xylene and ethylbenzene within the separation assembly 110 the stream 106 enters an adsorptive separation unit 112 the adsorptive separation unit 112 separates the incoming stream 106 into a raffinate stream 120 and an extract stream 122 the adsorptive unit 112 typically comprises two smb chambers and a rotary valve each individual chamber typically has 12 beds a bedline connects each bed to the rotary valve the rotary valve controls the flow of material into or out of each smb chamber in a step wise manner to create a simulated moving bed a heavy desorbent typically para diethylbenzene is used to facilitate the separation of the raffinate stream 120 and extract stream 122 the raffinate stream 120 comprises ethylbenzene meta xylene and ortho xylene diluted with desorbent and any heavies heavies are hydrocarbons with a boiling point greater than that of the c8 aromatic isomers and include c9 aromatics the extract stream 122 comprises para xylene diluted with desorbent and light ends light ends are hydrocarbons with a boiling point below that of the c8 aromatic isomers and include toluene and other c7 u2212 aromatics the raffinate stream 120 is directed to a raffinate column 142 the raffinate column 142 is a fractional distillation column that divides the incoming stream 120 into i an overhead raffinate stream 114 comprising ethylbenzene meta xylene and ortho xylene.