
165Refining Processes for Used Oil Recycling to Base Oils or Fuels
heated to a temperature required to achieve an operating temperature in the fourth
evaporator of between 320°C and 345°C and a pressure of between 5 and 15 mb
(0.5–1.5 kPa or 0.07–0.22 psi). The base oil fractions ashed off in the fourth stage
evaporator, shown as 250SN and 350+SN in Figure 7.4, constitute generally between
10% and 50% of the used oil feedstock and pass to storage units for further treatment.
The further treatment of the base oil products is not specied in the patent docu-
ment, other than to point to a chemical treatment to remove unstable or other unde-
sirable ...