Microwave-assisted pyrolysis of pine wood waste: system development, biofuels production, and characterization

In this work a pyrolysis system heated by microwave radiation (microwave-assisted pyrolysis, MAP) was developed to produce bio-oil, biochar, and biogas using pine wood residue as feedstock. For this purpose, a multimode microwave cavity was modified to allocate a quartz reactor used for pyrolysis. Some pieces of SiC were used as microwave absorbent material, which were placed externally to the quartz reactor (non-premixed approach), allowing a fast heating rate and cooling down the reactor. After assembling the system, the performance of the proposed MAP approach was investigated through the microwave irradiation time (10, 15, and 20 min) and the temperature of the process (500, 600, and 700 °C). The best results were obtained with 500 °C and a total process time of 10 min, which produced 65 %, 33 %, and 2 % of bio-oil, biochar, and biogas, respectively. Higher temperatures (600 or 700 ºC) resulted in an oily phase with higher acidity, besides a non-significant increment in the yields. The yields obtained using the proposed MAP approach were compared with those obtained using conventional pyrolysis (47 %, 32 %, and 21 % of bio-oil, biochar, and biogas, respectively). The biochar produced by MAP presented a high heating value (HHV) of 26 MJ/kg. As the main advantages of the proposed MAP approach, it is possible to highlight the shorter pyrolysis time, faster heating and cooling rates, no feedstock pretreatment before pyrolysis, nor the use of catalysts, and it was considered a clean source of production of bioproducts.