Organic Solvent Nanofiltration Membranes to Separate and Purify Fatty Acids

N.B. Bowden
University of Iowa,
United States

Keywords: fatty acids, vegetable oils, fish oils, membranes

Summary:

Separations in the chemical industry account for 40-70% of the total operating costs because most separations require high amounts of energy or the use of solvents that must be removed and recycled. Membranes are extensively used to purify gasses, water, and low boiling point liquids because membrane purifications are generally regarded as inexpensive. A largely unmet challenge in the field of membrane purifications is the development of membrane purification of organic chemicals with molecular weights above 100 grams per mole. The field of membrane science that describes how membranes can separate organic chemicals is labelled as organic solvent nanofiltration. We recently developed a series of membranes based on polyepoxies and nanomaterials that can separate organic chemicals. The polyepoxy membranes are fabricated by mixing diamines with di, tri, or tetraepoxide monomers to produce highly cross-linked polymeric membranes. The size-selectivities of these membranes can be tuned by varying which monomers are used in their synthesis. These membranes have been used to purify a range of chemicals. We applied these membranes to the separation and purification of fatty acids. Over 200 million tons of vegetable oils are grown and isolated each year, these oils and their corresponding fatty acids are important, green feedstocks for the chemical industry. One challenge in the use of fatty acids is that they are isolated a mixture of four or more fatty acids that are challenging to separate. Some real or proposed applications of fatty acids require a mixture of fatty acids isolated from a vegetable oil to be separated to produce highly pure streams of one fatty acid, but these purifications are challenging and prohibitively expensive for some applications. A membrane-based method to purify fatty acids would be highly welcome. We developed membranes that can separate these fatty acids from each other. These membranes can separate saturated fatty acids from each other and can separate unsaturated fatty acids from each other. We had success at separating the ethyl esters of EPA and DHA from each other by tuning the properties of the membranes. These are the critical fatty acids found in fish and are the basis of a >$2B industry.