Practical investigation on the hydrodynamic behaviour of chromatographic columns packed with compressible media

Chromatography is an integral part of downstream processes to enable highly selective separation of biopharmaceutical products. A relatively high portion of total production costs are associated with the chromatography stage, hence optimisation of this unit operation is desirable. In this thesis column hydrodynamics were investigated under different operating conditions to provide an understanding of the effect of the column and matrix properties on the maximum flow velocity that the column is capable of being operate1at, the so called critical velocity, ucrit. Two automated methods for locating the column critical velocity were developed and compared to the conventional manual method. These automated methods utilised proportional-integral controllers and set either flow or pressure drop as the independent variable. Both methods proved to be relatively more efficient and accurate than the conventional manual inspection method, with the level of improvement depended on parameter settings such as the initial flow/pressure set point, the equilibration period, the step size, and the PID settings, etc. Of the three methods tested, the automatic pressure step (APS) method showed a better overall level of performance by providing better efficiency and accuracy. During chromatographic separations the column resin is commonly subjected to varying, and sometimes extreme, physiochemical conditions as part of the column cleaning procedures. Techniques were developed in this thesis to investigate the effects of pH changes on the ucrit. Results show that by utilising rigid resin materials, the significant reduction in the ucrit that was observed when changing the pH of the mobile phase from 7 to 13 can be avoided. This study demonstrates the importance of considering the impact of mobile phase pH on the column stability, especially when operating over long campaigns in which the column may be subjected to many cycles of widely different physiochemical conditions. To improve the ucrit, the idea of utilising various designs of inserts within the column to provide additional wall support was developed and tested. Results showed that despite leading to a reduction in the column efficiency as measured by HETP, inserts provide a positive impact on the column bed stability with an ucrit improvement of up to 48 % recorded. The utilisation of insert may be useful for the capture stage of a downstream process, where the benefits of increasing the permissible operation flow velocity often outweigh any drawbacks of decreased column efficiency.