Sequoia’s Regenerative Adsorption system improves the quality of distilled lube oil. Specifically, oxidation stability, color, viscosity index are improved. Substantially all of the metal impurities, phosphorus, silicon and partially sulfur present in recovered lube stock are removed. The purification plant operates in two steps viz. first step is purification of oil by adsorption for improving its quality as described above while the second step involves regeneration of saturated adsorbent so it can be used again for next adsorption cycle. The plant operates in adsorption and regeneration cycles in sequence.