Comprehensive Overview of Nanofiltration Membrane's Technical Parameters
As a pivotal component in the realm of membrane separation technologies, nanofiltration membranes play an indispensable role across numerous industries. Their remarkable efficiency and effectiveness are governed by a myriad of technical specifications. Below, we unveil the essential technical parameters that define this extraordinary technology, illustrating the sophisticated interplay of science and innovation.
1. Molecular Weight Cut-off (MWCO): This vital parameter represents the minimum molecular weight of solutes that the nanofiltration membrane can retain with a remarkable efficiency exceeding 90%, typically expressed in Daltons (Da). Nanofiltration membranes generally exhibit molecular weight cut-offs ranging from 100 to 1000 Da. This specific cut-off decisively influences the separation capability of substances. For example, a membrane with a 200 Da cut-off skillfully captures disaccharides and small peptides, while selectively permitting the passage of certain monosaccharides and inorganic salts.
2. Salt Rejection Rate: This parameter assesses the membrane's adeptness in retaining salt substances, denoted as a percentage. Generally, the rejection rate for monovalent ions-such as sodium and chloride-ranges from 50% to 80%, whereas for divalent and multivalent ions-like calcium and magnesium-it surpasses 90%. Influential factors include the membrane's material, structural composition, operating pressure, and raw water concentration. Notably, heightened operating pressure often boosts the salt rejection rate, showcasing the membrane's adaptability.
3. Water Flux: Also known as the water permeability rate, this parameter quantifies the volume of water transmitted through each unit area of the membrane per hour, expressed in L/(m²·h). Water flux is closely tied to the membrane's material, pore size, operating pressure, ambient temperature, and raw water properties. Typically, increased operating pressure and temperature augment water flux, whereas higher pollutant levels in the raw water reduce permeability, highlighting the membrane's sensitivity to environmental conditions.
4. Membrane Pore Size: Strategically positioned between reverse osmosis and ultrafiltration membranes, the nanofiltration membrane's pore size typically ranges from 0.5 to 2 nanometers. Although precise measurement may remain elusive, pore size is intricately linked to the molecular weight cut-off, where a smaller pore size efficiently retains larger molecular weight substances, enabling superior separation and selective permeability.
5. Applicable pH Range: This parameter delineates the pH spectrum within which the nanofiltration membrane reliably operates, generally from 2 to 11. Operating beyond this range may lead to hydrolysis or membrane swelling, impairing performance and reducing lifespan. Under extreme acidic or alkaline conditions, the membrane's structural integrity may weaken, affecting both salt rejection rate and water flux, showcasing its sensitivity to pH variations.
6. Maximum Operating Temperature: This denotes the peak temperature at which the nanofiltration membrane retains its functional integrity, typically between 30 and 45°C. Excessive temperatures may compromise the thermal stability of the membrane materials, leading to deformation, aging, and subsequent performance deterioration, affecting water flux and retention characteristics, underscoring its temperature resilience.