Critical point drying: An effective drying method for direct measurement of the surface area of a pretreated cellulosic biomass

The surface area and pore size distribution of Eucalyptus samples that were pretreated by different methods were determined by the Brunauer-Emmett-Teller (BET) technique. Three methods were applied to prepare cellulosic biomass samples for the BET measurements, air, freeze, and critical point drying (CPD). The air and freeze drying caused a severe collapse of the biomass pore structures, but the CPD effectively preserved the biomass morphology. The surface area of the CPD prepared Eucalyptus samples were determined to be 58-161 m²/g, whereas the air and freeze dried samples were 0.5-1.3 and 1.0-2.4 m²/g, respectively. The average pore diameter of the CPD prepared Eucalyptus samples were 61-70 Å. The CPD preserved the Eucalyptus sample morphology by replacing water with a non-polar solvent, CO₂ fluid, which prevented hydrogen bond reformation in the cellulose.