The utilisation of waste biomass in biodiesel production as a sustainable energy source can lead to the incorporation of circular bioeconomy principles in the current economic systems. Herein, we synthesised a magnetically recyclable solid acid catalyst for the esterification of waste date seed oil. The catalysts possessed superparamagnetic behaviour and high saturation magnetisation, allowing them to be easily separated from the reaction mixture using an external magnetic filed. The esterification reaction was modelled and optimised by RSM (Design Expert program) and parametric study. The magnetic solid acid catalyst showed high catalytic performance with 91.4% biodiesel yield with optimum conditions of residence time, catalyst loading and temperature of 47 min, 1.5 wt %, and 55 °C, respectively. The solid catalyst was easily recovered by simple magnetic decantation and reused five consecutive times without significant degradation in its catalytic activity. This approach of using waste date seed coupled with cheap magnetic solid acid catalyst has the potential to create more sustainable and cost-effective catalytic systems for biodiesel production. This will complete the full cycle of waste date seed sustainably and facilitate the development of circular bioeconomy. The LCA results by using CML-IA baseline V3.06 midpoint indicators, for 1000 kg of biodiesel production showed the cumulative abiotic depletion of fossil resources over all the processes as 19037 MJ, global warming potential as 1114 kg CO2 eq, and human health toxicity as 633 kg 1,4-DB eq (kg 1,4 dichlorobenzene equivalent). The highest damage in all categories was observed during catalyst preparation, and reuse, which was also confirmed in endpoint LCA findings performed using ReCiPe 2016 Endpoint (E) V1.04.
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