbon mineralization compared to control soil samples.
This effect is more pronounced with biochars that have a higher fixed carbon content resulting from more severe thermal treatment.
This may be because the soil microbial community needs time to adapt to the new conditions.
Biochars with lower fixed carbon content, produced through mild thermal treatment, contain more volatile and easily biodegradable carbon compounds.
To produce high-quality biochars for agricultural use, slow pyrolysis is often considered the most feasible production process.
Slow pyrolysis involves heating the biomass in an oxygen-limited or oxygen-free environment at atmospheric pressure.
The heating rates are typically between 1 and 30 °C min−1.
Slow pyrolysis can result in biochar yields of up to 30 wt% on a dry feedstock weight basis.
However, the yield and properties of the biochar depend on factors such as the biomass feedstock, heating rate, pyrolysis temperature, and vapour residence time.
Among these factors, the highest treatment temperature has the greatest overall influence on the final product characteristics.
In summary, temperature affects various properties of biochar including yield, pH, specific surface area, degree of aromatization, stability, and the amount of oxygen functional groups.
The properties of biochar can also be influenced by the feedstock biomass and process conditions used in its production.
Slow pyrolysis is often preferred for producing high-quality biochars for agricultural use.
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