ISSN 0965-5441, Petroleum Chemistry, 2014, Vol. 54, No. 8, pp. 705–709. © Pleiades Publishing, Ltd., 2014. Original Russian Text © T.S. Philippova, A.N. Filippov, 2014, published in Membrany i Membrannye Tekhnologii, 2014, Vol. 4, No. 4, pp. 308–313. 705 INTRODUCTION It is known that the key drawback of any pressure- driven membrane process is concentration polariza- tion (CP) and CP-related phenomena [1]. Concentra- tion polarization is the phenomenon of concentration rise of a rejected component in a thin layer of solution adjacent to the upstream membrane surface, which leads to membrane “poisoning”, commonly termed as fouling, involving a variety of physicochemical pro- cesses of buildup of material on or in the membrane surface. Fouling deteriorates the membrane perfor- mance characteristics (flux, permeability) and increases the power consumption for maintaining a pressure-driven membrane process. At the first stage of microfiltration or in the case of dilute solutions or suspensions, the diffusion of large particles rejected by the membrane can be frequently ignored because of their sizes. However, these particles can be absorbed gradually onto the membrane surface, thereby block- ing its pores [2] and forming a layer of rejected parti- cles, the “dynamic membrane” [3] and, as a conse- quence, causing the reduction of membrane perfor- mance. According to Baker’s classification [1], microfiltration membranes are divided into two types: screen filters and depth filters. The screen filters cap- ture particles only on the effective surface, and the depth filters do it by the interior pore surface. In this work, we consider only the screen filters. In particular, track-etched membranes belong to the screen mem- brane type [4]. A probabilistic sieving model was developed in [5 9] to describe microfiltration of dilute suspensions in the dead-end (or in-line) mode when the flow is normal to the active membrane surface. This model was used to explain the decline in membrane perfor- mance and an increase in rejection with time at a con- stant transmembrane pressure. Moreover, it was shown that treatment of microfilters (such as MFF series fluoroplastic membranes with random hetero- geneous pore structure) as an idealized homogeneous membrane with capillary pore structure provided a good correlation between theoretical and experimen- tal data. In this work, we propose a method for determining the lifetime of uni- and biporous microfiltration mem- branes during concentration of polydisperse suspen- sions or their purification for removal of fine fractions in the dead-end mode when the flux is maintained constant. The dead-end regime is the most cost-effec- tive in the case of dilute suspensions with a low sus- pended solids content [1]. At high concentrations of solids in dispersion, when a suspended dense layer of rejected particles is formed at the membrane surface, cross-flow filtration is used, which allows the retained species to be washed away into concentrate by tangen- tial flow. Unlike reverse osmosis and nano- or ultrafil- tration in which maintenance of a constant trans- membrane pressure is usually practiced, microfiltra- tion is conducted in the constant flux regime [1] because of more intense membrane fouling. In this case, a certain high constant pressure is maintained in the feed stream (over membrane) and a lower pressure is applied in the permeate stream (under membrane), which gradually drops to a certain critical value with time as fouling progresses. Here, we use the theory developed in our previous studies [5–9]; the designations of values and parame- ters remain the same. Note that the afore-mentioned track membranes can be considered as idealized model uni- and biporous structures in different fields Theoretical Evaluation of the Microfiltration Membrane Lifetime T. S. Philippova and A. N. Filippov Gubkin Russian State University of Oil and Gas, Leninskii pr. 65, bld. 1, Moscow, 119991 Russia e-mail: anatoly.filippov@gmail.com Received July 15, 2014 Abstract—Theoretical estimates of the lifetime of uni- and biporous microfiltration membranes as applied to the filtration of polydispersions have been obtained. The optimal microfiltration regime that makes it pos- sible to increase the membrane lifetime has been found. The data were considered in terms of the probabilistic sieving model of the process with regard to surface pore blocking with time, which was recently developed by one of the authors. An explicit formula has been derived to determine the lifetime of a membrane with an arbitrary pore size distribution. Keywords: microfiltration of polydispersion, rupture pressure, membrane lifetime, uni- and biporous mem- branes DOI: 10.1134/S0965544114080064