The Impact of pH and Sodium Chloride Concentration on the Efficiency of the Process of Separating High-Molecular Compounds

Abstract

The aim of the present paper was to analyze the process of ultrafiltration of model protein solutions of bovine serum albumin (BSA) used for ultrafiltration of a ceramic membrane with the cut-off of 150 kDa. Working solutions were water solutions with 1 g/dm3 BSA concentration, 1% CH3COOH content and characterized by 4, 8 and 12% NaCl concentrations, respectively. The solutions were subjected to the process of ultrafiltration at various pH levels, i.e., 2, 4 and 6. The ultrafiltration tests were conducted at the pressure of 100 kPa and fixed temperature of 293K. The highest values of permeate flux were observed at pH 6 for all ionic strength variants. The lower the pH value, the lower the permeate flux. Concentrations of Na+ and Cl− ions did not have a significant influence on the volume of the permeate flow. At the same time, it was observed that at each pH variant the permeate flux was the lowest at the 4% concentration and was growing at the 8% concentration. The highest degree of protein retention in the membrane was observed when the value of pH equaled 2 (98.5–99.5%) and even though the degree of BSA retention was decreasing as the pH was growing, retention values remained at a high level (on average: 95.5% at pH 6). Obtained research results showed that optimal conditions for conducting the ultrafiltration process of water solutions of BSA characterized by various ionic strengths and with an addition of the acetic acid existed between the protein isoelectric point and the point of zero charge of the ultrafiltration membrane. Practical Applications Processes of membrane filtration are widely used in the food industry. Process streams of the industry are characterized by a broad pH range and the content of mineral salts or acids. This work may be helpful in the design of industrial filtration systems.