Destined for landfill, agricultural waste contains carbon sources that can be used to produce valuable compounds, such as p-coumaric acid, which is used in the manufacture of pharmaceuticals. Electrodeionization, a separation method that uses ion exchange membranes, is one way to capture acids and other useful components. However, to capture large quantities on a large scale, improvements in the method must be made.
A Penn State-led research team has invented a new class of ion-exchange membrane slice assemblies that dramatically improves electrodeionization’s ability to capture p-coumaric acid from liquid mixtures while using less energy and saving money. The researchers published their results in ACS Sustainable Chemical Engineering.
First marketed at purify water, electrodeionization has been used in recent years to capture valuable components from waste streams. In the process, a stream of liquid mixture is fed through a stack of several ion exchange membranes and resin pads, which resemble a sponge and are held together with a polymer adhesive. When electricity is applied, the ions in the liquid move through the cell and the p-coumaric acid separates into a concentrated process stream, where it can then be collected.
“To improve the process, we had to improve the resin wafer,” said corresponding author Chris Arges, associate professor of chemical engineering at Penn State. “Previously, membranes would sandwich the resin pad sponge with polyethylene adhesive, which is currently used in the industry as a resin ‘glue’, but this resulted in poor contact between the membrane and the pad. resin. We replaced the polyethylene with an imidazolium ionomer, a type of polymer, and glued an imidazolium membrane on top of the resin slice. »
By bonding the membrane to the wafer, the researchers reduced the amount of membrane needed by 30%, reducing the cost of the electrodeionization unit. The new design also reduced the interfacial resistance between the membrane and the wafer, as the same membrane and binder chemistries were bonded together rather than sitting over and under the sponge with air gaps. The reduction in resistance resulted in an increase in the capture rate of p-coumaric acid, allowing researchers to use a smaller unit.
“We knew the new material was capturing more p-coumaric acid, but we didn’t know why,” Arges said. “Our collaborator Revati Kumar ran simulations to find out why it worked better.”
Kumar, an associate professor of chemistry at Louisiana State University, found that imidazolium increased the solubility of p-coumaric acid and stimulated faster diffusion into the material.
“Multiplied together, solubility and diffusion equal permeability, or how quickly we remove acid as it moves through the network of membrane resin platelets into the concentrate compartment,” Arges said.
Arges compared permeability to the rate of travelers going through a security line at airports. As more security checkpoints are added, more people can move on the line, increasing the permeability of the line.
Therefore, increased permeability decreases the chance that p-coumaric acid will bind to membrane-resin platelet materials, known as fouling, instead of moving through the membrane.
“The imidazolium membrane resin wafer assembly promotes flux of p-coumaric acid through the membrane, which is a problem when other materials, such as polyethylene, are used,” Arges said.
Compared to the current resin wafer configuration, the new membrane configuration and new materials result in a sevenfold increase in p-courmaric acid capture while using 70% less energy, according to the researchers. The new assemblies also reduce the amount of membrane used in the process, resulting in significant cost savings.
Arges collaborators at Argonne National Laboratory have filed a patent for the new membrane-wafer assembly technology.