Blended tropical almond residue for fuel production: Characteristics, energy benefits, and emission reduction potential

Abstract

Besides the nuts produced from almond cultivation, it also generates several million tonnes of residue that include hulls, shells, leaves, pruning, and inedible kernels which are valuable feedstocks in clean fuel production. In this article, blended tropical almond residue of two particle sizes (NT15 and NT25) were investigated. The heating, proximate and ultimate values were reported while the chemical composition of the ash was determined. Also, the pore structure and the inherent functional groups were determined for the particle sizes. The thermogravimetric analysis was also carried out to determine the thermal behaviour at different heating rate (10, 15, 30 oCmin−1) in inert environment while the kinetic parameters were evaluated based on three non-isothermal methods (Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and distributed activation energy model). Notably, the ash content was higher in the finer particle size NT15 (1.11%) compared to NT25 (0.87%). Low pore surface area (1.218–0.970 m2g-1) agrees with literature values while a slight difference in pore size distribution was observed during adsorption at higher relative pressure. A representation of mixed functional groups whose wavelength falls within 527 cm−1, 848 cm−1, 991 cm−1, 1035 cm−1, 1179 cm−1, 1597 cm−1, 1772 cm−1, 2849 cm−1 was observed with no significant difference between the two particle sizes. The average activation energy, Ea for NT15 and NT25 were in the range of 127.4–131 kJmol-1 and 129–133 kJmol-1 respectively for all the three methods, with the lowest Ea (127.4 kJmol-1) and compensation factor, K0 (1.29E+12 min−1) obtained for the smaller particle size (NT15) based on Kissinger–Akahira–Sunose method. Finally, the energy benefits and CO2 emission reduction potential were estimated. The highest energy potential is in USA (4.17 Mtoe) while Morocco has the highest emission reduction at 3.28%. The information obtained from this study can be used in the scaling up of bioreactors which can further support the global clean energy drive and reduce environmental pollution.