(634f) A New Multicolumn, Open-Loop Process for Center-Cut Bioseparation by Solvent-Gradient Chromatography

A major part of the purification costs in downstream processing of biopharmaceuticals is related to chromatographic processes, which, at present, are still largely operated in batch mode. This is not because chromatography is inherently expensive, but because it is heavily used: chromatography plays a central role in fast and efficient separation of biochemical and pharmaceutical compounds; in fact, it still remains the work horse method in biopurification.

For most biopurification problems, the desired product is intermediate between weakly and strongly adsorbing impurities, and a central cut is thus required to get the desired product. Conventionally, the generic three-fraction biopurification problem is solved using batch column chromatography, often incorporating solvent gradients. Typically, the target product is separated from process-related impurities through a series of steps wherein a selected cut or fraction of the effluent from the previous step is selectively adsorbed and desorbed onto a given stationary phase using time and elution conditions as manipulated variables, until, ultimately, yielding the product purified to the desired level. Solvent gradients are easy to apply in sequential batch chromatography, but this operating mode suffers from high product dilution, low efficiency and productivity, and high solvent consumption.

In the present work, we describe a new multicolumn, open-loop process for center-cut bioseparation by solvent-gradient chromatography. The key idea is to extend solvent-gradient batch chromatography to a train of columns and to exploit the fractionation of the stationary phase. In this work we show that this can be done while working in a simple, open-loop system that resembles the batch system. Although our process implements a solvent-gradient moving around a ring of columns, it is similar to a batch process in terms of feeding and product collecting.

We provide experimental validation in a pilot unit, using the purification of a crude peptide mixture by reversed phase as a working example; this proof of concept serves to highlight the versatility, flexibility, and ease of operation of the process. By dynamically adjusting the switching interval while the process is running, to correctly position the composition profile with respect to the outlet ports, pure product satisfying the target specifications—98% purity and 95% recovery—was obtained under stable operation in the pilot unit.