Simulated moving bed absorption separation process

A method for adsorptively separating a selectively adsorbable component from a relatively less adsorbable component in a feed mixture using a simulated countercurrent moving bed adsorption system comprising a plurality of absorption beds, the method comprising the steps of:

• (1) supplying a feed mixture containing a selectively adsorbable component A and a relatively less adsorbable component B to an adsorption zone I, wherein the feed mixture contacts countercurrently with an adsorbent, said adsorbent selectively adsorbing from the feed, component A and to a lesser extent component P in pores of the adsorbent, thereby forming an adsorbate and a raffinate, the raffinate being enriched in component B;
• (2) contacting a stream containing component A and a desorbent with the adsorbate from step (1) in a purification zone II to displace component B from the pores of the adsorbent, thereby purifying component A in the pores of the adsorbent to provide a purified adsorbate;
• (3) contacting a desorbent with the purified adsorbate from step (2) in a desorption zone III to desorb component A from the pores of the adsorbent, thereby providing an extract enriched in component A, a first portion of the extract being used as the stream in step (2) and distilling the remainder of the extract to provide a high purity product A;
• (4) controlling the flowrate of a desorbent stream in a buffer zone IV to prevent the raffinate from entering the desorption zone III and contaminating the extract;
• (5) cyclically rotating zones I, II, III and IV by employing a rotary valve stream switching device to recycle inflowing and outflowing streams and, during the switching, using a flush stream enriched in desorbent to flush out residue in lines connecting the adsorption beds, a primary flush stream flow rate W.sub.h for each bed being calculated according to the formula:
• W.sub.H(in)n =W.sub.H(out)n =K.sub.n .multidot.V.sub.L T
• wherein:
• K.sub.n is the volume factor of the line connecting the nth adsorption bed, the value of the factor being expressed by the formula:
• K.sub.n =K'.multidot.V.sub.n /V.sub.L
• wherein:
• V.sub.n represents the volume of the nth connection line, measured in m.sup.3 ;
• V.sub.L represents the volume of the longest connection line, measured in m.sup.3 ;
• T represents the time interval of rotary valve stream switching, measured in hours;
• and
• K' represents the coefficient of volume factor of each connection line, which factor is from 0.5 to 3.5,
• wherein the flush stream flowrate for each flush stream is sequentially controlled in such a manner that a respective flush stream flowrate is adopted for each connection line.