Measuring the concentration of carboxylic acid groups in torrefied spruce wood

► Methylene blue sorption and titration were used to quantify the carboxylic groups. ► More than 50% of the carboxylic acid sites decomposed during 30 min. at 240 °C. ► The change in carboxylic acid content agrees with moisture content results. ► These methods can be used to help choose torrefaction conditions.