Biochar

Pyrolysis is a thermochemical process in which the organic material is decomposed into liquid (pyrolysis oil), solid (char) and gaseous (CO2, H2, CO, CH4) products. The process is carried out at moderate-to-high temperatures ranging from 300 ◦C to 650 ◦C and in the complete absence of oxygen. The type and particle size of biomass used, the heating rate and the residence times of, for instance, the feedstock and the generated primary pyrolysis vapours, are the major parameters that affect the performance and outcome of the pyrolysis process. The successful optimization of such process parameters determines the quantity, composition and quality of the products of the process [41,42]. There are several reports in the literature on AP pyrolysis (Table 1) [9,43–45]. In the work of Kosakowski et al. [43], the rapid pyrolysis of agricultural waste biomass (including AP) resulted in obtaining biochar characterised by higher combustion heat and calorific values than the biomass used [43]. Guerrero et al. [44] investigated the optimal conditions for the slow pyrolysis of AP for the production of gaseous products that can be used as a feedstock for the production of H2 [44]. Zhang et al. [45] used the biochar obtained in the AP pyrolysis process to create magnetic biochar that could effectively enrich the low concentration of Ag(I) ions in effluents [45]. Xu et al. [9] investigated the effect of the temperature and the type of biomass used on the production of biochar. The results showed that grape residues produced the highest biochar yield, while AP produced the least biochar [9]. According to Table 1, the biochar resulting from the pyrolysis/carbonization of AP had a net caloric value of between 25 and 31 MJ/kg. For comparison, a net value of good-quality milled coal, e.g., eco peat coal, is in the range of 24–26 MJ/kg [45].


*Materials* **2022**, *15*, 1788

**Table 1.** Apple pomace pyrolysis.
