235Refining Processes for Used Oil Recycling to Base Oils or Fuels
the feed into the column, and the other is injected directly into the bottom part of the
column to adjust the bottom temperature of the column and extract the oil still in the
residue. The extraction in this column is carried out at a temperature between 40°C
(104°F) and the critical temperature of the hydrocarbonat a pressure that is high
enough to keep the hydrocarbon in the liquid phase with the extraction zone having
the highest possible temperature gradient, preferably greater than 25°C (45°F). When
propane is used, the preferred temperature is between 45°C (113°F) and the critical
temperature of the hydrocarbon, and the pressure can be in the range of 30 to 40 bar
(3–