One of the many products derived from refining is lubricating oil, from which a byproduct called slack wax is obtained. Slack wax is a mixture of oil and wax
Crystallization: Slack wax is heated, mixed with solvent and then cooled. As it is cooled, wax crystallizes out leaving oil in solution. Wax specifications such as melt point, penetration, and oil content are controlled primarily by the amount of solvent added, the rate of cooling and the temperature from the crystallization process.
Filtration: The crystallized wax is filtered from the solvent in totally enclosed, inert gas blanketed, rotary drum filters. In order to obtain the low oil content required in final wax products, two and sometimes three stages of filtration are required.
Solvent Recovery: Two streams come from each drum filter, one containing the wax and some solvent and the other containing extracted oil and solvent. These streams go to the solvent recovery plant where solvent is removed by continuous distillation in steam-heated kettle heat exchangers and stripping towers. The recovered solvent is recycled to the crystallization process and to the drum filters as a wash. The solvent-free wax and oil streams go to separate storage. At this point the wax is known as a "product wax" and the oil is called "foots oil". The product wax is usually processed further and most of the foots oil is sold as catalytic cracker feedstock.
De-coloring & De-odorizing: To produce a "fully refined" wax from a product wax requires that the wax be passed through a bed of clay to remove color and through a vacuum stripping tower for odor removal. The de-coloring operation is known as "percolation" and is a batch process. The clay is regenerated before reuse by passing it through a multiple hearth furnace to remove the absorbed color bodies.
Blending and Manufacturing - Fully refined paraffin waxes are blended together to give certain desired properties such as melt point and penetration. These blended waxes are then either sold in a liquid state or converted into slabs, pastilles or granules. Blended waxes are also used for base stock for further blending with other petroleum based products such as resins and polymers to incorporate special properties such as flexibility, toughness and/or gloss.
Foots oil or residue wax, is a byproduct obtained by slack wax de-oiling or sweating in the paraffin wax manufacturing in the paraffin wax manufacturing process. It is used in textile, leather and rubber industries, as petroleum jelly and white oil manufacturing.
Slack Wax can be used as blending components or water proofing agent in the manufacture of various industrial products such as candles, canvass coatings and composite wood panels. These waxes can also function as controlled release agents for various chemicals and fertilizers.
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