Chemical process intensification, driven by societal needs for sustainable manufacturing, exploits processes designed to reduce energy demand and minimize environmental impact. Membrane reactors that continuously perform simultaneous catalytic reaction and separation are an important example of this technology. When fluid phases separated by the membrane are of differing polarity (e.g., oil and water), oil-soluble reagents can be reacted and separated from aqueous-soluble products (and vice versa), further adding to the flexibility of these systems. Membrane reactors have had significant impact in the pharmaceutical industry because of the ability to immobilize enzymes as catalysts to drive biochemical reactions at oil/water interfaces within the membrane. Because enzyme-catalyzed reactions operate under mild conditions and pH, they are considered a green processing approach to the continuous reactive separation of pharmaceuticals. Membrane reactors could also reduce the environmental impact of agricultural fertilizers and herbicides by removing inactive or detrimental chemical species. Such processes could also impact the processing of vegetable oils to form specialty products for consumer products ranging from dietary supplements, infant formulas, pharmaceuticals, cosmetics, food, and beverages. In these systems, however, interfacial area, which determines the rate of reaction, is limited to the oil-water interfaces in the membrane reactor pores. The objective of this research program is to transform the field of membrane-based reactive separations by introducing novel high-interfacial area structures with catalyst-laden interface areas (called bijels) as membrane elements. This material allows multiple key functionalities to occur in a thin layer, with remarkably high oil-water interfacial area estimated to be 100 times larger than conventional membranes. In this project, hydrolysis reactions of triglycerides to produce raw materials such as fatty acids and glycerol will be carried out in a bijel membrane reactor; this is an industrially significant process with an annual U.S. market in excess of $25B.
Bijels (bicontinuous interfacially jammed emulsion gels) are formed by quenching a miscible system through a critical point to induce phase separation. This quench occurs in the presence of nanoparticles, which form jammed layers trapped at the interface. High interfacial area is achieved because of the special, bicontinuous arrangement of oil and water in bijel membranes that allows interfacial area to increase with bijel membrane thickness. Furthermore, bijels have a sinuous continuous oil domain adjacent and intertwined with a sinuous, continuous water domain. The interface is stabilized and decorated with nanoparticles that can also support immobilized enzymes. The research team will build on their prior success in fabricating bijels and controlling their internal microstructure via a scalable method termed solvent transfer-induced phase separation (STRIPS). The researchers also will build on their collaboration with Pohang University of Science and Technology in South Korea in which batch mode reactive separation using an enzymatic catalysis was demonstrated. Based on these advances, the project objective is to develop bijel-based membrane reactors to facilitate heterogeneous enzyme-catalyzed reactions of reagents and products of differing polarity for continuous reaction and separation. Membrane reactor performance will be assessed using the lipase-catalyzed reaction of triglycerides with water to form glycerol and fatty acids. Specific aims of the research program include (1) studying the effects of STRIPS processing conditions on bijels; (2) demonstrating the continuous hydrolysis of esters through mathematical modeling and experiments; and (3) reduction of membrane transport limitations to create reaction-rate limited performance. The successful completion of this project will enable process intensification through the use of the novel nanostructured liquid films. The research team will learn how to optimally employ the bijel technology in processes of societal importance, including selective enantiomer production, production of specialty chemicals, pharmaceuticals, and fat splitting. Continuous enzymatic reactive separation in nanostructured bijels could have transformative impact on enantiomeric pharmaceutical production, a class of reactions with significant economic potential.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
