The heating rate and final temperature impacts on the coconut shell char structure characteristics during photo-thermal pyrolysis

The use of solar energy for biomass pyrolysis can help reduce carbon emissions in the process as well as enhance the efficient utilization of biomass resources. In this work, the solar concentrated photo-thermal pyrolysis process was considered and simulated. The characteristics of the coconut shell char generated at different heating rates (50 ℃/min, 200 ℃/min, and 500 ℃/min) and final temperatures (400 ℃, 600 ℃, and 800 ℃) were analyzed and evaluated. The results showed that the char's pore volume and the specific surface area increased from 0.021 cm³/g and 9.401 m²/g to 0.085 cm³/g and 75.887 m²/g with the increase in the heating rate and final temperature from 50 ℃/min and 400 ℃ to 500 ℃/min and 800 ℃, respectively. Moreover, the increase in the heating rate was mainly useful for creating a larger pore volume, while a higher final temperature contributed to the generation of micropores. Compared to the heating rate impact, the final temperature significantly affected the carbon skeleton structure and the surface functional group structure of char. As a result, at higher temperatures, the char became more aromatic and carbonaceous due to the splitting of substitutional groups. The hydrogen content of the coconut char was greatly reduced to about 20 % of the raw material at 800 ℃. In addition, a higher heating rate caused more O-bonds to break. The oxygen content was also found to decrease from 49.00 % to 46.44 % with the increase in the heating rate at the same final temperature of 800 ℃.