Metalworking lubricants are widely used in the aluminum industry for reducing the thickness of sheet metal in rolling mills. These lubricants are usually emulsions wherein a small quantity of oil is admixed with a larger volume of water. The lubricants lubricate an interface between the rolls and sheet metal, and they cool the metal as it passes between the rolls. After prolonged use, the oil in these systems becomes contaminated with finely divided metal particles, metal oxide particles, and other extraneous matter such as mill dirt. These contaminants decrease process efficiency, reduce the activity of the oil as a lubricant and eventually lead to smudging and other surface defects in the product.
When the lubricant is contaminated, its usefulness is reduced because of the difficulty of emulsification and because the metal contaminants and other suspended materials furnish a source of an undesired abrasive. Accordingly, it is desirable to remove solid contaminants from the lubricants so that they can be reused.
In both ferrous and non-ferrous metalworking operations, filtration systems are customarily established for reclaiming hydrocarbon oils from used lubricants. In these systems, the oil is separated from water and then the oil is filtered through a particulate filter medium. Some suitable filter media include calcined diatomaceous earth, sand and wood pulp. Diatomaceous earth is particularly preferred. The diatomaceous earth has an average particle size in the range of about 1-30 microns.
In the prior art, used diatomaceous earth has typically been discarded after being used to filter lubricant oils. However, the discarded diatomaceous earth poses a potential environmental hazard because of its residual oil content. Accordingly, there is a need for a process capable of reclaiming residual oil from used diatomaceous earth rather than discarding the oil together with the diatomaceous earth.
Lubricant compositions used in aluminum rolling mills generally contain mineral or synthetic oil together with various oil additives. The oil additives are generally organic compounds such as ethanolamines, carboxylic acids, alcohols and esters. One important advantage of the present invention is that our process will recover these additives together with the mineral or synthetic oil.
Another important advantage of the present invention is that our process avoids extracting the used filter medium with hydrocarbon solvents such as benzene, toluene, methanol and tetrahydrofuran. These solvents pose serious health, safety and environmental hazards and they dilute oil recovered from the process unless considerable energy is devoted to distilling them off.
A principal objective of the invention is to provide an efficient and economical process for extracting oil from oil-contaminated solid particulate filter media.
A related objective of the invention is to provide a process for extracting oil from oil-contaminated filter media wherein the process avoids using organic solvents such as benzene, toluene, methanol and tetrahydrofuran. Prior art processes relying upon such organic solvents inevitably release harmful pollutants into the environment and pose serious health hazards to persons inhaling or ingesting them.
Additional objectives and advantages of our invention will become readily apparent to persons skilled in the art from the following detailed description.