Green Solvent Extraction of Betulin from Birch Bark

Betulin, found in the outer layer of birch bark at levels of up to 20-30% by mass, is a promising monomer for biobased polyester production and also has potential other uses in the pharmaceuticals industry. Currently, larger scale betulin extraction is done with hazardous solvents such as chloroform or benzene requiring multiple process steps and large amounts of waste. This research attempts to create a greener process for betulin extraction and purification through the use of green solvents, which are solvents that have properties such as high recyclability or low toxicity for humans and the environment. Select green solvents were screened for their effectiveness for betulin extraction through yield and selectivity measured with liquid chromatography/ mass-spectrometry. The screenings were conducted through a series of small-scale extractions. It was determined that promising solvents include ethanol or a mixture of ethyl acetate and ethanol, both of which are also renewable. The methodology for extraction was also optimized including extraction technique as well as product purification. It was found that reflux boiling, combined with both filtration and antisolvent (water) precipitation, was the optimal method for creating betulin with high yield and relatively high purity. These results provide a foundation for future large-scale extraction of betulin from birch bark.