Patent ID: 6870073

Claim:
A process for separating normal paraffins from hydrocarbons, which is carried out in a zone having at least three adsorption columns operating in parallel, the adsorption column being loaded with zeolite molecular sieves, the separation in each of the adsorption columns comprising the following steps of: a) upwardly passing C 5-10 hydrocarbons feedstock in gas phase from a bottom of the adsorption column to selectively adsorb normal paraffins contained therein, while passing through unadsorbed non-normal paraffins from the adsorption column; b) cocurrent-purging the adsorption column with butane to discharge hydrocarbons containing high concentration of non-normal paraffins which remain in void space of the zeolite molecular sieves; and c) countercurrent-desorbing the adsorption column with butane as a desorbent to expel the normal paraffins adsorbed in pores of the zeolite molecular sieves, the steps a), b) and c) in the adsorption columns being cycled in sequence at intervals of switching time in such a way that the separation in the zone is continuously carried out, the switching time being determined by analyzing components of the hydrocarbons feedstock and effluents from the adsorption column through an on-line real time analytic system, wherein a bottom stream comprising normal paraffins and butane, which is the effluent from the step c), is separated by distillation in an extract column, an overhead stream comprising non-normal paraffins and butane, which is the effluent from the steps a) and b), is separated by distillation in a raffinate column, and butane separated from the extract and the raffinate columns is recycled to the adsorption column.