Algal bio-oil refinery: A review of heterogeneously catalyzed denitrogenation and demetallization reactions for renewable process

Severe ecological and environmental problems such as acid rain, greenhouse gas emission, atmospheric pollution etc. emerged with the wide application of fossil fuels force human beings to seek new green energy to alleviate the heavy dependency on those petrochemical products. Converting renewable microalgae biomass into liquid fuels is one of the promising way. However, the existence of nitrogen heteroatom and metal elements in microalgal bio-crude oil will extremely deteriorate the quality and inhibit the commercial utilization of microalgal bio oil. It is highly necessary to remove those nitrogen and metal elements from microalgal bio oil phase to meet the strict environmental and clean production requirements. Therefore, this paper extensively reviewed the updated results on catalytic denitrogenation and demetallization of microalgal bio-crude oil, including summary on the mechanism of C–N bond breaking, reaction pathways of major N-containing and metalloporphrins model compounds. Besides, the challenges facing the catalytic process, for example, catalyst stability and operating conditions during the denitrogenation and demetallization reactions were appraised as well.