Isocratic SMBC Mode
The original SMBC process was developed in the 1950’s by UOP for the large-scale separation of n-paraffins. Although many variations have been published in recent years, “classical” SMBC is carried out under isocratic conditions.
The countercurrent ﬂow created by SMBC enables extremely efficient utilization of solid and liquid phases. In single-column systems, isocratic separation actually occurs in a small portion of the column at any one time, with the rest of the column performing no function other than occupying solvent and broadening bands. With isocratic SMBC, typically 50-70% of the solid phase is engaged in the separation zone, while the rest of the adsorbent material is being prepared for the next cycle of separation. Moreover, SMBC provides essentially an “infinite” column bed length without the costs associated with obtaining, operating, and maintaining large single columns.
In isocratic SMBC there are typically two inlet streams (Feed and Desorbent) and two outlet streams (Raffinate and Extract). Valves between the columns are systematically switched open or closed at timed intervals (switch time) to introduce the inlet streams and withdraw the outlet streams between the separation zones. After each interval, all four streams are simultaneously switched to successive columns in the direction of fluid flow, simulating countercurrent movement of the columns. Separation occurs due to the differential migration of the Feed mixture components through the column material. Components that interact more strongly with the column material are carried into the Extract, whereas weaker-interacting components move into the Raffinate. By adjusting the stream flow rates, the switch time, and the Desorbent composition, a cycle is established in which Feed and Desorbent are continuously added and highly purified products continuously recovered.
The following video [11:35] illustrates the basic principles of isocratic SMBC and contains introductory information about Semba’s Octave® System.
Benefits of isocratic SMBC:
- Productivity: up to 20-fold higher vs. batch
- Separation power: high purity achieved with larger stationary phase particles, lower pressures
- Simplicity: robust, compact valve block and easy-to-use software
- Economy: saves up to 90% in resin and 40% in solvent volumes vs. batch
- Scalability: from mg to tons of purified product
Isocratic mode can be used for large molecule separations, including size exclusion and desalting. The video below illustrates isocratic mode operation of the Octave System. In this example, a mixture of two dyes is separated using size exclusion chromatography. A 3-2-3 column configuration is used. The red dye (Vitamin B12) is preferentially retained and is purified in the Extract, whereas the blue dye (Blue Dextran) is excluded from the resin and moves into the Raffinate.