The acidity of spent lubricant was treated using sodium hydroxide solution. The effect of three variables on the treatment have been studied . These are mixing time rangingfrom 5-35 minutes, NaOH to lubricant weight ratio ranging from 0.25-1.25 and weight percentage of NaOH ranging from 2-6 % .
The experimental design of Box-Wilson method is adopted to find a useful relationship between the three controllable variables and the lowering in the acidity of the spent lubricant. Then the effective variables and interactions are identified using the statistical analysis(F-test) of three variable fractional design. The mathematical model is well represented by a second order polynomial.
By the analysis of the experimental results, the best treatment conditions which achieved an acceptable acidity of the spent lubricant are 20 minutes mixing time , 1 weight ratio of NaOH to spent lubricant and 4.5 weight percentage of N aOH. At these condition the acidity of the lubricant decreases from 0.62 to 0.0602 mg KOH/g oil.