An engineering study of compression and fouling of chromatographic matrices

The soft or semi-rigid matrices used in the chromatographic separation of biomolecules have the tendency to compress at high flow rates limiting the throughput and therefore the process productivity. The first part of this study has focused on the effects of bed compression on column hydrodynamics and chromatographic performance. The predictive capabilities of two hydrodynamic models developed for columns packed with compressible matrices have been assessed. These models were used to predict the pressure drop and the maximum flow rate that can be achieved with a specific matrix for particular sets of column dimensions. In order to evaluate the models the mechanical properties of Sepharose 6B and Sepharose C1-6B have been measured by means of experimental techniques similar to those employed in soil mechanics. In order to analyze the effects of bed compression on column performance, key chromatographic parameters were measured with gel filtration columns packed under different compression conditions. Pulse techniques, in particular the HETP method, were used to determine the distribution coefficient, the intraparticle diffusivity coefficient and the axial dispersion coefficient. These parameters have been inputted into a chromatography model to simulate the chromatographic peaks obtained with compressed gel filtration columns in order to corroborate the validity of the estimated parameters. Chromatographic columns are prone to fouling, however the level of contaminants that can be accepted by a particular column and therefore the required degree of sample pretreatment are not well defined. In the second pan of this study the changes that occur in the transport parameters, when a column is fouled with a process stream containing different levels of foulants, have been determined in order to assess the effects of fouling on the matrix and bed structure and therefore on column performance. The results of this study will enable better prediction of chromatographic separations carried out with columns operating at conditions closely resembling those encountered at the process scale level