The problem of reactivating saturated sorbent is an important part of any used oil regeneration process.
It is the reactivation stage that defines the economy of the adsorption process. If the cost of the sorbent is below the costs of reactivation, and the difference is not covered by the cost of the products extracted during purification, sorbent reactivation is not efficient and the saturated adsorbent is disposed of.
Used sorbents can be reactivated by hot water wash (to remove adsorbed oil), by hot air drying, and in some cases by burning the sorbent to remove the remaining oil and resin.
It is possible to reactivated used sorbents by treating them with various chemicals (synthetic fatty acids, naphthenate soap, oxidized petrolatum) in basic solution (5% water solution of sodium carbonate) at 90°С. The oil from the sorbent floats upward, while the sorbent settles to the bottom, then washed with hot water mixed with with acetic acid or ethane diacid to neutral reaction and dried to remove the remaining water.
Some of the most common methods of sorbent reactivation is purging with steam or gas, as well as thermal reactivation by gas combustion products or water steam. Chemical reactivation is used for ion exchange adsorbents. Charcoal and other carbon based sorbents can be reactivated in a number of different ways.
The most common reactivation technology is burning of the sorbent. The material is purged with 200°С air with consequent high temperature treatment at 600-800°С. Oil is removed from the sorbent by the hot air purge, and the remaining oil, resin and other impurities are then burned. The unit consists of a fan with an electric motor, an electrical air heater and a reactivation tank. Reactivation of sorbents saturated with transformer oil takes 5 hours.
Therefore, it is only economical to regenerate used oil with such sorbents as synthetic zeolite, activated alumina etc if the sorbent can be reactivated and reused many times. Possible cheaper alternatives are natural clays (zeolite, tripolite or bentonite).