Torrefaction and low temperature carbonization of oil palm fiber and eucalyptus in nitrogen and air atmospheres

► Property variation of biomass pretreated in nitrogen and air atmospheres is studied. ► An herbaceous biomass (oil palm fiber) and a wood (eucalyptus) biomass are considered. ► The reaction temperature is in the range of 250-350 °C and the duration is 1 h. ► An energy-mass co-benefit index (EMCI) is introduced to seek the optimum operation. ► EMCI simultaneously considers energy yield and solid yield.