For pharmaceutical purposes, regardless of the source of origin (synthesis, saponification of fats, biodiesel production, or fermentation), glycerin is thoroughly purified in several stages: distillation, deodorization, decolorization.
Since the production of biodiesel, the synthesis of glycerin from petrochemical propylene has ceased to be profitable. Currently, excess glycerin is processed into compounds previously obtained from propylene.
During the semi-synthetic preparation of glycerin and its purification, the entire carbon-oxygen skeleton does not undergo any changes - so we can say that it is the natural glycerin, only purer.