Dual desorbent composition and temperature separation processes

Abstract

Dual desorbent composition and dual temperature techniques are provided as improvements for a simulated moving bed adsorption-desorption separation process which help reduce total desorbent requirements. The invention describes a process for continuously separating, in a liquid phase, components of a C.sub.8 aromatic feed mixture by contacting said feed mixture with a solid sorbent and utilizing a simulated countercurrent flow system wherein a liquid stream flows through serially and circularly interconnected desorption, rectification and sorption zones. One of the embodiments envisioned in the present improved process is directed to the employment of two desorbent streams of different strengths. This embodiment minimizes total amount of desorbent requirements by using a strong desorbent stream in the desorption zone and a suitable weaker desorbent stream in the rectification zone to achieve the desired separation. In another embodiment, the concept of temperature gradient is utilized to increase the desorbing power of the desorbent employed. Such an embodiment is carried out by providing a means of heating the desorbent stream prior to its introduction to the desorption zone and thereafter removing any residual heat before the desorbent stream passes to the rectification zone by means of a heat exchanger. Further, both the dual desorbent composition and the dual temperature techniques can be also simultaneously employed as another embodiment.