AbstractBACKGROUNDOil palm shell (OPS) is a biomass widely available from palm oil mills. Self‐purging microwave pyrolysis (SPMP) was performed to produce carbon‐rich biochar from OPS for the adsorption of methylene blue dye. The effect of feedstock amount on the pyrolysis temperature, yield and characteristics of the biochar were investigated.RESULTThe amount of feedstock was directly proportional to the final pyrolysis temperature. The pyrolysis reached a maximum final temperature of 760 °C when ≥300 g of OPS was loaded into the reactor without microwave absorbent. A heating rate of up to 105 °C min−1 was recorded, producing a yield of 40 wt% of biochar at a short processing time of 20 min. The biochar obtained at 700 °C showed relatively low volatile matter (24 wt%), higher fixed carbon content (66 wt%), carbon (78.5 wt%), oxygen (17.7 wt%), a highly porous structure with high BET surface area of 410 m2 g−1 and pore volume of 0.16 cm3 g−1, and recorded a methylene blue dye adsorption efficiency of 20 mg g−1.CONCLUSIONThe SPMP approach showed exceptional promise to produce biochar with low H/C ratio (0.5) and O/C ratio (0.2), which indicated a high degree of carbonization and stability of the biochar to act as a durable agent in wastewater treatment. © 2018 Society of Chemical Industry