There is renewed interest in the possibility of using precipitation for initial capture of high value therapeutic proteins as part of an integrated continuous downstream process. These precipitates can be continuously washed using tangential flow filtration (TFF), with long term operation achieved by operating the membrane modules below the critical filtrate flux for fouling. Our hypothesis was that the critical flux for the precipitated protein would be a function of the properties of the precipitate as determined by the precipitation conditions. We evaluated the critical flux using a flux-stepping procedure for model precipitates of bovine serum albumin generated using a combination of a crosslinking agent (zinc chloride) and an excluded volume precipitant (polyethylene glycol). Data were obtained using both 0.2 µm pore size hollow fiber and flat sheet (disk) polyethersulfone microfiltration membranes over a range of filtration conditions. Independent measurements were obtained for the viscosity of the precipitated protein solutions, the precipitate size distribution (by laser diffraction), the yield of protein in the precipitate (after centrifugation), and the resistance of the protein deposit. The critical flux in the hollow fiber module varied with shear rate to approximately the 1/3 power, consistent with predictions of the classical polarization model. The critical flux increased significantly with increasing zinc chloride concentration, going from 60 L/m2/h for a 2 mM ZnCl2 solution to 200 L/m2/h for an 8 mM ZnCl2 solution. The critical flux in the stirred cell followed the same trend as a function of ZnCl2 concentration, but with much lower values of the critical flux due to the different device hydrodynamics. The critical flux in the hollow fiber module achieved a maximum value at an intermediate polyethylene glycol (PEG) concentration of around 6 weight percent at a fixed ZnCl2 concentration of 3.5 mM. The effects of ZnCl2 and PEG were interpreted in terms of the changes in effective size and viscosity of the protein precipitates. Additional insights were obtained from the compressibility of the cake layer formed after filtration of the protein precipitate in a stirred cell. These results provide important insights into the development of effective tangential flow filtration systems for processing large quantities of precipitated protein as would be required for large scale continuous protein purification by precipitation.

Effect of zinc chloride and PEG concentrations on the critical flux during tangential and normal flow microfiltration of BSA precipitates

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.