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[Display omitted] • WTE assessment of biomass residue valorization pathway. • Optimization of WTE via multi-criteria decision method. • Pequi seed without extractives reported improved biochar properties. • Optimal gasification condition was obtained with O 2 /H 2 O/N 2 carrier gas. • WTE could be optimized by the seed fat extraction previously to pyrolysis. The waste-to-energy (WTE) valorization pathway of Caryocar brasiliense (pequi) seeds was investigated via pyrolysis, gasification, and transesterification to understand its potential as biochar, syngas, and biodiesel. First, the pyrolysis (300–700 °C) was conducted in N 2 atmosphere for pequi seeds (PS) and pequi seeds without its extractives (PSWE), characterizing its biochar properties. The PSWE was then gasified at 1000 °C under O 2 /N 2 , O 2 /CO 2 /N 2 and O 2 /H 2 O/N 2 atmospheres to evaluate the characteristics of the producer gas. The PS extractives were then transesterified and characterized for biodiesel production. Finally, a multiple-criteria decision analysis assessed the PS products' potential within the thermochemical routes. The results evidenced better biochar (up to 22.29% HHV enhancement, higher mass and energy yield, up to 75.9 and 85.5% reduction of O/C and H/C, respectively, and enriched N content) via PSWE pyrolysis than PS considering biofuel application and optimistic perceptions for soil amendment. This indicates that the preceding extraction of vegetal fat from PS strengthens the WTE by including further processing of extracted oil. The produced syngas under O 2 /H 2 O/N 2 gasification atmosphere showed better applicability as a biofuel (16.37 MJ·kg−1 lower heating value, 107.33% cold gas efficiency, and 113.55% carbon conversion efficiency) with up to 24% higher success rate. The transesterification of the extractives revealed its potential (98% conversion rate) for use as feedstock for in situ power generation, or blended for biodiesel production. The results provide insights into the circular economy in agro-extractivist communities that may support Brazil's small and medium agro-food industries with their energy demands. [ABSTRACT FROM AUTHOR]

Biodiesel production faces environmental and economic challenges due to the use of homogeneous catalysts, such as NaOH, KOH, NaOCH 3 , and KOCH 3. Despite their good activity, these catalysts are toxic and almost impossible to recycle/reuse. Heterogeneous catalysts, otherwise, can be reused and easily separated from the final product, resulting in more sustainable and cost-effective production. However, these catalysts leach, losing activity through reaction cycles and contaminating the biodiesel This review has therefore addressed the use of CaO – a promising catalyst for biodiesel synthesis – and various biochar-derived catalysts. Particular attention was paid to studies involving the use of CaO in a biochar matrix (CaO/Biochar), given the support essential role in making the CaO use feasible. The use of catalysts derived from sugarcane bagasse biochar was also highlighted, given this biomass importance, especially in Brazil. Studies have shown that biochar-derived catalysts have good activity, excellent stability, and can be reused for up to 10 cycles. Concerning CaO/Biochar, it was found that biochar significantly reduced Ca2+ leaching, but there is still a need to further reduce the Ca2+ release into biodiesel. There is also a need to give more focus on CaO leaching. Finally, a lack of studies on the use of catalysts derived from sugarcane bagasse biochar is notiable, showing no study involving the CaO-embedded sugarcane bagasse biochar. • There are no studies about biodiesel synthesis with CaO/Sugarcane biochar. • Biochars from different sources significantly reduced the Ca2+ leaching. • Biochar-based catalysts provided nearly 100 % biodiesel yield under relatively mild conditions. • Biochar support significantly increases catalysts' reusability. • Ca– O –Si bonds may be associated with the CaO anchoring. [ABSTRACT FROM AUTHOR]