(647d) Time Series Analysis of Membrane Aging in Organic Environments

Chemical separation processes are usually the single most energy-intensive step in a given process, often accounting for up to 50% of the total energy requirements. Membrane-based chemical separations offer a promising alternative to current thermally-driven separation units. Polymeric membranes are up to 90% more energy-efficient that thermal methods, like distillation, because they can be operated at or near ambient temperatures. Indeed, membranes already see wide application in areas such as water desalination and gas purification. Despite their growing adoption, there are still challenges that need to be addressed before membrane technology can further expand across the chemical industry. One of the primary challenges is that of membrane aging. Most commercial membranes are glassy polymers that are in an inherently non-equilibrium state. Over time, their permeances will decline as the polymer asymptotically settles into a denser state closer to equilibrium, leading to lower productivities. The aging process is poorly understood, especially in complex organic environments. It is also difficult to predict aging behavior a priori because it strongly depends on polymer identity, processing history, and operating conditions. Here, we take an empirical approach to study polyimide aging in methanol by performing a time series analysis of the change in permeation and solute rejection over time. Time series analysis may be better suited to analyzing membrane aging because it only requires process data and not polymer structural properties that cannot be determined as aging occurs in real-time. We also indirectly track the disappearance of varying size free volume elements by measuring varying size solute rejection over time. This information is then used in combination with regression on past data to forecast membrane performance. We compare our data-driven approach to the deterministic Struik model and find that it is a useful tool for researchers to investigate membrane aging phenomena in reasonable time frames.