Biomass pyrolysis with alkaline-earth-metal additive for co-production of bio-oil and biochar-based soil amendment

Abstract The alkaline-earth-metal (AEM) has a good performance on modification of both bio-oil and biochar during biomass pyrolysis. In this work, the pyrolysis of rice husk (RH) in the presence of CaO, CaCO3, MgO and MgCO3 was comparatively studied for selecting an appropriate AEM additive to balance the qualities of pyrolytic products. Pyrolysis of RH with the AEM additives could decrease the acids content and increase the hydrocarbons content in bio-oil. Compared with the Ca-additives (i.e., CaO, CaCO3), the Mg-additives (i.e., MgO, MgCO3) were more beneficial for enhancing the hydrocarbons production. The addition of biochar to soil can significantly enhance the water retention. RHC-MgCO3 had a maximum water retention capacity, while RHC-MgO had a minimum water retention capacity due to its lowest specific surface area. Additionally, the Mg-modified biochar had a much higher nutrient (i.e., K+, PO43−) adsorption capacity. In particular, RHC-MgO with a lowest specific surface area had a highest PO43− adsorption capacity, which was evidenced by the adsorption of PO43− onto biochar mainly controlled by the chemisorption process. PO43− adsorbed in the RHC-MgO released rapidly indicating its low PO43− retention capacity. In general, MgCO3 would be an appropriate candidate that is used in pyrolysis of biomass for co-production of bio-oil and biochar composite with high capacities of water/nutrient adsorption and retention for soil amendment.