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Separating Water from Aqueous Mixtures

Removing water from anything is typically a very expensive step, requiring significant energy, and is therefore also highly environmentally damaging. Finding lower-energy ways to remove water from other chemicals is therefore an important task for green chemists and chemical engineers.

1. Forward Osmosis

Forward osmosis (FO) is an innovative water filtration technique that has the potential to use significantly less electricity than conventional techniques. FO can be used in diverse applications, including the production of potable water, the processing of food products (e.g., milk, sap, juice), the recovery of products prepared from biomass by fermentation, and the concentration of wastewaters. In FO, a concentrated “draw solution” pulls clean water across a membrane from a “feed solution”. Once the feed is concentrated, the draw solute is removed from the draw solution, leaving behind pure water. CO2-responsive materials make excellent draw solutes as, unlike conventional materials, they can both pull water efficiently from the feed (under CO2) while remaining easily removed post filtration (under air). Polymers are an attractive class of CO2-responsive draw solutes for applications which require high purity feeds (e.g., the food industry). Current work is focusing on further improving the polymer’s filtration ability. This research is being performed in collaboration with Prof. Cunningham of Chemical Engineering and Prof. Champagne of Civil Engineering at Queen’s.

Key references are listed below.

Reprinted with permission from Ind. Eng. Chem. Res. 2019, 58, 50, 22579-22586. Copyright 2019 American Chemical Society.
2. Switchable Drying Agents

Organic liquids like solvents or fuels are often contaminated with water. Removing the water is usually achieved with a drying agent. Single-use drying agents like Na2SO4 are wasteful and harmful to the environment, but reusable drying agents are little better – some of them bind water so weakly that they don’t capture much water, while others bind water so strongly that regenerating them after use takes too much energy. What’s needed is a drying agent that binds water strongly when it’s drying a solvent, but binds water weakly when it’s being regenerated. We’ve made such a “switchable” drying agent. This research is being performed in collaboration with Prof. Cunningham of Chemical Engineering at Queen’s.

Key references are listed below.

  1. Recovering organic products from aqueous solutions

Which is greener – making organic products from biomass or from fossil fuels? You’d think that using biomass would be greener, but biomass conversion into organic products, whether by acid catalysts or by fermentation, typically results in an aqueous solution of the organic products. Removal of the water from the product is so energy-intensive and therefore harmful to the environment that it is, at present, better to make the products from fossil fuels (see picture). Of course, in the long term, that’s not sustainable. If this problem can not be solved, then synthesis of organic products from biomass may never be greener or cheaper than synthesis from fossil fuels. We are currently pursuing two different strategies for solving this critical problem in green chemistry.


About FO
  • S. N. Ellis, A. Riabtseva, R. R. Dykeman, S. Hargreaves, T. Robert, P. Champagne, M. F. Cunningham, P. G. Jessop, “Nitrogen Rich CO2-Responsive Polymers as Forward Osmosis Draw Solutes”, Ind. Eng. Chem. Res. (2019) 58, 22579-22586.
  • P. G. Jessop, “Forming a Treated Switchable Polymer and Use Thereof in a Forward Osmosis System”, U.S. provisional patent application 62/722,275 (filed 24 August 2018). PCT application PCT/CA2019/051166 filed 23 August 2019.
  • P. G. Jessop, S. M. Mercer, T. Robert, R. S. Brown, T. J. Clark, B. E. Mariampillai, R. Resendes, D. Wechsler, “Systems and Methods for use of Water with Switchable Ionic Strength”, Provisional U. S. Patent Application 61/423,458 filed 15 Dec 2010, International Patent application PCT/CA2011/050777 filed 15 Dec 2011, published 21 June 2012, issued in many countries.
  • P. G. Jessop, S. Mercer, R. S. Brown, T. Robert, “Aqueous Solvents with Reversibly Switchable Ionic Strength”, Provisional U. S. Patent Application 61/303,170, filed February 2010. “Water with Switchable Ionic Strength”, International Patent application PCT/CA2011/050075 filed 10 Feb 2011, published 18 August 2011, issued in many countries.
About drying agents
  • K. J. Boniface, H.-B. Wang, R. R. Dykeman, A. Cormier, S. M. Mercer, G. Liu, M. F. Cunningham and P. G. Jessop, “CO2-switchable drying agents”, Green Chem. (2016) 18, 208-213.
About separating organic products from water
  • P. J. Dyson, and P. G. Jessop, “Characterizing the Effects of a Switchable Water Additive on the Aqueous Solubility of Small Molecules”, ChemPhysChem (2018) 19, 2093-2100.