CHME 690. Graduate Seminar

Date(s) - Fri 10/20/17
1:30 pm - 2:20 pm

Jett Hall (JH) 259 CHME Lecture Hall


Advanced Separation Methods for Efficient Recovery of High-Purity Polymers and Flame Retardants from Polymer Wastes

Nien-Hwa Linda Wang, Maxine Spencer Nichols Professor

Davison School of Chemical Engineering, Purdue University, West Lafayette, IN 47907. Phone: 765-494-4081.

More than 350 million tons of plastic were produced in 2015. The global plastic production and waste generation continued to rise over the past 50 years. The majority (90%) of the world’s plastic waste goes into landfills, but some of it (3%) ends up in the oceans. Most plastics take more than one hundred years to degrade, while releasing small particles and toxic chemicals into the environment. This pollution threatens the ecosystems and our water and food supply. By 2050, the planet may have up to 33 billion tons of plastics. Advanced separation methods may provide a solution for this problem. Mixed solvent extraction and simulated moving bed methods were developed at Purdue for recovering high-purity polycarbonates, polystyrene acrylonitrile (SAN), and two flame retardants from a Type 7 plastic waste. The polymers in the waste have similar properties and broad and overlapping molecular weight distributions.  Literature methods using single solvents at different temperatures for extraction failed to recover high-purity polymers from the waste. An efficient method based on Hansen solubility parameters and gradient polymer elution chromatography was developed to identify the mixed solvents for selective dissolution or precipitation of a target polymer for separation.  Two mixed solvents were used sequentially to recover high-purity polycarbonates (>99%) with high yields (>95%). The recovered polycarbonates have similar purities and molecular weight distributions as the virgin polycarbonates.  A side stream of the extraction process contained two major flame retardants and SAN. A size-exclusion simulated moving bed process (SEC-SMB) was developed to separate SAN from the flame retardants with high purity (>99%) and high yield (>99%).  The SEC-SMB was ten times more efficient than conventional batch chromatography processes.  Fast startup methods were developed to reduce the SMB start-up time by an order of magnitude.  The estimated cost of recovery was less than 30% of the market price for the polycarbonates and the flame retardants.  This method has the potential to reduce the amount of crude oil needed for polymer synthesis and uses 84% less energy. Moreover, it can reduce emissions by 1-6 tons CO­2­ per ton of polymer recovered. This approach has potential for recovering high-purity polymers from other types of plastic waste.


Dr. Nien-Hwa Linda Wang is the Maxine Spencer Nichols Professor of Chemical Engineering at Purdue University. She received her PhD in Chemical Engineering from the University of Minnesota in 1978. She is internationally known for her research contributions in separations, mass transfer, adsorption, multi-component chromatography, and simulated moving bed technologies.