Michael Dugas

Chemical and Biomolecular Engineering

Faculty Advisor: William Phillip

Understanding Electrostatic Interactions in Functionalized Copolymer Organic Solvent Nanofiltration Membranes

Organic solvent nanofiltration (OSN) has become an area of interest for organic solvent separation applications due to the energy efficiency, modular designs, and simple operations as compared to conventional thermally driven separations such as distillation. However, many of the polymeric membranes currently used in industrial applications cannot withstand the harsh chemical conditions. Copolymer membranes are able to be tailored using the physical properties of the repeat units in order to create membranes with distinct domains with distinct transport properties. In addition, functionalities can be incorporated into the membrane to not only crosslink and strengthen the nanostructure, but also incorporate charges into the membrane to electrostatically separate solutes. This type of interaction has been studied in a limited capacity in OSN.

This project is designed to investigate the effect of functionalities with known static charges on the transport of a poly(trifluoroethyl methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate-co-glycidyl methacrylate) membrane that has been crosslinked with hexamethylene diamine. Investigating functionalities that exhibit a permanent positive charge, like a ternary ammonium, and a negative charge, such as a sulphonic acid, could help understand the outreach of surface and pore charge on the transport of ions in organic solvent environments. Analyzing the effect of the functionality on the dielectric constant of the membrane in each individual solvent, in addition to ion rejections, could also help to understand the rejections with known electrostatic models, such as Donnan Exclusion. Finally, by using the knowledge gathered in the fundamental studies, the membrane can be tailored to a specific application, such as removing a homogenous catalyst from organic solvents. Understanding the electrostatic interactions in organic solvents with the use of functional groups could help to further the applicability of OSN membranes and increase the energy efficiency of organic separation processes. 

Project Objectives

Objective 1: Assess and characterize the functionalization of the copolymer membrane. The hypothesis is that by incorporating charged functionalities into the copolymer membrane, the electrostatic characteristics of the membrane will be altered. To assess this, copolymer membranes will be casted using both a flat-sheet blade casting and hollow fiber dip-coating methodology. The membranes will then be crosslinked with hexamethylene diamine using an epoxide-amine ring opening reaction. The charge groups will be incorporated after this reaction by either using an amine-isothiocyanate reaction, to get a sulphonic acid functionalization incorporated, or by utilizing another epoxide ring opening reaction, to incorporate a ternary ammonium group. Once the membranes are reacted, FTIR analysis will ensure that the reaction has taken place successfully. In addition, Zeta Potential as well as dielectric constant analyses will determine how the electrochemical potential of the membrane has changed with the incorporation of the functional group. This would help to understand the electrostatic characteristics of the membrane.

Objective 2: Understand how the functionalization effects the transport through the membrane. The hypothesis is with the incorporation of charged functionalities, the membrane will interact with solutes based on Donnan exclusion principles rather than pure size exclusion. To investigate this hypothesis, ion rejection experiments of sodium and calcium nitrate in varying organic solvents, such as methanol, ethanol, isopropanol, and hexane, will be conducted to determine the rejection of the salts in the organic environment. In addition, diafiltration experiments will be conducted to elucidate the effect of concentration on the rejection of the ions. These experiments, combined with characterization, can be utilized to link the rejection behavior to known electrostatic models in literature.

Objective 3: Utilize the knowledge and apply to industrially relevant feed solutions. The hypothesis is that by understanding the transport behavior of the membrane with each functionality, we can begin to accurately predict the transport behavior of industrially relevant feed streams through the membrane. One such example is to remove homogenous catalysts from the organic solvent to be recycled into the chemical process. In this study, homogenous charged catalysts will be separated from the products and organic solvents. This would demonstrate the ability of the membrane to separate solutes based on electrostatic interactions rather than pure size exclusion.