Montan wax
Contents
Description
Montan wax is a hard, brittle, lustrous wax extracted from lignites, principally in Central Europe and also mined in Australia, New Zealand, Czechoslovakia, Russia, Great Britain and in the United States. The coal is granulated, dried and solvent extracted to remove the wax. The crude wax is usually further processed to produce an acceptable market product. One type of refining is by vacuum distillation, using steam and producing the so-called "double-refined" montan wax. In a second a more important refining process, the wax may be deresinified by solvent processing, and then treated by chromic acid oxidation. The crude wax is dark brown and the refined wax of a yellowish color. The so-called white montan wax is a mixture of refined montan wax with paraffin wax. Depending on the geographical occurrence, the resin content of the wax varies. For example, the German deposits are noted for their relatively low resin content, thus yielding a satisfactory product more economically[1].
Process of Extraction
Crude montan wax is obtained from lignite (brown coal) by extracting it with a suitable solvent. The lignite is crushed or granulated and dried to a 10-12% moisture content. The granules are then sieved to remove powder therefrom, and the powder-free granules are extracted with a mixture containing about 85% benzene and 15%unrefined wood alcohol containing methyl and isopropyl alcohols. This extraction is normally carried out at 90-100ºC. the alcohols dissolve the cell walls of the brown coal granules and free the wax therefrom, thereby enabling the wax to be dissolved by the benzene. The wax solution is separated, and the solvent distilled off, leaving the crude montan wax as a residue. The crude montan wax is dark-colored and contains resinous and asphaltic impurities. The yield of wax is 10-18%[2].
Purification and Refining
The crude montan waxes are somewhat limited in their utility because of their dark color. In order to use them in the manufacture of esterified waxes, it is necessary to remove the excessive amount of resinous and asphaltic matters, and also to lighten the color. Various methods have been proposed and used to produce a montan wax of sufficiently light color to enable its use in those instances where light color is required. Strong acids have generally been used to refine the wax, although strong alkalies have also been employed. Distillation at low pressures produces a light-colored wax, but of altered composition. Selective solvents are also used as a means of purification of the semirefined wax. Although the various methods of bleaching result in a product of light color, the bleached waxes so produced tend to crystallize under certain conditions of use, ostensibly because of their high content of free wax acids of high molecular weight (26 to 29 atoms)[3].
Properties
| Melting Point | 72 -92 ºC |
| Specific Gravity | 1.00 |
| Acid Number | 15 - 85 |
| Saponification Number | 58 - 89 |
| Unsaponifiables | 35 - 45% |
| Iodine Number | 7.75 |
| Acetyl Number | 11.2 |
| Color | tan, brown |
| Dielectric Constant | 2 - 68 |
| Effective A.C. Conductivity | 25 -55 |
| Volume Resistivity | 270 - 630 |
Solubility
Montan wax is soluble in: benzol, carbon tetrachloride, chloroform, dichloroethylene, isopropyl ether, naphtha, tetralin, toluol, trichloroethylene, turpentine, xylol.
Montan wax solutions set more slowly than carnauba wax solutions and, therefore, should be filled into containers at a lower temperature. Pure montan wax can scarcely be scratched by the fingernail. It breaks with a conchoidal fracture. It is a good solvent (when melted) for basic dyes and shows good wetting and flow in oil solutions. It is the hardest of the natural nonvegetable waxes and is fairly resistant to oxidation.
The bleached or highly refined wax loses some of the listed characteristics, becoming softer and less emulsifiable[5].
Uses
It can be used in place of carnauba wax in many compositions because of its hardness, toughness, high melting point and emulsifiability; polish, rubber, printing-ink, electrical insulating compositions, leather finishes and dressings, carbon papers, grease, phonograph records, waterproofing[6].
Comparison of the properties of different waxes
| German Montan Wax |
Devon Lignite Wax |
English Peat Wax |
Scottish Peat Wax | |
|---|---|---|---|---|
| Melting Point ºC | 74 - 82 | 73 - 83 | 63 -68 | 64 - 73 |
| Acid Value | 33 | 30 | 50 | 48 |
| Saponification Value | 76 | 75 | 119 | 113 |
| Ester Value | 43 | 45 | 69 | 65 |
| Resin Content, % | 14 | 40 | - | 23 |
| Specific Gravity at 20ºC | 1.05 | 1.04 | 1.03 | - |
References
- ↑ Bennett, H., Commercial Waxes, Second edition, p. 109
- ↑ Warth, A. H.; The Chemistry and Technology of Waxes. Reinhold Publishing Corporation. Second Edition, p. 361
- ↑ Warth, A. H.; The Chemistry and Technology of Waxes. Reinhold Publishing Corporation. Second Edition, p. 362
- ↑ Bennett, H., Commercial Waxes, Second edition, p. 110
- ↑ Bennett, H., Commercial Waxes, Second edition, p. 110
- ↑ Bennett, H., Commercial Waxes, Second edition, p. 110
- ↑ Bennett, H., Commercial Waxes, Second edition, p. 113