(446a) Membrane Processes--a Disruptive Technology?

Almost a decade ago, the concept of ?disruptive technologies? was introduced to describe new approaches that were radically different from the incumbent technology in a field. Disruptive technologies were also noted to initially perform less well than the incumbent leader, but by improvement, to become a dominant force in the field. In this context, membrane processes are a potentially disruptive technology. The energy required to achieve some large scale separation tasks, for instance water purification, can be as much as a full order of magnitude lower via the membrane approach vs. thermal alternatives. Clearly, membranes can't defeat the 2nd Law of Thermodynamics, but they can minimize its limitations by avoiding the use of heat to drive separation. While distillation remains the clearly dominant separation technology, improvements in materials and device manufacturing could create membrane products able to claim a significant fraction of the separations landscape. As size differences between desired permeating components vs. rejected components decrease, molecular scale ?sorption-diffusion? discrimination is required to enable selective permeation. Reverse osmosis purification of water, the first such large scale commercially viable membrane fractionation of low molecular weight liquid mixtures, relies upon ?partitioning selectivity? and ?mobility selectivity? contributions between water and hydrated ions. Optimization of membranes for this application took place over two decades, and these membranes are now rapidly displacing thermal desalting. Understanding how and why reverse osmosis displaced thermally intensive distillation in this large scale application will be considered.

Besides polymeric media, ceramic, carbon, zeolitic and metal membranes are appealing from the standpoint of separation precision and chemical inertness. Nonetheless, these appealing materials have not yet succeeded as economical large scale competitors to conventional approaches for organic separations. To move beyond a ?niche technology?, discoveries in materials processing are needed to provide realistic approaches for creation of lower cost, robust membrane modules based on these advanced materials. In this regard, hybrid organic-inorganic materials may be the keys to meeting such challenges in many cases, and it is encouraging to see a dramatic increase in activity in this area. Possible paths forward using this hybrid material approach will be discussed.