Extensive research on the effects of cellulose thermal pretreatment on char yields without cooling between the thermal pretreatment steps (step 1 between 250 °C and 290 °C from 0 to 999 min, step 2 at 370 °C from 60 min to 999 min, and the final step at 500 °C for 25 min) was performed by Varhegyi