A molecular sieve guard bed used in an adsorptive process for separating olefinic hydrocarbons from paraffinic hydrocarbons is regenerated in a method which recovers valuable hydrocarbons from the guard bed void volumes. The method comprises first contacting the sieve with a purge stream, with the initial effluent of the guard bed passed into a raffinate column to recover the olefinic hydrocarbons in the void volume of the bed. The flow of the effluent of the guard bed is then switched to a different fractionation column.