Agricultural byproducts from nut processing present significant disposal challenges while offering potential opportunities for sustainable material recovery. Converting these hard shells into carbonized materials provides a viable path toward carbon sequestration and soil enhancement. Researchers evaluated the thermal conversion of almond and pistachio shells using both micro-scale thermal analysis and fixed-bed processing to establish operational parameters and product characteristics.

The thermal breakdown profiles demonstrated clear operational differences between the two feedstocks. Almond shells underwent a broad primary decomposition phase, whereas pistachio shells degraded through a distinct two-stage process. Kinetic modeling using a first-order reaction structure confirmed that pistachio shells required higher apparent activation energy for thermal conversion than almond shells. Model predictions closely matched experimental measurements across multiple heating rates.

Processing in the fixed-bed system demonstrated that operational temperature, residence timeResidence time refers to the duration that the biomass is heated during the pyrolysis process. The residence time can influence the properties of the biochar produced.   More, and shell variety significantly affected overall material recovery. Almond shells yielded consistently higher amounts of carbonized product than pistachio shells under matched conditions. Elevating processing temperatures or extending residence duration reduced total solid recovery across all treatments as volatile components escaped. Furthermore, fixed-bed processing achieved higher yields than micro-scale thermal testing, highlighting differences in heat and mass transfer.

Chemical evaluation of the resulting products revealed distinct mineral and structural differences. Almond shell carbonized material contained higher concentrations of nitrogen, calcium, potassium, magnesium, and soluble salts than the pistachio material. Increasing processing temperature led to progressive carbonization, loss of hydroxyl functional groups, and relative enrichment of stable aromatic structures. However, the higher soluble salt content in almond material suggests application rates must be managed carefully to avoid elevated soil conductivity.

Source: El Mashad, H. M., Edalati, A., Chiou, B.-S., McCaffrey, Z., Cao, T., Hart-Cooper, W., Zhang, R., & Mitloehner, F. (2026). PyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More Kinetics and BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More Production of Almond and Pistachio Shells in a Fixed-Bed Pyrolyzer. Bioresources and Bioproducts, 2(3), 17.