HPLC - UV/VIS Spectroscopy
Fiber Optic and Diode Array Applications
Software - Fluorescence
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Why SMB?Simulated Moving Bed is a process chromatography method that enables a mixture of substances to be continuously separated and extracted into two fractions.
The advantages of SMB technology compared to classical batch chromatography
- The entire stationary phase is in use during the separation process resulting in much higher productivity.
- A 90% reduction in solvent consumption is possible due to solvent recycling.
- High plate counts or small particle sizes are no longer required, thus reducing packing material costs by 80%.
- Extract and raffinate are extracted in high concentrations, which makes it easier to remove solvent.
- The patented multi-function valve results in an extremely small dead volume for the overall system.
The simulated counter-current process (Simulated Moving Bed - SMB) was developed in the early 1960's by the Universal Oil Products Company. It was mainly applied to industrial-scale separations, e.g. fructose-glucose separation.
In the SMB process a large column is effectively divided into a finite number of small sections. The withdrawal tubes are situated between two such sections as shown in the diagram. These tubes are connected in a cycle mode with the inlets and outlets via a special designed and patented rotary valve.
An observer sitting on the inlet or outlet sees an apparent movement of solid against the fluid flow at each switching process although the solid is actually fixed in the column. For this reason the process is known as Simulated Moving Bed.
Using a suitable combination of adsorbent and eluent, the feed stream is separated into two withdrawal streams containing the pure components of a binary or pseudo-binary mixture.
The diagram on this page shows a four-zone SMB system for 8 columns. The feed, eluent, extract and raffinate inlets and outlets, which divide the circle of columns into four sections, are clearly labelled.
Special valves allow liquid flow in one direction only. Inlets and outlets are arranged in a pre-defined manner and switched in the same direction as the fluid flow. This is the principle used by the Knauer CSEP SMB systems. In the zones II and III the binary mixture is separated and in the zones I and IV the solid and the liquid phases are cleaned.
Where can SMB separations be used?
The SMB principle of continuous extraction of pure substances on a preparative scale is successfully used in many areas of chemistry and biochemistry. The yearly production using the available systems is between lOO and 1,000 kg of pure substance.
| Application Area | Typical Separation Examples | |||
| Pharmaceuticals | Chiral compounds (e.g. steroids, peptides, antibiotics) | |||
| Food chemistry | Fatty acids, carbohydrate mixtures | |||
| Biochemistry | Citric acid, phenylalanine | |||
| Petrochemistry | C8-Hydrocarbons (i.e. xylene/toluene) | |||
The successful application of an SMB process is linked to the following prerequisites:
- Required componenent elutes first or last
- Good solubility in the liquid phase
- It must be possible to carry out an isocratic separation
- Retention time of the substance should be under 20 minutes
- Knowledge of the adsorption isotherms
- Selectivity values between 1.2 and 2.0