Betulin isolation from birch bark by vacuum and atmospheric sublimation. A thermogravimetric study

Isolation of betulin from Betula papyfera bark can be performed both by chemical extraction or thermal sublimation. With the thermal sublimation method, no toxic nor expensive solvent is used. The scientific literature, however, reports very limited information about the sublimation method. In this work, a thermogravimetric study has been performed for the thermal sublimation of betulin from B. papyfera bark; the objective was to determine the optimum sublimation conditions. The study was carried out over a wide range of temperatures (30–550 °C) under two different pressures: atmospheric pressure and a pressure of 3.3 kPa. Under atmospheric pressure, the betulin sublimation takes place in the temperature range of 250–370 °C. Betulin evolves simultaneously with volatile materials evolving during the thermal decomposition of the bark. As a result, large amounts of impurities are found. Under a low pressure of 3.3 kPa absolute, the betulin sublimation temperature decreases by 50–70 °C. The betulin is, thus, more neatly separated from the bark thermal decomposition products. The remaining products can be separated from the betulin by choosing adequate condensation conditions.