Tubular ultrafiltration membranes are a membrane technology that, under pressure, utilizes the selective permeation and mechanical sieving action of the membrane to achieve efficient separation of components of different particle sizes in a solution. Its core working principle lies in the difference between the membrane pore size and the particle size of the components in the feed solution. Through a unique tubular flow channel design, a cross-flow filtration mode is formed to suppress fouling and maintain a stable flux.
From a separation mechanism perspective, the separation layer of a tubular ultrafiltration membrane has a uniform pore size ranging from nanometers to micrometers, typically in the range of 2–100 nanometers, corresponding to a molecular weight cutoff of approximately 1,000–500,000 Daltons. When the feed solution flows through the inner or outer wall of the membrane tube under a certain pressure (typically 0.1–0.5 MPa), water molecules and small-molecule solutes smaller than the membrane pore size can permeate through the membrane layer into the permeate side, forming purified permeate. Meanwhile, suspended particles, colloids, bacteria, proteins, polysaccharides, etc., larger than the membrane pore size are retained by the membrane and discharged axially along the membrane tube with the concentrate. This process is essentially physical sieving, further enhanced by the electrostatic repulsion of charged particles by the membrane surface charge, thus improving separation accuracy.
The tubular flow channel design is a crucial support for its working principle. Unlike compact membranes such as hollow fiber membranes, tubular membranes use porous support tubes with diameters ranging from several millimeters to tens of millimeters as a carrier, creating a high-speed cross-flow of the feed solution inside or outside the tube. This cross-flow pattern ensures that the bulk of the feed solution flows continuously parallel to the membrane surface, with only a small amount of liquid permeating through the membrane layer, effectively reducing the membrane boundary layer and lowering the concentration polarization and deposition rate of solutes on the membrane surface. Meanwhile, the wide flow channels reduce the risk of particulate clogging. Even with high suspended solids or high-viscosity feed solutions, turbulent scouring maintains membrane surface cleanliness, which is key to its superior antifouling ability compared to other configurations.
During operation, the coordinated control of pressure, flow rate, and temperature directly affects operational efficiency. Appropriately increasing pressure can increase flux, but excessive pressure will exacerbate membrane fouling and energy consumption. Maintaining a sufficiently high cross-flow velocity (typically >2 m/s) is crucial for suppressing fouling. Moderate heating can reduce feed viscosity and improve mass transfer efficiency, but it must be controlled within the membrane material's temperature resistance range.
In summary, tubular ultrafiltration membranes, through a synergistic mechanism of "pressure-driven-pore size sieving-cross-flow fouling suppression," achieve efficient clarification, concentration, and fractionation of complex feed solutions. Its working principle follows the basic principles of membrane separation while its structural innovation overcomes the limitations of traditional membrane technology in terms of antifouling and adaptability to operating conditions, making it a reliable solution for challenging liquid separation tasks.
