Pharmaceuticals of Paraffin Wax

Paraffin wax is a white or colorless soft, solid wax that is composed of a complex mixture of hydrocarbon derivatives with the following general properties: (i) nonreactive, (ii) nontoxic, (iii) water barrier, and (iv) colorless. Paraffin wax is characterized by a clearly defined crystal structure and has the tendency to be hard and brittle with a melting point typically in the range 50–70°C (122–158°F). On a more specific basis, petroleum wax is of two general types: (i) paraffin wax in crude oil distillates and (ii) microcrystalline wax in crude oil residua. The melting point of wax is not directly related to its boiling point because waxes contain hydrocarbon derivatives of different chemical nature. Nevertheless, waxes are graded according to their melting point and oil content.

 

In the process for wax manufacture known as wax sweating (Parkash, 2003; Gary et al., 2007; Speight, 2011, 2014; Hsu and Robinson, 2017; Speight, 2017), a cake of slack wax (paraffin wax from a solvent dewaxing operation) is slowly warmed to a temperature at which the oil in the wax and the lower melting waxes become fluid and drip (or sweat) from the bottom of the cake, leaving a residue of higher melting wax. However, wax sweating can be carried out only when the residual wax consists of large crystals that have spaces between them, through which the oil and lower melting waxes can percolate; it is therefore limited to wax obtained from low-boiling paraffin distillate.

 

Wax recrystallization, like wax sweating, separates slack wax into fractions, but instead of using the differences in melting points, it makes use of the different solubility of the wax fractions in a solvent, such as the ketone used in the dewaxing process. When a mixture of ketone and slack wax is heated, the slack wax usually dissolves completely, and if the solution is cooled slowly, a temperature is reached at which a crop of wax crystals is formed. These crystals will all be of the same melting point, and if they are removed by filtration, a wax fraction with a specific melting point is obtained. If the clear filtrate is further cooled, a second crop of wax crystals with a lower melting point is obtained. Thus, by alternate cooling and filtration, the slack wax can be subdivided into a large number of wax fractions, each with different melting points.

Comments are closed