Can the pyrolysis of lignocellulose unlock efficient production of biochar?

Biochar is a carbon-containing material formed by the pyrolysis of biomass under anoxic conditions. It features a well-developed pore structure and excellent adsorption performance, and holds significant value in aspects such as soil remediation, carbon sequestration, and environmental restoration. According to statistics, if 0.4% of biochar is added to the global agricultural soil every year, it can sequester an amount of carbon equivalent to 12 billion tons of carbon dioxide. However, the current high production cost of biochar restricts its large-scale application. Among them, although lignocellulosic biomass (such as straw and forestry waste) has a wide range of sources, the traditional pyrolysis process has problems such as uncontrollable product distribution and low energy conversion efficiency. So, can the efficient preparation of biochar be achieved by systematically optimizing the parameters of the pyrolysis process?

Nguyen Xuan Loc and Do Thi My Phuong from Can Tho University in Vietnam have conducted an in-depth discussion on this issue, and the relevant research has been published in Frontiers of Agricultural Science and Engineering (DOI: 10.15302/J-FASE-2024597).

The pyrolysis technologies of lignocellulose include traditional methods and emerging methods. The traditional slow, fast, and flash pyrolysis each have their own advantages and disadvantages. Slow pyrolysis has a slow heating rate and takes a long time, but it can produce biochar with high yield and good quality. Fast and flash pyrolysis focus more on the production of bio-oil. In contrast, emerging technologies have obvious advantages. Microwave-assisted pyrolysis can utilize the rapid heating characteristics of microwaves to greatly improve the reaction efficiency; co-pyrolysis can exert a synergistic effect by mixing multiple raw materials to optimize product performance; hydrothermal carbonization can be carried out at a relatively low temperature, especially suitable for high-moisture biomass, which greatly expands the applicable range of raw materials; auto-pyrolysis can use the heat generated by its own reaction to significantly reduce energy consumption, achieving efficient utilization of energy. These new technologies provide more possibilities for optimizing the pyrolysis process.

Pyrolysis conditions and biochar modification technologies play a crucial role in shaping the properties of biochar. The pyrolysis temperature has a significant impact on the properties of biochar. Increasing the temperature can increase the fixed carbon content, enhance the aromaticity, and expand the surface area, but the yield will decrease accordingly. At the same time, changes in the residence time and heating rate will also change the characteristics of biochar. By optimizing the pyrolysis parameters and precisely controlling these factors, the yield and quality of biochar can be balanced. In addition, chemical and physical modification technologies can effectively improve the surface properties of biochar, enhance its effects in specific applications such as soil remediation and environmental purification, and expand the application range of biochar.

In conclusion, it is expected to achieve the efficient production of biochar by optimizing pyrolysis parameters and applying modification technologies.