Ultrafiltration Process :: ultrafiltration nanofibrous membranes

What exactly do we mean by Ultrafiltration, and for what processes can it be used? Ultrafiltration is a process by which one uses a pressure-driven process utilizing a specific-sized membrane to separate macromolecular weights of a solution, allowing the transfer of the low molecular weight (permeate). Ultrafiltration is exclusively defined by the pore size range (0.1 – 0.001 microns) (Dhawan). Ultrafiltration is used in a wide array of applications, such as food and beverage, chemical, pharmaceutical, medical, drinking water, wastewater and etc. This research review will focus on industrial applications, and transport processes that make ultrafiltration unique, as well as the industry standard for separation. The rapid development of ultrafiltration for industrial processes is possible by the advent of anisotropic, high-flux membranes capable of distinguishing among molecular sizes of 10 A to 10  µ size ranges (Porter, 1972). The high molecular solute which flows through, but does not pass through the membrane is released as retentate (concentrate). The solution that passes through the membrane is known as permeate, which is shown Figure 1. This figure demonstrates the basic structure of a hollow membrane where the feed of the material you want to separate enters, and where the permeate (ultrafiltrate), and retentate exits. In different industrial processes one may want to retain the permeate, retentate, or combination of both. Mass Balance, Momentum Balance and Flux Figure 1: Flows and fluxes in a hollow fiber for ultrafiltration (Yeh, 2009) Let us take a closer look at what drives ultrafiltration from a mathematical point of view. In Figure 1, the feed solution is being driven by a volumetric flow rate (qi/Ni), pressure (∆Pi), and concentration (Ci). This feed solution produces a mass balance which results in the flux (J) vs fiber (dz): (Yeh, 2009) The momentum balance must be accounted for also: (Yeh, 2009) It can be presumed that the volumetric flow rate will be reduced similarly to the Hagen–Poiseuille equation, due to the laminar flow within the tube in Yeh, H. experiment in 2009, he takes into account convection as well as mass, and momentum balance: (Yeh, 2009) Equation 3 assumes that the volumetric flow rate is relatively large compared to that of the permeation rate. This occurs mainly in an exponential model along the membrane tube. This model simply states that when working with a pressure-drive ultrafiltration process, as pressure is increased, a ceiling (limiting) flux will occur regardless of increasing the pressure. We know that the relationship between membrane pressure (∆Ï ) and the permeate flux leads us to the following conclusion (Yeh, 2009).