Influence of microwave power, metal oxides and metal salts on the pyrolysis of algae

•The energy cost was considered in order to get absolute productivity.•1500W was the optimal pyrolysis power to achieve bio-oil.•There was a descending branch on the temperature curve after mixing CaO.•Microwave absorption effect of three metal oxides was MgO>CaO>CuO.•MgO showed the best effect when taking power consumption into account. The work was to investigate the influence of microwave power, metal oxides and metal salts onto the pyrolysis of algae (4.55wt.% moisture). It was found that the heating rate and the final temperature would increase as enhancing the microwave power. When microwave power increased from 750W to 2250W, the yield of solid residue decreased by 22.05%, and gas yield increased 39.45%. After adding 5% (mass basis) CuO and MgO, the yield of solid residue and bio-oil appeared the greatest decreasing ranges of 14.35% and 11.04%, respectively. Electrical energy consumption increased by 1.44% and reduced by 40.76% after CuO and MgO was added, separately. When algae was mixed with 5% (mass basis) MgCl2, ZnCl2 and NaH2PO3, respectively, the yield of solid residue increased by 3.98%, 1.13% and 2.31%, and the bio-oil yield increased by 6.3%, 16.92% and 0.71%, respectively. The effect of microwave absorption was ZnCl2>NaH2PO3>MgCl2.