Durability of Membrane (Lifetime of Membrane)

Abstract

Durability (or lifetime) of membranes is a critical factor in the commercialization potential of any membrane material, as it must be resilient to the process conditions over an extended period of time. The lifetime of a membrane is also an important factor in the economic evaluation of a membrane process, as replacement of membranes is a significant cost burden. A range of factors influence the durability of membrane materials. These include chemical degradation of either the active layer or support structure due to harsh chemical components in the feed stream, for example, feeds with low or high pH conditions, as well as high electrolyte concentrations, polymeric aging, and polymer plasticization, leading to increased probability of the active layer rupturing. An example of this is cellulose acetate membranes being plasticized by exposure to hydrocarbons in petrochemical gas separation applications; active layer compaction due to the extended exposure to highpressure differentials across the membrane, resulting in reduced flux because of loss in diffusivity; and membrane fouling, which is the buildup of foreign matter on a membrane’s surface resulting in decreased performance. An example is microbial growth in water treatment. Finally, mechanical abrasion of the active and support layers is caused by particulate matter being present in system. Each of these factors influences membrane materials differently, depending on the application. There are a number of approaches to extend membrane lifetimes, most of which focused on overcoming membrane fouling. These include feed pretreatment, chemical and mechanical cleaning, feed stream pulsation, and pressure variation, as well as chemical additives to prevent fouling in the first place. These techniques can extend a membrane module’s lifetime but will not address issues such as chemical degradation, polymeric aging, and mechanical abrasion. Hence, all membrane modules’ separation performances decrease over time in all industrial processes and replacement is necessary. Currently, the industry standard is for a membrane module lifetime of 5 years under standard process conditions (Li et al. 2008). For the majority of reverse osmosis membrane plants currently being commissioned or under construction, the RO membranes are guaranteed by the manufacturer for 5 years. Similarly, vapor separation membranes in the petrochemical industry have a lifetime of 3–5 years, dependent on the conditions of the feed. Seawater ultrafiltration membranes last up to 7 years because of their resilient material and the ability to avoid regular chemical