Membrane separation processes is a technology whose time has come. Membranes have long been an intellectual and academic curiosity, but limited commercially to relatively few or more sophisticated operations such as reverse osmosis or dialysis.
The emerging value of membrane contactors for contacting and separation operations may best be described in terms of a relatively new engineering discipline called Process Intensification. In an article in the January 2000 Chemical Engineering Progress, Adrezej I. Stankiewicz and Jacob A. Moulijn define Process Intensification as consisting of:
“…the development of novel apparatuses and techniques that, compared to those commonly used today, are expected to bring dramatic improvements in manufacturing and processing, substantially decreasing equipment-size/production-capacity ratio, energy consumption, or waste production, and ultimately resulting in cheaper, sustainable technologies.”
The intense interest in membrane separation processes has been sparked by several factors, including:
- Decentralization of the chemical process industry
- Focus on the reduction of energy consumption of traditional separation processes
- Need for increasingly sophisticated separation operations to recover difficult-to-recover molecules
- Environmental issues
- Advances in polymeric and inorganic manufacturing skills for the production of membranes
Membrane separation processes such as gas/liquid separation or membrane distillation are replacing their bulk counterparts (distillation towers, stripping columns) due to improved energy efficiency, scalability, the ability to operate isothermally, and smaller physical footprints. In addition, membrane separators and contactors generally have no moving parts and are physically simple and rugged, resulting in low maintenance cost.
A membrane contactor consists of a membrane or set of membranes held in such a manner as to separate two regions of flow and enable the membrane to act as a means of separation between the two phases, and a housing to enclose the membrane and contain and direct the flow of the multiple phases. The membrane acts as a barrier between the two fluid phases and selectively allows or prohibits the transport of one or more chemical species or particles from one fluid stream to the other. The housing has one or more ports to allow flow to and from the membrane.
Markel has developed a family of modules for contacting and separations applications.
Markel porous PTFE hollow fibers, alone or in conjunction with the Markel potting technology and housing design are ideal membranes for a wide spectrum of contacting or separations operations. The severe conditions often required of a membrane contactor for separations operations place demands on both the fiber and the potting system for high service temperature, chemical resistance, strength and durability of the fiber, and often times require either a hydrophobic surface and one that is chemically inert and pure.