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Cleaning/sanitization fluid

Cleaning/sanitization fluid

Hydraulic fluid

Figure 4. Experimental set-up for production-scale expanded-bed adsorption using a 600-mm inner diameter column. Source: From Ref. 27.

a downward flow direction at 300 cm/h, for at least one settled bed volume or until the UV curve levels out. When the wash step has been optimized approximately, it then requires 15 settled bed volumes of wash buffer to flush out particulates and unbound proteins (59).

Elution. Elution is usually performed in settled bed mode with downward flow. The flow velocity is lower than during the previous steps, usually 100 cm/h, in order to keep the elution volume as small as possible. A high flow velocity during elution will increase the elution volume. It has been shown that elution in expanded-bed mode may increase the volume by approximately 40% (58).

Cleaning. Cleaning is performed in expanded bed mode to allow any trapped particulates in the bed or column to be flushed out. The adaptor is typically placed at a position corresponding to twice the settled bed height, and the flow velocity is about 100 cm/h. Cleaning is facilitated if it is performed directly after each purification cycle. As with any protocol for cleaning, it will depend on the adsorbent and on the nature of the feedstock, etc. A general cleaning protocol suggested by the manufacturer for the different types of adsorbents (e.g., ion exchanger) is always a good starting point, as is a cleaning protocol used for a corresponding packed-bed process (if such exists). As previously mentioned, the cleaning is facilitated if as many of the par-ticulates as possible have been washed out during the previous wash step. Back-flushes disturb the build-up of par-ticulates, and it has been shown that back-flushes at a high flow velocity were effective in removing the build-up of sticky yeast from the distributor plate in an industrial-scale expanded-bed column (27).

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