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 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 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 samples were 61⁻70 Å. The CPD preserved the sample morphology by replacing water with a non-polar solvent, CO₂ fluid, which prevented hydrogen bond reformation in the cellulose.