(5cn) Generation of Renewable Fuels and Chemicals From Fatty Acids Via Supercritical Fluid Processing

Identifying renewable sources for fuels and chemicals is currently a paramount global research initiative. Lipids derived from renewable feedstocks such as vegetable oils, animal fats, and microorganisms are a promising alternative to petroleum. For example, lipids derived from soybean oil are used to produce biodiesel, which is currently the dominant fuel alternative to petroleum diesel. In order to generate fuels and chemicals from lipids, typically the lipids are first extracted from lipid-containing biomass. Traditionally, this unit operation is accomplished by extraction with an organic solvent such as hexane. However, hexane is a volatile, flammable material that can leave behind a toxic residue. Hence, if the extracted lipids are to be further processed into food-grade products, extra processing costs can be incurred to ensure that any remaining hexane is at a safe level. Extraction of lipids with supercritical carbon dioxide is an appealing alternative because carbon dioxide is inexpensive, readily available, non-toxic, and non-flammable. Also, supercritical carbon dioxide is considered a tunable extraction medium because changes in temperature or density of the solvent can greatly alter its solvating effectiveness.

Supercritical carbon dioxide can also be an effective reaction medium. Many lipids are composed of unsaturated fatty acids, and once lipids have been extracted from a biomass matrix, the unsaturated fatty acids can be oxidized in a controlled manner (as opposed to autoxidation) to produce a variety of valuable chemical intermediates. The oxidation products are useful in a spectrum of products such as pharmaceuticals and polymers. By conducting the reaction in a supercritical fluid, several advantages can be realized. For example, the reaction rate and conversion can be improved by increasing pressure. Also, if the solubilities of the reaction products in the supercritical fluid are different, then a supercritical fluid separation can be used to fractionate the products. For oxidation reactions, the use of carbon dioxide as the supercritical fluid is very appealing because it is already completely oxidized; therefore it will not break down during the reaction.

This poster will emphasize the author's graduate work under the guidance of Dr. Rafael Hernandez at Mississippi State University. In the first phase of the author's research, supercritical carbon dioxide was evaluated as an alternative lipid extraction media to hexane. The first lipid source considered was rice bran, a component of rice kernels removed during whitening and polishing. Extraction of rice bran lipids with supercritical carbon dioxide provided similar oil yields as hexane on a gravimetric basis; however, use of supercritical carbon dioxide resulted in a much higher solvent efficiency [1]. The other lipid source was municipal wastewater sewage sludge [2]. Once again, supercritical carbon dioxide was comparable to hexane in terms of oil yield. However, addition of a small amount of methanol to the carbon dioxide increased extraction yield significantly [3]. In the second phase, the oxidation of oleic acid (a common lipid component) was performed in supercritical carbon dioxide [4]. Ozonolysis of oleic acid is the most common oxidation reaction performed commercially to generate azelaic acid and pelargonic acid. Although solubility data for oleic acid are readily available, the solubility of azelaic acid and pelargonic acid had to be determined. Pelargonic acid had a much higher solubility in supercritical carbon dioxide than azelaic acid [5, 6]. In order to fully understand the solubility results, several models were utilized, including the Peng-Robinson equation of state and Chrastil's equation. The effectiveness of these models was evaluated in predicting the solubility behavior of a range of compounds [7].

The author's primary research interests are in the areas of renewable fuels and chemicals, supercritical fluids, and lipids. As part of completing the Ph.D. qualifying exam, the author wrote and successfully defended a NSF-style proposal. As a result, the author has several proposal ideas in the aforementioned areas. Potential funding sources for these areas are the Department of Energy, the Department of Agriculture, and the National Science Foundation.

Though confident in the ability to teach any chemical engineering course at both the undergraduate and graduate levels, the author's teaching interests include mass transfer operations, reaction kinetics, thermodynamics, and elective courses in renewable fuels and lipid chemistry. The author served as a tutor for Mass and Energy Balances for several years and has taught a junior-level undergraduate course entitled Mass Transfer Operations multiple times. Additionally, the author developed a new chemical engineering elective course at Mississippi State University on bio-analytical research methods. Hence, the author has experience interacting with students and is excitedly anticipating the opportunity to teach students on a permanent basis.

[1] Sparks, D., R. Hernandez, M. Zappi, D. Blackwell, and T. Fleming, 2006, Extraction of Rice Bran Oil Using Supercritical Carbon Dioxide and Propane, JAOCS 83: 885-891.

[2] Zappi, M., French, T., Hernandez R., Dufreche S., and Sparks, D., Production of Biodiesel and Other Valuable Chemicals from Wastewater Treatment Plant Sludges, United States Patent Application 20050112735.

[3] Dufreche, S., R. Hernandez, T. French, D. Sparks, M. Zappi, and E. Alley, 2007, Extraction of Lipids from Municipal Wastewater Plant Microorganisms for Production of Biodiesel, JAOCS 84: 181-187.

[4] Sparks, D.L., L.A. Estévez, and R. Hernandez, 2009, Supercritical-Fluid-Assisted Oxidation of Oleic Acid with Ozone and Potassium Permanganate, Green Chemistry, Accepted for Publication.

[5] Sparks, D.L., L.A. Estévez, N. Meyer, and R. Hernandez, 2007, Solubility of Azelaic Acid in Supercritical Carbon Dioxide, J. Chem. Eng. Data 52: 1246-1249.

[6] Sparks, D.L., L.A. Estévez, K. Barlow, and R. Hernandez, 2008, Solubility of Pelargonic Acid in Supercritical Carbon Dioxide, J. Chem. Eng. Data 53: 407-410.

[7] Sparks, D.L., L.A. Estévez, and R. Hernandez, 2008, Evaluation of Density-Based Models for the Solubility of Solids in Supercritical Carbon Dioxide and Formulation of a New Model, Chem. Eng. Sci. 63: 4292-4301.