In the purification of waste lube oil to give clean lube oil, as shown in figure, the waste lube oil containing 87 wt% unwanted solids and 13 wt% liquid lube oil is fed to an extractor. Extraction of lube oil from waste lube oil is achieved by contacting the waste oil with hexane. The extractor feed ratio of hexane to waste oil is 3 kg hexane/kg waste oil. The unwanted solids are suspended in the liquid and essentially all of the lube oil in the waste lube oil is extracted into the hexane. The extractor effluent passes to a filter. The filter cake contains 75% unwanted solids and the balance lube oil and hexane, The ratio of lube oil to hexane in the filter cake is equal to the ratio of lube oil to hexane in the effluent extractor. The filter cake is discarded and the liquid filtrate is fed to a heated evaporator in which the all of the hexane is vaporized and lube oil remains as a liquid. The hexane vapor is subsequently cooled and condensed, and the liquid hexane condensate is recycled to the extractor. filter z Calculate a)the yield of clean lube oil product (kg clean lube oil/kg waste lube oil) b)the required fresh hexane feed c)the recycle to fresh feed ratio (kg hexane recycled/kg fresh hexane feed) Condenser Hexane (liquid) Hexane (vapor) Extractor Evaporato: Hexane (Liquid) 100(kg) 33.33kg Clean tube ol