Highly Cross-Linked Epoxy Nanofiltration Membranes for the Separation of Organic Chemicals and Fish Oil Ethyl Esters

Separation of C18 Fatty Acid Esters and Fatty Acids Derived from Vegetable Oils Using Nanometer-Sized Covalent Organic Frameworks Incorporated in Polyepoxy Membranes

Fatty acids (FAs) and FA methyl esters (FAMEs) are easily isolated from vegetable oil and are important starting materials for the chemical industry to produce commercial products that are green, biorenewable, and nontoxic. A challenge in these applications is that mixtures of five or more FAs and FAMEs are isolated from a vegetable oil source, and methods to separate these mixtures are decades old and have increasingly high costs associated with the production of high-purity single-component FAs or FAMEs. We developed a method to separate these mixtures using mixed matrix membranes containing nanometer-sized covalent organic frameworks. The 2D, crystalline COFs possessed narrow distributions of pore sizes of 1.3, 1.8, 2.3, and 3.4 nm that separated FAs and FAMEs based on their degrees of unsaturation. The COFs were synthesized, characterized, and then encapsulated at 10 or 20% by weight into a prepolymer of epoxy that was then fully cured. For all mixed matrix membranes, as the degree of unsaturation increased, the FAs or FAMEs had a slower flux. The largest difference in flux was obtained for a COF/epoxy membrane with a pore size of 1.8 nm, and methyl stearate had a 5.9× faster flux than methyl linolenate. These are the first membranes that can separate the important C18 FAs and FAMEs found in vegetable oil.

Highly Valuable Fish Oil: Formation Process, Enrichment, Subsequent Utilization, and Storage of Eicosapentaenoic Acid Ethyl Esters

In recent years, as the demand for precision nutrition is continuously increasing, scientific studies have shown that high-purity eicosapentaenoic acid ethyl ester (EPA-EE) functions more efficiently than mixed omega-3 polyunsaturated fatty acid preparations in diseases such as hyperlipidemia, heart disease, major depression, and heart disease; therefore, the market demand for EPA-EE is growing by the day. In this paper, we attempt to review EPA-EE from a whole-manufacturing-chain perspective. First, the extraction, refining, and ethanolysis processes (fish oil and ethanol undergo transesterification) of EPA-EE are described, emphasizing the potential of green substitute technologies. Then, the method of EPA enrichment is thoroughly detailed, the pros and cons of different methods are compared, and current developments in monomer production techniques are addressed. Finally, a summary of current advanced strategies for dealing with the low oxidative stability and low bioavailability of EPA-EE is presented. In conclusion, understanding the entire production process of EPA-EE will enable us to govern each step from a macro perspective and accomplish the best use of EPA-EE in a more cost-effective and environmentally friendly way.

Reactive Epoxy Nanofiltration Membranes with Disulfide Bonds for the Separation of Multicomponent Chemical Mixtures

This article reports the fabrication of organic solvent nanofiltration membranes containing a labile disulfide bond, which is broken by reaction with a chemical stimulus. These membranes are a new generation of smart membranes that have tailored selectivities and flux that can be altered by reacting with a chemical stimulus. The selectivity and flux of chemicals through the membranes was controlled by varying the concentration of disulfide bonds in the membrane. When the disulfide bonds were cleaved, the pores in the membrane became larger and yielded different separation properties. The membrane selectivity was changed by up to 70% and flux was increased up to 5×. The rapid change in selectivity of the membrane allowed for the separation of three-component mixtures. A three-component mixture of 33.3% m-dinitrobenzene, 33.3% triphenylmethane, and 33.3% 1,3,5-tris(diphenylamino)benzene (TDAB) was separated into three different fractions that were significantly enriched in one of the three molecules. The first fraction contained m-dinitrobenzene at 82% purity and 84% yield, the second fraction contained triphenylmethane at 67% purity and 49% yield, and the third fraction contained TDAB at 71% purity and 88% yield.

Separation of Saturated Fatty Acids and Fatty Acid Methyl Esters with Epoxy Nanofiltration Membranes

Epoxy nanofiltration membranes were fabricated by the step polymerization of a primary diamine and a diepoxide or triepoxide conomomer. Membrane selectivity and flux were tuned by changing the identity of the diepoxides and by increasing the concentration of triepoxides in the polymerization. The membranes were used to separate even chain length saturated fatty acids (FAs) and saturated fatty acid methyl esters (FAMEs) that possessed molecular weights between 80 - 300 g mol^-1. Our membranes show excellent selectivities of up to 100:1 for the separation of the C₄-C₁₈ FAMEs. The flux of the FAMEs through the membranes showed an exponential dependence based on the number of carbons. Fabrication of thin epoxy membranes with thicknesses of 150 nm allowed for an increase in flux of FAMEs through the membrane and demonstrated that these separations can be used under industrially relevant conditions.

Electroactive Biofilms for Sensing: Reflections and Perspectives

Microbial electrochemistry has from the onset been recognized for its sensing potential due to the microbial ability to enhance signals through metabolic cascades, its relative selectivity toward substrates, and the higher stability conferred by the microbial ability to self-replicate. The greatest challenge has been to achieve stable and efficient transduction between a microorganism and an electrode surface. Over the past decades, a new kind of microbial architecture has been observed to spontaneously develop on polarized electrodes: the electroactive biofilm (EAB). The EAB conducts electrons over long distances and performs quasi-reversible electron transfer on conventional electrode surfaces. It also possesses self-regenerative properties. In only a few years, EABs have inspired considerable research interest for use as biosensors for environmental or bioprocess monitoring. Multiple challenges still need to be overcome before implementation at larger scale of this new kind of biosensors can be realized. This perspective first introduces the specific characteristics of the EAB with respect to other electrochemical biosensors. It summarizes the sensing applications currently proposed for EABs, stresses their limitations, and suggests strategies toward potential solutions. Conceptual prospects to engineer EABs for sensing purposes are also discussed.