The adsorptive (activated carbon) filters that generate attraction on the surface have some issues, such as limited usage cycles and a reduction in their adsorption capacity after absorbing oil. The primary materials used in adsorptive air filters, such as wool, oil felt, and cotton, lose their structural advantages and quickly become ineffective once they are saturated with liquid. Mechanical separators and mesh-type air filters are typically categorized based on 5, 10, 20μm, and 40μm, but they are ineffective for most of the tiny particles present in oil droplets.