There are three basic grades of glycerol [4]. Crude glycerol, which is
how biodiesel-waste glycerol is classified, contains 70–90% glycerol. For
use in industrial application, glycerol must be in technical grade (96.0–
99.5% glycerol). To be used in cosmetics, pharmaceuticals, and the food
and drink industry, the glycerol must be 99.5–99.7% pure. Refining the
crude glycerol into pure glycerol is time and energy intensive [5]. It
must go through a process of neutralization, stripping, filtration/centrifugation,
and vacuum distillation before it reaches the purity standards
required [6]. These purification methods are generally only accessible to
larger biodiesel manufacturers because of the time and expense required
to perform this purification process.