Patent ID: 8123952

Claim:
A process for simulated moving bed (SMB) separation of a feed F in a SMB device having at least one column, said column being composed of a plurality of beds of adsorbant separated by plates P i each comprising a distribution/extraction system, in which process the feed F and a desorbant D are supplied, and at least one extract E and at least one raffinate R are withdrawn, the supply and withdrawal points being offset over time by a value corresponding to one bed of adsorbant, with a switch time ST, and determining a plurality of operational zones of the SMB, in particular the following 4 principal zones: a zone 1 for desorption of the compounds produced in the extract, comprised between the supply of the desorbant D and withdrawal of the extract E; a zone 2 for desorption of the compounds produced in the raffinate, comprised between the withdrawal of the extract E and the supply of the feed F; a zone 3 for adsorption of the compounds produced in the extract, comprised between the supply of the feed and the withdrawal of the raffinate R; a zone 4 located between the withdrawal of the raffinate R and the supply of the desorbant D; the device further comprising external by-pass lines L i/i+1 joining two successive plates P i , P i+1 directly, allowing said plates to be flushed, in which each of the by-pass lines L i/i+1 comprises automated means for regulating the flushing flow rate, the degree of opening of said regulating means being defined by the following two rules: 1) in an operational zone where there is at least one closed by-pass line, a super-synchronicity of the flushing flow rate is established in all of the by-pass lines which are not closed belonging to the zone under consideration, said super-synchronicity being defined by the following formula: S=a+b ( nf/nt ) in which the constant a is a constant in the range −5 to 5 and b is a constant in the range 40 to 100, which is multiplied by the ratio of the number of closed by-pass lines (nf) over the total number of by-pass lines (nt) of the zone under consideration; 2) if there is no closed by-pass line in the zone under consideration (in other words if all of the by-pass lines of the zone are open), then a flow is established in all of the flushing lines of said zone which corresponds to the synchronicity plus or minus 8%; the synchronicity flow rate being defined as (V i +V i+1 +VL i/i+1 )/ST, in which expression V i denotes the volume of the distribution/extraction system of the departing plate P i ; V i+1 denotes the volume of the distribution/extraction system of the arriving plate P i+1 ; VL i/i+1 denotes the volume of the by-pass line between P i and P i+1 ; and ST denotes the switch time; and the super-synchronicity being defined by the formula: super-synchronicity(%)=100×[(real flow rate in by-pass line under consideration/synchronous flow rate)−1].