(1) precipitation: let the waste oil stand, so that impurities fall and are separated. The settling time is determined by oil quality and oil temperature. The higher the oil temperature, the smaller the viscosity, the easier it is for impurities to fall and the shorter the settling time. Usually, the precipitation time of impurities in engine oil is related to temperature, as shown in the following table.
(2) Distillation: put the waste engine oil after precipitation and removal into a distillation bottle. Install distillation device and heat atmospheric distillation. 180℃ distillate is gasoline, 180 ~ 360℃ distillate is diesel, leaving engine oil. If it is known that the waste engine oil does not contain impurities such as gasoline and diesel oil, this step can be omitted.
(3) Pickling Put the precipitated and distilled engine oil into a big beaker, heat it to 35℃, and slowly add concentrated sulfuric acid (about 6-8% of the engine oil volume) under stirring (complete addition within 30 minutes). At this time, concentrated sulfuric acid reacts with colloid and asphaltene impurities in waste engine oil. In order to remove these sulfonated impurities, 10% caustic soda solution, which accounts for 1% of the engine oil volume, is added as a coagulant to accelerate the separation of impurities. After adding alkali, stir for 5 minutes and let stand for a period of time, there will be obvious stratification, and the upper oil will be yellow-green, without black particles and other impurities.
(4) The purpose of alkali washing is to remove organic acids from waste engine oil and neutralize the residual sulfuric acid during pickling. Add the acid-washed engine oil into another beaker, heat it to 90℃, slowly add sodium carbonate powder accounting for 5% of the engine oil mass under stirring, and check the pH of the engine oil after 20 minutes. Take two test tubes and add 1mL distilled water, one of which adds 2 drops of phenolphthalein reagent and the other adds 2 drops of methyl orange reagent. Then add 1 ml oil sample into the two test tubes respectively, and shake for 3 minutes. If the color of the aqueous solution layer in the two test tubes remains the same, it means that the oil is neutral, and the oil should become clear at this time.
(5) The oil filter is used for filtration in the filtration industry. Household engine oil can be repeatedly filtered with 4 ~ 6 layers of silk cloth for 2 ~ 4 times to obtain qualified diesel oil.
Explain that if you know all kinds of impurities in waste engine oil, you can adjust the above operation steps according to the actual situation. For example, engine oil only contains solid impurities such as metal chips, which can be separated by precipitation. If only gasoline, diesel oil and other substances are mixed into engine oil, regenerated diesel oil can be obtained by distillation. If only the engine oil is oxidized and deteriorated, impurities such as organic acids can be removed by acid washing and alkali washing.